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   4592篇
  免费   139篇
  国内免费   16篇
化学   2913篇
晶体学   13篇
力学   242篇
数学   804篇
物理学   775篇
  2023年   40篇
  2022年   136篇
  2021年   133篇
  2020年   109篇
  2019年   97篇
  2018年   82篇
  2017年   91篇
  2016年   185篇
  2015年   144篇
  2014年   142篇
  2013年   246篇
  2012年   260篇
  2011年   288篇
  2010年   173篇
  2009年   150篇
  2008年   279篇
  2007年   270篇
  2006年   221篇
  2005年   236篇
  2004年   165篇
  2003年   157篇
  2002年   112篇
  2001年   50篇
  2000年   50篇
  1999年   45篇
  1998年   32篇
  1997年   32篇
  1996年   52篇
  1995年   45篇
  1994年   37篇
  1993年   36篇
  1992年   28篇
  1991年   27篇
  1990年   30篇
  1989年   32篇
  1988年   31篇
  1987年   47篇
  1986年   24篇
  1985年   40篇
  1984年   38篇
  1983年   19篇
  1982年   25篇
  1981年   27篇
  1980年   27篇
  1979年   19篇
  1978年   17篇
  1977年   31篇
  1976年   13篇
  1975年   14篇
  1974年   14篇
排序方式: 共有4747条查询结果,搜索用时 31 毫秒
991.
Abstract A group is called metahamiltonian if all its non-abelian subgroups are normal; it is known that locally soluble metahamiltonian groups have finite commutator subgroup. Here the structure of locally graded groups with finitely many normalizers of (infinite) non-abelian subgroups is investigated, and the above result is extended to this more general situation. Keywords: normalizer subgroup, metahamiltonian group Mathematics Subject Classification (2000): 20F24  相似文献   
992.
Evaluation of the number of components by the Davis-Giddings single chromatogram method is applied to capillary gas chromatograms of a dichloromethane extract of camomile. Various runs with OV-1 or Carbowax 20M as the stationary phase were done under different experimental conditions (column temperature programming rate and column length). The results showed that the number of components obtained by this statistical procedure does not depend greatly on the nature of the stationary phase or on the experimental conditions. The component number of the camomile extract was about 200 and the stand-alone probability at unit resolution was 0.2–0.3.  相似文献   
993.
994.
New Pd(II) and Pt(II) 3,6-bis(2′-pyridyl)pyridazine (dppn) mononuclear complexes of the type M(dppn)Cl2 were prepared and characterized. From M(dppn)Cl2, the bimetallic homonuclear complexes M(dppn)MCl4 were prepared by reaction with Pd(PhCN)2Cl2 or K2PtCl4. Bimetallic heteronuclear species of the type M(dppn)M′Cl4, were prepared reacting the mononuclear complexes with the stoichiometric amount of M′Cl2 (M′ = Cu, Co, Ni). All the described reaction give product in high yield. The isolated compounds, almost completely insoluble in most organic solvents, were characterized by elemental analysis, IR, ESR, reflectance spectra, and magnetic moment measurements. On the basis of these data the geometries around the metals are discussed.  相似文献   
995.
In 1979 Kazhdan and Lusztig defined, for every Coxeter group W, a family of polynomials, indexed by pairs of elements of W, which have become known as the Kazhdan-Lusztig polynomials of W, and which have proven to be of importance in several areas of mathematics. In this paper, we show that the combinatorial concept of a special matching plays a fundamental role in the computation of these polynomials. Our results also imply, and generalize, the recent one in [Adv. in Math. 180 (2003) 146-175] on the combinatorial invariance of Kazhdan-Lusztig polynomials.  相似文献   
996.
Combinatorial Expansions of Kazhdan-Lusztig Polynomials   总被引:2,自引:0,他引:2  
We introduce two related families of polynomials, easily computableby simple recursions into which any Kazhdan–Lusztig (andinverse Kazhdan–Lusztig) polynomial of any Coxeter groupcan be expanded linearly, and we give combinatorial interpretationsto the coefficients in these expansions. This yields a combinatorialrule for computing the Kazhdan–Lusztig polynomials interms of paths in a directed graph, and a completely combinatorialreformulation of the nonnegativity conjecture [15, p. 166].  相似文献   
997.
Properties of fluoroelastomer/semicrystalline perfluoropolymer nano-blends   总被引:1,自引:0,他引:1  
Properties of blends of semicrystalline perfluoropolymers in fluoroelastomers strongly depend on the size of the dispersed phase and are at the best when dispersed phase dimension is well below 0.1 μm, i.e. in the nano-scale region. This fine dispersion is obtained with an innovative mixing technology based on microemulsion polymerization. Further increase of properties can be obtained by generating chemical links between fluoroelastomer and semicrystalline fluoropolymer. Nano-blends combine the performing properties of fluoroelastomers with those of semicrystalline perfluoropolymers. For example, these nano-blends have at the same time the sealing and mechanical properties of fluoroelastomers and the exceptional thermal and chemical resistance, low permeability and low friction coefficient of semicrystalline perfluoropolymers. In addition, as dispersed phase size is below visible light wavelength, finished items made with these nano-blends are optically transparent even when they contain as much as 40 wt.% of semicrystalline perfluoropolymer.  相似文献   
998.
JPC – Journal of Planar Chromatography – Modern TLC - A normal-phase (NP) TLC method has been established for separation of the five antiarrhythmics - disopyramide, flecainide,...  相似文献   
999.
1000.
Rearrangement under acidic conditions of the pyrrolylbenzotriazinone 7 afforded the pyrrolylbenzamides 10 and 11 . By thermal rearrangement instead, the first fully aromatic derivative of the pyrrolo[3,4-c]isoquinoline ring system 9 was obtained.  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