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   398390篇
  免费   3149篇
  国内免费   1196篇
化学   202088篇
晶体学   6618篇
力学   19602篇
综合类   11篇
数学   45439篇
物理学   128977篇
  2020年   3481篇
  2019年   4165篇
  2018年   5716篇
  2017年   5657篇
  2016年   7894篇
  2015年   4366篇
  2014年   7531篇
  2013年   17283篇
  2012年   13148篇
  2011年   15961篇
  2010年   11978篇
  2009年   12082篇
  2008年   14949篇
  2007年   14839篇
  2006年   13628篇
  2005年   12118篇
  2004年   11490篇
  2003年   10276篇
  2002年   10172篇
  2001年   11553篇
  2000年   8769篇
  1999年   6773篇
  1998年   5726篇
  1997年   5729篇
  1996年   5355篇
  1995年   4825篇
  1994年   4857篇
  1993年   4810篇
  1992年   5223篇
  1991年   5426篇
  1990年   5144篇
  1989年   5159篇
  1988年   5111篇
  1987年   4989篇
  1986年   4777篇
  1985年   6292篇
  1984年   6552篇
  1983年   5306篇
  1982年   5525篇
  1981年   5409篇
  1980年   5165篇
  1979年   5552篇
  1978年   5590篇
  1977年   5666篇
  1976年   5760篇
  1975年   5290篇
  1974年   5257篇
  1973年   5388篇
  1972年   3936篇
  1971年   3428篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field.  相似文献   
23.
24.
The results of experimental investigations on thermal nonequilibrium ionization in CO2: N2: He mixtures are presented. Measurements of electron density, ne, in vibrationally excited nitrogen were made in a supersonic flow with different CO2 contents as well as in a CO2: N2: He = 1 : 5 : 4 mixture laser gas. The mixtures were heated in a shock tube and expanded through a supersonic nozzle. Furthermore, supersonic mixing of N2 and CO2 + He was used in some experiments. The measured values of ne in the plenum chamber and in the supersonic nozzle are reported, and the processes responsible for nonequilibrium ionization in a laser-active medium are discussed.  相似文献   
25.
26.
    
3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenylsydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding carbamates (3a-h), 4,4′-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a-l). Compounds (5a-l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a-l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a-l). All these compounds exhibited moderate antimicrobial activity against the few microbes tested. The carbamates have been found to be more toxic against fourth instar larvae ofAedes aegypti, in particular, then-butyl derivative (3e).  相似文献   
27.
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   
28.
A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally related series to evaluate the effect of lateral chloro group and its position on mesomorphism This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003.  相似文献   
29.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures.  相似文献   
30.
Radio Engineering and Electronics Institute, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1113–1124, September, 1989.  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