全文获取类型
收费全文 | 7903篇 |
免费 | 1266篇 |
国内免费 | 1545篇 |
专业分类
航空 | 4530篇 |
航天技术 | 2237篇 |
综合类 | 1482篇 |
航天 | 2465篇 |
出版年
2024年 | 9篇 |
2023年 | 27篇 |
2022年 | 112篇 |
2021年 | 118篇 |
2020年 | 177篇 |
2019年 | 84篇 |
2018年 | 99篇 |
2017年 | 85篇 |
2016年 | 107篇 |
2015年 | 216篇 |
2014年 | 427篇 |
2013年 | 458篇 |
2012年 | 497篇 |
2011年 | 526篇 |
2010年 | 636篇 |
2009年 | 639篇 |
2008年 | 579篇 |
2007年 | 536篇 |
2006年 | 476篇 |
2005年 | 384篇 |
2004年 | 266篇 |
2003年 | 224篇 |
2002年 | 229篇 |
2001年 | 318篇 |
2000年 | 322篇 |
1999年 | 435篇 |
1998年 | 412篇 |
1997年 | 318篇 |
1996年 | 326篇 |
1995年 | 261篇 |
1994年 | 251篇 |
1993年 | 239篇 |
1992年 | 204篇 |
1991年 | 167篇 |
1990年 | 143篇 |
1989年 | 120篇 |
1988年 | 92篇 |
1987年 | 80篇 |
1986年 | 40篇 |
1985年 | 24篇 |
1984年 | 11篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1976年 | 1篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1965年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
1.
The hierarchical porous N/O co-functionalized carbon(HPNOC)was scalably prepared by using the lowcost and renewable blighted grains as the raw material coupled with mild KHCO_3 activation for electrochemical capacitors(ECs).The elemental N was in situ doped in the obtained HPNOC without any N-containing additives.Remarkably,the obtained HPNOC was endowed with a large specific surface area(about 2 624m~2·g~(-1)),high pore volume(about 1.35cm~3·g~(-1)),as well as high-content N/O functionalization(about 1.9%(in atom)N and about 10.2%(in atom)O.Furthermore,the as-resulted HPNOC electrode with a high mass loading of 5mg·cm~(-2 )exhibited competitive gravimetric capacitances of about 373.6F·g~(-1 )at 0.5A·g~(-1),and even about 260.4F·g~(-1 )at a high rate of 10A·g~(-1);superior capacitance retention of about 98.8%at 1A·g~(-1 )over 10 000consecutive cycles;and high specific energy of about 9.6W·h·kg~(-1 )at a power of 500W·kg~(-1),when evaluated as a promising electrode in 6mol KOH for advanced electrochemical supercapacitors.More encouragingly,the green synthetic strategy we developed holds a huge promise in generalizing for other biomass-derived carbon materials for versatile energy-related applications. 相似文献
2.
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
3.
Magnetic field was introduced in laser melting deposition to reduce the pores in workpieces.Finite 3-D model of the coil-deposition layer-substrate was established.Simulation results show that the electromagnetic force in deposition layer mainly concentrates in the projection area of the coil.Axial electromagnetic force shows repulsion in one cycle.The experimental results indicate that the magnetic field is beneficial for grain refinement,microhardness increasement and decline of quantities and average sizes of pores. 相似文献
5.
L O Bjorn S Widell T Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(6):1557-1562
Plants have evolved under the influence of UV-B radiation and have acquired systems for monitoring it and investing appropriate resources for protection against it, i.e., filters, quenchers of radicals and reactive oxygen species, and repair systems. An hypothesis for how plants monitor radiation has been presented. 相似文献
6.
晶体管h参数微变等效电路是电子技术中求解低频、小信号放大电路常用的分析方法.本文通过具体分析,将模拟放大电路进行了新的分类,并且明确而系统地给出运用微变等效电路求解各类模拟放大电路动态指标Av、ri和γ0公式、解题难点及规律. 相似文献
7.
赵承龙 《南京航空航天大学学报》1990,(2)
本文在阐述基准的热力学概念基础上,提出了燃气基准的计算方法,应用CHAPPELL推荐的有关燃气热力性质表达式,导出计算燃气基准的公式,通过微机计算,将结果整理成燃气基准的有关表、图。 相似文献
8.
论述了我国加入世界贸易组织后,如何搞好航空产品的包装和包装标准化工作,以提高航空工业军品和民品在国际市场的竞争能力。 相似文献
9.
王宜龙 《航空精密制造技术》2002,38(1):38-40
对污水处理装置的技术参数、技术要求及设计方案的选择、工作原理做了进一步的阐述。对工业循环冷却水的处理有实际指导意义。 相似文献
10.
Wang L. Dawson J.M. Hornak L.A. Famouri P. Ghaffarian R. 《IEEE transactions on aerospace and electronic systems》2004,40(2):567-575
Closed-loop control has been successfully applied to a microelectromechanical systems (MEMS) lateral comb resonator device in real-time to perform impulse disturbance damping and sinusoidal position control, enabled by the use of a through-wafer optical microprobe to obtain position feedback. This result leverages the application of lifetime, in-situ control of MEMS in order to provide quality assurance of microsystems in safety critical applications. A position feedback signal produced by a through-wafer optical microprobe has been used for comb resonator system model identification by two independent methods to accurately determine the effective mass, damping, and spring constant values of the device. After accurate determination of system parameters, closed-loop impulse disturbance damping and proportional-integral-differential (PID) translational control were applied. Closed-loop control results presented indicate controllability of such microstructures and response times on the order of the natural frequency of the device. 相似文献