全文获取类型
收费全文 | 6074篇 |
免费 | 93篇 |
国内免费 | 112篇 |
专业分类
航空 | 2873篇 |
航天技术 | 2247篇 |
综合类 | 41篇 |
航天 | 1118篇 |
出版年
2022年 | 41篇 |
2021年 | 83篇 |
2019年 | 56篇 |
2018年 | 139篇 |
2017年 | 104篇 |
2016年 | 85篇 |
2015年 | 47篇 |
2014年 | 144篇 |
2013年 | 181篇 |
2012年 | 177篇 |
2011年 | 244篇 |
2010年 | 177篇 |
2009年 | 288篇 |
2008年 | 334篇 |
2007年 | 184篇 |
2006年 | 166篇 |
2005年 | 191篇 |
2004年 | 196篇 |
2003年 | 212篇 |
2002年 | 136篇 |
2001年 | 189篇 |
2000年 | 138篇 |
1999年 | 154篇 |
1998年 | 180篇 |
1997年 | 134篇 |
1996年 | 161篇 |
1995年 | 200篇 |
1994年 | 181篇 |
1993年 | 100篇 |
1992年 | 148篇 |
1991年 | 53篇 |
1990年 | 57篇 |
1989年 | 130篇 |
1988年 | 44篇 |
1987年 | 42篇 |
1986年 | 58篇 |
1985年 | 173篇 |
1984年 | 133篇 |
1983年 | 106篇 |
1982年 | 132篇 |
1981年 | 156篇 |
1980年 | 45篇 |
1979年 | 31篇 |
1978年 | 37篇 |
1977年 | 36篇 |
1976年 | 29篇 |
1975年 | 26篇 |
1974年 | 34篇 |
1970年 | 28篇 |
1969年 | 25篇 |
排序方式: 共有6279条查询结果,搜索用时 671 毫秒
491.
492.
The results of the comprehensive numerical analysis for dynamics of intrachamber processes that appear at nozzleless solid propellant rocket engine (SPRE) actuation are presented. A complete cycle of rocket engine operation is analyzed. We solve a conjugate problem involving the igniter actuation; heating, ignition and following combustion of a solid propellant charge; a combustion product flow in the combustion chamber; depressurization of the combustion chamber, and the subsequent motion of the rocket engine blank; variation of the combustion surface geometry at the expense of the gradual and nonuniform burnout of solid propellant web. 相似文献
493.
Epocast 50-A1/946 epoxy was primarily developed for joining and repairing of composite aircraft structural components. The objective of the present work is to modify the Epocast epoxy resin by different nanofillers infusion. The used nanofillers include multi-walled carbon nanotubes(MWCNTs), SiC and Al2O3 nanoparticles. The nanofillers with different weight percentages are ultrasonically dispersed in the epoxy resin. The sonication time and amplitude for MWCNTs are reduced compared to Al2O3 and SiC nanoparticles to avoid the damage of MWCNTs during sonication processes. The fabricated neat epoxy and twelve nanocomposite panels were characterized via standard tension and in-plane shear tests. The experimental results show that the nanocomposites materials with 0.5wt% MWCNTs, 1.5wt% SiC and 1.5wt% Al2O3 nanoparticles have the highest improvement in the tensile properties compared to the other nanofiller loading percentages.The improvements in the shear properties of these nanocomposite materials were respectively equal to 5.5%, 4.9%, and 6.3% for shear strengths, and 10.3%, 16.0%, and 8.1% for shear moduli. The optimum nanofiller loading percentages will be used in the following papers concerning their effect on the bonded joints/repairs of carbon fiber reinforced composites. 相似文献
494.
对比了MRTD(最小可分辨温差)和TOD(三角形方向辨别)法在测试图样、观察任务、测试规程、结果处理、判断准则上的不同。通过对采样作用、动态响应、客观测量3个方面的分析,得出了TOD法在测试性能上的优势,引用国外相关单位的试验结果,说明了TOD测试的适用性。 相似文献
495.
496.
497.
Determination of the Microacceleration Quasisteady Component onboard the International Space Station
Babkin E. V. Belyaev M. Yu. Efimov N. I. Sazonov V. V. Stazhkov V. M. 《Cosmic Research》2004,42(2):155-164
A comparison of two methods of determination of the microacceleration quasisteady component arising onboard the International Space Station was performed. In the first method the acceleration was calculated using the relative motion of the station reconstructed on the basis of telemetry data. The second method was a direct measurement of the microacceleration by a low-frequency accelerometer and a smoothing of the data obtained. The used measurements were made by the American accelerometer MAMS. The above comparison can theoretically be used to refine the position of the station center of mass relative to its body. 相似文献
498.
499.
500.
John M. Logsdon 《Space Policy》1987,3(2)
This response to Alex Roland's article, ‘Priorities in space for the USA’, argues that his analysis and conclusions are based on shaky historical evidence. Professor Roland's interpretation of NASA's priorities since 1959 is challenged, and it is pointed out that the manned spaceflight programme has widespread support in the USA. The most important issue, raised by the article but not treated extensively enough, is whether the pursuit of the widely accepted emphasis on manned spaceflight is a large-scale societal mistake. 相似文献