全文获取类型
收费全文 | 138篇 |
免费 | 2篇 |
专业分类
航空 | 44篇 |
航天技术 | 67篇 |
综合类 | 1篇 |
航天 | 28篇 |
出版年
2021年 | 4篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 9篇 |
2013年 | 6篇 |
2012年 | 5篇 |
2011年 | 15篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 5篇 |
2006年 | 10篇 |
2005年 | 1篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1998年 | 3篇 |
1996年 | 2篇 |
1993年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1970年 | 1篇 |
1968年 | 2篇 |
排序方式: 共有140条查询结果,搜索用时 15 毫秒
61.
F.E. Bauer C. Vignali D.M. Alexander W.N. Brandt G.P. Garmire A.E. Hornschemeier P.S. Broos L.K. Townsley D.P. Schneider 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2555-2560
We investigate the nature of the faint X-ray source population through X-ray spectroscopy and variability analyses of 136 active galactic nuclei (AGN) detected in the 2 Ms Chandra Deep Field-North Survey with >200 background-subtracted 0.5–8.0 keV counts [F0.5–8.0 keV = (1.4−200) × 10−15 erg cm−2 s−1]. Our preliminary spectral analyses yield median spectral parameters of Γ = 1.61 and intrinsic NH = 6.2 × 1021 cm−2 (z = 1 assumed when no redshift available) when the AGN spectra are fitted with a simple absorbed power-law model. However, considerable spectral complexity is apparent (e.g., reflection, partial covering) and must be taken into account to model the data accurately. Moreover, the choice of spectral model (i.e., free vs. fixed photon index) has a pronounced effect on the derived JVH distribution and, to a lesser extent, the X-ray luminosity distribution. We also find that among the 136 AGN, 10 (≈7%) show significant Fe K emission-line features with equivalent widths in the range 0.1–1.3 keV. Two of these emission-line AGN could potentially be Compton thick (i.e., Γ < 1.0 and large Fe K equivalent width). Finally, we find that 81 (≈60%) of the 136 AGN show signs of variability, and that this fraction increases significantly (≈80–90%) when better photon statistics are available. 相似文献
62.
冯·卡门(Von Kármán)撞击坑位于月球背面的SPA盆地西北部,切穿了浅层月壳,具有异常的矿物成分分布。基于微波辐射计数据的月壤微波辐射特性分析,对月球热演化和岩浆演化研究具有重要的参考价值。本研究基于“嫦娥2号”卫星微波辐射计数据,采用时角分析、双线性插值方法,生成了研究区域的亮温(TB)图和亮温差(dTB)图像;结合Arcgis软件,叠加地质图,并结合成分、地形图,研究了Von Kármán撞击坑微波辐射特性。研究结果表明:研究区北部出现高TB异常,初步判定为下垫面温度较高;研究区南部出现与钛铁矿(FeO+TiO2)含量分布相对应的亮温表现;结合研究区的微波辐射特性,重新进行了冯·卡门撞击坑地质解译;根据冯·卡门撞击坑的亮温表现,建议北部为着陆区重点选择区,其次为南部和西部。 相似文献
63.
基于CELMS数据的月球东海微波辐射特性研究 总被引:1,自引:1,他引:1
根据月壤(FeO+TiO2)含量数据和"嫦娥2号"卫星CELMS数据,对月球东海地区微波辐射特性进行了研究。结果表明,在东海内部(FeO+TiO2)含量较高的地区,其正午和午夜时刻的亮温值都比较高,亮温差值也比较大,但亮温及亮温差值的分布随频率变化呈现不均匀性;Maunder撞击坑的(FeO+TiO2)含量较低,但其低频和高频亮温及亮温差值的表现正好相反;区域F(约10°S/106°W)、G(约5°S/104°W)和以(13°S/103°W)为中心的区域的微波辐射存在明显异常。这些区域的微波辐射特性对研究东海地区的形成演化过程具有重要意义。 相似文献
64.
Alexander Ollongren 《Acta Astronautica》2011,68(3-4):539-543
Ingredients of the author's Lingua Cosmica for communication with extra-terrestrial intelligent beings are examined with self-interpretation in mind. The most important ingredients for that purpose are inductive definitions. These definitions contain ordered sequences of induction hypotheses, identified by mutually distinctive constructors. If an assertion involving an inductive definition is to be verified, all induction hypotheses must be taken into account, i.e. they must be eliminated one by one. The implementation of the elimination procedure can be expressed within LINCOS itself. Therefore the system admits self-interpretation. 相似文献
65.
Yurii Balnokin Myasoedov Nikolai Popova Larisa Tikhomirov Alexander Ushakova Sofya Lasseur Christophe Gros Jean-Bernard 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The purpose of this work was to develop technology for recycling NaCl containing in human liquid waste as intrasystem matter in a bioregenerative life support system (BLSS). The circulation of Na+ and Cl− excreted in urine is achieved by inclusion of halophytes, i.e. plants that naturally inhabit salt-rich soils and accumulate NaCl in their organs. A model of Na+ and Cl− recycling in a BLSS was designed, based on the NaCl turnover in the human–urine–nutrient solution–halophytic plant–human cycle. The study consisted of (i) selecting a halophyte suitable for inclusion in a BLSS, and (ii) determining growth conditions supporting maximal Na+ and Cl− accumulation in the shoots of the halophyte growing in a nutrient solution simulating mineralized urine. For the selected halophytic plant, Salicornia europaea, growth rate under optimal conditions, biomass production and quantities of Na+ and Cl− absorbed were determined. Characteristics of a plant production conveyor consisting of S.europaea at various ages, and allowing continuity of Na+ and Cl− turnover, were estimated. It was shown that closure of the NaCl cycle in a BLSS can be attained if the daily ration of fresh Salicornia biomass for a BLSS inhabitant is approximately 360 g. 相似文献
66.
A. de la Torre P. Llamedo P. Alexander T. Schmidt J. Wickert 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
In a previous paper by Schmidt et al. (2008), from CHAllenging Minisatellite Payload (CHAMP) Global Positioning System (GPS) radio occultation data, a comparison was made between a Gaussian filter applied to the “complete” temperature profile and to its “separate” tropospheric and stratospheric height intervals, for gravity wave analyses. It was found that the separate filtering method considerably reduces a wave activity artificial enhancement near the tropopause, presumably due to the isolation process of the wave component. We now propose a simple approach to estimate the uncertainty in the calculation of the mean specific wave potential energy content, due exclusively to the filtering process of vertical temperature profiles, independently of the experimental origin of the data. The approach is developed through a statistical simulation, built up from the superposition of synthetic wave perturbations. These are adjusted by a recent gravity wave (GW) climatology and temperature profiles from reanalyses. A systematic overestimation of the mean specific wave potential energy content is detected and its variability with latitude, altitude, season and averaging height interval is highlighted. 相似文献
67.
The author offers a revolutionary method—non-rocket transfer of energy and thrust into Space with a distance of millions of kilometers. The author has developed the theory and made the computations. The method is more efficient than transmission of energy by high-frequency waves. The method may be used for space launch and for accelerating the spaceship and probes for very high speeds, up to a relativistic speed by the current technology. The research also contains prospective projects which illustrate the possibilities of the suggested method. 相似文献
68.
D. Luna P. Alexander A. de la Torre 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The application of the Global Positioning System (GPS) radio occultation (RO) method to the atmosphere enables the determination of height profiles of temperature, among other variables. From these measurements, gravity wave activity is usually quantified by calculating the potential energy through the integration of the ratio of perturbation and background temperatures between two given altitudes in each profile. The uncertainty in the estimation of wave activity depends on the systematic biases and random errors of the measured temperature, but also on additional factors like the selected vertical integration layer and the separation method between background and perturbation temperatures. In this study, the contributions of different parameters and variables to the uncertainty in the calculation of gravity wave potential energy in the lower stratosphere are investigated and quantified. In particular, a Monte Carlo method is used to evaluate the uncertainty that results from different GPS RO temperature error distributions. In addition, our analysis shows that RO data above 30 km height becomes dubious for gravity waves potential energy calculations. 相似文献
69.
Patrick Petitjean Raghunathan Srianand Hum Chand Alexander Ivanchik Pasquier Noterdaeme Neeraj Gupta 《Space Science Reviews》2009,148(1-4):289-300
We summarize the attempts by our group and others to derive constraints on variations of fundamental constants over cosmic time using quasar absorption lines. Most upper limits reside in the range 0.5–1.5×10?5 at the 3σ level over a redshift range of approximately 0.5–2.5 for the fine-structure constant, α, the proton-to-electron mass ratio, μ and a combination of the proton gyromagnetic factor and the two previous constants, g p(α 2/μ) ν , for only one claimed variation of α. It is therefore very important to perform new measurements to improve the sensitivity of the numerous methods to at least <0.1×10?5 which should be possible in the next few years. Future instrumentations on ELTs in the optical and/or ALMA, EVLA and SKA pathfinders in the radio will undoutedly boost this field by allowing to reach much better signal-to-noise ratios at higher spectral resolution and to perform measurements on molecules in the ISM of high redshift galaxies. 相似文献
70.
G.I. Pugacheva A.A. Gusev T. Kohno I.M. Martin W.N. Spjeldvik 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2000,25(12):2319-2322
The results of measurements of absolute flux values and long term temporal evolution of the spatial distribution of trapped He ions in the energy range 1.2 – 9.2 MeV/nucleon below L = 4 are reported. The observations were made with ion counter on board the Japanese OHZORA satellite during the period of January 1984 through March 1987. 相似文献