全文获取类型
| 收费全文 | 6822篇 |
| 免费 | 16篇 |
| 国内免费 | 16篇 |
专业分类
| 航空 | 3590篇 |
| 航天技术 | 2194篇 |
| 综合类 | 190篇 |
| 航天 | 880篇 |
出版年
| 2021年 | 42篇 |
| 2018年 | 93篇 |
| 2017年 | 41篇 |
| 2016年 | 46篇 |
| 2014年 | 105篇 |
| 2013年 | 145篇 |
| 2012年 | 139篇 |
| 2011年 | 216篇 |
| 2010年 | 157篇 |
| 2009年 | 256篇 |
| 2008年 | 307篇 |
| 2007年 | 164篇 |
| 2006年 | 127篇 |
| 2005年 | 138篇 |
| 2004年 | 160篇 |
| 2003年 | 203篇 |
| 2002年 | 216篇 |
| 2001年 | 256篇 |
| 2000年 | 121篇 |
| 1999年 | 178篇 |
| 1998年 | 207篇 |
| 1997年 | 148篇 |
| 1996年 | 190篇 |
| 1995年 | 247篇 |
| 1994年 | 211篇 |
| 1993年 | 139篇 |
| 1992年 | 172篇 |
| 1991年 | 85篇 |
| 1990年 | 90篇 |
| 1989年 | 187篇 |
| 1988年 | 80篇 |
| 1987年 | 78篇 |
| 1986年 | 77篇 |
| 1985年 | 212篇 |
| 1984年 | 175篇 |
| 1983年 | 140篇 |
| 1982年 | 169篇 |
| 1981年 | 211篇 |
| 1980年 | 81篇 |
| 1979年 | 75篇 |
| 1978年 | 79篇 |
| 1977年 | 49篇 |
| 1976年 | 54篇 |
| 1975年 | 77篇 |
| 1974年 | 55篇 |
| 1973年 | 39篇 |
| 1972年 | 68篇 |
| 1971年 | 57篇 |
| 1970年 | 40篇 |
| 1969年 | 48篇 |
排序方式： 共有6854条查询结果，搜索用时 0 毫秒
851.
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
852.
For Space Transportation System (i.e. Space Shuttle) launched satellites destined for a Geosynchronous Earth Orbit (GEO), there is a need for cost-effective, versatile propulsion systems to provide the perigee burn, i.e. to boost the satellite from Low Earth Orbit (LEO) to Geosynchronous Transfer Orbit (GTO). Surveys of commercial spacecraft activities and future GEO satellite requirements indicate that a spacecraft propulsion system that will provide the perigee burn for a broad range of future commercial satellites would have an excellent market potential.Parametric studies to investigate and define attractive perigee-burn upper propulsion systems (i.e. an Upper Propulsion Stage, or a UPS) are presented. The feasibility and payload capacilities that could be provided by a UPS assembled from essentially off-the-shelf components and subsystems, and the benefits that could be achieved by using major subsystems specifically tailored for the application are presented. The results indicate that attractive UPS configurations can be defined using either off-the-shelf or optimized major subsystems. 相似文献
853.
Lehman D. Clark K. Cook B. Gavit S. Kayali S. McKinney J. Milkovich D. Reh K. Taylor R. Casani J. Griebel T. 《Aerospace and Electronic Systems Magazine, IEEE》2009,24(3):12-21
Congress authorized NASA's Prometheus Project in February 2003, with the first Prometheus mission slated to explore the icy moons of Jupiter. The project had two major objectives: 1) to develop a nuclear reactor that would provide unprecedented levels of power and show that it could be processed safely and operated reliably in space for long-duration, deep-space exploration; and 2) to explore the three icy moons of Jupiter - Callisto, Ganymede, and Europa - and return science data that would meet the scientific goals as set forth in the Decadal Survey Report of the National Academy of Sciences. Early in project planning, it was determined that the development of the Prometheus nuclear-powered spaceship would be complex and require the intellectual knowledge residing at numerous organizations across the country. In addition, because of the complex nature of the project and the multiple partners, approaches beyond those successfully used to manage a typical JPL project would be needed. This describes the key experiences in managing Prometheus, which should prove useful for future projects of similar scope and magnitude. 相似文献
854.
855.
R. Wickramatunga 《Space Policy》1991,7(1)
Parties to the Registration Convention are committed to providing the United Nations with certain information about objects they launch into space. This report describes the categories of information required, outlines the inadequacies of the present Register and suggests modifications. 相似文献
856.
Access to space-based remote sensing data is critical for Earth science and the study of global change. This article summarizes a variety of US government Earth science data policies and problems. The authors examine current efforts to develop data policies for the next generation of US remote sensing programmes, noting likely problems based on past experiences. They argue that the goal of US Earth science data policy should be to provide the widest possible dissemination of data. Setting such a goal permits the development of a simple, coherent data policy that serves scientific, commercial and US government interests. 相似文献
857.
858.
An experimental study of the turbulence generated by an enclosed, premixed, propane-air flame has been carried out in a combustion chamber of 25 × 20 cm cross section. Care was taken to reduce any effects of the axial pressure gradient. By suitable changes in the grid geometry, the turbulence intensity and scale of the approach flow were varied independently. The results of these experiments show that a strong link exists between the mechanisms of turbulent flame propagation and flame-generated turbulence. Thus three distinct regions may be identified, each having different characteristics in regard to the effects of turbulence scale on flame-generated turbulence. For each region, a physical mechanism for flame-generated turbulence is proposed. In particular, it is observed that over a wide range of intensity and scale of the approach turbulence, (a) the relative turbulence intensity in the flame zone varies in the range 1–2 times the relative turbulence intensity of the cold flow, (b) in the region of intermediate turbulence levels () the flame-generated turbulence intensity reaches a minimum value which is equal to the approach stream turbulence intensity, (c) the flame-generated turbulence intensity reaches a maximum value when the rate of production of turbulent vorticity is equal to about half its rate of viscous dissipation. 相似文献
859.
F. R. Cleminson 《Space Policy》1988,4(2):97-102
Verification of arms control treaties is essential to provide adequate international confidence in treaty compliance. This Viewpoint underlines the responsibility of non-superpower countries to become more closely involved in space surveillance of treaties to which they are parties. In Canada, Paxsat research has focused on two potential applications of space-based remote sensing to multi-lateral arms control verification. The necessary technology is readily available in non-superpower countries for the Paxsat concept to be put into operation. 相似文献
860.
Harris PR 《Space Policy》1989,5(2):147-154
Space exploration is now moving beyond the stage when technical development dominated research. As thinking shifts towards the problems of long-term colonization of the Solar System, the biological and behavioural sciences must make major contributions. This article outlines some of the issues which must be addressed, such as group behaviour and dynamics in space flight, the environment created at space stations and other outposts, recruitment and training of suitable spacefarers, and the planning and governing of space settlements. Ten dimensions of the human aspect of space habitation are described and an indication given of how they may form the basis for a new taxonomy of space planning, operations and management. 相似文献