全文获取类型
收费全文 | 194篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
航空 | 76篇 |
航天技术 | 36篇 |
综合类 | 2篇 |
航天 | 81篇 |
出版年
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2015年 | 1篇 |
2014年 | 9篇 |
2013年 | 7篇 |
2012年 | 9篇 |
2011年 | 15篇 |
2010年 | 9篇 |
2009年 | 16篇 |
2008年 | 6篇 |
2007年 | 12篇 |
2006年 | 11篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有195条查询结果,搜索用时 78 毫秒
171.
Large-scale solar dynamo models were first built by Parker (1955). Over the past half a century these models have evolved significantly. We discuss here the development of a class of large-scale dynamo models which include, along with the α-effect and Ω-effect, an important third process, flux transport by meridional circulation. We present the properties of this ‘flux-transport’ dynamo, including the crucial role meridional circulation plays in giving this dynamo predictive power. 相似文献
172.
We review the structure and dynamics of the solar chromosphere with emphasis on the quiet Sun and properties that are relevant
to element fractionation mechanisms. Attention is given to the chromospheric magnetic field, its connections to the photosphere,
and to the dynamical evolution of the chromosphere. While some profound advances have been made in the “unmagnetized” chromosphere,
our knowledge of the magnetically controlled chromosphere, more relevant for the discussion of element fractionation, is limited.
Given the dynamic nature of the chromosphere and the poorly understood magnetic linkage to the corona, it is unlikely that
we will soon know the detailed processes leading to FIP fractionation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
173.
A 60 GHz phased array system for mm-wave frequency in 5 G is introduced and a 5 bit digitally controlled phase shifter in 40 nm CMOS technology is presented. In a phased array system,the signal to noise ratio(SNR)of the receiver is improved with the beaming forming function. Therefore,the communication data rate and distance are improved accordingly. The phase shifter is the key component for achieving the beam forming function,and its resolution and power consumption are also very critical. In the second half of this paper,an analysis of phase shifter is introduced,and a 60 GHz 5 bit digitally controlled phase shifter in 40 nm complementary metal oxide semiconductor(CMOS)technology is presented. In this presented phase shifter,a hybrid structure is implemented for its advantage on lower phase deviation while keeping comparable loss. Meanwhile,this digitally controlled phase shifter is much more compact than other works. For all 32 states,the minimum phase error is 1.5°,and the maximum phase error is 6.8°. The measured insertion loss is-20.9±1 d B including pad loss at 60 GHz and the return loss is more than 10 d B over 57—64 GHz. The total chip size is 0.24 mm2 with 0 m W DC power consumption. 相似文献
174.
Peter R. Young Hui Tian Hardi Peter Robert J. Rutten Chris J. Nelson Zhenghua Huang Brigitte Schmieder Gregal J. M. Vissers Shin Toriumi Luc H. M. Rouppe van der Voort Maria S. Madjarska Sanja Danilovic Arkadiusz Berlicki L. P. Chitta Mark C. M. Cheung Chad Madsen Kevin P. Reardon Yukio Katsukawa Petr Heinzel 《Space Science Reviews》2018,214(8):120
The term “ultraviolet (UV) burst” is introduced to describe small, intense, transient brightenings in ultraviolet images of solar active regions. We inventorize their properties and provide a definition based on image sequences in transition-region lines. Coronal signatures are rare, and most bursts are associated with small-scale, canceling opposite-polarity fields in the photosphere that occur in emerging flux regions, moving magnetic features in sunspot moats, and sunspot light bridges. We also compare UV bursts with similar transition-region phenomena found previously in solar ultraviolet spectrometry and with similar phenomena at optical wavelengths, in particular Ellerman bombs. Akin to the latter, UV bursts are probably small-scale magnetic reconnection events occurring in the low atmosphere, at photospheric and/or chromospheric heights. Their intense emission in lines with optically thin formation gives unique diagnostic opportunities for studying the physics of magnetic reconnection in the low solar atmosphere. This paper is a review report from an International Space Science Institute team that met in 2016–2017. 相似文献
175.
Martin Wieser Leif Kalla Stas Barabash Tomas Hedqvist Stig Kemi Ola Widell Dominic Abplanalp Peter Wurz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The MEAP (Mars Environment Analogue Platform) mission was to fly a stratospheric balloon on a semicircular trajectory around the North Pole in summer 2008. The balloon platform carried the high-resolution neutral gas mass spectrometer P-BACE (Polar Balloon Atmospheric Composition Experiment) as scientific payload. MEAP/P-BACE is a joint project between the Esrange Space Center, Sweden, the University of Bern, Switzerland and the Swedish Institute of Space Physics (IRF), Kiruna, Sweden. Mission objectives were to validate the platform for future long duration flights around the North pole, to validate the P-BACE instrument design for planetary mission applications (conditions in the Earth stratosphere are similar to the conditions at the Mars surface), to study variation of the stratospheric composition during the flight and to gain experience in balloon based mass spectrometry. All objectives were fulfilled. 相似文献
176.
The Lunar Orbiter Laser Altimeter Investigation on the Lunar Reconnaissance Orbiter Mission 总被引:3,自引:0,他引:3
David E. Smith Maria T. Zuber Glenn B. Jackson John F. Cavanaugh Gregory A. Neumann Haris Riris Xiaoli Sun Ronald S. Zellar Craig Coltharp Joseph Connelly Richard B. Katz Igor Kleyner Peter Liiva Adam Matuszeski Erwan M. Mazarico Jan F. McGarry Anne-Marie Novo-Gradac Melanie N. Ott Carlton Peters Luis A. Ramos-Izquierdo Lawrence Ramsey David D. Rowlands Stephen Schmidt V. Stanley Scott III George B. Shaw James C. Smith Joseph-Paul Swinski Mark H. Torrence Glenn Unger Anthony W. Yu Thomas W. Zagwodzki 《Space Science Reviews》2010,150(1-4):209-241
The Lunar Orbiter Laser Altimeter (LOLA) is an instrument on the payload of NASA’s Lunar Reconnaissance Orbiter spacecraft (LRO) (Chin et al., in Space Sci. Rev. 129:391–419, 2007). The instrument is designed to measure the shape of the Moon by measuring precisely the range from the spacecraft to the lunar surface, and incorporating precision orbit determination of LRO, referencing surface ranges to the Moon’s center of mass. LOLA has 5 beams and operates at 28 Hz, with a nominal accuracy of 10 cm. Its primary objective is to produce a global geodetic grid for the Moon to which all other observations can be precisely referenced. 相似文献
177.
Xuexi Tie Guy Brasseur Peter Hess Martin Riese 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,24(12):1631-1636
Differences between the dynamical characteristics of the northern hemisphere (NH) and southern hemisphere (SH) stratosphere (e.g., the temperature, the strength of polar vortex, and the mean meridional circulation) produce hemispherically asymmetrical distributions of chemical species. In this paper, we use global models to briefly discuss various effects on chemical species caused by this asymmetrical distribution, especially on stratospheric ozone. The role of hemispheric asymmetries in chlorine and bromine loadings on mid- and high latitude ozone depletion is particularly discussed. 相似文献
178.
Our study of solar cycle irradiance variability in the UV between 200 and 400 nm requires a detailed knowledge of the composition of the solar spectrum in this wavelength range. We compute the synthetic spectrum from 250 to 300 nm and compare it with ATLAS3 and SOLSTICE observations. Synthetic solar spectra for solar minimum and maximum conditions show large variations in broad, strong UV lines. Strong lines of FeI between 260 nm and 264 nm show increases between 0.4× and 3×in their max/min ratio. Our ``broad lines' database shows 167 lines with similar properties between 200 nm and 400 nm. Our results raise issues of the importance of such large variability in narrow bands and the difficulty of detection in measurements with spectral resolutions of 1 nm. 相似文献
179.
Tarter JC Backus PR Mancinelli RL Aurnou JM Backman DE Basri GS Boss AP Clarke A Deming D Doyle LR Feigelson ED Freund F Grinspoon DH Haberle RM Hauck SA Heath MJ Henry TJ Hollingsworth JL Joshi MM Kilston S Liu MC Meikle E Reid IN Rothschild LJ Scalo J Segura A Tang CM Tiedje JM Turnbull MC Walkowicz LM Weber AL Young RE 《Astrobiology》2007,7(1):30-65
Stable, hydrogen-burning, M dwarf stars make up about 75% of all stars in the Galaxy. They are extremely long-lived, and because they are much smaller in mass than the Sun (between 0.5 and 0.08 M(Sun)), their temperature and stellar luminosity are low and peaked in the red. We have re-examined what is known at present about the potential for a terrestrial planet forming within, or migrating into, the classic liquid-surface-water habitable zone close to an M dwarf star. Observations of protoplanetary disks suggest that planet-building materials are common around M dwarfs, but N-body simulations differ in their estimations of the likelihood of potentially habitable, wet planets that reside within their habitable zones, which are only about one-fifth to 1/50th of the width of that for a G star. Particularly in light of the claimed detection of the planets with masses as small as 5.5 and 7.5 M(Earth) orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone does not necessarily lead to atmospheric collapse, and active stellar flaring may not be as much of an evolutionarily disadvantageous factor as has previously been supposed. We conclude that M dwarf stars may indeed be viable hosts for planets on which the origin and evolution of life can occur. A number of planetary processes such as cessation of geothermal activity or thermal and nonthermal atmospheric loss processes may limit the duration of planetary habitability to periods far shorter than the extreme lifetime of the M dwarf star. Nevertheless, it makes sense to include M dwarf stars in programs that seek to find habitable worlds and evidence of life. This paper presents the summary conclusions of an interdisciplinary workshop (http://mstars.seti.org) sponsored by the NASA Astrobiology Institute and convened at the SETI Institute. 相似文献
180.