全文获取类型
收费全文 | 48947篇 |
免费 | 6334篇 |
国内免费 | 4952篇 |
专业分类
化学 | 17947篇 |
晶体学 | 1273篇 |
力学 | 9874篇 |
综合类 | 585篇 |
数学 | 14738篇 |
物理学 | 15816篇 |
出版年
2024年 | 108篇 |
2023年 | 549篇 |
2022年 | 986篇 |
2021年 | 1124篇 |
2020年 | 1415篇 |
2019年 | 1255篇 |
2018年 | 1226篇 |
2017年 | 1720篇 |
2016年 | 1926篇 |
2015年 | 1591篇 |
2014年 | 2420篇 |
2013年 | 3335篇 |
2012年 | 3000篇 |
2011年 | 3488篇 |
2010年 | 2979篇 |
2009年 | 3297篇 |
2008年 | 3077篇 |
2007年 | 3134篇 |
2006年 | 3010篇 |
2005年 | 2951篇 |
2004年 | 2386篇 |
2003年 | 2127篇 |
2002年 | 1767篇 |
2001年 | 1470篇 |
2000年 | 1384篇 |
1999年 | 1276篇 |
1998年 | 1164篇 |
1997年 | 999篇 |
1996年 | 840篇 |
1995年 | 687篇 |
1994年 | 611篇 |
1993年 | 484篇 |
1992年 | 504篇 |
1991年 | 380篇 |
1990年 | 297篇 |
1989年 | 226篇 |
1988年 | 185篇 |
1987年 | 141篇 |
1986年 | 91篇 |
1985年 | 118篇 |
1984年 | 111篇 |
1983年 | 55篇 |
1982年 | 75篇 |
1981年 | 53篇 |
1980年 | 30篇 |
1979年 | 51篇 |
1978年 | 31篇 |
1977年 | 37篇 |
1976年 | 13篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
Efficient Sequential Quadratic Programming Implementations for Equality-Constrained Discrete-Time Optimal Control 总被引:1,自引:0,他引:1
Efficient sequential quadratic programming (SQP) implementations are presented for equality-constrained, discrete-time, optimal control problems. The algorithm developed calculates the search direction for the equality-based variant of SQP and is applicable to problems with either fixed or free final time. Problem solutions are obtained by solving iteratively a series of constrained quadratic programs. The number of mathematical operations required for each iteration is proportional to the number of discrete times N. This is contrasted by conventional methods in which this number is proportional to N
3. The algorithm results in quadratic convergence of the iterates under the same conditions as those for SQP and simplifies to an existing dynamic programming approach when there are no constraints and the final time is fixed. A simple test problem and two application problems are presented. The application examples include a satellite dynamics problem and a set of brachistochrone problems involving viscous friction. 相似文献
73.
对一类变形的变分不等式:求,使得提出了一类投影收缩算法,并得到了该算法的收敛性及相关性质. 相似文献
74.
沈惠川 《数学物理学报(A辑)》1998,18(1):78-88
将弹性有限变形问题纳入Lagrange力学的理论体系中,并用经典力学中业已存在的Routh方法构建了有限变形平面应变问题和有限变形平面应力问题的基本微分方程,讨论了有限变形大挠度问题vonkarman方程中存在的矛盾进而提出了两种改进方案. 相似文献
75.
76.
Modeling and numerical simulations of the convective flows induced by the vibration of the monocrystal during crystal growth have been performed for two configurations simulating the Cz and FZ methods. This permitted to emphasize the role of different vibrational mechanisms in the formation of the average flows. It is shown that an appropriate combination of these mechanisms can be used to counteract the usual convective flows (buoyancy- and/or thermocapillary-driven) inherent to crystal growth processes from the liquid phase. While vibrational convection is rather complex due to these identified mechanisms, the new modeling used in the present paper opens up very promising perspectives to efficiently control heat and mass transfer during real industrial applications of crystal growth from the liquid phase. 相似文献
77.
A globally convergent Newton method for solving strongly monotone variational inequalities 总被引:14,自引:0,他引:14
Variational inequality problems have been used to formulate and study equilibrium problems, which arise in many fields including economics, operations research and regional sciences. For solving variational inequality problems, various iterative methods such as projection methods and the nonlinear Jacobi method have been developed. These methods are convergent to a solution under certain conditions, but their rates of convergence are typically linear. In this paper we propose to modify the Newton method for variational inequality problems by using a certain differentiable merit function to determine a suitable step length. The purpose of introducing this merit function is to provide some measure of the discrepancy between the solution and the current iterate. It is then shown that, under the strong monotonicity assumption, the method is globally convergent and, under some additional assumptions, the rate of convergence is quadratic. Limited computational experience indicates the high efficiency of the proposed method. 相似文献
78.
本文以fp 同伦方法为工具,借助于一些适当的变换,研究有序的(B)空间中的集值映象方程的多正解问题;在文中的有关工作中,还使用了集值映象的拟导数的某些性质. 相似文献
79.
I.IntroductionWhenastructurcvibratcs,itsvibratingsurfacewillmakesurroundingmediummovetogethcrwithit.Ifthernotionissofastthatthcmediumroundthestructureproduccaloca1contractionandcxpansionandthcypropagatefaraway,thesoundradiationisformed.Itispossiblctodcscribeanalytica11ytheradiationfic1dofsimplyandregularlyshapcdsourcessuchaspointsoundsourccs,spherica1soundsourccsandinflnite1engthllnearsoundsourccs,butitisa1mostimpossib1ctosolvetheradiationfiledbyanyanalyt-ica1methodforsourcesofvcrycomplicateds… 相似文献
80.
L. Contesse-Becker 《Journal of Optimization Theory and Applications》1993,79(2):273-310
In this paper, we extend the classical convergence and rate of convergence results for the method of multipliers for equality constrained problems to general inequality constrained problems, without assuming the strict complementarity hypothesis at the local optimal solution. Instead, we consider an alternative second-order sufficient condition for a strict local minimum, which coincides with the standard one in the case of strict complementary slackness. As a consequence, new stopping rules are derived in order to guarantee a local linear rate of convergence for the method, even if the current Lagrangian is only asymptotically minimized in this more general setting. These extended results allow us to broaden the scope of applicability of the method of multipliers, in order to cover all those problems admitting loosely binding constraints at some optimal solution. This fact is not meaningless, since in practice this kind of problem seems to be more the rule rather than the exception.In proving the different results, we follow the classical primaldual approach to the method of multipliers, considering the approximate minimizers for the original augmented Lagrangian as the exact solutions for some adequate approximate augmented Lagrangian. In particular, we prove a general uniform continuity property concerning both their primal and their dual optimal solution set maps, a property that could be useful beyond the scope of this paper. This approach leads to very simple proofs of the preliminary results and to a straight-forward proof of the main results.The author gratefully acknowledges the referees for their helpful comments and remarks. This research was supported by FONDECYT (Fondo Nacional de Desarrollo Científico y Technológico de Chile). 相似文献