全文获取类型
收费全文 | 85篇 |
免费 | 0篇 |
国内免费 | 4篇 |
专业分类
航空 | 34篇 |
航天技术 | 29篇 |
航天 | 26篇 |
出版年
2021年 | 4篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 8篇 |
2012年 | 5篇 |
2011年 | 8篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 4篇 |
2007年 | 1篇 |
2006年 | 1篇 |
2005年 | 2篇 |
2003年 | 2篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1965年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有89条查询结果,搜索用时 31 毫秒
81.
Laboratory experiments carried out under plausible prebiotic conditions (under conditions that might have occurred at primitive deep-sea hydrothermal vents) in water and involving constituents that occur in the vicinity of submarine hydrothermal vents (e.g., CO, H(2)S, NiS) have disclosed an iterative Ni-catalyzed pathway of C-C bond formation. This pathway leads from CO to various organic molecules that comprise, notably, thiols, alkylmono- and disulfides, carboxylic acids, and related thioesters containing up to four carbon atoms. Furthermore, similar experiments with organic compounds containing various functionalities, such as thiols, carboxylic acids, thioesters, and alcohols, gave clues to the mechanisms of this novel synthetic process in which reduced metal species, in particular Ni(0), appear to be the key catalysts. Moreover, the formation of aldehydes (and ketones) as labile intermediates via a hydroformylation-related process proved to be at the core of the chain elongation process. Since this process can potentially lead to organic compounds with any chain length, it could have played a significant role in the prebiotic formation of lipidic amphiphilic molecules such as fatty acids, potential precursors of membrane constituents. 相似文献
82.
Paul Morgan Matthias Grott Brigitte Knapmeyer-Endrun Matt Golombek Pierre Delage Philippe Lognonné Sylvain Piqueux Ingrid Daubar Naomi Murdoch Constantinos Charalambous William T. Pike Nils Müller Axel Hagermann Matt Siegler Roy Lichtenheldt Nick Teanby Sharon Kedar 《Space Science Reviews》2018,214(6):104
This article discusses relevant physical properties of the regolith at the Mars InSight landing site as understood prior to landing of the spacecraft. InSight will land in the northern lowland plains of Mars, close to the equator, where the regolith is estimated to be \(\geq3\mbox{--}5~\mbox{m}\) thick. These investigations of physical properties have relied on data collected from Mars orbital measurements, previously collected lander and rover data, results of studies of data and samples from Apollo lunar missions, laboratory measurements on regolith simulants, and theoretical studies. The investigations include changes in properties with depth and temperature. Mechanical properties investigated include density, grain-size distribution, cohesion, and angle of internal friction. Thermophysical properties include thermal inertia, surface emissivity and albedo, thermal conductivity and diffusivity, and specific heat. Regolith elastic properties not only include parameters that control seismic wave velocities in the immediate vicinity of the Insight lander but also coupling of the lander and other potential noise sources to the InSight broadband seismometer. The related properties include Poisson’s ratio, P- and S-wave velocities, Young’s modulus, and seismic attenuation. Finally, mass diffusivity was investigated to estimate gas movements in the regolith driven by atmospheric pressure changes. Physical properties presented here are all to some degree speculative. However, they form a basis for interpretation of the early data to be returned from the InSight mission. 相似文献
83.
The smoothed particle hydrodynamics (SPH) method is usually expected to be an effi-cient numerical tool for calculating the fluid-structure interactions in compressors; however, an endogenetic restriction is the problem of low-order consistency. A high-order SPH method by intro-ducing inverse kernels, which is quite easy to be implemented but efficient, is proposed for solving this restriction. The basic inverse method and the special treatment near boundary are introduced with also the discussion of the combination of the Least-Square (LS) and Moving-Least-Square (MLS) methods. Then detailed analysis in spectral space is presented for people to better under-stand this method. Finally we show three test examples to verify the method behavior. 相似文献
84.
Lucile Fayon Brigitte Knapmeyer-Endrun Philippe Lognonné Marco Bierwirth Aron Kramer Pierre Delage Foivos Karakostas Sharon Kedar Naomi Murdoch Raphael F. Garcia Nicolas Verdier Sylvain Tillier William T. Pike Ken Hurst Cédric Schmelzbach William B. Banerdt 《Space Science Reviews》2018,214(8):119
Both sensors of the SEIS instrument (VBBs and SPs) are mounted on the mechanical leveling system (LVL), which has to ensure a level placement on the Martian ground under currently unknown local conditions, and provide the mechanical coupling of the seismometers to the ground. We developed a simplified analytical model of the LVL structure in order to reproduce its mechanical behavior by predicting its resonances and transfer function. This model is implemented numerically and allows to estimate the effects of the LVL on the data recorded by the VBBs and SPs on Mars. The model is validated through comparison with the horizontal resonances (between 35 and 50 Hz) observed in laboratory measurements. These modes prove to be highly dependent of the ground horizontal stiffness and torque. For this reason, an inversion study is performed and the results are compared with some experimental measurements of the LVL feet’s penetration in a martian regolith analog. This comparison shows that the analytical model can be used to estimate the elastic ground properties of the InSight landing site. Another application consists in modeling the 6 sensors on the LVL at their real positions, also considering their sensitivity axes, to study the performances of the global SEIS instrument in translation and rotation. It is found that the high frequency ground rotation can be measured by SEIS and, when compared to the ground acceleration, can provide ways to estimate the phase velocity of the seismic surface waves at shallow depths. Finally, synthetic data from the active seismic experiment made during the HP3 penetration and SEIS rotation noise are compared and used for an inversion of the Rayleigh phase velocity. This confirms the perspectives for rotational seismology with SEIS which will be developed with the SEIS data acquired during the commissioning phase after landing. 相似文献
85.
Detection of Envisat RA2/ICE-1 retracked radar altimetry bias over the Amazon basin rivers using GPS
Stéphane Calmant Joecila Santos da Silva Daniel Medeiros Moreira Frédérique Seyler C.K. Shum Jean François Crétaux Germinal Gabalda 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Altimetry is now routinely used to monitor stage variations over rivers, including in the Amazon basin. It is desirable for hydrologic studies to be able to combine altimetry from different satellite missions with other hydrogeodesy datasets such as leveled gauges and watershed topography. One requirement is to accurately determine altimetry bias, which could be different for river studies from the altimetry calibrated for deep ocean or lake applications. In this study, we estimate the bias in the Envisat ranges derived from the ICE-1 waveform retracking, which are nowadays widely used in hydrologic applications. As a reference, we use an extensive dataset of altitudes of gauge zeros measured by GPS collocated at the gauges. The thirty-nine gauges are spread along the major tributaries of the Amazon basin. The methodology consists in jointly modeling the vertical bias and spatial and temporal slope variations between altimetry series located upstream and downstream of each gauge. The resulting bias of the Envisat ICE-1 retracked altimetry over rivers is 1.044 ± 0.212 m, revealing a significant departure from other Envisat calibrations or from the Jason-2 ICE-1 calibration. 相似文献
86.
O. Ooms Hans Van Der Woerd Henny J. G. L. M. Lamers Josip Kleczek J. Kovalevsky R. Gathier T. Jarzebowski J. P. Swings K. A. van der Hucht O. Namba R. Mewe D. Lynden-Bell Jan Kuijpers M. van der Klis D. de Hoop H. Wittenberg W. Iwanowska P. S. Thé J. Schrijver S. R. Pottasch 《Space Science Reviews》1984,38(3-4):385-387
87.
Emilie Habart Malcolm Walmsley Laurent Verstraete Stephanie Cazaux Roberto Maiolino Pierre Cox Francois Boulanger Guillaume Pineau Des Forêts 《Space Science Reviews》2005,119(1-4):71-91
Observations of H2 line emission in galactic and extragalactic environments obtained with the Infrared Space Observatory (ISO) are reviewed.
The diagnostic capability of H2 observations is illustrated. We discuss what one has learned about such diverse astrophysical sources as photon-dominated
regions, shocks, young stellar objects, planetary nebulae and starburst galaxies from ISO observations of H2 emission. In this context, we emphasise use of measured H2 line intensities to infer important physical quantities such as the gas temperature, gas density and radiation field and
we discuss the different possible excitation mechanisms of H2. We also briefly consider future prospects for observation of H2 from space and from the ground.
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA. 相似文献
88.
Sharon Kedar Jose Andrade Bruce Banerdt Pierre Delage Matt Golombek Matthias Grott Troy Hudson Aaron Kiely Martin Knapmeyer Brigitte Knapmeyer-Endrun Christian Krause Taichi Kawamura Philippe Lognonne Tom Pike Youyi Ruan Tilman Spohn Nick Teanby Jeroen Tromp James Wookey 《Space Science Reviews》2017,211(1-4):315-337
InSight’s Seismic Experiment for Interior Structure (SEIS) provides a unique and unprecedented opportunity to conduct the first geotechnical survey of the Martian soil by taking advantage of the repeated seismic signals that will be generated by the mole of the Heat Flow and Physical Properties Package (HP3). Knowledge of the elastic properties of the Martian regolith have implications to material strength and can constrain models of water content, and provide context to geological processes and history that have acted on the landing site in western Elysium Planitia. Moreover, it will help to reduce travel-time errors introduced into the analysis of seismic data due to poor knowledge of the shallow subsurface. The challenge faced by the InSight team is to overcome the limited temporal resolution of the sharp hammer signals, which have significantly higher frequency content than the SEIS 100 Hz sampling rate. Fortunately, since the mole propagates at a rate of \(\sim1~\mbox{mm}\) per stroke down to 5 m depth, we anticipate thousands of seismic signals, which will vary very gradually as the mole travels.Using a combination of field measurements and modeling we simulate a seismic data set that mimics the InSight HP3-SEIS scenario, and the resolution of the InSight seismometer data. We demonstrate that the direct signal, and more importantly an anticipated reflected signal from the interface between the bottom of the regolith layer and an underlying lava flow, are likely to be observed both by Insight’s Very Broad Band (VBB) seismometer and Short Period (SP) seismometer. We have outlined several strategies to increase the signal temporal resolution using the multitude of hammer stroke and internal timing information to stack and interpolate multiple signals, and demonstrated that in spite of the low resolution, the key parameters—seismic velocities and regolith depth—can be retrieved with a high degree of confidence. 相似文献
89.
Emirant Bertillas Amabayo J. Cilliers Pierre 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
This paper presents results pertaining to the response of the mid-latitude ionosphere to strong geomagnetic storms that occurred from 31 March to 02 April 2001 and 07–09 September 2002. The results are based on (i) Global Positioning Systems (GPSs) derived total electron content (TEC) variations accompanying the storm, (ii) ionosonde measurements of the ionospheric electrodynamic response towards the storms and (iii) effect of storm induced travelling ionospheric disturbances (TIDs) on GPS derived TEC. Ionospheric data comprising of ionospheric TEC obtained from GPS measurements, ionograms, solar wind data obtained from Advanced Composition Explorer (ACE) and magnetic data from ground based magnetometers were used in this study. Storm induced features in vertical TEC (VTEC) have been obtained and compared with the mean VTEC of quiet days. The response of the mid-latitude ionosphere during the two storm periods examined may be characterised in terms of increased or decreased level of VTEC, wave-like structures in VTEC perturbation and sudden enhancement in hmF2 and h′F. The study reveals both positive and negative ionospheric storm effects on the ionosphere over South Africa during the two strong storm conditions. These ionospheric features have been mainly attributed to the travelling ionospheric disturbances (TIDs) as the driving mechanism for the irregularities causing the perturbations observed. TEC perturbations due to the irregularities encountered by the satellites were observed on satellites with pseudo random numbers (PRNs) 15, 17, 18 and 23 between 17:00 and 23:00 UT on 07 September 2002. 相似文献