全文获取类型
收费全文 | 5255篇 |
免费 | 677篇 |
国内免费 | 173篇 |
专业分类
化学 | 145篇 |
力学 | 471篇 |
综合类 | 73篇 |
数学 | 4183篇 |
物理学 | 1233篇 |
出版年
2023年 | 43篇 |
2022年 | 94篇 |
2021年 | 133篇 |
2020年 | 166篇 |
2019年 | 137篇 |
2018年 | 158篇 |
2017年 | 176篇 |
2016年 | 194篇 |
2015年 | 124篇 |
2014年 | 229篇 |
2013年 | 597篇 |
2012年 | 269篇 |
2011年 | 255篇 |
2010年 | 241篇 |
2009年 | 245篇 |
2008年 | 232篇 |
2007年 | 264篇 |
2006年 | 258篇 |
2005年 | 247篇 |
2004年 | 177篇 |
2003年 | 187篇 |
2002年 | 176篇 |
2001年 | 180篇 |
2000年 | 187篇 |
1999年 | 124篇 |
1998年 | 131篇 |
1997年 | 107篇 |
1996年 | 82篇 |
1995年 | 77篇 |
1994年 | 68篇 |
1993年 | 51篇 |
1992年 | 55篇 |
1991年 | 47篇 |
1990年 | 40篇 |
1989年 | 34篇 |
1988年 | 32篇 |
1987年 | 24篇 |
1986年 | 27篇 |
1985年 | 45篇 |
1984年 | 37篇 |
1983年 | 15篇 |
1982年 | 22篇 |
1981年 | 17篇 |
1980年 | 13篇 |
1979年 | 15篇 |
1978年 | 12篇 |
1977年 | 19篇 |
1976年 | 11篇 |
1973年 | 6篇 |
1972年 | 5篇 |
排序方式: 共有6105条查询结果,搜索用时 15 毫秒
881.
An analysis is made of the effects on the diffusion of Brownian particles whose Knudsen number is large compared to unity, of nonuniformities in the host gas. As examples, in one type of nonuniformity of the host gas, the Chapman-Enskog velocity distribution function for the gas molecules is used; in the other, the host gas is a free-molecule Couette flow. In both cases, a new force on the Brownian particles appears. Two techniques are used (extending Kramers' method and utilizing the Chapman-Enskog method) to transform the new Fokker-Planck equation into generalized Smoluchowski and convective diffusion equations. In these equations, the diffusion coefficient appears as a second-order tensor. Thus, it is demonstrated that Brownian diffusion in a nonuniform gas is anisotropic.The work of Slinn was financially supported in part by Battelle Memorial Institute and in part by U.S. Atomic Energy Commission Contract AT(45-1)-1830. The work of Shen was supported in part by U.S. Air Force Office of Scientific Research Contract 49(638)-1346. 相似文献
882.
Jan Grandell 《Stochastic Processes and their Applications》1979,8(3):243-255
We consider the classical model for an insurance business where the claims occur according to a Poisson process and where the distribution for the cost of each claim fulfills Cramér's tail-condition. Under these conditions Lundberg's constant R is of fundamental importance for ruin calculations.We derive estimates of R, based on an observation of the insurance business and investigate the statistical properties of those estimates. We further derive bounds and confidence intervals for ruin probabilities. 相似文献
883.
J.?Vigo-AguiarEmail author R.?Ardanuy-Albajar Bruce?A.?Wade 《Journal of Mathematical Modelling and Algorithms》2005,4(3):317-330
Using an equivalent expression for solutions of second order Dirichlet problems in terms of Ito type stochastic differential
equations, we develop a numerical solution method for Dirichlet boundary value problems. It is possible with this idea to
solve for solution values of a partial differential equation at isolated points without having to construct any kind of mesh
and without knowing approximations for the solution at any other points. Our method is similar to a recently published approach,
but differs primarily in the handling of the boundary. Some numerical examples are presented, applying these techniques to
model Laplace and Poisson equations on the unit disk.
Visiting Professor, Universidad de Salamanca. 相似文献
884.
We study the semidiscrete Galerkin approximation of a stochastic parabolic partial differential equation forced by an additive space-time noise. The discretization in space is done by a piecewise linear finite element method. The space-time noise is approximated by using the generalized L2 projection operator. Optimal strong convergence error estimates in the L2 and
norms with respect to the spatial variable are obtained. The proof is based on appropriate nonsmooth data error estimates for the corresponding deterministic parabolic problem. The error estimates are applicable in the multi-dimensional case.
AMS subject classification (2000) 65M, 60H15, 65C30, 65M65.Received April 2004. Revised September 2004. Communicated by Anders Szepessy. 相似文献
885.
We investigate the motion of high-energy particles in a crystal with regard to their interaction with the thermal vibrations of the lattice atoms using analytic methods in the theory of Markov processes including the local Fokker–Planck equation. We construct a local matrix of random actions, which is used to introduce the main kinetic functions in the traverse-energy space, namely, the function a() of energy losses due to the dynamic friction and the diffusion function b(). We show that the singularities of the functions a() and b() are related to the distinction between the contributions to the kinetics from particles moving in three different regimes, namely, in the channeling, quasichanneling, and chaotic motion modes. 相似文献
886.
Roman Luis J. Zhang Xinsheng Zheng Weian 《Mathematical Physics, Analysis and Geometry》2003,6(2):113-124
We consider the solutions to /tu
(n)=a
(n)(x)u
(n) where {a
(n)(x)}
n=1,2,... are random fields satisfying a well-mixing condition (which is different to the usual strong mixing condition). In this paper we estimate the rate of convergence of u
(n) to the solution of a heat equation. Since our equation is of simple form, we get quite strong result which covers the previous homogenization results obtained on this equation. 相似文献
887.
M. K. Pandey R. K. Dubey D. N. Tripathi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):275-279
The Classical Trajectory Monte Carlo (CTMC) Method has
been used to calculate the differential, partial and total single electron
capture cross sections for the collision of H+/D+ with Ca and Mg
atoms in the energy range of 1–100 keV. The differential cross sections
at angles near the diffraction limit (<0.1○) in both systems
show a forward peak followed by an asymptotic fall at higher angles. Total
and partial capture cross sections are found to be in good agreement with
the experimental observations. Oscillations in the partial capture cross sections have been explained due to the swapping
of the field electron.
Isotope effect in the electron transfer is reported to be negligible. 相似文献
888.
E. Scalas U. Garibaldi S. Donadio 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):271-272
This erratum corrects a mistake in reference [E. Scalas, U. Garibaldi, S. Donadio, Eur. Phys. J. B 53, 267 (2006)].
In that paper,
we needed an aperiodic version of the BDY game, but, in formula (1),
we incorrectly presented
a periodic transition matrix of period 2 in the special case of g = 2 agents.
Here, we present the right aperiodic version. 相似文献
889.
《Stochastics An International Journal of Probability and Stochastic Processes》2013,85(3-4):137-161
An optimal stochastic control problem is considered in this paper, where the diffusion coefficient also depends on the control and is possibly degenerate. In addition to the usual adjoint process, a second-order adjoint process is introduced. Some relationships between the value function and the adjoint processes are presented via the “super- and sub-differential” which is related to the viscosity solution, without assuming the smoothness of the value function. The maximum principle, dynamic programming and their connections are then established within a unified framework of viscosity solution 相似文献
890.
E. Katzav 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(2):137-140
In the paper the role of long range interactions on the
growth of a volume conserving surface is studied using the Nonlocal
Conserved Kardar-Parisi-Zhang (NCKPZ) equation. It is shown that
previous theoretical predictions are inconsistent with an exact
one-dimensional result. This serves as a motivation for construction
of a Self-Consistent Expansion (SCE) that recovers the exact
one-dimensional result, and gives the scaling exponents in higher
dimensions as well. A possible application of this result to
colloidal systems is discussed. 相似文献