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   1310842篇
  免费   28747篇
  国内免费   7722篇
化学   651743篇
晶体学   20105篇
力学   74139篇
综合类   103篇
数学   240365篇
物理学   360856篇
  2021年   13515篇
  2020年   15945篇
  2019年   16074篇
  2016年   27429篇
  2015年   20658篇
  2014年   30392篇
  2013年   74431篇
  2012年   36527篇
  2011年   32278篇
  2010年   36005篇
  2009年   38570篇
  2008年   31955篇
  2007年   27209篇
  2006年   34676篇
  2005年   26422篇
  2004年   28334篇
  2003年   26946篇
  2002年   28340篇
  2001年   26286篇
  2000年   23556篇
  1999年   21944篇
  1998年   20829篇
  1997年   20831篇
  1996年   21060篇
  1995年   19140篇
  1994年   18575篇
  1993年   18127篇
  1992年   17819篇
  1991年   18146篇
  1990年   17373篇
  1989年   17439篇
  1988年   16991篇
  1987年   17022篇
  1986年   15890篇
  1985年   22374篇
  1984年   23697篇
  1983年   19932篇
  1982年   21644篇
  1981年   20891篇
  1980年   20204篇
  1979年   20298篇
  1978年   21690篇
  1977年   21211篇
  1976年   20914篇
  1975年   19599篇
  1974年   19235篇
  1973年   19704篇
  1972年   14211篇
  1968年   12065篇
  1967年   12410篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Employing radical bridges between anisotropic metal ions has been a viable route to achieve high-performance single-molecule magnets (SMMs). While the bridges have been mainly considered for their ability to promote exchange interactions, the crystal-field effect arising from them has not been taken into account explicitly. This lack of consideration may distort the understanding and limit the development of the entire family. To shed light on this aspect, herein we report a theoretical investigation of a series of N -radical-bridged diterbium complexes. It is found that while promoting strong exchange coupling between the terbium ions, the N -radical induces a crystal field that interferes destructively with that of the outer ligands, and thus reduces the overall SMM behavior. Based on the theoretical results, we conclude that the SMM behavior in this series could be further maximized if the crystal field of the outer ligands is designed to be collinear with that of the radical bridge. This conclusion can be generalized to all exchange-coupled SMMs.  相似文献   
2.
3.
4.
5.
A liquid dewetting method for the determination of the viscoelastic properties of ultrathin polymer films has been extended to study thickness effects on the properties of ultrathin polycarbonate (PC) films. PC films with film thicknesses ranging from 4 to 299 nm were placed on glycerol at temperatures from below the macroscopic glass transition temperature (Tg) to above it with the dewetting responses being monitored. It is found that the isothermal creep results for films of the same thickness, but dewetted at different temperatures can be superposed into one master curve, which is consistent with the fact of PC being a thermorheologically simple material. Furthermore, the results show that the Tg of PC thin films is thickness dependent, but the dependence is weaker than the results for freely standing films and similar to literature data for PC films supported on rigid substrates. It was also found that the rubbery plateau region for the PC films stiffens dramatically, but still less than what has been observed for freely standing polycarbonate films. The rubbery stiffening is discussed in terms of a recently reported model that relates macroscopic segmental dynamics with the stiffening. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1559–1566  相似文献   
6.
7.
8.
9.
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   
10.
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