全文获取类型
收费全文 | 5632篇 |
免费 | 27篇 |
国内免费 | 23篇 |
专业分类
航空 | 2805篇 |
航天技术 | 1957篇 |
综合类 | 13篇 |
航天 | 907篇 |
出版年
2021年 | 35篇 |
2019年 | 33篇 |
2018年 | 78篇 |
2017年 | 55篇 |
2016年 | 53篇 |
2015年 | 36篇 |
2014年 | 108篇 |
2013年 | 148篇 |
2012年 | 131篇 |
2011年 | 194篇 |
2010年 | 136篇 |
2009年 | 209篇 |
2008年 | 280篇 |
2007年 | 153篇 |
2006年 | 118篇 |
2005年 | 150篇 |
2004年 | 143篇 |
2003年 | 172篇 |
2002年 | 112篇 |
2001年 | 179篇 |
2000年 | 97篇 |
1999年 | 133篇 |
1998年 | 155篇 |
1997年 | 116篇 |
1996年 | 166篇 |
1995年 | 202篇 |
1994年 | 186篇 |
1993年 | 105篇 |
1992年 | 145篇 |
1991年 | 68篇 |
1990年 | 60篇 |
1989年 | 142篇 |
1988年 | 54篇 |
1987年 | 51篇 |
1986年 | 61篇 |
1985年 | 167篇 |
1984年 | 168篇 |
1983年 | 111篇 |
1982年 | 136篇 |
1981年 | 172篇 |
1980年 | 50篇 |
1979年 | 60篇 |
1978年 | 57篇 |
1977年 | 38篇 |
1975年 | 56篇 |
1974年 | 44篇 |
1973年 | 36篇 |
1972年 | 47篇 |
1969年 | 35篇 |
1967年 | 36篇 |
排序方式: 共有5682条查询结果,搜索用时 78 毫秒
521.
W. Menn O. Adriani G.C. Barbarino G.A. Bazilevskaya R. Bellotti M. Boezio E.A. Bogomolov L. Bonechi M. Bongi V. Bonvicini S. Borisov S. Bottai A. Bruno F. Cafagna D. Campana R. Carbone P. Carlson M. Casolino G. Castellini L. Consiglio M.P. De Pascale C. De Santis N. De Simone V. Di Felice A.M. Galper W. Gillard L. Grishantseva G. Jerse A.V. Karelin S.V. Koldashov S.Y. Krutkov A.N. Kvashnin A. Leonov V. Malakhov V. Malvezzi L. Marcelli A.G. Mayorov V.V. Mikhailov E. Mocchiutti A. Monaco N. Mori N. Nikonov G. Osteria F. Palma P. Papini M. Pearce P. Picozza C. Pizzolotto M. Ricci S.B. Ricciarini 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
522.
Le Cadre J.-P. Jaetffret C. 《IEEE transactions on aerospace and electronic systems》1999,35(3):801-818
This paper deals with the analysis of the convergence of iterative methods for bearings only tracking (BOT). A geometric and unified framework is developed. Explicit sufficient conditions ensuring convergence of iterative methods for maximization of the likelihood functional are then derived 相似文献
523.
Flutter and time errors are critical factors in all instrumentation recording. This paper presents analytically the relationship between flutter, time base error, and time base error difference (sometimes called jitter), and the effects of these factors on direct and FM recording. Methods of measuring these quantities are discussed and experimental examples are given. Finally, a measurement method for the interchannel time error is presented, and some trends of correlation among all channels are discussed. 相似文献
524.
The possibility of using solar sails in Earth orbit is investigated. The characteristic parameters of a solar sail consisting of six spheres attached by mutually orthogonal long rods are estimated. 相似文献
525.
Coding gain is described as used in space communications engineering, and an empirical formula for coding gain is presented. The formula is designed to fit available performance data for Viterbi soft-decision decoding of various nonsystematic convolutional codes and to have a functional form suitable for computer implementation. 相似文献
526.
We study the directional stability of rigid and deformable spinning satellites in terms of two attitude angles. The linearized attitude motion of a free system about an assumed uniform-spin reference solution leads to a generic MGK system when the satellite is rigid or deformable. In terms of Lyapunov’s stability theory, we investigate the stability with respect to a subset of the variables. For a rigid body, the MGK system is 6-dimensional, i.e., 3 rotational and 3 translational variables. When flexible parts are present the system can have any arbitrary dimension. The 2×2 McIntyre–Myiagi stability matrix gives sufficient conditions for the attitude stability. A further development of this method has led to the Equivalent Rigid Body method. We propose an alternative practical method to establish sufficiency conditions for directional stability by using the Frobenius–Schur reduction formula. As practical applications we discuss a spinning satellite augmented with a spring–mass system and a rigid body appended with two cables and tip masses. In practice, the attitude stability must also be investigated when the spinning satellite is subject to a constant axial thrust. The generic format becomes MGKN as the thrust is a follower force. For a perfectly aligned thrust along the spin axis, Lyapunov’s indirect method remains valid also when deformable parts are present. We illustrate this case with an apogee motor burn in the presence of slag. When the thrust is not on the spin axis or not pointing parallel to the spin axis, the uniform-spin reference motion does not exist and none of the previous methods is applicable. In this case, the linearization may be performed about the initial state. Even when the linearized system has bounded solutions, the non-linear system can be unstable in general. We illustrate this situation by an instability that actually happened in-flight during a station-keeping maneuver of ESA’s GEOS-I satellite in 1979. 相似文献
527.
528.
Nicole D. Buckley Claude P. Champagne Adriana I. Masotti Lisa E. Wagar Thomas A. Tompkins Julia M. Green-Johnson 《Acta Astronautica》2011,68(7-8):731-738
Astronauts face numerous health challenges during long-duration space missions, including diminished immunity, bone loss and increased risk of radiation-induced carcinogenesis. Changes in the intestinal flora of astronauts may contribute to these problems. Soy-based fermented food products could provide a nutritional strategy to help alleviate these challenges by incorporating beneficial lactic acid bacteria, while reaping the benefits of soy isoflavones. We carried out strain selection for the development of soy ferments, selecting strains of lactic acid bacteria showing the most effective growth and fermentation ability in soy milk (Streptococcus thermophilus ST5, Bifidobacterium longum R0175 and Lactobacillus helveticus R0052). Immunomodulatory bioactivity of selected ferments was assessed using an in vitro challenge system with human intestinal epithelial and macrophage cell lines, and selected ferments show the ability to down-regulate production of the pro-inflammatory cytokine interleukin-8 following challenge with tumour necrosis factor-alpha. The impact of fermentation on vitamin B1 and B6 levels and on isoflavone biotransformation to agluconic forms was also assessed, with strain variation-dependent biotransformation ability detected. Overall this suggests that probiotic bacteria can be successfully utilized to develop soy-based fermented products targeted against health problems associated with long-term space travel. 相似文献
529.
This correspondence reports measurements taken in both the 4- and 6-GHz frequency bands of the protection afforded a pit-shielded Earth-station antenna. The measurement program described is an expansion of a previous one and was designed to determine the effects of artificial site shielding for a range of satellite locations rather than a single position. 相似文献
530.