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   306786篇
  免费   4273篇
  国内免费   1426篇
化学   171819篇
晶体学   4442篇
力学   12453篇
综合类   23篇
数学   34842篇
物理学   88906篇
  2021年   1838篇
  2020年   2240篇
  2019年   2240篇
  2018年   2102篇
  2017年   2050篇
  2016年   4330篇
  2015年   3558篇
  2014年   4593篇
  2013年   13463篇
  2012年   10998篇
  2011年   13676篇
  2010年   8339篇
  2009年   8203篇
  2008年   12505篇
  2007年   12366篇
  2006年   12064篇
  2005年   11359篇
  2004年   10101篇
  2003年   8752篇
  2002年   8544篇
  2001年   9096篇
  2000年   7140篇
  1999年   5622篇
  1998年   4486篇
  1997年   4523篇
  1996年   4414篇
  1995年   4063篇
  1994年   3808篇
  1993年   3640篇
  1992年   4069篇
  1991年   3992篇
  1990年   3623篇
  1989年   3609篇
  1988年   3620篇
  1987年   3584篇
  1986年   3366篇
  1985年   4932篇
  1984年   4958篇
  1983年   4059篇
  1982年   4536篇
  1981年   4270篇
  1980年   4236篇
  1979年   4165篇
  1978年   4337篇
  1977年   4204篇
  1976年   4122篇
  1975年   4047篇
  1974年   3785篇
  1973年   4040篇
  1972年   2403篇
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
101.
The conformational properties of polymers derived from isocyanodipeptides have been investigated with a combination of model calculations, X‐ray diffraction, and circular dichroism spectroscopy. Depending on the configuration of the side chains, defined arrays of hydrogen bonds along the polymeric backbone are formed. This leads to a well‐defined conformation as, for example, expressed in the formation of lyotropic liquid‐crystalline phases and increased helical stability. Upon the disruption of the hydrogen bonds by a strong acid, a less well‐defined macromolecular conformation is observed. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1725–1736, 2003  相似文献   
102.
We have analyzed the methyl fluoride RQ(J,0)Q branch lines located near 1475 cm−1 using a simultaneous multi-spectrum fitting technique. In this analysis we have used previously recorded diode-laser data in which we collected many data points covering only one or two Q branch lines in a particular run. The analysis consists of simultaneously fitting 57 spectra collected with numerous pressure and path length conditions for all absorption lines. The data are concatenated to create one continuous spectrum of the Q branch. We have determined the intensity and self-broadened widths at 296 K for 23 RQ(J,0) lines.  相似文献   
103.
104.
105.
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   
106.
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described.  相似文献   
107.
108.
109.
To further evaluate the causality between endogenous pyrogen (EP)-induced fever and cyclic adenosine-3',5'-monophosphate (cyclic AMP) level, the effects of sodium salicylate (SS) on the febrile response and increased levels of cyclic AMP in both cerebrospinal fluid (c.s.f.) and plasma during EP-induced fever in rabbits were observed. The results suggest that cyclic AMP is probably involved in the central mediation of EP-induced fever and that increased concentration of cyclic AMP in c.s.f. associated with EP-induced fever is not the result of temperature elevation but appears to be caused by the increased synthesis in the central nervous system. In addition it is confirmed that blood is impossibly a contributory source of increased cyclic AMP in c.s.f. during EP fever, and that SS may act subsequent to the increase in cyclic AMP.  相似文献   
110.
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