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   214799篇
  免费   2040篇
  国内免费   472篇
化学   113701篇
晶体学   3472篇
力学   10450篇
综合类   10篇
数学   23505篇
物理学   66173篇
  2021年   2320篇
  2020年   2310篇
  2019年   2831篇
  2018年   3922篇
  2017年   3907篇
  2016年   5274篇
  2015年   2761篇
  2014年   4743篇
  2013年   9399篇
  2012年   7713篇
  2011年   8986篇
  2010年   7068篇
  2009年   7263篇
  2008年   8458篇
  2007年   8363篇
  2006年   7344篇
  2005年   6538篇
  2004年   6125篇
  2003年   5564篇
  2002年   5528篇
  2001年   5802篇
  2000年   4323篇
  1999年   3258篇
  1998年   2817篇
  1997年   2872篇
  1996年   2676篇
  1995年   2300篇
  1994年   2409篇
  1993年   2293篇
  1992年   2593篇
  1991年   2707篇
  1990年   2596篇
  1989年   2657篇
  1988年   2557篇
  1987年   2581篇
  1986年   2440篇
  1985年   3076篇
  1984年   3137篇
  1983年   2619篇
  1982年   2592篇
  1981年   2549篇
  1980年   2355篇
  1979年   2720篇
  1978年   2685篇
  1977年   2881篇
  1976年   2876篇
  1975年   2673篇
  1974年   2608篇
  1973年   2722篇
  1972年   2088篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
301.
Bibliography: 42 titles.__________Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 306, 2003, pp. 7–15.  相似文献   
302.
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   
303.
    
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   
304.
305.
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   
306.
307.
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   
308.
309.
310.
The composition of the vacuum arc plasma for five elements (Cd, Mg, Al, Ni, and Mo) is calculated by the Saha equation, which assumes local thermodynamic equilibrium conditions within the ionization region of the cathode spot(s). The lowering of the ionization potential due to the high density of charged particles is considered. By matching the computed and the measured plasma ionic composition, the electron density and the temperature are estimated. The experimental plasma compositions can be approximated only at a high electron density (1019-10 21 cm-3) and at electron temperatures in the range of a few electronvolts  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