全文获取类型
收费全文 | 36562篇 |
免费 | 4161篇 |
国内免费 | 2439篇 |
专业分类
化学 | 4239篇 |
晶体学 | 50篇 |
力学 | 3638篇 |
综合类 | 444篇 |
数学 | 24899篇 |
物理学 | 9892篇 |
出版年
2024年 | 79篇 |
2023年 | 362篇 |
2022年 | 470篇 |
2021年 | 598篇 |
2020年 | 1075篇 |
2019年 | 1082篇 |
2018年 | 1003篇 |
2017年 | 968篇 |
2016年 | 1084篇 |
2015年 | 916篇 |
2014年 | 1631篇 |
2013年 | 3265篇 |
2012年 | 1747篇 |
2011年 | 2108篇 |
2010年 | 1977篇 |
2009年 | 2240篇 |
2008年 | 2342篇 |
2007年 | 2330篇 |
2006年 | 2015篇 |
2005年 | 1976篇 |
2004年 | 1675篇 |
2003年 | 1644篇 |
2002年 | 1473篇 |
2001年 | 1153篇 |
2000年 | 1094篇 |
1999年 | 1026篇 |
1998年 | 939篇 |
1997年 | 821篇 |
1996年 | 597篇 |
1995年 | 488篇 |
1994年 | 400篇 |
1993年 | 278篇 |
1992年 | 273篇 |
1991年 | 249篇 |
1990年 | 226篇 |
1989年 | 140篇 |
1988年 | 138篇 |
1987年 | 134篇 |
1986年 | 130篇 |
1985年 | 143篇 |
1984年 | 138篇 |
1983年 | 68篇 |
1982年 | 124篇 |
1981年 | 112篇 |
1980年 | 90篇 |
1979年 | 88篇 |
1978年 | 53篇 |
1977年 | 56篇 |
1976年 | 49篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
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
32.
This paper gives some global and uniform convergence estimates for a class of subspace correction (based on space decomposition) iterative methods applied to some unconstrained convex optimization problems. Some multigrid and domain decomposition methods are also discussed as special examples for solving some nonlinear elliptic boundary value problems.
33.
34.
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
35.
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
36.
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
37.
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
38.
39.
This paper undertakes a systematic treatment of the low regularity local wellposedness and ill-posedness theory in Hs andHs for semilinear wave equations with polynomial nonlinearity in u and (e)u. This ill-posed result concerns the focusing type equations with nonlinearity on u and (e)tu. 相似文献
40.