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   62503篇
  免费   4934篇
  国内免费   2980篇
化学   35726篇
晶体学   919篇
力学   3463篇
综合类   219篇
数学   6955篇
物理学   23135篇
  2023年   630篇
  2022年   1032篇
  2021年   1264篇
  2020年   1397篇
  2019年   1315篇
  2018年   1422篇
  2017年   1322篇
  2016年   1972篇
  2015年   1610篇
  2014年   2153篇
  2013年   3508篇
  2012年   3812篇
  2011年   4214篇
  2010年   2927篇
  2009年   2891篇
  2008年   3226篇
  2007年   2977篇
  2006年   2731篇
  2005年   2321篇
  2004年   1966篇
  2003年   1649篇
  2002年   1532篇
  2001年   1817篇
  2000年   1452篇
  1999年   1402篇
  1998年   1118篇
  1997年   1088篇
  1996年   980篇
  1995年   921篇
  1994年   820篇
  1993年   729篇
  1992年   744篇
  1991年   708篇
  1990年   684篇
  1989年   605篇
  1988年   586篇
  1987年   547篇
  1986年   466篇
  1985年   533篇
  1984年   533篇
  1983年   392篇
  1982年   437篇
  1981年   397篇
  1980年   330篇
  1979年   402篇
  1978年   378篇
  1977年   394篇
  1976年   391篇
  1975年   342篇
  1973年   339篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
161.
The purpose of this paper is to give the Reid ``Roundabout Theorem' for quadratic functionals with general boundary conditions. In particular, we describe the so-called coupled point and regularity condition introduced in [16] in terms of Riccati equation solutions. Accepted 27 February 1996  相似文献   
162.
163.
A Modified SQP Method and Its Global Convergence   总被引:6,自引:0,他引:6  
The sequential quadratic programming method developed by Wilson, Han andPowell may fail if the quadratic programming subproblems become infeasibleor if the associated sequence of search directions is unbounded. In [1], Hanand Burke give a modification to this method wherein the QP subproblem isaltered in a way which guarantees that the associated constraint region isnonempty and for which a robust convergence theory is established. In thispaper, we give a modification to the QP subproblem and provide a modifiedSQP method. Under some conditions, we prove that the algorithm eitherterminates at a Kuhn–Tucker point within finite steps or generates aninfinite sequence whose every cluster is a Kuhn–Tucker point.Finally, we give some numerical examples.  相似文献   
164.
Some of the motivations for as well as the main points of the quantization of the Nappi-Witten string in the light-cone gauge are reviewed.  相似文献   
165.
Unique crystallization and melting behavior in poly(aryl ether ketone ketone) containing alternated terephthalic and isophthalic moieties were studied by time-resolved synchrotron x-ray methods. Recently, this material has been shown to exhibit three polymorphs (forms I, II, and III). In this work, we further investigated their distinctive thermal properties and found that form I is the dominating and the most thermally stable phase while form II is favored by fast nucleation conditions and is the least stable phase. On the other hand, form III represents a minor intermediate phase that usually coexists with form I and can be transferred from form II and to form I. Structural and morphological changes in form I have been followed by simultaneous wide-angle x-ray diffraction (WAXD)/small-angle x-ray scattering (SAXS) measurements during cold- or melt-crystallization and subsequent melting. In all cases, a larger dimensional change was found in the crystallographic a-axis than the b-axis during heating and cooling. This may be due to the greater lateral stress variation with respect to temperature along the a direction of the primary lamellae which is induced by either the formation of secondary lamellae or the preferential chain-folding direction in poly(aryl ether ketone ketone)s. During the phase transitions of form II ← III in the cold-crystallized specimen and form III ← I in the melt-crystallized samples, lamellar variables (long period, lamellar thickness, and invariant) obtained from SAXS remain almost constant. This indicates that the density distribution in the long spacing is independent of the melting in form II or III. For melt-crystallization, the corresponding changes in unit-cell dimensions and lamellar morphology during the annealing-induced low endotherm are most consistent with the argument that these changes are due to the melting of thin lamellar population. © 1995 John Wiley & Sons, Inc.  相似文献   
166.
Parasupersymmetric quantum mechanics is generalized to the case of an arbitrary number of parasuperchanrgesN and the order of paraquantizationp. We show that parasuperpotentials can be explicitly expressed via a single arbitrary function. Institute of Mathematics, Ukrainian Academy of Sciences, Kiev. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 48, No. 9, pp. 1291–1294, September, 1996.  相似文献   
167.
168.
169.
激光除锈过程的实时监测技术研究   总被引:6,自引:1,他引:5  
徐军  孙振永  周文明  翁晓东 《光子学报》2002,31(9):1090-1092
对激光除锈过程中的实时监测技术进行了实验研究,结果表明:除锈过程中产生的声波强度会随着表面清洁度的变化而发生明显的变化,声波信号包含了除锈过程中的大量信息,可作为激光除锈实时监测的基本信号.  相似文献   
170.
张(1884—1950),植物学家和生物学教育家.中国近代植物学的先驱、现代实验性植物生理学和植物生态学的奠基人.最先自编我国第一套植物学、植物形态学、植物解剖学、种子植物分类学、植物生态学和植物生理学教科书.长期从事植物学科的教学和研究工作,为我国的生物科学和教育事业的建立和发展,贡献了自己的一切知识和力量.  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