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   2426篇
  免费   95篇
  国内免费   12篇
化学   1746篇
晶体学   12篇
力学   37篇
数学   465篇
物理学   273篇
  2023年   15篇
  2022年   18篇
  2021年   41篇
  2020年   45篇
  2019年   47篇
  2018年   24篇
  2017年   21篇
  2016年   65篇
  2015年   41篇
  2014年   56篇
  2013年   82篇
  2012年   113篇
  2011年   110篇
  2010年   59篇
  2009年   84篇
  2008年   134篇
  2007年   111篇
  2006年   106篇
  2005年   97篇
  2004年   88篇
  2003年   98篇
  2002年   96篇
  2001年   43篇
  2000年   65篇
  1999年   39篇
  1998年   50篇
  1997年   54篇
  1996年   51篇
  1995年   40篇
  1994年   48篇
  1993年   37篇
  1992年   30篇
  1991年   37篇
  1990年   24篇
  1989年   22篇
  1988年   31篇
  1987年   27篇
  1986年   17篇
  1985年   27篇
  1984年   42篇
  1983年   25篇
  1982年   35篇
  1981年   33篇
  1980年   30篇
  1979年   16篇
  1978年   17篇
  1977年   20篇
  1976年   17篇
  1975年   11篇
  1974年   9篇
排序方式: 共有2533条查询结果,搜索用时 15 毫秒
151.
152.
153.
154.
In the absence of gauge interactions the spontaneous breakdown of supersymmetry (Susy) is accompanied by a scalar field whose vacuum expectation value is not determined by the tree potential. Inclusion of the gauge interactions can fix this vev at the tree level. The situation is exemplified by a simpleSU(2)-model yielding nonvanishingF-andD-vevs.  相似文献   
155.
The graph G has star number n if any n vertices of G belong to a subgraph which is a star. Let f(n, k) be the smallest number m such that the complete graph on m vertices can be factorized into k factors with star number n. In the present paper we prove that c1nk ≤ f(n, k) < c2nk.  相似文献   
156.
The structures of 1,3,5-trisilylbenzene and hexasilylbenzene in the gas phase have been determined by electron diffraction, and that of 1,3,5-trisilylbenzene by X-ray crystallography. The structures of three trisilylbenzene isomers, three tetrasilylbenzenes, pentasilylbenzene and hexasilylbenzene have been computed, ab initio and using Density Functional Theory, at levels up to MP2/6-31G*. The primary effect of silyl substituents is to narrow the ring angle at the substituted carbon atoms. Steric interactions between silyl groups on neighbouring carbon atoms lead first to displacement of these groups away from one another, and then to displacement out of the ring plane, with alternate groups moving to opposite sides of the ring. In the extreme example, hexasilylbenzene, the SiCCSi dihedral angle is 17.8(8) degrees .  相似文献   
157.
The aim of this paper is to demonstrate the importance of providing time-resolved information in catalysis research. Two truly in situ methods will be presented and compared for their merits and drawbacks: chemical transient kinetics (CTK) and pulsed field desorption mass spectrometry (PFDMS). The presentation will be given by way of example choosing the syngas (CO/H2) reaction over cobalt-based catalysts as a catalytic process. Despite numerous efforts in the past, the mechanism of this reaction is still under debate. In CTK the reaction is studied on a metal-supported catalyst under flow conditions in a pressure range extending from atmospheric pressure down to 100 Pa. Sudden changes in the partial pressures of the reactants then allow following the relaxation to either steady-state conditions ("transients") or cleanoff ("back transients"). In PFDMS short field pulses of several volts per nanometer are applied to a model catalyst which resembles a single metal particle grain (a "tip"). These pulses intervene during the ongoing reaction under flow conditions at pressures ranging from 10(-1) to 10(-5) Pa and cause field desorption of adsorbed species. This method is particularly suited to detect reaction intermediates in a time-dependent manner since the repetition frequency of the pulses can be systematically varied. It is shown that both methods lead to complementary results. While CTK allows conclusions on the mechanism of CO hydrogenation by following the time-dependent formation of hydrocarbon species, PFDMS provides insight into the initial steps leading to adsorbed CxHy species. A quantitative assessment of the CTK data allows the demonstration that the catalyst under working conditions is in an oxidized rather than metallic state. The initial steps to oxidation are also traced by PFDMS. Most importantly, however, CTK results allow formulation of a reaction mechanism that is common for both hydrocarbon and oxygenate formation and is based on the occurrence of a formate-type species as the most abundant surface intermediate.  相似文献   
158.
High-dimensional, multispectral data on complex physical systems are increasingly common. As the amount of information in data sets increases, the difficulty of effectively utilizing it also increases. For such data, summary information is required for understanding and modeling the underlying dynamics. It is here proposed to use an extension of computational mechanics [C. R. Shalizi and J. P. Crutchfield, J. Stat. Phys. 104, 817 (2001)] to arbitrary spatiotemporal and spectral dimension, for providing such summary information. An example of the use of these tools to identify state evolution in the brain, an archetypal, complex biophysical system, serves as an illustration.  相似文献   
159.
The energy-level alignment at interfaces between three electroactive conjugated organic materials and Au was systematically varied by adjusting the precoverage of the metal substrate with the electron acceptor tetrafluoro-tetracyanoquinodimethane (F4-TCNQ). Photoelectron spectroscopy revealed that electron transfer from Au to adsorbed F4-TCNQ was responsible for lowering the hole-injection barrier by as much as 1.2 eV. This novel interface modification scheme is independent of the charge transfer complex formation ability of the organic materials with the electron acceptor.  相似文献   
160.
We propose to quantify the correlation inherent in a many-electron (or many-fermion) wave function psi by comparing it to the unique uncorrelated state that has the same 1-particle density operator as does /|psi>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