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   534993篇
  免费   5118篇
  国内免费   2014篇
化学   262886篇
晶体学   8427篇
力学   27166篇
综合类   45篇
数学   74278篇
物理学   169323篇
  2020年   3867篇
  2019年   4267篇
  2018年   12331篇
  2017年   12916篇
  2016年   11218篇
  2015年   5664篇
  2014年   8025篇
  2013年   19659篇
  2012年   18335篇
  2011年   27758篇
  2010年   18486篇
  2009年   18350篇
  2008年   24848篇
  2007年   27532篇
  2006年   15958篇
  2005年   19125篇
  2004年   15621篇
  2003年   14424篇
  2002年   12686篇
  2001年   13015篇
  2000年   10226篇
  1999年   7851篇
  1998年   6859篇
  1997年   6668篇
  1996年   6499篇
  1995年   5910篇
  1994年   5968篇
  1993年   5765篇
  1992年   6241篇
  1991年   6404篇
  1990年   6099篇
  1989年   5907篇
  1988年   6048篇
  1987年   5813篇
  1986年   5484篇
  1985年   7442篇
  1984年   7783篇
  1983年   6461篇
  1982年   6716篇
  1981年   6623篇
  1980年   6499篇
  1979年   6592篇
  1978年   6974篇
  1977年   6724篇
  1976年   6912篇
  1975年   6371篇
  1974年   6394篇
  1973年   6600篇
  1972年   4620篇
  1971年   3863篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
We present the results of an experimental investigation of a RF splitting of57Fe hyperfine lines in the regime of NMR and Mössbauer double resonance. The experiments have been performed as a function of RF field intensity and static magnetic field magnitude. The intensity of the RF components and the separation between them are extremely sensitive to the frequency and amplitude of the RF magnetic field. The RF splitting of hyperfine lines is inversely proportional to the strength of the static magnetic field.  相似文献   
53.
Oxidation of the title compounds yields, besides the reported isoimides 3 and/or the amides 4 , also the imides 5 . The observed product dichotomy is considered as the result of an intramolecular nucleophilic attack on the aroyl group, of the pressumed zwitterionic intermediate 2 , by O or N present in the ambident N-aroylimine site of 2 . The results of AM1 calculations agree with the product studies and both permit the formulation of a set of rules correlating structure and selectivity.  相似文献   
54.
55.
The electrical conductivity of hydrosols of ultradispersed diamonds was studied. The electromembrane method for cleaning and concentrating of ultradispersed diamonds in hydrosols was considered. The influence exerted by the concentration of the dispersed phase on the electrical characteristics of the cleaning process was analyzed. A mathematical relation making it possible to evaluate the output characteristics of the process and to determine the geometrical characteristics of the apparatus was proposed.  相似文献   
56.
Nonperturbative nolocal structure of QCD vacuum is well described by instanton model. Specific helicity and flavor structure of zero modes of quarks, in instanton field allows simultaneously to explain some important features of low-and high-energy hadron phenomemology. The basic characteristics of hadron spectrum, partonic sum rules, heavyquark potential etc within the instanton liquid model are briefly discussed.  相似文献   
57.
The radiation emitted by charged, scalar particles in a Schwarzschild field with maximal acceleration corrections is calculated classically and in the tree approximation of quantum field theory. In both instances the particles emit radiation that has characteristics similar to those of gamma-ray bursters.  相似文献   
58.
This paper reports on the first experimental observation of quantum-well states and sp-type resonances in thin single-crystal gold, silver, and copper layers formed on single-crystal W(110) surfaces, which result from spatial localization of Bloch-type electronic wave functions in a quantum well with potential barriers at the vacuum/metal and metal/W(110) interfaces. The quantization of the valence-band electronic structure in Au/W(110), Ag/W(110), and Cu/W(110) systems was studied experimentally using angle-resolved photoelectron spectroscopy.  相似文献   
59.
60.
In this paper, the authors studied certain properties of the estimate of Liang and Krishnaiah (1985, J. Multivariate Anal. 16, 162–172) for multivariate binary density. An alternative shrinkage estimate is also obtained. The above results are generalized to general orthonormal systems.  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