全文获取类型
收费全文 | 443篇 |
免费 | 63篇 |
国内免费 | 154篇 |
专业分类
航空 | 240篇 |
航天技术 | 160篇 |
综合类 | 24篇 |
航天 | 236篇 |
出版年
2024年 | 4篇 |
2023年 | 11篇 |
2022年 | 7篇 |
2021年 | 22篇 |
2020年 | 34篇 |
2019年 | 11篇 |
2018年 | 23篇 |
2017年 | 19篇 |
2016年 | 27篇 |
2015年 | 26篇 |
2014年 | 40篇 |
2013年 | 31篇 |
2012年 | 38篇 |
2011年 | 30篇 |
2010年 | 35篇 |
2009年 | 18篇 |
2008年 | 20篇 |
2007年 | 33篇 |
2006年 | 66篇 |
2005年 | 29篇 |
2004年 | 9篇 |
2003年 | 23篇 |
2002年 | 15篇 |
2001年 | 1篇 |
2000年 | 7篇 |
1999年 | 25篇 |
1998年 | 14篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 13篇 |
1994年 | 10篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有660条查询结果,搜索用时 15 毫秒
191.
In this paper, a method of using a root hinge drive assembly (RHDA) to control the solar array deployment is provided and a multi-DOF mechanism dynamic model of the system is established. In this way, the root hinge torque can be calculated iteratively. Then taking the predicted torque as a reference, a RHDA is designed for a large multiple-stage packaging and deployable solar array system. The control effect of the drive assembly is validated by ground tests. The test results indicate that the solar arrays can be deployed smoothly, and the deployment velocities are restricted by the drive assembly as expected. During the tests, the RHDA output speed and output torque are obtained. In order to examine the impact force when the yoke is lock-up with a hard stop, dynamics simulations are performed according to the actual behavior. The simulation result indicates that the designed RHDA reduces the impact force significantly and improves the lock-up reliability effectively. 相似文献
192.
热层大气密度直接影响低轨道航天器的精密定轨,热层大气密度模型的误差是影响载人航天定轨精度的关键因素。选取400km为载人航天轨道的代表高度,利用CHAMP卫星数据修正热层大气密度模型,进而反演得到2002年的热层大气密度,统计其中长期变化特征,并分析大气密度与太阳活动和地磁活动的关系,得出热层大气密度与两种指数的总体变化趋势一致的结论,且地磁活动与大气密度的相关性更好。同时将大气密度的反演值与神舟三号飞船的实测密度值进行对比,结果显示二者有较好的一致性,其平均残差和均方根误差分别为0.03和0.24,并且地磁平静期的误差明显小于磁暴期。结果表明,利用星载加速度计数据反演载人航天轨道大气密度是一种有效的方法。 相似文献
193.
激光与金属材料相互作用的热效应是激光束辐照材料后发生的主要物理现象之一.激光加热使材料温度急剧上升,很快达到材料的熔点.通过使用商业CFD软件FLUENT数值模拟激光辐照金属材料的相互作用,并在一定的假设和边界条件下得到金属材料未熔化之前温度场沿径向和轴向分布情况、气流最高温度的变化和位置的转移、氧化反应和对流换热对热效应的影响. 相似文献
194.
A. Kontogeorgos P. Tsitsipis X. Moussas G. Preka-Papadema A. Hillaris C. Caroubalos C. Alissandrakis J.-L. Bougeret G. Dumas 《Space Science Reviews》2006,122(1-4):169-179
Fine structure of type IV radio solar bursts with a great variety and complexity often give much information in different
ways and enable estimation of various coronal characteristics. In this work, we expose our new method for fine structure revealing
and separation of two basic kinds of type IV fine structure, as fibers and pulsations. We also estimate frequency drift of
fibers from dynamic spectra, clean from continuous background, with a prototype method using 2-D Fourier transform and we
estimate periodicities of fibers as well as pulsations with continuous wavelet transform. Working with the last method we
found periodicities close to 3 min umbral oscillations and 5 min global solar oscillations. 相似文献
195.
Ester Antonucci 《Space Science Reviews》2006,124(1-4):35-50
The dynamics of the solar corona as observed during solar minimum with the Ultraviolet Coronagraph Spectrometer, UVCS, on
SOHO is discussed. The large quiescent coronal streamers existing during this phase of the solar cycle are very likely composed
by sub-streamers, formed by closed loops and separated by open field lines that are channelling a slow plasma that flows close
to the heliospheric current sheet. The polar coronal holes, with magnetic topology significantly varying from their core to
their edges, emit fast wind in their central region and slow wind close to the streamer boundary. The transition from fast
to slow wind then appears to be gradual in the corona, in contrast with the sharp transition between the two wind regimes
observed in the heliosphere. It is suggested that speed, abundance and kinetic energy of the wind are modulated by the topology
of the coronal magnetic field. Energy deposition occurs both in the slow and fast wind but its effect on the kinetic temperature
and expansion rate is different for the slow and fast wind. 相似文献
196.
R. F. Wimmer-Schweingruber N. U. Crooker A. Balogh V. Bothmer R. J. Forsyth P. Gazis J. T. Gosling T. Horbury A. Kilchenmann I. G. Richardson J. D. Richardson P. Riley L. Rodriguez R. von Steiger P. Wurz T. H. Zurbuchen 《Space Science Reviews》2006,123(1-3):177-216
While interplanetary coronal mass ejections (ICMEs) are understood to be the heliospheric counterparts of CMEs, with signatures
undeniably linked to the CME process, the variability of these signatures and questions about mapping to observed CME features
raise issues that remain on the cutting edge of ICME research. These issues are discussed in the context of traditional understanding,
and recent results using innovative analysis techniques are reviewed. 相似文献
197.
S. A. Stern D. C. Slater J. Scherrer J. Stone M. Versteeg M. F. A’hearn J. L. Bertaux P. D. Feldman M. C. Festou Joel Wm. Parker O. H. W. Siegmund 《Space Science Reviews》2007,128(1-4):507-527
We describe the design, performance and scientific objectives of the NASA-funded ALICE instrument aboard the ESA Rosetta asteroid flyby/comet rendezvous mission. ALICE is a lightweight, low-power, and low-cost imaging spectrograph optimized for cometary far-ultraviolet (FUV) spectroscopy. It will be the first UV spectrograph to study a comet at close range. It is designed to obtain spatially-resolved spectra of Rosetta mission targets in the 700–2050 Å spectral band with a spectral resolution between 8 Å and 12 Å for extended sources that fill its ~0.05^ × 6.0^ field-of-view. ALICE employs an off-axis telescope feeding a 0.15-m normal incidence Rowland circle spectrograph with a toroidal concave holographic reflection grating. The microchannel plate detector utilizes dual solar-blind opaque photocathodes (KBr and CsI) and employs a two-dimensional delay-line readout array. The instrument is controlled by an internal microprocessor. During the prime Rosetta mission, ALICE will characterize comet 67P/Churyumov-Gerasimenko's coma, its nucleus, and nucleus/coma coupling; during cruise to the comet, ALICE will make observations of the mission's two asteroid flyby targets and of Mars, its moons, and of Earth's moon. ALICE has already successfully completed the in-flight commissioning phase and is operating well in flight. It has been characterized in flight with stellar flux calibrations, observations of the Moon during the first Earth fly-by, and observations of comet C/2002 T7 (LINEAR) in 2004 and comet 9P/Tempel 1 during the 2005 Deep Impact comet-collision observing campaign. 相似文献
198.
C. Giammanco P. Bochsler R. Karrer F. M. Ipavich J. A. Paquette P. Wurz 《Space Science Reviews》2007,130(1-4):329-333
Solar chemical abundances are determined by comparing solar photospheric spectra with synthetic ones obtained for different
sets of abundances and physical conditions. Although such inferred results are reliable, they are model dependent. Therefore,
one compares them with the values for the local interstellar medium (LISM). The argument is that they must be similar, but
even for LISM abundance determinations models play a fundamental role (i.e., temperature fluctuations, clumpiness, photon
leaks). There are still two possible comparisons—one with the meteoritic values and the second with solar wind abundances.
In this work we derive a first estimation of the solar wind element ratios of sulfur relative to calcium and magnesium, two
neighboring low-FIP elements, using 10 years of CELIAS/MTOF data. We compare the sulfur abundance with the abundance determined
from spectroscopic observations and from solar energetic particles. Sulfur is a moderately volatile element, hence, meteoritic
sulfur may be depleted relative to non-volatile elements, if compared to its original solar system value. 相似文献
199.
H. Nilsson R. Lundin K. Lundin S. Barabash H. Borg O. Norberg A. Fedorov J.-A Sauvaud H. Koskinen E. Kallio P. Riihelä J. L. Burch 《Space Science Reviews》2007,128(1-4):671-695
The Ion Composition Analyzer (ICA) is part of the Rosetta Plasma Consortium (RPC). ICA is designed to measure the three-dimensional
distribution function of positive ions in order to study the interaction between the solar wind and cometary particles. The
instrument has a mass resolution high enough to resolve the major species such as protons, helium, oxygen, molecular ions,
and heavy ions characteristic of dusty plasma regions. ICA consists of an electrostatic acceptance angle filter, an electrostatic
energy filter, and a magnetic momentum filter. Particles are detected using large diameter (100 mm) microchannel plates and
a two-dimensional anode system. ICA has its own processor for data reduction/compression and formatting. The energy range
of the instrument is from 25 eV to 40 keV and an angular field-of-view of 360° × 90° is achieved through electrostatic deflection
of incoming particles. 相似文献
200.