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   423866篇
  免费   3679篇
  国内免费   864篇
化学   212136篇
晶体学   6640篇
力学   20343篇
综合类   17篇
数学   56310篇
物理学   132963篇
  2020年   2705篇
  2019年   2951篇
  2018年   11449篇
  2017年   12242篇
  2016年   9337篇
  2015年   4343篇
  2014年   5817篇
  2013年   14871篇
  2012年   14730篇
  2011年   24621篇
  2010年   15830篇
  2009年   15968篇
  2008年   21617篇
  2007年   24811篇
  2006年   11571篇
  2005年   16573篇
  2004年   12432篇
  2003年   11502篇
  2002年   9506篇
  2001年   9948篇
  2000年   7763篇
  1999年   5806篇
  1998年   4789篇
  1997年   4652篇
  1996年   4514篇
  1995年   4214篇
  1994年   4077篇
  1993年   3764篇
  1992年   4613篇
  1991年   4631篇
  1990年   4412篇
  1989年   4458篇
  1988年   4430篇
  1987年   4329篇
  1986年   4110篇
  1985年   5309篇
  1984年   5472篇
  1983年   4376篇
  1982年   4621篇
  1981年   4542篇
  1980年   4274篇
  1979年   4725篇
  1978年   4906篇
  1977年   4819篇
  1976年   4719篇
  1975年   4408篇
  1974年   4407篇
  1973年   4389篇
  1972年   2977篇
  1968年   2751篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
31.
32.
To achieve efficient proton pumping in the light-driven proton pump bacteriorhodopsin (bR), the protein must be tightly coupled to the retinal to rapidly convert retinal isomerization into protein structural rearrangements. Methyl group dynamics of bR embedded in lipid nanodiscs were determined in the dark-adapted state, and were found to be mostly well ordered at the cytosolic side. Methyl groups in the M145A mutant of bR, which displays only 10 % residual proton pumping activity, are less well ordered, suggesting a link between side-chain dynamics on the cytosolic side of the bR cavity and proton pumping activity. In addition, slow conformational exchange, attributed to low frequency motions of aromatic rings, was indirectly observed for residues on the extracellular side of the bR cavity. This may be related to reorganization of the water network. These observations provide a detailed picture of previously undescribed equilibrium dynamics on different time scales for ground-state bR.  相似文献   
33.
Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C5H5)Ru(NCMe)3]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations.  相似文献   
34.
ABSTRACT

The Coupled-Cluster (CC) theory is one of the most successful high precision methods used to solve the stationary Schrödinger equation. In this article, we address the mathematical foundation of this theory with focus on the advances made in the past decade. Rather than solely relying on spectral gap assumptions (non-degeneracy of the ground state), we highlight the importance of coercivity assumptions – Gårding type inequalities – for the local uniqueness of the CC solution. Based on local strong monotonicity, different sufficient conditions for a local unique solution are suggested. One of the criteria assumes the relative smallness of the total cluster amplitudes (after possibly removing the single amplitudes) compared to the Gårding constants. In the extended CC theory the Lagrange multipliers are wave function parameters and, by means of the bivariational principle, we here derive a connection between the exact cluster amplitudes and the Lagrange multipliers. This relation might prove useful when determining the quality of a CC solution. Furthermore, the use of an Aubin–Nitsche duality type method in different CC approaches is discussed and contrasted with the bivariational principle.  相似文献   
35.
Russian Journal of Physical Chemistry A - Rapidly quenched alloys of aluminum with cobalt and zirconium are investigated using a combination of means of physicochemical analysis to study the...  相似文献   
36.
37.
38.
39.
40.
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