全文获取类型
| 收费全文 | 289篇 |
| 免费 | 11篇 |
| 国内免费 | 3篇 |
专业分类
| 航空 | 150篇 |
| 航天技术 | 30篇 |
| 综合类 | 9篇 |
| 航天 | 114篇 |
出版年
| 2020年 | 1篇 |
| 2019年 | 1篇 |
| 2018年 | 1篇 |
| 2017年 | 2篇 |
| 2015年 | 1篇 |
| 2013年 | 1篇 |
| 2012年 | 4篇 |
| 2011年 | 3篇 |
| 2010年 | 1篇 |
| 2009年 | 7篇 |
| 2008年 | 2篇 |
| 2007年 | 7篇 |
| 2006年 | 4篇 |
| 2005年 | 13篇 |
| 2004年 | 13篇 |
| 2003年 | 11篇 |
| 2002年 | 4篇 |
| 2001年 | 10篇 |
| 2000年 | 8篇 |
| 1999年 | 6篇 |
| 1998年 | 21篇 |
| 1997年 | 13篇 |
| 1996年 | 15篇 |
| 1995年 | 20篇 |
| 1994年 | 13篇 |
| 1993年 | 2篇 |
| 1992年 | 2篇 |
| 1991年 | 7篇 |
| 1990年 | 5篇 |
| 1989年 | 5篇 |
| 1988年 | 13篇 |
| 1987年 | 10篇 |
| 1986年 | 5篇 |
| 1985年 | 14篇 |
| 1984年 | 10篇 |
| 1983年 | 16篇 |
| 1982年 | 12篇 |
| 1981年 | 5篇 |
| 1980年 | 6篇 |
| 1979年 | 3篇 |
| 1978年 | 2篇 |
| 1977年 | 1篇 |
| 1976年 | 1篇 |
| 1975年 | 1篇 |
| 1974年 | 1篇 |
排序方式： 共有303条查询结果，搜索用时 0 毫秒
101.
Horikawa DD Kunieda T Abe W Watanabe M Nakahara Y Yukuhiro F Sakashita T Hamada N Wada S Funayama T Katagiri C Kobayashi Y Higashi S Okuda T 《Astrobiology》2008,8(3):549-556
Studies on the ability of multicellular organisms to tolerate specific environmental extremes are relatively rare compared to those of unicellular microorganisms in extreme environments. Tardigrades are extremotolerant animals that can enter an ametabolic dry state called anhydrobiosis and have high tolerance to a variety of extreme environmental conditions, particularly while in anhydrobiosis. Although tardigrades have been expected to be a potential model animal for astrobiological studies due to their excellent anhydrobiotic and extremotolerant abilities, few studies of tolerance with cultured tardigrades have been reported, possibly due to the absence of a model species that can be easily maintained under rearing conditions. We report the successful rearing of the herbivorous tardigrade, Ramazzottius varieornatus, by supplying the green alga Chlorella vulgaris as food. The life span was 35 +/- 16.4 d, deposited eggs required 5.7 +/- 1.1 d to hatch, and animals began to deposit eggs 9 d after hatching. The reared individuals of this species had an anhydrobiotic capacity throughout their life cycle in egg, juvenile, and adult stages. Furthermore, the reared adults in an anhydrobiotic state were tolerant of temperatures of 90 degrees C and -196 degrees C, and exposure to 99.8% acetonitrile or irradiation with 4000 Gy (4)He ions. Based on their life history traits and tolerance to extreme stresses, R. varieornatus may be a suitable model for astrobiological studies of multicellular organisms. 相似文献
102.
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
103.
本文所述的飞行试验大纲的目的,是为了精确测量相干干扰机对雷达产生的干扰作用。这个资料可直接用来验证以往各种分析方法,并使ECM系统工作最佳化。飞行试验的主要试验部分包括:相干干扰系统、MORAD雷达、T-29B飞机以及数据采集用的仪器/支援设备。试验工作中大部分采用常用的方法,只有数据处理和分析才需要靠协作来完成,这是乔治亚理工学院与佛罗里达的爱格林空军基地的麻休科学实验室之间的分工,这主要是为了最有效地促进工作和有利于人员进行数据处理。 相似文献
104.
ＧＥＣ ＴｈｏｍｏｓｏｎＤＡＳＡ机载雷达联合体正在按照与法国国防部的合同执行欧洲机载多功能固态有源阵列雷达计划，旨在验证基于有源电扫描阵列的机载雷达系统的能力。 相似文献
105.
由于飞行测试数据采集和遥测系统引用了能提供动态控制能力的微型计算机,所以软件正日益成为机载数据系统的一个不可缺少的组成部分。通常,软件的重要性总是被机载系统的许多用户所低估,甚至迄今,他们还在担心能否把PCM数据循环图编程到电可编程序只读存储器(EPROM)并将它们插入机载硬件中去。由于较新的可编程序系统使用带有电可擦可编程序只读存储器(E~2PROM)和随机存储器(RAM)的微型计算机来提供实时工程单位(EU)显示和控制能力,因而机载软件就成为整个系统计划的一个中心环节。在这些数据采集系统中,实时数据显示和控制所提出的程序设计要求,使地面站的数据处理软件和飞机上的数据采集软件之间要有软件结构控制和一种软件(固件)连接变得非常重要。本文介绍飞行测试过程中新出现的这类问题的一种解决办法。 相似文献
106.
为达到国防部的综合高性能涡轮发动机技术计划(IHPTET)第一阶段的目标,普惠公司于1994年9月完成第一台全尺寸动力装置的试验。1994年9月进行的试验表明,该公司的XTE-65/2联合技术验证机(JTDE)已经达到并超过IH-PTET目标——推重比比现代先进技术发动机高出30％。 相似文献
107.
The ultrasonic bubble detection technique has been used as a versatile tool in the investigation of hypobaric decompression procedures for the last two decades. However, this method can only detect relatively large bubbles > 30-50 micrometers (usually in venous blood) and not the very first stages of bubble formation. Recently, the mechanical oscillator technique has been applied in air diving trials in order to detect small blood density changes due to hypothetical fluid shifts. However, sharp density drops were found in the decompression process, and these have been attributed to gas bubble formation. In this study, this method was applied together with Doppler controls to a series of altitude decompressions to 300 and 500 hPa, which represents the range of EVA operational pressures currently used or planned. Six subjects participated in both series; the oscillator sample tube could be pressurized. By the application of pressure on a blood sample containing questionable gas bubbles, these are reduced in volume, like in recompression therapy, and thus the density of the sample is increased. This effect has been shown in all 6 subjects undergoing decompression to 300 hPa, whereas in the 500 hPa series only 3 out of 6 subjects corresponded with gas phase formation immediately after decompression. Typically, Doppler bubbles appeared only after some latency time between 20 and 60 min; after this time, the density effect had nearly vanished. It is concluded that the mechanical oscillator technique represents a complementary research instrument to the Doppler method, because it is able to deliver a quantitative resolution of the early stage of gas phase formation. 相似文献
108.
麦道公司最近已经开始用一架在翼梢装有“响尾蛇”导弹的AV-8B飞机进行一系列的飞行试验工作。试验的目的在于论证该公司研究的一些先进的制造工具、生产技术和VSTOL飞行技术。麦道公司于去年成立了一个垂直/短距起飞和着陆(VSTOL)飞机研究与发展中心,其长期的工作任务是致力于美国JAST/ASTOVL飞机计划的研究,短期内的工作则侧重于对AV-8B进行各种改进的可行性研究。该中心于去年初发起了一个由公司投资进行的飞行试验计划,共分8个试验项目,于去年底完成的翼梢装“响尾蛇”导弹的AV-8B的飞行试验是其中一部分。整个计划的目的就是论证公司研究的各种先进生产、制造技术和VS-TOL新技术。 相似文献
109.
本文叙述了目前的NASA通信同(NASCOM)以及该网为所有NASA航天计划提供长途工作通信的发展过程。还介绍了为满足80年代NASA远程通信要求而正在实施的一些方案和技术。 相似文献
110.
本文介绍一种正在研制的自动 X 射线定向系统用于双旋转(即 SC 切)石英晶体片切角的精密测量。研制该系统的目的在于研制一种能够测量一般的φ/θ切角的原型机,其精度对于 SC 切在±10弧秒,对于 AT 切为±6秒,而对于其他切型为±30秒(在θ>0的体波零温度系数情况下)。测量速度至少每小时50片。假定这些晶片都被预切到正确定向的大约1/4°以内。经过选择的设计是设计一台在微计算机控制下的激光辅助的劳埃(Laue)衍射仪。采用劳埃法只要求晶片的运动有一个自由度,因而使设计较为灵活、开阔。 相似文献