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在保障粮食安全的现实背景下,如何通过化肥的减量施用来保证粮食生产效率不变乃至有所提高是本文研究的目的。本文基于中国20个玉米生产省份2004—2015年的面板数据,运用超越对数函数模型测算出全国以及各省玉米生产中的化肥投入效率,并利用Tobit模型进一步对全国、东、中、西部地区化肥投入效率影响因素进行分析比较,研究结果表明：全国玉米生产效率为0.754,化肥投入效率均值为0.448,节肥潜力巨大;中国玉米种植规模、化肥价格、农业补贴与玉米化肥投入效率显著正相关,而农业保护政策与玉米化肥投入效率显著负相关。分区域而言,东部地区化肥价格与化肥投入效率正相关,玉米种植规模与化肥投入效率负相关;中部地区化肥价格、农业补贴与化肥投入效率正相关,非农劳动就业率与化肥投入效率负相关;西部地区化肥价格与玉米化肥投入效率正相关,农业保护政策与玉米化肥投入效率负相关。 相似文献
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我国农业科研投入对农业增长的贡献研究——基于1995-2007年省级面板数据的实证分析 总被引：4，自引：0，他引：4
本文利用1995 - 2007年全国各省数据计算狭义的农业科研对农业增长的贡献水平,以估算农业科技存量为基础,利用静态面板估计了不同函数形式下科研变量对农业生产的弹性,计算了农业的边际回报率和内部收益率两个重要的指标.通过比较相关研究结论,本文发现从国家层面看,农业科研投入在过去取得了很高的回报率并在促进农业科技进步、... 相似文献
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我国大学英语阅读教学长期以来偏重于学生的语言输入,却忽视学生的语言输出,这种失衡造成学生阅读能力低下。根据语言输入输出理论,英语学习中的输入和输出是密切联系、相辅相成的。在输入阅读材料的同时,需要通过输出来强化输入,大学英语阅读教学应是二者的有机结合。只有创建输入输出平衡并重的大学英语阅读教学模式,才能真正提高学生的语言综合运用能力,从而取得良好的教学效果。 相似文献
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《Information processing & management》2022,59(3):102913
Abstractive summarization aims to generate a concise summary covering salient content from single or multiple text documents. Many recent abstractive summarization methods are built on the transformer model to capture long-range dependencies in the input text and achieve parallelization. In the transformer encoder, calculating attention weights is a crucial step for encoding input documents. Input documents usually contain some key phrases conveying salient information, and it is important to encode these phrases completely. However, existing transformer-based summarization works did not consider key phrases in input when determining attention weights. Consequently, some of the tokens within key phrases only receive small attention weights, which is not conducive to encoding the semantic information of input documents. In this paper, we introduce some prior knowledge of key phrases into the transformer-based summarization model and guide the model to encode key phrases. For the contextual representation of each token in the key phrase, we assume the tokens within the same key phrase make larger contributions compared with other tokens in the input sequence. Based on this assumption, we propose the Key Phrase Aware Transformer (KPAT), a model with the highlighting mechanism in the encoder to assign greater attention weights for tokens within key phrases. Specifically, we first extract key phrases from the input document and score the phrases’ importance. Then we build the block diagonal highlighting matrix to indicate these phrases’ importance scores and positions. To combine self-attention weights with key phrases’ importance scores, we design two structures of highlighting attention for each head and the multi-head highlighting attention. Experimental results on two datasets (Multi-News and PubMed) from different summarization tasks and domains show that our KPAT model significantly outperforms advanced summarization baselines. We conduct more experiments to analyze the impact of each part of our model on the summarization performance and verify the effectiveness of our proposed highlighting mechanism. 相似文献
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航空装备制造企业作为知识密集型企业,多年来主要依赖于自主创新驱动发展。以2010-2019年的航空装备制造上市企业为样本,深入剖析数字化投入对企业创新绩效的直接和间接影响机制。研究结果表明：航空装备制造企业数字化投入与其创新绩效之间显著正相关;知识能力和风险承担水平在企业数字化投入促进企业创新绩效的作用机制中起着中介作用;政府资助正向调节数字化投入对知识吸收能力的影响,并在数字化投入对企业创新绩效的影响中起正向调节作用。研究结果对于研究调控数字化投入提高企业创新绩效的路径选择具有一定的理论和实践参考价值。 相似文献
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以2010-2011年我国披露研发数据的沪市A股制造业上市公司为样本,共获得609个观察值.实证检验了CEO任职年限对企业创新投入强度的影响,在此基础上进一步探究CEO个人特征对上述影响的调节作用.得出以下主要结论：第一,企业研发投入强度随CEO任职年限的增加而下降,但下降的速度逐渐减慢.第二,CEO年龄和性别对其任职年限与研发投入强度之间的关系具有调节作用.最后根据实证研究结果给出了相应的对策建议. 相似文献
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This note is concerned with global stabilization of linear systems subject to input saturation and time delays. Based on the Luenberger canonical form, two new decoupling methods are proposed. For the decoupled system, according to some special canonical forms, we propose two control laws for systems with input time-delays and systems with input saturation and time-delays, and give explicit conditions to ensure the global stability of the closed-loop system. Two special canonical forms contain time delays in input and state vectors, which is essential in recursive design. In addition, for the system subject to input saturation and time-delay, we introduce some free parameters when designing the controller, which can improve the instantaneous performance of the closed-loop system. Finally, the proposed approach is applied on the multi-agent system to design global stabilizing controllers and the effectiveness of the proposed controllers are illustrated by numerical simulations. 相似文献
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种子作为最基础的农业生产资料，在粮食生产中起到十分重要的作用，但国内学者在研究粮食投入要素替代方面，没有把种子投入作为重要变量进行研究。因此，文章以用种量投入作为重要变量之一构建粮食生产模型，测算各投入要素的产出弹性，边际产量及要素间的替代弹性，研究要素替代。研究结果表明，用种量对劳动力具有一定的替代作用，但对劳动力发挥替代作用的主要是农机动力，而用种量主要发挥粮食增产作用。根据研究结果得到相关启示，农机和种子等现代农业生产要素投入在粮食生产中发挥十分重要的作用。为保障粮食产量稳定增长，应提高品种改良技术水平，充分发挥种子投入的增产作用；应加大农业机械补贴政策的支持力度，鼓励农户购买农机并投入生产，充分发挥农业机械的替代作用。 相似文献
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农业生产中实际投入的具体资源及形成的产出均不单一,在缺少产出与特定资源对应数据的条件下,为方便讨论,一种可行之法是用几何意义清楚、又相对简便的TOPSIS法对多种产出进行综合;将其与资源的“边际投入量”结合,可以较清晰地了解种植业中人工添加资源的利用状况。用此方法探讨和分析安徽各市种植业的资源利用状态,结果显示,资源利用存在3种状态：可以继续追加资源投入以提高产出;不必追加资源仍可提高产出;不宜再用追加资源的办法来提高产出。前两种资源利用状态相对合理,尤其不必追加资源仍可增产正符合资源节约型农业的要求,是农业可持续发展需要的资源利用状态;相比之下,不宜再追加资源则意味着当地种植业已到了转变生产方式的时候。 相似文献
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Yue-E Wang Ben Niu Bao-wei Wu Caiyun Wu Xue-Jun Xie 《Journal of The Franklin Institute》2018,355(5):2912-2931
We study the input-to-state stability (ISS) of switched nonlinear input delay systems under asynchronous switching. Our results apply to cases where some subsystems of the switched systems are not necessarily stable under the influence of input delay. By making a compromise among the matched-stable period, the matched-unstable period, and the unmatched period and allowing the increase of the Lyapunov–Krasovskii functional (LKF) on all the switching times, the extended stability criteria for switched delay systems in generally nonlinear setting are derived first. Then, we focus on switched nonlinear input delay systems where the presence of the input delay leads to the instability of some subsystems of it. By explicitly constructing input-to-state stable LKF, the sufficient conditions for ISS of switched nonlinear input delay systems under asynchronous switching are presented. Finally, two examples are given to illustrate the effectiveness of the proposed theory. 相似文献
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Most existing search engines focus on document retrieval. However, information needs are certainly not limited to finding relevant documents. Instead, a user may want to find relevant entities such as persons and organizations. In this paper, we study the problem of related entity finding. Our goal is to rank entities based on their relevance to a structured query, which specifies an input entity, the type of related entities and the relation between the input and related entities. We first discuss a general probabilistic framework, derive six possible retrieval models to rank the related entities, and then compare these models both analytically and empirically. To further improve performance, we study the problem of feedback in the context of related entity finding. Specifically, we propose a mixture model based feedback method that can utilize the pseudo feedback entities to estimate an enriched model for the relation between the input and related entities. Experimental results over two standard TREC collections show that the derived relation generation model combined with a relation feedback method performs better than other models. 相似文献
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以2003—2013年在深圳和上海证券交易所主板上市的企业为研究样本,对创新活动采用存量的研究方法,厘清企业创新投入、产出与企业价值之间的影响路径。研究结果发现:(1)与以前文献相似,企业创新投入会影响企业创新产出,但是这种影响仅具有1~2年的滞后期,这表明我国的创新活动持续时间很短,大多为短平快的项目,没有长期的研发过程。(2)与以前文献结论不同,发现由于创新活动的不确定性与累积性,企业的创新投入不会直接影响企业价值,但企业创新产出对企业价值有直接贡献,实际上企业的创新活动是必须通过其产出面来直接影响企业价值的。(3)除采用泊松回归方法,亦采用负二项回归等多种回归方法,检验结果仍然稳健。 相似文献
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This paper proposes an observer-based fuzzy adaptive output feedback control scheme for a class of uncertain single-input and single-output (SISO) nonlinear stochastic systems with quantized input signals and arbitrary switchings. The SISO system under consideration contains completely unknown nonlinear functions, unmeasured system states and quantized input signals quantized by a hysteretic quantizer. By adopting a new nonlinear disposal of the quantized input, the relationship between the control input and the quantized input is established. The hysteretic quantizer that we take can effectively avoid the chattering phenomena. Furthermore, the introduction of a linear observer makes the estimation of the states possible. Based on the universal approximation ability of the fuzzy logic systems (FLSs) and backstepping recursive design with the common stochastic Lyapunov function approach, a quantized output feedback control scheme is constructed, where the dynamic surface control (DSC) is explored to alleviate the computation burden. The proposed control scheme cannot only guarantee the boundedness of signals but also make the output of the system converge to a small neighborhood of the origin. The simulation results are exhibited to demonstrate the validity of the control scheme. 相似文献
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Automatic word spacing in Korean remains a significant task in natural language processing owing to the extremely complex word spacing rules involved. Most previous models remove all spaces in input sentences and insert new spaces in the modified input sentences. If input sentences include only a small number of spacing errors, the previous models often return sentences with even more spacing errors than the input sentences because they remove the correct spaces that were typed intentionally by the users. To reduce this problem, we propose an automatic word spacing model based on a neural network that effectively uses word spacing information from input sentences. The proposed model comprises a space insertion layer and a spacing-error correction layer. Using an approach similar to previous models, the space insertion layer inserts word spaces into input sentences from which all spaces have been removed. The spacing error correction layer post-corrects the spacing errors of the space insertion model using word spacing typed by users. Because the two layers are tightly connected in the proposed model, the backpropagation flows are not blocked. As a result, the space insertion and error correction are performed simultaneously. In experiments, the proposed model outperformed all compared models on all measures on the same test data. In addition, it exhibited reliable performance (word-unit F1-measures of 94.17%～97.87%) regardless of how many word spacing errors were present in the input sentences. 相似文献
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以长江经济带11省市2000—2015年的财政科技支出及其国内3种专利申请受理量数据为例,采用NICH指数对各省市政府科技投入与技术创新的相对增长速度进行静态对比分析,进而利用脱钩分析研究各省市政府科技投入与技术创新的动态演化轨迹,在此基础上运用响应指数定量分析各省市技术创新对政府科技投入的响应程度。研究结果表明:长江经济带各省市政府科技投入与技术创新的相对增长速度存在差异,且出现"双高"与"双低"增长区的两极分化;各省市的政府科技投入与技术创新整体上以扩张性复钩与弱脱钩为主;各省市的技术创新对政府科技投入具有不同的响应程度,正向响应与负向响应叠加,且响应具有明显的趋势变化特征。 相似文献
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增加科技投入是提升创新能力的重要手段和有效途径。近年来我国科技投入力度不断加强,庞大的科技投入对国家创新能力的作用效果到底如何?不同的投入形式和途径带来的结果有何差异?本文以专利申请数量和新产品销售收入为国家创新能力的指标要素,采用系统动力学的方法建立了科技投入对国家创新能力提升机制的仿真模型。通过Vensim PLE软件对系统内科研资金、人员和政策的变动以及企业、科研机构和高校三大科研主体间资金和人员流动对国家创新能力的影响进行了模拟,揭示了不同形式和来源的科技投入对国家创新能力的作用途径和效果。研究发现:(1)科研资金在配置过程中向高校流动,科研人员在配置过程中向高校和企业流动更有利于提升国家创新能力;(2)从科技政策来看,加大教育投入和专利保护强度都能有效地提升国家创新能力。 相似文献
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【目的/意义】跨学科输入知识是指其他学科（跨学科）的知识被目标学科多次引用,并逐渐成为目标学科的研究内容,刺激知识创新与生长,进而促进学科发展。因此,识别跨学科输入知识,测量其对目标学科发展的影响力,有利于分析学科进步的跨学科来源及作用力大小,有利于把握学科创新发展的现状与趋势。【方法/过程】基于跨学科引用,从跨学科输入知识在目标学科的研究热度、研究广度、研究深度3个方面,构建跨学科输入知识对目标学科发展的影响力模型,测度影响力程度。并以图书情报学跨学科程度较高的6种期刊数据为研究对象进行实证研究。【结果/结论】通过影响力模型,测量跨学科输入知识对图书情报学的影响力大小,并根据趋势分析法将跨学科知识的影响力趋势分为上升型、稳定型和下降型。【创新/局限】本文构建跨学科知识对学科发展的影响力模型并验证其有效性,后续将进一步分析跨学科知识对目标学科的作用点,识别跨学科知识生长点。 相似文献