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   356081篇
  免费   2377篇
  国内免费   640篇
化学   170375篇
晶体学   5410篇
力学   18521篇
综合类   9篇
数学   52547篇
物理学   112236篇
  2019年   2291篇
  2018年   11088篇
  2017年   11870篇
  2016年   8211篇
  2015年   3411篇
  2014年   4388篇
  2013年   10778篇
  2012年   12034篇
  2011年   21169篇
  2010年   13569篇
  2009年   13465篇
  2008年   18861篇
  2007年   22218篇
  2006年   9055篇
  2005年   13927篇
  2004年   10448篇
  2003年   9879篇
  2002年   7943篇
  2001年   7474篇
  2000年   5964篇
  1999年   4396篇
  1998年   3897篇
  1997年   3861篇
  1996年   3756篇
  1995年   3435篇
  1994年   3580篇
  1993年   3266篇
  1992年   3731篇
  1991年   3735篇
  1990年   3672篇
  1989年   3540篇
  1988年   3655篇
  1987年   3543篇
  1986年   3359篇
  1985年   4444篇
  1984年   4730篇
  1983年   3959篇
  1982年   4091篇
  1981年   4017篇
  1980年   3990篇
  1979年   3975篇
  1978年   4293篇
  1977年   4140篇
  1976年   4229篇
  1975年   3897篇
  1974年   3938篇
  1973年   4127篇
  1972年   2883篇
  1971年   2399篇
  1970年   2205篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Publication list     
The helium atom in its ground state, subject to strong magnetic fields, is treated using a variational method. Trial functions consisting of Gaussians with nonlinear parameters variationally optimized are used. The form of these functions is a generalized s-symmetry-state properly modified to admit spatial deformation along the direction on which the magnetic field is applied. © 1994 John Wiley & Sons, Inc.  相似文献   
112.
113.
The capability of gated saturable absorbers for single-pulse selection is studied theoretically using the classical space-time-dependent rate-equation model. The dynamics of operation is followed experimentally by the well-known pump—probe technique. Comparing the theoretical and experimental results, it is found that gated saturable absorbers can efficiently be used for pulse forming and pulse selection of pulses longer than picosecond.  相似文献   
114.
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   
115.
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   
116.
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   
117.
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   
118.
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   
119.
This paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included.  相似文献   
120.
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