全文获取类型
收费全文 | 7420篇 |
免费 | 257篇 |
国内免费 | 129篇 |
专业分类
化学 | 174篇 |
晶体学 | 1篇 |
力学 | 257篇 |
综合类 | 76篇 |
数学 | 7067篇 |
物理学 | 231篇 |
出版年
2023年 | 30篇 |
2022年 | 90篇 |
2021年 | 101篇 |
2020年 | 82篇 |
2019年 | 91篇 |
2018年 | 101篇 |
2017年 | 133篇 |
2016年 | 122篇 |
2015年 | 105篇 |
2014年 | 313篇 |
2013年 | 331篇 |
2012年 | 409篇 |
2011年 | 298篇 |
2010年 | 314篇 |
2009年 | 448篇 |
2008年 | 466篇 |
2007年 | 506篇 |
2006年 | 319篇 |
2005年 | 297篇 |
2004年 | 229篇 |
2003年 | 222篇 |
2002年 | 225篇 |
2001年 | 202篇 |
2000年 | 217篇 |
1999年 | 173篇 |
1998年 | 147篇 |
1997年 | 140篇 |
1996年 | 174篇 |
1995年 | 163篇 |
1994年 | 114篇 |
1993年 | 125篇 |
1992年 | 124篇 |
1991年 | 116篇 |
1990年 | 94篇 |
1989年 | 64篇 |
1988年 | 84篇 |
1987年 | 53篇 |
1986年 | 79篇 |
1985年 | 108篇 |
1984年 | 75篇 |
1983年 | 21篇 |
1982年 | 46篇 |
1981年 | 37篇 |
1980年 | 33篇 |
1979年 | 26篇 |
1978年 | 47篇 |
1977年 | 46篇 |
1976年 | 26篇 |
1975年 | 12篇 |
1974年 | 12篇 |
排序方式: 共有7806条查询结果,搜索用时 15 毫秒
71.
关于E-凸函数及E-凸规划几个错误结论的修正 总被引:2,自引:0,他引:2
本文研究Youness在1999年建立的有关E凸函数和E规划的结论.利用E凸函数和E凸规划的基本性质和优化分析技术,获得了有关E凸函数E凸规划的几个错误结论的修正.. 相似文献
72.
Abdulaziz S. Alidi 《Applied Mathematical Modelling》1992,16(12):645-651
The improper handling and disposal of hazardous wastes cause threats to human health and the environment. One reason for the improper handling and disposal of these wastes is that not much consideration is usually given to the logistical aspects of hazardous waste systems. In this paper an integer goal programming model is developed that takes into consideration the multiple goals and needs of many groups involved in managing and planning hazardous waste systems. The model can easily be implemented and can be used to address many of the issues related to facility location, recycling, treatment, and disposal of hazardous wastes. 相似文献
73.
An interval-parameter fuzzy linear programming method (IFMOLP) is proposed in this study for multiple objective decision-making
under uncertainty. As a hybrid of interval-parameter and fuzzy methodologies, the IFMOLP incorporates interval-parameter linear
programming and fuzzy multiobjective programming approaches to form an integrated optimization system. The method inherits
advantages of interval-parameter programming, and allows uncertainties and decision-makers’ aspirations to be effectively
communicated into its programming processes and resulting solutions. Membership functions for both objectives and constraints
are formulated to reflect uncertainties in different system components and their interrelationships. An interactive solution
procedure has been developed based on solution approaches of the interval-parameter and fuzzy programming techniques, plus
necessary measures for handling the multiobjective feature. A didactic example is provided in the paper to illustrate the
detailed solution process. Possibilities of further improvements by seeking Pareto optimum and incorporating flexible preference
within constraints are also discussed. 相似文献
74.
针对重力输水管道设计中存在的问题,文章以管道造价最小为目标,应用动态规划,提出了一种新的重力输水管道优化设计方法,对输水管的当量管径、流量分配、连接管设置与可靠性校核计算等问题作了探讨。该方法可用于沿线有节点流量流出的并联输水管道优化设计,能明显节省投资,有良好的实用性 相似文献
75.
对一类遗传程序设计问题,提出了简单等长的分布式染色体,取代复杂变长的树结构染色体,使演化算子操作更方便,个体复杂度得到有效控制.用该染色体形式解决割草问题,分析了分布式染色体带来的一些性质,并给出了很好的计算结果. 相似文献
76.
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
77.
Smooth Solutions to Optimal Investment Models with Stochastic Volatilities and Portfolio Constraints
Pham 《Applied Mathematics and Optimization》2002,46(1):55-78
Abstract. This paper deals with an extension of Merton's optimal investment problem to a multidimensional model with stochastic volatility
and portfolio constraints. The classical dynamic programming approach leads to a characterization of the value function as
a viscosity solution of the highly nonlinear associated Bellman equation. A logarithmic transformation expresses the value
function in terms of the solution to a semilinear parabolic equation with quadratic growth on the derivative term. Using a
stochastic control representation and some approximations, we prove the existence of a smooth solution to this semilinear
equation. An optimal portfolio is shown to exist, and is expressed in terms of the classical solution to this semilinear equation.
This reduction is useful for studying numerical schemes for both the value function and the optimal portfolio. We illustrate
our results with several examples of stochastic volatility models popular in the financial literature. 相似文献
78.
We present a new linearized model for the zero-one quadratic programming problem, whose size is linear in terms of the number of variables in the original nonlinear problem. Our derivation yields three alternative reformulations, each varying in model size and tightness. We show that our models are at least as tight as the one recently proposed in [7], and examine the theoretical relationship of our models to a standard linearization of the zero-one quadratic programming problem. Finally, we demonstrate the efficacy of solving each of these models on a set of randomly generated test instances. 相似文献
79.
Converging Marriage in Honey-Bees Optimization and Application to Stochastic Dynamic Programming 总被引:1,自引:0,他引:1
Hyeong Soo Chang 《Journal of Global Optimization》2006,35(3):423-441
In this paper, we first refine a recently proposed metaheuristic called “Marriage in Honey-Bees Optimization” (MBO) for solving
combinatorial optimization problems with some modifications to formally show that MBO converges to the global optimum value.
We then adapt MBO into an algorithm called “Honey-Bees Policy Iteration” (HBPI) for solving infinite horizon-discounted cost
stochastic dynamic programming problems and show that HBPI also converges to the optimal value. 相似文献
80.
We examine a sequential selection problem in which a single option must be selected. Each option's value is a function of its attributes, whose precise values can be ascertained at a given cost. We prove the optimality of a threshold stopping rule for a general class of objective functions. 相似文献