全文获取类型
收费全文 | 25060篇 |
免费 | 3036篇 |
国内免费 | 951篇 |
专业分类
化学 | 4630篇 |
晶体学 | 115篇 |
力学 | 8682篇 |
综合类 | 283篇 |
数学 | 7423篇 |
物理学 | 7914篇 |
出版年
2024年 | 39篇 |
2023年 | 301篇 |
2022年 | 531篇 |
2021年 | 595篇 |
2020年 | 642篇 |
2019年 | 546篇 |
2018年 | 595篇 |
2017年 | 814篇 |
2016年 | 912篇 |
2015年 | 900篇 |
2014年 | 1143篇 |
2013年 | 1836篇 |
2012年 | 1292篇 |
2011年 | 1515篇 |
2010年 | 1181篇 |
2009年 | 1446篇 |
2008年 | 1457篇 |
2007年 | 1470篇 |
2006年 | 1256篇 |
2005年 | 1022篇 |
2004年 | 1071篇 |
2003年 | 987篇 |
2002年 | 873篇 |
2001年 | 658篇 |
2000年 | 678篇 |
1999年 | 603篇 |
1998年 | 571篇 |
1997年 | 502篇 |
1996年 | 477篇 |
1995年 | 418篇 |
1994年 | 366篇 |
1993年 | 318篇 |
1992年 | 285篇 |
1991年 | 235篇 |
1990年 | 211篇 |
1989年 | 171篇 |
1988年 | 166篇 |
1987年 | 119篇 |
1986年 | 109篇 |
1985年 | 139篇 |
1984年 | 104篇 |
1983年 | 63篇 |
1982年 | 110篇 |
1981年 | 46篇 |
1980年 | 59篇 |
1979年 | 50篇 |
1978年 | 33篇 |
1977年 | 35篇 |
1976年 | 41篇 |
1957年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 47 毫秒
81.
82.
针对受参数不确定和外扰影响的混沌Lorenz系统,提出一种基于径向基函数(RBF)神经网 络的滑模控制方法.基于被控系统在不稳定平衡点处状态误差的可控规范形,设计滑模切换 面并将其作为神经网络的唯一输入.单入单出形式的RBF控制器隐层只需7个径向基函数,网 络的权值则依滑模趋近条件在线确定.仿真表明该控制器对系统参数突变和外部干扰具有鲁棒性,同时抑制了抖振.
关键词:
混沌控制
滑模
径向基函数神经网络
Lorenz系统 相似文献
83.
Differential game formulations provide an adequate basis for a guidance law synthesis against highly maneuvering targets. This paper deals with a guidance law based on a linear-quadratic differential game formulation. This guidance law has many attractive properties: it is continuous, linear with respect to the state variables, and its gain coefficients can be precalculated offline. Nevertheless, due to the lack of hard control constraints in the formulation, the magnitude of the control can exceed the admissible level imposed by the nature of the problem. In this paper, the upper bound of the interceptor control is obtained depending on the system parameters and the penalty coefficients of the game performance index. It is shown that the interceptor can guarantee an arbitrarily small miss distance without exceeding the control constraints if it has sufficient maneuverability and if the penalty coefficients are chosen properly. By manipulating the penalty coefficients, it is possible to reduce significantly the maneuverability requirements compared to the case of zero interceptor penalty coefficient. 相似文献
84.
The control of piecewise-deterministic processes is studied where only local boundedness of the data is assumed. Moreover the discount rate may be zero. The value function is shown to be solution to the Bellman equation in a weak sense; however the solution concept is strong enough to generate optimal policies. Continuity and compactness conditions are given for the existence of nonrelaxed optimal feedback controls. 相似文献
85.
Toshihiro Kobayashi 《Mathematical Methods in the Applied Sciences》2004,27(1):79-89
This paper is concerned with global stabilization of an undamped non‐linear string in the case where any velocity feedback is not available. The linearized system has an infinite number of poles and zeros on the imaginary axis. In the case where any velocity feedback is not available, a parallel compensator is effective. The stabilizer is constructed for the augmented system which consists of the controlled system and a parallel compensator. It is proved that the string can be stabilized by linear boundary control. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
86.
The rotating flow in the presence of a magnetic field is a problem belonging to hydromagnetics and deserves to be more widely studied than it has been to date. In the non‐linear regime the literature is scarce. We develop the governing equations for the unsteady hydromagnetic rotating flow of a fourth‐order fluid past a porous plate. The steady flow is governed by a boundary value problem in which the order of differential equations is more than the number of available boundary conditions. It is shown that by augmenting the boundary conditions based on asymptotic structures at infinity it is possible to obtain numerical solutions of the nonlinear hydromagnetic equations. Effects of uniform suction or blowing past the porous plate, exerted magnetic field and rotation on the flow phenomena, especially on the boundary layer structure near the plate, are numerically analysed and discussed. The flow behaviours of the Newtonian fluid and second‐, third‐ and fourth‐order non‐Newtonian fluids are compared for the special flow problem, respectively. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
87.
M. A. Efendiev J. Fuhrmann S. V. Zelik 《Mathematical Methods in the Applied Sciences》2004,27(8):907-930
For the Boussinesq approximation of the equations of coupled heat and fluid flow in a porous medium we show that the corresponding system of partial differential equations possesses a global attractor. We give lower and upper bounds of the Hausdorff dimension of the attractor depending on a physical parameter of the system, namely the Rayleigh number of the flow. Numerical experiments confirm the theoretical findings and raise new questions on the structure of the solutions of the system. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
88.
Mari Grobbelaar‐Van Dalsen 《Mathematical Methods in the Applied Sciences》2004,27(11):1301-1315
This paper is concerned with well‐posedness results for a mathematical model for the transversal vibrations of a two‐dimensional hybrid elastic structure consisting of a rectangular Reissner–Mindlin plate with a Timoshenko beam attached to its free edge. The model incorporates linear dynamic feedback controls along the interface between the plate and the beam. Classical semigroup methods are employed to show the unique solvability of the coupled initial‐boundary‐value problem. We also show that the energy associated with the system exhibits the property of strong stability. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
89.
Larbi Berrahmoune 《Mathematical Methods in the Applied Sciences》2004,27(12):1385-1398
We consider an initial and boundary value problem for a homogenous string subject to an internal pointwise control. The solution resulting from a non‐linear feedback is studied. We give various explicit decay estimates depending on the control position and the feedback non‐linearity. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
90.
L. E. Payne P. W. Schaefer J. C. Song 《Mathematical Methods in the Applied Sciences》2004,27(17):2045-2053
Energy bounds are derived for Dirichlet type boundary value problems for the Navier–Stokes and Stokes equations when a combination of the solution values initially and at a later time is prescribed. The bounds are obtained by means of a differential inequality and imply uniqueness and continuous data dependence of the solutions for a range of values of the parameter in the non‐standard auxiliary condition. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献