全文获取类型
| 收费全文 | 610篇 |
| 免费 | 34篇 |
| 国内免费 | 4篇 |
专业分类
| 648篇 |
出版年
| 2025年 | 10篇 |
| 2024年 | 8篇 |
| 2023年 | 18篇 |
| 2022年 | 9篇 |
| 2021年 | 17篇 |
| 2020年 | 6篇 |
| 2019年 | 11篇 |
| 2018年 | 11篇 |
| 2017年 | 19篇 |
| 2016年 | 32篇 |
| 2015年 | 24篇 |
| 2014年 | 43篇 |
| 2013年 | 35篇 |
| 2012年 | 41篇 |
| 2011年 | 30篇 |
| 2010年 | 24篇 |
| 2009年 | 28篇 |
| 2008年 | 26篇 |
| 2007年 | 33篇 |
| 2006年 | 20篇 |
| 2005年 | 21篇 |
| 2004年 | 30篇 |
| 2003年 | 18篇 |
| 2002年 | 15篇 |
| 2001年 | 17篇 |
| 2000年 | 19篇 |
| 1999年 | 17篇 |
| 1998年 | 9篇 |
| 1997年 | 5篇 |
| 1996年 | 9篇 |
| 1995年 | 7篇 |
| 1994年 | 4篇 |
| 1993年 | 9篇 |
| 1992年 | 4篇 |
| 1991年 | 8篇 |
| 1990年 | 7篇 |
| 1989年 | 3篇 |
| 1988年 | 1篇 |
排序方式： 共有648条查询结果，搜索用时 15 毫秒
541.
542.
采用改进后的双方程湍流模型和SIMPLE计算方法,对切流式单入口油-水旋流器内部流场进行了模拟研究。结果表明:旋流器内部三维流场各向异性,即同一位置流体在不同方向的流动参数变化很大,流体质点在不同条件下的运动轨迹、速度、分离特性等方面都有较大差别;圆柱段与圆锥段的流场在柱锥结合面发生变化,旋流器的主要分离过程在圆锥段完成;单入口旋流器的流场中心与几何中心有偏差,对流场的稳定和分离会产生影响。该模拟结果与他人所做实验结果比较接近,说明该模型和算法是可靠的,为旋流器的实际应用提供了参考。 相似文献
543.
一般带容量限制的网络图中流出源点与流入汇点的流量相等,但在实际应用中,存在一类流量经过弧发生变化的网络,使得流出源点与流入汇点的流量不相等。针对此类问题,建立了增益网络最大流模型,并通过增设虚弧将增益网络转换成循环网络,利用循环网络中汇点流量瞬间平衡的优点简化了模型。最后,结合实例进行分析,编写程序对实例进行了计算,计算结果验证了该模型的有效性。 相似文献
544.
Jiayi Lin;Hrayer Aprahamian;George Golovko; 《海军后勤学研究》2024,71(1):87-108
We study the problem of designing optimal targeted mass screening of non-uniform populations. Mass screening is an essential tool that is widely utilized in a variety of settings, for example, preventing infertility through screening programs for sexually transmitted diseases, ensuring a safe blood supply for transfusion, and mitigating the transmission of infectious diseases. The objective of mass screening is to maximize the overall classification accuracy under limited budget. In this paper, we address this problem by proposing a proactive optimization-based framework that factors in population heterogeneity, limited budget, different testing schemes, the availability of multiple assays, and imperfect assays. By analyzing the resulting optimization problem, we take advantage of the structure of the problem as a multi-dimensional fractional knapsack problem and identify an efficient globally convergent threshold-style solution scheme that fully characterizes an optimal solution across the entire budget spectrum. Using real-world data, we conduct a geographic-based nationwide case study on targeted COVID-19 screening in the United States. Our results reveal that the identified screening strategies substantially outperform conventional practices by significantly lowering misclassifications while utilizing the same amount of budget. Moreover, our results provide valuable managerial insights with regard to the distribution of testing schemes, assays, and budget across different geographic regions. 相似文献
545.
To reduce the time-to-market of newly developed systems, manufacturers increasingly adopt strategies where systems are brought to market while system field reliability is still uncertain. These systems are typically sold under performance-based contracts, which incentivizes potential customers to invest in them despite reliability uncertainty. Such contracts make the manufacturer (partly) responsible for the availability of the system. Subsequently, when field reliability is lower than anticipated, the manufacturer may choose to redesign the system to avoid high contract penalties. Redesign is a costly effort which may substantially increase field reliability. Deciding when to redesign is challenging, especially because the initial failure rate estimate by the system's engineers is refined over time as failure data accrues. We propose a model that endogenizes the failure rate updating to analyze this tactical redesign decision. We study additive and multiplicative redesigns and show that the optimal policy has a control limit structure. We benchmark our optimal policy against a static counterpart numerically, and conclude that basing redesign decisions on the updated estimate of the failure rate can substantially reduce costs. 相似文献
546.
The allocation of redundancies in a system to optimize the reliability of system performance is an interesting problem in reliability engineering and system security. In this article, we focus on the optimal allocation of two exponentially distributed active (standby) redundancies in a two‐component series system using the tool of stochastic ordering. For the case of active redundancy, stochastic comparisons are carried out in terms of the likelihood ratio and reversed hazard rate orders. For the case of standby redundancy, a likelihood ratio ordering result is developed. The results established here generalize and strengthen corresponding results in the recent literature. In addition, several numerical examples are used to explicate the results. © 2013 Wiley Periodicals, Inc. Naval Research Logistics, 2013 相似文献
547.
Dan Kuwali 《African Security Review》2013,22(3):248-269
The Constitutive Act of the African Union (AU) provides for the right of the continental body to intervene in the face of war crimes, genocide and crimes against humanity. According to its formulation, Article 4(h) intervention entails military force, which is triggered when a target state fails to discharge its duty to protect its population from mass atrocities. Although Article 4(h) is an ambitious statutory commitment to intervene in a member state by the AU, the Libyan crisis in 2011 showed the ambivalence of the continental institution to act in a decisive and timely manner. The AU's failure to invoke Article 4(h) exposed the need for building the capacity and political will to intervene and to interpret Article 4(h). Therefore, the primary focus of this article is on how Article 4(h) should be interpreted. Flowing from the Pretoria Principles, which seek to provide clarity on the implementation of the AU's right of intervention, Article 4(h) should be viewed as a duty rather than a right to prevent or stop mass atrocities. The duty dimension of Article 4(h) derives from the international instruments that AU member states have ratified to prevent mass atrocities. Rather than being a paper tiger, Article 4(h) should be used in a proactive and timely manner as a military option available to the AU to persuade member states to prevent or halt atrocities. As a last resort, military force pursuant to Article 4(h) should aim at protecting the population at risk and pursuing the perpetrators in order to avoid contravening Article 2(4) of the Charter of the United Nations (UN). Although military intervention can save lives in the short term, it cannot necessarily address the underlying, structural causes of atrocities, such as ethnic rivalries, economic inequalities and scramble for natural resources, among others. Therefore, the prevention of mass atrocities should not be equated with, or be seen through the prism of, Article 4(h) intervention alone. The focus should instead be on the entire spectrum of preventive strategies at the disposal of the AU in the face of mass atrocities, including the African human rights system and the African Peer Review Mechanism. 相似文献
548.
Scheduling IT projects and assigning the project work to human resources are an important and common tasks in almost any IT service company. It is particularly complex because human resources usually have multiple skills. Up to now only little work has considered IT‐specific properties of the project structure and human resources. In this article, we present an optimization model that simultaneously schedules the activities of multiple IT projects with serial network structures and assigns the project work to multiskilled internal and external human resources with different efficiencies. The goal is to minimize costs. We introduce a metaheuristic that decomposes the problem into a binary scheduling problem and a continuous staffing problem where the latter is solved efficiently by exploiting its underlying network structure. For comparison, we solve the mixed–binary linear program with a state–of–the–art commercial solver. The impacts of problem parameters on computation time and solution gaps between the metaheuristic and the solver are assessed in an experimental study. Our results show that the metaheuristic provides very favorable results in considerable less time than the solver for midsize problems. For larger problems, it shows a similar performance while the solver fails to return feasible solutions. © 2012 Wiley Periodicals, Inc. Naval Research Logistics 59: 111–127, 2012 相似文献
549.
针对舰船特点和任务要求,提出了舰船航渡中的松弛时间问题。在对问题分析的基础上,给出了松弛时间的定义并对其进行了建模,讨论了航渡失败的判断准则,给出了松弛时间的上下限以及航渡中实际的松弛时间的计算方法,并采用仿真的方法进行了典型航渡过程的松弛时间和成功概率的计算。在大量计算的基础上,初步探讨了航渡成功概率与各类航渡参数之间的关系,并对舰船最优航渡策略问题进行了初步分析,最后对于优化目标、计算初值、结果的表达方式等提出了一个可行的解决方案。 相似文献
550.
基于任务的连续出动舰载机航空保障重调度研究 总被引：1，自引：0，他引：1
对舰载机和各种保障资源进行调度是提高舰载机航空保障效率、保证舰载机所承担作战任务顺利完成的有效手段。为了克服以往研究中没有考虑作战任务变更对舰载机航空保障调度的影响,使用重调度的理论与方法研究了基于任务的连续出动舰载机航空保障重调度问题,建立了连续出动舰载机航空保障重调度模型。采用免疫算法对模型进行求解,可以避免模型的解空间可能出现组合爆炸问题。最后通过一个实例表明该模型可以很好的应对由作战任务变更所引起的重调度问起,算法求解速度满足作战需求,从而验证了模型的准确性及算法的有效性。 相似文献