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   26660篇
  免费   1039篇
  国内免费   143篇
化学   19190篇
晶体学   221篇
力学   542篇
数学   3356篇
物理学   4533篇
  2023年   180篇
  2022年   230篇
  2021年   378篇
  2020年   497篇
  2019年   474篇
  2018年   321篇
  2017年   281篇
  2016年   756篇
  2015年   638篇
  2014年   763篇
  2013年   1267篇
  2012年   1665篇
  2011年   1851篇
  2010年   1047篇
  2009年   883篇
  2008年   1517篇
  2007年   1442篇
  2006年   1436篇
  2005年   1328篇
  2004年   1162篇
  2003年   872篇
  2002年   925篇
  2001年   457篇
  2000年   385篇
  1999年   382篇
  1998年   372篇
  1997年   348篇
  1996年   361篇
  1995年   307篇
  1994年   333篇
  1993年   322篇
  1992年   275篇
  1991年   208篇
  1990年   235篇
  1989年   202篇
  1988年   210篇
  1987年   186篇
  1986年   170篇
  1985年   290篇
  1984年   269篇
  1983年   187篇
  1982年   210篇
  1981年   193篇
  1980年   186篇
  1979年   171篇
  1978年   199篇
  1977年   187篇
  1976年   148篇
  1974年   170篇
  1973年   141篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
We report the coexistence of γ(γ′) and θ alumina grown on the CoAl(1 0 0) surface. Both phases were observed after annealing of alumina at 1150 K by means of scanning tunnelling microscopy (STM). The crystal structures of γ(γ′) and θ alumina were indexed based on low energy electron diffraction (LEED) and STM experimental data.  相似文献   
92.
Thomas McCauley 《Pramana》2006,67(4):681-689
I briefly review the present and future status of the burgeoning field of neutrino astronomy. I outline the astrophysics and particle physics goals, design, and performance of the various current and proposed neutrino telescopes. Also described are present results and future expectations.  相似文献   
93.
We construct random locally compact real trees called Lévy trees that are the genealogical trees associated with continuous-state branching processes. More precisely, we define a growing family of discrete Galton–Watson trees with i.i.d. exponential branch lengths that is consistent under Bernoulli percolation on leaves; we define the Lévy tree as the limit of this growing family with respect to the Gromov–Hausdorff topology on metric spaces. This elementary approach notably includes supercritical trees and does not make use of the height process introduced by Le Gall and Le Jan to code the genealogy of (sub)critical continuous-state branching processes. We construct the mass measure of Lévy trees and we give a decomposition along the ancestral subtree of a Poisson sampling directed by the mass measure. T. Duquesne is supported by NSF Grants DMS-0203066 and DMS-0405779. M. Winkel is supported by Aon and the Institute of Actuaries, EPSRC Grant GR/T26368/01, le département de mathématique de l’Université d’Orsay and NSF Grant DMS-0405779.  相似文献   
94.
Signaling in living systems needs to achieve high specificity, to be reversible, and to achieve high signal to noise. Signaling mediated by multiprotein systems has evolved that avoids the requirement for high-affinity binary complexes that would be difficult to reverse and which, in the overcrowded cell, would lead to excessive noise in the system. Symmetrical structures are only occasionally formed. When they are, it is principally to colocate components, for example, the tyrosyl kinases of growth factors, where dimers form. Symmetry is, however, often broken, presumably to create more sensitivity and specificity in the signaling system by assembling other components, into higher-order multiprotein systems. The binding of a single heparin to two 1:1 FGF:FGFR complexes is an example, as is the binding of a single ligase to the Xrcc4 dimer, perhaps so creating a further DNA-binding site.  相似文献   
95.
The palladium-catalyzed α-arylation of ketones on solid support is described. Using modified Buchwald-Hartwig reaction conditions, the coupling of immobilized 4-bromobenzamide with various aromatic, heteroaromatic, and aliphatic ketones was investigated. Subsequent cleavage from the resin provided the desired α-aryl ketones almost in moderate to high yields and good to excellent purities. The scope and limitations of this protocol will be discussed.  相似文献   
96.
Thomas  Hugh 《Order》2002,19(4):327-342
This paper is concerned with the d-dimensional cyclic polytope with n vertices, C(n,d), and the set of its triangulations, S(n,d). We show that there is a bijection between S(n,d) and certain partitions of the set of increasing d-tuples on the integers 1 to n–1. We give a combinatorial characterization of the second higher Stasheff–Tamari poset, which is a partial ordering of S(n,d), and we determine its 2-dimension. There is a well-known representation of triangulations of an n-gon by right bracket vectors. We generalize this to cyclic polytopes of higher dimensions.  相似文献   
97.
We construct a generic extension in which the ℵ2nd canonical function on ℵ1 exists. Supported by NSF and by a Fulbright grant. Publ. 378. Partially supported by the B.S.F.  相似文献   
98.
99.
There does not exist a Borel choice of generators for each finitely generated group which has the property that isomorphic groups are assigned isomorphic Cayley graphs.

  相似文献   

100.
Ohne Zusammenfassung  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