全文获取类型
收费全文 | 6948篇 |
免费 | 34篇 |
国内免费 | 14篇 |
专业分类
航空 | 3346篇 |
航天技术 | 2450篇 |
综合类 | 27篇 |
航天 | 1173篇 |
出版年
2021年 | 62篇 |
2019年 | 42篇 |
2018年 | 140篇 |
2017年 | 93篇 |
2016年 | 97篇 |
2015年 | 52篇 |
2014年 | 168篇 |
2013年 | 181篇 |
2012年 | 190篇 |
2011年 | 260篇 |
2010年 | 184篇 |
2009年 | 311篇 |
2008年 | 395篇 |
2007年 | 181篇 |
2006年 | 157篇 |
2005年 | 202篇 |
2004年 | 173篇 |
2003年 | 243篇 |
2002年 | 138篇 |
2001年 | 246篇 |
2000年 | 126篇 |
1999年 | 160篇 |
1998年 | 189篇 |
1997年 | 131篇 |
1996年 | 156篇 |
1995年 | 223篇 |
1994年 | 202篇 |
1993年 | 110篇 |
1992年 | 162篇 |
1991年 | 79篇 |
1990年 | 68篇 |
1989年 | 160篇 |
1988年 | 73篇 |
1987年 | 76篇 |
1986年 | 69篇 |
1985年 | 181篇 |
1984年 | 157篇 |
1983年 | 143篇 |
1982年 | 153篇 |
1981年 | 190篇 |
1980年 | 64篇 |
1979年 | 60篇 |
1978年 | 56篇 |
1977年 | 45篇 |
1976年 | 44篇 |
1975年 | 55篇 |
1974年 | 45篇 |
1973年 | 40篇 |
1972年 | 52篇 |
1971年 | 38篇 |
排序方式: 共有6996条查询结果,搜索用时 15 毫秒
311.
An exact solution of the Navier - Stokes equations is given that describes the vorticity of a viscous incompressible liquid or gas, dissipative mediums, stationary shear counter-current of continuous vortical medium in the absence of the Coriolis field. 相似文献
312.
313.
In this paper, we consider an example of estimating and comparing the efficiency of different concepts for a high-altitude unmanned aerial vehicle (UAV) under diversity of efficiency criteria. 相似文献
314.
A novel modular multistep algorithm is proposed for multi-criteria analysis of fracture of aircraft structures with complex geometries. In order to evaluate the algorithm, the crack growth analysis is realized by the following three criteria, namely, the stress intensity factor, the strain energy release rate, and the J-integral. The algorithm implementation by the finite element method is considered and prospects of alternative implementation based on the meshfree methods are assigned. 相似文献
315.
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
316.
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
317.
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
318.
D. V. Nedel’ko 《Russian Aeronautics (Iz VUZ)》2016,59(3):297-302
A method of determining the maximum permissible values for diagnostic signs, being an integral part of health and usage monitoring systems (HUMS) of the helicopter transmission units, has been developed based on a probabilistic approach. 相似文献
319.
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
320.
A.D. Danilov A.V. Konstantinova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(1):359-370
Long-term changes in the E-layer critical frequency, foE, at three stations of the European region (Juliusruh, Slough and Rome) and also at Moscow and Wakkanai stations are analyzed by the method developed by the authors and described in detail in the previous papers. It is found that Juliusruh and Slough stations demonstrate a well-pronounced change in foE (a trend) during two previous decades. At the same time, the same features of the behavior of the aforementioned trend k(foE) are obtained. The trend is positive and negative in the morning and evening hours, respectively. Similar diurnal behavior of k(foE) is found also for Moscow station but with lower absolute values of the trends. A well-pronounced seasonal behavior of k(foE) is detected at Juliusruh and Slough: the trend is minimal and maximal in the summer period and at the end of fall—beginning of winter, respectively. The maximal amplitude in the morning hours reaches +0.04?MHz per year, whereas the minimal amplitude in evening hours is ?0.06?MHz per year. No systematic changes exceeding by the magnitude 0.01?MHz per year are found for Rome and Wakkanai stations. It is assumed that the observed trends are related to changes (trends) in the meridional wind bringing NO molecules from the auroral oval to lower latitudes. 相似文献