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221.
222.
未来的地球—轨道运载工具应能在作出决定后的几小时、甚至几分钟内发射.这种运载工具的研究工作已经开始.在第一阶段的研究中,设计出了11种能将2.27t载荷送入极轨道的运载工具,并验证了设计参数的变化(增加轨道机动飞行动作、增加载荷重量等).根据第一阶段研究结果,第二阶段的设计工作选择了两种方案,即垂直起飞的两级系统和水平起飞的两级系统.给出了几种推进方式的评估结果,包括起飞时的推重比效果、水平起飞的双燃料推进方案和使用氟的效果等. 相似文献
223.
当前,全世界的制造厂商已意识到他们自己正处于十字路口。为了有效地进行竞争,公司必须努力地以异常低的成本生产出先进的产品,并确保产品的高质量,以及向顾客提供出色的服务。同时他们还必须以极大的灵活性来应付产品短促的寿命周期,以及来自国外的日益增大的竞争。 相似文献
224.
去年11月,美空军正式透露了两种可逃避雷达监测的秘密的隐身飞机。一种隐身飞机是由诺思罗普公司和波音公司联合研制的B-2先进技术轰炸机,在加州棕榈谷工厂首次公开展出并进行了初期试验。另一种隐身飞机命名为F-117A战斗机,现已被空军所证实,展示了飞机照片,并进行了简要的新闻发布会。这种似蝙蝠的短而粗的喷气式飞机是由洛克希德公司制造的,自1983年起已陆续交付使用,目前在内华达州的内利斯空军基地共部署了52架。五角大楼之所以公开F-117A飞机的秘密;主要是因为该机要进行更广泛的日间飞行。 相似文献
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Aldrin A Amara A Aris L Baierl N Beatty P Beaulieu C Behnke T Castegini R Chauhan A Cojanis P Dayawansa P Diop M Eito K Engle S Feretti S Gassama H Genova B Goulding C Janjua J Jansaeng T Jousset F Kopik A Laurin C Leggatt J Li H Mezzadri M Miura A Nolet S Ogami S Patry J Patten L Payerne C Peer G Prampolini M Rheaume C Saary J Spehar D Sufi A Sun B Thompson JB Thomson W Trautner R Tursunmuratov M Venet V Wilems E Wilson H Wittwer K Wokke F Wu Y Zhou S Zilioli I 《Acta Astronautica》2002,51(1-9):637-646
Issues about commercialization of space have been a growing concern in the past decade for the space community. This paper focuses on the work from a team of 51 students attending the Summer Session Program of the International Space University in Bremen, Germany. CASH 2021 (Commercial Access and Space Habitation) documents a plan that identifies commercial opportunities for space utilization that will extend human presence in space, and will chart the way forward for the next 20 years. The group selected four commercial sectors that show the most promise for the future: tourism, entertainment, space system service, assembly and debris removal, and research and development/production. The content of this document presents the results of their research. Historical activities in each of the commercial sectors are reviewed along with the current market situation. To provide a coherent background for future commercialization possibilities a scenario has been developed. This scenario includes a postulated upon ideal future and includes social, political and economic factors that may affect the space industry over the timeline of the study. The study also presents a roadmap, within the limited optimistic scenario developed, for the successful commercialization of space leading to future human presence in space. A broad range of commercially viable opportunities, not only within the current limits of the International Space Station, but also among the many new developments that are expected by 2021 are discussed. 相似文献
227.
本文从理论上阐明了为什么能够用四个已知阻抗的终端来校准六端口反射计,以测量其它终端未知阻抗的原理。求出校准常数的公式是严格的,但是非线性的,需要迭代解。文申介绍了关于六端口反射计利用这些常数来计算被测终端阻抗的几种方法。 相似文献
228.
Astronauts are often required to work in shift schedules. To test pre-mission adaptation strategies and effects on the circadian system, a study was performed using microgravity simulation by head-down bedrest. Eight male subjects were studied over 4 control days, and 7 days each for pre-mission adaptation, bedrest, and readjustment. The circadian system was assessed by monitoring ECG and temperature, and by collecting urine for determination of hormones and electrolytes. Rhythms did not achieve complete adjustment within the adaptation period when the sleep-wake cycle was shortened by 1 h/day, but resynchronization continued during bedrest. After the bedrest period when the time shift was reversed by a 7-h delay within 2 days, resynchronization was achieved satisfactorily only within 7 days. From the results it is concluded that a sleep-wake cycle advance as used in this study is insufficient to keep the circadian system in pace. Under operational conditions the circadian system of astronauts may become longer and more destabilized than under controlled laboratory conditions. 相似文献
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Gorbushina A 《Astrobiology》2003,3(3):543-554
So far mainly spores or other "differentiated-for-survival" structures were considered to be resistant against extreme environmental constraints (including extraterrestrial challenges). Microcolonial fungi (MCF) are unique growth structures formed by eukaryotic microorganisms inhabiting rock varnish surfaces in terrestrial deserts. They are here proposed as a new object for exobiological study. Sun-exposed desert rocks provide surface habitats with intense solar radiation, a scarce water supply, drastic changes in temperature, and episodic to sporadic availability of nutrients. These challenging conditions reduce the diversity of life to MCF, whose resistance to desiccation and tolerance for ultraviolet (UV) radiation make them survival specialists. Based upon our studies of MCF, we propose that the following mechanisms are universally employed for survival on rock surfaces: (1) compact tissue-like colony organization formed by thermodynamically optimal round cells embedded in extracellular polymeric substances, (2) the presence of several types of UV-absorbing compounds (melanins and mycosporines) and antioxidants (carotenoids, melanins, and mycosporines) that convey multiple stress resistance to desiccation, temperature, and irradiation changes, and (3) intracellular developmental mechanisms typical for these structures. 相似文献