全文获取类型
收费全文 | 8121篇 |
免费 | 656篇 |
国内免费 | 485篇 |
专业分类
航空 | 4423篇 |
航天技术 | 2298篇 |
综合类 | 443篇 |
航天 | 2098篇 |
出版年
2023年 | 47篇 |
2022年 | 115篇 |
2021年 | 184篇 |
2020年 | 131篇 |
2019年 | 129篇 |
2018年 | 307篇 |
2017年 | 271篇 |
2016年 | 201篇 |
2015年 | 199篇 |
2014年 | 302篇 |
2013年 | 307篇 |
2012年 | 351篇 |
2011年 | 482篇 |
2010年 | 463篇 |
2009年 | 552篇 |
2008年 | 537篇 |
2007年 | 392篇 |
2006年 | 254篇 |
2005年 | 309篇 |
2004年 | 208篇 |
2003年 | 257篇 |
2002年 | 238篇 |
2001年 | 256篇 |
2000年 | 174篇 |
1999年 | 198篇 |
1998年 | 186篇 |
1997年 | 164篇 |
1996年 | 151篇 |
1995年 | 193篇 |
1994年 | 174篇 |
1993年 | 104篇 |
1992年 | 135篇 |
1991年 | 87篇 |
1990年 | 62篇 |
1989年 | 103篇 |
1988年 | 58篇 |
1987年 | 50篇 |
1986年 | 46篇 |
1985年 | 108篇 |
1984年 | 92篇 |
1983年 | 77篇 |
1982年 | 94篇 |
1981年 | 129篇 |
1980年 | 42篇 |
1979年 | 38篇 |
1978年 | 34篇 |
1977年 | 26篇 |
1976年 | 30篇 |
1974年 | 25篇 |
1973年 | 24篇 |
排序方式: 共有9262条查询结果,搜索用时 812 毫秒
411.
Solar Wind Electron Proton Alpha Monitor (SWEPAM) for the Advanced Composition Explorer 总被引:1,自引:0,他引:1
McComas D.J. Bame S.J. Barker P. Feldman W.C. Phillips J.L. Riley P. Griffee J.W. 《Space Science Reviews》1998,86(1-4):563-612
The Solar Wind Electron Proton Alpha Monitor (SWEPAM) experiment provides the bulk solar wind observations for the Advanced
Composition Explorer (ACE). These observations provide the context for elemental and isotopic composition measurements made
on ACE as well as allowing the direct examination of numerous solar wind phenomena such as coronal mass ejections, interplanetary
shocks, and solar wind fine structure, with advanced, 3-D plasma instrumentation. They also provide an ideal data set for
both heliospheric and magnetospheric multi-spacecraft studies where they can be used in conjunction with other, simultaneous
observations from spacecraft such as Ulysses. The SWEPAM observations are made simultaneously with independent electron and
ion instruments. In order to save costs for the ACE project, we recycled the flight spares from the joint NASA/ESA Ulysses
mission. Both instruments have undergone selective refurbishment as well as modernization and modifications required to meet
the ACE mission and spacecraft accommodation requirements. Both incorporate electrostatic analyzers whose fan-shaped fields
of view sweep out all pertinent look directions as the spacecraft spins. Enhancements in the SWEPAM instruments from their
original forms as Ulysses spare instruments include (1) a factor of 16 increase in the accumulation interval (and hence sensitivity)
for high energy, halo electrons; (2) halving of the effective ion-detecting CEM spacing from ∼5° on Ulysses to ∼2.5° for ACE;
and (3) the inclusion of a 20° conical swath of enhanced sensitivity coverage in order to measure suprathermal ions outside
of the solar wind beam. New control electronics and programming provide for 64-s resolution of the full electron and ion distribution
functions and cull out a subset of these observations for continuous real-time telemetry for space weather purposes.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
412.
EXPERIMENTALINVESTIGATIONABOUTTHEUNSTEADYAERODYNAMICCHARACTERISTICSOFWINGSYuXinzhi;YangYongnian;WuZe(Aircra.ftEngineeringDepa... 相似文献
413.
给出了一个计算亚、跨音涡轮叶栅叶型损失的数值计算方法。主流采用时间推进有限体积法求解积分型欧拉方程,并采用了局部网格修正技术;附面层采用全隐格式求解有限差分方程;在叶栅出口与远后方均匀流之间进行了叶片尾迹与主流的掺混损失计算。算例表明本文的数值方法可准确地预测涡轮叶栅的叶型损失。 相似文献
414.
Effects of polarization and resolution on SAR ATR 总被引:3,自引:0,他引:3
Novak L.M. Halversen S.D. Owirka G. Hiett M. 《IEEE transactions on aerospace and electronic systems》1997,33(1):102-116
Lincoln Laboratory is investigating the detection and classification of stationary ground targets using high resolution, fully polarimetric, synthetic aperture radar (SAR) imagery. A study is summarized in which data collected by the Lincoln Laboratory 33 GHz SAR were used to perform a comprehensive comparison of automatic target recognition (ATR) performance for several polarization/resolution combinations. The Lincoln Laboratory baseline ATR algorithm suite was used, and was optimized for each polarization/resolution case. Both the HH polarization alone and the optimal combination of HH, HV, and VV were evaluated; the resolutions evaluated were 1 ft/spl times/1 ft and 1 m/spl times/1 m. The data set used for this study contained approximately 74 km/sup 2/ of clutter (56 km/sup 2/ of mixed clutter plus 18 km/sup 2/ of highly cultural clutter) and 136 tactical target images (divided equally between tanks and howitzers). 相似文献
415.
空间环境下的有机热控涂层 总被引:6,自引:3,他引:6
本文综述了国外在空间有机热控涂层领域中的研究工作和试验,着重分析了空间极端环境中紫外光辐照和原子氧侵蚀这两大因素对有机热控涂层的影响。 相似文献
416.
417.
418.
419.
惯性导航系统各种传递对准方法讨论 总被引:16,自引:0,他引:16
本文按对准基本原理将惯性导航系统各种传递对准方法分为两大类,一类可称为计算参数匹配法,它包括速度匹配和位置匹配;另一类可称为测量参数匹配法,它包括加速度匹配、姿态匹配和角速度匹配。文中详细讨论了这两类方法的性质,指出:计算参数匹配法类似静基座自对准和空间率对准,在载体无机动动作时对准时间较长。测量参数匹配法对准时间短,但受载体挠性变形的影响大。 相似文献
420.
Frequency estimation techniques for high dynamic trajectories 总被引:7,自引:0,他引:7
Vilnrotter V.A. Hinedi S. Kumar R. 《IEEE transactions on aerospace and electronic systems》1989,25(4):559-577
A comparison is presented of four different estimation techniques applied to the problem of continuously estimating the rapidly varying parameters of a sinusoidal signal, observed in the presence of additive noise. Frequency estimates are emphasized, although phase and/or frequency rate are also estimated by some of the algorithms. These parameters are related to the velocity, position, and acceleration of the maneuvering receiver or transmitter. Estimated performance at low carrier-to-noise ratios and high dynamics is investigated for the purpose of determining the useful operating range of an approximate maximum likelihood estimator, an extended Kalman filter, a cross-product automatic frequency loop and a phase-locked loop. Numerical simulations are used to evaluate performance while tracking a common trajectory exhibiting high dynamics 相似文献