全文获取类型
收费全文 | 8118篇 |
免费 | 990篇 |
国内免费 | 634篇 |
专业分类
化学 | 1150篇 |
晶体学 | 29篇 |
力学 | 837篇 |
综合类 | 148篇 |
数学 | 4404篇 |
物理学 | 3174篇 |
出版年
2024年 | 18篇 |
2023年 | 82篇 |
2022年 | 455篇 |
2021年 | 439篇 |
2020年 | 252篇 |
2019年 | 219篇 |
2018年 | 235篇 |
2017年 | 235篇 |
2016年 | 294篇 |
2015年 | 245篇 |
2014年 | 374篇 |
2013年 | 572篇 |
2012年 | 356篇 |
2011年 | 438篇 |
2010年 | 356篇 |
2009年 | 471篇 |
2008年 | 521篇 |
2007年 | 493篇 |
2006年 | 447篇 |
2005年 | 428篇 |
2004年 | 359篇 |
2003年 | 362篇 |
2002年 | 325篇 |
2001年 | 232篇 |
2000年 | 223篇 |
1999年 | 208篇 |
1998年 | 173篇 |
1997年 | 153篇 |
1996年 | 116篇 |
1995年 | 73篇 |
1994年 | 98篇 |
1993年 | 59篇 |
1992年 | 72篇 |
1991年 | 45篇 |
1990年 | 39篇 |
1989年 | 41篇 |
1988年 | 38篇 |
1987年 | 29篇 |
1986年 | 18篇 |
1985年 | 22篇 |
1984年 | 24篇 |
1983年 | 5篇 |
1982年 | 24篇 |
1981年 | 15篇 |
1980年 | 14篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1976年 | 4篇 |
1969年 | 4篇 |
排序方式: 共有9742条查询结果,搜索用时 0 毫秒
1.
Space-time directional Lyapunov exponents are introduced. They describe the maximal velocity of propagation to the right or to the left of fronts of perturbations in a frame moving with a given velocity. The continuity of these exponents as function of the velocity and an inequality relating them to the directional entropy is proved. 相似文献
2.
Volker Elling. 《Mathematics of Computation》2006,75(256):1721-1733
A particular case of initial data for the two-dimensional Euler equations is studied numerically. The results show that the Godunov method does not always converge to the physical solution, at least not on feasible grids. Moreover, they suggest that entropy solutions (in the weak entropy inequality sense) are not well posed.
3.
We obtain upper bounds for the tail distribution of the first nonnegative sum of a random walk and for the moments of the overshoot over an arbitrary nonnegative level if the expectation of jumps is positive and close to zero. In addition, we find an estimate for the expectation of the first ladder epoch. 相似文献
4.
In this work we study nonnegativity and positivity of a discrete quadratic functional with separately varying endpoints. We introduce a notion of an interval coupled with 0, and hence, extend the notion of conjugate interval to 0 from the case of fixed to variable endpoint(s). We show that the nonnegativity of the discrete quadratic functional is equivalent to each of the following conditions: The nonexistence of intervals coupled with 0, the existence of a solution to Riccati matrix equation and its boundary conditions. Natural strengthening of each of these conditions yields a characterization of the positivity of the discrete quadratic functional. Since the quadratic functional under consideration could be a second variation of a discrete calculus of variations problem with varying endpoints, we apply our results to obtain necessary and sufficient optimality conditions for such problems. This paper generalizes our recent work in [R. Hilscher, V. Zeidan, Comput. Math. Appl., to appear], where the right endpoint is fixed. 相似文献
5.
Shunlong Luo 《Foundations of Physics》2002,32(11):1757-1772
We formulate an elementary statistical game which captures the essence of some fundamental quantum experiments such as photon polarization and spin measurement. We explore and compare the significance of the principle of maximum Shannon entropy and the principle of minimum Fisher information in solving such a game. The solution based on the principle of minimum Fisher information coincides with the solution based on an invariance principle, and provides an informational explanation of Malus' law for photon polarization. There is no solution based on the principle of maximum Shannon entropy. The result demonstrates the merits of Fisher information, and the demerits of Shannon entropy, in treating some fundamental quantum problems. It also provides a quantitative example in support of a general philosophy: Nature intends to hide Fisher information, while obeying some simple rules. 相似文献
6.
A Modified Quasi-Newton Method for Structured Optimization with Partial Information on the Hessian 总被引:2,自引:0,他引:2
This paper develops a modified quasi-Newton method for structured unconstrained optimization with partial information on the
Hessian, based on a better approximation to the Hessian in current search direction. The new approximation is decided by both
function values and gradients at the last two iterations unlike the original one which only uses the gradients at the last
two iterations. The modified method owns local and superlinear convergence. Numerical experiments show that the proposed method
is encouraging comparing with the methods proposed in [4] for structured unconstrained optimization
Presented at the 6th International Conference on Optimization: Techniques and Applications, Ballarat, Australia, December
9–11, 2004 相似文献
7.
Mehdi Dehghan 《Numerical Methods for Partial Differential Equations》2002,18(2):193-202
Developement of numerical methods for obtaining approximate solutions to the three dimensional diffusion equation with an integral condition will be carried out. The numerical techniques discussed are based on the fully explicit (1,7) finite difference technique and the fully implicit (7,1) finite difference method and the (7,7) Crank‐Nicolson type finite difference formula. The new developed methods are tested on a problem. Truncation error analysis and numerical examples are used to illustrate the accuracy of the new algorithms. The results of numerical testing show that the numerical methods based on the finite difference techniques discussed in the present article produce good results. © 2002 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 18: 193–202, 2002; DOI 10.1002/num.1040 相似文献
8.
Equilibrium Problems with Applications to Eigenvalue Problems 总被引:5,自引:0,他引:5
In this paper, we consider equilibrium problems and introduce the concept of (S)+ condition for bifunctions. Existence results for equilibrium problems with the (S)+ condition are derived. As special cases, we obtain several existence results for the generalized nonlinear variational inequality studied by Ding and Tarafdar (Ref. 1) and the generalized variational inequality studied by Cubiotti and Yao (Ref. 2). Finally, applications to a class of eigenvalue problems are given. 相似文献
9.
Dan Voiculescu 《Reports on Mathematical Physics》2005,55(1):127-133
This short note summarizes the circumstances of the birth of free probability theory andsome of the recent achievements. 相似文献
10.
M. D. Srinivas 《Pramana》2003,60(6):1137-1152
We derive an optimal bound on the sum of entropic uncertainties of two or more observables when they are sequentially measured
on the same ensemble of systems. This optimal bound is shown to be greater than or equal to the bounds derived in the literature
on the sum of entropie uncertainties of two observables which are measured on distinct but identically prepared ensembles
of systems. In the case of a two-dimensional Hilbert space, the optimum bound for successive measurements of two-spin components,
is seen to be strictly greater than the optimal bound for the case when they are measured on distinct ensembles, except when
the spin components are mutually parallel or perpendicular 相似文献