全文获取类型
收费全文 | 8937篇 |
免费 | 1486篇 |
国内免费 | 1165篇 |
专业分类
航空 | 7018篇 |
航天技术 | 1543篇 |
综合类 | 912篇 |
航天 | 2115篇 |
出版年
2024年 | 50篇 |
2023年 | 137篇 |
2022年 | 199篇 |
2021年 | 280篇 |
2020年 | 293篇 |
2019年 | 294篇 |
2018年 | 297篇 |
2017年 | 338篇 |
2016年 | 438篇 |
2015年 | 385篇 |
2014年 | 492篇 |
2013年 | 453篇 |
2012年 | 593篇 |
2011年 | 601篇 |
2010年 | 449篇 |
2009年 | 438篇 |
2008年 | 664篇 |
2007年 | 812篇 |
2006年 | 658篇 |
2005年 | 598篇 |
2004年 | 503篇 |
2003年 | 446篇 |
2002年 | 298篇 |
2001年 | 258篇 |
2000年 | 221篇 |
1999年 | 210篇 |
1998年 | 193篇 |
1997年 | 162篇 |
1996年 | 102篇 |
1995年 | 119篇 |
1994年 | 96篇 |
1993年 | 99篇 |
1992年 | 97篇 |
1991年 | 97篇 |
1990年 | 80篇 |
1989年 | 55篇 |
1988年 | 56篇 |
1987年 | 21篇 |
1986年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 990 毫秒
271.
272.
273.
274.
275.
276.
喷油螺钉是某型航空活塞式发动机曲轴组合中的重要零件,单纯采用超声波清洗难以清除该零件内部积炭。结合生产实践对工艺进行改良,使该零件修理后的抽检合格率由20%提升至70%,缩短了发动机的翻修时间,节约了维修成本。 相似文献
277.
278.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2020,65(11):2507-2514
The effect of the rocket exhaust products on the D-region of the ionosphere is investigated with the help of Very low frequency (VLF) electromagnetic wave propagation characteristics within the Earth-ionosphere waveguide. The changes in the electron density profile are computed from the observed VLF signal amplitude perturbations about 3 dB during the rocket launch. We find a localized electron depletion in the lower ionosphere at an altitude of around 58 km, that is thought to be originated by the attachment of ionospheric ion and molecular hydrogen along with water molecule in the exhaust product of first stage burn of Geosynchronous Launch Vehicle (GSLV) rocket at the time of GSLV launched from Sriharikota, India, on 27 August 2015 at 11:22 UT (16:52 IST). The ionospheric depletion perturbed the navigational VLF signal (VTX = 17 kHz) 134 s after the launch of the GSLV rocket. 相似文献
279.
280.
Electromechanical actuators (EMAs) are becoming increasingly attractive in the field of more electric aircraft because of their outstanding benefits, which include reduced fuel burn and maintenance cost, enhanced system flexibility, and improved management of fault detection and isolation. However, electromechanical actuation raises specific issues when being used for safety-critical aerospace applications like flight controls: huge reflected inertia to load, jamming-type failure, and increase of backlash with service due to wear and local dissipation of heat losses for thermal balance. This study proposes an incremental approach for virtual prototyping of EMAs. It is driven by a model-based system engineering process in order to enable simulation-aided design. Best practices supported by Bond graph formalism are suggested to develop a model’s structure efficiently and to make the model ready for use (or extension) by addressing the above mentioned issues. Physical effects are progressively introduced, and the realism of lumped-parameter models is increased step-by-step. In particular, multi-level component models are architected to ensure continuity between engineering activities. The models are implemented in the AMESim simulation environment, and simulation responses are given to illustrate how they can be used for preliminary sizing, control design, thermal balance verification, and faults to failure analysis. The proposed best practices intend to provide engineers with fast, reusable, and efficient means to assess performance virtually and enhance maturity, performance, and robustness. 相似文献