全文获取类型
收费全文 | 10898篇 |
免费 | 1869篇 |
国内免费 | 509篇 |
专业分类
化学 | 1975篇 |
晶体学 | 46篇 |
力学 | 1785篇 |
综合类 | 212篇 |
数学 | 5325篇 |
物理学 | 3933篇 |
出版年
2024年 | 17篇 |
2023年 | 181篇 |
2022年 | 263篇 |
2021年 | 300篇 |
2020年 | 256篇 |
2019年 | 244篇 |
2018年 | 263篇 |
2017年 | 467篇 |
2016年 | 525篇 |
2015年 | 476篇 |
2014年 | 590篇 |
2013年 | 827篇 |
2012年 | 597篇 |
2011年 | 616篇 |
2010年 | 557篇 |
2009年 | 654篇 |
2008年 | 697篇 |
2007年 | 703篇 |
2006年 | 555篇 |
2005年 | 422篇 |
2004年 | 435篇 |
2003年 | 458篇 |
2002年 | 373篇 |
2001年 | 296篇 |
2000年 | 309篇 |
1999年 | 296篇 |
1998年 | 240篇 |
1997年 | 191篇 |
1996年 | 181篇 |
1995年 | 167篇 |
1994年 | 136篇 |
1993年 | 101篇 |
1992年 | 80篇 |
1991年 | 88篇 |
1990年 | 72篇 |
1989年 | 54篇 |
1988年 | 69篇 |
1987年 | 52篇 |
1986年 | 40篇 |
1985年 | 64篇 |
1984年 | 39篇 |
1983年 | 29篇 |
1982年 | 34篇 |
1981年 | 27篇 |
1980年 | 47篇 |
1979年 | 46篇 |
1978年 | 26篇 |
1977年 | 36篇 |
1976年 | 37篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
991.
In this article, we study some robust control problems associated with the multilayer quasi-geostrophic equations of the ocean and related to data assimilation in oceanography. We consider higher norms (compared to [T. Tachim Medjo, Robust control problems associated with the multilayer quasi-geostrophic equations of the ocean, Appl. Math. Optim. 51(3) (2005) 333–360]) in the definition of the cost functionals. We prove the existence and uniqueness of solutions. The result relies on better a priori estimates on the solutions to the multilayer quasi-geostrophic system obtained using a new formulation that we introduce for the multilayer quasi-geostrophic equation of the ocean. The new formulation replaces the non-homogenous boundary conditions (and the non-local constraint) on the stream-function by a simple homogenous Dirichlet boundary condition. 相似文献
992.
Ze-Rong He 《Journal of Mathematical Analysis and Applications》2005,305(1):11-28
We study optimal birth policies for two age-dependent populations in a competing system, which is controlled by fertilities. New results on problems with free final time and integral phase constraints are presented, and the approximate controllability of system is discussed. 相似文献
993.
LI Huajun DU Chang XUAN Weimin PEN Jianfei HU Haotian LIU Lin KANG Li XU Lirong HUANG Zhaorong WANG Fen WANG Xiaoping WANG Haibing 《核工业西南物理研究院年报(英文版)》2005,(1):71-73
The power of the toroidal field (TF) coil in HL-2A is supplied with two 80 MVA motor generators (MGs) together through a diode rectifier. The TF system is designed to obtain the parameters as follows: the highest toroidal filed of 2.8 T, the biggest coil current of 45 kA, the fiat top time of 3-5 s. So the released energy of each MG set for one pulse discharge mast be more than 500 MJ. 相似文献
994.
Summary We present a two-dimensional, nonlinear map, arising from a simple adaptive control problem, which exhibits disconnected boundaries separating the basins of attraction of its coexisting attractors. We perform a detailed study of the relation between this phenomenon and the noninvertible nature of the map and demonstrate how the complex basin structure is caused by a change in the number of preimages of points along a stable manifold. 相似文献
995.
Prof. Dr. U. Rieder 《Mathematical Methods of Operations Research》1991,35(6):473-490
A general partially observed control model with discrete time parameter is investigated. Our main interest concerns monotonicity results and bounds for the value functions and for optimal policies. In particular, we show how the value functions depend on the observation kernels and we present conditions for a lower bound of an optimal policy. Our approach is based on two multivariate stochastic orderings: theTP
2 ordering and the Blackwell ordering.Dedicated to Prof. Dr. K. Hinderer on the occassion of his 60th birthday 相似文献
996.
A control theory optimization of iteroparous life histories indicates that if growth and reproduction are nonlinear functions of energy allocations, graded allocations of energy to potential reproduction can be optimal. 相似文献
997.
Aziz Belmiloudi 《Journal of Mathematical Analysis and Applications》2002,273(2):428-456
In this paper, we study a linear and a nonlinear boundary control problems arising from viscous flows. The equations are of nonlinear Navier-Stokes type for the velocity and pressure, of transport-diffusion type for the temperature and the salinity. The essential difficulties are due to the nonlinear nature of a part of the boundary conditions and to the nature of the equations: time-dependent, coupled and nonlinear. The existence and the conditions of the uniqueness of the solution, for the variational problem, are studied. The control is of linear or nonlinear Robin-type and acts on a part of the boundary during a time T. The cost function measures the distance between the observed and the computed vorticity. The existence of an optimal control in the admissible set of states and controls is proved. A first order necessary conditions of optimality are obtained. 相似文献
998.
Wardi Y. Melamed B. Cassandras C.G. Panayiòtou C.G. 《Journal of Optimization Theory and Applications》2002,115(2):369-405
This paper applies infinitesimal perturbation analysis (IPA) to loss-related and workload-related metrics in a class of stochastic flow models (SFM). It derives closed-form formulas for the gradient estimators of these metrics with respect to various parameters of interest, such as buffer size, service rate, and inflow rate. The IPA estimators derived are simple and fast to compute, and are further shown to be unbiased and nonparametric, in the sense that they can be computed directly from the observed data without any knowledge of the underlying probability law. These properties hold out the promise of utilizing IPA gradient estimates as ingredients of online management and control of telecommunications networks. While this paper considers single-node SFMs, the analysis method developed is amenable to extensions to networks of SFM nodes with more general topologies. 相似文献
999.
1000.
《Operations Research Letters》2023,51(4):393-400
In this paper, we discuss an application of the Stochastic Dual Dynamic Programming (SDDP) type algorithm to nested risk-averse formulations of Stochastic Optimal Control (SOC) problems. We propose a construction of a statistical upper bound for the optimal value of risk-averse SOC problems. This outlines an approach to a solution of a long standing problem in that area of research. The bound holds for a large class of convex and monotone conditional risk mappings. Finally, we show the validity of the statistical upper bound to solve a real-life stochastic hydro-thermal planning problem. 相似文献