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11.
Preservation of microbial lipids in geothermal sinters 总被引:1,自引:0,他引:1
Lipid biomarkers are widely used to study the earliest life on Earth and have been invoked as potential astrobiological markers, but few studies have assessed their survival and persistence in geothermal settings. Here, we investigate lipid preservation in active and inactive geothermal silica sinters, with ages of up to 900 years, from Champagne Pool, Waiotapu, New Zealand. Analyses revealed a wide range of bacterial biomarkers, including free and bound fatty acids, 1,2-di-O-alkylglycerols (diethers), and various hopanoids. Dominant archaeal lipids include archaeol and glycerol dialkyl glycerol tetraethers (GDGTs). The predominance of generally similar biomarker groups in all sinters suggests a stable microbial community throughout Champagne Pool's history and indicates that incorporated lipids can be well preserved. Moreover, subtle differences in lipid distributions suggest that past changes in environmental conditions can be elucidated. In this case, higher archaeol abundances relative to the bacterial diethers, a greater proportion of cyclic GDGTs, the high average chain length of the bacterial diethers, and greater concentrations of hopanoic acids in the older sinters all suggest hotter conditions at Champagne Pool in the past. 相似文献
12.
Bruce M. Jakosky 《Space Science Reviews》1985,41(1-2):131-200
A review of the behavior of water in the Mars atmosphere and subsurface is appropriate now that data from the Mariner and Viking spacecraft have been analyzed and discussed for several years following completion of those missions. Observations and analyses pertinent to the seasonal cycle of water vapor in the atmosphere of Mars are reviewed, with attention toward transport of water and the seasonal exchange of water between the atmosphere and various non-atmospheric reservoirs. Possible seasonally-accessible sources and sinks for water include water ice on or within the seasonal and residual polar caps; surface or subsurface ice in the high-latitude regions of the planet; adsorbed or chemically-bound water within the near-surface regolith; or surface or subsurface liquid water. The stability of water within each of these reservoirs is discussed, as are the mechanisms for driving exchange of the water with the atmosphere and the timescales for exchange. Specific conclusions are reached about the distribution of water and the viability of each mechanism as a seasonal reservoir. Discussion is also included of the behaviour of water on longer timescales, driven by the variations in solar forcing due to the quasi-periodic variations of the orbital obliquity. Finally, specific suggestions are made for future observations from spacecraft which would further define or constrain the seasonal cycle of water. 相似文献
13.
Bruce Fegley Jr. 《Space Science Reviews》2000,92(1-2):177-200
Thermochemical equilibrium calculations predict gas phase, gas-grain, and solid phase reactions as a function of pressure
and temperature in the solar nebula. However, chemical reactions proceed at different rates, which generally decrease exponentially
with decreasing temperature. At sufficiently low temperatures (which vary depending on the specific reaction) there may not
have been enough time for the predicted equilibrium chemistry to have taken place before the local environment cooled significantly
or before the gaseous solar nebula was dispersed. As a consequence, some of the high temperature chemistry established in
sufficiently hot regions of the solar nebula may be quenched or frozen in without the production of predicted low temperature
phases. Experimental studies and theoretical models of three exemplary low temperature reactions, the formation of troilite
(FeS), magnetite (Fe3O4), and hydrous silicates, have been done to quantify these ideas. A comparison of the chemical reaction rates with the estimated
nebular lifetime of 0.1-10 million years indicates that troilite formation proceeded to completion in the solar nebula. Magnetite
formation was much slower and only thin magnetite rims could have formed on metal grains. Hydrous silicate formation is predicted
to be even slower, and hydrous silicates in meteorites and interplanetary dust particles probably formed later on the parent
bodies of these objects, instead of in the solar nebula.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
14.
Bruce J. Haines Shailen D. Desai George H. Born 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
We describe results from two decades of monitoring vertical seafloor motion at the Harvest oil platform, NASA’s prime verification site for the TOPEX/Poseidon and Jason series of reference altimeter missions. Using continuous GPS observations, we refine estimates of the platform subsidence—due most likely to fluid withdrawal linked to oil production—and describe the impact on estimates of stability for the altimeter measurement systems. The cumulative seafloor subsidence over 20 yrs is approximately 10 cm, but the rate does not appear constant. The apparent non-linear nature of the vertical motion, coupled with long-period GPS errors, implies that the quality of the seafloor motion estimates is not uniform over the 20-yr period. For the Jason-1 era (2002–2009), competing estimates for the subsidence show agreement to better than 1 mm yr−1. Longer durations of data are needed before the seafloor motion estimates for the Jason-2 era (2008–present) can approach this level of accuracy. 相似文献
15.
High accuracy satellite drag model (HASDM) 总被引:2,自引:0,他引:2
Mark F. Storz Bruce R. Bowman Major James I. Branson Stephen J. Casali W. Kent Tobiska 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2497-2505
The dominant error source in force models used to predict low-perigee satellite trajectories is atmospheric drag. Errors in operational thermospheric density models cause significant errors in predicted satellite positions, since these models do not account for dynamic changes in atmospheric drag for orbit predictions. The Air Force Space Battlelab’s High Accuracy Satellite Drag Model (HASDM) estimates and predicts (out three days) a dynamically varying global density field. HASDM includes the Dynamic Calibration Atmosphere (DCA) algorithm that solves for the phases and amplitudes of the diurnal and semidiurnal variations of thermospheric density near real-time from the observed drag effects on a set of Low Earth Orbit (LEO) calibration satellites. The density correction is expressed as a function of latitude, local solar time and altitude. In HASDM, a time series prediction filter relates the extreme ultraviolet (EUV) energy index E10.7 and the geomagnetic storm index ap, to the DCA density correction parameters. The E10.7 index is generated by the SOLAR2000 model, the first full spectrum model of solar irradiance. The estimated and predicted density fields will be used operationally to significantly improve the accuracy of predicted trajectories for all low-perigee satellites. 相似文献
16.
Sterken Veerle J. Baalmann Lennart R. Draine Bruce T. Godenko Egor Herbst Konstantin Hsu Hsiang-Wen Hunziker Silvan Izmodenov Vladislav Lallement Rosine Slavin Jonathan D. 《Space Science Reviews》2022,218(8):1-15
Space Science Reviews - The ESA Swarm mission, launched on 22 November 2013, consists of three spacecraft each equipped with a Micro Advanced Stellar Compass ( $\mu $ ASC) from the Technical... 相似文献
17.
D. Winterhalter M. Neugebauer B. E. Goldstein E. J. Smith B. T. Tsurutani S. J. Bame A. Balogh 《Space Science Reviews》1995,72(1-2):201-204
Data obtained by the Ulysses magnetometer and solar wind analyzer have been combined to study the properties of magnetic holes in the solar wind between 1 and 5.4 AU and to 23° south latitude. Although the plasma surrounding the holes was generally stable against the mirror instability, there are indications that the holes may have been remnants of mirror mode structures created upstream of the points of observation. Those indications include: (1) For the few holes for which proton or alpha-particle pressure could be measured inside the hole, the ion thermal pressure was always greater than in the plasma adjacent to the holes. (2) The plasma surrounding many of the holes was marginally stable for the mirror mode, while the plasma environment of all the holes was significantly closer to mirror instability than was the average solar wind. (3) The plasma containing trains of closely spaced holes was closer to mirror instability than was the plasma containing isolated holes. (4) The near-hole plasma had much higher ion (ratio of thermal to magnetic pressure) than did the average solar wind. 相似文献
18.
N.U. Crooker J.T. Gosling V. Bothmer R.J. Forsyth P.R. Gazis A. Hewish T.S. Horbury D.S. Intriligator J.R. Jokipii J. Kóta A.J. Lazarus M.A. Lee E. Lucek E. Marsch A. Posner I.G. Richardson E.C. Roelof J.M. Schmidt G.L. Siscoe B.T. Tsurutani R.F. Wimmer-Schweingruber 《Space Science Reviews》1999,89(1-2):179-220
Corotating interaction regions (CIRs) in the middle heliosphere have distinct morphological features and associated patterns
of turbulence and energetic particles. This report summarizes current understanding of those features and patterns, discusses
how they can vary from case to case and with distance from the Sun and possible causes of those variations, presents an analytical
model of the morphological features found in earlier qualitative models and numerical simulations, and identifies aspects
of the features and patterns that have yet to be resolved.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
20.
B.T. Tsurutani R.M. Thorne 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(2):439-444
A critical appraisal is made of the hypothesis that power-line harmonic radiation can influence the Earth's radiation belts by triggering intense magnetospheric emissions which in turn resonantly scatter trapped electrons into the atmospheric loss cone. While such triggering may indeed occur, a combination of theoretical arguments supplemented by an indepth analysis of OGO-5 satellite data is employed to show that triggered waves comprise at best a small fraction of the total magnetospheric wave population. Previous claims to the contrary have been either based on erroneous statistical arguments or biased by the limited sample of ducted waves detectable by ground based receivers. The totality of satellite data is consistent with a predominantly natural origin for the two classes of electromagnetic waves (chorus and plasmaspheric hiss) which are known to interact strongly with energetic radiation belt electrons. 相似文献