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   215445篇
  免费   1558篇
  国内免费   627篇
化学   117924篇
晶体学   3270篇
力学   8349篇
综合类   6篇
数学   23305篇
物理学   64776篇
  2020年   1970篇
  2019年   2263篇
  2018年   3205篇
  2017年   3113篇
  2016年   4267篇
  2015年   2371篇
  2014年   3818篇
  2013年   9261篇
  2012年   6892篇
  2011年   8434篇
  2010年   6071篇
  2009年   5921篇
  2008年   8136篇
  2007年   8206篇
  2006年   7629篇
  2005年   6936篇
  2004年   6166篇
  2003年   5641篇
  2002年   5498篇
  2001年   5939篇
  2000年   4684篇
  1999年   3472篇
  1998年   3007篇
  1997年   3033篇
  1996年   2823篇
  1995年   2319篇
  1994年   2419篇
  1993年   2450篇
  1992年   2595篇
  1991年   2657篇
  1990年   2559篇
  1989年   2533篇
  1988年   2463篇
  1987年   2434篇
  1986年   2357篇
  1985年   3037篇
  1984年   3194篇
  1983年   2559篇
  1982年   2827篇
  1981年   2703篇
  1980年   2503篇
  1979年   2718篇
  1978年   2833篇
  1977年   2856篇
  1976年   2832篇
  1975年   2687篇
  1974年   2665篇
  1973年   2810篇
  1972年   1875篇
  1967年   1830篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Capabilities of the imaging techniques, in which X-rays are converted to electrons and then the emitted electrons are registered by means of an electron microscope, are analyzed, the focus being on the factors limiting lateral resolution at the stage of electron emission. Bearing in mind the tendency to use harder synchrotron X-rays for some combined X-ray-electron microscopy methods, calculations were made for two significantly different X-ray energies: E = 1.828 keV (K-edge of Si) and E = 11.923 keV (L3-edge of Au). By using Monte Carlo simulations of the electron trajectories beneath the surface of the sample we show that the radius of the spot from which photoelectrons are emitted could be as small as 1 nm. However, when proper account is taken of an entire electron cascade associated with the re-building of electron shells after photoelectron emission, spots more than one order of magnitude larger result, limiting the best lateral resolution to 20–30 nm.  相似文献   
993.
In this paper we approximate the solution of a linear initial-value problem, making use of a Schauder basis for certain Banach space associated with such a differential problem. In addition, we apply that results in order to calculate numerically the response from a structure modelled by a three degree-of-freedom mass–damper–spring system.  相似文献   
994.
The synthesis of 2-hydroxymethyl-2-propylmorphine ( 5 ) and 2-hydroxymethyl-2-propylnormorphine ( 7 ), the major rat urinary metabolites of 3-O-t-butylmorphine ( 3 ) are described.  相似文献   
995.
996.
997.
998.
The connection is considered of multiplicity distributions in three stages: partonic, hadronization, and hadronic. An interpretation of the LoPHD parameter is found. It is shown that under specific hypotheses on the form of the mass spectrum, the statistical bootstrap model leads to the negative binomial distribution (NBD) at the hadronic stage of development of the multiple production process with specific analytic dependences of the parameters of the NBD.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 28–32, May, 1991.One of the authors (V. I. Kuvshinov) is thankful to R. Hagedorn and G. Burgers for numerous discussions.  相似文献   
999.
1000.
Coupled and decoupled Taylor-Galerkin algorithms are considered for viscoelastic flow and a model problem—transient startup Poiseuille flow in a channel under a fixed pressure gradient. All algorithms reproduce the steady-state solutions and are stable at high elasticity numbers (E). For a fixed mesh, the coupled and decoupled versions (TGC and TGD) give exceptional time-accuracy at low elasticity numbers [to within O(1%) at E = 1] and reasonable accuracy at high elasticity numbers [to within O(10%) at E = 10, 100]. By definition, the decoupled false-transient scheme (TGF), which uses different time scales for velocity and stress time stepping, provides a poor transient history. Where the main requirement is to compute a steady-state algorithm efficiency is crucial. The TGF scheme attains a steady state between six to eight times faster than does the TGC scheme, and the latter is over twice as fast as the TGD form. © 1994 John Wiley & Sons, Inc.  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