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1.
During simultaneous discrimination training, there is evidence that some of the value of the S+ transfers to the S?. When the value of the S+ is altered outside the context of the simultaneous discrimination, two very different predictions are made concerning its effect on its S?, depending on whether one views the S+ as an occasion setter or as a stimulus capable of transferring value. In four experiments, pigeons were trained with two similar simultaneous discriminations, A+B? and C+D?, and two single-stimulus trial types, A and C, (in which A always had greater nominal value than C). According to value transfer theory, on test trials, B should always be preferred over D, because B and D should be affected by the net values of A and C, respectively. According to an occasion setting account, however, D should be preferred over B because the presence of D signals a higher probability of reinforcement for responding to C than when C is alone, and/or the presence of B signals a lower probability of reinforcement for responding to A than when A is alone. In all four experiments, the pigeons preferred B over D, a result consistent with value transfer theory. Thus, an S? can acquire value from an S+ even when that value is conditioned in a “context” different from that of the simultaneous discrimination.  相似文献   

2.
Previous work with rats showed slower active avoidance (AA) and passive avoidance (PA) learning in a light-go/noise-light no-go task (L+NL?) than in a noise-go/light-noise no-go task (N+LN?), independently of noise intensity and of presence or absence of AA pretraining. Experiment I compared these two tasks and the corresponding discriminations with a compound AA and a simple PA signal. The latter were learned at a faster rate, with only negligible differences between the two types of stimulus arrangements (NL+L? vs LN+N?). Experiment II investigated the acquisition and reversal of four go/no-go tasks with a simple AA signal, with either a simple or a compound no-go signal and asymmetrical reinforcement, i.e., with an extinction instead of a PA contingency during the presentation of no-go signals. As in previous experiments with symmetrical reinforcement, the groups with a simple no-go signal (L+N?, N+L?) acquired AA with little or no generalization to the other stimulus. In reversal, however, the L+N? group (formerly N+L?) responded to the no-go signal much more frequently than the other (N+L?, formerly L+N?). Both the L+NL? and the N+LN? groups gave a large number of responses to the extinction signal, but the differences between the two groups were at least as large as in previous work with a PA contingency. These data show that perceptual or attentional phenomena cannot explain stimulus nonequivalences in situations with a compound no-go signal. Furthermore, the similar nonequivalences found in situations with and without differential fear conditioning (AA-extinction tests vs AA-PA tests) leads to complex, highly speculative models concerning possible interactions between response and drive-modulating properties of various stimuli.  相似文献   

3.
4.
Minimal procedures for the demonstration of transitive inference (TI) in animals have involved the training of four simultaneous discriminations: for example, A+B?, B+C?, C+D?, and D+E?, followed by the demonstration of a preference for B over D on test trials. In Experiment 1, we found that TI in pigeons can be found with successive training involving A+B?, B+C?, A+C?, C+D?, D+E?, C+E?, and A+E?. In Experiment 2, we found that demonstration of TI did not require inclusion of experience with the nonadjacent stimulus pairs (A+C?, C+E?, A+E?). Experiment 3 provided a test of value transfer theory (VTT; Fersen, Wynne, Delius, & Staddon, 1991). When pigeons were trained with stimulus pairs that did not permit the transitive ordering of stimuli, but did permit the differential transfer of value (e.g., A+B?, C?E+, C+D?, & A+E?), preference for B over D was still found. Analyses of the relation between direct experiences with reinforced and nonreinforced responding and stimulus preferences on test trials failed to support a reinforcement-history account of TI.  相似文献   

5.
Four groups of 16 rats were trained in a go-no go discrimination with symmetrical negative reinforcement (active-passive avoidance task). A 2 by 2 design was used with stimulus combinations as one factor [light-go, noise/light-no go, (L+ NL?) vs noise-go, light/noise-no go (N+ LN?)] and noise intensity as the other factor (90 dB, high, vs 70 dB, low). The two N+ LN? groups learned both active and passive avoidance responses much more rapidly than the L+ NL? groups. In later phases of training, high noise intensity facilitated passive avoidance in the L+ NL? condition and exerted a slight effect in the opposite direction in the other condition. While the differences in active avoidance learning were the same as in previous work on light and noise CSs, the interactions between stimuli of different modalities appeared to be more important than stimulus modality or stimulus intensity per se in determining rate of passive avoidance learning.  相似文献   

6.
Abstract

The purpose of this investigation was to determine the nature of the relationship among three variables: diadocho‐kinetic rate, speaking rate, and reading rate. A group of 40 individuals, 20 males and 20 females, performed three experimental tasks: (1) three repetitions at maximumt speed of each of the following: /p?//t?//k?/, and /p? t? k?/; (2) 10 readings of a standard prose passage; and (3) the presentation of a two‐minute impromptu speech based on the content of stimulus pictures. Results of subjects’ performances indicate that: (1) reading rate is highly related to speaking rate; (2) there is no strong relationship between diadochokinetic rate and speaking rate; and (3) diadochokinetic rate is not highly related to reading rate.  相似文献   

7.

Objectives

To investigate the effects of different nitrate sources on the uptake, transport, and distribution of molybdenum (Mo) between two oilseed rape (Brassica napus L.) cultivars, L0917 and ZS11.

Methods

A hydroponic culture experiment was conducted with four nitrate/ammonium (NO3 ?:NH4 +) ratios (14:1, 9:6, 7.5:7.5, and 1:14) at a constant nitrogen concentration of 15 mmol/L. We examined Mo concentrations in roots, shoots, xylem and phloem sap, and subcellular fractions of leaves to contrast Mo uptake, transport, and subcellular distribution between ZS11 and L0917.

Results

Both the cultivars showed maximum biomass and Mo accumulation at the 7.5:7.5 ratio of NO3 ?:NH4 + while those were decreased by the 14:1 and 1:14 treatments. However, the percentages of root Mo (14.8% and 15.0% for L0917 and ZS11, respectively) were low under the 7.5:7.5 treatment, suggesting that the equal NO3 ?:NH4 + ratio promoted Mo transportation from root to shoot. The xylem sap Mo concentration and phloem sap Mo accumulation of L0917 were lower than those of ZS11 under the 1:14 treatment, which suggests that higher NO3 ?:NH4 + ratio was more beneficial for L0917. On the contrary, a lower NO3 ?:NH4 + ratio was more beneficial for ZS11 to transport and remobilize Mo. Furthermore, the Mo concentrations of both the cultivars’ leaf organelles were increased but the Mo accumulations of the cell wall and soluble fraction were reduced significantly under the 14:1 treatment, meaning that more Mo was accumulated in organelles under the highest NO3 ?:NH4 + ratio.

Conclusions

This investigation demonstrated that the capacities of Mo absorption, transportation and subcellular distribution play an important role in genotype-dependent differences in Mo accumulation under low or high NO3 ?:NH4 + ratio conditions.
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8.
The reuse of wastewater for the irrigation of farmlands is gaining popularity, and the nutrient leaching associated with wastewater irrigation is becoming a matter of concern. The variability of nitrogen and phosphorus fractions in wastewater-irrigated soil was investigated in both horizontal and vertical directions in Kongjiaxiang, Tongliao, Inner Mongolia, China. The results showed that wastewater irrigation resulted in the concentrations of available N and P being 40.36% and 66.49% higher, respectively, than those with groundwater irrigation. Different forms of N and P exhibited significantly different distribution patterns. Higher concentrations of NO3- and total available N, as well as of those of Ca-P and total available P were observed near wastewater irrigation channels. Ca-P has a spatial distribution pattern similar to that of available P. The concentrations of NO3- and NH4+ were the highest in top soil and decreased with depth. The complex interactions between nitrate leaching and nitrogen transformation processes (e.g., nitrification, denitrification, and mineralization) determined the vertical profile of NO3- . The significant amount of NH4+ loss inhibited its deep seepage. The Ca-bound compound contained more P than other inorganic fractions as a result of high Ca levels throughout the soil profile. The differences in the concentrations of Ca-bound P at different depths could be due to the upward flux or translocation of Ca from subsurface to surface soil and the sequestration of P.  相似文献   

9.
The enantioselective assay for S( )- and R(-)-propafenone (PPF) in human urine that developed in this work involves extraction of propafenone from human urine and using S( )-propafenone as internal standard, chiral derivatization with 2,3,4,6-tetra-O-β-D-glucopranosyl isothiocyanate, and quantitation by an RP-HPLC system with UV detection (λ=220nm). A baseline separation ofpropafenone enantiomers was achieved on a 5-μm reverse phase ODS column, with a mixture of methanol:water:glacial acetic acid (25:12:0.02,v/v) as mobile phase. There was good linear relationship from 24.9 ng/ml to 1875.0 ng/ml for both of enantiomers. The regression equations of the standard curves based on Cs-PPF (or CR-PPF ) versus ratio of As-PPF/As (or AR-PPF/As ) were y=0.0032x-0.081, (r=0.999) for S-PPF and y=0.0033x 0.0039, (r=0.998) for R-PPF,respectively. The method's limit of detection was 12.5 ng/ml for both enantiomers, and the method's limit ofquantitation was 28.2±0.52 ng/ml for S-PPF, 30.4±0.53 ng/ml for R-PPF (RSD<8%, n=5). The analytical method yielded average recovery of 98.9% and 100.4% for S-PPF and R-PPF, respectively. The relative standard deviation was no more than 6.11% and 6.22% for S-PPF and R-PPF, respectively. The method enabled study of metabolism of S( )- and R(-)-propafenone in human urine. The results from 7 volunteers administered 150 mg racemic propafenone indicated that propafenone enantiomers undergo stereoselective metabolism and that in the human body, S( )-propafenone is metabolized more extensively than R(-)propafenone.  相似文献   

10.
In three experiments, rats received appetitive conditioning with two unconditioned stimuli (US+ and US*) that supported a similar conditioned response. Stimulus A was first paired with US+, and then, for a second stage of training, the compound AB was paired with US*. Subsequent test trials with A revealed an abnormally strong conditioned response. The findings from additional groups indicated that such enhanced conditioning with A depended on the presence of B in the second stage and on the use of US+ and US* for the two training stages. A modification to a configural theory of conditioning is proposed in order to explain the results.  相似文献   

11.
Three experiments were conducted using an autoshaping procedure in pigeons to examine the conditions under which facilitation develops toB in anA? IBA+ paradigm. WhenB is a diffuse stimulus and A is a localized keylight, this paradigm results in B’s facilitating pecking at A. Prior inhibitory conditioning ofA promoted the development of this facilitation more successfully than did prior excitatory or control treatment of A. These results suggest that facilitation develops especially well when an inhibitory stimulus is reinforced in the presence of the diffuseB. That outcome is consistent with the view that facilitation involves the removal of inhibition.  相似文献   

12.
With the increasing occurrence of haze during the summer, the physicochemical characteristics and toxicity differences in PM2.5 in different seasons are of great concern. Hangzhou is located in an area that has a subtropical monsoon climate where the humidity is very high during both the summer and winter. However, there are limited studies on the seasonal differences in PM2.5 in these weather conditions. In this test, PM2.5 samples were collected in the winter and summer, the morphology and chemical composition of PM2.5 were analyzed, the toxicity of PM2.5 to human bronchial cells BEAS-2B was compared, and the correlation between PM2.5 toxicity and the chemical composition was discussed. The results showed that during both the winter and summer, the main compounds in the PM2.5 samples were water-soluble ions, particularly SO42?, NO3?, and NH4+, followed by organic components, while heavy metals were present at lower levels. The higher the mass concentration of PM2.5, the greater its impact on cell viability and ROS levels. However, when the mass concentration of PM2.5 was similar, the water extraction from the summer samples showed a greater impact on BEAS-2B than that from the winter samples. The cytotoxicity of PM2.5 was closely associated with heavy metals and organic pollutants but less related to water-soluble ions.  相似文献   

13.
According to most theories, in a simple contingency learning situation, excitatory learning occurs when the probability of the unconditioned stimulus in the presence of the conditioned stimulus (p1) is higher than the probability of the unconditioned stimulus in the absence of the conditioned stimulus (p2). In Rescorla and Wagner??s (1972) model, this prediction varies, depending on the parameters used. In the following experiments, we evaluated whether the difference between p1 and p2 that is required to produce excitatory conditioning is the same, independent of the specific value of p1, or whether this difference varies proportionally to p1??s value. To do so, an appetitive procedure of Pavlovian conditioning with rats was used. In four experiments, we compared different levels of contingency (low, medium and high) and found that the difference between p1 and p2 that is required to produce excitatory conditioning increases when the value of p1 is higher. The possibility of analyzing contingency learning as a discrimination between p1 and p2 is also discussed.  相似文献   

14.
研究目的:腐殖酸(HA)对富勒烯(C60)粉末的悬浮作用以及pH、离子强度对HA-C60悬浮性能的影响。创新要点:研究水质条件对C60悬浮性能的影响。研究方法:测定C60粉末在HA溶液中的zeta电位,水力学粒径和悬浮浓度;HA存在下,C60悬浮体系的zeta电位与水力学粒径随pH的变化及C60悬浮体系团聚动力学随离子强度的变化。重要结论:HA对C60粉末起到一定的分散作用,但不能使其长时间稳定悬浮于水中。当pH〈4时,C60水悬液开始沉淀;而当HA存在时,C60水悬液在pH 3-11范围内都保持稳定,这是由于HA吸附于C60表面,通过静电排斥和空间位阻作用,促进C60分散悬浮。C60水悬液的稳定性随盐离子价位和浓度升高而降低。HA会抑制Na+对C60水悬液的脱稳作用;但高价离子Ca2+和La3+存在时,HA与C60之间会发生桥联从而促进C60水悬液脱稳沉淀。  相似文献   

15.
Rats were trained and tested on delayed conditional discriminations (DCDs) consisting of four possible light and tone stimulus sequences: light-light, tone-tone, light-tone, and tone-light. A lever was presented after the offset of the second or test stimulus, S2. Two retention intervals (RIs) were present within the DCD task, one (RI-1) between the sample or first stimulus (S1) and S2, and the other (RI-2) between S2 and presentation of the lever. Liquid reinforcement was contingent upon pressing only when S2 matched S1 in Experiment 1 or only when S2 differed from S1 in Experiment 2. RI-1 and RI-2 were separately increased to 5,10, and 20 sec from 1-sec training conditions. Increasing RI-1 produced greater declines in performance to light S1 than to tone S1 in both experiments. No such stimulus modality effect occurred for increases in RI-2 in these experiments. These results indicate that retrospection of S1 occurred during RI-1 and prospection of a response decision and reward expectancy primarily occurred during RI-2.  相似文献   

16.
Graduate teaching assistants (GTAs) in science, technology, engineering, and mathematics (STEM) have a large impact on undergraduate instruction but are often poorly prepared to teach. Teaching self-efficacy, an instructor’s belief in his or her ability to teach specific student populations a specific subject, is an important predictor of teaching skill and student achievement. A model of sources of teaching self-efficacy is developed from the GTA literature. This model indicates that teaching experience, departmental teaching climate (including peer and supervisor relationships), and GTA professional development (PD) can act as sources of teaching self-efficacy. The model is pilot tested with 128 GTAs from nine different STEM departments at a midsized research university. Structural equation modeling reveals that K–12 teaching experience, hours and perceived quality of GTA PD, and perception of the departmental facilitating environment are significant factors that explain 32% of the variance in the teaching self-efficacy of STEM GTAs. This model highlights the important contributions of the departmental environment and GTA PD in the development of teaching self-efficacy for STEM GTAs.Science, technology, engineering, and mathematics (STEM) graduate teaching assistants (GTAs) play a significant role in the learning environment of undergraduate students. They are heavily involved in the instruction of undergraduate students at master’s- and doctoral-granting universities (Nyquist et al., 1991 ; Johnson and McCarthy, 2000 ; Sundberg et al., 2005 ; Gardner and Jones, 2011 ). GTAs are commonly in charge of laboratory or recitation sections, in which they often have more contact and interaction with the students than the professor who is teaching the course (Abraham et al., 1997 ; Sundberg et al., 2005 ; Prieto and Scheel, 2008 ; Gardner and Jones, 2011 ).Despite the heavy reliance on GTAs for instruction and the large potential for them to influence student learning, there is evidence that many GTAs are completely unprepared or at best poorly prepared for their role as instructors (Abraham et al., 1997 ; Rushin et al., 1997 ; Shannon et al., 1998 ; Golde and Dore, 2001 ; Fagen and Wells, 2004 ; Luft et al., 2004 ; Sundberg et al., 2005 ; Prieto and Scheel, 2008 ). For example, in molecular biology, 71% of doctoral students are GTAs, but only 30% have had an opportunity to take a GTA professional development (PD) course that lasted at least one semester (Golde and Dore, 2001 ). GTAs often teach in a primarily directive manner and have intuitive notions about student learning, motivation, and abilities (Luft et al., 2004 ). For those who experience PD, university-wide PD is often too general (e.g., covering university policies and procedures, resources for students), and departmental PD does not address GTAs’ specific teaching needs; instead departmental PD repeats the university PD (Jones, 1993 ; Golde and Dore, 2001 ; Luft et al., 2004 ). Nor do graduate experiences prepare GTAs to become faculty and teach lecture courses (Golde and Dore, 2001 ).While there is ample evidence that many GTAs are poorly prepared, as well as studies of effective GTA PD programs (biology examples include Schussler et al., 2008 ; Miller et al., 2014 ; Wyse et al., 2014 ), the preparation of a graduate student as an instructor does not occur in a vacuum. GTAs are also integral members of their departments and are interacting with faculty and other GTAs in many different ways, including around teaching (Bomotti, 1994 ; Notarianni-Girard, 1999 ; Belnap, 2005 ; Calkins and Kelly, 2005 ). It is important to build good working relationships among the GTAs and between the GTAs and their supervisors (Gardner and Jones, 2011 ). However, there are few studies that examine the development of GTAs as integral members of their departments and determine how departmental teaching climate, GTA PD, and prior teaching experiences can impact GTAs.To guide our understanding of the development of GTAs as instructors, a theoretical framework is important. Social cognitive theory is a well-developed theoretical framework for describing behavior and can be applied specifically to teaching (Bandura, 1977 , 1986 , 1997 , 2001 ). A key concept in social cognitive theory is self-efficacy, which is a person’s belief in his or her ability to perform a specific task in a specific context (Bandura, 1997 ). High self-efficacy correlates with strong performance in a task such teaching (Bandura, 1997 ; Tschannen-Moran and Hoy, 2007 ). Teaching self-efficacy focuses on teachers’ perceptions of their ability to “organize and execute courses of action required to successfully accomplish a specific teaching task in a particular context” (Tschannen-Moran et al., 1998 , p. 233). High teaching self-efficacy has been shown to predict a variety of types of student achievement among K–12 teachers (Ashton and Webb, 1986 ; Anderson et al., 1988 ; Ross, 1992 ; Dellinger et al., 2008 ; Klassen et al., 2011 ). In GTAs, teaching self-efficacy has been shown to be related to persistence in academia (Elkins, 2005 ) and student achievement in mathematics (Johnson, 1998 ). High teaching self-efficacy is evidenced by classroom behaviors such as efficient classroom management, organization and planning, and enthusiasm (Guskey, 1984 ; Allinder, 1994 ; Dellinger et al., 2008 ). Instructors with high teaching self-efficacy work continually with students to help them in learning the material (Gibson and Dembo, 1984 ). These instructors are also willing to try a variety of teaching methods to improve their teaching (Stein and Wang, 1988 ; Allinder, 1994 ). Instructors with high teaching self-efficacy perform better as teachers, are persistent in difficult teaching tasks, and can positively affect their student’s achievement.These behaviors of successful instructors, which can contribute to student success, are important to foster in STEM GTAs. Understanding of what influences the development of teaching self-efficacy in STEM GTAs can be used to improve their teaching self-efficacy and ultimately their teaching. Therefore, it is important to understand what impacts teaching self-efficacy in STEM GTAs. Current research into factors that influence GTA teaching self-efficacy are generally limited to one or two factors in a study (Heppner, 1994 ; Prieto and Altmaier, 1994 ; Prieto and Meyers, 1999 ; Prieto et al., 2007 ; Liaw, 2004 ; Meyers et al., 2007 ). Studying these factors in isolation does not allow us to understand how they work together to influence GTA teaching self-efficacy. Additionally, most studies of GTA teaching self-efficacy are not conducted with STEM GTAs. STEM instructors teach in a different environment and with different responsibilities than instructors in the social sciences and liberal arts (Lindbloom-Ylanne et al., 2006 ). These differences could impact the development of teaching self-efficacy of STEM GTAs compared with social science and liberal arts GTAs. To further our understanding of the development of STEM GTA teaching self-efficacy, this paper aims to 1) describe a model of factors that could influence GTA teaching self-efficacy, and 2) pilot test the model using structural equation modeling (SEM) on data gathered from STEM GTAs. The model is developed from social cognitive theory and GTA teaching literature, with support from the K–12 teaching self-efficacy literature. This study is an essential first step in improving our understanding of the important factors impacting STEM GTA teaching self-efficacy, which can then be used to inform and support the preparation of effective STEM GTAs.  相似文献   

17.
INTRODUCTION Steel rebar embedded in concrete is protectedagainst corrosion by the thin passive film on its sur-face and the physical protection from concrete. Thealkaline environment (pH≥12.5) of the concrete poresolution triggers passivation on the rebar surface andformation of the protective oxide film. The physicaprotection of concrete coverage hinders the invasionof aggressive agents. However, this passivity can bebroken down by local pH loss as a result of concretecracking or the…  相似文献   

18.
In matching-to-sample, comparison choice should be controlled by the identity of the sample and, when the sample is not available, by the overall probability of reinforcement associated with each of the comparisons. In the present research, pigeons were trained to match a frequent sample (appearing on 80% of the trials) to one comparison (C fr) and an infrequent sample (appearing on 20% of the trials) to the other (C inf), with the number of reinforcements associated with each sample equated. In Experiment 1, the task was identity matching; in Experiments 2 and 3, it was symbolic matching. We asked whether, when control of comparison choice by the sample was reduced (by inserting a delay between the sample and the comparisons), pigeons would choose comparisons on the basis of (1) the number of reinforcements per comparison (and thus show no comparison bias), (2) the comparison associated with the more frequent sample during training (and show a preference forC fr), or (3) the probability of reinforcement given a correct response (and show a preference forC inf), or (4) inhibition produced by nonreinforced choice of the more frequently correct comparison (and show a preference forC inf). Pigeons showed a significant tendency to chooseC fr. In Experiment 3, we showed that this bias did not result from the effects of intertrial facilitation or interference. Thus, it appears that when control of comparison choice by the sample is reduced, pigeons’ choice is controlled not merely by the probability of reinforcement but also by overall sample frequency.  相似文献   

19.
Two experiments using garden snails (Helix aspersa) showed conditioned inhibition using both retardation and summation tests. Conditioned inhibition is a procedure by which a stimulus becomes a predictor of the absence of a relevant event—the unconditioned stimulus (US). Typically, conditioned inhibition consists of pairings between an initially neutral conditioned stimulus, CS2, and an effective excitatory conditioned stimulus, CS1, in the absence of the US. Retardation and summation tests are required in order to confirm that CS2 has acquired inhibitory properties. Conditioned inhibition has previously been found in invertebrates; however, these demonstrations did not use the retardation and summation tests required for an unambiguous demonstration of inhibition, allowing for alternative explanations. The implications of our results for the fields of comparative cognition and invertebrate physiological models of learning are discussed.  相似文献   

20.
Separate groups of rats were trained and tested on asymmetrically and symmetrically reinforced successive delayed matching-to-sample (DMTS) or delayed discrimination (DD) tasks in Experiment 1. Each rat received training and testing on symmetrically reinforced DMTS and DD tasks in Experiment 2. The only difference between each task was that the rats had to respond correctly to a light or tone test stimulus, S2, if it matched a light or tone sample stimulus, S1, in DMTS, but could respond to either S2 if S1 had been a particular stimulus in DD. Only correct leverpresses were reinforced in the asymmetrically reinforced version of each task. Both correct presses and correct omissions were reinforced in the symmetrically reinforced version of each task. Response biases to leverpress during tests for delayed responding to S1 were reduced in both symmetrically reinforced tasks, but only in the DD task did such contingencies produce consistently poorer performance in responding to either S, in Experiment 1. Declines in accuracy of performance that occurred in both experiments were greater to the visual than to the auditory S1 only in the DMTS tasks with increased intervals between S1 and S2. A third experiment, in which rats had to respond to S2 if it matched S1 (DMTS) or if S2 mismatched S, (DMmTS), was carried out. Modality of S1 similarly affected accuracy of delayed responding in each task, as in the first two experiments. Methodological and theoretical implications of these results are discussed in terms of Honig and Thompson’s (1982) dual-process theory of working memory.  相似文献   

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