全文获取类型
收费全文 | 1711篇 |
免费 | 739篇 |
国内免费 | 170篇 |
出版年
2024年 | 14篇 |
2023年 | 19篇 |
2022年 | 30篇 |
2021年 | 32篇 |
2020年 | 40篇 |
2019年 | 41篇 |
2018年 | 41篇 |
2017年 | 102篇 |
2016年 | 139篇 |
2015年 | 116篇 |
2014年 | 160篇 |
2013年 | 139篇 |
2012年 | 156篇 |
2011年 | 142篇 |
2010年 | 126篇 |
2009年 | 152篇 |
2008年 | 113篇 |
2007年 | 136篇 |
2006年 | 140篇 |
2005年 | 112篇 |
2004年 | 114篇 |
2003年 | 68篇 |
2002年 | 73篇 |
2001年 | 73篇 |
2000年 | 49篇 |
1999年 | 50篇 |
1998年 | 40篇 |
1997年 | 35篇 |
1996年 | 34篇 |
1995年 | 18篇 |
1994年 | 29篇 |
1993年 | 18篇 |
1992年 | 22篇 |
1991年 | 15篇 |
1990年 | 19篇 |
1989年 | 10篇 |
1988年 | 3篇 |
排序方式: 共有2620条查询结果,搜索用时 15 毫秒
841.
842.
This paper provides a political economy analysis of the evolution of unmanned aerial vehicles (UAV), or ‘drones’ in the USA. Focus is placed on the interplay between the polity and private economic influences, and their impact on the trajectory of political, economic, and military outcomes. We identify the initial formation of the drone industry, trace how the initial relationships between the military and the private sector expanded over time, and discuss present relationships. Understanding the historical evolution of UAV technology, as well as the major players in the industry today, is important for ongoing policy debates regarding the use of drones both domestically and internationally. 相似文献
843.
为研究复杂电磁环境对某引信的影响,从双源连续波入手,运用双源连续波对工作状态某引信辐照的实验方法进行实验.实验结果表明,在以引信工作频率为中心的150MHz频率范围内对加电引信进行双源连续波辐照实验可使引信发火,辐照结束后引信工作正常,实验的重复性较好.两连续波频率间隔不同,可使引信发火的场强组合数值大小不相同,实验中当两连续波远离引信工作频率且频差10MHz以上时,发火场强组合近似呈线性.最后对双源连续波对引信的辐照效应机理作了分析,两连续波频率间隔不同,引信发火机理不同. 相似文献
844.
Kevin Siqueira 《Defence and Peace Economics》2013,24(6):405-413
Unlike most of the literature, this paper includes domestic political considerations in which two countries must decide defensive countermeasures against a common terrorist threat. A delegation problem arises as voters strategically choose a policymaker whose preferences differ from their own. As a consequence, countries limit the presumed oversupply of defensive countermeasures. Thus, the inclusion of domestic politics gives a new perspective on counterterrorism. The timing of elections is also shown to make a difference. 相似文献
845.
If international terrorism is on a rising trend, an important source of confirmation or refutation of this is time‐series data on terrorist activity. Using chiefly data collected by the RAND/MIPT consortium we show using basic statistical analysis that in the period 1968–2005 the yearly number of all international terrorist incidents shows no trend over time, but fluctuates year on year in a random manner. On the other hand some indicators do show a definite trend over time, principally the steady rise in the number of incidents that are death‐dealing in nature. A further conclusion is drawn, showing that the proportion of these incidents leading to deaths above a given level is virtually fixed. 相似文献
846.
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
847.
Automated responses are an inevitable aspect of cyberwarfare, but there has not been a systematic treatment of the conditions in which they are morally permissible. We argue that there are three substantial barriers to the moral permissibility of an automated response: the attribution, chain reaction, and projection bias problems. Moreover, these three challenges together provide a set of operational tests that can be used to assess the moral permissibility of a particular automated response in a specific situation. Defensive automated responses will almost always pass all three challenges, while offensive automated responses typically face a substantial positive burden in order to overcome the chain reaction and projection bias challenges. Perhaps the most interesting cases arise in the middle ground between cyber-offense and cyber-defense, such as automated cyber-exploitation responses. In those situations, much depends on the finer details of the response, the context, and the adversary. Importantly, however, the operationalizations of the three challenges provide a clear guide for decision-makers to assess the moral permissibility of automated responses that could potentially be implemented. 相似文献
848.
为提高音波法气体管道泄漏定位的精度,对影响该方法泄漏定位的主要因素以及定位算法进行了研究。通过假设计算,分析了绝热指数和压缩因子对定位精度的影响。结果表明,压力较大时绝热指数和压缩因子变化较大,在定位计算中不能忽略。在此基础上,考虑管内沿线气体的流速、温度和压力分布等因素,对音速公式、气体流速公式以及定位公式进行修正,从而得到可以较为精确求解泄漏位置的计算公式,并通过牛顿-科茨公式改进算法。研究结果对进一步完善音波法管道气体泄漏检测技术具有一定的设计和理论指导意义。 相似文献
849.
地球外部空间扰动引力并行计算 总被引:1,自引:0,他引:1
针对传统的司托克斯积分方法计算量大、模型复杂的缺点,通过将地球球面以适当的经纬度差进行划分及合理简化,实现了司托克斯积分法计算外部空间扰动引力的积分方程的离散化,建立了地球扰动引力的快速计算模型,并在快速计算模型的基础上采用并行计算技术,实现扰动引力的实时计算。仿真结果表明,提出的快速并行计算模型能较好地实现地球扰动引力的快速、高精度计算。 相似文献
850.
可能性决策能较好地应对军事领域常常出现的概率难以获得,或者强调“出奇制胜”而有意规避概率风险的情形,是解决知识不完备情况下敌对行动预测的有力手段。从可能性理论基本公理体系出发,结合动态规划方法,提出并证明可能性决策的最优化定理,给出多步条件下可能性决策的实现算法,结合危机条件下敌对行动预测的范例和仿真分析,与传统概率风险决策进行比较,体现可能性决策的优越性,为该方法的推广应用创造条件。 相似文献