全文获取类型
收费全文 | 3604篇 |
免费 | 798篇 |
国内免费 | 702篇 |
专业分类
航空 | 2762篇 |
航天技术 | 845篇 |
综合类 | 463篇 |
航天 | 1034篇 |
出版年
2024年 | 13篇 |
2023年 | 42篇 |
2022年 | 125篇 |
2021年 | 132篇 |
2020年 | 156篇 |
2019年 | 117篇 |
2018年 | 129篇 |
2017年 | 171篇 |
2016年 | 134篇 |
2015年 | 198篇 |
2014年 | 231篇 |
2013年 | 241篇 |
2012年 | 254篇 |
2011年 | 244篇 |
2010年 | 297篇 |
2009年 | 294篇 |
2008年 | 276篇 |
2007年 | 268篇 |
2006年 | 233篇 |
2005年 | 177篇 |
2004年 | 130篇 |
2003年 | 148篇 |
2002年 | 124篇 |
2001年 | 105篇 |
2000年 | 125篇 |
1999年 | 108篇 |
1998年 | 100篇 |
1997年 | 80篇 |
1996年 | 85篇 |
1995年 | 53篇 |
1994年 | 57篇 |
1993年 | 50篇 |
1992年 | 47篇 |
1991年 | 49篇 |
1990年 | 31篇 |
1989年 | 25篇 |
1988年 | 22篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有5104条查询结果,搜索用时 578 毫秒
1.
2.
3.
Fault mode probability factor based fault-tolerant control for dissimilar redundant actuation system
This paper presents a Fault Mode Probability Factor (FMPF) based Fault-Tolerant Control (FTC) strategy for multiple faults of Dissimilar Redundant Actuation System (DRAS) composed of Hydraulic Actuator (HA) and Electro-Hydrostatic Actuator (EHA). The long-term service and severe working conditions can result in multiple gradual faults which can ultimately degrade the system performance, resulting in the system model drift into the fault state characterized with parameter uncertainty. The paper proposes to address this problem by using the historical statistics of the multiple gradual faults and the proposed FMPF to amend the system model with parameter uncertainty. To balance the system model precision and computation time, a Moving Window (MW) method is used to determine the applied historical statistics. The FMPF based FTC strategy is developed for the amended system model where the system estimation and Linear Quadratic Regulator (LQR) are updated at the end of system sampling period. The simulations of DRAS system subjected to multiple faults have been performed and the results indicate the effectiveness of the proposed approach. 相似文献
5.
X.B. Zhao W.Z. Shao L.B. Zhao Y. Gao Y.Y. Hu X.Z. Yuan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(10):3072-3086
The main objective of our work was to investigate the impact of rain on wave observations from C-band (~5.3 GHz) synthetic aperture radar (SAR) in tropical cyclones. In this study, 10 Sentinel-1 SAR images were available from the Satellite Hurricane Observation Campaign, which were taken under cyclonic conditions during the 2016 hurricane season. The third-generation wave model, known as Simulating WAves Nearshore (SWAN) (version 41.31), was used to simulate the wave fields corresponding to these Sentinel-1 SAR images. In addition, rainfall data from the Tropical Rainfall Measuring Mission satellite passing over the spatial coverage of the Sentinel-1 SAR images were collected. The simulated results were validated against significant wave heights (SWHs) from the Jason-2 altimeter and European Centre for Medium-Range Weather Forecasts data, revealing a root mean square error (RMSE) of ~0.5 m with a 0.25 scatter index. Winds retrieved from the VH-polarized Sentinel-1 SAR images using the Sentinel-1 Extra Wide-swath Mode Wind Speed Retrieval Model after Noise Removal were taken as prior information for wave retrieval. It was discovered that rain did indeed affect the SAR wave retrieval, as evidenced by the 3.21-m RMSE of SWHs between the SAR images and the SWAN model, which was obtained for the ~1000 match-ups with raindrops. The raindrops dampened the wave retrieval when the rain rate was < ~5 mm/hr; however, they enhanced wave retrieval for higher rain rates. It was also found that the portion of the rain-induced ring wave with a wave number > 0.05 rad/m (~125 m wavelength) was clearly observed in the SAR-derived wave spectra. 相似文献
6.
7.
葛军 《航空精密制造技术》2001,37(4):45-46
着重阐述了中华世纪坛在实际工作中为解决噪音问题所采用的测试方法,寻求一种解决长时间、多数据测试分析的途径。 相似文献
8.
本文介绍了一种数字多用表的自动检定校准系统的构成及软件设计 ,并对系统软件的设计方法 ,主要功能及主要特色进行了讨论。 相似文献
9.
导弹在大攻角再入飞行过程中,偏航通道和滚动通道存在着气动交连耦合,当耦合影响较大时,采用传统的把耦合项当作随机干扰的办法来处理,容易造成系统失稳。因此采用基于H∞混合灵敏度解耦控制的方法对通道间进行解耦,对于H∞混合灵敏度加权函数,通过遗传算法优化获得,并推导了H∞混合灵敏度标准型的建立过程和遗传算法优化加权函数的步骤。应用该方法,对导弹大攻角飞行过程中通道间的解耦控制进行设计。仿真表明,对参数不确定性的耦合系统,该方法具有良好的解耦性和鲁棒稳定性。 相似文献