全文获取类型
收费全文 | 178篇 |
免费 | 28篇 |
国内免费 | 32篇 |
专业分类
航空 | 93篇 |
航天技术 | 92篇 |
综合类 | 20篇 |
航天 | 33篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 6篇 |
2020年 | 1篇 |
2019年 | 14篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 6篇 |
2014年 | 11篇 |
2013年 | 9篇 |
2012年 | 16篇 |
2011年 | 10篇 |
2010年 | 8篇 |
2009年 | 22篇 |
2008年 | 22篇 |
2007年 | 19篇 |
2006年 | 13篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有238条查询结果,搜索用时 187 毫秒
141.
The characteristics of the recurrent electron (38–53 keV) and ion (>0.5 MeV) enhancements observed by Ulysses from mid-1992 to April 1994 are presented. The magnitude of the ion flux increases reached a maximum at a latitude of 20°S and decreased afterwards by 23%/degree until early 1994. The magnitude of the electron increases showed a similar trend until May, 1993, after which time it became approximately constant, until it started to increase again in early 1994. The electron enhancements have lagged the protons by up to 5 days once Ulysses left the heliospheric current sheet (mid-1993). The electron spectral index tended to harden (a) during the decay of the event and (b) as the latitude increased, up to 50°S. The events have recurred on a 26.0 day period, but with significant phase shifts over the 25 rotations studied. The H/He ratio decreases across the maximum intensity. The mean minimum value for H/He was 3.5±0.3, lower than that measured in previous studies in the ecliptic plane. 相似文献
142.
143.
Research on Auto-detection for Remainder Particles of Aerospace Relay Based on Wavelet Analysis 总被引:2,自引:0,他引:2
GAO Hong-liang ZHANG Hui WANG Shu-juan 《中国航空学报》2007,20(1):75-80
Aerospace relay is one kind of electronic components which is used widely in national defense system and aerospace system. The existence of remainder particles induces the reliability declining, which has become a severe problem in the development of aerospace relay. Traditional particle impact noise detection (PIND) method for remainder detection is ineffective for small particles, due to its low precision and involvement of subjective factors. An auto-detection method for PIND output signals is proposed in this paper, which is based on direct wavelet de-noising (DWD), cross-correlation analysis (CCA) and homo-filtering (HF), the method enhances the affectiv-ity of PIND test about the small particles. In the end, some practical PIND output signals are analysed, and the validity of this new method is proved. 相似文献
144.
YANG Fen ZHANG Xue-jun TIAN Fang WU Xu GAN Fu-xing 《中国航空学报》2007,20(2):181-186
Antimony-doped tin hydroxide colloid precipitates have been synthesized by hydrolysis of SnCl4 and SbCl3 using: (1) an ion-exchange hydrolysis to remove chlorine ions, and (2) isoamyl acetate as an azeotropic solvent to obviate water. The obtained dried powder is of high dispersivity without any need for further grinding. The size and dispersivity of the final particles are investigated with the aid of TG-DTA, BET, XRD and TEM. After having calcined, the antimony-doped tin oxide nanopowder possesses a tetragonal rutile structure with high dispersivity, uniform particles and low hard agglomeration. 相似文献
145.
146.
为了获得高能合成煤油(GN-1煤油)物化性能随温度和压力的变化规律,掌握GN-1煤油与现役火箭煤油在应用特性方面的差异,采用理论计算和实验方法,对GN-1煤油在物化性能(密度、黏度、定压比热容、导热系数、表面张力)变化规律、安全特性(闪点、自燃温度、燃点、爆炸极限、毒性)、流动传热与结焦特性以及点火延迟特性进行了研究,并与火箭煤油进行了对比。通过实验研究得到了最高温度不超过200℃,最高压力不超过25MPa下GN-1煤油的密度、黏度、定压比热容、导热系数、表面张力实验数据,结合理论计算,获得了GN-1煤油在-40~350℃,0.1~60MPa内热物性变化规律,并与火箭煤油进行了对比。此外,研究结果还表明:GN-1煤油的闪点为40℃(低于火箭煤油闪点74℃),自燃温度为305℃(高于火箭煤油自燃温度225℃),燃点为47℃(低于火箭煤油燃点82℃),爆炸极限为0.44%~2.9%(40℃),GN-1煤油和火箭煤油急性经口毒性LD50>5000mg/kg。在入口压力10MPa,流速10m/s,内壁温480℃条件下,GN-1煤油的传热系数比火箭煤油提高14.4%。在采用GH3128高温合金管条件下,GN-1煤油出口油温220℃时试验段平均结焦速率是出口油温150℃时的4.43倍,GN-1煤油316L不锈钢管路中试验段平均结焦速率为GH3128高温合金管路中的22.3%。在970~1105K内,GN-1煤油的点火延迟时间为火箭煤油的55.6%~69.3%。 相似文献
147.
148.
Abdur Rauf Hailong Li Safi Ullah Lin Meng Bin Wang Maoyan Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(1):309-316
This paper is based on the observations of Polar Mesosphere Summer Echoes (PMSE) with the EISCAT VHF 224?MHz radar during the summer month 08–12 July 2013. The effect of high energy particle precipitation on PMSE intensity, particularly during their simultaneous occurrence for longer time interval (longer than or equal to 3-h) has been investigated. The correlation between the two phenomena has been computed using the Spearman rank and Pearson linear correlation coefficient. The variations in high energy particle precipitation reaching down to altitude of 91?km and PMSE intensity in the altitude range of 80–90?km are positively correlated. The electron density irregularity due to ionization caused by precipitating particles might be one of the possible reasons for this positive correlation. Moreover, some other background parameters i.e. K-indices (proxy of high energy particle precipitation) and electron fluxes during the simultaneous occurrence of the two phenomena also support one of the possible reasons given for explanation of the observed positive correlation. The X-rays and proton fluxes have no noticeable effect on PMSE echoes in this study. 相似文献
149.
Panagiota Petkaki Alexander L. MacKinnon 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Release of stored magnetic energy via particle acceleration is a characteristic feature of astrophysical plasmas. Magnetic reconnection is one of the mechanisms for releasing energy from magnetized plasmas. Collisionless magnetic reconnection could provide both the energy release mechanism and the particle accelerator in space plasmas. Here we studied particle acceleration when fluctuating (in-time) electric fields are superposed on an static X-type magnetic field in collisionless hot solar plasma. This system is chosen to mimic the reconnective dissipation of a linear MHD disturbance. Our results are compared to particle acceleration from constant electric field superposed on an X-type magnetic field. The constant electric field configuration represents the effects of steady state magnetic reconnection. Time evolution of ion and electron distributions are obtained by numerically integrating particle trajectories. The frequencies of the electric field represent a turbulent range of waves. Depending on the frequency and amplitude of the electric field, electrons and ions are accelerated to different degrees and have energy distributions of bimodal form consisting of a lower energy part and a high energy tail. For frequencies (ω in dimensioless units) in the range 0.5 ? ω ? 1.0 a substantial fraction (20%–30%) of the proton distribution is accelerated to gamma-ray producing energies. For frequencies in the range 1 ? ω ? 100.0 the bulk of the electron distribution is accelerated to hard X-ray producing energies. The acceleration mechanism is important for solar flares and solar noise storms but it could be applicable to all collisionless astrophysical plasmas. 相似文献
150.
K. J. Seidensticker D. Möhlmann I. Apathy W. Schmidt K. Thiel W. Arnold H.-H. Fischer M. Kretschmer D. Madlener A. Péter R. Trautner S. Schieke 《Space Science Reviews》2007,128(1-4):301-337
SESAME is an instrument complex built in international co-operation and carried by the Rosetta lander Philae intended to land
on comet 67P/Churyumov-Gerasimenko in 2014. The main goals of this instrument suite are to measure mechanical and electrical
properties of the cometary surface and the shallow subsurface as well as of the particles emitted from the cometary surface.
Most of the sensors are mounted within the six soles of the landing gear feet in order to provide good contact with or proximity
to the cometary surface. The measuring principles, instrument designs, technical layout, operational concepts and the results
from the first in-flight measurements are described. We conclude with comments on the consequences of the last minute change
of the target comet and how to improve and to preserve the knowledge during the long-duration Rosetta mission. 相似文献