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   4047篇
  免费   139篇
  国内免费   77篇
化学   542篇
力学   129篇
综合类   4篇
数学   1198篇
物理学   584篇
无线电   1806篇
  2024年   13篇
  2023年   87篇
  2022年   84篇
  2021年   73篇
  2020年   74篇
  2019年   86篇
  2018年   77篇
  2017年   108篇
  2016年   114篇
  2015年   106篇
  2014年   263篇
  2013年   273篇
  2012年   207篇
  2011年   265篇
  2010年   232篇
  2009年   254篇
  2008年   255篇
  2007年   271篇
  2006年   238篇
  2005年   164篇
  2004年   148篇
  2003年   126篇
  2002年   111篇
  2001年   75篇
  2000年   79篇
  1999年   75篇
  1998年   68篇
  1997年   60篇
  1996年   51篇
  1995年   28篇
  1994年   36篇
  1993年   22篇
  1992年   20篇
  1991年   17篇
  1990年   10篇
  1989年   12篇
  1988年   17篇
  1987年   3篇
  1986年   5篇
  1985年   8篇
  1984年   9篇
  1983年   3篇
  1982年   2篇
  1981年   7篇
  1980年   6篇
  1979年   6篇
  1978年   4篇
  1977年   6篇
  1976年   3篇
  1966年   1篇
排序方式: 共有4263条查询结果,搜索用时 15 毫秒
81.
基于RPR的高生存性网络   总被引:1,自引:0,他引:1  
刘开银  敖发良 《光通信研究》2006,32(4):10-12,23
弹性分组环(RPR)技术定义了一种新型的媒体接入控制(MAC)层协议,采用了共享介质传输和空间复用协议以及低于50 ms的故障恢复保护的弹性机制,支持服务等级协定(SLA,Service Level Agreement),即插即用,基于MAC的高速交换,可承载具有突发性的IP业务,同时支持传统的语音传送,是未来城域网技术的重要发展方向.光纤技术的飞速发展使得RPR不再仅仅局限于城域网,还可以用于广域网.文章在基于RPR的低于50 ms的故障恢复保护的基础上,提出了具有高生存性的解决方案.  相似文献   
82.
本文介绍了通过中间件访问数据库的方法,建立了通过中间件完成对数据库访问配置、实现数据库访问控制的系统。可以把需要共享的数据资源放在局域网上,网内用户可根据给定的权限,访问数据,实现资源共享。也可用本系统在因特网上实现通过宽带或电话线上网访问共享数据,使系统应用范围更广。  相似文献   
83.
We investigate in a simple bi-criteria experimental study, whether subjects are consistent with a linear value function while making binary choices. Many inconsistencies appeared in our experiment. However, the impact of inconsistencies on the linearity vs. non-linearity of the value function was minor. Moreover, a linear value function seems to predict choices for bi-criteria problems quite well. This ability to predict is independent of whether the value function is diagnosed linear or not. Inconsistencies in responses did not necessarily change the original diagnosis of the form of the value function. Our findings have implications for the design and development of decision support tools for Multiple Criteria Decision Making problems.  相似文献   
84.
We present an approach to interactive Multiple Criteria Decision Making based on preference driven Evolutionary Multiobjective Optimization with controllable accuracy.The approach relies on formulae for lower and upper bounds on coordinates of the outcome of an arbitrary efficient variant corresponding to preference information expressed by the Decision Maker. In contrast to earlier works on that subject, here lower and upper bounds can be calculated and their accuracy controlled entirely within evolutionary computation framework. This is made possible by exploration of not only the region of feasible variants - a standard within evolutionary optimization, but also the region of infeasible variants, the latter to our best knowledge being a novel approach within Evolutionary Multiobjective Optimization.To illustrate how this concept can be applied to interactive Multiple Criteria Decision Making, two algorithms employing evolutionary computations are proposed and their usefulness demonstrated by a numerical example.  相似文献   
85.
A dual hesitant fuzzy set (DHFS) consists of two parts, that is, the membership hesitancy function and the nonmembership hesitancy function, supporting a more exemplary and flexible access to assign values for each element in the domain, and can handle two kinds of hesitancy in this situation. It can be considered as a powerful tool to express uncertain information in the process of group decision making. Therefore, we propose a correlation coefficient between DHFSs as a new extension of existing correlation coefficients for hesitant fuzzy sets and intuitionistic fuzzy sets and apply it to multiple attribute decision making under dual hesitant fuzzy environments. Through the weighted correlation coefficient between each alternative and the ideal alternative, the ranking order of all alternatives can be determined and the best alternative can be easily identified as well. Finally, a practical example of investment alternatives is given to demonstrate the practicality and effectiveness of the developed approach.  相似文献   
86.
The purpose of this paper is to design a new extension of the ELECTRE, known as the elimination and choice translating reality method, for multi-criteria group decision-making problems based on intuitionistic fuzzy sets. This method is widely utilized when a set of alternatives should be identified and evaluated with respect to a set of conflicting criteria by reflecting decision makers’ (DMs’) preferences. However, handling the exact data and numerical measure is difficult to be precisely focused because the DMs’ judgments are often vague in real-life decision problems and applications. A more realistic and practical approach can be to use linguistic variables expressed in intuitionistic fuzzy numbers instead of numerical data to model DMs’ judgments and to describe the inputs in the ELECTRE method. The proposed intuitionsitic fuzzy ELECTRE utilizes the truth-membership function and non-truth-membership function to indicate the degrees of satisfiability and non-satisfiability of each alternative with respect to each criterion and the relative importance of each criterion, respectively. Then, a new discordance intuitionistic index is introduced, which is extended from the concept of the fuzzy distance measure. Outranking relations are defined by pairwise comparisons and a decision graph is depicted to determine which alternative is preferable, incomparable or indifferent in the intuitionistic fuzzy environment. Finally, a comprehensive sensitivity analysis is employed to further study regarding the impact of threshold values on the final evaluation, and a comparative analysis is demonstrated with an application example in flexible manufacturing systems between the proposed ELECTRE method and the existing intuitionistic fuzzy technique for order preference by similarity to ideal solution (IF-TOPSIS) method.  相似文献   
87.
This paper describes changes in students’ geometrical knowledge and their creativity associated with implementation of Multiple Solution Tasks (MSTs) in school geometry courses. Three hundred and three students from 14 geometry classes participated in the study, of whom 229 students from 11 classes learned in an experimental environment that employed MSTs while the rest learned without any special intervention in the course of one school year. This longitudinal study compares the development of knowledge and creativity between the experimental and control groups as reflected in students’ written tests. Geometry knowledge was measured by the correctness and connectedness of the solutions presented. The criteria for creativity were: fluency, flexibility, and originality. The findings show that students’ connectedness as well as their fluency and flexibility benefited from implementation of MSTs. The study supports the idea that originality is a more internal characteristic than fluency and flexibility, and therefore more related with creativity and less dynamic. Nevertheless, the MSTs approach provides greater opportunity for potentially creative students to present their creative products than conventional learning environment. Cluster analysis of the experimental group identified three clusters that correspond to three levels of student performance, according to the five measured criteria in pre- and post-tests, and showed that, with the exception of originality, performance in all three clusters generally improved on the various criteria.  相似文献   
88.
Most existing social learning models assume that there is only one underlying true state. In this work, we consider a social learning model with multiple true states, in which agents in different groups receive different signal sequences generated by their corresponding underlying true states. Each agent updates his belief by combining his rational self-adjustment based on the external signals he received and the influence of his neighbors according to their communication. We observe chaotic oscillation in the belief evolution, which implies that neither true state could be learnt correctly by calculating the largest Lyapunov exponents and Hurst exponents.  相似文献   
89.
《Microelectronics Reliability》2014,54(12):2951-2955
We present a method for predicting the failure rate and thus the reliability of an electronic system by summing the failure rate of each known failure mechanism. We use a competing acceleration factor methodology by combining the physics of failure for each mechanism with its own effect as observed by High/Low temperature and High/Low voltage stresses. Our Multiple High Temperature Overstress Life-test (M-HTOL) method assumes that the lifetime of each failure mechanism follows constant rate distribution whereby each mechanism is independently accelerated by its own stress factors. Stresses include temperature, frequency, current, and other factors that can be entered into a reliability model. The overall failure rate thus, also follows an exponential distribution and is described as the standard FIT (Failure unIT or Failure in Time). This method combines mathematical models for known failure mechanism and solves them simultaneously for a multiplicity of accelerated life test results to find a consistent set of weighting factors for each mechanism. The result of solving the system of equations is a more accurate and a unique combination for each system model by proportional summation of each of the contributing failure mechanisms.  相似文献   
90.
We consider two final-offer arbitration procedures in the case where there is more than one arbitrator. Two players, labeled 1 and 2 and interpreted here as Labor and Management, respectively, are in dispute about an increase in the wage rate. They submit final offers to a Referee. There are N arbitrators. Each of the arbitrators has her own assessment and selects the offer which is closest to her assessment. After that each arbitrator informs the Referee about her decision. The Referee counts the votes and declares the player obtaining the most votes to be the winner. Under the second arbitration scheme, the Referee takes into account only the assessments which lie between the players’ offers. The game is modeled as a zero-sum game. The Nash equilibrium in this arbitration game is derived.  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