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   1316163篇
  免费   29596篇
  国内免费   7731篇
化学   654698篇
晶体学   20314篇
力学   74222篇
综合类   103篇
数学   239755篇
物理学   364398篇
  2021年   13436篇
  2020年   15870篇
  2019年   16008篇
  2018年   12685篇
  2016年   27658篇
  2015年   20691篇
  2014年   30268篇
  2013年   74057篇
  2012年   36625篇
  2011年   32857篇
  2010年   36628篇
  2009年   39118篇
  2008年   32731篇
  2007年   28260篇
  2006年   34478篇
  2005年   27208篇
  2004年   28438篇
  2003年   27115篇
  2002年   28294篇
  2001年   26572篇
  2000年   23777篇
  1999年   22027篇
  1998年   20783篇
  1997年   20797篇
  1996年   20991篇
  1995年   19077篇
  1994年   18502篇
  1993年   18061篇
  1992年   17813篇
  1991年   18151篇
  1990年   17381篇
  1989年   17414篇
  1988年   17006篇
  1987年   17021篇
  1986年   15922篇
  1985年   22365篇
  1984年   23667篇
  1983年   19875篇
  1982年   21575篇
  1981年   20821篇
  1980年   20170篇
  1979年   20287篇
  1978年   21614篇
  1977年   21204篇
  1976年   20898篇
  1975年   19634篇
  1974年   19238篇
  1973年   19765篇
  1972年   14257篇
  1967年   12488篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
891.
The characterization of the clusters formed on alkaline hydrolysis of [PdCl4]2– was performed using17O,23Na,35Cl,133Cs NMR and UV spectroscopy. The chemical composition of the clusters was found to be [Pd(OH)2] n ·nNaCl. No mononuclear oxo- or hydroxocomplexes were detected. The spatial structure of the clusters is stabilized by alkali metal cations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 675–679, April, 1993.  相似文献   
892.
893.
894.
895.
Phase Relations and Sodium Ion Conductivity within the Quasi-binary System Na2SiF6/Na2AIF6 . The phase diagram of the Na2SiF6/Na3AlF6 system has been determined by means of x-ray powder diffraction, thermal analysis and conductivity measurements in the sub-solidus region. Na3AlF6 accomodates up to 73 mol.-% Na2SiF6 maintaining the crystal structure type. The sodium ion conductivity increases by about five orders of magnitude upon doping Na3AlF6 with Na2SiF6.  相似文献   
896.
Oxidation of the title compounds yields, besides the reported isoimides 3 and/or the amides 4 , also the imides 5 . The observed product dichotomy is considered as the result of an intramolecular nucleophilic attack on the aroyl group, of the pressumed zwitterionic intermediate 2 , by O or N present in the ambident N-aroylimine site of 2 . The results of AM1 calculations agree with the product studies and both permit the formulation of a set of rules correlating structure and selectivity.  相似文献   
897.
New analytical formulas for the torsionL-tensor are reported, which are used in molecular normal mode analysis calculations for the nonlinear transformation of the force constants from internal coordinates to normal coordinates. The proposed formalism exhibits a relative simplicity as compared to previous reported results. Sample calculations for methanol and hydrazine are presented.  相似文献   
898.
We consider tilde-geometries (orT-geometries), which are geometries belonging to diagrams of the following shape: Here the rightmost edge stands for the famous triple cover of the classical generalized quadrangle related to the group Sp4(2). The automorphism group of the cover is the nonsplit extension 3·Sp4(2) – 3 ·S 6. Five examples of flag-transitiveT-geometries were known. These are rank 3 geometries related to the groupsM 24 (the Mathieu group),He (the Held group) and and 37·Sp6(2) (a nonsplit extension); a rank 4 geometry related to the Conway groupCo 1 and a rank 5 geometry related to the Fischer-Griess Monster groupF 1. In the present paper we construct an infinite family of flag-transitiveT-geometries and prove that all the new geometries are simply connected. The automorphism group of the rankn geometry in the family is a nonsplit extension of a 3-group by the symplectic group Sp2n (2). The rank of the 3-group is equal to the number of 2-dimensional subspaces in ann-dimensional vector space over GF(2).  相似文献   
899.
Several interesting and important quantum field theories must contain the coupling constant in the boundary conditions. The theories considered include quantum electrodynamics of spin-1/2 fermions and gauge field theories.  相似文献   
900.
We develop an approach to the solution of the spinless Bethe-Salpeter equation for the different-mass case. Although the calculations are developed for spinzero particles in any arbitratry spherically symmetric potential, the non-Coulombic effective power-law potential is used as a kernel to produce the spin-averaged bound states of the non-self-conjugate mesons. The analytical formulas are also applicable to the self-conjugate mesons in the equal-mass case. The flavor-independent case is investigated in this work. The calculations are carried out to the third-order correction of the energy series. Results are consistent with those obtained before.  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