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   15篇
  免费   0篇
航空   2篇
航天技术   3篇
航天   10篇
  2021年   1篇
  2014年   1篇
  2012年   1篇
  2011年   2篇
  2010年   1篇
  2008年   1篇
  2007年   1篇
  2005年   1篇
  2004年   1篇
  2003年   1篇
  2002年   1篇
  2001年   2篇
  1999年   1篇
排序方式: 共有15条查询结果,搜索用时 15 毫秒
11.
Waltham D 《Astrobiology》2004,4(4):460-468
This paper investigates whether anthropic selection explains the unusually large size of our Moon. It is shown that obliquity stability of the Earth is possible across a wide range of different starting conditions for the Earth-Moon system. However, the lunar mass and angular momentum from the actual Earth-Moon system are remarkable in that they very nearly produce an unstable obliquity. This may be because the particular properties of our Earth-Moon system simultaneously allow a stable obliquity and a slow rotation rate. A slow rotation rate may have been anthropically selected because it minimizes the equator-pole temperature difference, thus minimizing climatic fluctuations. The great merit of this idea is that it can be tested using extrasolar planet search programs planned for the near future. If correct, such anthropic selection predicts that most extrasolar planetary systems will have significantly larger perturbation frequencies than our own Solar System.  相似文献   
12.
This experiment was conducted as part of a risk mitigation payload aboard the Space Shuttle Atlantis on STS-101. The objectives were to test a newly developed water delivery system, and to determine the optimal combination of water volume and substrate for the imbibition and germination of flax (Linum usitatissimum) seeds in space. Two different combinations of germination paper were tested for their ability to absorb, distribute, and retain water in microgravity. A single layer of thick germination paper was compared with one layer of thin germination paper under a layer of thick paper. Paper strips were cut to fit snugly into seed cassettes, and seeds were glued to them with the micropyle ends pointing outward. Water was delivered in small increments that traveled through the paper via capillary action. Three water delivery volumes were tested, with the largest (480 microliters) outperforming the 400 microliters and 320 microliters volumes for percent germination (90.6%) and root growth (mean=4.1 mm) during the 34-hour spaceflight experiment. The ground control experiment yielded similar results, but with lower rates of germination (84.4%) and shorter root lengths (mean=2.8 mm). It is not clear if the roots emerged more quickly in microgravity and/or grew faster than the ground controls. The single layer of thick germination paper generally exhibited better overall growth than the two layered option. Significant seed position effects were observed in both the flight and ground control experiments. Overall, the design of the water delivery system, seed cassettes and the germination paper strip concept was validated as an effective method for promoting seed germination and root growth under microgravity conditions.  相似文献   
13.
Dave Wright   《Space Policy》2007,23(3):180-181
The conference began with The Charles Martin Lecture, given this year by George Abbey, formerly Director of the NASA Johnson Spaceflight Center. George spoke of the significant contribution of British scientists and engineers to the early days of NASA. He was followed by an ebullient tour d’horizon from the admirable Dr David Southwood, Head of Science at ESA. Lucie Green from Mullard Space Science Laboratory (MSSL), who is leading the outreach component of the International Heliophysical Year, then brought the first session to a close. The conference then split into three parallels.  相似文献   
14.
The UK government appears to be taking space more seriously, even if funding for the sector remains limited. Speeches and attendees at the conference confirm this trend, with a particular emphasis on innovation and a general sense that prospects for the UK space industry are good. The various themes and highlights of the conference are discussed.  相似文献   
15.
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