全文获取类型
收费全文 | 5496篇 |
免费 | 532篇 |
国内免费 | 251篇 |
专业分类
化学 | 330篇 |
晶体学 | 4篇 |
力学 | 480篇 |
综合类 | 109篇 |
数学 | 4478篇 |
物理学 | 878篇 |
出版年
2024年 | 9篇 |
2023年 | 64篇 |
2022年 | 91篇 |
2021年 | 115篇 |
2020年 | 145篇 |
2019年 | 145篇 |
2018年 | 142篇 |
2017年 | 180篇 |
2016年 | 217篇 |
2015年 | 149篇 |
2014年 | 266篇 |
2013年 | 420篇 |
2012年 | 285篇 |
2011年 | 281篇 |
2010年 | 245篇 |
2009年 | 321篇 |
2008年 | 324篇 |
2007年 | 291篇 |
2006年 | 276篇 |
2005年 | 245篇 |
2004年 | 189篇 |
2003年 | 190篇 |
2002年 | 176篇 |
2001年 | 179篇 |
2000年 | 168篇 |
1999年 | 146篇 |
1998年 | 115篇 |
1997年 | 95篇 |
1996年 | 79篇 |
1995年 | 94篇 |
1994年 | 48篇 |
1993年 | 41篇 |
1992年 | 49篇 |
1991年 | 47篇 |
1990年 | 31篇 |
1989年 | 27篇 |
1988年 | 51篇 |
1987年 | 32篇 |
1986年 | 29篇 |
1985年 | 45篇 |
1984年 | 37篇 |
1983年 | 21篇 |
1982年 | 35篇 |
1981年 | 17篇 |
1980年 | 32篇 |
1979年 | 21篇 |
1978年 | 11篇 |
1977年 | 24篇 |
1976年 | 20篇 |
1975年 | 6篇 |
排序方式: 共有6279条查询结果,搜索用时 140 毫秒
101.
The constrained optimization problem with a quadratic cost functional and two quadratic equality constraints has been studied by Bar-on and Grasse, with positive-definite matrix in the objective. In this note, we shall relax the matrix in the objective to be positive semidefinite. A necessary and sufficient condition to characterize a local optimal solution to be global is established. Also, a perturbation scheme is proposed to solve this generalized problem. 相似文献
102.
103.
Iddo Eliazar 《Queueing Systems》2007,55(1):71-82
We explore M/G/∞ systems ‘fed’ by Poissonian inflows with infinite arrival rates. Three processes – corresponding to the system's state, workload, and queue-size – are studied and analyzed. Closed form formulae characterizing the system's stationary structure and correlation structure are derived. And, the issues of queue finiteness, workload summability, and Long Range Dependence are investigated.
We then turn to devise a ‘reverse engineering’ scheme for the design of the system's correlation structure. Namely: how to construct an M/G/∞ system with a pre-desired ‘target’ workload/queue auto-covariance function. The ‘reverse engineering’ scheme is applied
to various examples, including ones with infinite queues and non-summable workloads.
AMS Subject Classifications Primary: 60K25; Secondary: 60G55, 60G10 相似文献
104.
A self-consistent system of gravitational field with a binary mixture of perfect fluid and dark energy given by a cosmological
constant has been considered in Bianchi Type-V universe. The perfect fluid is chosen to be obeying either the equation of
state p=γρ with γ ε |0,1| or a van der Waals equation of state. The role of A-term in the evolution of the Bianchi Type-V universe has been
studied. 相似文献
105.
3族新的不含紧优与几乎紧优的有向双环网络无限族 总被引:2,自引:0,他引:2
给出了3族新的不含紧优与几乎紧优的有向双环网络. 相似文献
106.
本文讨论定义于Banach空间的多目标数学规划,得到一些ε-最优解和(弱)有效解的必要条件,充分条件和必要充分条件。 相似文献
107.
This paper describes a methodology for allocating resources in hospitals. The methodology uses two linear goal-programming models. One model sets case mix and volume for physicians, while holding service costs fixed; the other translates case mix decisions into a commensurate set of practice changes for physicians. The models allow decision makers to set case mix and case costs in such a way that the institution is able to break even, while preserving physician income and minimizing disturbance to practice. The models also permit investigation of trade-offs between case mix and physician practice parameters. Results are presented from a decision-making scenario facing the surgical division of Toronto's Mount Sinai Hospital after the announcement of a 3-year, 18% reduction in funding. 相似文献
108.
朱方生 《武汉大学学报(理学版)》1995,(3)
构造了线性二次型最优控制的并行算法,介绍了这个并行算法在武汉大学“WUDP91”并行分布式处理系统上试算的数值应用软件的框图.本软件适用于既定动态系统的平衡问题.对于经济系统,可通过政策控制变量来调节和改善其状态和响应.对于自治系统可找出最优控制使得消耗函数达到最小值.通过对一系列例子进行试算,结果证实,所构造的并行算法和相应的数值软件是有效的,其加速比约为7. 相似文献
109.
A. Meister 《Mathematical Methods of Statistics》2007,16(1):63-76
This paper addresses the statistical problem of density deconvolution under the condition that the density to be estimated
has compact support. We introduce a new estimation procedure, which establishes faster rates of convergence for smooth densities
as compared to the optimal rates for smooth densities with unbounded support. This framework also allows us to relax the usual
condition of known error density with non-vanishing Fourier transform, so that a nonparametric class of densities is valid;
therefore, even the shape of the noise density need not be assumed. These results can also be generalized for fast decaying
densities with unbounded support. We prove optimality of the rates in the underlying experiment and study the practical performance
of our estimator by numerical simulations.
相似文献
110.
航空公司在给定的运力和机队配置条件下,如何适应航线需求的不断变化而合理地分配运力,使航空公司的经营效益最大化是我国航空经营管理的一个重大课题.根据航班效益分析,在一定的经营时间,航行班次的条件下,建立一个航线贡献最大化的含有随机变量的动态规划模型.求解方法是先用M ON TE C ARLO方法计算机仿真把模型转化为非线性的整数规划.再用动态规划中资源分配算法求出模型的最优解,编排最优各航线规划. 相似文献