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   39938篇
  免费   718篇
  国内免费   327篇
化学   18680篇
晶体学   294篇
力学   1642篇
综合类   12篇
数学   10709篇
物理学   9646篇
  2023年   94篇
  2022年   100篇
  2021年   217篇
  2020年   306篇
  2019年   314篇
  2018年   1322篇
  2017年   1598篇
  2016年   1124篇
  2015年   1005篇
  2014年   937篇
  2013年   1262篇
  2012年   3963篇
  2011年   3176篇
  2010年   2328篇
  2009年   1994篇
  2008年   1249篇
  2007年   1269篇
  2006年   1204篇
  2005年   4997篇
  2004年   4336篇
  2003年   2667篇
  2002年   854篇
  2001年   459篇
  2000年   234篇
  1999年   309篇
  1998年   257篇
  1997年   211篇
  1996年   161篇
  1995年   132篇
  1994年   127篇
  1993年   118篇
  1992年   239篇
  1991年   221篇
  1990年   191篇
  1989年   178篇
  1988年   153篇
  1987年   94篇
  1986年   84篇
  1985年   95篇
  1984年   77篇
  1983年   76篇
  1982年   69篇
  1981年   76篇
  1979年   76篇
  1978年   68篇
  1977年   62篇
  1976年   129篇
  1975年   79篇
  1974年   63篇
  1973年   82篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We prove that the nodal set (zero set) of a solution of a generalized Dirac equation on a Riemannian manifold has codimension 2 at least. If the underlying manifold is a surface, then the nodal set is discrete. We obtain a quick proof of the fact that the nodal set of an eigenfunction for the Laplace-Beltrami operator on a Riemannian manifold consists of a smooth hypersurface and a singular set of lower dimension. We also see that the nodal set of a Δ-harmonic differential form on a closed manifold has codimension 2 at least; a fact which is not true if the manifold is not closed. Examples show that all bounds are optimal. Received: 28 October 1996 / Accepted: 3 March 1997  相似文献   
92.
93.
We investigate the origin of the attraction in theK¯K channel around the threshold by introducing an additional channel to theππ andK¯K channels in a separable potential formalism assuming, in general, no direct interaction in theK¯K channel. To reproduce the features of the data, we find that the threshold of the additional channel is much above thef 0(975) meson position. We show that this three-channel problem can be reduced to an effective two-channel problem where thef 0(975) behaves as if it were aK¯K molecule bound by the coupling to the exotic channel. This picture is also supported by the fact that a single pole only, in the complexK¯K momentum plane, is associated to thef 0(975) meson. Various physical observables, like the decay branching ratio and theK¯K scattering length, are then discussed in an effective two-channel framework.  相似文献   
94.
The separation of the toxicologically important aldehyde acrolein from other carbonyl compounds by high performance liquid chromatography after derivatization to 2,4-dinitrophenylhydrazones is critically discussed on the basis of a selection of published methods. A method is proposed whereby the compounds acrolein, acetone, and propanal may be reproducibly separated to baseline by a reversed phase HPLC procedure employing a ternary mixture of methanol, water, and acetonitrile as mobile phase.  相似文献   
95.
The invariance of the geometric mean G with respect to the Lagrangian mean-type mapping (Lf,Lg), i.e. the equation G○(Lf,Lg)=G, is considered. We show that the functions f and g must be of high class regularity. This fact allows to reduce the problem to a differential equation and determine the second derivatives of the generators f and g.  相似文献   
96.
In the paper we indicate an error made in the proof of the main result of the paper [M.A. Darwish, On quadratic integral equation of fractional orders, J. Math. Anal. Appl. 311 (2005) 112-119]. Moreover, we provide correct proof of a slightly modified version of the mentioned result. The main tool used in our proof is the technique associated with the Hausdorff measure of noncompactness.  相似文献   
97.
Recently-formulated centrifugal distortion corrections to the spin-spin Hamiltonian have been used to analyse the first excited triplet state (ã3A2) of deuterated selenoformaldehyde. By including six spin-spin centrifugal distortion parameters, it is possible to account for the energy levels of this state using a single set of three rotational constants, A, B, and C, where previously nine spin-dependent parameters were required.  相似文献   
98.
In this paper we deal with nonlinear second-order boundary value problems with impulses. The impulsive functions depend implicitly on the different considered variables and the boundary value conditions are nonlinear. In both cases functional dependence on the solution is allowed. The existence results follow from the existence of a pair of well-ordered lower and upper solutions.  相似文献   
99.
We study linear dynamical systems with multidimensional time in Banach spaces. Using Taylor functional calculus we prove that under additional assumptions hyperbolic systems have shadowing property.  相似文献   
100.
A Fubini theorem     
Let I0 be the σ-ideal of subsets of a Polish group generated by Borel sets which have perfectly many pairwise disjoint translates. We prove that a Fubini-type theorem holds between I0 and the σ-ideals of Haar measure zero sets and of meager sets. We use this result to give a simple proof of a generalization of a theorem of Balcerzak-Ros?anowski-Shelah stating that I0 on N2 strongly violates the countable chain condition.  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