首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   57篇
  免费   0篇
航空   9篇
航天技术   17篇
航天   31篇
  2021年   1篇
  2018年   1篇
  2014年   1篇
  2012年   1篇
  2011年   6篇
  2010年   2篇
  2009年   1篇
  2008年   3篇
  2007年   2篇
  2006年   3篇
  2005年   1篇
  2004年   2篇
  2003年   3篇
  2002年   3篇
  2001年   3篇
  2000年   3篇
  1999年   1篇
  1998年   2篇
  1997年   1篇
  1994年   1篇
  1993年   1篇
  1992年   2篇
  1987年   4篇
  1986年   2篇
  1985年   2篇
  1984年   1篇
  1982年   1篇
  1980年   1篇
  1967年   1篇
  1965年   1篇
排序方式: 共有57条查询结果,搜索用时 0 毫秒
51.
52.
The International Heliophysical Year (IHY) aims to advance our understanding of the fundamental processes that govern the Sun, Earth, and heliosphere. The IHY Education and Outreach Program is dedicated to inspiring the next generation of space and Earth scientists as well as spreading the knowledge, beauty, and relevance of our solar system to the people of the world. In our Space Weather Monitor project we deploy a global network of sensors to high schools and universities to provide quantitative diagnostics of solar-induced ionospheric disturbances, thunderstorm intensity, and magnetospheric activity. We bring real scientific instruments and data in a cost-effective way to students throughout the world. Instruments meet the objectives of being sensitive enough to produce research-quality data, yet inexpensive enough for placement in high schools and universities. The instruments and data have been shown to be appropriate to, and usable by, high school age and early university students. Data contributed to the Stanford data center is openly shared and partnerships between groups in different nations develop naturally. Students and teachers have direct access to scientific expertise.  相似文献   
53.
There exists a population of defunct satellites in the geo-stationary arc that potentially pose a hazard to current and future operational satellites. These drifting, non-station-kept objects have a variety of ages and sizes, and many are trapped in libration orbits around the Earth?s two gravitational potential wells (the non-spherical nature of the Earth gives rise to two geo-potential wells or “stable points” that affect objects in geostationary and geosynchronous orbits), whereas others were boosted to higher altitudes into so-called “graveyard” orbits.  相似文献   
54.
The International Terrestrial Reference Frame (ITRF), as a realization of the International Terrestrial Reference System (ITRS), is represented by a set of station positions and linear velocities. They are intended to be used as regularized coordinates to which some corrections should be added to access instantaneous coordinates. The latest ITRS realization is the ITRF2005, which has integrated time series of station positions to form long-term solutions for the four space geodetic techniques. Currently, a purely linear model is used to parameterize station displacements in the estimation process, plus occasional discontinuities in case of earthquakes or equipment changes. However the input data have been derived without applying surface loading models and so surface loading effects are supposed to be embedded in the coordinates as measured quantities. We evaluate the effect of applying a posteriori loading corrections, which include the effect of atmospheric, non-tidal ocean, and continental water loading, to time series of positions estimated from Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Global Positioning System (GPS) data. We notice that they reduce about 50% or more of the annual signals in the translation and scale parameter time series of the SLR and VLBI techniques, except in SLR Z translation. In general, the estimated secular frame definition is negligibly affected and estimated positions and velocities are not significantly modified for stations that have accumulated a large number of observations. A multi-technique combination of such derived frames allows concluding that, for some cases, loading model corrections might degrade co-located station coordinates almost as much as they benefit them. However, most significant improvement of the estimated secular coordinates is observed for stations with less than 100 estimated positions as demonstrated with a multi-technique combination.  相似文献   
55.
56.
The following report presents the main conclusions of the sixth and seventh EOPOLE workshops, held in Hydra, Greece, 3–4 May and Leiden, the Netherlands, 3–5 July 2000, respectively. The objectives of the first workshop were to evaluate different approaches to pricing policy and to assess how new developments in Earth observation and information technology are having an impact on Earth observation data pricing policy. Those of the second were to assess the constraints that legal frameworks impose on Earth observation and to explore ways in which they can be used to its advantage.  相似文献   
57.
The US space programme continues to face difficulties in restructuring to meet existing political and fiscal conditions, in part because the basic structure and focus of the programme derive from the tensions of the Cold War. This paper argues that the world's new, more complicated political and economic conditions present a challenge for US policy makers that can be met with a renewed focus on the pursuit of science and the public good, within the context of international economic competition and political and scientific cooperation.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号