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   11929篇
  免费   356篇
  国内免费   63篇
化学   7698篇
晶体学   71篇
力学   375篇
数学   2157篇
物理学   2047篇
  2023年   66篇
  2022年   196篇
  2021年   220篇
  2020年   177篇
  2019年   230篇
  2018年   208篇
  2017年   221篇
  2016年   367篇
  2015年   358篇
  2014年   345篇
  2013年   726篇
  2012年   786篇
  2011年   847篇
  2010年   503篇
  2009年   443篇
  2008年   685篇
  2007年   633篇
  2006年   621篇
  2005年   569篇
  2004年   471篇
  2003年   443篇
  2002年   338篇
  2001年   197篇
  2000年   161篇
  1999年   139篇
  1998年   109篇
  1997年   101篇
  1996年   113篇
  1995年   93篇
  1994年   101篇
  1993年   116篇
  1992年   86篇
  1991年   89篇
  1990年   87篇
  1989年   79篇
  1988年   69篇
  1987年   61篇
  1986年   49篇
  1985年   95篇
  1984年   107篇
  1983年   78篇
  1982年   85篇
  1981年   65篇
  1980年   79篇
  1979年   63篇
  1978年   51篇
  1977年   77篇
  1976年   56篇
  1975年   56篇
  1974年   48篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
Book rewiev     
Howard Anton and Robert C. Busby, John Wiley & Sons, Inc., 2002.  相似文献   
3.
In order to understand better the way in which radioactive contamination may be transferred from the atmosphere to other ecological compartments it is necessary to obtain information of the deposition mechanisms of radionuclides. Concentration and speciation of 137Cs and 7Be in the atmospheric aerosol and deposition were studied. The mixed deposition velocities of water-soluble and insoluble 137Cs and 7Be were determined. The relation between activity concentrations of insoluble 7Be in the atmosphere and its amount in deposition was observed. It is supposed that in the deposition process of radiocesium the precipitation plays an important role in scavenging of water-soluble radiocesium by falling raindrops, in contrast to insoluble 137Cs where the dry deposition becomes predominant.  相似文献   
4.
In this paper we highlighted the synthesis, characterization, and practical exploitation of different types of polyphosphazenes substituted with fluorinated groups. There are several ways in which fluorine atoms can be inserted into polyphosphazenes, all of which leading to different polymers showing a wide range of characteristics. In general it is true that the insertion of fluorine atoms into phosphazene macromolecules leads to an enhancement of the thermal stability, flame resistance, low-temperature elastomericity, and chemical inertness of the phosphazenes obtained. The contribution of Italian research groups to the preparation and exploitation of organic commercial macromolecules grafted onto fluorinated polyphosphazenes is also reviewed.  相似文献   
5.
The control of piecewise-deterministic processes is studied where only local boundedness of the data is assumed. Moreover the discount rate may be zero. The value function is shown to be solution to the Bellman equation in a weak sense; however the solution concept is strong enough to generate optimal policies. Continuity and compactness conditions are given for the existence of nonrelaxed optimal feedback controls.  相似文献   
6.
This is a conceptual overview on a polemical subject: the problem of time asymmetry. It is proved that time asymmetry can be considered as a global generalized symmetry breaking, produced by a choice of a physically admissible state space, in a global Gel'fand triplet. The well-known physics of irreversible process can be studied using this mathematical structure and all the arrows of time can be explained and coordinated. But the deeper problems of time definition and time arrow in quantum gravity remain outside of this landscape.  相似文献   
7.
The purpose of this paper is to give the Reid ``Roundabout Theorem' for quadratic functionals with general boundary conditions. In particular, we describe the so-called coupled point and regularity condition introduced in [16] in terms of Riccati equation solutions. Accepted 27 February 1996  相似文献   
8.
The article referenced above was first published online on 30 August 2007 with incorrect pagination; the pagination has now been corrected online and in print. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
9.
10.
Pentacyclic isoxazolines were obtained by the cycloaddition of benzonitrile oxide to norbornene-azetidinone-fused 3,1-oxazines. The constitutions of two of the isomers obtained, and the configurations and conformations of all products, were determined by means of 1H and 13C NMR spectroscopy and DNOE experiments.  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