全文获取类型
收费全文 | 716篇 |
免费 | 13篇 |
国内免费 | 19篇 |
专业分类
教育 | 556篇 |
科学研究 | 90篇 |
体育 | 41篇 |
综合类 | 45篇 |
文化理论 | 6篇 |
信息传播 | 10篇 |
出版年
2024年 | 1篇 |
2022年 | 4篇 |
2021年 | 12篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 3篇 |
2015年 | 15篇 |
2014年 | 62篇 |
2013年 | 60篇 |
2012年 | 63篇 |
2011年 | 69篇 |
2010年 | 39篇 |
2009年 | 38篇 |
2008年 | 43篇 |
2007年 | 60篇 |
2006年 | 43篇 |
2005年 | 47篇 |
2004年 | 34篇 |
2003年 | 25篇 |
2002年 | 18篇 |
2001年 | 11篇 |
2000年 | 15篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有748条查询结果,搜索用时 31 毫秒
71.
不同抗性的向日葵品种接种锈菌后叶片中可溶性蛋白、可溶性总糖及叶绿素含量的变化 总被引:2,自引:0,他引:2
通过对两个不同抗性向日葵品种在苗期接种向日葵锈菌,测定了接种后不同时间叶片的可溶性总糖、可溶性蛋白及叶绿素含量的变化.研究结果表明:抗病品种的可溶性总糖比感病品种高;可溶性蛋白质含量、叶绿素b含量和类胡萝卜素含量的变化与向日葵抗病性有密切关系,而和叶绿素a含量的变化与抗病性没有直接关系. 相似文献
72.
73.
本文讨论了带右删失数据的非线性随机效应模型的参数估计,给出Gauss-Newton迭代法和改进后的Gauss-Newton迭代法,根据参数估计和算法给出数值模拟,验证了参数估计和算法的可行性. 相似文献
74.
以邻苯二胺、吡啶甲酸为原料,多聚磷酸为催化剂和溶剂,经微波辐射合成了2-(3-吡啶基)苯并咪唑、2-(2-吡啶基)苯并咪唑。通过熔点、元素分析、IR和1H NMR对其纯度和结构进行表征,探讨了目标化合物在微波辐射下合成的工艺条件及荧光特性。 相似文献
75.
TIRF microscopy has provided a means to view mobile granules within 100 nm in size in two dimensions. However quantitative analysis of the position and motion of those granules requires an appropriate tracking method. In this paper, we present a new tracking algorithm combined with the unique features of TIRF. Firstly a fluorescence correction procedure was processed to solve the problem of fluorescence bleaching over time. Mobile granules were then segmented from a time-lapse image stack by an adaptive background subtraction method. Kalman filter was introduced to estimate and track the granules that allowed reducing searching range and hence greater reliability in tracking process. After the tracked granules were located in x-y plane, the z-position was indirectly inferred from the changes in their intensities. In the experiments the algorithm was applied in tracking GLUT4 vesicles in living adipose cells. The results indicate that the algorithm has achieved robust estimation and tracking of the vesicles in three dimensions. 相似文献
76.
A series of photochromic diarylethene derivatives containing different fluorophores was synthesized by the Sonogashira coupling reaction and characterized by ^1H nuclear magnetic resonance (NMR), ^13C NMR and mass spectroscopy. Photochromic conversion of Cz-MS was observed and its structural change was confirmed by proton NMR, Switchable absorption and emission phenomena were observed for these molecules. These phenomena were attributed to the reversible photochromic fluorescence resonance energy transfer (pcFRET) process. The design of this novel photochromic system of Py-4MS enables information to be processed in a non-destructive manner. This overcomes the problem of the destructive nature of tracking photochromism using ultraviolet (UV)-vis spectroscopy. 相似文献
77.
This paper presents a novel mega-Hz-level super high frequency zero-voltage soft-switching converter for induction heating power supplies. The prominent advantage of this topology is that it can absorb both inductive and capacitive parasitic components in the converter. The switch devices operate in a zero-voltage soft-switching mode. Consequently, the high voltage and high current spikes caused by parasitic inductors or capacitors oscillation do not occur in this circuit, and the high power loss caused by high frequency switching can be greatly reduced. A large value inductor is adopted between the input capacitor and the switches, thus, this novel converter shares the benefits of both voltage-type and current-type circuits simultaneously, and there are no needs of dead time between two switches. The working principles in different modes are introduced. Results of simulation and experiments operated at around 1 MHz frequency verify the validity of parasitic components absorption and show that this convener is competent for super high frequency applications. 相似文献
78.
采用荧光光谱和紫外可见吸收光谱法研究了地美硝唑与牛血清蛋白的结合反应,发现地美硝唑对牛血清白蛋白有较强的荧光猝灭作用,该猝灭过程主要为静态猝灭过程。从荧光光谱数据,由Stern—Volmer方程和Lineweaver—Burk方程分析并处理实验数据得到了23℃时结合反应的结合常数K=1.03×10^4L/mol,结合位点数为0.70,结合反应的标准焓变、标准熵变、和标准吉布斯自由能变分别为~63.48kJ/mol,-96.22J/K,-35.00kJ/mol。 相似文献
79.
NAK80材料曲面高速铣削表面质量实验研究 总被引:1,自引:0,他引:1
通过实验,研究了模具制造业中常用的NAK80材料的表面粗糙度形成及曲面高速加工工艺参数的选择策略,分析了NAK80材料在高速铣削加工中以铣代磨的切削机理。结果表明,NAK80材料适合高速加工,在未来将成为高级橡塑模具的主要应用材料。 相似文献
80.
VORA Aditya Mahabhai 《上海大学学报(英文版)》2008,12(4)
A well-known pseudopotential is used to investigate the superconducting state parameters (SSP), viz., electron-phonon coupling strength, Coulomb pseudopotential, transition temperature, isotope effect exponent and effective interaction strength for AgxZn1-x and AgxAl1-x binary alloys theoretically for the first time. We have incorporated here five different types of the local field correction functions to show the effect of exchange and correlation on the aforesaid properties. Very strong influence of various exchange and correlation functions is concluded from the present study. Comparison with others such experimental values is encouraging, which confirms applicability of the model potential in explaining the superconducting state parameters of binary mixture. 相似文献