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141.
We consider the classical problem of whether certain classes of lifetime distributions are preserved under the formation of coherent systems. Under the assumption of independent and identically distributed (i.i.d.) component lifetimes, we consider the NBUE (new better than used in expectation) and NWUE (new worse than used in expectation) classes. First, a necessary condition for a coherent system to preserve the NBUE class is given. Sufficient conditions are then obtained for systems satisfying this necessary condition. The sufficient conditions are satisfied for a collection of systems which includes all parallel systems, but the collection is shown to be strictly larger. We also prove that no coherent system preserves the NWUE class. As byproducts of our study, we obtain the following results for the case of i.i.d. component lifetimes: (a) the DFR (decreasing failure rate) class is preserved by no coherent systems other than series systems, and (b) the IMRL (increasing mean residual life) class is not preserved by any coherent systems. Generalizations to the case of dependent component lifetimes are briefly discussed. 相似文献
142.
David J. Galbreath 《Defence Studies》2019,19(1):49-61
This paper looks at the impact of military technology diffusion on military assistance operations (MAO), in the United States known as Security Force Assistance or SFA. The discussion looks conceptually at the role of technological change and how it interacts with martial cultures in military assistant operations. I argue that growing trends in science and technology suggest potential conflicts between culture and technology. Relying on a culture-technology model drawn from anthropology, the paper contends that new technologies will present increasing challenges for the emerging MAO landscape. The paper will illustrate that the techno-science gap will continue to grow as innovations such as robotics, sensors, and networks continue to develop. Finally, the paper will look at ways to overcome this conflict between culture and technology. 相似文献
143.
A double-ended queue with a Poisson arrival pattern is examined in a situation where the rates depend (in a restricted sense) on both the time and the state of the system. Under some circumstances, the rates can be controlled. This article studies the distribution of the difference in queue sizes for each member of a large class of control strategies and introduces the problem of determining the optimal times at which the control should be in effect in order to maximize certain objective functions. 相似文献
144.
Alan J. Kaplan 《海军后勤学研究》1976,23(4):687-695
We address a single product, continuous review model with stationary Poisson demand. Such a model has been effectively studied when mean demand is known. However, we are concerned with managing new items for which only a Bayesian prior distribution on the mean is available. As demand occurs, the prior is updated and our control parameters are revised. These include the reorder point (R) and reorder quantity (Q). Deemer, taking a clue from some earlier RAND work, suggested using a model appropriate for known mean, but using a Compound Poisson distribution for demand rather than Poisson to reflect uncertainty about the mean. Brown and Rogers also used this approach but within a periodic review context. In this paper we show how to compute optimum reorder points for a special problem closely related to the problem of real interest. In terms of the real problem, subject to a qualification to be discussed, the reorder points found are upper bounds for the optimum. At the same time, the reorder points found can never exceed those found by the Compound Poisson (Deemer) approach. And they can be smaller than those found when there is no uncertainty about the mean. As a check, the Compound Poisson and proposed approach are compared by simulation. 相似文献
145.
Bernard J. McCabe 《海军后勤学研究》1974,21(4):673-682
In any model for a sonar detection process, some assumption must be made about the nature of the acoustic fluctuation process. Two processes that are widely used in this role are the jump process and the Gauss-Markov process. These processes are similar in that they are both stationer) Markov processes and have autocovariance functions of the form s?2exp(—γt). For these reasons, it might be believed that one could use either of these processes and get comparable results if all one is interested in is computing cumulative detection probabilities or mean time to gain or lose contact. However, such is not the case in that vastly different results can be obtained in some applications. An application of this sort is presented. We also present necessary and sufficient conditions for a threshold to have the property that it is almost surely crossed by the jump process, or by the Gauss-Markov process. This affords another method of comparison. 相似文献
146.
The present paper extends the results of [7] to cases of multistation lower echelon. For this purpose an algorithm for the optimal allocation of the upper echelon stock among the lower echelon stations is developed. The policy of ordering for the upper echelon is an extension of the Bayes prediction policy developed in [7]. Explicit formulae are presented for the execution of this policy. Several simulation runs are presented and analyzed for the purpose of obtaining information on the behavior of the system, under the above control policy, over short and long periods. 相似文献
147.
Philip J. Boland 《海军后勤学研究》1982,29(4):541-546
A policy of periodic replacement with minimal repair at failure is considered for a complex system. Under such a policy the system is replaced at multiples of some period T while minimal repair is performed at any intervening system failures. The cost of a minimal repair to the system is assumed to be a nonde-creasing function of its age. A simple expression is derived for the expected minimal repair cost in an interval in terms of the cost function and the failure rate of the system. Necessary and sufficient conditions for the existence of an optimal replacement interval are exhibited in the case where the system life distribution is strictly increasing failure rate (IFR). 相似文献
148.
Despite the large number and variety of studies addressing the relationship between military spending and economic growth, a consensus regarding the exact nature of any relationship between the two has proven elusive. This study uses a panel co-integration approach to examine the relationship between military spending and economic growth in the five South Asian countries of India, Pakistan, Nepal, Sri Lanka and Bangladesh over the period of 1988–2007. It finds that a 1% increase in military spending increases real GDP by only 0.04%, suggesting that the substantial amount of public expenditure that is currently directed towards military purposes in these countries has a negligible impact upon economic growth. 相似文献
149.
Stephen J. Cimbala 《Defense & Security Analysis》2012,28(1):65-80
Minimum deterrence is a compromise, or halfway house, between nuclear abolition or nearly zero and assured destruction, the dominant paradigm for strategic nuclear arms control during and after the cold war. Minimum deterrence as applied to the current relationship between the United States and Russia would require downsizing the numbers of operationally deployed long-range nuclear weapons to 1000, or fewer, on each side. More drastic bilateral Russian–American reductions would require the cooperation of other nuclear weapons states in making proportional reductions in their own arsenals. In addition, US plans for European-based and global missile defenses cause considerable angst in Russia and threaten to derail the Obama “reset” in Russian–American relations, despite the uncertainties about current and plausible future performances of missile defense technologies. 相似文献
150.
Leo J. Blanken 《Defense & Security Analysis》2012,28(4):275-287
Three distinct, and seemingly irreconcilable, schools of thought are identified within the strategic studies literature. One which searches for “universal principles of war,” a second, “context-dependent,” approach that seeks to embed each instance of warfare within its concurrent social, political, technological milieu and, finally a “paradoxical logic” school, which equates strategy with the generation of uncertainty. The author offers some intuitive concepts from non-cooperative game theory to develop a “dominate-mix” approach to strategy choice. In doing so, he helps to reconcile these disparate approaches and provides a simple framework to assist researchers in framing military decisions as well as to assist planners in choosing among strategies. 相似文献