首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   315211篇
  免费   3755篇
  国内免费   1093篇
化学   170933篇
晶体学   4466篇
力学   13161篇
综合类   7篇
数学   36372篇
物理学   95120篇
  2020年   1987篇
  2019年   1957篇
  2018年   1971篇
  2017年   1880篇
  2016年   3870篇
  2015年   3244篇
  2014年   4437篇
  2013年   14030篇
  2012年   10756篇
  2011年   13402篇
  2010年   8291篇
  2009年   8291篇
  2008年   12360篇
  2007年   12598篇
  2006年   12241篇
  2005年   11170篇
  2004年   10060篇
  2003年   8874篇
  2002年   8730篇
  2001年   10133篇
  2000年   7733篇
  1999年   6145篇
  1998年   4915篇
  1997年   4765篇
  1996年   4809篇
  1995年   4388篇
  1994年   4133篇
  1993年   3955篇
  1992年   4455篇
  1991年   4310篇
  1990年   4016篇
  1989年   3838篇
  1988年   4134篇
  1987年   3799篇
  1986年   3684篇
  1985年   5328篇
  1984年   5405篇
  1983年   4385篇
  1982年   4759篇
  1981年   4799篇
  1980年   4556篇
  1979年   4673篇
  1978年   4673篇
  1977年   4656篇
  1976年   4620篇
  1975年   4515篇
  1974年   4361篇
  1973年   4530篇
  1972年   2575篇
  1971年   1882篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
We study the induced measure obtained from a 1-step Markov measure, supported by a topological Markov chain, after the mapping of the original alphabet onto another one. We give sufficient conditions for the induced measure to be a Gibbs measure (in the sense of Bowen) when the factor system is again a topological Markov chain. This amounts to constructing, when it does exist, the induced potential and proving its Hölder continuity. This is achieved through a matrix method. We provide examples and counterexamples to illustrate our results.  相似文献   
53.
The conformational properties of polymers derived from isocyanodipeptides have been investigated with a combination of model calculations, X‐ray diffraction, and circular dichroism spectroscopy. Depending on the configuration of the side chains, defined arrays of hydrogen bonds along the polymeric backbone are formed. This leads to a well‐defined conformation as, for example, expressed in the formation of lyotropic liquid‐crystalline phases and increased helical stability. Upon the disruption of the hydrogen bonds by a strong acid, a less well‐defined macromolecular conformation is observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1725–1736, 2003  相似文献   
54.
55.
The decomposition of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) molecules during evaporation of unpurified raw material in ultra high vacuum was studied. The fragments were identified by mass spectrometry and the influence of these fragments and further contaminations of the raw material on the electronic structure of PTCDA thin films was measured by photoemission spectroscopy. Annealing of contaminated PTCDA films was tested as cheap and easy to perform method for (partial) post deposition purification of the contaminated films.  相似文献   
56.
Equilibrium Problems with Applications to Eigenvalue Problems   总被引:5,自引:0,他引:5  
In this paper, we consider equilibrium problems and introduce the concept of (S)+ condition for bifunctions. Existence results for equilibrium problems with the (S)+ condition are derived. As special cases, we obtain several existence results for the generalized nonlinear variational inequality studied by Ding and Tarafdar (Ref. 1) and the generalized variational inequality studied by Cubiotti and Yao (Ref. 2). Finally, applications to a class of eigenvalue problems are given.  相似文献   
57.
In a recent paper to this journal (Whitman A M et al 2003 Waves Random Media 13 269-86) we derived a set of coupled equations that describe the intermodal scattering of acoustic radiation in a duct whose speed of sound varies randomly in space and time. In the paper we were mainly interested in modes that were not near cutoff. Here we study the solution of these equations in the vicinity of the cutoff. We find that near cutoff almost all the energy is reflected back independent of the other duct parameters. In addition to presenting these results, we analyse the mathematical structure of the equations in these regions in order to elucidate the reason for this behaviour.  相似文献   
58.
We show that there are close relations between extremal problems in dual Brunn-Minkowski theory and isotropic-type properties for some Borel measures on the sphere. The methods we use allow us to obtain similar results in the context of Firey-Brunn-Minkowski theory. We also study reverse inequalities for dual mixed volumes which are related with classical positions, such as ?-position or isotropic position.  相似文献   
59.
60.
Summary This paper presents some applications of cyclic voltammetry at the interface of two immiscible electrolyte solutions by means of an experimental set-up described in a former publication. When using special sample preparation good results are obtained for the determination of iodide and quinine in pharmaceutical products as well as for the determination of quinine in tonic water and dodecylsulfate in a tooth-salt.

Herrn Prof. Dr. Günther Tölg zum 60. Geburtstag gewidmet  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号