全文获取类型
收费全文 | 8567篇 |
免费 | 20篇 |
国内免费 | 36篇 |
专业分类
航空 | 4006篇 |
航天技术 | 3100篇 |
综合类 | 34篇 |
航天 | 1483篇 |
出版年
2021年 | 79篇 |
2019年 | 56篇 |
2018年 | 224篇 |
2017年 | 139篇 |
2016年 | 110篇 |
2015年 | 52篇 |
2014年 | 199篇 |
2013年 | 243篇 |
2012年 | 247篇 |
2011年 | 345篇 |
2010年 | 234篇 |
2009年 | 391篇 |
2008年 | 469篇 |
2007年 | 240篇 |
2006年 | 201篇 |
2005年 | 260篇 |
2004年 | 235篇 |
2003年 | 296篇 |
2002年 | 182篇 |
2001年 | 286篇 |
2000年 | 166篇 |
1999年 | 203篇 |
1998年 | 231篇 |
1997年 | 173篇 |
1996年 | 206篇 |
1995年 | 263篇 |
1994年 | 260篇 |
1993年 | 136篇 |
1992年 | 201篇 |
1991年 | 88篇 |
1990年 | 77篇 |
1989年 | 178篇 |
1988年 | 74篇 |
1987年 | 77篇 |
1986年 | 88篇 |
1985年 | 231篇 |
1984年 | 191篇 |
1983年 | 153篇 |
1982年 | 189篇 |
1981年 | 236篇 |
1980年 | 79篇 |
1979年 | 59篇 |
1978年 | 64篇 |
1977年 | 53篇 |
1976年 | 50篇 |
1975年 | 45篇 |
1974年 | 51篇 |
1973年 | 46篇 |
1970年 | 42篇 |
1969年 | 39篇 |
排序方式: 共有8623条查询结果,搜索用时 31 毫秒
391.
The vortical mixing concept in the ramjet channel is analyzed. The results of simulating the gasodynamic scheme permit the concept of increasing efficiency for ramjet operation to be substantiated. 相似文献
392.
S. V. Russkikh 《Russian Aeronautics (Iz VUZ)》2014,57(1):107-110
Transverse nonstationary vibrations of a guide beam having the initial flexure are considered. An absolutely rigid missile moves under the propulsive force along this guide beam on two sliding supports. The beam displacements introduced by its vibrations are presented as an expansion with respect to the given functions according to the Ritz method. The equations of nonstationary vibration of the beam with the missile moving along it are obtained in the generalized coordinates, the expansion coefficients being chosen as them. The example is presented. Also studied is the effect of different beam and missile parameters on the beam displacement and transverse and angular velocity of the missile. 相似文献
393.
Very Long Baseline Interferometry (VLBI) is a differential technique observing radiation of compact extra-galactic radio sources with pairs of radio telescopes. For these observations, the frequency standards at the telescopes need to have very high stability. In this article we discuss why this is, and we investigate exactly how precise the frequency standards need to be. Four areas where good clock performance is needed are considered: coherence, geodetic parameter estimation, correlator synchronization, and UT1 determination. We show that in order to ensure the highest accuracy of VLBI, stability similar to that of a hydrogen maser is needed for time-scales up to a few hours. In the article, we are considering both traditional VLBI where extra-galactic radio sources are observed, as well as observation of man-made artificial radio sources emitted by satellites or spacecrafts. 相似文献
394.
P. V. Bulat M. P. Bulat I. A. Volobuev A. A. Levikhin 《Russian Aeronautics (Iz VUZ)》2018,61(3):420-424
The bearing capacity of hybrid segmented bearings with different groove systems is compared. The research establishes that the system with a crescent groove has the best characteristics. 相似文献
395.
S. Sadeghi M.R. Emami 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(8):2050-2056
This paper studies an auroral event using data from three spacecraft of the Cluster mission, one inside and two at the poleward edge of the bottom of the Auroral Acceleration Region (AAR). The study reveals the three-dimensional profile of the region’s poleward boundary, showing spatial segmentation of the electric potential structures and their decay in time. It also depicts localized magnetic field variations and field-aligned currents that appear to have remained stable for at least 80?s. Such observations became possible due to the fortuitous motion of the three spacecraft nearly parallel to each other and tangential to the AAR edge, so that the differences and variations can be seen when the spacecraft enter and exit the segmentations, hence revealing their position with respect to the AAR. 相似文献
396.
397.
398.
399.
López-Valverde Miguel A. Gerard Jean-Claude González-Galindo Francisco Vandaele Ann-Carine Thomas Ian Korablev Oleg Ignatiev Nikolai Fedorova Anna Montmessin Franck Määttänen Anni Guilbon Sabrina Lefevre Franck Patel Manish R. Jiménez-Monferrer Sergio García-Comas Maya Cardesin Alejandro Wilson Colin F. Clancy R. T. Kleinböhl Armin McCleese Daniel J. Kass David M. Schneider Nick M. Chaffin Michael S. López-Moreno José Juan Rodríguez Julio 《Space Science Reviews》2018,214(1):1-31
Space Science Reviews - Time measured by an ideal clock crucially depends on the gravitational potential and velocity of the clock according to general relativity. Technological advances in... 相似文献
400.
A.K. Sharma O.B. Gurav Anindya Bose H.P. Gaikwad G.A. Chavan Atanu Santra S.S. Kamble R.S. Vhatkar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(10):3131-3138
Indian Space Research Organization (ISRO) has developed an indigenous system named Indian Regional Navigation Satellite System (IRNSS) or NavIC (Navigation with Indian Constellation), that consists of 7 satellites and transmits navigation signal in L and S bands. ISRO, for validation of the system, has installed many IGS (IRNSS/GPS/SBAS) receivers scattered over the Indian region. Using preliminary data from two geographically widely separated stations over India, this paper presents the results on studies on parameters of IRNSS signal quality and discusses how these parameters may be used to study the ionospheric behavior over the Indian region. The results show the importance and advantages of using IRNSS data for such studies. 相似文献