全文获取类型
收费全文 | 1367篇 |
免费 | 360篇 |
国内免费 | 17篇 |
专业分类
化学 | 57篇 |
力学 | 60篇 |
综合类 | 125篇 |
数学 | 1016篇 |
物理学 | 486篇 |
出版年
2023年 | 11篇 |
2022年 | 36篇 |
2021年 | 57篇 |
2020年 | 48篇 |
2019年 | 35篇 |
2018年 | 36篇 |
2017年 | 65篇 |
2016年 | 89篇 |
2015年 | 34篇 |
2014年 | 96篇 |
2013年 | 122篇 |
2012年 | 101篇 |
2011年 | 103篇 |
2010年 | 94篇 |
2009年 | 109篇 |
2008年 | 83篇 |
2007年 | 96篇 |
2006年 | 73篇 |
2005年 | 71篇 |
2004年 | 55篇 |
2003年 | 50篇 |
2002年 | 59篇 |
2001年 | 33篇 |
2000年 | 27篇 |
1999年 | 23篇 |
1998年 | 22篇 |
1997年 | 20篇 |
1996年 | 6篇 |
1995年 | 12篇 |
1994年 | 15篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有1744条查询结果,搜索用时 15 毫秒
1.
In circuit-switched networks call streams are characterized by their mean and peakedness (two-moment method). The GI/M/C/0 system is used to model a single link, where the GI-stream is determined by fitting moments appropriately. For the moments of the overflow traffic of a GI/M/C/0 system there are efficient numerical algorithms available. However, for the moments of the freed carried traffic, defined as the moments of a virtual link of infinite capacity to which the process of calls accepted by the link (carried arrival process) is virtually directed and where the virtual calls get fresh exponential i.i.d. holding times, only complex numerical algorithms are available. This is the reason why the concept of the freed carried traffic is not used. The main result of this paper is a numerically stable and efficient algorithm for computing the moments of freed carried traffic, in particular an explicit formula for its peakedness. This result offers a unified handling of both overflow and carried traffics in networks. Furthermore, some refined characteristics for the overflow and freed carried streams are derived. 相似文献
2.
3.
We obtain upper bounds for the tail distribution of the first nonnegative sum of a random walk and for the moments of the overshoot over an arbitrary nonnegative level if the expectation of jumps is positive and close to zero. In addition, we find an estimate for the expectation of the first ladder epoch. 相似文献
4.
William J. Reed 《Natural Resource Modeling》1989,3(4):463-480
It is assumed that the probability of destruction of a biological asset by natural hazards can be reduced through investment in protection. Specifically a model, in which the hazard rate depends on both the age of the asset and the accumulated invested protection capital, is assumed. The protection capital depreciates through time and its effectiveness in reducing the hazard rate is subject to diminishing returns. It is shown how the investment schedule to maximize the expected net present value of the asset can be determined using the methods of deterministic optimal control, with the survival probability regarded as a state variable. The optimal investment pattern involves “bang-bang-singular” control. A numerical scheme for determining jointly the optimal investment policy and the optimal harvest (or replacement) age is outlined and a numerical example involving forest fire protection is given. 相似文献
5.
本文把数学和管理科学有机结合,为数学应用提出问题,得出新结果,推广了J.Michel
Harrison(1985)[1]第43页的命题27,并给出了在金融中的应用. 相似文献
6.
The paper deals with the riskiness analysis for a large portfolio of life annuities. By means of the limiting distribution of the present value of the portfolio, in the first part of the paper a model for evaluating the investment and the projection risks is presented. In the second part, with regard to the investment risk's effects, the insolvency risk is measured considering the cumulative probability distribution function of the discounted average cost per policy. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
8.
For vector quasivariational inequalities involving multifunctions in topological vector spaces, an existence result is obtained without a monotonicity assumption and with a convergence assumption weaker than semicontinuity. A new type of quasivariational inequality is proposed. Applications to quasicomplementarity problems and traffic network equilibria are considered. In particular, definitions of weak and strong Wardrop equilibria are introduced for the case of multivalued cost functions. 相似文献
9.
随机化交通灯的二维元胞自动机交通模型 总被引:8,自引:0,他引:8
元胞自动机交通模型以简单的规则反映交通系统中的多种因素,可以分析各种交通现象,且可在计算机上方便、高效地运作·Biham-Middleton-Levine模型(BML模型)实现了二维交通问题的元胞自动机模型的模拟研究·本文对BML模型作了改进,解除了该模型中关于交通灯同步变化的限制·在新模型中,每个路口的交通灯可以自由选定起始工作时间和变化节奏,于是可以更全面、准确地反映交通灯对交通系统性能的影响·本文还对新模型中出现的若干新效应作了解释· 相似文献
10.
In this paper, we present a unified treatment and analysis of a dynamic traffic network model with elastic demands formulated and studied as a projected dynamical system. We propose a travel route choice adjustment process that satisfies the projected dynamical system. Under certain conditions, stability and asymptotical stability of the equilibrium patterns are then derived. Finally, two discrete-time algorithms, the Euler method and the Heun method, are proposed for the computation of the solutions, and convergence results established. The convergence results depend crucially on stability analysis. The performance of the algorithms is then illustrated on several transportation networks. 相似文献