全文获取类型
收费全文 | 1698篇 |
免费 | 172篇 |
国内免费 | 261篇 |
专业分类
航空 | 1175篇 |
航天技术 | 297篇 |
综合类 | 629篇 |
航天 | 30篇 |
出版年
2024年 | 4篇 |
2023年 | 14篇 |
2022年 | 17篇 |
2021年 | 37篇 |
2020年 | 60篇 |
2019年 | 63篇 |
2018年 | 58篇 |
2017年 | 54篇 |
2016年 | 86篇 |
2015年 | 76篇 |
2014年 | 91篇 |
2013年 | 103篇 |
2012年 | 140篇 |
2011年 | 130篇 |
2010年 | 108篇 |
2009年 | 112篇 |
2008年 | 80篇 |
2007年 | 89篇 |
2006年 | 73篇 |
2005年 | 84篇 |
2004年 | 59篇 |
2003年 | 42篇 |
2002年 | 51篇 |
2001年 | 39篇 |
2000年 | 38篇 |
1999年 | 54篇 |
1998年 | 24篇 |
1997年 | 43篇 |
1996年 | 35篇 |
1995年 | 48篇 |
1994年 | 51篇 |
1993年 | 34篇 |
1992年 | 39篇 |
1991年 | 26篇 |
1990年 | 24篇 |
1989年 | 23篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 3篇 |
排序方式: 共有2131条查询结果,搜索用时 649 毫秒
471.
472.
R. M. Suleiman J.L. Kohl A. V. Panasyuk A. Ciaravella S.R. Cranmer L.D. Gardner R. Frazin R. Hauck P.L. Smith G. Noci 《Space Science Reviews》1999,87(1-2):327-330
The Ultraviolet Coronagraph Spectrometer (UVCS) on the Solar and Heliospheric Observatory (SOHO) has been used to measure
spectral line profiles for H I Lyα in the south polar coronal hole at projected heliocentric heights from 3.5 to 6.0 R⊙ during 1998 January 5–11. Observations from 1.5 to 2.5 R⊙ were made for comparison. The H I Lyα profile is the only one observable with UVCS above 3.5 R⊙ in coronal holes. Within this region the outflowing coronal plasma becomes nearly collisionless and the ionization balance
is believed to become frozen.
In this paper, the 1/e half widths of the coronal velocity distributions are provided for the observed heights. The velocity
distributions include all motions contributing to the velocities along the line of sight (LOS). The observations have been
corrected for instrumental effects and interplanetary H I Lyα. The half widths were found to increase with projected heliographic
height from 1.5 to 2.5 R⊙ and decrease with height from 3.5 to 5 R⊙.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
473.
474.
Nikolai V. Pogorelov Gary P. Zank Tatsuki Ogino 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(2):306-317
An overview is presented of magnetic-field-related effects in the solar wind (SW) interaction with the local interstellar medium (LISM) and the different theoretical approaches used in their investigation. We discuss the possibility that the interstellar magnetic field (ISMF) introduces north–south and east–west asymmetries of the heliosphere, which might explain observational data obtained by the Voyager 1 and Voyager 2 spacecraft. The SW–LISM interaction parameters that are responsible for the deflection of the interstellar neutral hydrogen flow from the direction of propagation of neutral helium in the inner heliosheath are outlined. The possibility of a strong ISMF, which increases the heliospheric asymmetry and the H–He flow deflection, is discussed. The effect of the combination of a slow-fast solar wind during solar minimum over the Sun’s 11-year activity cycle is illustrated. The consequences of a tilt between the Sun’s magnetic and rotational axes are analyzed. Band-like areas of an increased magnetic field distribution in the outer heliosheath are sought in order to discover regions of possible 2–3 kHz radio emission. 相似文献
475.
476.
采用某飞机大迎角大振幅运动风洞实验结果,分析了大迎角非定常空气动力的一些特性。结果表明,飞机机动飞行时多自由度运动的气动特性比单自由度运动复杂,耦合运动时的气动特性和两个单自由度运动的气动特性的叠加结果相比有一定差别。此外,旋转天平实验结果同本实验的结果相比差别较大。 相似文献
477.
Recently we have shown how the slow solar wind can be formed within a coronal helmet streamer. The solar wind is modeled by
a "wake-neutral" sheet, whose subsequent linear and nonlinear evolution provides clues to the development of the wind. In
this paper we describe the first results of our extension of this model to the compressible regime. In particular, we show
that traveling density enhancements are formed, similar to those observed by LASCO. The compressible equations are solved
by an extension to MHD of the SPECLS algorithm.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
478.
We review aspects of anomalous cosmic rays (ACRs) that bear on the solar modulation of energetic particles in the heliosphere. We show that the latitudinal and radial gradients of these particles exhibit a 22-year periodicity in concert with the reversal of the Sun's magnetic field. The power-law index of the low energy portion of the energy spectrum of ACRs at the shock in 1996 appears to be -1.3, suggesting that the strength of the solar wind termination shock at the helioequatorial plane is relatively weak, with s 2.8. The rigidity dependence of the perpendicular interplanetary mean free path in the outer heliosphere for particles with rigidities between 0.2 and 0.7 GV varies approximately as R2, where R is particle rigidity. There is evidence that ACR oxygen is primarily multiply charged above 20 MeV/nuc and primarily singly-charged below 16 MeV/nuc. The location of the termination shock was at 65 AU in 1987 and 85 AU in 1994. 相似文献
479.
在1m口径圆形截面低速风洞中用一组大小不同外形相似的前缘后掠角为70°的三角翼模型,测量了模型作俯仰运动时的上表面的动态压力分布,研究了洞壁对模型表面动态压力分布的影响.在3m×2.5m矩形截面低速风洞中,用另一组外形相似的前缘后掠角为70°的三角翼模型进行非定常测力试验,并测定了洞壁上有限测压点的动态压力,研究了模型大小对非定常壁压的影响和洞壁对模型非定常法向力系数的影响,并用混合法对大模型的非定常法向力进行了洞壁干扰修正,大模型的法向力系数修正结果与小模型的法向力系数基本一致. 相似文献
480.
联接翼布局低速纵向气动特性研究 总被引:5,自引:0,他引:5
本文基于低速风洞纵向测力以及涡格法的理论计算结果,初步研究了联接翼布局的低速 向气动特性,并与相应的机翼、尾翼相分离的正常布局的试验结果作了比较。结果表明,联接翼布局具有许多优点,如较大的升力线斜率C、较大的最大升力系数Cymax、较大的纵向稳定度、相当小的诱导阻力Cxi和较高的巡航或阻比K,以及具有直接升力和直接侧力控制的可能性。文章还表明在联接翼前部配置鸭翼对进一步提高和改善其纵向气动性能的可 相似文献