全文获取类型
收费全文 | 123740篇 |
免费 | 7918篇 |
国内免费 | 13762篇 |
专业分类
化学 | 75954篇 |
晶体学 | 1287篇 |
力学 | 6356篇 |
综合类 | 1184篇 |
数学 | 31978篇 |
物理学 | 28661篇 |
出版年
2024年 | 180篇 |
2023年 | 1058篇 |
2022年 | 2373篇 |
2021年 | 2389篇 |
2020年 | 3233篇 |
2019年 | 3129篇 |
2018年 | 2727篇 |
2017年 | 3563篇 |
2016年 | 3831篇 |
2015年 | 3227篇 |
2014年 | 4839篇 |
2013年 | 9387篇 |
2012年 | 7750篇 |
2011年 | 6994篇 |
2010年 | 6036篇 |
2009年 | 7850篇 |
2008年 | 8126篇 |
2007年 | 8334篇 |
2006年 | 7422篇 |
2005年 | 6498篇 |
2004年 | 5876篇 |
2003年 | 5038篇 |
2002年 | 6087篇 |
2001年 | 3710篇 |
2000年 | 3499篇 |
1999年 | 3299篇 |
1998年 | 2887篇 |
1997年 | 2320篇 |
1996年 | 1900篇 |
1995年 | 1754篇 |
1994年 | 1540篇 |
1993年 | 1236篇 |
1992年 | 1170篇 |
1991年 | 852篇 |
1990年 | 730篇 |
1989年 | 621篇 |
1988年 | 496篇 |
1987年 | 404篇 |
1986年 | 380篇 |
1985年 | 320篇 |
1984年 | 324篇 |
1983年 | 183篇 |
1982年 | 298篇 |
1981年 | 249篇 |
1980年 | 248篇 |
1979年 | 241篇 |
1978年 | 206篇 |
1977年 | 155篇 |
1976年 | 134篇 |
1973年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
It is long known that the Fokker-Planck equation with prescribed constant coefficients of diffusion and linear friction describes
the ensemble average of the stochastic evolutions in velocity space of a Brownian test particle immersed in a heat bath of
fixed temperature. Apparently, it is not so well known that the same partial differential equation, but now with constant
coefficients which are functionals of the solution itself rather than being prescribed, describes the kinetic evolution (in
the N→∞ limit) of an
isolated
N-particle system with certain stochastic interactions. Here we discuss in detail this recently discovered interpretation.
An erratum to this article can be found at 相似文献
53.
本文对具有有限时滞的泛函微分方程建立了关于依照两种测度的实际稳定性的Razumikhin型判定定理,其中未采用通常的辅助函数,且可运用多个含有状态变量x的部分变元的Lyapunov函数,得出部分变远实际稳定性的判定定理,从而改进了已有的结果。 相似文献
54.
In this paper necessary and sufficient conditions of null-controllability and approximate null-controllability are obtained for the wave equation on a half-axis. Controls solving these problems are found explicitly. Moreover, bang-bang controls solving the approximate null-controllability problem are constructed with the aid of solutions of a frequency extinguishing problem in the restricted band (−a,a) for this equation and the Markov power moment problem. 相似文献
55.
Monte Carlo simulation within the grand canonical ensemble, the histogram reweighting technique, and finite size scaling analysis are used to explore the phase behaviour of heteronuclear dimers, composed of A and B type atoms, on a square lattice. We have found that for the models with attractive BB and AB nearest-neighbour energy, uBB=uAB=−1, and for non-repulsive energy between AA nearest-neighbour sites, uAA<0, the system belongs to the universality class of the two-dimensional Ising model. However, when uAA>0, the system exhibits a non-universal critical behaviour. We have evaluated the dependences of the critical point characteristics on the value of uAA. 相似文献
56.
ON HYPERBOLIC TIME DISCOUNTING IN EXHAUSTIBLE RESOURCE MODELS: AN APPLICATION TO WORLD OIL RESOURCES
JOHN ROWSE 《Natural Resource Modeling》2006,19(2):243-277
ABSTRACT. Recent research on discounting in long term economic models involves hyperbolic discounting, in which the marginal discount rate shrinks as time passes. To investigate hyperbolic discounting and exhaustible resource allocation, this work develops a discrete‐time world oil model and model solution procedure, then uses the model to examine the consequences of adopting conventional (constant annual) discounting when hyperbolic discounting is appropriate, of adopting one hyperbolic discount rate path when a different hyperbolic path is appropriate, and of adopting hyperbolic discounting when conventional discounting is appropriate. Five conventional and two hyperbolic discount rate paths are considered. One hyperbolic path is that used by Nordhaus and Boyer [2000]; the other is that recommended by Weitzman [2001]. The generality of the findings is also assessed. 相似文献
57.
An implicit quasi-monotone second-order accurate method is proposed for analyzing the spiral Couette flow of a rarefied gas between coaxial cylinders. The basic advantages of the method over the conventional method of stationry iterations are that the former is conservative with respect to the collision integral, has a simple software implementation for any types of boundary conditions, and applies to a wide range of Knudsen numbers. 相似文献
58.
本文首先将文[1]中的BLD映射推广为弱(L1,L2)-BLD映射,并证明了如下正则性结果:存在两个可积指数 P1=P1(n,L1,L2)<n<q1=q1(n,L1,L2),使得对任意弱(L1,L2)-BLD映射f∈(Ω,Rn),都有f∈(Ω,Rn),即f为(L1,L2)-BLD映射. 相似文献
59.
Nicolas Bergeron 《Mathematische Zeitschrift》2002,241(1):101-125
Let M be an arithmetic hyperbolic manifold and be a codimension 1 geodesic cycle. In this paper, we study the asymptotic growth of the -norm of the lifts of F in the congruence tower above M. We obtain an explicit value for the growth rate of this norm. In particular, we provide a new proof of a celebrated result
of Millson [Mi] on the homology of the arithmetic hyperbolic manifolds. The method is quite general and gives a new way of
getting non zero homology classes in certain locally symmetric spaces.
Received: 20 April 2001; in final form: 26 September 2001 / Published online: 28 February 2002 相似文献
60.
Soliton interaction under the influence of higher-order effects 总被引:6,自引:0,他引:6
In this paper, we present exact N-soliton solution by employing simple, straightforward Darboux transformation based on the Lax pair for Hirota equation, a higher-order nonlinear Schrödinger (HNLS) equation. As examples, one- and two-soliton solutions in explicit forms are given and their properties are also analyzed. A bound solution without interaction will be theoretically predicted if one can adjust frequency shift for each soliton appropriately. Further, we obtain the approximate eigenvalues by employing two-soliton solution and discuss analytically the interaction between neighboring solitons under the influence of the higher-order effects. It is shown that the combined effects of the higher-order effects can restrain the interaction between neighboring solitons to some extent. The results are proved by directly solving HNLS equation numerically. 相似文献