全文获取类型
收费全文 | 1962篇 |
免费 | 594篇 |
国内免费 | 328篇 |
专业分类
航空 | 1562篇 |
航天技术 | 398篇 |
综合类 | 270篇 |
航天 | 654篇 |
出版年
2024年 | 16篇 |
2023年 | 42篇 |
2022年 | 123篇 |
2021年 | 133篇 |
2020年 | 94篇 |
2019年 | 97篇 |
2018年 | 116篇 |
2017年 | 117篇 |
2016年 | 99篇 |
2015年 | 109篇 |
2014年 | 124篇 |
2013年 | 129篇 |
2012年 | 145篇 |
2011年 | 162篇 |
2010年 | 165篇 |
2009年 | 153篇 |
2008年 | 157篇 |
2007年 | 132篇 |
2006年 | 150篇 |
2005年 | 108篇 |
2004年 | 75篇 |
2003年 | 46篇 |
2002年 | 36篇 |
2001年 | 40篇 |
2000年 | 51篇 |
1999年 | 69篇 |
1998年 | 33篇 |
1997年 | 26篇 |
1996年 | 24篇 |
1995年 | 26篇 |
1994年 | 23篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 1篇 |
排序方式: 共有2884条查询结果,搜索用时 15 毫秒
31.
介绍了飞航式导弹主要动力装置的弹用涡喷、涡扇发动机的发展概况,包括发展历史、特点、技术现状,并论述了发展趋势。 相似文献
32.
为提高模用锌合金ZA4-3的性能,扩大其应用范围,本项工作采用流变铸造法成功地制备了性能稳定的Al2O3P/ZA4-3复合材料。对该材料进行了弯曲强度、冲击韧性、压缩强度、硬度及耐磨性等性能试验,结果表明:Al2O3p的加入,使锌合金的压缩强度、室温和高温硬度以及耐磨性明显提高,其弯曲强度略有降低,而其冲击韧性下降了 。最后还讨论了成形工艺参数、颗粒含量和颗粒直径对该复合材料性能的影响。 相似文献
33.
危害性分析中的模糊数学方法 总被引:3,自引:0,他引:3
利用模糊集合理论对影响故障模式危害性的各因素进行了模糊化处理,建立了故障模式危害性评定的模糊评判模型,并阐述了模糊评判方法的基本步骤。 相似文献
34.
On 14 October 1999, the Chinese-Brazil earth resource satellite (CBERS-1) was launched in China. On board of the satellite there was an instrument designed at Peking University to detect the energetic particle radiation inside the satellite so the radiation fluxes of energetic particles in the cabin can be monitored continuously. Inside a satellite cabin, radiation environment consists of ether penetrated energetic particles or secondary radiation from satellite materials due to the interactions with primary cosmic rays.Purpose of the detectors are twofold, to monitor the particle radiation in the cabin and also to study the space radiation environment The data can be used to study the radiation environment and their effects on the electronics inside the satelhte cabin. On the other hand, the data are useful in study of geo-space energetic particle events such as solar proton events, particle precipitation and variations of the radiation belt since there should be some correlation between the radiation situation inside and outside the satellite.The instrument consists of two semi-conductor detectors for protons and electrons respectively. Each detector has two channels of energy ranges. They are 0.5-2MeV and ≥2MeV for electrons and 5-30MeV and 30-60MeV for protons. Counting rate for all channels are up to 104/(cm2@s)and power consumption is about 2.5 W. There are also the additional functions of CMOS TID (total integrated dose) effect and direct SEU monitoring. The data of CBMC was first sent back on Oct. 17 1999 and it's almost three years from then on. The detector has been working normally and the quality of data is good.The preliminary results of data analysis of CBMC not only reveal the effects of polar particle precipitation and radiation belt on radiation environment inside a satellite, but also show some important features of the geo-space energetic particle radiation.As one of the most important parameters of space weather, the energetic charged particles have great influences on space activities and ground tech nology. CBMC is perhaps the first long-term on-board special equipment to monitor the energetic particle radiation environment inside the satellite and the data it accnmulated are very useful in both satellite designing and space research. 相似文献
35.
36.
37.
38.