全文获取类型
收费全文 | 678篇 |
免费 | 137篇 |
国内免费 | 57篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 16篇 |
2020年 | 29篇 |
2019年 | 19篇 |
2018年 | 14篇 |
2017年 | 30篇 |
2016年 | 37篇 |
2015年 | 23篇 |
2014年 | 63篇 |
2013年 | 59篇 |
2012年 | 37篇 |
2011年 | 41篇 |
2010年 | 43篇 |
2009年 | 54篇 |
2008年 | 50篇 |
2007年 | 34篇 |
2006年 | 45篇 |
2005年 | 36篇 |
2004年 | 41篇 |
2003年 | 25篇 |
2002年 | 15篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 18篇 |
1998年 | 18篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 15篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有872条查询结果,搜索用时 15 毫秒
251.
超精密单点金刚石飞刀切削技术是一种比较新颖的微槽类结构加工方式。在飞切过程中,切削力是切削过程中重要的物理量,对加工后的表面质量、刀具磨损等有着直接影响。提出了一种基于直角微切削理论的动态微槽类结构飞切的力学模型,基于微切削理论,得到了前、后刀面切削力的理论模型。根据飞切的几何运动特征,建立了飞切过程中剪切角的计算模型,并根据单圈飞切实验得到了飞切过程中剪切面的变化规律。为了验证模型的正确性,采用不同切削参数进行了多圈重叠飞切实验,对切削力进行了测量和分析。实验得到的切削力大小和变化规律与理论模型计算得到的基本一致,证明了该切削力模型的有效性。 相似文献
252.
测试序列优化设计是故障诊断中的重要组成部分,最优测试序列能提高故障诊断的效率,常见的故障诊断系统均基于二值属性,而多值属性系统的测试优化问题研究的较少。针对多值属性系统测试序列优化问题的特点,提出了一种改进蚁群算法,结合二值属性系统和多值属性系统的关系,设计了适应于多值属性优化的状态转移规则和信息素更新机制。针对在等测试费用和故障先验概率的情况下不能寻优的问题,制定了对应的优化标准,符合实际的测试需求。通过对比试验,证明了其能解决电子系统多值属性系统的序列优化问题,扩展了多值属性电子系统的测试优化策略。 相似文献
253.
254.
Malte Brosig 《African Security Review》2014,23(3):225-242
This article presents survey data on the African Peace and Security Architecture (APSA). It focuses explicitly on two aspects: the internal constitution and achievements of the APSA; and coordination and cooperation with external actors, such as Regional Economic Communities, the United Nations and the European Union. The survey, conducted between October 2011 and December 2012, targeted 198 security experts in international organisations, think tanks, academia and non-governmental organisations. It reveals the APSA's current stage of development, achievements and challenges. 相似文献
255.
This study revisits the causal linkages between military spending and economic growth in China and G7 countries (i.e. Canada, France, Germany, Italy, Japan, the UK, and the USA) by focusing country-specific analysis for the period 1988–2010. The panel causality analysis, which accounts for both cross-country dependency and heterogeneity across countries, is employed in this study. Our results find evidence of the neutrality hypothesis for Italy, France, and Germany, the military spending–growth detriment hypothesis for both Canada and the UK, and one-way Granger causality running from economic growth to military spending for China. Furthermore, we find a feedback between military spending and economic growth in both Japan and the USA. Thus, our results do not support that one size fits all. 相似文献
256.
针对某自行反坦克炮射击后,抽筒时出现药筒钢底座底缘与圆柱部断裂现象这一抽筒故障,分析计算该火炮正常抽筒所需的理论抽筒力和半自动开闩机构所能提供的实际抽筒力,由此定量分析该故障的主要原因,并提出火炮实弹射击预防抽筒故障的具体措施,对半自动开闩结构设计与改进、部队装备训练与射击具有一定指导和参考价值. 相似文献
257.
介绍步进应力加速寿命试验原理,通过对制导弹药自动导引头贮存状态和失效机理的分析,确定了加速寿命试验应力和应力水平.假设产品寿命服从威布尔分布,应用极大似然估计和Bayes的方法处理数据,建立制导弹药可靠储存寿命预测模型,并计算得到自动导引头在正常应力水平下的可靠储存寿命. 相似文献
258.
Majak D'Agoôt 《Defense & Security Analysis》2013,29(2):104-116
In a world virtually free of slavery and colonialism and one mainly driven by the sovereign state rationale, allusion to manifestations or the existence of some form of these phenomena within a state is often received with dumbfounding indifference or denial. However, a form of rule that had continued in South Sudan long after the departure of the British in 1956 was colonial both in its quintessence and flair in that it disenfranchised its citizens and denied them the most basic freedoms, services and development. Under this establishment, resistance against the coercive vision of the state was brutally suppressed for many decades. This state of affairs finally ended in July 2011. Nonetheless, there is a miscellany of unresolved post-colonial issues between the two countries that warrant attention. These include security and the demarcation of borders, the issue of ludicrous transit fees for South Sudan's oil exportation through Sudan, citizenship, external debt repayment, etc. These issues are part of traps inherited from the anti-colonial struggle, which have now supplanted the old ensemble of North–South conflict paroxysm. As a matter of urgency, the two countries will have to wrap up the incomplete process of negotiation on these substantive issues. The talks should be approached with a new mindset based on the new reality of two sovereign states. To the extent that it is widely established that South Sudan and Sudan must coexist peacefully in order to develop into viable entities, such mutual dependency must be based on equality and respect. 相似文献
259.
260.
Andrew Sanders 《Small Wars & Insurgencies》2013,24(3):465-492
The role of the British Army in Northern Ireland during Operation Banner (1969–2007) is an instructive case study of counterinsurgency operations as well as an important chapter in recent British military history. Given troops deployed to the province as aid to the civil power, it is particularly useful in discussions about the principle of minimum force. This article seeks to explore the issue of minimum force through the example of Operation Motorman, the Army's successful attempt to remove the barricades, which had established so-go areas for the security forces in Northern Ireland. 相似文献