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   13009篇
  免费   1083篇
  国内免费   1492篇
化学   1533篇
晶体学   84篇
力学   686篇
综合类   307篇
数学   10217篇
物理学   2757篇
  2024年   18篇
  2023年   144篇
  2022年   190篇
  2021年   237篇
  2020年   256篇
  2019年   334篇
  2018年   303篇
  2017年   343篇
  2016年   360篇
  2015年   300篇
  2014年   571篇
  2013年   885篇
  2012年   516篇
  2011年   753篇
  2010年   698篇
  2009年   889篇
  2008年   968篇
  2007年   1013篇
  2006年   811篇
  2005年   759篇
  2004年   590篇
  2003年   651篇
  2002年   570篇
  2001年   438篇
  2000年   494篇
  1999年   451篇
  1998年   410篇
  1997年   327篇
  1996年   266篇
  1995年   151篇
  1994年   164篇
  1993年   109篇
  1992年   94篇
  1991年   80篇
  1990年   58篇
  1989年   34篇
  1988年   38篇
  1987年   24篇
  1986年   16篇
  1985年   43篇
  1984年   43篇
  1983年   14篇
  1982年   32篇
  1981年   23篇
  1980年   22篇
  1979年   23篇
  1978年   14篇
  1977年   13篇
  1976年   9篇
  1975年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Let A(X) be the space defined by Waldhausen whose homotopy groups define the algebraic K-groups of the space X and let . Here (X) denotes the free loop space of X and Q denotes the functor . For X = Y, the suspension of a connected space Y, we shall prove that the homotopy fibers Ã(X), B(X) of the maps A(X) A (point), B(X) B (point) are equivalent as infinite loop spaces.  相似文献   
12.
The field of isothermal microcalorimetry as applied to systems of interest for aqueous solution chemistry, biochemistry and in cellular biology is briefly reviewed. Some techniques recently developed in the author's laboratory are described.  相似文献   
13.
A strictly pseudoconvex pseudo-Hermitian manifoldM admits a canonical Lorentz metric as well as a canonical Riemannian metric. Using these metrics, we can define a curvaturelike function onM. AsM supports a contact form, there exists a characteristic vector field dual to the contact structure. If induces a local one-parameter group ofCR transformations, then a strictly pseudoconvex pseudo-Hermitian manifoldM is said to be a standard pseudo-Hermitian manifold. We study topological and geometric properties of standard pseudo-Hermitian manifolds of positive curvature or of nonpositive curvature . By the definition, standard pseudo-Hermitian manifolds are calledK-contact manifolds by Sasaki. In particular, standard pseudo-Hermitian manifolds of constant curvature turn out to be Sasakian space forms. It is well known that a conformally flat manifold contains a class of Riemannian manifolds of constant curvature. A sphericalCR manifold is aCR manifold whose Chern-Moser curvature form vanishes (equivalently, Weyl pseudo-conformal curvature tensor vanishes). In contrast, it is emphasized that a sphericalCR manifold contains a class of standard pseudo-Hermitian manifolds of constant curvature (i.e., Sasakian space forms). We shall classify those compact Sasakian space forms. When 0, standard pseudo-Hermitian closed aspherical manifolds are shown to be Seifert fiber spaces. We consider a deformation of standard pseudo-Hermitian structure preserving a sphericalCR structure.Dedicated to Professor Sasao Seiya for his sixtieth birthday  相似文献   
14.
CHAOS FOR MIXING TRANSFORMATIONS   总被引:3,自引:0,他引:3  
CHAOSFORMIXINGTRANSFORMATIONS¥LIAOGONGFU(DepartmentofMathematics,JilinUniversity,Changchun130023,China.)Abstract:Foraclassofm...  相似文献   
15.
We discuss the Cauchy problem of a certain stochastic parabolic partial differential equation arising in the nonlinear filtering theory, where the initial data and the nonhomogeneous noise term of the equation are given by Schwartz distributions. The generalized (distributional) solution is represented by a partial (conditional) generalized expectation ofT(t)° 0,t –1 , whereT(t) is a stochastic process with values in distributions and s,t is a stochastic flow generated by a certain stochastic differential equation. The representation is used for getting estimates of the solution with respect to Sobolev norms.Further, by applying the partial Malliavin calculus of Kusuoka-Stroock, we show that any generalized solution is aC -function under a condition similar to Hörmander's hypoellipticity condition.  相似文献   
16.
钟怀杰 《数学学报》1994,37(4):563-569
给出 Banach空间列{Xi}i=1∞的 lp乘积B-凸的特征刻划, 证明B-凸空间上的每个黎斯算子可West分解,即分解成一个紧算子和一个拟幂 零算子的和.  相似文献   
17.
One more model of aq-harmonic oscillator based on theq-orthogonal polynomials of Al-Salam and Carlitz is discussed. The explicit form ofq-creation andq-annihilation operators,q-coherent states and an analog of the Fourier transformation are established. A connection of the kernel of this transform with a family of self-dual biorthogonal rational functions is observed.  相似文献   
18.
Density functional (BLYP, B3LYP and BHLYP) and highly correlated MP2 and CCSD(T) calculations have been performed to investigate conformers, energy barriers, intramolecular H-bond strength, gas-phase basicity and deprotonation energies of glyoxilic acid oxime (gao) and related ions in gas phase and in aqueous solution (SCRF-PCM method). BHLYP/6-311G(d,p) and B3LYP/6-31++G(d) predictions for the global minimum conformer of gao were consistent with experiment. BLYP level overestimated the H-bond and stabilized incorrectly the H-bonded conformer. The calculations in solution indicated destabilization of H-bonded conformers due to the small polarizability and weaken of the H-bond. The same global minimum structures in gas phase and aqueous solution were found for gao-neutral (ectt) and gao-dianion (e2), whereas they were different for gao-anion because of the strong decrease of the conformational energies in solution. The global minimum structures of the neutral, anion and dianion of gao, obtained in solution, are in agreement with experiment. The gas-phase basicity (GB) and molecular electrostatic potential (MEP) calculations revealed the same sites for electrophilic attack, supported by the nature of HOMO: the carbonylic oxygen for the neutral, the carboxylic oxygen for the anion and the oxime nitrogen for the dianion. MEP results in gas phase and in solution suggested a region between the two atoms, but not on one atom in accordance with bidentate binding of gao ions to a metal. The BHLYP/6-31++G(d,p) molecular properties of gao were in best consistent with CCSD(T) results. The thermodynamical properties (GB and bond deprotonation energy) of gao were better estimated at B3LYP level.  相似文献   
19.
Two sufficient criteria for the convergence of the Rayleigh-Ritz Method (RRM) with respect to the eigenvalues (E-convergence) of non-relativistic electronic Hamiltonians of molecules are discussed and compared. Moreover, a necessary and sufficient criterion is given. By example (Sect. 9) it is shown that the L 2-completeness of the basis is not sufficient to guarantee E-convergence. The convergence of the wave functions in different norms (-convergence) is also investigated. In particular, sufficient conditions for the one-particle basis functions (orbitals) are given, such that a CI calculation in this basis is both E- and -convergent.  相似文献   
20.
The -function method for evaluating effective actions is applied to an operator containing a potential localized on two parallel planes. This operator is characterized by a continuous spectrum and broken translation invariance. In this case, the -method leads to a divergent volume factor independent of the physical parameters. In a suitable regularization scheme, only the next to leading order term reproduces a physically interesting result.  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