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   176843篇
  免费   16905篇
  国内免费   12156篇
化学   94322篇
晶体学   1850篇
力学   12063篇
综合类   666篇
数学   43455篇
物理学   53548篇
  2024年   351篇
  2023年   2067篇
  2022年   3668篇
  2021年   3866篇
  2020年   4175篇
  2019年   3958篇
  2018年   13234篇
  2017年   12765篇
  2016年   10562篇
  2015年   5703篇
  2014年   6328篇
  2013年   8069篇
  2012年   12852篇
  2011年   19330篇
  2010年   11927篇
  2009年   11964篇
  2008年   12901篇
  2007年   14256篇
  2006年   5772篇
  2005年   5888篇
  2004年   5097篇
  2003年   4818篇
  2002年   3627篇
  2001年   2459篇
  2000年   2229篇
  1999年   2203篇
  1998年   1924篇
  1997年   1701篇
  1996年   1748篇
  1995年   1480篇
  1994年   1314篇
  1993年   1096篇
  1992年   955篇
  1991年   838篇
  1990年   701篇
  1989年   560篇
  1988年   436篇
  1987年   395篇
  1986年   392篇
  1985年   308篇
  1984年   230篇
  1983年   189篇
  1982年   166篇
  1981年   116篇
  1980年   105篇
  1979年   70篇
  1978年   56篇
  1973年   42篇
  1914年   45篇
  1909年   41篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
In the present paper it is shown that if S1 and S2 are two Clifford topological semigroups satisfying certain conditions and T is an isometric isomorphism of LUC(S1*) onto LUC(S2*), then T maps S1 topologically isomorphically onto S2. Furthermore, T maps M l n(S1) (M(S1), respectively) isometrically isomorphically onto M l n(S2) (M(S2), respectively). Indeed, we have obtained a generalization of a well-known result of Ghahramani, Lau and Losert for locally compact groups to a more general setting of Clifford topological semigroups.  相似文献   
42.
This paper describes some work carried out in the Scientific Research and Development Branch (SRDB) of the Home Office, intended to contribute to an overall aim of building up internal expertise in the field of expert systems. This was done by carrying out a number of pilot and demonstrator projects, two of which are described in some detail. The plan, which proved successful, was to build as far as possible on the relevant skills already possessed by an OR group in the branch. The lessons learned from these are summarized in the hope that they will be of use to other groups who wish to become involved in this important area.  相似文献   
43.
Summary The electronic absorption and e.s.r. spectra of a crystal of the title compound [Cu(H2O)2 (C4H5O5)2] were recorded and experimental results are discussed quantitatively, using ligand field theory and the radial wave function of bound CuII. The electronic structure of the compound is consistent with its crystal structure.  相似文献   
44.
45.
本文讨论了每个元都有幂等元作为右单位元的左消半群与幂单半群N的Schuzenberger积M◇N的ρ类,证明了这种半群M与N的Schuzenberger积M◇N的ρ类是右E一半适合半群和弱E-headged半群.  相似文献   
46.
47.
48.
What strategy should a football (soccer, in American parlance) club adopt when deciding whether to sack its manager? This paper introduces a simple model assuming that a club's objective is to maximize the number of league points that it scores per season. The club's strategy consists of three choices: the length of the honeymoon period during which it will not consider sacking a new manager, the level of the performance trapdoor below which the manager get the sack, and the weight that it will give to more recent games compared to earlier ones. Some data from the last six seasons of the English Premiership are used to calibrate the model. At this early stage of the research, the best strategy appears to have only a short honeymoon period of eight games (much less than the actual shortest period of 12 games), to set the trapdoor at 0.74 points per game, and to put 47% of the weight on the last five games. A club adopting this strategy would obtain on average 56.8 points per season, compared to a Premiership average of 51.8 points.  相似文献   
49.
Effects of ion impinging on the microstructure and field electron emission properties of screen-printed carbon nanotube films were investigated. We observed that the plasma treatment modified the microstructure of CNTs along with the remarkable increase of emission site density. With the prolongation of ion impinging time, the emission current falls down first, and then rises up to higher than that of the untreated films. It is proposed that the change of emission characteristics is due to the different emission mechanisms. After the treatment, electrons are emitted predominantly from the nano-nodes on the tube wall instead from the nanotube tips.  相似文献   
50.
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