全文获取类型
收费全文 | 150篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
航空 | 54篇 |
航天技术 | 59篇 |
航天 | 39篇 |
出版年
2021年 | 7篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2017年 | 4篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 6篇 |
2012年 | 8篇 |
2011年 | 16篇 |
2010年 | 5篇 |
2009年 | 2篇 |
2008年 | 6篇 |
2006年 | 3篇 |
2005年 | 10篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 9篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 13篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有152条查询结果,搜索用时 15 毫秒
81.
Mohamed Khalil Ben-Larbi Kattia Flores Pozo Mirue Choi Tom Haylok Benjamin Grzesik Andreas Haas Dominik Krupke Harald Konstanski Volker Schaus Sándor P. Fekete Christian Schurig Enrico Stoll 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(11):3620-3637
Recent developments have seen a trend towards larger constellations of spacecraft, with some proposals featuring constellations of more than 10.000 satellites. While similar concepts for large constellations already existed in the past, traditional satellite deployments hardly ever feature groups of more than 100 satellites. This trend towards considerably larger satellite numbers originates from non-traditional design and operations of spacecraft by non-traditional space companies. The evolution in the space sector, precipitated by new players, is often referred to as “Space 4.0” or “New Space”. It necessitates a rethinking of the way satellites and satellite constellations are planned, designed, and operated. New operational paradigms are needed to enable automatic, optimal task definition, and scheduling in a holistic approach.This is the second of two companion papers that investigate the operations of distributed satellite systems. This second article investigates the classification of distributed satellite systems and evaluates commercial tools for automated spacecraft operations, whereas the first article performed a survey of conventional and “new space”operations of spacecraft constellations.Classification metrics for constellations are derived and evaluated with respect to their informative value concerning the operation, the automation, and the scalability of the constellation. The proposed classification system is applied to the Dove and RapidEye constellation and allows for a comparison between the presented automation approaches. Commercial tools for automated spacecraft operations are evaluated for several mission task elements, such as orbit control, orbit maintenance, and collision avoidance. Subsequently, the trends, benefits, and standardization needs for operational automation are identified. 相似文献
82.
Andrea Kunder Elena Valenti Massimo Dall’Ora Pawel Pietrukowicz Chris Sneden Giuseppe Bono Vittorio F. Braga Ivan Ferraro Giuliana Fiorentino Giacinto Iannicola Marcella Marconi Clara E. Martínez-Vázquez Matteo Monelli Ilaria Musella Vincenzo Ripepi Maurizio Salaris Peter B. Stetson 《Space Science Reviews》2018,214(5):90
Here we review the efforts of a number of recent results that use old tracers to understand the build up of the Galaxy. Details that lead directly to using these old tracers to measure distances are discussed. We concentrate on the following: (1) the structure and evolution of the Galactic bulge and inner Galaxy constrained from the dynamics of individual stars residing therein; (2) the spatial structure of the old Galactic bulge through photometric observations of RR Lyrae-type stars; (3) the three-dimensional structure, stellar density, mass, chemical composition, and age of the Milky Way bulge as traced by its old stellar populations; (4) an overview of RR Lyrae stars known in the ultra-faint dwarfs and their relation to the Galactic halo; and (5) different approaches for estimating absolute and relative cluster ages. 相似文献
83.
84.
Shikha Raizada Christiano G.M. Brum John D. Mathews Cristina Gonzalez Efmi Franco 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(7):1850-1857
Electron concentration (Ne) inferred from Incoherent Scatter Radar (ISR) measurements has been used to determine the influence of solar flux and geomagnetic activity in the ionospheric E-region over Arecibo Observatory (AO). The approach is based on the determination of column integrated Ne, referred to as E-region total electron content (ErTEC) between 80 and 150 km altitude regions. The results discussed in this work are for the AO nighttime period. The study reveals higher ErTEC values during the low solar flux periods for all the seasons except for summer period. It is found that the E-region column abundance is higher in equinox periods than in the winter for low solar activity conditions. The column integrated Ne during the post-sunset/pre-sunrise periods always exceeds the midnight minima, independent of season or solar activity. This behavior has been attributed to the variations in the coupling processes from the F-region. The response of ErTEC to the geomagnetic variability is also examined for different solar flux conditions and seasons. During high solar flux periods, changes in Kp cause an ErTEC increase in summer and equinox, while producing a negative storm-like effect during the winter. Variations in ErTEC due to geomagnetic activity during low solar flux periods produce maximum variability in the E-region during equinox periods, while resulting in an increase/decrease in ErTEC before local midnight during the winter/summer periods, respectively. 相似文献
85.
Parro V de Diego-Castilla G Moreno-Paz M Blanco Y Cruz-Gil P Rodríguez-Manfredi JA Fernández-Remolar D Gómez F Gómez MJ Rivas LA Demergasso C Echeverría A Urtuvia VN Ruiz-Bermejo M García-Villadangos M Postigo M Sánchez-Román M Chong-Díaz G Gómez-Elvira J 《Astrobiology》2011,11(10):969-996
The Atacama Desert has long been considered a good Mars analogue for testing instrumentation for planetary exploration, but very few data (if any) have been reported about the geomicrobiology of its salt-rich subsurface. We performed a Mars analogue drilling campaign next to the Salar Grande (Atacama, Chile) in July 2009, and several cores and powder samples from up to 5?m deep were analyzed in situ with LDChip300 (a Life Detector Chip containing 300 antibodies). Here, we show the discovery of a hypersaline subsurface microbial habitat associated with halite-, nitrate-, and perchlorate-containing salts at 2?m deep. LDChip300 detected bacteria, archaea, and other biological material (DNA, exopolysaccharides, some peptides) from the analysis of less than 0.5?g of ground core sample. The results were supported by oligonucleotide microarray hybridization in the field and finally confirmed by molecular phylogenetic analysis and direct visualization of microbial cells bound to halite crystals in the laboratory. Geochemical analyses revealed a habitat with abundant hygroscopic salts like halite (up to 260?g kg(-1)) and perchlorate (41.13?μg g(-1) maximum), which allow deliquescence events at low relative humidity. Thin liquid water films would permit microbes to proliferate by using detected organic acids like acetate (19.14?μg g(-1)) or formate (76.06?μg g(-1)) as electron donors, and sulfate (15875?μg g(-1)), nitrate (13490?μg g(-1)), or perchlorate as acceptors. Our results correlate with the discovery of similar hygroscopic salts and possible deliquescence processes on Mars, and open new search strategies for subsurface martian biota. The performance demonstrated by our LDChip300 validates this technology for planetary exploration, particularly for the search for life on Mars. 相似文献
86.
de Diego-Castilla G Cruz-Gil P Mateo-Martí E Fernández-Calvo P Rivas LA Parro V 《Astrobiology》2011,11(8):759-773
Antibody microarrays are becoming frequently used tools for analytical purposes. A key factor for optimal performance is the stability of the immobilized (capturing) antibodies as well as those that have been fluorescently labeled to achieve the immunological test (tracers). This is especially critical for long-distance transport, field testing, or planetary exploration. A number of different environmental stresses may affect the antibody integrity, such as dryness, sudden temperature shift cycles, or, as in the case of space science, exposure to large quantities of the highly penetrating gamma radiation. Here, we report on the effect of certain stabilizing solutions for long-term storage of printed antibody microarrays under different conditions. We tested the effect of gamma radiation on printed and freeze- or vacuum-dried fluorescent antibodies at working concentrations (tracer antibodies), as well as the effect of multiple cycles of sudden and prolonged temperature shifts on the stability of fluorescently labeled tracer antibody cocktails. Our results show that (i) antibody microarrays are stable at room temperature when printed on stabilizing spotting solutions for at least 6 months, (ii) lyophilized and vacuum-dried fluorescently labeled tracer antibodies are stable for more than 9 months of sudden temperature shift cycles (-20°C to 25°C and 50°C), and (iii) both printed and freeze- or vacuum-dried fluorescent tracer antibodies are stable after several-fold excess of the dose of gamma radiation expected during a mission to Mars. Although different antibodies may exhibit different susceptibilities, we conclude that, in general, antibodies are suitable for use in planetary exploration purposes if they are properly treated and stored with the use of stabilizing substances. 相似文献
87.
Paulino-Lima IG Janot-Pacheco E Galante D Cockell C Olsson-Francis K Brucato JR Baratta GA Strazzulla G Merrigan T McCullough R Mason N Lage C 《Astrobiology》2011,11(9):875-882
In this experimental study, cells of the radiation-resistant bacterium Deinococcus radiodurans were exposed to several different sources of radiation chosen to replicate the charged particles found in the solar wind. Naked cells or cells mixed with dust grains (basalt or sandstone) differing in elemental composition were exposed to electrons, protons, and ions to determine the probability of cell survival after irradiation. Doses necessary to reduce the viability of cell population to 10% (LD(10)) were determined under different experimental conditions. The results of this study indicate that low-energy particle radiation (2-4?keV), typically present in the slow component of the solar wind, had no effect on dehydrated cells, even if exposed at fluences only reached in more than 1000 years at Sun-Earth distance (1 AU). Higher-energy ions (200?keV) found in solar flares would inactivate 90% of exposed cells after several events in less than 1 year at 1 AU. When mixed with dust grains, LD(10) increases about 10-fold. These results show that, compared to the highly deleterious effects of UV radiation, solar wind charged particles are relatively benign, and organisms protected under grains from UV radiation would also be protected from the charged particles considered in this study. 相似文献
88.
ISO performed a large variety of observing programmes on comets, asteroids and zodiacal light – covering about 1% of the archived
observations – with a surprisingly rewarding scientific return. Outstanding results were related to the exceptionally bright
comet Hale–Bopp and to ISO's capability to study in detail the water spectrum in a direct way. But many other results were
broadly recognised: Discovery of new molecules in comets, the studies of crystalline silicates, the work on asteroid surface
mineralogy, results from thermophysical studies of asteroids, a new determination of the asteroid number density in the main-belt
and last but not least, the investigations on the spatial and spectral features of the zodiacal light. 相似文献
89.
L. Boirin M. Mndez M. Díaz Trigo A.N. Parmar J.S. Kaastra 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2759-2761
We report the XMM-Newton detection of narrow Fe xxv and Fe xxvi X-ray absorption lines at 7 keV in the persistent emission of the dipping low-mass X-ray binary (LMXB) 4U 1323−62. Such features have now been reported in a growing number of LMXBs seen almost edge-on, indicating that the highly-ionized plasma probably originates in an accretion disk atmosphere or wind. During dipping intervals of 4U 1323−62, the strength of the Fe xxv feature increases while that of the Fe xxvi feature decreases, consistent with the presence of less strongly ionized material in the line-of-sight. As observed previously, the changes in the X-ray spectrum during dips are inconsistent with a simple increase in absorption by cool material. However, we show that the changes in both the narrow absorption features and the continuum can be modeled self-consistently by variations in the properties of an ionized absorber. From persistent to deep dipping the photo-ionization parameter decreases while the equivalent hydrogen column density of the ionized absorber increases. No partial covering of any component of the spectrum, and hence no extended corona, are required. Since highly-ionized absorption features are seen from many other dip sources, this mechanism may also explain the overall changes in X-ray spectrum observed during dipping intervals from these systems. 相似文献
90.
A methodology based on point-like sources is discussed, enabling a reliable estimate of the acceleration of the Pioneer 10 and 11 probes caused by thermal effects. A sensitivity analysis of the several parameters of the model allows for a clear indication of the possible thermal origin of the so-called Pioneer anomaly. 相似文献