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   593篇
  免费   15篇
  2021年   11篇
  2019年   21篇
  2018年   11篇
  2017年   11篇
  2016年   15篇
  2015年   13篇
  2014年   13篇
  2013年   139篇
  2009年   6篇
  2008年   8篇
  2007年   5篇
  2006年   5篇
  2005年   9篇
  2004年   9篇
  2003年   6篇
  2002年   6篇
  2000年   7篇
  1998年   10篇
  1997年   16篇
  1996年   10篇
  1995年   5篇
  1994年   10篇
  1993年   5篇
  1992年   8篇
  1991年   15篇
  1990年   6篇
  1989年   7篇
  1988年   12篇
  1987年   16篇
  1986年   11篇
  1985年   8篇
  1984年   6篇
  1983年   9篇
  1982年   8篇
  1981年   6篇
  1980年   7篇
  1979年   14篇
  1978年   7篇
  1977年   8篇
  1976年   8篇
  1975年   8篇
  1974年   7篇
  1973年   13篇
  1972年   9篇
  1971年   7篇
  1970年   10篇
  1969年   7篇
  1968年   5篇
  1967年   8篇
  1966年   5篇
排序方式: 共有608条查询结果,搜索用时 15 毫秒
471.
Given point-to-point demand forecasts of transmission facilities for services such as voice or data transmission in each period of a finite planning horizon, a decision has to be made as to which types of transmission facilities—together with the amounts of transmission circuits—are to be installed, if any, on each link of the telecommunications network, in each period of the planning horizon. The availability of alternative transmission systems with significantly different costs and circuit capacities necessitates the determination of a minimum (discounted) cost facility installation scheme. This combinatoric choice problem is complicated by the availability of switching equipments enabling the transmission of some of the traffic through intermediary points. This possibility of alternately routing the traffic or the facility requirements of certain point pairs further complicates the problem while creating the opportunity to benefit from economies of scale. We present here a heuristic method for finding a good solution for the general problem; namely, we consider multiple transmission systems and multiple alternate routes. Numerical examples are given and computational experience is reported.  相似文献   
472.
This article deals with the solution of convex quadratic programs by iteratively solving a master problem and a subproblem as proposed previously by Sacher. The approach has the advantage that the subproblems are linear programs so that advantage can be taken of existing schemes for solving large linear problems. At each step in solving the master problem, a closed-form solution can be specified so that the procedure is well suited for solving large quadratic programs and can take advantage of the constraint structure.  相似文献   
473.
Previous lot-sizing models incorporating learning effects focus exclusively on worker learning. We extend these models to include the presence of setup learning, which occurs when setup costs exhibit a learning curve effect as a function of the number of lots produced. The joint worker/setup learning problem can be solved to optimality by dynamic programming. Computational experience indicates, however, that solution times are sensitive to certain problem parameters, such as the planning horizon and/or the presence of a lower bound on worker learning. We define a two-phase EOQ-based heuristic for the problem when total transmission of worker learning occurs. Numerical results show that the heuristic consistently generates solutions well within 1% of optimality.  相似文献   
474.
A brief historical overview of the development of multiple criteria decision making (MCDM) in the USSR during the last fifteen years is presented. Soviet MCDM research is reviewed. Several applications of MCDM methodology in the USSR are described. Long-term trends in the research and application of MCDM in the Soviet Union are discussed.  相似文献   
475.
A model which allows the prediction of long-term average report rates against an array of radio emitters by a scanning sensor is presented. The model is based on Markov renewal theory.  相似文献   
476.
In this article we extend the work of Mehrez and Stulman [5] on the expected value of perfect information (EVPI) to the expected value of sample information (EVSI) for a class of economic problems dealing with the decision to reject or accept an investment project. It is shown that shifting the mean of the underlying a priori distribution of X, the project's monetary value from zero in either direction will decrease the associated EVSI of Y, the random sampled information. A theorem is then presented which gives an upper bound on the EVSI over all distributions of Y, as well as the structure of the posterior mean E[X|Y] for which this upper bound is achieved. Finally, the case where E[X|Y] is linear in Y is discussed and its performance compared with that of the optimal case.  相似文献   
477.
The structural changes inside the French innovation system have impacted the role of defense firms since the late 1980s. Major changes have affected the defense budget and public R&D funding system in particular. The aim of this article is to understand French defense firms’ repositioning within the National Innovation System (NIS) based on an analysis of their R&D behavior over a long period of time (1987–2010). We show that French defense firms remain major players in the NIS and faced up to these major changes by adapting the funding of their R&D and their research priorities and rolling out new innovation capabilities. Additionally, they developed new innovation models to take advantage of new collaborative partnerships developed for civil and military markets.  相似文献   
478.
Why does terrorist violence escalate from some ethnic groups but not others? According to theoretical insights, many groups endure conditions that should spur on terrorist campaigns, but in reality only some carry them out. In contrast to studies emphasising motivations, this article constructs a framework centred on opportunity structures that contributes to our understanding of the rise of terrorism waged along ethnic lines. It argues that beyond grievances or other motivations, terrorist campaigns develop from communities when moderate political leaders depart from their positions in nationalist movements, causing terrorists to fill the subsequent power vacuum, while little terrorism occurs when leaders do not relinquish the nationalist agenda. This argument is evaluated with evidence from the Tamil and Muslim cases in the context of the Sri Lankan Civil War. Tamil United Liberation Front leaders left the Tamil nationalist movement in the early 1980s, enabling the Liberation Tigers of Tamil Eelam’s rise to dominate the nationalist agenda for three decades, while the Sri Lanka Muslim Congress did not relinquish the Muslim cause, which in part precluded the normalisation of violence in the community.  相似文献   
479.
Canada is now at a crossroads unlike any other period in its history and needs to carefully consider which path to take. With the new Trudeau government comfortably ensconced since the defeat of the Harper government in the fall of 2015, a variety of competing interests have emerged in an attempt to turn Canadian policy back to a more nostalgic period of the 1970s that some see as preferable to the institutional lash-up that existed since the rolling out of the Canada First policy in the 2000s. That nostalgic period is, however, misunderstood both willfully for political purposes but also through a lack of historical context. Firmly rooting future actions in a blunt analysis of national interests is preferable to the alternative.  相似文献   
480.
The literature on how European states have adapted to the post-cold war security environment ffocuses invariably on different understandings of military transformation, a process which is seen as inherently different from other forms of organizational change. However, as this paper argues, new management practices, going back to the introduction of so-called New Public Management (NPM) reforms throughout Europe in the 1980s, have eventually penetrated also the last bastion of the old state – the defense sector. Taking a critical approach to the idea of military transformation and existing theories of military change, the paper demonstrates how other international developments have pushed towards what may be seen as a “normalization” of Europe’s defense sectors. This has important implications for how we approach and understand change in contemporary defense organizations.  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