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161.
We develop a heuristic procedure for partitioning graphs into clusters of nodes such that each cluster of nodes induces a connected subgraph with the objective of minimizing the differences within clusters as measured by the total differences between all pairs of nodes of a cluster. We apply our procedure to determine optimal delivery zones for community sections of a major newspaper while including a number of operational constraints. Our results demonstrate a 18–56% improvement in the total differences within the zones designed over the usual intuitive heuristics. Given the magnitude of the revenue generated by larger local newspapers through zoning, our method demonstrates how better zoning can significantly enhance the value of segmentation. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2005. 相似文献
162.
We study joint preventive maintenance (PM) and production policies for an unreliable production‐inventory system in which maintenance/repair times are non‐negligible and stochastic. A joint policy decides (a) whether or not to perform PM and (b) if PM is not performed, then how much to produce. We consider a discrete‐time system, formulating the problem as a Markov decision process (MDP) model. The focus of the work is on the structural properties of optimal joint policies, given the system state comprised of the system's age and the inventory level. Although our analysis indicates that the structure of optimal joint policies is very complex in general, we are able to characterize several properties regarding PM and production, including optimal production/maintenance actions under backlogging and high inventory levels, and conditions under which the PM portion of the joint policy has a control‐limit structure. In further special cases, such as when PM set‐up costs are negligible compared to PM times, we are able to establish some additional structural properties. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005. 相似文献
163.
We present a shifting bottleneck heuristic for minimizing the total weighted tardiness in a job shop. The method decomposes the job shop into a number of single‐machine subproblems that are solved one after another. Each machine is scheduled according to the solution of its corresponding subproblem. The order in which the single machine subproblems are solved has a significant impact on the quality of the overall solution and on the time required to obtain this solution. We therefore test a number of different orders for solving the subproblems. Computational results on 66 instances with ten jobs and ten machines show that our heuristic yields solutions that are close to optimal, and it clearly outperforms a well‐known dispatching rule enhanced with backtracking mechanisms. © 1999 John Wiley & Sons, Inc. Naval Research Logistics 46: 1–17, 1999 相似文献
164.
n independent jobs are to be scheduled nonpreemptively on a single machine so as to minimize some performance measure. Federgruen and Mosheiov [2] show that a large class of such scheduling problems can be optimized by solving either a single instance or a finite sequence of instances of the so-called SQC problem, in which all the jobs have a fixed or controllable common due date and the sum of general quasiconvex functions of the job completion times is to be minimized. In this note we point out that this is not always true. In particular, we show that the algorithm proposed in [2] does not always find a global optimal schedule to the problem of minimizing the weighted sum of the mean and variance of job completion times. © 1996 John Wiley & Sons, Inc. 相似文献
165.
Capacity expansion refers to the process of adding facilities or manpower to meet increasing demand. Typical capacity expansion decisions are characterized by uncertain demand forecasts and uncertainty in the eventual cost of expansion projects. This article models capacity expansion within the framework of piecewise deterministic Markov processes and investigates the problem of controlling investment in a succession of same type projects in order to meet increasing demand with minimum cost. In particular, we investigate the optimality of a class of investment strategies called cutoff strategies. These strategies have the property that there exists some undercapacity level M such that the strategy invests at the maximum available rate at all levels above M and does not invest at any level below M. Cutoff strategies are appealing because they are straightforward to implement. We determine conditions on the undercapacity penalty function that ensure the existence of optimal cutoff strategies when the cost of completing a project is exponentially distributed. A by-product of the proof is an algorithm for determining the optimal strategy and its cost. © 1995 John Wiley & Sons, Inc. 相似文献
166.
Consider a two machine flow shop and n jobs. The processing time of job j on machine i is equal to the random variable Xij One of the two machines is subject to breakdown and repair. The objective is to find the schedule that minimizes the expected makespan. Two results are shown. First, ifP(X2j ≧ X1j) = 1 for all j and the random variables X11, X12,…, X1n are likelihood ratio ordered, then the SEPT sequence minimizes the expected makespan when machine 2 is subject to an arbitrary breakdown process; if P(X1j≧X2j) = 1 and X21, X22,….,X2n are likelihood ratio ordered, then the LEPT sequence minimizes the expected makespan when machine 1 is subject to an arbitrary breakdown process. A generalization is presented for flow shops with m machines. Second, consider the case where X1j and X2j are i.i.d. exponentially distributed with rate λj. The SEPT sequence minimizes the expected makespan when machine 2 is subject to an arbitrary breakdown process and the LEPT sequence is optimal when machine 1 is subject to an arbitrary breakdown process. © 1995 John Wiley & Sons, Inc. 相似文献
167.
Michael Makara 《Defense & Security Analysis》2016,32(3):209-223
Why did some Arab militaries remain loyal to authoritarian rulers amid mass uprisings during the Arab Spring while others defected to the opposition? One popular explanation shows this variation with reference to the degree of military institutionalization: institutionalized militaries defected, while patrimonial militaries remained loyal. This article argues that the institutionalization hypothesis does not provide a complete account of the mechanisms through which the degree of military institutionalization leads to either defection or continued loyalty. This shortcoming stems from the fact that scholars have treated military institutionalization as a catch-all concept for three distinct variables: ethnic stacking of the military, patronage distribution, and organizational factionalization. Examining the interaction between these variables highlights the mechanisms through which military defection occurs, and therefore that disaggregating institutionalization into its component parts provides a more complete explanation of military behavior during the Arab Spring. 相似文献
168.
Michael Bastian 《海军后勤学研究》1992,39(5):651-668
This article considers the dynamic lot-size problem under discounting, allowing a speculative motive for holding inventory. A forward procedure is developed that determines the first lot-size decision in a rolling horizon environment by using forecast data of the minimum possible number of future periods. © 1992 John Wiley & Sons, Inc. 相似文献
169.
170.