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   38460篇
  免费   1403篇
  国内免费   160篇
化学   24126篇
晶体学   244篇
力学   658篇
综合类   4篇
数学   5909篇
物理学   9082篇
  2023年   262篇
  2022年   338篇
  2021年   596篇
  2020年   565篇
  2019年   559篇
  2018年   571篇
  2017年   565篇
  2016年   1151篇
  2015年   1023篇
  2014年   1068篇
  2013年   2023篇
  2012年   2081篇
  2011年   2488篇
  2010年   1387篇
  2009年   1307篇
  2008年   2183篇
  2007年   2082篇
  2006年   1960篇
  2005年   1743篇
  2004年   1380篇
  2003年   1222篇
  2002年   1063篇
  2001年   840篇
  2000年   712篇
  1999年   585篇
  1998年   465篇
  1997年   477篇
  1996年   536篇
  1995年   432篇
  1994年   425篇
  1993年   437篇
  1992年   424篇
  1991年   341篇
  1990年   312篇
  1989年   260篇
  1988年   245篇
  1987年   275篇
  1986年   276篇
  1985年   312篇
  1984年   353篇
  1983年   274篇
  1982年   302篇
  1981年   292篇
  1980年   273篇
  1979年   236篇
  1978年   241篇
  1977年   233篇
  1976年   203篇
  1975年   180篇
  1973年   173篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
We introduce the concept of quotient in PN spaces and give some examples. We prove some theorems with regard to the completeness of a quotient.  相似文献   
92.
Bubble pressure points of ethanol–1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea refrigerant) mixtures from the third Industrial Fluid Properties Simulation Challenge are computed using publicly available molecular simulation software. Several published force fields are compared against the known answers provided in the contest guidelines and the best force fields are used to make predictions for the unknown results.  相似文献   
93.
94.
Generally, in homotopy theory a cylinder object (or, its dual, a path object) is used to define homotopy between morphisms, and a cone object is used to build exact sequences of homotopy groups. Here, an axiomatic theory based on a cone functor is given. Suspension objects are associated to based objects and cofibrations, obtaining homotopy groups referred to an object and relative to a cofibration, respectively. Exact sequences of these groups are built. Algebraic and particular examples are given. We point out that the main results of this paper were already stated in [3], and the purpose of this article is to give full details of the foregoing.  相似文献   
95.
A six level rate equation system was used to investigate the impact of photodepletion to amplified spontaneous emission (ASE) of intramolecular proton-transfer (IPT) dyes incorporated into polymeric hosts. The model includes the most important transitions for the normal and tautomer form of the molecule as well as intersystem crossing and triplet–triplet transitions. The experimentally observed pulse shape as well as photodepletion phenomena, i.e. a first order exponential decay of the ASE intensity and a shortening in ASE pulse width, have been simulated successfully. Additionally, the model was used to propose an explanation of the unexpected high photodepletion of proton-transfer dyes in solids. The results show that the emission cross section and reabsorption cross section of the tautomer form of the molecule are the most important parameter not only for efficiency but also for photodepletion. The model was tested by comparison with experimental results of 2-(2’-hydroxyphenyl)benzimidazole in polymethylmethacrylate (PMMA), polystyrene (PS) and a 1:1 alternating copolymer matrix PS-co-PMMA. PACS 78.45.th; 42.55.Mv; 42.70.Jk  相似文献   
96.
97.
98.
99.
Schätz  T.  Schramm  U.  Habs  D. 《Hyperfine Interactions》2003,146(1-4):203-207
Hyperfine Interactions - In this paper, the conditions for which three-dimensional crystalline ion beams were attained in the rf quadrupole storage ring PALLAS at a velocity of around 2800 m/s are...  相似文献   
100.
It is shown that, if a parametrized fämily of extremals F can be stratified in a way compatible with the flow map generated by F, then those trajectories of the family which realize the minimal values of the cost in F are indeed optimal in comparison with all trajectories which lie in the region R covered by the trajectories of F. It is not assumed that F is a field covering the state space injectively. As illustration, an optimal synthesis is constructed for a system where the flow of extremals exhibits a simple cusp singularity.  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