全文获取类型
收费全文 | 435篇 |
免费 | 224篇 |
国内免费 | 56篇 |
出版年
2024年 | 6篇 |
2023年 | 9篇 |
2022年 | 12篇 |
2021年 | 10篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 11篇 |
2017年 | 39篇 |
2016年 | 48篇 |
2015年 | 27篇 |
2014年 | 52篇 |
2013年 | 33篇 |
2012年 | 51篇 |
2011年 | 46篇 |
2010年 | 30篇 |
2009年 | 45篇 |
2008年 | 27篇 |
2007年 | 27篇 |
2006年 | 51篇 |
2005年 | 29篇 |
2004年 | 21篇 |
2003年 | 14篇 |
2002年 | 14篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 5篇 |
排序方式: 共有715条查询结果,搜索用时 15 毫秒
351.
We consider a problem of optimal division of stock between a logistic depot and several geographically dispersed bases, in a two‐echelon supply chain. The objective is to minimize the total cost of inventory shipment, taking into account direct shipments between the depot and the bases, and lateral transshipments between bases. We prove the convexity of the objective function and suggest a procedure for identifying the optimal solution. Small‐dimensional cases, as well as a limit case in which the number of bases tends to infinity, are solved analytically for arbitrary distributions of demand. For a general case, an approximation is suggested. We show that, in many practical cases, partial pooling is the best strategy, and large proportions of the inventory should be kept at the bases rather than at the depot. The analytical and numerical examples show that complete pooling is obtained only as a limit case in which the transshipment cost tends to infinity. © 2017 Wiley Periodicals, Inc. Naval Research Logistics, 64: 3–18, 2017 相似文献
352.
Observational data are prevalent in many fields of research, and it is desirable to use this data to make causal inferences. Because this data is nonrandom, additional assumptions are needed in order to construct unbiased estimators for causal effects. The standard assumption is strong ignorability, though it is often impossible to achieve the level of covariate balance that it requires. As such, researchers often settle for lesser balance levels within their datasets. However, these balance levels are generally insufficient to guarantee an unbiased estimate of the treatment effect without further assumptions. This article presents several extensions to the strong ignorability assumption that address this issue. Under these additional assumptions, specific levels of covariate balance are both necessary and sufficient for the treatment effect estimate to be unbiased. There is a trade‐off, however: as balance decreases, stronger assumptions are required to guarantee estimator unbiasedness. These results unify parametric and nonparametric adjustment methods for causal inference and are actualized by the Balance Optimization Subset Selection framework, which identifies the best level of balance that can be achieved within a dataset. © 2017 Wiley Periodicals, Inc. Naval Research Logistics 64: 323–344, 2017 相似文献
353.
354.
355.
顶置武器站具有系统组成类型复杂、子系统间存在耦合作用的特点,导致多学科协同仿真的优化模型难以建立。通过Adams、Simulink分别建立了顶置武器站机械系统及控制系统模型,并在多学科优化设计平台Model Center中对该机电联合仿真模型进行系统集成;在此基础上,以顶置武器站稳定精度为目标函数,采用一阶差分模型对炮控系统比例系数及积分系数进行了灵敏度分析,并采用设计探索优化器对该参数进行了优化设计。仿真结果表明,所建立的顶置武器站稳定精度多学科协同优化模型设计周期短、计算效率高,为下一步进行顶置武器站多工况、多结构参数的优化设计提供技术支撑。 相似文献
356.
遗传算法及其在导弹火力分配上的应用 总被引:18,自引:3,他引:15
遗传算法是一种近年来新发展起来的优化算法,目前它已被广泛应用于解决许多实际问题,如函数优化、图像识别、机器学习、人工神经网络、人工生命、优化调度等许多领域。通过对一种遗传算法的研究,阐述其在导弹武器火力分配上的应用。首先设计和实现了一种遗传算法;然后描述了导弹火力分配优化问题,建立了其数学模型;最后运用遗传算法求解了该问题。 相似文献
357.
A mathematical model of portfolio optimization is usually represented as a bicriteria optimization problem where a reasonable tradeoff between expected rate of return and risk is sought. In a classical Markowitz model, the risk is measured by a variance, thus resulting in a quadratic programming model. As an alternative, the MAD model was developed by Konno and Yamazaki, where risk is measured by (mean) absolute deviation instead of a variance. The MAD model is computationally attractive, since it is easily transformed into a linear programming problem. An extension to the MAD model proposed in this paper allows us to measure risk using downside deviations, with the ability to penalize larger downside deviations. Hence, it provides for better modeling of risk averse preferences. The resulting m‐MAD model generates efficient solutions with respect to second degree stochastic dominance, while at the same time preserving the simplicity and linearity of the original MAD model. © 2001 John Wiley & Sons, Inc. Naval Research Logistics 48: 185–200, 2001 相似文献
358.
基于专家系统的消磁电流决策 总被引:2,自引:1,他引:1
分析了建立消磁电流决策的专家系统的可行性 ,从基本概念和实际应用等方面介绍了基于专家系统的消磁电流决策的状态描述、数据库的建立以及推理机的确立等 相似文献
359.
为解决单架无人机在城市环境中对辐射源目标的定位问题,提出了一种基于环境预测法的单无人机测向定位航迹优化算法。使用交互多模型-扩展卡尔曼滤波进行视距和非视距信号混合环境下的目标估计。结合估计的目标位置和城市地理信息模型,基于视线追踪法求解信号遮挡区域和多径信号干扰区域。在滚动时域控制算法框架下生成无人机预测轨迹,以最大化Fisher信息矩阵行列式为测向定位评价准则,考虑建筑物障碍以及其对信号的遮挡和反射效应对无人机测向定位航迹的影响,控制无人机选择最优航向飞行。仿真结果表明,该方法能够使无人机在存在障碍、信号遮挡和多径干扰的环境下实现对目标的高精度测向定位,为解决城市环境下的单架无人机测向定位问题提供了新思路。 相似文献
360.
模糊综合评判在指挥信息优势评估中的应用 总被引:3,自引:0,他引:3
如何准确地对军队作战行动中获得信息优势的潜在能力进行综合考查和分析具有重要意义,为更好地指导我军信息化建设,分析了现行指挥信息优势评估中的方法的不足.在现有评估方法基础上,基于模糊综合评判,提出了一种更优的隶属度函数来建立模糊评判矩阵中的元素值,并论证确定该隶属度函数的合理性,给出用该隶属度函数确定的模糊评判矩阵的一个实例.用提出的模糊综合评判方法来评估指挥信息优势评估指标体系,在一定程度上提高了对指挥信息优势评估的合理性. 相似文献