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   107篇
  免费   0篇
航空   60篇
航天技术   34篇
综合类   1篇
航天   12篇
  2021年   2篇
  2018年   2篇
  2017年   1篇
  2016年   2篇
  2014年   4篇
  2013年   3篇
  2012年   1篇
  2011年   8篇
  2010年   5篇
  2009年   4篇
  2008年   4篇
  2007年   1篇
  2005年   10篇
  2004年   3篇
  2002年   2篇
  2001年   2篇
  2000年   1篇
  1999年   6篇
  1998年   1篇
  1997年   3篇
  1995年   2篇
  1994年   2篇
  1993年   1篇
  1991年   1篇
  1989年   6篇
  1984年   6篇
  1983年   3篇
  1982年   2篇
  1981年   1篇
  1980年   2篇
  1978年   4篇
  1976年   2篇
  1975年   1篇
  1973年   1篇
  1972年   1篇
  1971年   2篇
  1968年   4篇
  1967年   1篇
排序方式: 共有107条查询结果,搜索用时 15 毫秒
51.
NASA's advanced life support technologies are being combined with Arctic science and engineering knowledge in the Advanced Life Systems for Extreme Environments (ALSEE) project. This project addresses treatment and reduction of waste, purification and recycling of water, and production of food in remote communities of Alaska. The project focus is a major issue in the state of Alaska and other areas of the Circumpolar North; the health and welfare of people, their lives and the subsistence lifestyle in remote communities, care for the environment, and economic opportunity through technology transfer. The challenge is to implement the technologies in a manner compatible with the social and economic structures of native communities, the state, and the commercial sector. NASA goals are technology selection, system design and methods development of regenerative life support systems for planetary and Lunar bases and other space exploration missions. The ALSEE project will provide similar advanced technologies to address the multiple problems facing the remote communities of Alaska and provide an extreme environment testbed for future space applications. These technologies have never been assembled for this purpose. They offer an integrated approach to solving pressing problems in remote communities.  相似文献   
52.
A Continuous Flow Electrophoresis System (CFES) was used on Space Shuttle flight STS-8 to separate specific secretory cells from suspensions of cultured primary human embryonic kidney cells and rat pituitary cells. The objectives were to isolate the subfractions of kidney cells that produce the largest amounts of urokinase (plasminogen activator), and to isolate the subfractions of rat pituitary cells that secrete growth hormone, prolactin, and other hormones. Kidney cells were separated into more than 32 fractions in each of two electrophoretic runs. Electrophoretic mobility distributions in flight experiments were spread more than the ground controls. Multiple assay methods confirmed that all cultured kidney cell fractions produced some urokinase, and five to six fractions produced significantly more urokinase than the other fractions. Several fractions also produced tissue plasminogen activator. The pituitary cells were separated into 48 fractions in each of the two electrophoretic runs, and the amounts of growth hormone (GH) and prolactin (PRL) released into the medium for each cell fraction were determined. Cell fractions were grouped into eight mobility classes and immunocytochemically assayed for the presence of GH, PRL, ACTH, LH, TSH, and FSH. The patterns of hormone distribution indicate that the specialized cells producing GH and PRL are isolatable due to the differences in electrophoretic mobilities.  相似文献   
53.
AY Vulpeculae     
  相似文献   
54.
    
During the pre-launch phase of NASA’s THEMIS mission, the Education and Public Outreach (E/PO) program successfully brought the excitement of THEMIS to the public, students and teachers through a variety of programs. The Geomagnetic Event Observation Network by Students (GEONS) was the main effort during this time, a project in which 13 magnetometers were placed in or near 13 rural schools across the country. High school teachers and a few middle school teachers at these and/or neighboring schools took part in a long-term professional development program based around space science and the magnetometer data. The teachers created week-long to semester-long projects during which their students worked on THEMIS lessons that they, their colleagues, and the E/PO team created. In addition to this program, THEMIS E/PO also launched the only Lawrence Hall of Science (LHS) Great Explorations in Mathematics and Science (GEMS) site in Nevada. This site provides a sustainable place for teacher professional development using hands-on GEMS activities, and has been used by teachers around the state of Nevada. Short-term professional development for K-12 teachers (one-hour to two-day workshops), with a focus on the Tribal College and Society for the Advancement of Chicanos and Native Americans in Science (SACNAS) communities have reached hundreds of teachers across the country. A Space Telescope Science Institute (STScI) ViewSpace show on auroras and THEMIS was created and distributed, and shown in over a hundred science centers and museums nationwide. The THEMIS E/PO program developed and maintained a THEMIS E/PO Website for dissemination of (1) information and multimedia about the science and engineering of THEMIS, (2) updated news about the mission in language appropriate for the public, (3) the GEONS data, the GEONS teacher guides with classroom activities, and (4) information about the THEMIS E/PO program. Hundreds of thousands of visitors have viewed this website. In this paper, we describe these programs along with the evaluation results, and discuss what lessons we learned along the way.  相似文献   
55.
Primitive photosynthetic microorganisms, either dormant or dead, may remain today on the martian surface, akin to terrestrial cyanobacteria surviving endolithically in martian analog sites on Earth such as the Antarctic Dry Valleys and the Atacama Desert. Potential markers of martian photoautotrophs include the red edge of chlorophyll reflectance spectra or fluorescence emission from systems of light-harvesting pigments. Such biosignatures, however, would be modified and degraded by long-term exposure to ionizing radiation from the unshielded cosmic ray flux onto the martian surface. In this initial study into this issue, three analytical techniques--absorbance, reflectance, and fluorescence spectroscopy--were employed to determine the progression of the radiolytic destruction of cyanobacteria. The pattern of signal loss for chlorophyll reflection and fluorescence from several biomolecules is characterized and quantified after increasing exposures to ionizing gamma radiation. This allows estimation of the degradation rates of cyanobacterial biosignatures on the martian surface and the identification of promising detectable fluorescent break-down products.  相似文献   
56.
57.
58.
After one year of operation the GEOS-1 Ion Composition Experiment has surveyed plasma composition at all local times in the L range 3 8 and the energy per charge range from thermal to 16 keV/e. From measurements made in the keV range during eleven magnetic storms we find that the percentage of heavy (M/Q > 1) ions present in the outer magnetosphere increases by a factor of 3 to 10 during disturbances. We conclude that two independent sources (solar wind, characterized by 4He2+, and ionosphere, characterized by O+) give on the average comparable contributions to injected populations, although in a single event one or the other source may dominate. However, in magnetically quiet periods protons are the dominant species with a few percent of heavy ions. With the help of special satellite manoeuvres magnetic field aligned fluxes of 0.05-3 keV/e H+, He+, O+ with traces of O2+ have been observed which may be related to ion beams found previously at lower altitudes in the auroral zone. At still lower energies ( 1 eV/e) the thermal plasma population is found to be made up of six ion species, three of which, D+, He2+ and O2+, were unknown in the magnetosphere prior to the GEOS-1 measurements. We present here a study of the evolution of doubly charged ions and their parent populations over four consecutive days. Various production mechanisms for doubly charged ions are discussed. We argue that ionization of singly charged ions by UV and energetic electrons and protons is the dominant process for plasmasphere production. Furthermore, the observed high concentrations of O2+ at high altitudes are a result of production in the upper ionosphere and plasmasphere combined with upward transport by thermal diffusion. Throughout the 1 year lifetime of GEOS-1 the ICE functioned perfectly and, because of its novel design, a short review of technical performance is included here.  相似文献   
59.
60.
Two new polyphase pulse compression codes and efficient digital implementation techniques are presented that are very Doppler tolerant and that can provide large pulse compression ratios. One of these codes is tolerant of precompression bandwidth limitations.  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