全文获取类型
收费全文 | 2503篇 |
免费 | 2篇 |
国内免费 | 6篇 |
专业分类
航空 | 1227篇 |
航天技术 | 1003篇 |
综合类 | 5篇 |
航天 | 276篇 |
出版年
2021年 | 14篇 |
2019年 | 15篇 |
2018年 | 40篇 |
2017年 | 34篇 |
2016年 | 25篇 |
2015年 | 11篇 |
2014年 | 50篇 |
2013年 | 61篇 |
2012年 | 51篇 |
2011年 | 88篇 |
2010年 | 65篇 |
2009年 | 108篇 |
2008年 | 152篇 |
2007年 | 62篇 |
2006年 | 46篇 |
2005年 | 62篇 |
2004年 | 72篇 |
2003年 | 91篇 |
2002年 | 46篇 |
2001年 | 101篇 |
2000年 | 45篇 |
1999年 | 86篇 |
1998年 | 85篇 |
1997年 | 63篇 |
1996年 | 63篇 |
1995年 | 89篇 |
1994年 | 97篇 |
1993年 | 38篇 |
1992年 | 60篇 |
1991年 | 22篇 |
1990年 | 28篇 |
1989年 | 57篇 |
1988年 | 20篇 |
1987年 | 36篇 |
1986年 | 19篇 |
1985年 | 75篇 |
1984年 | 42篇 |
1983年 | 46篇 |
1982年 | 55篇 |
1981年 | 77篇 |
1980年 | 26篇 |
1979年 | 24篇 |
1978年 | 22篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1975年 | 18篇 |
1974年 | 12篇 |
1972年 | 17篇 |
1969年 | 13篇 |
1966年 | 8篇 |
排序方式: 共有2511条查询结果,搜索用时 890 毫秒
521.
On-orbit anomalies related to the deployment of spacecraft appendage and possible causes of such failures are considered. The discussion covers mechanical launch loading, on-orbit thermal and solar concerns, reliability of spacecraft pyrotechnics, and practical limitations of ground-based deployment testing. Lessons learned from the successful recovery of the Telesat Canada Anik-E2 satellite in 1991 are examined 相似文献
522.
It is shown how a uniform linear array of crossed dipoles may be used with the ESPRIT algorithm and spatial smoothing techniques to estimate the arrival directions and polarizations of incoming coherent plane waves. Some examples showing typical performance are presented. One method of smoothing can be used where it is necessary to estimate both the arrival angles and polarizations of signals. Two other methods can be used when only the arrival angles are of interest 相似文献
523.
I V Getselev P P Ignatiev N A Kabashova N N Kontor A R Moszhukhina G A Timofeev T G Khotilovskaya 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(2-3):441-444
Based on the available measurement data, simulations of radiation conditions during spacecraft flights in the interplanetary space and in the Earth's and Jupiter's radiation belts has been carried out. The > or = 10 MeV and > or = 30 MeV solar flare proton fluence forecast has been proposed for Cycle 22. Radiation conditions due to both magnetospheric electrons and protons and to solar flare protons, magnetic rigidity cutoff being taken into account, have been evaluated on spacecraft trajectories in the Earth's and Jupiter's magnetospheres. 相似文献
524.
Automatic target recognition (ATR) is an important capability for defense applications. Many aspects of image understanding (IU) research are traditionally used to solve ATR problems. The authors discuss ATR applications and problems in developing real-world ATR systems and present the status of technology for these systems. They identify several IU problems that need to be resolved in order to enhance the effectiveness of ATR-based weapon systems. They conclude that technological gains in developing robust ATR systems will lead to significant advances in many other areas of applications of image understanding 相似文献
525.
T.G. Adeishvili T.I. Gagua G.G. Managadze 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(4):251-254
This paper discusses photometric measurements made of the ionospheric excitation of the line at the time of electron beam injection from a rocket into the Earth's ionosphere. The gradual increase of the glow intensity per impulse occurs due to accumulation of the energy of excited states of N2(A3Σ+u) and O(′S) during their lifetimes. The large disturbed zone in the near-rocket environment (size >500 m) is connected via the interaction of ions accelerated in the rocket potential field with ionospheric components. The glow intensity modulation is observed at a height of ~98 km during the electron beam injection simultaneously with the ignition of the beam-plasma discharge (BPD). The intensity minima are explained by a decrease of the energy of accelerated ions due to effective neutralization of the rocket body by the BPD plasma. The height profile of the glow intensity revealed two maxima at heights of ~103 km and ~115 km. The second maximum (at ~115 km) indicates that, at these heights, both collision and collision-free mechanisms of accelerated ion energy transport to ionospheric components exist. 相似文献
526.
A combination probe for time-resolved measurements of unsteady compressible flows in transonic wind tunnels is described. The probe measures stagnation (total) temperature and pressure, static pressure, and flow angles in two planes. From these, the fluctuating mass flux, Mach number, and velocity, as well as their components in three directions, can be deduced. The combination probe consists of a dual hot-wire aspirating temperature and pressure probe mounted piggyback with a high-frequency angle probe. The angle probe has four surface-mounted silicon pressure sensors. A scheme for retrieving from the four pressure signals the stagnation and static pressures. Mach number, and flow angles in two planes, is described. The calibrations forming the base for this procedure, obtained from steady-state tests, are given. Typical data obtained in the Karman vortex street shed from a cylinder and at the exit of a Mach 0.4 air jet are presented 相似文献
527.
This paper presents brief profiles of 19 airborne hyperspectral sensor systems currently or nearly available for data acquisition. These systems represent various design concepts and innovations in hyperspectral information collection technology. A number of companies now have the ability to acquire data from these systems. As the scientific and commercial communities become aware of hyperspectral imaging data acquisition opportunities, more applications for this type of data will be investigated and implemented 相似文献
528.
B.E. Woodgate M.-J. Martres J.B. Smith K.T. Strong M.K. McCabe M.E. Machado V. Gaisauskas R.T. Stewart P.A. Sturrock 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):11-17
Studies of groups of homologous flares in active regions in 1980 have been made using a variety of space and ground based instruments. Detailed properties of three of these groups have been studied, and are combined to form a possible sequence of events. 相似文献
529.
This paper reports on EXOSAT observations of four bright QSO's and active galaxies. The QSO PHL 1657 has a simple spectrum that can be fit with power law plus some low energy absorption. A soft excess is observed for both MR 2251 and E 1352.24+1830. Finally, PKS 2126-158 was detected and the results are consistent with a 0.7 energy index. 相似文献
530.
This paper analyzes a buck/boost regulator employing current-injected control (CIC). It reveals the complex interactions between the dc loop and the current-injected loop and underlines the fundamental principle that governs the loop gain determination. Three commonly used compensation techniques are compared. The integral and lead/lag compensation are shown to be most desirable for performance optimization and stability. 相似文献