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   13604篇
  免费   1502篇
  国内免费   1210篇
化学   9872篇
晶体学   89篇
力学   56篇
综合类   55篇
数学   4890篇
物理学   1354篇
  2024年   29篇
  2023年   292篇
  2022年   215篇
  2021年   234篇
  2020年   468篇
  2019年   454篇
  2018年   462篇
  2017年   313篇
  2016年   515篇
  2015年   613篇
  2014年   838篇
  2013年   1239篇
  2012年   780篇
  2011年   915篇
  2010年   800篇
  2009年   867篇
  2008年   928篇
  2007年   879篇
  2006年   720篇
  2005年   533篇
  2004年   492篇
  2003年   496篇
  2002年   431篇
  2001年   298篇
  2000年   275篇
  1999年   270篇
  1998年   249篇
  1997年   164篇
  1996年   176篇
  1995年   217篇
  1994年   175篇
  1993年   123篇
  1992年   132篇
  1991年   65篇
  1990年   63篇
  1989年   55篇
  1988年   54篇
  1987年   31篇
  1986年   32篇
  1985年   56篇
  1984年   46篇
  1982年   53篇
  1981年   40篇
  1980年   30篇
  1979年   36篇
  1978年   34篇
  1977年   25篇
  1976年   29篇
  1975年   19篇
  1973年   19篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
A simple modification of the standard cross-polarization method designed for quenching the proton T dependence when studying polarization transfer is presented. It is demonstrated that by using this simple procedure, new and subtle details of cross-polarization dynamics, previously hidden by the T(1H) effect, can be observed in dipolar-coupled spin systems.  相似文献   
132.
ONTHEEXISTENCEANDUNIQUENESSTHEOREMSOFSOLUTIONSFORACLASSOFTHESYSTEMSOFMIXEDMONOTONEOPERATOREQUATIONSWITHAPPLICATIONSHENPEILONG...  相似文献   
133.
张贵芬 《光学学报》1994,14(6):79-582
报道了掺硫和掺氧NaCl:(F2^+)H色心激光器最新实验结果。最高输出功率分别达3W和4.8W。实验比较了掺硫及掺氧(F2^+)H心的热光稳定性。  相似文献   
134.
Results of H. Cartan about holomorphic automorphisms on bounded domains are generalized to the case of hyperbolic manifolds in the sense of Kobayashi. In this setting, we give an identity theorem together with its topological version. We show also that a sequence of automorphisms which converges uniformly on some nonempty open set, has a limit on the whole space which is an automorphism. At the end of the paper, conditions are given for the sequence of iterates of a self holomorphic map in order to be an automorphism.  相似文献   
135.
In 1957 Robert Ellis proved that a group with a locally compact Hausdorff topology T making all translations continuous also has jointly continuous multiplication and continuous inversion, and is thus a topological group. The theorem does not apply to locally compact asymmetric spaces such as the reals with addition and the topology of upper open rays. We first show a bitopological Ellis theorem, and then introduce a generalization of locally compact Hausdorff, called locally skew compact, and a topological dual, Tk, to obtain the following asymmetric Ellis theorem which applies to the example above:Whenever (X,⋅,T) is a group with a locally skew compact topology making all translations continuous, then multiplication is jointly continuous in both (X,⋅,T) and (X,⋅,Tk), and inversion is a homeomorphism between (X,T) and (X,Tk).This generalizes the classical Ellis theorem, because T=Tk when (X,T) is locally compact Hausdorff.  相似文献   
136.
We show that the existence of a non-metrizable compact subspace of a topological group G often implies that G contains an uncountable supersequence (a copy of the one-point compactification of an uncountable discrete space). The existence of uncountable supersequences in a topological group has a strong impact on bounded subsets of the group. For example, if a topological group G contains an uncountable supersequence and K is a closed bounded subset of G which does not contain uncountable supersequences, then any subset A of K is bounded in G?(K?A). We also show that every precompact Abelian topological group H can be embedded as a closed subgroup into a precompact Abelian topological group G such that H is bounded in G and all bounded subsets of the quotient group G/H are finite. This complements Ursul's result on closed embeddings of precompact groups to pseudocompact groups.  相似文献   
137.
The hyperspaces of strongly countable dimensional compacta of positive dimension and of strongly countable dimensional continua of dimension greater than 1 in the Hilbert cube are homeomorphic to the Hurewicz set of all nonempty countable closed subsets of the unit interval [0,1]. These facts hold true, in particular, for covering dimension dim and cohomological dimension dimG, where G is any Abelian group.  相似文献   
138.
We show that a theorem of Shchepin and Repovš concerning the smoothness of compacta follows from the theory of semicontinuous relations.  相似文献   
139.
苯对N,N-二甲基甲酰胺化合物1H NMR的影响研究   总被引:1,自引:0,他引:1  
本文研究了N,N-二甲基甲酰胺(DMF)在四氯化碳和苯混合溶剂中的1H NMR。观察到N,N-二甲基甲酰胺(DMF)分子中两个甲基和混合溶剂中苯的共振吸收峰的化学位移随苯的摩尔分数增加而逐渐移向高场,而且两个甲基共振吸收峰向高场移动的程度不同,α甲基较β甲基为甚。DMF分子中两个甲基和混合溶剂中苯的化学位移可以用线性方程表示(δ=A+Bx),这里x是混合溶剂中苯的摩尔分数。相关系数R接近于-1。  相似文献   
140.
We study a degenerate nonlinear variational inequality which can be reduced to a multivalued inclusion by an appropriate change of the unknown function. We establish existence, uniqueness and regularity results. An application arising in the theory of water diffusion in porous media is discussed as an example.   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