首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   341篇
  免费   74篇
  国内免费   25篇
化学   70篇
晶体学   1篇
力学   3篇
综合类   35篇
数学   268篇
物理学   63篇
  2024年   1篇
  2023年   6篇
  2022年   20篇
  2021年   29篇
  2020年   27篇
  2019年   23篇
  2018年   19篇
  2017年   12篇
  2016年   19篇
  2015年   7篇
  2014年   24篇
  2013年   25篇
  2012年   17篇
  2011年   24篇
  2010年   15篇
  2009年   16篇
  2008年   24篇
  2007年   21篇
  2006年   20篇
  2005年   23篇
  2004年   12篇
  2003年   10篇
  2002年   9篇
  2001年   5篇
  2000年   2篇
  1999年   2篇
  1998年   7篇
  1997年   4篇
  1996年   2篇
  1994年   1篇
  1993年   1篇
  1991年   1篇
  1990年   1篇
  1987年   1篇
  1986年   2篇
  1985年   2篇
  1984年   2篇
  1982年   1篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
排序方式: 共有440条查询结果,搜索用时 29 毫秒
121.
This paper provides an approximating programming technique to solve the multi-product newsvendor model in which product demands are independent and stocking quantities are subject to two or more ex-ante linear contraints, such as budget or volume constraints. Previous research has attempted to solve this problem with Lagrange relaxation techniques or by limiting the distribution of demand. However, by taking advantage of the separable nature of the problem, a close approximation of the optimal solution can be found using convex separable programming for any demand distribution in the traditional newsvendor model and extensions. Sensitivity analysis of the linear program provides managerial insight into the effects of parameters of the problem on the optimal solution and future decisions.  相似文献   
122.
Model predictive control (MPC) has been used in process control systems with constraints, however, the constrained optimization problem involved in control systems has generally been solved in practice in a piece-meal fashion. To solve the problem systemically, in this paper, the Multi-Objective Fuzzy-Optimization (MOFO) is used in the constrained predictive control for online applications as a means of dealing with fuzzy goals and fuzzy constraints in control systems. The conventional model predictive control is integrated with the techniques from fuzzy multicriteria decision making, translating the goals and the constraints to predictive control in a transparent way. The information regarding the fuzzy goals and the fuzzy constraints of the control problem is combined by using a decision function from the fuzzy theory, so it is possible to aggregate the fuzzy goals and the fuzzy constraints using fuzzy operators, e.g. t-norms, s-norms or the convex sum. It is shown that the model predictive controller based on MOFO allows the designers a more flexible aggregation of the control objectives than the usual weighting sum of squared errors in MPC. The efficiency of the presented algorithm is validated by the visual robot path planning.  相似文献   
123.
Jian-Wei Wang 《中国物理 B》2021,30(12):128701-128701
Payoff-driven strategy updating rule has always been adopted as a classic mechanism, but up to now, there have been a great many of researches on considering other forms of strategy updating rules, among which pursuing high fitness is one of the most direct and conventional motivations in the decision-making using game theory. But there are few or no researches on fitness from the perspective of others' evaluation. In view of this, we propose a new model in which the evaluation effect with fitness-driven strategy updating rule is taken into consideration, and introduce an evaluation coefficient to present the degree of others' evaluation on individual's behavior. The cooperative individuals can get positive evaluation, otherwise defective individuals get negative evaluation, and the degree of evaluation is related to the number of neighbors who have the same strategy of individual. Through numerical simulation, we find that the evaluation effect of others can enhance the network reciprocity, thus promoting the cooperation. For a strong dilemma, the higher evaluation coefficient can greatly weaken the cooperation dilemma; for a weak one, the higher evaluation coefficient can make cooperator clusters spread faster, however, there is no significant difference in the level of cooperation in the final stable state among different evaluation coefficients. The cooperation becomes more flourish as the number of fitness-driven individuals increases, when all individuals adopt fitness-driven strategy updating rule, the cooperators can quickly occupy the whole population. Besides, we demonstrate the robustness of the results on the WS small-world network, ER random network, and BA scale-free network.  相似文献   
124.
Xian-Jia Wang 《中国物理 B》2022,31(8):80204-080204
Having a large number of timely donations during the early stages of a COVID-19 breakout would normally be considered rare. Donation is a special public goods game with zero yield for donors, and it has the characteristics of the prisoners' dilemma. This paper discusses why timely donations in the early stages of COVID-19 occurred. Based on the idea that donation is a strategy adopted by players during interconnection on account of their understanding of the environment, donation-related populations are placed on social networks and the inter-correlation structures in the population are described by scale-free networks. Players in donation-related populations are of four types: donors, illegal beneficiaries, legal beneficiaries, and inactive people. We model the evolutionary game of donation on a scale-free network. Donors, illegal beneficiaries and inactive people learn and update strategies under the Fermi update rule, whereas the conversion between legal beneficiaries and the other three types is determined by the environment surrounding the players. We study the evolution of cooperative action when the agglomeration coefficient, the parameters of the utility function, the noise intensity, the utility coefficient, the donation coefficient and the initial states of the population on the scale-free network change. For population sizes of 50, 100, 150, and 200, we give the utility functions and the agglomeration coefficients for promoting cooperation and study the corresponding steady states and structural characteristics of the population. We identify the best ranges of the noise intensity K, the donation coefficient α and the utility coefficient β for promoting cooperation at different population sizes. Furthermore, with the increase of the population size, the donor traps are found. At the same time, it is discovered that the initial states of the population have a great impact on the steady states; thus the upper and lower triangle phenomena are proposed. We also find that the population size itself is also an important factor for promoting donation, pointing out the direction of efforts to further promote donation and achieve better social homeostasis under the donation model.  相似文献   
125.
Message passing algorithms, whose iterative nature captures complicated interactions among interconnected variables in complex systems and extracts information from the fixed point of iterated messages, provide a powerful toolkit in tackling hard computational tasks in optimization, inference, and learning problems. In the context of constraint satisfaction problems (CSPs), when a control parameter (such as constraint density) is tuned, multiple threshold phenomena emerge, signaling fundamental structural transitions in their solution space. Finding solutions around these transition points is exceedingly challenging for algorithm design, where message passing algorithms suffer from a large message fluctuation far from convergence. Here we introduce a residual-based updating step into message passing algorithms, in which messages with large variation between consecutive steps are given high priority in the updating process. For the specific example of model RB (revised B), a typical prototype of random CSPs with growing domains, we show that our algorithm improves the convergence of message updating and increases the success probability in finding solutions around the satisfiability threshold with a low computational cost. Our approach to message passing algorithms should be of value for exploring their power in developing algorithms to find ground-state solutions and understand the detailed structure of solution space of hard optimization problems.  相似文献   
126.
多元统计分析在本科毕业论文指导满意度研究中的应用   总被引:1,自引:0,他引:1  
毕业论文指导水平是影响毕业论文水平的重要因素,本文根据实际满意度调查的数据,利用主成份分析方法,对毕业论文指导满意度的影响因素进行了实证分析,得出是影响毕业论文指导质量的主要因素,同时,根据实证研究结论,就提高毕业论文指导满意度提出了若干建议.  相似文献   
127.
A modern approach to logistics allows it to be understood and used for its capacity to generate value, because value is managerially important as a strategic objective for any firm. In the present work a particular view of this approach is offered by providing a structural model where logistics service quality and sacrifices contribute to the formation of logistics value, but where service quality is also an important determinant of satisfaction. This combined approach, tested with multiblock partial least‐sqaures path modelling, in the particular setting of a business‐to‐business encounter, provides empirical support for a chain of effects between service quality–logistics value–satisfaction–loyalty without underestimating the important effect of service quality on satisfaction and satisfaction on loyalty in industrial settings. This proposed conceptual model of the relationship between customer loyalty and the various contributing factors to that loyalty is the main contribution in this paper. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
128.
矿产资源开采行为容易造成矿区生态环境的恶化,国内外目前主要采取矿山环境恢复治理保证金制度以强制矿山企业对矿区开采后生态环境进行一系列修复。在缺少公众监督的情况下,保证金制度容易出现道德风险,即矿山企业和地方政府监管者的合谋行为。目前,我国各地推行的矿山环境恢复治理保证金制度均没有让公众参与进来,这就需要对这一制度缺陷进行弥补与修正。本文基于公众参与理论和博弈论构建了公众、矿山企业和政府监管者三方博弈模型,并利用对其混合纳什均衡解的分析,得出结论为:通过提高公众监督概率和公众监督有效概率、降低公众监督成本来防范和控制合谋行为。最后,根据以上分析提出了相关的政策建议。  相似文献   
129.
In 1 Matsumoto and Imai developed a new public key scheme, called C*, for enciphering or signing. (This scheme is completely different from and should not be mistaken with another scheme of Matsumoto and Imai developed in 1983 in 7 and broken in 1984 in 8). No attacks have been published as yet for this scheme. However, in this paper, we will see that—for almost all keys—almost every cleartext can be found from its ciphertext after only approximately m 2 n 4 log n computations, where m is the degree of the chosen field K and mn is the number of bits of text. Moreover, for absolutely all keys that give a practical size for the messages, it will be possible to find almost all cleartexts from the corresponding ciphertexts after a feasible computation. Thus the algorithm of 1 is insecure.  相似文献   
130.
研究基于满意选择的群体决策的一个基本数学理论问题. 给出并证明了群体在方案集上的任一群体满意偏好映射是多数满意偏好规则的充分必要条件.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号