全文获取类型
| 收费全文 | 5163篇 |
| 免费 | 13篇 |
| 国内免费 | 20篇 |
专业分类
| 航空 | 2642篇 |
| 航天技术 | 1868篇 |
| 综合类 | 18篇 |
| 航天 | 668篇 |
出版年
| 2019年 | 29篇 |
| 2018年 | 53篇 |
| 2016年 | 30篇 |
| 2014年 | 89篇 |
| 2013年 | 112篇 |
| 2012年 | 102篇 |
| 2011年 | 162篇 |
| 2010年 | 119篇 |
| 2009年 | 187篇 |
| 2008年 | 263篇 |
| 2007年 | 124篇 |
| 2006年 | 109篇 |
| 2005年 | 135篇 |
| 2004年 | 134篇 |
| 2003年 | 166篇 |
| 2002年 | 92篇 |
| 2001年 | 159篇 |
| 2000年 | 89篇 |
| 1999年 | 133篇 |
| 1998年 | 156篇 |
| 1997年 | 105篇 |
| 1996年 | 141篇 |
| 1995年 | 177篇 |
| 1994年 | 155篇 |
| 1993年 | 106篇 |
| 1992年 | 148篇 |
| 1991年 | 69篇 |
| 1990年 | 62篇 |
| 1989年 | 141篇 |
| 1988年 | 56篇 |
| 1987年 | 51篇 |
| 1986年 | 59篇 |
| 1985年 | 189篇 |
| 1984年 | 143篇 |
| 1983年 | 108篇 |
| 1982年 | 124篇 |
| 1981年 | 176篇 |
| 1980年 | 60篇 |
| 1979年 | 62篇 |
| 1978年 | 50篇 |
| 1977年 | 40篇 |
| 1976年 | 37篇 |
| 1975年 | 64篇 |
| 1974年 | 40篇 |
| 1973年 | 40篇 |
| 1972年 | 48篇 |
| 1971年 | 30篇 |
| 1970年 | 32篇 |
| 1969年 | 39篇 |
| 1967年 | 31篇 |
排序方式： 共有5196条查询结果，搜索用时 15 毫秒
111.
J.C. Flandrin 《Acta Astronautica》1985,12(10):731-739
A novel statistical method has been devised for evaluating the ground and the sky coverage of an observation experiment on board a satellite. Owing to its unrivalled rapidity compared with other conventional calculation techniques, the method can be applied to evaluate the coverage percentages for the whole globe or any area on it, to calculate the visibility percentages for one or more ground stations and to determine the percentages of observation time of any given celestial direction including Sun, Moon, Earth and Ground Stations constraints. The orbits considered can be elliptical and account is taken of the drift due to the Earth's oblateness. 相似文献
112.
A formula is derived for interpolation between output samples of a fast Fourier transform (FFT), i.e., in the frequency domain. Such a formula is useful for obtaining greater frequency resolution when two coarse FFT outputs are available. Consideration is also given to the effect of such interpolation on a weighted FFT. 相似文献
113.
Koivo A.J. Kahne S.J. Koivo H.N. 《IEEE transactions on aerospace and electronic systems》1970,(3):306-312
The effect of bounded deterministic disturbances (external and/or internal) on a chosen performance index (PI) is investigated. Upper and lower bounds of the PI about a nominal value are determined by the application of the optimum control theory. A computational procedure is also proposed to determine an approximately optimal feedback controller for time-lag systems. Such a controller is designed here on the basis of min-max criteria. Numerical examples illustrate the proposed approach. 相似文献
114.
An implementation of the multidimensional modified LMS algorithm is provided from its relationship to a recently developed class of lhyperstable adaptive filters. 相似文献
115.
P. Willis J.C. Ries N.P. Zelensky L. Soudarin H. Fagard E.C. Pavlis F.G. Lemoine 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
For Precise Orbit Determination of altimetry missions, we have computed a data set of DORIS station coordinates defined for specific time intervals called DPOD2005. This terrestrial reference set is an extension of ITRF2005. However, it includes all new DORIS stations and is more reliable, as we disregard stations with large velocity formal errors as they could contaminate POD computations in the near future. About 1/4 of the station coordinates need to be defined as they do not appear in the original ITRF2005 realization. These results were verified with available DORIS and GPS results, as the integrity of DPOD2005 is almost as critical as its accuracy. Besides station coordinates and velocities, we also provide additional information such as periods for which DORIS data should be disregarded for specific DORIS stations, and epochs of coordinate and velocity discontinuities (related to either geophysical events, equipment problem or human intervention). The DPOD model was tested for orbit determination for TOPEX/Poseidon (T/P), Jason-1 and Jason-2. Test results show DPOD2005 offers improvement over the original ITRF2005, improvement that rapidly and significantly increases after 2005. Improvement is also significant for the early T/P cycles indicating improved station velocities in the DPOD2005 model and a more complete station set. Following 2005 the radial accuracy and centering of the ITRF2005-original orbits rapidly degrades due to station loss. 相似文献
116.
Yihua Zheng Anthony T.Y. Lui Mei-Ching Fok Brian J. Anderson Pontus C. Brandt Donald G. Mitchell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(8):1234-1242
One essential component of magnetosphere and ionosphere coupling is the closure of the ring current through Region 2 field-aligned current (FAC). Using the Comprehensive Ring Current Model (CRCM), which includes magnetosphere and ionosphere coupling by solving the kinetic equation of ring current particles and the closure of the electric currents between the two regions, we have investigated the effects of high latitude potential, ionospheric conductivity, plasma sheet density and different magnetic field models on the development of Region 2 field-aligned currents, and the relationship between R2 FACs and the ring current. It is shown that an increase in high latitude potential, ionospheric conductivity or plasma sheet density generally results in an increase in Region 2 FACs’ intensity, but R2 FACs display different local time and latitudinal distributions for changes in each parameter due to the different mechanisms involved. Our simulation results show that the magnetic field configuration of the inner magnetosphere is also an important factor in the development of Region 2 field-aligned current. More numerical experiments and observational results are needed in further our understanding of the complex relationship of the two current systems. 相似文献
117.
Jizhang Sang James C. Bennett Craig H. Smith 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
This paper presents a new method for estimating ballistic coefficients (BCs) of low perigee debris objects from their historical two line elements (TLEs). The method uses the drag perturbation equation of the semi-major axis of the orbit. For an object with perigee altitude below 700 km, the variation in the mean semi-major axis derived from the TLE is mainly caused by the atmospheric drag effect, and therefore is used as the source in the estimation of the ballistic coefficient. The method is tested using the GRACE satellites, and a number of debris objects with external ballistic coefficient values, and agreements of about 10% are achieved. 相似文献
118.
A. Galli P. Wurz H. Lammer H. I. M. Lichtenegger R. Lundin S. Barabash A. Grigoriev M. Holmström H. Gunell 《Space Science Reviews》2006,126(1-4):447-467
We have evaluated the Lyman-α limb emission from the exospheric hydrogen of Mars measured by the neutral particle detector of the ASPERA-3 instrument on Mars Express in 2004 at low solar activity (solar activity index = 42, F10.7=100). We derive estimates for the hydrogen exobase density, n H = 1010 m?3, and for the apparent temperature, T > 600 K. We conclude that the limb emission measurement is dominated by a hydrogen component that is considerably hotter than the bulk temperature at the exobase. The derived values for the exosphere density and temperature are compared with similar measurements done by the Mariner space probes in the 1969. The values found with Mars Express and Mariner data are brought in a broader context of exosphere models including the possibility of having two hydrogen components in the Martian exosphere. The present observation of the Martian hydrogen exosphere is the first one at high altitudes during low solar activity, and shows that for low solar activity exospheric densities are not higher than for high solar activity. 相似文献
119.
A process for the identification of emergency locator transmitter (ELT) signals related to search and rescue satellite-aided tracking (SARSAT) is presented. The ELT identification process is particularly important in order to increase the probability of detection and eliminate sources of interference from the data set. A set of ELT signal parameters is introduced and methods for estimating these parameters are developed. A theoretical analysis and performance evaluation of these methods is provided. 相似文献
120.