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   70373篇
  免费   9863篇
  国内免费   6642篇
化学   46984篇
晶体学   659篇
力学   4661篇
综合类   515篇
数学   8449篇
物理学   25610篇
  2024年   228篇
  2023年   1399篇
  2022年   2280篇
  2021年   2468篇
  2020年   2522篇
  2019年   2422篇
  2018年   2189篇
  2017年   1939篇
  2016年   2964篇
  2015年   3078篇
  2014年   3650篇
  2013年   4843篇
  2012年   5889篇
  2011年   6014篇
  2010年   4079篇
  2009年   4018篇
  2008年   4187篇
  2007年   3788篇
  2006年   3567篇
  2005年   3092篇
  2004年   2478篇
  2003年   1895篇
  2002年   1682篇
  2001年   1520篇
  2000年   1418篇
  1999年   1563篇
  1998年   1330篇
  1997年   1169篇
  1996年   1227篇
  1995年   1071篇
  1994年   1007篇
  1993年   865篇
  1992年   768篇
  1991年   664篇
  1990年   555篇
  1989年   481篇
  1988年   366篇
  1987年   349篇
  1986年   297篇
  1985年   300篇
  1984年   202篇
  1983年   176篇
  1982年   145篇
  1981年   112篇
  1980年   82篇
  1978年   56篇
  1977年   52篇
  1976年   50篇
  1975年   57篇
  1973年   57篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
211.
Zhang W  Chen CH 《Tetrahedron letters》2005,46(11):1807-1810
A solution-phase synthesis of bicyclic prolines containing four points of diversity has been developed by a two-step synthesis involving 1,3-dipolar cycloaddition of perfluoroalkylsulfonyl-protected hydroxybenzaldehydes followed by Pd-catalyzed Suzuki coupling reaction of fluorous sulfonates with boronic acids. Both reactions are conducted under microwave irradiation and reaction mixtures are purified by solid-phase extractions without performing chromatography.  相似文献   
212.
A novel micro-injector has been fabricated for capillary electrophoresis (CE). It was successfully used for the determination of some indole derivatives for example melatonin (MT), serotonin (5-HT), tryptophan (Trp), and 5-hydroxy-tryptophane (5-HTrp) in the rat pineal gland by capillary electrophoresis with electrochemical detection (CE-EC). CE was performed in 0.20 mol L(-1) phosphate buffer (pH 8.0). The compounds investigated can be well separated and detected within 15 min. The working electrode used was a 300-microm diameter carbon electrode positioned opposite the outlet of the capillary. The relationship between peak current and analyte concentration was highly linear in the range from 0.10 to 500 micromol L(-1); detection limits (S/N = 3) were 0.03-0.13 micromol L(-1). The proposed method has been successfully used to analyze real biological samples.  相似文献   
213.
In this paper, we deal with the nonlinear second-order differential equation with damped vibration term involving p-Laplacian operator. Of particular interest is the resolution of an open problem. An interesting outcome from our result is that we can obtain the fast homoclinic solution with general superlinear growth assumption in suitable Sobolev space. To our knowledge, our theorems appear to be the first such result about damped vibration problem with p-Laplacian operator.  相似文献   
214.
Methodology and Computing in Applied Probability - Risk measures for tail risk have an important application in the dynamic portfolio insurance strategies. We propose a new risk measure called...  相似文献   
215.
In this paper, we prove the global well-posedness of the 3-D magnetohydrodynamics(MHD) equations with partial diffusion in the periodic domain when the initial velocity is small and the initial magnetic field is close to a background magnetic field satisfying the Diophantine condition.  相似文献   
216.
Summary A second order error bound is obtained for approximating h d by h d , where is a convolution of measures andQ a compound Poisson measure on a measurable abelian group, and the functionh is not necessarily bounded. This error bound is more refined than the usual total variation bound in the sense that it contains the functionh. The method used is inspired by Stein's method and hinges on bounding Radon-Nikodym derivatives related to . The approximation theorem is then applied to obtain a large deviation result on groups, which in turn is applied to multivariate Poisson approximation.Research of the second author was supported by Schweizerischer Nationalfonds  相似文献   
217.
Differential operator Lie algebras on the ring of Laurent polynomials   总被引:1,自引:0,他引:1  
A class of differential operator Lie algebras on the unit circle is introduced and discussed. They are the natural generalizations of the Witt algebra and the Virasoro algebra. Among them are the higher-spin algebrasW 1+ andW which occur in the physics literature.  相似文献   
218.
We estimate the kinematic measure of one convex domain moving to another under the groupG of rigid motions in n . We first estimate the kinematic formula for the total scalar curvature D 0gD 1 Rdv of then–2 dimensional intersection submanifold D 0gD 1. Then we use Chern and Yen's kinematic fundamental formula and our integral inequality to obtain a sufficient condition for one convex domain to contain another in n (4). Forn=4, we directly obtain another sufficient condition in 4.  相似文献   
219.
220.
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