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   114207篇
  免费   7071篇
  国内免费   8387篇
化学   28157篇
晶体学   1907篇
力学   3542篇
综合类   354篇
数学   18905篇
物理学   43641篇
综合类   33159篇
  2022年   399篇
  2021年   458篇
  2020年   804篇
  2019年   1126篇
  2018年   1051篇
  2017年   816篇
  2016年   653篇
  2015年   678篇
  2014年   1771篇
  2013年   2312篇
  2012年   2001篇
  2011年   2556篇
  2010年   3011篇
  2009年   7804篇
  2008年   9008篇
  2007年   8291篇
  2006年   7687篇
  2005年   5727篇
  2004年   5590篇
  2003年   5786篇
  2002年   6546篇
  2001年   5187篇
  2000年   4633篇
  1999年   4706篇
  1998年   3744篇
  1997年   3085篇
  1996年   3153篇
  1995年   3621篇
  1994年   3703篇
  1993年   2799篇
  1992年   2118篇
  1991年   2253篇
  1990年   2276篇
  1989年   1982篇
  1988年   1837篇
  1987年   1189篇
  1986年   695篇
  1985年   1248篇
  1984年   759篇
  1983年   556篇
  1982年   656篇
  1981年   799篇
  1980年   724篇
  1979年   561篇
  1978年   584篇
  1977年   539篇
  1976年   542篇
  1975年   322篇
  1974年   360篇
  1973年   465篇
排序方式: 共有10000条查询结果,搜索用时 891 毫秒
991.
一类二阶两点边值问题的单调迭代方法   总被引:2,自引:0,他引:2  
通过改进经典的单调迭代方法对于一类二阶两点边值的问题的正解建立了单调迭代程序。这些迭代程序都是从常值函数开始的,因而是可行并且有效的。  相似文献   
992.
1 IntroductionForsolvingstiffinitialvalueproblemsforsystemsofODEsy′=f(y) ,y(t0 ) =y0 ,t0 <t≤T ,y0 ,y∈Rm,f :Ω Rm →Rm (1 .1 )manyparticularone blockmethodsoftheformYn+1= AYn+h( B0 F(Yn) + B1F(Yn+1) ) , A =A Im, Bi=Bi Im,A ,Bi∈Rr×r,Yn =(YTnr,… ,yT(n+1)r- 1) T,F(Yn) =(fT(ynr) ,… ,fT(y(n+1)r- 1) ) T,yj≈ y(tj) ,…  相似文献   
993.
It was proved in 1957 by Huber that any complete surface with integrable Gauss curvature is conformally equivalent to a compact surface with a finite number of points removed. Counterexamples show that the curvature assumption must necessarily be strengthened in order to get an analogous conclusion in higher dimensions. We show in this paper that any non compact Riemannian manifold with finite -norm of the Ricci curvature satisfies Huber-type conclusions if either it is a conformal domain with volume growth controlled from above in a compact Riemannian manifold or if it is conformally flat of dimension 4 and a natural Sobolev inequality together with a mild scalar curvature decay assumption hold. We also get partial results in other dimensions. Received: April 14, 2000; revised version: March 20, 2001  相似文献   
994.
In this paper a uniqueness theorem for a skewperiodic boundary value problem is obtained. By using the optimal control method, we derive the best estimate for the integration mean ensuring that the results hold.  相似文献   
995.
A high-pressure structural study of SrCeO3 has been performed at room temperature by Raman spectroscopy and X-ray diffraction up to 32 and 45 GPa, respectively. A first-order reversible phase transition is observed at about 12 GPa in both techniques. A second weak structural change, taking place between 18 and 25 GPa, can be suspected from Raman data. The increase in the number of Raman bands and diffraction lines is an indication that the symmetry is lowered and the compound does not evolve towards the ideal cubic perovskite structure. A Rietveld analysis of X-ray data was performed for the low-pressure phase and the atomic positions and the cell lattice parameters variations are reported in this paper. The volume compressibility derived from Raman modes (5.6×10−12 Pa−1), involving mainly bond-stretching for each type of polyhedron, is found to be close to the one obtained from volume cell variations measured by X-ray diffraction (7.9×10−12 Pa−1).  相似文献   
996.
环上矩阵的广义Moore-Penrose逆   总被引:14,自引:0,他引:14  
刘淑丹  游宏 《数学杂志》2002,22(1):116-120
本文给出带有对合的有1的结合环上一类矩阵的广义Moore-Penrose逆存在的充要条件,而这类矩阵概括了左右主理想整环,单Artin环上所有矩阵。  相似文献   
997.
本文利用ασ仿紧子集的概念,给出了在正则空间条件下,仿紧空间在连续闭映射下的原象是仿紧空间的一个充分条件.这一结果,统一推广了高国士教授与陈必胜教授在两篇论文中的结果.  相似文献   
998.
A new formulation derived from thermal characters of inclusions and host films for estimating laser induced damage threshold has been deduced. This formulation is applicable for dielectric films when they are irradiated by laser beam with pulse width longer than tens picoseconds. This formulation can interpret the relationship between pulse-width and damage threshold energy density of laser pulse obtained experimentally. Using this formulation, we can analyze which kind of inclusion is the most harmful inclusion. Combining it with fractal distribution of inclusions, we have obtained an equation which describes relationship between number density of inclusions and damage probability. Using this equation, according to damage probability and corresponding laser energy density, we can evaluate the number density and distribution in size dimension of the most harmful inclusions.  相似文献   
999.
We attempt a justification of a generalisation of the consistent histories programme using a notion of probability that is valid for all complete sets of history propositions. This consists of introducing Cox's axioms of probability theory and showing that our candidate notion of probability obeys them. We also give a generalisation of Bayes' theorem and comment upon how Bayesianism should be useful for the quantum gravity/cosmology programmes. PACS: 02.50.Cw;03.65.Ta;04.60.-m.  相似文献   
1000.
We present Hall effect measurements on highly oriented pyrolytic graphite that indicate the occurrence of the integer quantum-Hall-effect. The evidence is given by the observation of regular plateau-like structures in the field dependence of the transverse conductivity obtained in van der Pauw configuration. Measurements with the Corbino-disk configuration support this result and indicate that the quasi-linear and non-saturating longitudinal magnetoresistance in graphite is governed by the Hall effect in agreement with a recent theoretical model for disordered semiconductors.  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