全文获取类型
收费全文 | 450篇 |
免费 | 5篇 |
出版年
2021年 | 5篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2017年 | 10篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 55篇 |
2012年 | 22篇 |
2011年 | 26篇 |
2010年 | 21篇 |
2009年 | 14篇 |
2008年 | 27篇 |
2007年 | 13篇 |
2006年 | 15篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2002年 | 3篇 |
2001年 | 3篇 |
1999年 | 2篇 |
1998年 | 6篇 |
1997年 | 6篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 12篇 |
1988年 | 3篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 12篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1969年 | 9篇 |
1968年 | 7篇 |
1966年 | 3篇 |
排序方式: 共有455条查询结果,搜索用时 15 毫秒
191.
A dynamic version of the transportation (Hitchcock) problem occurs when there are demands at each of n sinks for T periods which can be fulfilled by shipments from m sources. A requirement in period t2 can be satisfied by a shipment in the same period (a linear shipping cost is incurred) or by a shipment in period t1 < t2 (in addition to the linear shipping cost a linear inventory cost is incurred for every period in which the commodity is stored). A well known method for solving this problem is to transform it into an equivalent single period transportation problem with mT sources and nT sinks. Our approach treats the model as a transshipment problem consisting of T, m source — n sink transportation problems linked together by inventory variables. Storage requirements are proportional to T2 for the single period equivalent transportation algorithm, proportional to T, for our algorithm without decomposition, and independent of T for our algorithm with decomposition. This storage saving feature enables much larger problems to be solved than were previously possible. Futhermore, we can easily incorporate upper bounds on inventories. This is not possible in the single period transportation equivalent. 相似文献
192.
利用振动原理,研究、设计、制造微型电磁振动给料机(筛).设计了激磁铁芯、半波可控硅整流及控制电路.在对振动机械的隔振分析及优化设计理论的基础上,设计了整部机器的结构图纸,并制造了一部样机,给出了振动利用的一个范例.所研究制造的微型电磁振动机集机电为一体,在焊接、制药等诸多行业中具有广泛的应用价值. 相似文献
193.
194.
In the absence, to date, of an exact method for solving the linear programming problem with fixed charges, two heuristic methods have been proposed and extensively investigated, computationally, for moderate sized problems. The results indicate that the heuristic methods produce optimal solutions in well over 90 percent of the several hundred problems investigated and very close to optimal (a few percent) in the remaining cases. Hence it should be of practical significance to practitioners in the field. 相似文献
195.
本文以实验结果为依据,首先分析了塑料弹体影响弹丸膛内运动的物理性能,然后结合旋转弹丸的膛内运动特征,经过模拟试验,采用数学拟合法,初步建立旋转稳定弹塑料弹体工程设计计算的数学模型(包括结构尺寸设计计算、强度计算和内弹道计算)。 相似文献
196.
A promising approach to failure modeling, in particular to developing failure-time distributions, is discussed. Under this approach, system state or wear and tear is modeled by an appropriately chosen random process—for example, a diffusion process—and the occurrences of fatal shocks are modeled by a Poisson process whose rate function is state dependent. The system is said to fail when either wear and tear accumulates beyond an acceptable or safe level or a fatal shock occurs. This approach has significant merit. First, it provides revealing new insights into most of the famous and frequently used lifetime distributions in reliability theory. Moreover, it suggests intuitively appealing ways for enhancing those standard models. Indeed, this approach provides a means of representing the underlying dynamics inherent in failure processes. Reasonable postulates for the dynamics of failure should lend credence to the prediction and estimation of reliability, maintainability, and availability. In other words, accuracy of representation could lead to better, more reliable prediction of failure. 相似文献
197.
Richard L. Russell 《战略研究杂志》2013,36(1):136-155
Some scholars counter-intuitively argue that the proliferation of nuclear weapons increases international security by substantially reducing the chances for inter-state armed conflict. This school of thought draws heavily on the history of the American-Soviet Cold War rivalry to inform its analysis. The security dilemmas in the contemporary Middle East and South Asia where numerous states have or want nuclear weapons, however, are profoundly different than the competition between the United States and the Soviet Union. States in the Middle East and South Asia today may see nuclear weapons as usable instruments of warfare in contrast to conventional wisdom in the West that views them as weapons of deterrence and last resort. As common sense would have it, American and Allied policy designed to stem the proliferation of nuclear weapons is prudent. American diplomatic intervention, moreover, in regional crises as a third party may be needed in the future in the Middle East and South Asia to lessen the risks of nuclear warfare. Nevertheless, American policy-makers are likely in the future to find themselves facing a nuclear-armed nation-state-or soon to be nuclear weapons-capable state-in a crisis and will have to grapple with the risks of pre-emptive or preventive military action. 相似文献
198.
Robert L. Feldman 《Small Wars & Insurgencies》2013,24(2):295-306
Though parts of Somalia appear mired in intractable conflict, both domestic and foreign trade continues. As a result amidst the conflict, corruption, and chaos Somalia's business community is a small force for peace and stability. Thus, efforts directed at enhancing the business community, possibly via the Transitional Federal Government or its successor, could play a small role in improving the situation in this strategically poised country with a very entrepreneurial population. However, such success is far from certain, and numerous other factors besides a strengthened business community would have to occur for Somalia even to begin the journey on the long road to recovery. 相似文献
199.
ABSTRACTThe present international standard allows non-nuclear weapon states (NNWS) to forego safeguards when nuclear material is used in a “non-proscribed military activity,” though no criteria have been established to determine when NNWS can remove naval nuclear material from safeguards. Though at present, only nuclear-armed states possess nuclear submarines, the global nuclear naval landscape may soon change with the advancement of Brazil's fledgling program and the possible precedent it would set for other NNWS. A framework is needed to shore up nuclear security and prevent nuclear material diversion from the nuclear naval sector. Proposed and existing nonproliferation frameworks, including a Fissile Material Cut-off Treaty and commitments through the nuclear security summits, are insufficient to close this loophole. A Naval Use Safeguards Agreement (NUSA), modeled after the Additional Protocol of the International Atomic Energy Agency, would provide a framework to remove the opacity surrounding nuclear material in the naval sector. Designed for NNWS and encouraged as confidence-building measures for nuclear weapon states, NUSA would explicitly outline those stages in the naval nuclear fuel cycle where safeguards are to be applied and in what context. This viewpoint also further provides direction for targeted research and development in technical naval nuclear safeguards solutions. 相似文献
200.