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   442637篇
  免费   5063篇
  国内免费   1281篇
化学   238487篇
晶体学   6560篇
力学   18941篇
综合类   14篇
数学   50835篇
物理学   134144篇
  2021年   3887篇
  2020年   4299篇
  2019年   4624篇
  2018年   5943篇
  2017年   5821篇
  2016年   9003篇
  2015年   5722篇
  2014年   8742篇
  2013年   20520篇
  2012年   16093篇
  2011年   19758篇
  2010年   13790篇
  2009年   13551篇
  2008年   18052篇
  2007年   17964篇
  2006年   16688篇
  2005年   14976篇
  2004年   13893篇
  2003年   12192篇
  2002年   11980篇
  2001年   13517篇
  2000年   10163篇
  1999年   7980篇
  1998年   6628篇
  1997年   6380篇
  1996年   6162篇
  1995年   5525篇
  1994年   5453篇
  1993年   5259篇
  1992年   5870篇
  1991年   5951篇
  1990年   5688篇
  1989年   5499篇
  1988年   5536篇
  1987年   5399篇
  1986年   5118篇
  1985年   6624篇
  1984年   6732篇
  1983年   5323篇
  1982年   5439篇
  1981年   5401篇
  1980年   4979篇
  1979年   5383篇
  1978年   5518篇
  1977年   5415篇
  1976年   5348篇
  1975年   4933篇
  1974年   4915篇
  1973年   4902篇
  1972年   3467篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
The luminescence and scintillation properties of poly(methyl methacrylate) containing 1,1,3-trimethyl-3-phenylindan were studied.  相似文献   
102.
103.
Ascidia malaca gametes before fertilization incubated in 10?5 or 10?7 M solutions of tributyltin(IV) chloride, TBTCl, for 3 h appear highly damaged under transmission electron microscopy observation. Also, the fertilization process is affected by the compound: the damaged spermatozoa are present in the vitelline coat and the egg does not cleave. An increase of microbodies, structurally similar to peroxisomes, have been detected in the egg peripheral cytoplasm, probably in relation to their role in alleviating damage to some cellular components. The results have shown that the reproduction of ascidians under unfavourable environmental conditions is prevented. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
104.
The main transitions of cellulose fatty esters with different degrees of substitution (DSs) were investigated with dynamic mechanical thermal analysis. Two distinct main relaxations were observed in partially substituted cellulose esters (PSCEs). They were attributed to the glass‐transition temperature and to the chain local motion of the aliphatic substituents. The temperatures of both transitions decreased when DS or the number of carbon atoms (n) of the acyl substituent increased. Conversely, all the transitions of fully substituted cellulose esters occurred within a narrow temperature range, and they did not vary significantly with n. This phenomenon was explained by the formation of a crystalline phase of the fatty substituents. The presence of few residual OH groups in PSCEs was responsible for a large increase in the storage bending modulus, and it eliminated the effect of n on damping. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 281–288, 2003  相似文献   
105.
In this paper, we find the approximate solution of a second order nonlinear partial differential equation on a simple connected region inR 2. We transfer this problem to a new problem of second order nonlinear partial differential equation on a rectangle. Then, we transformed the later one to an equivalent optimization problem. Then we consider the optimization problem as a distributed parameter system with artificial controls. Finally, by using the theory of measure, we obtain the approximate solution of the original problem. In this paper also the global error inL 1 is controlled.  相似文献   
106.
An arbitrary operator-valued function from the generalized Shur class is realized as the transfer function of a minimal optimal and minimal *-optimal dissipative scattering system with the Pontryagin state space. These results generalize Arov's results for the case of the Hilbert state space. Bibliography: 11 titles.  相似文献   
107.
108.
109.
The projection approach is applied to construct and investigate an operator-difference scheme for fluid dynamics in Lagrangean variables which has first-order local approximation in the axisymmetric case near the symmetry axis. The scheme also has operator properties that make it suitable for rederiving and substantiating previous results, methods, and algorithms.  相似文献   
110.
Journal of Nanoparticle Research - It was shown that the thermoelastic martensite transformation B2 ? B19 inside nanoparticles surrounded by amorphous matrix in Ni–Ti–Cu alloys as...  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