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   2202篇
  免费   45篇
  国内免费   76篇
化学   288篇
晶体学   10篇
力学   15篇
数学   1788篇
物理学   222篇
  2023年   5篇
  2022年   5篇
  2021年   8篇
  2020年   12篇
  2019年   56篇
  2018年   51篇
  2017年   36篇
  2016年   28篇
  2015年   28篇
  2014年   66篇
  2013年   132篇
  2012年   51篇
  2011年   132篇
  2010年   103篇
  2009年   141篇
  2008年   197篇
  2007年   160篇
  2006年   144篇
  2005年   124篇
  2004年   95篇
  2003年   73篇
  2002年   56篇
  2001年   67篇
  2000年   46篇
  1999年   54篇
  1998年   41篇
  1997年   39篇
  1996年   75篇
  1995年   52篇
  1994年   42篇
  1993年   43篇
  1992年   29篇
  1991年   24篇
  1990年   26篇
  1989年   9篇
  1988年   4篇
  1987年   16篇
  1986年   7篇
  1985年   7篇
  1984年   4篇
  1983年   4篇
  1982年   8篇
  1981年   3篇
  1980年   3篇
  1979年   1篇
  1978年   2篇
  1977年   5篇
  1976年   5篇
  1975年   1篇
  1973年   3篇
排序方式: 共有2323条查询结果,搜索用时 62 毫秒
71.
This Letter contains constructions of complex action variables for both the full Kostant-Toda Lattice in sl(n, 22866047/xxlarge8450.gif" alt="Copf" align="BASELINE" BORDER="0">) and the generalized nonperiodic tridiagonal Toda lattice associated to an arbitrary complex semisimple Lie algebra g. The main tool is the explicit factorization solution for certain Hamiltonian flows. The Letter also contains a generalization of the standard factorization solution theorem necessary for the analysis of the full Kostant-Toda lattice.  相似文献   
72.
We realize the current algebra at an arbitrary level in terms of one deformed free bosonic field and a pair of deformed parafermionic fields. It is shown that the operator product expansions of these parafermionic fields involve an infinite number of simple poles and simple zeros, which then condensate to form a branch cut in the classical limitq1. Our realization coincides with those of Frenkel-Jing and Bernard when the levelk takes the values 1 and 2, respectively.  相似文献   
73.
We classify extended Poincaré Lie superalgebras and Lie algebras of any signature (p, q), i.e. Lie superalgebras and 2-graded Lie algebras g = g0 + g1, where g0 = s0(V) + V is the (generalized) Poincaré Lie algebra of the pseudo Euclidean vector space V = p, q of signature (p, q) and g1 is a spin 1/2 s0(V)-module extended to a s0-module with kernel V.As a result of the classification, we obtain, if g1 = S is the spinor module, the numbers L +(n, s) (resp. L (n, s)) of independent such Lie super algebras (resp. Lie algebras), which are periodic functions of the dimension n=p+q (mod 8) and the signature s=p–q (mod 8) and satisfy: L +(–n, s)=L (n, s).Supported by Max-Planck-Institut für Mathematik (Bonn).Supported by the Alexander von Humboldt Foundation, MSRI (Berkeley) and SFB 256 (Bonn University).  相似文献   
74.
75.
Aluminum and manganese derivatives of lithiated bis-lactim ethers of cyclo-(L-Ala-L-Ala) were used for the enantioselective synthesis of 22hh/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-hydroxy and polyhydroxy 22hh/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-amino acids of the 2-methyIserine series. A new variant of the synthesis of these acids via 3-acyl-2, 5-dialkoxy-3, 6-dimethyl-3, 6-dihydropyrazines is proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 590–595, March, 1993.  相似文献   
76.
For any locally compact groupG, we show that any locally tight homomorphism from a real directed semigroup intoM 1 (G) (semigroup of probability measures onG) has a shift which extends to a continuous one-parameter semigroup. IfG is ap-adic algebraic group then the above holds even iff is not locally tight. These results are applied to give sufficient conditions for embeddability of some translate of limits of sequences of the form {v n kn } and M 1 (G) such that ()= M , for somek>1 and AutG (cf. Theorems 2.1, 2.4, 3.7).  相似文献   
77.
Macrocycle opening in derivatives of benzocrown ethers under the action of amines is affected by the nature of the heteroatoms in the macrocycle, the nature of the functional group in the benzene ring of the crown ether, and the length, branching, and number of hydrocarbon radicals at the amine nitrogen atom. A distinguishing feature of this reaction is the template effect of MeNH3 +, Me2NH2 +, Na+, and K+ ions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 687–692, March, 1996.For Part I see Ref. 1.  相似文献   
78.
79.
A comparison of methane dehydroaromatization (MDA) on 6Mo/MCM-22 and 6Mo/ZSM-5 was carried out using a gas mixture of 90%CH4, 2%CO2 and 8%Ar as the feed. The results indicate that the stability of 6Mo/MCM-22 is better than that of 6Mo/ZSM-5. A detailed study reveals that the ability for coke accommodation and the retention of the shape selectivity for aromatics formation is responsible for the stability of a MDA catalyst. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
80.
The intermediate 22h85258h146j7/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0">-adducts of chloromethyl phenyl sulfone with 3-nitro-, 5-nitro-, 6-nitro-, 7-nitro- and 8-nitroquinoline are detected by 1H NMR spectroscopy.  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