全文获取类型
收费全文 | 1044篇 |
免费 | 62篇 |
国内免费 | 14篇 |
专业分类
航空 | 106篇 |
航天技术 | 885篇 |
综合类 | 4篇 |
航天 | 125篇 |
出版年
2024年 | 1篇 |
2023年 | 30篇 |
2022年 | 9篇 |
2021年 | 57篇 |
2020年 | 31篇 |
2019年 | 33篇 |
2018年 | 37篇 |
2017年 | 8篇 |
2016年 | 9篇 |
2015年 | 12篇 |
2014年 | 75篇 |
2013年 | 60篇 |
2012年 | 56篇 |
2011年 | 79篇 |
2010年 | 66篇 |
2009年 | 88篇 |
2008年 | 89篇 |
2007年 | 47篇 |
2006年 | 22篇 |
2005年 | 70篇 |
2004年 | 25篇 |
2003年 | 10篇 |
2002年 | 16篇 |
2001年 | 18篇 |
2000年 | 19篇 |
1999年 | 12篇 |
1998年 | 23篇 |
1997年 | 22篇 |
1996年 | 9篇 |
1995年 | 12篇 |
1994年 | 28篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 9篇 |
1989年 | 3篇 |
1987年 | 1篇 |
排序方式: 共有1120条查询结果,搜索用时 724 毫秒
971.
Planetary protection is NASA's term for the practice of protecting solar system bodies from Earth life while protecting Earth from life that may be brought back from other solar system bodies. Spacefaring nations will soon begin retrieving samples from Mars and other solar system bodies. For these samples, planetary protection is in order, and measures are already in place to prevent the forward contamination of Mars and other bodies by Earth microbes and the backward contamination of Earth by possible extraterrestrial life. A major goal of planetary protection controls on forward contamination is to preserve the planetary record of natural processes by preventing human-caused microbial introductions. 相似文献
972.
B.M. Pilkerton M.R. Collier T.E. Moore 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,35(12):2152-2156
We report results of a statistical study correlating ionized solar wind (ISW) fluxes observed by ACE during late 2000 and throughout 2001 with neutral solar wind (NSW) fluxes observed by IMAGE/LENA over the same period. The average correlation coefficient between the neutral and ionized solar wind is 0.66 with correlations greater than 0.80 occurring about 29% of the time. Correlations appear to be driven by high solar wind flux variability, similar to results obtained by in situ multi-spacecraft correlation studies. In this study, however, IMAGE remains inside the magnetosphere on over 95% of its orbits. As a function of day of year, or equivalently ecliptic longitude, the slope of the relationship between the neutral solar wind flux and the ionized solar wind flux shows an enhancement near the upstream direction, but the symmetry point appears shifted toward higher ecliptic longitudes than the interstellar neutral (ISN) flow direction by about 20°. The estimated peak interstellar neutral upstream density inside of 1 AU is about 7 × 10−3 cm−3. 相似文献
973.
This brief report summarized the latest advances of the interplanetary physics research in China during the period of 2004-2005, made independently by Chinese space physicists and through international collaboration. The report covers all aspects of the interplanetary physics, including theoretical studies, numerical simulation and data analysis. 相似文献
974.
Yang Su W.Q. GanY.P. Li 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(6):988-991
Based on the light curves and images of RHESSI flares, we tried to make a preliminary classification of solar flares. Three basic types of flares seem to be existed: accordantly gradual flares, accordantly impulsive flares, and early impulsive flares. The proportion for each type is given. The possible physical meaning related to different types is discussed. 相似文献
975.
M. Fujimoto W. Baumjohann K. Kabin R. Nakamura J. A. Slavin N. Terada L. Zelenyi 《Space Science Reviews》2007,132(2-4):529-550
The small intrinsic magnetic field of Mercury together with its proximity to the Sun makes the Hermean magnetosphere unique in the context of comparative magnetosphere study. The basic framework of the Hermean magnetosphere is believed to be the same as that of Earth. However, there exist various differences which cause new and exciting effects not present at Earth to appear. These new effects may force a substantial correction of our naïve predictions concerning the magnetosphere of Mercury. Here, we outline the predictions based on our experience at Earth and what effects can drastically change this picture. The basic structure of the magnetosphere is likely to be understood by scaling the Earth’s case but its dynamic aspect is likely modified significantly by the smallness of the Hermean magnetosphere and the substantial presence of heavy ions coming from the planet’s surface. 相似文献
976.
V. V. Izmodenov 《Space Science Reviews》2007,130(1-4):377-387
Interstellar atoms penetrate deep into the heliosphere after passing through the heliospheric interface—the region of the
interaction of the solar wind with the interstellar medium. The heliospheric interface serves as a filter for the interstellar
atoms of hydrogen and oxygen, and, to a lesser extent, nitrogen, due to their coupling with interstellar and heliospheric
plasmas by charge exchange and electron impact ionization. The filtration has great importance for the determination of local
interstellar abundances of these elements, which becomes now possible due to measurements of interstellar pickup by Ulysses
and ACE, and anomalous cosmic rays by Voyagers, Ulysses, ACE, SAMPEX and Wind. The filtration of the different elements depends
on the level of their coupling with the plasma in the interaction region. The recent studies of the filtration of the interstellar
atoms in the heliospheric interface region is reviewed in this paper. The dependence of the filtration on the local interstellar
proton and H atom number densities is discussed and the roles of the charge exchange and electron impact ionization on the
filtration are evaluated. The influence of electron temperature in the inner heliosheath on the filtration process is discussed
as well. Using the filtration coefficients obtained from the modeling and SWICS/Ulysses pickup ion measurements, the local
interstellar abundances of the considered elements are determined. 相似文献
977.
Observations in the solar wind have revealed important insights into how energetic particles are accelerated in astrophysical
plasmas. In circumstances where stochastic acceleration is expected, a suprathermal tail on the distribution function is formed
with a common spectral shape: the spectrum is a power law in particle speed with a spectral index of −5. Recent theories for
this phenomenon, in which thermodynamic constraints are applied to explain the common spectral shape, are reviewed. As an
example of potential extensions of this theoretical work, consideration is given to the acceleration of Anomalous Cosmic Rays
in the heliosheath. 相似文献
978.
G. Murtaza S. IqbalM.A. Ameen A. Iqbal 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
We have used the technique of expansion in Empirical Orthogonal Functions (EOFs) to develop regional models of the critical frequencies of E and F2 layers (foE, foF2), peak height (hmF2), and semi-thickness of F2 layer (YmF2) over Pakistan. In the present study levels of solar activity specified by Smoothed Sunspot Number (R) from 10 to 200 are taken into account. The magnetic dip angle for the model ranges from 30° to 60°. We have compared the regional model and the International Reference Ionosphere (IRI) with measurements of three ionosondes in Pakistan. The model parameters foE and foF2 are found overall comparable to the observed hourly median values during daytime at Karachi (geographic latitude = 24.95°N, longitude = 67.13°E, magnetic inclination = 37°), Multan (30.18°N, 71.48°E, 45°) and Islamabad (33.75°N, 73.13°E, 51.5°) during the years 1988, 1996 and 2000. For hmF2 the computed values by regional and IRI model for the year 1995 are found close to each other. However, for YmF2the results are better during daytime as compared to nighttime. 相似文献
979.
980.
K. Issautier C. Perche S. Hoang C. Lacombe M. Maksimovic J.-L. Bougeret C. Salem 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,35(12):2141-2146
We present the solar wind plasma parameters obtained from the Wind spacecraft during more than nine years, encompassing almost the whole solar cycle 23. Since its launch in November 1994 Wind has frequently observed the in-ecliptic solar wind upstream of the Earth’s bow shock. The WIND/WAVES thermal noise receiver was specially designed to measure the in situ plasma thermal noise spectra, from which the electron density and temperature can be accurately determined. We present and discuss histograms of such measurements performed from 1994 to 2003. Using these large data sets, we study the density and core temperature variations with solar activity cycle and with different regimes of the solar wind. We confirm the anticorrelation of the electron density with the sunspot number, and obtain a positive correlation of the core temperature, with the sunspot number. 相似文献