全文获取类型
收费全文 | 654篇 |
免费 | 92篇 |
国内免费 | 152篇 |
专业分类
航空 | 515篇 |
航天技术 | 178篇 |
综合类 | 101篇 |
航天 | 104篇 |
出版年
2024年 | 4篇 |
2023年 | 6篇 |
2022年 | 13篇 |
2021年 | 24篇 |
2020年 | 37篇 |
2019年 | 36篇 |
2018年 | 36篇 |
2017年 | 56篇 |
2016年 | 37篇 |
2015年 | 49篇 |
2014年 | 55篇 |
2013年 | 50篇 |
2012年 | 73篇 |
2011年 | 77篇 |
2010年 | 39篇 |
2009年 | 66篇 |
2008年 | 36篇 |
2007年 | 43篇 |
2006年 | 28篇 |
2005年 | 20篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 11篇 |
2001年 | 21篇 |
2000年 | 13篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 3篇 |
排序方式: 共有898条查询结果,搜索用时 250 毫秒
721.
Xiaocan Li Brahmananda Dasgupta Gang Li 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
We investigate the acceleration of charged particles in a time-dependent chaotic magnetic field in this work. In earlier works, it has been demonstrated that in an asymmetric wire-loop current systems (WLCSs), the magnetic field is of chaotic in nature. Furthermore, observations also showed that there exist time-varying current loops and current filaments in solar corona. It is therefore natural to conceive that the magnetic field on the solar surface is chaotic and time-dependent. Here, we develop a numerical model to study the acceleration process of charged particles in a time-varying chaotic magnetic field that is generated by an ensemble of 8 WLCSs. We found that the motion of energetic particles in the system is of diffusive in nature and a power law spectrum can quickly develop. The mechanism examined here may serve as an efficient pre-acceleration mechanism that generates the so-called seed particles for diffusive shock acceleration at a coronal mass ejection (CME) driven shock in large solar energetic particle (SEP) events. 相似文献
722.
723.
以双基地雷达"四抗"能力分析为基础,提出了双/多基地雷达布站优化的原则并对这些原则进行了量化,建立了双/多基地雷达布站优化的数学模型.随后,对量子粒子群算法进行了改进,提出了自适应量子粒子群算法,并将其用于双/多基地雷达布站优化数学模型的求解,解决了双/多基地雷达雷达站的部署问题.最后,通过MATLAB对优化后的雷达站... 相似文献
724.
725.
726.
727.
YANG Xiaojuna XING Keyib FENG Xinglea aSchool of Information Engineering Chang'an University Xi'an China bThe National Key Laboratory for Manufacturing System Engineering Xi'an Jiaotong University Xi'an China 《中国航空学报》2011,24(2):171-180
An improved particle filtering(IPF) is presented to perform maneuvering target tracking in dense clutter.The proposed filter uses several efficient variance reduction methods to combat particle degeneracy,low mode prior probabilities and measure-ment-origin uncertainty.Within the framework of a hybrid state estimation,each particle samples a discrete mode from its poste-rior distribution and the continuous state variables are approximated by a multivariate Gaussian mixture that is updated by an unscented Ka... 相似文献
728.
为提高热电偶的测温精度,在对热电偶进行数学建模时,结合粒子群算法对PID神经网络进行优化,并设计了实际多路电偶数据采集电路对温度数据进行采集和验证。通过实验验证,粒子群算法的运用加快了PID神经网络的收敛速度、提高了系统稳定性,从而得到了更加精确的热电偶模型,提高了系统的测温精度。 相似文献
729.
730.
V. Florinski 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
This paper discusses the transport of energetic charged particles through a sectored magnetic field in distant regions of the inner heliosheath. As the plasma flow slows down on approach to the stagnation point on the heliopause, the distance between the folds of the current sheet decreases to the point where it becomes comparable to the cyclotron radius of a cosmic ray particle. Under these conditions a particle can effectively drift across the stack of magnetic sectors with a speed comparable with the particle’s velocity. For a random distribution of current sheet separation distances, a diffusive transport across the stack of sectors occurs instead. The proposed mechanism could have contributed to unusually high intensities of galactic cosmic rays measured by Voyager 1 in the heliosheath during 2009–2010. 相似文献