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   148590篇
  免费   11276篇
  国内免费   7789篇
化学   72949篇
晶体学   1514篇
力学   11259篇
综合类   566篇
数学   40319篇
物理学   41048篇
  2024年   158篇
  2023年   1451篇
  2022年   2118篇
  2021年   2472篇
  2020年   2778篇
  2019年   2650篇
  2018年   12194篇
  2017年   11842篇
  2016年   8916篇
  2015年   4075篇
  2014年   4095篇
  2013年   5456篇
  2012年   9893篇
  2011年   16531篇
  2010年   9797篇
  2009年   10098篇
  2008年   10868篇
  2007年   12545篇
  2006年   4070篇
  2005年   4620篇
  2004年   4168篇
  2003年   3964篇
  2002年   2829篇
  2001年   1872篇
  2000年   1803篇
  1999年   1809篇
  1998年   1560篇
  1997年   1358篇
  1996年   1459篇
  1995年   1227篇
  1994年   1096篇
  1993年   987篇
  1992年   843篇
  1991年   751篇
  1990年   620篇
  1989年   548篇
  1988年   449篇
  1987年   413篇
  1986年   371篇
  1985年   364篇
  1984年   260篇
  1983年   219篇
  1982年   198篇
  1981年   155篇
  1980年   134篇
  1979年   102篇
  1978年   98篇
  1977年   77篇
  1975年   81篇
  1973年   88篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
761.
762.
Using the quiver technique we construct a class of non-graded bi-Frobenius algebras. We also classify a class of graded bi-Frobenius algebras via certain equations of structure coefficients.  相似文献   
763.
The roles of the magnetic field and electric field of the light are investigated when the light is refracted in the medium. The model of the electron cloud conductor is presented. Electron cloud in a molecule is treated as a conductor and the Faraday’s Law is applied to this conductor that is in the alternating magnetic field of the light. dB M/dt of the light gives rise to an alternating induced current on the electron cloud conductor, and the light exchanges energy, i.e. the refractive energy, with the electron cloud conductor. Formulas of refractive index, which is the ratio of light speed in vacuum to that in the medium, are derived with this model. These formulas are tested with several mediums and Langevin’s diamagnetic susceptibility of helium gas, and the results are in good agreement with the measured data. The anisotropy and the nonlinearity of the refractive index are explained with the theory described in this work. Supported by Beijing Science and Technology New Star Program (Grant No. 952870400), the Beijing Municipal Commission of Education and the Excellent Young Teachers Program of Ministry of Education of China  相似文献   
764.
In this paper, we study an existence theorem of systems of generalized quasivariational inclusions problem. By this result, we establish the existence theorems of solutions of systems of generalized equations, systems of generalized vector quasiequilibrium problem, collective variational fixed point, systems of generalized quasiloose saddle point, systems of minimax theorem, mathematical program with systems of variational inclusions constraints, mathematical program with systems of equilibrium constraints and systems of bilevel problem and semi-infinite problem with systems of equilibrium problem constraints. This research was supported by the National Science Council of the Republic of China.  相似文献   
765.
任秀敏 《数学学报》2007,50(1):175-182
研究混合方次的Waring--Goldbach  相似文献   
766.
In this paper we prove the validity of the Maximum Principle for some class of elliptic and parabolic equations of diffusion type in infinite dimension. The main tools are Asplund’s theorem and Preiss’ theorem on differentiability of Lipschitz functions in Banach space.   相似文献   
767.
文章讨论无界区域上GBBM方程的Cauchy问题,对方程的解进行了先验估计,并证明了在H1弱拓扑中整体吸引子的存在性.  相似文献   
768.
一种塑解剂经高压液体色谱分离制备出主要成份2,2′—二硫代双(4,6二叔丁基苯酚)。由质谱分析得到分子量为474化学式为C_(28)H_(2)O_2S_2、晶体呈现孪生。基体单晶属三斜晶系,空间群为(?)PI(NO.2),晶体结构用直接法解出,=0.07。研究结果表明该分子是二硫代酚类化合物。在EI场中,S—S键断裂是主要断裂过程。晶体中,分子的一个环上的羟基是无序分布的。羟基与最邻近的硫原子形成氢键。  相似文献   
769.
We prove some basic properties of Donaldson’s flow of surfaces in a hyperkähler 4-manifold. When the initial submanifold is symplectic with respect to one Kähler form and Lagrangian with respect to another, we show that certain kinds of singularities cannot form, and we prove a convergence result under a condition related to one considered by M.-T. Wang for the mean curvature flow.  相似文献   
770.
Consider a semigroup generated by matrices associated with an edge-coloring of a strongly connected, aperiodic digraph. We call the semigroup Lie-solvable if the Lie algebra generated by its elements is solvable. We show that if the semigroup is Lie-solvable then its kernel is a right group. Next, we study the Lie algebra generated by the kernel. Lie algebras generated by two idempotents are analyzed in detail. We find that these have homomorphic images that are generalized quaternion algebras. We show that if the kernel is not a direct product, then the Lie algebra generated by the kernel is not solvable by describing the structure of these algebras. Finally, we discuss an infinite class of examples that are shown to always produce strongly connected aperiodic digraphs having kernels that are not right groups.  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