全文获取类型
收费全文 | 322篇 |
免费 | 124篇 |
国内免费 | 18篇 |
出版年
2024年 | 1篇 |
2022年 | 3篇 |
2021年 | 14篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 17篇 |
2016年 | 24篇 |
2015年 | 11篇 |
2014年 | 23篇 |
2013年 | 33篇 |
2012年 | 21篇 |
2011年 | 24篇 |
2010年 | 15篇 |
2009年 | 28篇 |
2008年 | 31篇 |
2007年 | 26篇 |
2006年 | 19篇 |
2005年 | 26篇 |
2004年 | 15篇 |
2003年 | 18篇 |
2002年 | 15篇 |
2001年 | 11篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 11篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 17篇 |
1989年 | 2篇 |
排序方式: 共有464条查询结果,搜索用时 13 毫秒
101.
一种可实现TF/TA2的无人飞行器三维航迹规划方法 总被引:2,自引:1,他引:1
从规划空间的有效表达着手对无人飞行器三维航迹规划展开研究,基于地形和威胁提出的飞行器航迹规划方法将航迹规划分为学习阶段和查询阶段,环境信息和飞行器的大部分约束条件结合在路线图的构造过程中,航迹搜索在此路线图中进行并最终实现全部约束条件.试验结果显示,该方法可以实时获得实现TF/TA2的三维航迹. 相似文献
102.
为研究应用于全流量补燃循环发动机的不同气/气喷嘴得到的燃烧流场,通过求解NavierStokes方程组,对不同燃料与氧化剂速度比下的流动燃烧过程进行了数值计算,计算结果与实验结果吻合。仿真结果表明:增加速度比能使燃烧火焰面提前,燃烧效率变大。如果发动机的长度受到限制,可以适当增加速度比以实现高效燃烧。 相似文献
103.
104.
The drivers of HIV/AIDS in the South African Police Service (SAPS) and impact of the disease on this workforce are neglected areas of research. Existing evidence suggests that while the occupational risk for contracting HIV is low, there are factors associated with the profession that, if left unmanaged, place police officers at risk of contracting HIV. This study's two aims are to identify the potential pathways of HIV infection within policing services and determine the probable impact of HIV/AIDS on SAPS. Through a systematic literature review on HIV/AIDS within police services, and by analysing selected SAPS human resource data, the causal pathways and impact of HIV/AIDS on police services are explored. The study finds that police officers (particularly male officers) are likely to be highly susceptible to HIV infection as a result of risky sexual behaviours born out of occupational characteristics such as high levels of stress, difficult working conditions, living away from home and interactions with sex workers. The problem is exacerbated by the ‘macho’ culture that often prevails among police officers. HIV/AIDS interventions within SAPS must focus on sustained behaviour change. Further, HIV programmes must equip officers with the knowledge and awareness to avoid engaging in high-risk sexual practices that may compromise their health and the effectiveness of the policing service. 相似文献
105.
Sean Mirski 《战略研究杂志》2013,36(3):385-421
The mounting challenge posed by China's military modernization has highlighted the need for the United States to analyze its ability to execute a naval blockade. A blockade strategy is viable, but it would be limited to a narrow context: the United States would have to be engaged in a protracted conflict over vital interests, and it would need the support of key regional powers. The United States would also need to implement a mix between a close and distant blockade in order to avoid imperiling the conflict's strategic context. If enacted, a blockade could exact a ruinous cost on the Chinese economy and state. 相似文献
106.
Ordered flow shop models have appeared in the literature since the mid‐1970s and proportionate flow shop models have appeared since the early 1980s. We provide a detailed review of these models along with some analysis and potential topics for future research. © 2012 Wiley Periodicals, Inc. Naval Research Logistics, 2013 相似文献
107.
108.
Martin Rupiah 《African Security Review》2013,22(4):51-59
In May 2012, Zambia's Inspector-General of Police announced a crackdown on sex workers. This commentary discusses the rationale behind this proposed crackdown and the problems associated with such a policy response. 相似文献
109.
在传统的含储能单元分布式供电系统中,一般都需要多个单向直流变换器和双向直流变换器才能实现其功能。提出一种新的双输入多通道直流变换器,它的功能等效于一个单向直流变换器和一个双向直流变换器。分析了双输入多通道直流变换器的工作原理,给出了变换器的稳态关系式以及能量管理方法,并运用Saber软件进行仿真,验证了理论分析的正确性。该直流变换器除具有双输入Buck直流变换器的优点外,还能实现可再生能源向储电输入源充电。 相似文献
110.