全文获取类型
收费全文 | 5128篇 |
免费 | 597篇 |
国内免费 | 397篇 |
专业分类
化学 | 365篇 |
晶体学 | 3篇 |
力学 | 471篇 |
综合类 | 228篇 |
数学 | 4143篇 |
物理学 | 912篇 |
出版年
2024年 | 8篇 |
2023年 | 23篇 |
2022年 | 92篇 |
2021年 | 135篇 |
2020年 | 101篇 |
2019年 | 79篇 |
2018年 | 86篇 |
2017年 | 167篇 |
2016年 | 230篇 |
2015年 | 132篇 |
2014年 | 290篇 |
2013年 | 314篇 |
2012年 | 296篇 |
2011年 | 330篇 |
2010年 | 298篇 |
2009年 | 361篇 |
2008年 | 330篇 |
2007年 | 363篇 |
2006年 | 329篇 |
2005年 | 289篇 |
2004年 | 237篇 |
2003年 | 250篇 |
2002年 | 196篇 |
2001年 | 159篇 |
2000年 | 136篇 |
1999年 | 120篇 |
1998年 | 143篇 |
1997年 | 98篇 |
1996年 | 86篇 |
1995年 | 56篇 |
1994年 | 51篇 |
1993年 | 44篇 |
1992年 | 51篇 |
1991年 | 28篇 |
1990年 | 15篇 |
1989年 | 26篇 |
1988年 | 18篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 35篇 |
1984年 | 18篇 |
1983年 | 18篇 |
1982年 | 18篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1959年 | 1篇 |
1936年 | 2篇 |
排序方式: 共有6122条查询结果,搜索用时 15 毫秒
101.
A multiparameter boundary-value problem of fresh infiltration water seepage in a drained fringe above quiescent saline water is solved in the direct statement and studied in detail. 相似文献
102.
研究函数族的正规性定则是复变函数论中的一个重要且有意义的工作.引进多元K-拟全纯函数的定义,并给出了多元K-拟全纯函数族的一个正规定则. 相似文献
103.
Summary Some stability and convergence theorems of the modified Ishikawa iterative sequences with errors for asymptotically nonexpansive
mapping in the intermediate sense and asymptotically pseudo contractive and uniformly Lipschitzian mappings in Banach spaces
are obtained. 相似文献
104.
《Surface and interface analysis : SIA》2006,38(1):19-24
We have been developing a new analytical transmission electron microscope (TEM), called a coincidence TEM, which in principle enables elemental mapping images to be observed at a high signal‐to‐noise (S/N) ratio under very low dose radiation conditions. In this paper, we report the development of a coincidence TEM with a digital waveform measuring system for obtaining a coincidence elemental mapping image. In this system, analog signals detected by a Si(Li) detector and a multianode, position‐sensitive photomultiplier (PSPM) are continuously converted into 12‐bit digital waveform data at a rate of 100 MHz, and transferred to a PC. From the transferred digital waveform data, information on X‐ray photon energy, electron incident position, and detection times of both X rays and electrons are calculated by digital waveform measurement, which lead to the observation of a successful coincidence elemental mapping image. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
105.
模糊神经网络在复合地基沉降量预测中的应用 总被引:1,自引:0,他引:1
复合地基后期沉降变形对于建筑物设计及安全具有重要意义,针对通过长期沉降观测以得到复合地基的最终沉降需要耗费较多资源的问题,提出了一种基于模糊神经网络的预测方法.该方法考虑沉降变化过程有较大的随机性和模糊性,直接将样本数据进行模糊化,所得的模糊数代表了样本点集与控制点集中各分量之间的相关度,并依此建立模糊BP神经网络进行学习和估算.实验结果表明了该方法对沉降进行预测是可行与有效的,且在相对误差的有效控制方面优于BP网络方法与灰色方法. 相似文献
106.
P. A. V. Ferreira M. E. S. Machado 《Journal of Optimization Theory and Applications》1996,89(3):659-680
Projection and relaxation techniques are employed to decompose a multiobjective problem into a two-level structure. The basic manipulation consists in projecting the decision variables onto the space of the implicit tradeoffs, allowing the definition of a relaxed multiobjective master problem directly in the objective space. An additional subproblem tests the feasibility of the solution encountered by the relaxed problem. Some properties of the relaxed problem (linearity, small number of variables, etc.) render its solution efficient by a number of methods. Representatives of two different classes of multiobjective methods [the Geoffrion, Dyer, Feinberg (GDF) method and the fuzzy method of Baptistella and Ollero] are implemented and applied within this context to a water resources allocation problem. The results attest the computational viability of the overall procedure and its usefulness for the solution of multiobjective problems.This work was partially sponsored by grants from CNPq and FAPESP, Brazil. The authors are indebted to the anonymous reviewers for their valuable comments. 相似文献
107.
本文用Fuzzy数学的观点探讨了Fuzzy聚类分析,并通过对脊髓灰质炎病毒抗体水平的Fuzzy聚类分析,获得了良好的聚类效果,为该项问题的研究提供了科学依据。 相似文献
108.
A. Shapiro 《Journal of Optimization Theory and Applications》1990,66(3):477-487
Various definitions of directional derivatives in topological vector spaces are compared. Directional derivatives in the sense of Gâteaux, Fréchet, and Hadamard are singled out from the general framework of -directional differentiability. It is pointed out that, in the case of finite-dimensional spaces and locally Lipschitz mappings, all these concepts of directional differentiability are equivalent. The chain rule for directional derivatives of a composite mapping is discussed. 相似文献
109.
A decision scheme for the interpretation of spectra from wavelength dispersive X-ray fluorescence spectrometry is described that encompasses elements from three areas of artificial intelligence: fuzzy logic, rule based expert systems and neural net technology.After transforming the recorded spectra to line spectra by appropriate background correction a reasoning scheme is applied that takes into account not only the observed spectra, but also the recording conditions and prior spectroscopic information regarding the relative emission probabilities and the usefulness of the different lines for the purpose of element identification. The latter is done on the basis of a previously described scheme to compute conditional a posteriori Bayes probabilities for a mean matrix. These different pieces of information are then assembled into a battery of fuzzy rules. The importance of the rules as well as the importance of the X-ray lines is determined in a training process, similar to the one in a feedforward back-propagation network.To further stabilize the results this network is pruned in a second training cycle. This, however, had little effect on the quality of interpretation.The advantages of this approach to the interpretation of X-ray spectra over older ones are numerous: the system adapts itself to better interpret spectra that are of greater importance to a laboratory as these are better represented in the training set; the fuzzy logic is capable of working with incomplete and uncertain knowledge, and the neural network results based on these fuzzy rules is readily interpretable by the X-ray spectroscopist as every rule can be expressed also in natural language as in any classical rule based system.On leave from Silesian University, Katowice, Poland 相似文献
110.
Xiufang Xu Guichang Wang Xuezhuang Zhao Yinming Pan Yunxiao Liang Zhenfeng Shang 《Journal of mathematical chemistry》2007,41(2):143-160
In this paper, the fuzzy symmetry of some prototypical linear molecules has been analyzed. The results show that some molecular
orbitals (MOs) are less symmetrical but some others are more symmetrical than the molecular skeleton, which the MOs correspond
to. The membership functions of space inversion for MOs are closely related to the chemical characteristics of the MOs. Sometimes,
although the symmetry of a molecular skeleton is not obvious, however that of some MO is quite obvious. The membership functions
of the fuzzy inversion symmetry depend on the choice of the position of the center of inversion. As compared to those of diatomic
molecules and linear tri-atomic molecules, the linear polyatomic molecules in which a distinctive fuzzy symmetry of space
translation may exist, and thus a significant effect on their properties can be expected. 相似文献