全文获取类型
收费全文 | 6448篇 |
免费 | 789篇 |
国内免费 | 221篇 |
专业分类
化学 | 617篇 |
晶体学 | 5篇 |
力学 | 605篇 |
综合类 | 71篇 |
数学 | 4719篇 |
物理学 | 1441篇 |
出版年
2023年 | 53篇 |
2022年 | 88篇 |
2021年 | 135篇 |
2020年 | 184篇 |
2019年 | 186篇 |
2018年 | 185篇 |
2017年 | 207篇 |
2016年 | 234篇 |
2015年 | 160篇 |
2014年 | 243篇 |
2013年 | 633篇 |
2012年 | 293篇 |
2011年 | 302篇 |
2010年 | 284篇 |
2009年 | 306篇 |
2008年 | 306篇 |
2007年 | 298篇 |
2006年 | 279篇 |
2005年 | 285篇 |
2004年 | 226篇 |
2003年 | 245篇 |
2002年 | 370篇 |
2001年 | 240篇 |
2000年 | 243篇 |
1999年 | 164篇 |
1998年 | 164篇 |
1997年 | 132篇 |
1996年 | 93篇 |
1995年 | 86篇 |
1994年 | 85篇 |
1993年 | 54篇 |
1992年 | 69篇 |
1991年 | 62篇 |
1990年 | 55篇 |
1989年 | 44篇 |
1988年 | 43篇 |
1987年 | 36篇 |
1986年 | 40篇 |
1985年 | 58篇 |
1984年 | 49篇 |
1983年 | 18篇 |
1982年 | 35篇 |
1981年 | 25篇 |
1980年 | 23篇 |
1979年 | 29篇 |
1978年 | 16篇 |
1977年 | 25篇 |
1976年 | 28篇 |
1974年 | 10篇 |
1973年 | 7篇 |
排序方式: 共有7458条查询结果,搜索用时 15 毫秒
101.
In a general measure-theoretic context, it is proved that the action of a stochastic map on a pair of probability distributions can be characterized by the criterion of decreasing mixing distance. 相似文献
102.
A class of circuit-switching open queueing networks is discussed. The main result of the paper is that if extra message flows are not too intensive and the path distribution is mainly concentrated on the paths of (graph) distance 1 (nearest neighbour connections), then the network has a unique stationary working regime, no matter how large the configuration graph of the network is. Standard properties of this regime are established such as decay of correlation and continuity. 相似文献
103.
A recursive method is developed for the solution of coupled algebraic Riccati equations and corresponding linear Nash strategies of weakly interconnected systems. It is shown that the given algorithm converges to the exact solution with the rate of convergence ofO(2), where is a small coupling parameter. In addition, only low-order systems are involved in algebrdic computations; the amount of computations required does not grow per iteration and no analyticity assumption is imposed on the system coefficients.This work was supported by Rutgers University Research Council under Grant No. 2-02188. 相似文献
104.
105.
We consider the relaxation dynamics of two quantum levels coupled to a stochastic bath. We emphasize that even if the matrix elements of the fluctuating Hamiltonian are Gaussian, a second-order cumulant truncation is not exact. For various stochastic models, including the case of a spin-1/2 particle in a fluctuating magnetic field, we calculate 1/T
1, the population relaxation rate, and 1/T
2, the phase relaxation rate, up to fourth order in perturbation theory. We show that unlike the commonly accepted second-order result that 1/T
21/2T
1, when fourth-order terms are included, in some instances 1/T
2<1/2T
1. 相似文献
106.
The relation between the aperiodic solution of the Lorenz model and that of a stochastic anharmonic oscillator is explored. The stochastic oscillator is constructed by replacing (t) in the Lorenz model by a stochastic variable(t) of specified statistics. The resulting system is of course not isomorphic to the Lorenz model, but does share with it a number of statistical properties. Thus, within the confines of these measures the two systems are physically very similar. 相似文献
107.
J. Lewin 《Journal of Optimization Theory and Applications》1986,49(3):411-430
A pursuerP, whose speed is bounded by 1, wants to get closer to an evaderE, whose speed is bounded by >1.P wants to reduce his distancePE fromE below the capture radius . Both players are confined to a circular arena. This problem is equivalent to a problem discussed by Flynn, who characterized and gave numerical bounds to the least upper boundd* on the values ofPE thatE can maintain. He used direct methods and did not use Isaacs' theory.We solve our problem relying on the theory of singular surfaces in differential games. We construct and investigate barriers of the game of kind, and we replace Flynn's bounds ond* by analytical (exact) values for various speeds .The support of the TW Department of THT, Enschede, Holland, is gratefully acknowledged. 相似文献
108.
109.
Darian E Hnizdo V Fedorowicz A Singh H Demchuk E 《Journal of computational chemistry》2005,26(7):651-660
A method of statistical estimation is applied to the problem of evaluating the absolute entropy of internal rotation in a molecule with two torsional degrees of freedom. The configurational part of the entropy is obtained as that of the joint probability density of an arbitrary form represented by a two-dimensional Fourier series, the coefficients of which are statistically estimated using a sample of the torsional angles of the molecule obtained by a stochastic simulation. The internal rotors in the molecule are assumed to be attached to a common frame, and their reduced moments of inertia are initially calculated as functions of the two torsional angles, but averaged over all the remaining internal degrees of freedom using the stochastic-simulation sample of the atomic configurations of the molecule. The torsional-angle dependence of the reduced moments of inertia can be also averaged out, and the absolute internal-rotation entropy of the molecule is obtained in a good approximation as the sum of the configurational entropy and a kinetic contribution fully determined by the averaged reduced moments of inertia. The method is illustrated using Monte Carlo simulations of isomers of stilbene and halogenated derivatives of propane. The two torsional angles in cis-stilbene are found to be much more strongly correlated than those in trans-stilbene, while the degree of the angular correlation in propane increases strongly on substitution of hydrogen atoms with chlorine. 相似文献
110.
A novel hybrid optimization method called quantum stochastic tunneling has been recently introduced. Here, we report its implementation within a new docking program called EasyDock and a validation with the CCDC/Astex data set of ligand-protein complexes using the PLP score to represent the ligand-protein potential energy surface and ScreenScore to score the ligand-protein binding energies. When taking the top energy-ranked ligand binding mode pose, we were able to predict the correct crystallographic ligand binding mode in up to 75% of the cases. By using this novel optimization method run times for typical docking simulations are significantly shortened. 相似文献