全文获取类型
收费全文 | 5790篇 |
免费 | 1024篇 |
国内免费 | 1239篇 |
专业分类
航空 | 3569篇 |
航天技术 | 1566篇 |
综合类 | 1045篇 |
航天 | 1873篇 |
出版年
2024年 | 12篇 |
2023年 | 32篇 |
2022年 | 113篇 |
2021年 | 101篇 |
2020年 | 177篇 |
2019年 | 82篇 |
2018年 | 90篇 |
2017年 | 96篇 |
2016年 | 121篇 |
2015年 | 228篇 |
2014年 | 367篇 |
2013年 | 379篇 |
2012年 | 382篇 |
2011年 | 398篇 |
2010年 | 570篇 |
2009年 | 430篇 |
2008年 | 430篇 |
2007年 | 410篇 |
2006年 | 300篇 |
2005年 | 275篇 |
2004年 | 184篇 |
2003年 | 187篇 |
2002年 | 156篇 |
2001年 | 239篇 |
2000年 | 234篇 |
1999年 | 279篇 |
1998年 | 263篇 |
1997年 | 226篇 |
1996年 | 205篇 |
1995年 | 169篇 |
1994年 | 144篇 |
1993年 | 165篇 |
1992年 | 121篇 |
1991年 | 123篇 |
1990年 | 98篇 |
1989年 | 95篇 |
1988年 | 66篇 |
1987年 | 37篇 |
1986年 | 25篇 |
1985年 | 15篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1969年 | 1篇 |
1900年 | 1篇 |
排序方式: 共有8053条查询结果,搜索用时 31 毫秒
11.
何雪梅 《航空标准化与质量》2005,(2):27-29
介绍了中国西南电子设备研究所设计文件管理平台——图档管理系统的特点、组成和功能,阐述了图档管理系统对文件管理的作用和意义,说明基于产品结构对设计文件进行管理的必要性和可行性。 相似文献
12.
13.
用数值方法模拟双锥,圆柱,椭球、圆锥和倒圆锥五类等质量异形铝粒子五种高宽比共25种粒子对半无限铝靶的超高速撞击侵蚀,撞击速度为4km/s,给出了坑深、坑径、坑形参数和坑体积随粒子形状及高宽比的变化曲线。结果与非圆球异形粒子超高速撞击侵蚀计算有重要参考价值。 相似文献
14.
介绍一种高压快开阀装置。它可产生370MPa上升时间小于20μs的阶跃压力,用于对高压传感器进行动态校准。 相似文献
15.
本文利用弹性力学和断裂力学方法对纤维增强复合材料的横向拉伸强度进行了分析,其中考虑了90度开裂层厚度和开裂邻层的约束效应的影响,推导出正交各向异性对称铺层中昨合就位横向拉伸强度的数学表达式,得出开裂层的厚度和约束邻层铺设角对就位横向拉伸强度都有影响的结论,理论计算与Flaggs实验结果吻合较好。 相似文献
16.
Organizing space cooperation in the Asia-Pacific region 总被引:1,自引:0,他引:1
He Qizhi 《Space Policy》1993,9(3)
The time for regional cooperation in the Asia-Pacific region is now ripe. Steps have been taken towards this via a workshop sponsored by China - previously wary of cooperation but now seeming to acknowledge that, along with interested countries, it could contribute more to space in the region. The author examines areas of shared interest over which parties might collaborate and the best way to achieve this: a gradual approach emulating the development (but not the present configuration) of ESA is recommended. Finally, he examines the legal framework within which cooperation might function, using a liaison committee to formulate and coordiante proposals. Action must be taken now if the region is not to fall behind in the development of space technologies. 相似文献
17.
18.
The architecture of digital sheet metal manufacturing system is proposed based on the classification of sheet metal manufacturing information.The essence of digital manufacturing is the definition,management and transfer of information,and the key technologies are brought forward and described.It is pointed out that knowledge-based manufacturing elements design is necessary to make digital technology efficient.The management of all kinds of sheet metal manufacturing element information is to build single source of manufacturing data.Multi-state model-based digital transfer and coordination method is designed to provide a foundation for digital manufacturing of aircraft sheet metal part.The application of digital sheet metal manufacturing is exemplified with an aircraft sheet metal part.The application result is compared to that of the traditional analog transfer technology.It is shown that the developed technology can improve part quality,shorten manufacturing time and lower manufacturing cost. 相似文献
19.
This paper proposes a neural-network current-regulated switching strategy and an intelligent controller for a matrix converter permanent magnet synchronous motor (PMSM) drive system. By using this new switching strategy, the current harmonics of the system are effectively reduced. In addition, by using the intelligent controller, position control of the drive system can be achieved and an adjustable speed range from 1 r/min to 1500 r/min can be obtained. All the current-loop, speed-loop, and position-loop control algorithms are implemented by a 32-bit TMS320C40 digital signal processor. Several experimental results are shown to validate the theoretical analysis 相似文献
20.
Liu S. Singer C.H. Dougal R.A. 《IEEE transactions on aerospace and electronic systems》2006,42(2):612-624
Electric power anomalies or disturbances can disrupt the normal operation of equipment, accelerate aging, or even cause outright failures thus resulting in increased costs of maintenance and reduced system reliability. Past research on the effects caused by power anomalies has been mostly focused on industrial, commercial, or residential systems, or on power distribution equipment. A literature survey reveals that there is no comprehensive review related to low-voltage (LV) power systems and utilization equipment applicable to military combat vehicles, such as aircraft and ships. This paper summarizes the results of a new literature survey that focused on the causes, effects, and mitigation methods for power anomalies typical of LV mobile power systems. Electric power anomaly cost data collected from the literature are also presented, from which the costs of anomalies to the national defense are estimated using some simple rationales. 相似文献