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1.
时间依赖的网络中最小时间路径算法   总被引:39,自引:3,他引:36  
谭国真  高文 《计算机学报》2002,25(2):165-172
时间依赖的网络与传统网络模型相比更具有现实意义,具有广泛的应用领域,交通网络和通信网络可以抽象为时间依赖的网络模型,当模型中弧的工度是时间依赖的变量,最短路径问题的求解变得非常困难,早期的研究者通过具体的网络实例认识到传统最短路径算法在这种情况下是不正确的,因此给出限制性条件使得传统最短路径算法是有效的。该文从最短路径算法的理论基础入手,从理论上证明了传统最短路径算法,如Dijkstra算法和标号设置算法,在时间依赖的网络上不能有效地求解最短路径问题,并且,在没有任何限制性条件下,给出了时间依赖的网络模型,理论基础,求解最小时间路径的优化条件和SPTDN算法,从理论上证明了SPTDN算法的正确性,算法的实验结果是正确的,最后给出了时间依赖的网络应用实例。  相似文献
2.
Distributed shortest-path protocols for time-dependent networks   总被引:11,自引:0,他引:11  
 This paper addresses algorithms for networks whose behavior changes with time according to known functions. Because the computation depends on the same functions it attempts to compute, its execution must obey strict timing constraints. When distributed versions of such algorithms are considered, a key difficulty is how to transfer local timing functions among the participating nodes. To that end it is necessary to characterize the parameterization of the functions and accommodate this parameterization in the computation. In particular, we consider the shortest-path problem in networks in which the delay of the edges changes with time according to continuous functions. We present distributed protocols for finding the shortest and minimum delay path under various waiting constraints. We investigate and analyze protocols that exchange local time-delay functions only within limited intervals yet allow every node to calculate its representation in the shortest path in time for it to be used. Received: November 1992 / Accepted: December 1995  相似文献
3.
随机时间依赖网络的K期望最短路径   总被引:9,自引:0,他引:9  
首先给出了随机时间依赖网络模型,K期望是短路径问题的形式化描述,并针对公交网络推导出到达弧头结点的时刻所服从的概率密度函数,路径期望耗费的计算方法,然后,基于随机一致性假设和胡机优势的概念给出了K期望最短路径问题的理论基础和算法并证明了算法的正确性,最后,给出了公交网络的应用实例和实验结果。  相似文献
4.
时间依赖型车辆路径问题的一种改进蚁群算法   总被引:5,自引:1,他引:4       下载免费PDF全文
时间依赖型车辆路径规划问题(TDVRP), 是研究路段行程时间随出发时刻变化的路网环境下的车辆路径优化. 传统车辆路径问题(VRP)已被证明是NP-hard问题, 因此, 考虑交通状况时变特征的TDVRP问题求解更为困难. 本文设计了一种TDVRP问题的改进蚁群算法, 采用基于最小成本的最邻近法(NNC算法)生成蚁群算法的初始可行解, 通过局部搜索操作提高可行解的质量, 采用最大--最小蚂蚁系统信息素更新策略. 测试结果表明, 与最邻近算法和遗传算法相比, 改进蚁群算法具有更高的效率, 能够得到更优的结果; 对于大规模TDVRP问题, 改进蚁群算法也表现出良好的性能, 即使客户节点数量达到1000, 算法的优化时间依然在可接受的范围内.  相似文献
5.
时间依赖有向无环网最小时间路径算法   总被引:3,自引:0,他引:3       下载免费PDF全文
经典模型及算法可解决固定弧权条件下的最短路问题,然而实际应用中弧权往往是动态的,即弧权依赖时间变化。本文提出一种特殊最短路径算法,即在有向无环网络中最小时间路径算法的一种实现。该算法是一种改进的扩散法,克服了扩散法的一些显著缺点。文中证明了该理论的正确性,最后列举了一个传统算法不能解决的实例,证明了该算法的正确性。  相似文献
6.
This paper presents an innovative method to analyze and visualize time-dependent evolution of features. The analysis and visualization of time-dependent data are complicated because of the immense number of data involved. However, if the scientist's main interest is the evolution of certain features, it suffices to show the evolution of these features. The task of the visualization method is to extract the features from all frames, to determine the correspondences between features in successive frames, to detect significant events or stages in the evolution of the features, and, finally, to visualize the results. The method described here performs all these steps, and it is applied to a number of applications.  相似文献
7.
动态搜索算法求解时间依赖型旅行商问题研究   总被引:2,自引:0,他引:2  
时间依赖型旅行商问题(TDTSP)是旅行商问题(TSP)的延伸.在该问题中,任意两节点间的旅行时间(成本)不仅取决于节点间的距离,还依赖于一天中具体时段或节点在哈密顿圈中所处的具体位置.对基于节点所处哈密顿圈中具体位置的TDTSP问题建立相应的数学模型,并提出求解该问题的动态搜索算法.通过实验仿真,验证了动态搜索算法优于目前在邻域搜索领域求解该问题最有效的动态规划启发式算法.  相似文献
8.
Daily traffic congestion forms a major problem for businesses such as logistic service providers and distribution firms. It causes late arrivals at customers and additional costs for hiring the truck drivers. Such costs caused by traffic congestion can be reduced by taking into account and avoiding predictable traffic congestion within vehicle route plans. In the literature, various strategies are proposed to avoid traffic congestion, such as selecting alternative routes, changing the customer visit sequences, and changing the vehicle-customer assignments. We investigate the impact of these and other strategies in off-line vehicle routing on the performance of vehicle route plans in reality. For this purpose, we develop a set of vehicle routing problem instances on real road networks, and a speed model that reflects the key elements of peak hour traffic congestion. The instances are solved for different levels of congestion avoidance using a modified Dijkstra algorithm and a restricted dynamic programming heuristic. Computational experiments show that 99% of late arrivals at customers can be eliminated if traffic congestion is accounted for off-line. On top of that, about 87% of the extra duty time caused by traffic congestion can be eliminated by clever congestion avoidance strategies.  相似文献
9.
Facility location dynamics: An overview of classifications and applications   总被引:2,自引:0,他引:2  
In order to modify the current facility or develop a new facility, the dynamics of facility location problems (FLPs) ought to be taken into account so as to efficiently deal with changing parameters such as market demand, internal and external factors, and populations. Since FLPs have a strategic or long-term essence, the inherited uncertainty of future parameters must be incorporated in relevant models, so these models can be considered applicable and ready to implement. Furthermore, due to largely capital outlaid, location or relocation of facilities is basically considered as a long-term planning. Hence, regarding the way in which relevant criteria will change over time, decision makers not only are concerned about the operability and profitability of facilities for an extended period, but also seek to robust locations fitting well with variable demands. Concerning this fact, a trade-off should be set between benefits brought by facility location changes and costs incurred by possible modifications. This review reports on literature pointing out some aspects and characteristics of the dynamics of FLPs. In fact, this paper aims not only to review most variants of these problems, but also to provide a broad overview of their mathematical formulations as well as case studies that have been studied by the literature. Finally, based on classified research works and available gaps in the literature, some possible research trends will be pointed out.  相似文献
10.
This paper presents an Ant Colony System algorithm hybridized with insertion heuristics for the Time-Dependent Vehicle Routing Problem with Time Windows (TDVRPTW). In the TDVRPTW a fleet of vehicles must deliver goods to a set of customers, time window constraints of the customers must be respected and the fact that the travel time between two points depends on the time of departure has to be taken into account. The latter assumption is particularly important in an urban context where the traffic plays a significant role.  相似文献
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