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   4060篇
  免费   214篇
  国内免费   409篇
化学   1506篇
晶体学   11篇
力学   37篇
综合类   20篇
数学   2736篇
物理学   373篇
  2024年   3篇
  2023年   55篇
  2022年   77篇
  2021年   82篇
  2020年   115篇
  2019年   120篇
  2018年   116篇
  2017年   103篇
  2016年   74篇
  2015年   90篇
  2014年   144篇
  2013年   583篇
  2012年   108篇
  2011年   153篇
  2010年   119篇
  2009年   197篇
  2008年   237篇
  2007年   258篇
  2006年   234篇
  2005年   218篇
  2004年   211篇
  2003年   194篇
  2002年   175篇
  2001年   143篇
  2000年   146篇
  1999年   120篇
  1998年   124篇
  1997年   126篇
  1996年   74篇
  1995年   43篇
  1994年   33篇
  1993年   36篇
  1992年   35篇
  1991年   17篇
  1990年   10篇
  1989年   16篇
  1988年   16篇
  1987年   6篇
  1986年   7篇
  1985年   17篇
  1984年   11篇
  1983年   4篇
  1982年   5篇
  1981年   5篇
  1980年   5篇
  1978年   4篇
  1977年   3篇
  1976年   3篇
  1974年   2篇
  1973年   2篇
排序方式: 共有4683条查询结果,搜索用时 328 毫秒
41.
Integrated Groups and Smooth Distribution Groups   总被引:1,自引:0,他引:1  
In this paper, we prove directly that α-times integrated groups define algebra homomorphisms. We also give a theorem of equivalence between smooth distribution groups and α-times integrated groups.  相似文献   
42.
Automorphisms of groups acting faithfully on rooted trees are studied. We find conditions under which every automorphism of such a group is induced by a conjugation from the full automorphism group of the rooted tree. These results are applied to known examples such as Grigorchuk groups, Gupta–Sidki group, etc.  相似文献   
43.
设R=Z/2\+kZ(k>1)是\{2\}[TX-]为非单位的有限局部环. 该文首先确定了R上斜对称矩阵标准形. 设G\+m\-p(R,H)={P∈GL\-m(R)|PHP′=H}是由矩阵H确定的伪辛群,其中H=[JB((][HL(2]0[]I\+\{(v)\}\=-I\+\{(v)\}[]0[HL)][JB))]Δ,Δ=[JB((][HL(2]\{2\}[TX-]\+\{k-1\}[]\{1\}[TX-]\=-\{1\}[TX-][]0[HL)][JB))]. 其次,计算了伪辛群G\+m\-P(R,H)的阶|G\+m\-P(R,H)|.  相似文献   
44.
Sz.-Nagy's dilation theorem for a contraction on a Hilbert space has been extended by Mlak to the case of a contraction semigroup whose indices are the positive elements of a totally ordered discrete group. We generalize to this case the intertwining lifting theorem of Sz.-Nagy and Foias. Some previous interpolation results on ordered groups are obtained as consequences.  相似文献   
45.
王燕鸣 《数学学报》1994,37(6):814-818
在本文中,我们讨论了带作用群的群系的临界结构,给出了处理允许某些作用群的群的问题的一般方法,作为应用,我们特别给出了关于幂零群及p-幂零群的一些结果。  相似文献   
46.
Synthesis and characterization of several new anomerically pure galactose derivatives, based on simple and effective protective group manipulations of benzyl β-d-galactopyranoside, are reported. The monosaccharides described contain selectively protected/deprotected hydroxyl functionalities at their 1,2,3,4- and 6-positions rendering them useful as building blocks for construction of branched oligosaccharides.  相似文献   
47.
A new hydrophilic copolymer having three kinds of hydroxyl groups, i.e. primary OH on -hydroxy allyl alcohol component, secondary OH on cyclic hemiacetal component and tertiary OH on -hydroxy acrylate component, was prepared by reducing a ‘polylactone’, poly(1-oxa-2-oxobutane-1,4:3,3-tetrayl), with NaBH4 in mixed solvents containing an alcohol. The structural analyses were performed by the solution 1H NMR and the solid state 13C NMR spectroscopies of the reduced samples. The composition of the three components turned out to be variable to the alcohol species used for the mixed solvent.  相似文献   
48.
If is a quasitriangular Lie bialgebra, the formal Poisson group can be given a braiding structure. This was achieved by Weinstein and Xu using purely geometrical means, and independently by the authors by means of quantum groups. In this paper we compare these two approaches. First, we show that the braidings they produce share several similar properties (in particular, the construction is functorial); secondly, in the simplest case (G=SL2) they do coincide. The question then rises of whether they are always the same this is positively answered in a separate paper.  相似文献   
49.
We answer a question of J. Anderson's by producing infinitely many commensurability classes of fibered hyperbolic 3-manifolds whose fundamental groups contain subgroups that are locally free and not free. These manifolds are obtained by performing 0–surgery on a collection of knots with the same properties.  相似文献   
50.
We give examples of direct products of three hyperbolic groups in which there cannot exist an algorithm to decide which finitely presented subgroups are isomorphic.

  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