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   543篇
  免费   12篇
  2021年   13篇
  2019年   10篇
  2018年   8篇
  2017年   5篇
  2016年   10篇
  2014年   9篇
  2013年   81篇
  2012年   5篇
  2009年   11篇
  2007年   16篇
  2005年   4篇
  2004年   7篇
  2003年   9篇
  2002年   13篇
  2001年   7篇
  2000年   7篇
  1999年   5篇
  1998年   10篇
  1997年   11篇
  1996年   10篇
  1995年   9篇
  1994年   8篇
  1993年   12篇
  1992年   10篇
  1991年   14篇
  1990年   14篇
  1989年   21篇
  1988年   17篇
  1987年   13篇
  1986年   17篇
  1985年   7篇
  1984年   8篇
  1983年   6篇
  1982年   11篇
  1981年   10篇
  1980年   10篇
  1979年   11篇
  1978年   11篇
  1977年   10篇
  1976年   6篇
  1975年   6篇
  1974年   10篇
  1973年   9篇
  1972年   4篇
  1971年   8篇
  1970年   8篇
  1969年   8篇
  1968年   3篇
  1967年   6篇
  1948年   4篇
排序方式: 共有555条查询结果,搜索用时 15 毫秒
541.
542.
Almost all discussions of cyberwarfare, other cyber-attacks, and cyber-espionage have focused entirely on the Internet as the chief means of damage – the Internet as a ‘vector,’ using a term from the theory of infectious diseases. However there are a variety of means, some of which have already been used, that involve cyber-exploitation using vectors other than the Internet. Malware can be installed in the integrated circuits of computers and servers, but also in any devices attached to them – thumb drives, CDs, printers, scanners, and so on. One can also use various forms of electromagnetic radiation at a distance of meters or more to exfiltrate data or to infiltrate corrupt data. I call this large and diverse family of unwanted interference with the functioning of information processing systems other-than-Internet (OTI) attacks on information systems. Stuxnet, and probably the 2007 Israeli corruption of Syrian air defenses, were OTI attacks. Such OTI techniques are more difficult to develop than creating malware, requiring electronic manufacturing facilities or novel technologies, and are thus accessible only to larger corporations and technologically sophisticated countries. Particularly vulnerable would be countries (like the United States and Europe) whose information processing devices are mainly produced outside of the country. Once exploitations via the Internet become harder to perpetrate, OTI exploitations are certain to grow dramatically, eventually requiring equipment for critical uses to be expensively fabricated in (and transported using) secure facilities; expensive detection measures will have to be instituted. This will create challenges for policy, law, and ethics, as well as greatly increasing the cost of many electronic devices.  相似文献   
543.
Piracy in international waters is on the rise again, in particular off the coast of Somalia. While the dynamic game between pirates, ship-owners, insurance firms and the military seems to have reached some kind of equilibrium, piracy risks generating significant negative externalities to third parties (e.g. in terms of environmental hazards and terrorism), justifying attempts to contain it. We argue that these attempts may benefit from a look back – through the analytical lens of rational choice theory – to the most successful counterpiracy campaign ever undertaken, namely, the one led by the Roman general Gnaeus Pompeius Magnus (Pompey the Great) in 67 BC.  相似文献   
544.
545.
Reliability Economics is a field that can be defined as the collection of all problems in which there is tension between the performance of systems of interest and their cost. Given such a problem, the aim is to resolve the tension through an optimization process that identifies the system which maximizes some appropriate criterion function (e.g. expected lifetime per unit cost). In this paper, we focus on coherent systems of n independent and identically distributed (iid) components and mixtures thereof, and characterize both a system's performance and cost as functions of the system's signature vector (Samaniego, IEEE Trans Reliabil (1985) 69–72). For a given family of criterion functions, a variety of optimality results are obtained for systems of arbitrary order n. Approximations are developed and justified when the underlying component distribution is unknown. Assuming the availability of an auxiliary sample of N component failure times, the asymptotic theory of L‐estimators is adapted for the purpose of establishing the consistency and asymptotic normality of the proposed estimators of the expected ordered failure times of the n components of the systems under study. These results lead to the identification of ε‐optimal systems relative to the chosen criterion function. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007  相似文献   
546.
We formulate exact expressions for the expected values of selected estimators of the variance parameter (that is, the sum of covariances at all lags) of a steady‐state simulation output process. Given in terms of the autocovariance function of the process, these expressions are derived for variance estimators based on the simulation analysis methods of nonoverlapping batch means, overlapping batch means, and standardized time series. Comparing estimator performance in a first‐order autoregressive process and the M/M/1 queue‐waiting‐time process, we find that certain standardized time series estimators outperform their competitors as the sample size becomes large. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007  相似文献   
547.
We consider a pricing problem in directed, uncapacitated networks. Tariffs must be defined by an operator, the leader, for a subset of m arcs, the tariff arcs. Costs of all other arcs in the network are assumed to be given. There are n clients, the followers, and after the tariffs have been determined, the clients route their demands independent of each other on paths with minimal total cost. The problem is to find tariffs that maximize the operator's revenue. Motivated by applications in telecommunication networks, we consider a restricted version of this problem, assuming that each client utilizes at most one of the operator's tariff arcs. The problem is equivalent to pricing bridges that clients can use in order to cross a river. We prove that this problem is APX‐hard. Moreover, we analyze the effect of uniform pricing, proving that it yields both an m approximation and a (1 + lnD)‐approximation. Here, D is upper bounded by the total demand of all clients. In addition, we consider the problem under the additional restriction that the operator must not reject any of the clients. We prove that this problem does not admit approximation algorithms with any reasonable performance guarantee, unless P = NP, and we prove the existence of an n‐approximation algorithm. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007  相似文献   
548.
We study the optimal contracting problem between two firms collaborating on capacity investment with information asymmetry. Without a contract, system efficiency is lost due to the profit‐margin differentials among the firms, demand uncertainty, and information asymmetry. With information asymmetry, we demonstrate that the optimal capacity level is characterized by a newsvendor formula with an upward‐adjusted capacity investment cost, and no first‐best solution can be achieved. Our analysis shows that system efficiency can always be improved by the optimal contract and the improvement in system efficience is due to two factors. While the optimal contract may bring the system's capacity level closer to the first‐best capacity level, it prevents the higher‐margin firm from overinvesting and aligns the capacity‐investment decisions of the two firms. Our analysis of a special case demonstrates that, under some circumstances, both firms can benefit from the principal having better information about the agent's costs. © 2007 Wiley Periodicals, Inc. Naval Research Logistics 54:, 2007  相似文献   
549.
We consider a manufacturer (i.e., a capacitated supplier) that produces to stock and has two classes of customers. The primary customer places orders at regular intervals of time for a random quantity, while the secondary customers request a single item at random times. At a predetermined time the manufacturer receives advance demand information regarding the order size of the primary customer. If the manufacturer is not able to fill the primary customer's demand, there is a penalty. On the other hand, serving the secondary customers results in additional profit; however, the manufacturer can refuse to serve the secondary customers in order to reserve inventory for the primary customer. We characterize the manufacturer's optimal production and stock reservation policies that maximize the manufacturer's discounted profit and the average profit per unit time. We show that these policies are threshold‐type policies, and these thresholds are monotone with respect to the primary customer's order size. Using a numerical study we provide insights into how the value of information is affected by the relative demand size of the primary and secondary customers. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007  相似文献   
550.
Consider a set of product variants that are differentiated by some secondary attributes such as flavor, color, or size. The retailer's problem is to jointly determine the set of variants to include in her product line (“assortment”), together with their prices and inventory levels, so as to maximize her expected profit. We model the consumer choice process using a multinomial logit choice model and consider a newsvendor type inventory setting. We derive the structure of the optimal assortment for some important special cases, including the case of horizontally differentiated items, and propose a dominance relationship for the general case that simplifies the search for an optimal assortment. We also discuss structural properties of the optimal prices. Finally, motivated by our analytical results, we propose a heuristic solution procedure, which is shown to be quite effective through a numerical study. © 2007 Wiley Periodicals, Inc. Naval Research Logistics, 2007  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