全文获取类型
收费全文 | 1102篇 |
免费 | 122篇 |
国内免费 | 237篇 |
专业分类
航空 | 624篇 |
航天技术 | 433篇 |
综合类 | 106篇 |
航天 | 298篇 |
出版年
2024年 | 2篇 |
2023年 | 15篇 |
2022年 | 14篇 |
2021年 | 35篇 |
2020年 | 58篇 |
2019年 | 44篇 |
2018年 | 76篇 |
2017年 | 48篇 |
2016年 | 52篇 |
2015年 | 44篇 |
2014年 | 71篇 |
2013年 | 56篇 |
2012年 | 69篇 |
2011年 | 65篇 |
2010年 | 67篇 |
2009年 | 66篇 |
2008年 | 72篇 |
2007年 | 72篇 |
2006年 | 113篇 |
2005年 | 66篇 |
2004年 | 35篇 |
2003年 | 51篇 |
2002年 | 27篇 |
2001年 | 11篇 |
2000年 | 30篇 |
1999年 | 37篇 |
1998年 | 26篇 |
1997年 | 22篇 |
1996年 | 23篇 |
1995年 | 26篇 |
1994年 | 32篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
排序方式: 共有1461条查询结果,搜索用时 406 毫秒
11.
Y. Futaana S. Barabash A. Grigoriev D. Winningham R. Frahm M. Yamauchi R. Lundin 《Space Science Reviews》2006,126(1-4):315-332
As a part of the global plasma environment study of Mars and its response to the solar wind, we have analyzed a peculiar case
of the subsolar energetic neutral atom (ENA) jet observed on June 7, 2004 by the Neutral Particle Detector (NPD) on board
the Mars Express satellite. The “subsolar ENA jet” is generated by the interaction between the solar wind and the Martian
exosphere, and is one of the most intense sources of ENA flux observed in the vicinity of Mars. On June 7, 2004 (orbit 485
of Mars Express), the NPD observed a very intense subsolar ENA jet, which then abruptly decreased within ∼10 sec followed
by quasi-periodic (∼1 min) flux variations. Simultaneously, the plasma sensors detected a solar wind structure, which was
most likely an interplanetary shock surface. The abrupt decrease of the ENA flux and the quasi-periodic flux variations can
be understood in the framework of the global response of the Martian plasma obstacle to the interplanetary shock. The generation
region of the subsolar ENA jet was pushed towards the planet by the interplanetary shock; and therefore, Mars Express went
out of the ENA jet region. Associated global vibrations of the Martian plasma obstacle may have been the cause of the quasi-periodic
flux variations of the ENA flux at the spacecraft location. 相似文献
12.
D.R. Japaridze M.Sh. Gigolashvili V.J. Kukhianidze 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2007,40(12):1912-1916
The differential rotation of the patterns of the large-scale solar magnetic field during solar activity cycles 20 and 21 is investigated. Compact magnetic elements with the polarity of the general solar magnetic field have larger speed of rotation than the elements with the opposite polarity. The surface of the Sun was divided by 10°-zones. In all of them the average rotation rate of the magnetic elements with negative polarity is little higher than that of the magnetic elements with positive polarity, except for 50°-zone of the south hemisphere and at the 10° latitude of the north hemisphere.
The rates of differential rotation for large-scale magnetic elements with negative and positive polarities have similar behavior for both cycles of the solar activity.
The rotation rate varies at polarity reversal of the circumpolar magnetic fields. For the cycle No 20 in 1969–1970 the threefold reversal took place in the northern hemisphere and variations of rotation rate can be noticed for magnetic elements both with positive and negative polarity for each 10°-zone in the same hemisphere. 相似文献
13.
The Bastille-day event in 2000 produced energetic 3B/X5.6 flare with a halo CME, which had great geo-effects consequently.
This event has been studied extensively and it is considered that it follows the two-ribbon flare model. The flare/CME event
was triggered by an erupting filament and TRACE observations showed formation of giant arcade structures during the flare
process. Hard X-ray (HXR) two ribbons revealed for the first time in this flare event (Masuda et al., 2001). The reconstruction of 3-D coronal magnetic fields revealed a magnetic flux rope structure, for the first time, from
extrapolation of observed photospheric vector magnetogram data and the flux rope structure was co-spatial with portion of
the filament and a UV bright lane (Yan et al., 2001a, 2001b). Here we review some recent work related to the flux rope structure and the HXR two ribbons by comparing their
locations and the flux temporal profiles during the flare process so as to understand the energy release and particle accelerations.
It is proposed that the rope instability may have triggered the flare event, and reconnection may occur during this process.
The drifting pulsation structure in the decimetric frequency range is considered to manifest the rope ejection, or the initial
phase of the coronal mass ejection. The HXR two ribbons were distributed along the flux rope and the rope foot points coincide
with HXR sources. The energy dissipation from IPS observations occurred within about 100 R
⋅ is consistent with the estimate for the flux rope system.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
介绍一种简单有效的纠错编码方法 ,用于资源卫星高密度数字磁记录器 ,使误码率由 10 -6降低到 10 -11,同时介绍它的基本工作原理、实现方案及试验结果。 相似文献
15.
电励磁双凸极电机调速系统的原理与实现 总被引:8,自引:3,他引:8
介绍了新型电励磁双凸极电机的结构和原理,然后结合全桥变换器阐述了电励磁双凸极电机的控制方法,接着详细介绍了电励磁双凸极电机转速、电流双闭环控制调速系统的原理和实现方法,最后以一台500W12/8极电励磁双凸极电机调速系统为例进行了系统实验。实验结果表明,电励磁双凸极电机调速系统具有结构简单、控制方便和良好的动静态性能。 相似文献
16.
月食过程月表太阳辐照和温度变化模拟 总被引:1,自引:2,他引:1
月食对月球轨道探测器的温度有重要的影响,分析月食时月表的太阳辐照和温度,具有重要意义。文章给出了通用的月表温度模型和月食时月表太阳辐照模型,根据某次月食的天文参数,用太阳辐照模型可求出月表任一点在月食时的太阳直接辐照变化过程,代入温度模型可求出任一点的温度变化过程。此模型和方法可用于对任何一次月食的分析,并以2007年8月28日的月食为例,模拟了该次月食的表面太阳直接辐照和温度的变化过程。 相似文献
17.
18.
19.
为了在级间分离期间提供反推力,许多固体火箭发动机前端都装有一组斜切反喷管。由于反喷管的气动型面具有许多尖点,并且在超声速区有一个台阶,喷管内存在一系列激波,而且亚声速区和超声速区互相混杂。本文用时间相关法数值模拟了反喷管流场,控制议程用Mac Cormack显格式求数值解,边界参数采用物理边界条件和从双特征线方法推导来的有效的特征方法为计算,为于固壁边界点,在不同的区域采用不同的方法对计算方程组求 相似文献
20.
空间等离子体导致高电压太阳阵的电流收集 总被引:3,自引:0,他引:3
给出一种能方便计算空间等离子体引起高电压太阳阵(HVSA)电流收集的理论统计模式,通过对物理过程分析认为空间等离子体致HVSA的功率损耗对HVASA的设计是不应忽视的。 相似文献