全文获取类型
收费全文 | 723篇 |
免费 | 8篇 |
国内免费 | 8篇 |
专业分类
航空 | 337篇 |
航天技术 | 122篇 |
综合类 | 39篇 |
航天 | 241篇 |
出版年
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2016年 | 1篇 |
2014年 | 27篇 |
2013年 | 7篇 |
2012年 | 25篇 |
2011年 | 29篇 |
2010年 | 23篇 |
2009年 | 11篇 |
2008年 | 21篇 |
2007年 | 21篇 |
2006年 | 17篇 |
2005年 | 40篇 |
2004年 | 23篇 |
2003年 | 23篇 |
2002年 | 21篇 |
2001年 | 35篇 |
2000年 | 8篇 |
1999年 | 16篇 |
1998年 | 29篇 |
1997年 | 22篇 |
1996年 | 28篇 |
1995年 | 49篇 |
1994年 | 49篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 20篇 |
1986年 | 5篇 |
1985年 | 19篇 |
1984年 | 18篇 |
1983年 | 23篇 |
1982年 | 26篇 |
1981年 | 17篇 |
1980年 | 11篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1975年 | 3篇 |
排序方式: 共有739条查询结果,搜索用时 78 毫秒
121.
级间分离试验的目的是改善关于在收叠位置的可延伸喷管出口锥(以下简称“ENEC”)在级分离期间的受载情况予测。缩比的固体火箭试验发动机系统带有收叠的 ENEC 和模拟级间分离的试验设备。海平面实验数据由发动机的短时间静态点火中获得。试验测到的点火瞬变状态和初始条件被输入到计算机编码,以模拟级间分离影响,用于与试验数据进行比较。结果表明,级间段平均压力、发动机推力,以及两级的相对轴向位移相当接近。测量的级间压力峰值高于计算值10%,作用在 ENEC 内外表面上的最大平均压力差是5磅/英寸~2。在缩比的级间分离环境中,通过 ENEC 载荷和级间压力的明显波动,指出了与气体流动现象有关 ENCE重要的动态加载条件。 相似文献
122.
本文摘译自安全基金会(FSF)主席斯图亚特·马修斯的一篇报告。他从全球航空运输未来20年的发展角度阐述了航空安全所面临的压力以及应采取的对策 相似文献
123.
124.
Kirkpatrick AW Nicolaou S Rowan K Liu D Cunningham J Sargsyan AE Hamilton D Dulchavsky SA 《Acta Astronautica》2005,56(9-12):831-838
The recent interest in the use of ultrasound (US) to detect pneumothoraces after acute trauma in North America was initially driven by an operational space medicine concern. Astronauts aboard the International Space Station (ISS) are at risk for pneumothoraces, and US is the only potential medical imaging available. Pneumothoraces are common following trauma, and are a preventable cause of death, as most are treatable with relatively simple interventions. While pneumothoraces are optimally diagnosed clinically, they are more often inapparent even on supine chest radiographs (CXR) with recent series reporting a greater than 50% rate of occult pneumothoraces. In the course of basic scientific investigations in a conventional and parabolic flight laboratory, investigators familiarized themselves with the sonographic features of both pneumothoraces and normal pulmonary ventilation. By examining the visceral–parietal pleural interface (VPPI) with US, investigators became confident in diagnosing pneumothoraces. This knowledge was subsequently translated into practice at an American and a Canadian trauma center. The sonographic examination was found to be more accurate and sensitive than CXR (US 96% and 100% versus US 74% and 36%) in specific circumstances. Initial studies have also suggested that detecting the US features of pleural pulmonary ventilation in the left lung field may offer the ability to exclude serious endotracheal tube malpositions such as right mainstem and esophageal intubations. Applied thoracic US is an example of a clinically useful space medicine spin-off that is improving health care on earth. 相似文献
125.
Ellery A Ball AJ Cockell C Dickensheets D Edwards H Kolb C Lammer H Patel M Richter L 《Acta Astronautica》2005,56(3):397-407
We present a new European Mars mission proposal to build on the UK-led Beagle2 Mars mission and continue its astrobiology-focussed investigation of Mars. The small surface element to be delivered to the Martian surface--Vanguard--is designed to be carried by a Mars Express-type spacecraft bus to Mars and adopts a similar entry, descent and landing system as Beagle2. The surface element comprises a triad of robotic devices--a lander, a micro-rover of the Sojourner class for surface mobility, and three ground-penetrating moles mounted onto the rover for sub-surface penetration to 5 m depth. The major onboard instruments on the rover include a Raman spectrometer/imager, a laser plasma spectrometer, an infrared spectrometer--these laser instruments provide the basis for in situ "remote" sensing of the sub-surface Martian environment within a powerful scientific package. The moles carry the instruments' sensor head array to the sub-surface. The moles are thus required to undergo a one-way trip down the boreholes without the need for recovery of moles or samples, eliminating much of the robotic complexity invoked by such operations. 相似文献
126.
The assessment of personality is recognized by space agencies as an approach to identify candidates likely to perform optimally during spaceflights. In the use of personality scales for selection, the impact of social desirability (SD) has been cited as a concern. Study 1 addressed the impact of SD on responses to the Personality Characteristic Inventory(PCI) and NEO-FFI. This was achieved by contrasting scores from active astronauts (N=65) with scores of successful astronaut applicants (N=63), and between pilots applicants (N=1271) and pilot research subjects (N=120). Secondly, personality scores were correlated with scores on the Marlow Crown Social Desirability Scale among applicants to managerial positions (N=120). The results indicated that SD inflated scores on PCI scales assessing negative interpersonal characteristics, and impacted on four of five scales in NEO-FFI. Still, the effect sizes were small or moderate. Study 2 addressed performance implications of SD during an assessment of males applying to work as rescue personnel operations in the North Sea (N=22). The results showed that SD correlated negatively with cognitive test performance, and positively with discrepancy in performance ratings between self and two observers. In conclusion, caution is needed in interpreting personality scores in applicant populations. SD maybe a negative predictor for performance under stress. 相似文献
127.
128.
“双子座”航天飞机计划的核心目的是进一步完善轨道会合及对接技术,为登上月球可能会用到的月球轨道会合技术提供数据支持。1966年年底。这一技术难题已经被完美解决,可是后来的研究者已经忘了这项研究的最初目的。 相似文献
129.
传闻:选择阿姆斯特朗做“阿波罗11”登月宇航员,是因为他的平民身份。白宫更希望第一个登陆月球的是普通老百姓,而不是军人。
真相:阿姆斯特朗能成为“阿波罗11”号的指令长。是因为他的不断进步。以及他在“双子座”航天飞机及早期“阿波罗”飞行任务中的表现。没人知道,他在成为“阿波罗11”号机组成员之前需要完成多少任务。 相似文献
130.