全文获取类型
收费全文 | 262篇 |
免费 | 45篇 |
国内免费 | 75篇 |
专业分类
航空 | 191篇 |
航天技术 | 88篇 |
综合类 | 19篇 |
航天 | 84篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 17篇 |
2019年 | 14篇 |
2018年 | 13篇 |
2017年 | 7篇 |
2016年 | 10篇 |
2015年 | 27篇 |
2014年 | 14篇 |
2013年 | 12篇 |
2012年 | 22篇 |
2011年 | 26篇 |
2010年 | 25篇 |
2009年 | 21篇 |
2008年 | 36篇 |
2007年 | 19篇 |
2006年 | 18篇 |
2005年 | 17篇 |
2004年 | 5篇 |
2003年 | 11篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
排序方式: 共有382条查询结果,搜索用时 16 毫秒
21.
J.S. Halekas D.A. BrainR.P. Lin J.G. LuhmannD.L. Mitchell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(9):1347-1352
We investigate accelerated electrons observed by Mars Global Surveyor (MGS), using data from the Electron Reflectometer (ER) instrument. We find three different types of accelerated electron events. Current sheet events occur over regions with weak or no crustal fields, have the highest electron energy fluxes, and are likely located on draped magnetotail fields. Extended events occur over regions with moderate crustal magnetic fields, and are most often observed on closed magnetic field lines. Localized events have the lowest energy fluxes, occur in strong magnetic cusp regions, and are the most likely kind of event to be found on open magnetic field lines. Some localized events have clear signatures of field-aligned currents; these events have much higher electron fluxes, and are preferentially observed on radially oriented open magnetic field lines. Electron acceleration events, especially localized events, are similar in many ways to events observed in the terrestrial auroral zone. However, physical processes related to those found in the terrestrial cusp and/or plasmasheet could also be responsible for accelerating electrons at Mars. 相似文献
22.
Pekka Janhunen Annika Olsson Christopher T. Russell Harri Laakso 《Space Science Reviews》2006,122(1-4):89-95
Auroral emission caused by electron precipitation (Hardy et al., 1987, J. Geophys. Res. 92, 12275–12294) is powered by magnetospheric driving processes. It is not yet fully understood how the energy transfer mechanisms
are responsible for the electron precipitation. It has been proposed (Hasegawa, 1976, J. Geophys. Res. 81, 5083–5090) that Alfvén waves coming from the magnetosphere play some role in powering the aurora (Wygant et al., 2000, J. Geophys. Res. 105, 18675–18692, Keiling et al., 2003, Science
299, 383–386). Alfvén-wave-induced electron acceleration is shown to be confined in a rather narrow radial distance range of
4–5 R
E
(Earth radii) and its importance, relative to other electron acceleration mechanisms, depends strongly on the magnetic disturbance
level so that it represents 10% of all electron precipitation power during quiet conditions and increased to 40% during disturbed
conditions. Our observations suggest that an electron Landau resonance mechanism operating in the “Alfvén resonosphere” is
responsible for the energy transfer. 相似文献
23.
针对只测向(B0)方法具有收敛速度慢、定位误差大等缺点,提出了一种利用角度及其变化率、离心加速度等信息进行单站无源测距定位的新方法。对该方法的单次测距误差进行了分析,经多次测量定位计算机仿真结果表明,该方法比只测角定位方法、角度及其变化率定位方法具有更高的定位精度和更快的收敛速度,并且具有更广的应用范围。 相似文献
24.
大气层内高超声速机动飞行器液体推进剂管理 总被引:1,自引:0,他引:1
为满足大气层内高超声速机动飞行器对液体推进剂管理提出的新要求,在分析常规和高超声速机动飞行特点的基础上,讨论了重力场中推进剂的连续输送和位移控制等特点,并分析了美国高超声速飞行器X-34的液体推进剂管理实例。研究结果认为,推进剂箱隔舱化是一种可行的管理模式,但仅适于一次启动的机动飞行。对多次启动的循环机动飞行中的推进剂管理,仍需继续进行研究。 相似文献
25.
Observations carried out from the coronagraphs on board space missions (LASCO/SOHO, Solar Maximum and Skylab) and ground-based facilities (HAO/Mauna Loa Observatory) show that coronal mass ejections
(CMEs) can be classified into two classes based on their kinematics evolution. These two classes of CMEs are so-called fast
and slow CMEs. The fast CME starts with a high initial speed that remains more or less constant; it is also called the constant-speed CME. On the other hand, the slow CME starts with a low initial speed, but shows a gradual acceleration; it is also called
the accelerated and slow CME. Low and Zhang [Astrophys. J. 564, L53–L56, 2002] suggested that these two classes of CMEs could be a result of a difference in the initial topology of the
magnetic fields associated with the underlying quiescent prominences. A normal prominence magnetic field topology will lead
to a fast CME, while an inverse quiescent prominence results in a slow CME, because of the nature of the magnetic reconnection
processes. In a recent study given by Wu et al. [Solar Phys. 225, 157–175, 2004], it was shown that an inverse quiescent prominence magnetic topology also could produce a fast CME. In this
study, we perform a numerical MHD simulation for CMEs occurring in both normal and inverse quiescent prominence magnetic topology.
This study demonstrates three major physical processes responsible for destabilization of these two types of prominence magnetic
field topologies that can launch CMEs. These three initiation processes are identical to those used by Wu et al. [Solar Phys. 225, 157–175, 2004]. The simulations show that both fast and slow CMEs can be initiated from these two different types of magnetic
topologies. However, the normal quiescent prominence magnetic topology does show the possibility for launching a reconnection island (or secondary O-line) that might be thought of as a “CME’’. 相似文献
26.
为减小运动部件加减速过程中对整个平台的冲击,在进行运动轨迹规划时,采用了S形曲线对定位系统的运动轨迹进行了平滑处理,有效地降低了运动部件对系统的冲击,有利于系统的减振。 相似文献
27.
Martin A. Lee 《Space Science Reviews》2007,130(1-4):221-229
Gradual solar energetic particle (SEP) events are evidently accelerated by coronal/interplanetary shocks driven by coronal
mass ejections. This talk addresses the different factors which determine the composition of the accelerated ions. The first
factor is the set of available seed populations including the solar wind core and suprathermal tail, remnant impulsive events
from preceding solar flares, and remnant gradual events. The second factor is the fractionation of the seed ions by the injection
process, that is, what fraction of the ions are extracted by the shock to participate in diffusive shock acceleration. Injection
is a controversial topic since it depends on the detailed electromagnetic structure of the shock transition and the transport
of ions in these structured fields, both of which are not well understood or determined theoretically. The third factor is
fractionation during the acceleration process, due to the dependence of ion transport in the turbulent electromagnetic fields
adjacent to the shock on the mass/charge ratio. Of crucial importance in the last two factors is the magnetic obliquity of
the shock. The form of the proton-excited hydromagnetic wave spectrum is also important. Finally, more subtle effects on ion
composition arise from the superposition of ion contributions over the time history of the shock along the observer’s magnetic
flux tube, and the sequence of flux tubes sampled by the observer. 相似文献
28.
H. J. Völk 《Space Science Reviews》2007,130(1-4):431-438
The dynamical and chemical effects of the Galactic Wind are discussed. This wind is primarily driven by the pressure gradient
of the Cosmic Rays. Assuming the latter to be accelerated in the Supernova Remnants of the disk which at the same time produce
the Hot Interstellar Medium, it is argued that the gas removed by the wind is enriched in the nucleosynthesis products of
Supernova explosions. Therefore the moderate mass loss through this wind should still be able to remove a substantial amount
of metals, opening the way for stars to produce more metals than observed in the disk, by e.g. assuming a Salpeter-type stellar
initial mass function beyond a few Solar masses. The wind also allows a global, physically appealing interpretation of Cosmic
Ray propagation and escape from the Galaxy. In addition the spiral structure of the disk induces periodic pressure waves in
the expanding wind that become a sawtooth shock wave train at large distances which can re-accelerate “knee” particles coming
from the disk sources. This new Galactic Cosmic Ray component can reach energies of a few×1018 eV and may contribute to the juncture between the particles of Galactic and extragalactic origin in the observed overall
Cosmic Ray spectrum. 相似文献
29.
30.
Space Science Reviews - We discuss afresh the problem of the auroral electron acceleration based on the controversy reports of Bryant, D. A. et al.: 1992, Phys. Rev. Lett. 68, 37, and Borovsky, J.:... 相似文献