全文获取类型
收费全文 | 23539篇 |
免费 | 3841篇 |
国内免费 | 1910篇 |
专业分类
化学 | 4519篇 |
晶体学 | 55篇 |
力学 | 3232篇 |
综合类 | 600篇 |
数学 | 11740篇 |
物理学 | 9144篇 |
出版年
2024年 | 36篇 |
2023年 | 231篇 |
2022年 | 460篇 |
2021年 | 564篇 |
2020年 | 585篇 |
2019年 | 550篇 |
2018年 | 553篇 |
2017年 | 804篇 |
2016年 | 932篇 |
2015年 | 752篇 |
2014年 | 1256篇 |
2013年 | 1690篇 |
2012年 | 1273篇 |
2011年 | 1450篇 |
2010年 | 1306篇 |
2009年 | 1468篇 |
2008年 | 1674篇 |
2007年 | 1718篇 |
2006年 | 1439篇 |
2005年 | 1315篇 |
2004年 | 1221篇 |
2003年 | 1044篇 |
2002年 | 992篇 |
2001年 | 801篇 |
2000年 | 711篇 |
1999年 | 664篇 |
1998年 | 584篇 |
1997年 | 498篇 |
1996年 | 425篇 |
1995年 | 422篇 |
1994年 | 282篇 |
1993年 | 245篇 |
1992年 | 183篇 |
1991年 | 214篇 |
1990年 | 145篇 |
1989年 | 95篇 |
1988年 | 124篇 |
1987年 | 88篇 |
1986年 | 70篇 |
1985年 | 83篇 |
1984年 | 53篇 |
1983年 | 35篇 |
1982年 | 41篇 |
1981年 | 46篇 |
1980年 | 35篇 |
1979年 | 34篇 |
1978年 | 30篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1957年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
121.
Bing Yong HSIE 《数学学报(英文版)》2006,22(2):507-514
This paper gives a p-adic analogue of the Mackey theory, which relates representations of a group of type G - H × t A to systems of imprimitivity. 相似文献
122.
123.
Armen Shirikyan 《Journal of Functional Analysis》2007,249(2):284-306
The paper is devoted to studying the distribution of stationary solutions for 3D Navier-Stokes equations perturbed by a random force. Under a non-degeneracy assumption, we show that the support of such a distribution coincides with the entire phase space, and its finite-dimensional projections are minorised by a measure possessing an almost surely positive smooth density with respect to the Lebesgue measure. Similar assertions are true for weak solutions of the Cauchy problem with a regular initial function. The results of this paper were announced in the short note [A. Shirikyan, Controllability of three-dimensional Navier-Stokes equations and applications, in: Sémin. Équ. Dériv. Partielles, 2005-2006, École Polytech., Palaiseau, 2006]. 相似文献
124.
基于事前评价过程和自然界生物进化过程的相似性,提出了系统结构、系统结构模式和系统环境模式矩阵的概念,并根据系统结构、系统结构模式与系统环境模式矩阵的适应程度,建立了模式评价决策模型,制定了评价系统的评价分类准则,并对评价系统作了一定的理论分析.将此模型和方法应用于城市生态安全评价中,通过与模糊综合评价法的比较,表明了该评价模型和方法的优越性. 相似文献
125.
Many recent algorithmic approaches involve the construction of a differential equation model for computational purposes, typically
by introducing an artificial time variable. The actual computational model involves a discretization of the now time-dependent differential system, usually
employing forward Euler. The resulting dynamics of such an algorithm is then a discrete dynamics, and it is expected to be
“close enough” to the dynamics of the continuous system (which is typically easier to analyze) provided that small – hence
many – time steps, or iterations, are taken. Indeed, recent papers in inverse problems and image processing routinely report
results requiring thousands of iterations to converge. This makes one wonder if and how the computational modeling process
can be improved to better reflect the actual properties sought.
In this article we elaborate on several problem instances that illustrate the above observations. Algorithms may often lend
themselves to a dual interpretation, in terms of a simply discretized differential equation with artificial time and in terms
of a simple optimization algorithm; such a dual interpretation can be advantageous. We show how a broader computational modeling
approach may possibly lead to algorithms with improved efficiency.
AMS subject classification (2000) 65L05, 65M32, 65N21, 65N22, 65D18 相似文献
126.
The equivalence of three (2 1)-dimensional soliton equations is proved, and the quite generalsolutionswitha some arbitrary functions of x, t and y respectively are obtained. By selecting the arbitrary functions, many specialtypes of the localized excitations like the solitoff solitons, multi-dromion solutions, lump, and multi-ring soliton solutionsare obtained. 相似文献
127.
王胜奎 《数学的实践与认识》2006,36(5):5-10
根据松纵坑切梢小蠹的主要生物学特征,通过分析抚育间伐持续控制松纵坑切梢小蠹虫害的机理,应用复杂适应系统(CA S)理论,建立了模拟松纵坑切梢小蠹虫害的一种动态演化数学模型,并讨论了模型的收敛性.然后选用昆明小哨林场为背景,进行了各种抚育间伐决策的仿真,从中优选抚育间伐决策.结果表明:模拟优化方案与实际调查统计分析结果一致:均为弱度间伐与中弱度间伐控制蠹害效果最好.最后通过森林积材量与虫害程度之间的优化,给出了抚育间伐的优化策略. 相似文献
128.
WU Ke ZHAO Weizhong & GUO Hanying Department of Mathematics Capital Normal University Beijing China Institute of Theoretical Physics Chinese Academy of Sciences Beijing China 《中国科学A辑(英文版)》2006,(11)
In a way similar to the continuous case formally, we define in different but equivalent manners the difference discrete connection and curvature on discrete vector bundle over the regular lattice as base space. We deal with the difference operators as the discrete counterparts of the derivatives based upon the differential calculus on the lattice. One of the definitions can be extended to the case over the random lattice. We also discuss the relation between our approach and the lattice gauge theory and apply to the discrete integrable systems. 相似文献
129.
In this paper, nonconvex multiobjective optimization problems are studied. New characterizations of a properly efficient solution in the sense of Geoffrion's are established in terms of the stability of one scalar optimization problem and the existence of an exact penalty function of a scalar constrained program, respectively. One of the characterizations is applied to derive necessary conditions for a properly efficient control-parameter pair of a nonconvex multiobjective discrete optimal control problem with linear constraints. 相似文献
130.
Mixed and hybrid finite element methods for the resolution of a wide range of linear and nonlinear boundary value problems (linear elasticity, Stokes problem, Navier–Stokes equations, Boussinesq equations, etc.) have known a great development in the last few years. These methods allow simultaneous computation of the original variable and its gradient, both of them being equally accurate. Moreover, they have local conservation properties (conservation of the mass and the momentum) as in the finite volume methods.The purpose of this paper is to give a review on some mixed finite elements developed recently for the resolution of Stokes and Navier–Stokes equations, and the linear elasticity problem. Further developments for a quasi-Newtonian flow obeying the power law are presented. 相似文献