全文获取类型
收费全文 | 1106篇 |
免费 | 188篇 |
国内免费 | 34篇 |
专业分类
化学 | 100篇 |
力学 | 19篇 |
综合类 | 33篇 |
数学 | 992篇 |
物理学 | 184篇 |
出版年
2024年 | 3篇 |
2023年 | 14篇 |
2022年 | 42篇 |
2021年 | 45篇 |
2020年 | 44篇 |
2019年 | 39篇 |
2018年 | 39篇 |
2017年 | 49篇 |
2016年 | 57篇 |
2015年 | 44篇 |
2014年 | 72篇 |
2013年 | 95篇 |
2012年 | 73篇 |
2011年 | 81篇 |
2010年 | 67篇 |
2009年 | 54篇 |
2008年 | 55篇 |
2007年 | 75篇 |
2006年 | 64篇 |
2005年 | 47篇 |
2004年 | 31篇 |
2003年 | 32篇 |
2002年 | 35篇 |
2001年 | 29篇 |
2000年 | 25篇 |
1999年 | 23篇 |
1998年 | 21篇 |
1997年 | 9篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有1328条查询结果,搜索用时 984 毫秒
81.
从生态学视角来研究企业竞争的动态演化已成为一个研究热点,针对现有研究文献中只讨论二维系统的不足,以三个企业之间的竞争为例,构造了企业间竞争的三维模型,运用微分方程稳定性理论分析其稳定性,并由此揭示出企业间竞争的动力学机制.数值仿真结果表明,该三维模型能有效地模拟企业间竞争的动态演化规律. 相似文献
82.
介绍了福建省目前的分时电价政策.基于冷库实例,模拟计算了制冷装置增加夜间运行时间,采用不同蓄冷运行方案的运行费用.结果显示,理想条件下冷库的运行电费可节省47.3%以上,现场调研的某冷库运行电费可减少约31%.根据气象台的逐时气象数据统计,厦门市夜间湿球温度下降1.2~1.8℃.计算表明,制冷装置夜间运行的COP因此比... 相似文献
83.
84.
85.
The paper formulates an extension of the traveling purchaser problem where multiple types of commodities are sold at spatially distributed locations with stochastic prices (each following a known probability distribution). A purchaser’s goal is to find the optimal routing and purchasing strategies that minimize the expected total travel and purchasing costs needed to purchase one unit of each commodity. The purchaser reveals the actual commodity price at a seller upon arrival, and then either purchases the commodity at the offered price, or rejects the price and visits a next seller. In this paper, we propose an exact solution algorithm based on dynamic programming, an iterative approximate algorithm that yields bounds for the minimum total expected cost, and a greedy heuristic for fast solutions to large-scale applications. We analyze the characteristics of the problem and test the computational performance of the proposed algorithms. The numerical results show that the approximate and heuristic algorithms yield near-optimum strategies and very good estimates of the minimum total cost. 相似文献
86.
ZHANGSHUNMING 《高校应用数学学报(英文版)》1998,13(1):77-94
This paper analyzes the aritrage-tree security markets and the general equilibrium ex-istence problem for a stochastic economy with incomplete financial markets. Information structure is given by an event tree. This paper restricts attention to puraly financial securities. It isassume that trading takes place in the sequence of spot markets and futures markets for securi-ties payable in units of account. Unlimited short-selling in securities is allowed. Financial markets may be incomplete, some consumption streams may be impossible to obtain by any tradingstrategy. Securities may be individually precluded from trade at arbitrary states and dates. Thesecurity price process is arbitrage-free the dividend process if and only if there exists a stochaticstate price (present value) process : the present value of the security prices at every vertex isthe present value of their dividend and capital values over the set of immediate successors ; thecurrent value of each security at every vertex is the present value of its future dividend streamover all succeeding vertices. The existence of such an equilibrium is proved under the followingcondition: continuous, weakly convex, strictly monotone and complete preferences, strictlypositive endowmenta and dividends processes. 相似文献
87.
Two make-to-order firms, each modelled as a single-server queue, compete for a common stream of (potential) customers by setting their service capacities (rates) and service prices. Each customer maximizes her expected return by getting service from a firm or by balking. We completely characterize the Nash equilibrium of the competition. 相似文献
88.
This paper applies financial option valuation methods to new wireless network capacity investment decision timing. In particular, we consider the case of network capacity for cellular telephone service. Given a cluster of base stations (with a certain traffic capacity per base station), we determine when it is optimal to increase capacity for each of the base stations contained in the cluster. We express this in terms of the fraction of total cluster capacity in use, i.e. we calculate the optimal time to upgrade in terms of the ratio of observed usage to existing capacity. We study the optimal decision problem of adding new capacity in the presence of stochastic wireless demand for services. A four factor algorithm is developed, based on a real options formulation. Numerical examples are provided to illustrate various aspects of the model. 相似文献
89.
90.