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   511423篇
  免费   10177篇
  国内免费   5838篇
化学   277713篇
晶体学   7399篇
力学   23552篇
综合类   334篇
数学   60092篇
物理学   158348篇
  2022年   4336篇
  2021年   5576篇
  2020年   6155篇
  2019年   6575篇
  2018年   8082篇
  2017年   7829篇
  2016年   11525篇
  2015年   7657篇
  2014年   11431篇
  2013年   24267篇
  2012年   19892篇
  2011年   23603篇
  2010年   16893篇
  2009年   16752篇
  2008年   21238篇
  2007年   20793篇
  2006年   19285篇
  2005年   17193篇
  2004年   15848篇
  2003年   13973篇
  2002年   13944篇
  2001年   15370篇
  2000年   11679篇
  1999年   9224篇
  1998年   7822篇
  1997年   7353篇
  1996年   7101篇
  1995年   6337篇
  1994年   6309篇
  1993年   6039篇
  1992年   6608篇
  1991年   6725篇
  1990年   6456篇
  1989年   6199篇
  1988年   6125篇
  1987年   6028篇
  1986年   5700篇
  1985年   7233篇
  1984年   7319篇
  1983年   5870篇
  1982年   5943篇
  1981年   5835篇
  1980年   5434篇
  1979年   5912篇
  1978年   6033篇
  1977年   5933篇
  1976年   5929篇
  1975年   5452篇
  1974年   5451篇
  1973年   5449篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
91.
The Liouville operator for an infinite-particle Hamiltonian dynamics corresponding to interaction potentialU is used to introduce the concept of a locally weakly invariant measure on the phase space and to show that if a Gibbs measure with potential of general form is locally weakly invariant then its Hamiltonian is asymptotically an additive integral of the motion of the particles with the interactionU.Moscow State University. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 90, No. 3, pp. 424–459, March, 1992.  相似文献   
92.
TheSU(2) rotation matricesD (j), specified in terms of axis and angle of rotation, are expressed as linear combination of normalized irreducible tensorial matricces (NITM) of rankl = 0 to 2j rotated to the polar angles of the axis. The rotated NITM are constructed from spherical harmonics of the same rank. Since this formulation requires no matrix products, it may be computationally more efficient than Euler angle formulas, particularly for largej. Rotated NITM and formulas for theD (j) withj = 1/2 andj = 1 are written out explicitly. A formula for the structure constants of the products of conformable NITM is also given in terms of 3-j and 6-j symbols.  相似文献   
93.
We examine the influence of relativistic and QED effects on the existence of the 1,3P o H- resonances between n = 2 and 3 hydrogen thresholds, the relativistic and QED corrections and the coupling effects between the high singlet and triplet states are considered as first-order perturbations. We firstly obtain accurate non-relativistic resonant energies and widths of fifteen 1P o resonances, and fifteen 3P o resonances. The fifteen 1P o resonances are classified to be 3 (2, 0) - n ( 4 ? n ? 12) and 3 (1, 1) + n ( 3 ? n ? 8). The fifteen 3P o resonances are classified to be 3 (2, 0) + n ( 3 ? n ? 12) and 3 (1, 1) - n ( 4 ? n ? 8). We found there exist six Feshbach resonances for 3 (2, 0) - n (1P o ) series, four Feshbach resonances for 3 (1, 1) + n (1P o ) series, seven Feshbach resonances for 3 (2, 0) + n (3P o ) series, and three Feshbach resonances for 3 (1, 1) - n (1P o ) series. Received 22 February 2002 Published online 24 September 2002  相似文献   
94.
This work is devoted to the numerical solution of the Navier–Stokes equations for compressible viscous fluids. Finite element approximations and stabilization techniques are addressed. We present methods to implement discontinuous approximations for the pressure and the density. An upwinding methodology is being investigated which combines the ideas behind the stream line Petrov–Galerkin method and the flux limiter methods aiming to introduce numerical diffusion only where it is necessary.  相似文献   
95.
The interaction between trivalent lanthanide ions and poly(1,4,7,10,13‐pentaoxacyclopentadecan‐2‐yl‐methyl methacrylate), PCR5, in aqueous solution and in the solid state have been studied. In aqueous solution, evidence of a weak interaction between the lanthanides and PCR5 comes from the small red shift of the Ce(III) emission spectra and the slight broadening of the Gd(III) EPR spectra. From the Tb(III) lifetimes in the presence of H2O and D2O the loss of one or two water coordinated molecules is confirmed when Tb(III) is bound to PCR5. An association constant of the order of 200 M?1 was obtained for a 1:1 (lanthanide:15‐crown‐5) complex from the shift of the polymer NMR signals induced by Tb(III). A similar association constant is obtained from the differences of the molar conductivity of Ce(III) solution at various concentrations in presence and absence of PCR5. When Tb(III) is adsorbed on PCR5 membranes, lifetime experiments in H2O and D2O confirm the loss of 5 or 6 water coordinated molecules indicating that in solid state the lanthanide(III)‐PCR5 interaction is stronger than in solution. The adsorption of Ce(III) in PCR5 membranes shows a Langmuir type isotherm, from which an equilibrium constant of 39 M?1 has been calculated. SEM shows that the membrane morphology is not much affected by lanthanide adsorption. Support for lanthanide ion–crown interactions comes from ab initio calculations on 15‐crown‐5/La(III) complex. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1788–1799, 2007  相似文献   
96.
97.
We investigate the existence and stability of solutions for higher-order two-point boundary value problems in case the differential operator is not necessarily positive definite, i.e. with superlinear nonlinearities. We write an abstract realization of the Dirichlet problem and provide abstract existence and stability results which are further applied to concrete problems.  相似文献   
98.
We show how methods for estimating the concentration function of the sum of independent random variables can be used to obtain estimates of the concentration function for the values of additive functions under suitable conditions. Previously obtained estimates of the concentration function are consequences of the estimate obtained in the present paper for functions from of the class under consideration.  相似文献   
99.
We report on a new type of Fano effect, named as Andreev-Fano effect, in a hybrid normal-metal/supeeconductor (N/S) interferometer embedded with a quantum dot. Compared with the conventional Fano effect, AndreevFano effect has some new features related to the characteristics of Andreev reflection. In the Iinear response regime, the line shape is the square of the conventional Fano shape, while in the nonlinear transport, a sharp resonant structure is superposed on an expanded interference pattern, which is qualitatively different from the conventional Fano effect. The phase dependence of the hybrid N/S interferometer is also distinguished from those of all-N or all-S interferometers.  相似文献   
100.
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