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   5859篇
  免费   207篇
  国内免费   33篇
化学   3658篇
晶体学   23篇
力学   192篇
数学   1196篇
物理学   1030篇
  2023年   58篇
  2022年   136篇
  2021年   180篇
  2020年   156篇
  2019年   153篇
  2018年   129篇
  2017年   116篇
  2016年   242篇
  2015年   229篇
  2014年   240篇
  2013年   334篇
  2012年   410篇
  2011年   463篇
  2010年   268篇
  2009年   246篇
  2008年   373篇
  2007年   337篇
  2006年   308篇
  2005年   296篇
  2004年   232篇
  2003年   176篇
  2002年   188篇
  2001年   70篇
  2000年   46篇
  1999年   63篇
  1998年   51篇
  1997年   64篇
  1996年   48篇
  1995年   47篇
  1994年   45篇
  1993年   33篇
  1992年   25篇
  1991年   28篇
  1990年   21篇
  1989年   19篇
  1988年   22篇
  1987年   25篇
  1986年   19篇
  1985年   25篇
  1984年   22篇
  1983年   13篇
  1982年   22篇
  1981年   12篇
  1980年   14篇
  1979年   14篇
  1978年   15篇
  1977年   9篇
  1976年   6篇
  1973年   7篇
  1972年   5篇
排序方式: 共有6099条查询结果,搜索用时 15 毫秒
61.
62.
We exhibit a general class of interactive decision situations in which all the agents benefit from more information. This class includes as a special case the classical comparison of statistical experiments à la Blackwell. AMS 2000 Subject Classification:Primary 91A35.The work of Bruno Bassan and Marco Scarsini was partially supported by MIUR-COFIN. The authors express their thanks to Sylvain Sorin for enlightening comments.  相似文献   
63.
 We consider some conditions under which a smooth projective variety X is actually the projective space. We also extend to the case of positive characteristic some results in the theory of vector bundle adjunction. We use methods and techniques of the so called Mori theory, in particular the study of rational curves on projective manifolds. Received: 16 May 2002 / Revised version: 18 November 2002 Published online: 3 March 2003 Mathematics Subject Classification (2000): 14E30, 14J40, 14J45  相似文献   
64.
We develop here a version of abstract homotopical algebra based onhomotopy kernels andcokernels, which are particular homotopy limits and colimits. These notions are introduced in anh-category, a sort of two-dimensional context more general than a 2-category, abstracting thenearly 2-categorical properties of topological spaces, continuous maps and homotopies. A setting which applies also, at different extents, to cubical or simplicial sets, chain complexes, chain algebras, ... and in which homotopical algebra can be established as a two-dimensional enrichment of homological algebra.Actually, a hierarchy of notions ofh-,h1-, ...h4-categories is introduced, through progressive enrichment of thevertical structure of homotopies, so that the strongest notion,h4-category, is a sort of relaxed 2-category. After investigating homotopy pullbacks and homotopical diagrammatical lemmas in these settings, we introduceright semihomotopical categories, ash-categories provided with terminal object and homotopy cokernels (mapping cones), andright homotopical categories, provided also with anh4-structure and verifying second-order regularity properties forh-cokernels.In these frames we study the Puppe sequence of a map, its comparison with the sequence of iterated homotopy cokernels and theh-cogroup structure of the suspension endofunctor. Left (semi-) homotopical categories, based on homotopy kernels, give the fibration sequence of a map and theh-group of loops. Finally, the self-dual notion of homotopical categories is considered, together with their stability properties.Lavoro esequito nell'ambito dei progetti di ricerca del MURST.  相似文献   
65.
The reactivity with air moisture of finely divided crystals of Na β and Li+-containing β-aluminas is analyzed with thermogravimetric and X-ray techniques. For Na β-alumina two distinct water intake processes are evident: 1) a fast one, controlled by the elastic interactions among water molecules near the crystal boundaries; 2) a slow one, driven by water diffusion away from the boundaries. For finely divided crystals of Li β-alumina the two processes cannot be distinguished but the slow one is observable in crystals of macroscopic dimensions. The water intake is generally accompanied by an expansion of the c-axis. However, the relationship between water content and c-parameter is highly non-linear and the c-axis length at room temperature depends upon the thermal history of the sample. Our results confirm previous reports suggesting that β-aluminas absorb about one water molecule per cation of the conducting plane.  相似文献   
66.
This paper discusses the numerical solution of eigenvalue problems for Hamiltonian systems of ordinary differential equations. Two new codes are presented which incorporate the algorithms described here; to the best of the author’s knowledge, these are the first codes capable of solving numerically such general eigenvalue problems. One of these implements a new new method of solving a differential equation whose solution is a unitary matrix. Both codes are fully documented and are written inPfort-verifiedFortran 77, and will be available in netlib/aicm/sl11f and netlib/aicm/sl12f.  相似文献   
67.
68.
Characterization of a Marshall-Olkin type class of distributions   总被引:1,自引:0,他引:1  
Summary A class of bivariate distributions that generalize Marshall-Olkin's one is characterized through a functional equation which involves two associative operations. The obtained distributions concentrate positive mass on the linex=y when the two associative operations coincide; otherwise a positive mass is concentrated on a continuous monotone function. Work performed while the authors were members of CNR-GNAFA.  相似文献   
69.
In this paper we study the conformal geometry of immersed submanifolds of the Möbius spaceS n introducing the conformal Gauss map. In particular we relate its harmonicity to an extended notion of Willmore surface which originated from the work of Bryant. For a more detailed account the reader is referred to the Introduction.(on leave)  相似文献   
70.
Proton-proton small angle correlations have been measured in neon-nucleus collisions, using the 4 pi detector Diogene, at 400 and 800 MeV per nucleon incident energies. Values of the size of the emitting region are obtained by comparison with the Koonin formula, taking into account the biases of the apparatus. The dependence of the density on target mass and incident energy is also analysed.  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