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   40084篇
  免费   1090篇
  国内免费   163篇
化学   25866篇
晶体学   310篇
力学   666篇
综合类   4篇
数学   7031篇
物理学   7460篇
  2023年   254篇
  2022年   472篇
  2021年   620篇
  2020年   596篇
  2019年   663篇
  2018年   745篇
  2017年   679篇
  2016年   1360篇
  2015年   1102篇
  2014年   1157篇
  2013年   2413篇
  2012年   2400篇
  2011年   2577篇
  2010年   1635篇
  2009年   1547篇
  2008年   2295篇
  2007年   2246篇
  2006年   2062篇
  2005年   1892篇
  2004年   1621篇
  2003年   1314篇
  2002年   1125篇
  2001年   863篇
  2000年   771篇
  1999年   605篇
  1998年   453篇
  1997年   440篇
  1996年   549篇
  1995年   410篇
  1994年   434篇
  1993年   389篇
  1992年   375篇
  1991年   334篇
  1990年   313篇
  1989年   260篇
  1988年   247篇
  1987年   245篇
  1986年   245篇
  1985年   318篇
  1984年   327篇
  1983年   218篇
  1982年   238篇
  1981年   237篇
  1980年   232篇
  1979年   165篇
  1978年   160篇
  1977年   163篇
  1976年   143篇
  1975年   129篇
  1973年   130篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
In this paper we study constant mean curvature compact surfaces with two Jordan curves in parallel planes as boundary and we investigate the point at which the surface inherits the symmetries of its boundary.  相似文献   
4.
5.
We prove a general compactness result for the solution set of the compressible Navier–Stokes equations with respect to the variation of the underlying spatial domain. Among various corollaries, we then prove a general existence theorem for the system in question with no restrictions on smoothness of the spatial domain. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
6.
Surface relief formation at holographic recording on amorphous selenium films was demonstrated and investigated. The presence of this optical phase modulation component is essential for ensuring significant, stable and erasable optical recording in a-Se films at 290–320 K temperatures, where conventional photodarkening was known as insignificant and unstable. Photocrystallization can only be observed in super-exposed a-Se films at the given experimental conditions of hologram recording. Erasing behavior of surface relief gratings under heat treatment was also investigated in order to reveal further details of the mechanism. Photoinduced structural transformations within the amorphous phase, connected to local ordering under the condition of light-induced fluidity, are proposed as an explanation for the relief formation and erasing. The observed reversible optical recording process may be useful for the various optoelectronic applications of photoconductive a-Se layers. Received: 12 June 2000 / Accepted: 6 June 2001 / Published online: 30 August 2001  相似文献   
7.
We give sufficient conditions for Sobolev and Lipschitz functions in terms of their lower scaled-oscillation. The sharpness of these conditions is shown by examples. Our examples also show that a Stepanov-type differentiability theorem does not hold under the boundedness assumption of the lower scaled-oscillation.

  相似文献   

8.
9.
Regioselective demethylation of 3,4-dihydropapaveraldine (2a) at 7 and 3' positions affords a properly substituted diphenolic key intermidiate (2d) for the synthesis of reticuline and N-norreticuline.  相似文献   
10.
The rational and sustainable exploitation of nature resources is one of the priority objectives of our society. In this article a method is proposed to evaluate and exploit the energetic resources contained in different forest formations. This method is based on the use of a combustion bomb calorimeter to determine the calorific values of the different samples studied. These results were complemented with chemical analysis of the samples and with environmental and geomorphological studies of the zones were samples were taken. The results obtained during the last 3 years for the residual biomass originated from the forest formations existing in Galicia ensure the reliability and usefulness of the method that can be extended to any forest formation all over the world.  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