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   330635篇
  免费   3075篇
  国内免费   936篇
化学   165226篇
晶体学   5409篇
力学   15535篇
综合类   7篇
数学   38545篇
物理学   109924篇
  2021年   3139篇
  2020年   3339篇
  2019年   3775篇
  2018年   5202篇
  2017年   5445篇
  2016年   7388篇
  2015年   4151篇
  2014年   7052篇
  2013年   15935篇
  2012年   12400篇
  2011年   14847篇
  2010年   11028篇
  2009年   10934篇
  2008年   13250篇
  2007年   13213篇
  2006年   12154篇
  2005年   10546篇
  2004年   9855篇
  2003年   8707篇
  2002年   8691篇
  2001年   10405篇
  2000年   7666篇
  1999年   5984篇
  1998年   4981篇
  1997年   4822篇
  1996年   4487篇
  1995年   3884篇
  1994年   3831篇
  1993年   3714篇
  1992年   4107篇
  1991年   4320篇
  1990年   4112篇
  1989年   4014篇
  1988年   3787篇
  1987年   3926篇
  1986年   3686篇
  1985年   4639篇
  1984年   4694篇
  1983年   3898篇
  1982年   3983篇
  1981年   3709篇
  1980年   3652篇
  1979年   3924篇
  1978年   3917篇
  1977年   3922篇
  1976年   3895篇
  1975年   3688篇
  1974年   3622篇
  1973年   3656篇
  1972年   2607篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
241.
This article studies some geometrical aspects of the semidefinite linear complementarity problem (SDLCP), which can be viewed as a generalization of the well-known linear complementarity problem (LCP). SDLCP is a special case of a complementarity problem over a closed convex cone, where the cone considered is the closed convex cone of positive semidefinite matrices. It arises naturally in the unified formulation of a pair of primal-dual semidefinite programming problems. In this article, we introduce the notion of complementary cones in the semidefinite setting using the faces of the cone of positive semidefinite matrices and show that unlike complementary cones induced by an LCP, semidefinite complementary cones need not be closed. However, under R0-property of the linear transformation, closedness of all the semidefinite complementary cones induced by L is ensured. We also introduce the notion of a principal subtransformation with respect to a face of the cone of positive semidefinite matrices and show that for a self-adjoint linear transformation, strict copositivity is equivalent to strict semimonotonicity of each principal subtransformation. Besides the above, various other solution properties of SDLCP will be interpreted and studied geometrically.  相似文献   
242.
E. J. S. Lage 《Physica A》1987,140(3):629-636
We study critical dynamics of general q-state Potts models on d-dimensional hypercubic lattices. The master equation is formulated according to a theory recently presented by the author. A simple bond moving technique, followed by decimation, is used to obtain the dynamical exponents. Although this approximation yields poor results for the static exponents, the dynamic behaviour is closer to Monte Carlo simulations. We compare our results with those obtained with a different formulation of dynamics. A final discussion is included.  相似文献   
243.
使用美国甚大天线阵(VLA).对Markarian 8星系进行了多频观测.多频VLA观测表明,Markarian 8星系有三个主要的射电子成份,它们浸在一个弥漫的星系包层中.包层的射电谱是陡的非热谱.本文根据VLA观测确定了包层的物理参量,并讨论了包层中相对论性电子的可能起因.本文估计了包层非热辐射所要求的超新星爆发率.  相似文献   
244.
245.
246.
The Ni(II) ion catalyzed thermal decomposition of peroxomonosulfate (PMS) was studied in the pH range 3.42–5.89. The rate is first order in [PMS] and Ni(II) ion concentrations. At pH greater than or equal to 5.23, the reaction becomes zero order in [PMS] and this changeover in the order of the reaction occurs at a higher concentration of nickel ions. The first‐order kinetics in PMS can be explained as a rate‐limiting step and is the transformation of nickel peroxomonosulfate into nickel peroxide. This peroxide intermediate reacts rapidly with another PMS to give oxygen and Ni(II). The formation of nickel peroxide is associated with a small negative or nearly zero entropy of activation. The zero‐order kinetics in [PMS] can be explained by the fact that the hydrolysis of aquated nickel(II) ions into hydroxocompounds is the rate‐limiting step. The turnover number is 2 at pH 3.42 and increases with pH. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 320–237, 2007  相似文献   
247.
The kinetics of oxidation of Fe2+ by [Co(C3H2O4)3]3? in acidic solutions at 605 nm showed a simple first-order dependence in each reactant concentration. The second-order rate constant dependence on [H+] is in accordance with eqn (i) k2 = k′2 + k3[H+] (i) where k′2 and k3 have values of 73.4 ± 14.0 M ?1 s?1 and 353 ± 41 M?2 s?1, respectively, at 1.0 M ionic strength (NaClO4) and 25°C. At 310 nm the formation and decomposition of an intermediate, believed to be [FeC3H2O4]+, was observed. The increase in the rate of oxidation with increasing [H+] was interpreted in terms of a “one-ended” dissociation mechanism which facilitates chelation of Fe2+ by the carbonyl oxygens of malonate in the transition state.  相似文献   
248.
A generalization of theG-theory defined by A. Heilet al. is presented.  相似文献   
249.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 4, pp. 613–618, October, 1991.  相似文献   
250.
The possibility of inflation without any genuine scalar is discussed. It is suggested that drops of primordial plasma may drive inflation. The model, although naive, is consistent with observational data.  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