全文获取类型
收费全文 | 3254篇 |
免费 | 30篇 |
国内免费 | 15篇 |
专业分类
航空 | 1575篇 |
航天技术 | 1154篇 |
综合类 | 4篇 |
航天 | 566篇 |
出版年
2021年 | 26篇 |
2019年 | 25篇 |
2018年 | 55篇 |
2017年 | 51篇 |
2016年 | 46篇 |
2015年 | 26篇 |
2014年 | 71篇 |
2013年 | 91篇 |
2012年 | 82篇 |
2011年 | 119篇 |
2010年 | 79篇 |
2009年 | 137篇 |
2008年 | 153篇 |
2007年 | 99篇 |
2006年 | 71篇 |
2005年 | 92篇 |
2004年 | 90篇 |
2003年 | 99篇 |
2002年 | 72篇 |
2001年 | 115篇 |
2000年 | 65篇 |
1999年 | 68篇 |
1998年 | 87篇 |
1997年 | 58篇 |
1996年 | 93篇 |
1995年 | 112篇 |
1994年 | 111篇 |
1993年 | 48篇 |
1992年 | 71篇 |
1991年 | 34篇 |
1990年 | 32篇 |
1989年 | 76篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 35篇 |
1985年 | 90篇 |
1984年 | 91篇 |
1983年 | 65篇 |
1982年 | 66篇 |
1981年 | 99篇 |
1980年 | 19篇 |
1979年 | 25篇 |
1978年 | 29篇 |
1977年 | 27篇 |
1975年 | 29篇 |
1974年 | 23篇 |
1973年 | 21篇 |
1972年 | 20篇 |
1969年 | 20篇 |
1968年 | 18篇 |
排序方式: 共有3299条查询结果,搜索用时 15 毫秒
841.
A hologram-like, 3-D, high-resolution, stereoscopic video display technique based on a color CRT is described. The technique is unique in that it is autostereoscopic, i.e., no special glasses, goggles, panels, helmets, or two-channel optical systems are required by the viewer to see depth. Any image that can be put into a television-like format can be displayed. This allows real-time scanning sensor data to be viewed with depth in a format familiar to the viewer. An implementation using real-time sensors is shown 相似文献
842.
Niggemann R.E. Peecher S. Rozman G. 《Aerospace and Electronic Systems Magazine, IEEE》1991,6(8):21-26
The approach, system architecture, instrumentation, and performance of a technology demonstrator system for the application of 270-VDC/hybrid 115-VAC electrical power generation and distribution to future military aircraft are examined. The design has focused on assembling a highly flexible test system. The loads are typical of those in a hybrid electrical system. The system consists of a single 3-phase, 115-VAC electrical generator whose output is rectified, filtered, and supplied through DC contactors to both a 270-VDC load bus and to the input of an inverter, which supplies a 400-Hz, 115-VAC load bus. A variable-frequency, 115-VAC bus is also available directly from the generator. A prototype variable-speed constant-frequency 120-kVA generator is used. The test facility is designed to provide loads to all power types capable of being produced by the system. The system has provided particularly good insight into various aspects of 270-VDC/115-VAC hybrid systems and their components 相似文献
843.
J.S. Latham D.C. Ferns J.E. Colwell R. Reinhold E.H. Jebe 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(8):57-68
The inventory of large often non-homogeneous tracts of land by resource agencies has led to the development of estimation methods and sampling strategies that produce estimates of the aereal extent of various features from ‘limited’ observations of the universe of interest. Landsat data has furnished a tool that allows for potential improvement in estimates of resource parameters over extensive areas. This paper examines the methodology and results of a procedure which uses an economical sampling procedure allied with the large area covering qualities of the satellite imaging system to make improved estimates of irrigated land in a more timely, efficient and ‘accurate’ manner. 相似文献
844.
G.E. Brueckner 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(4):177-183
The present measurement accuracy of the solar spectral irradiance is insufficient to derive the real long-term solar spectral irradiance variability at all wavelengths. Possible error sources are discussed. A series of new second generation solar irradiance photometers are now under construction which should considerably improve these measurements. At the same time, efforts are made to improve the absolute UV calibration methods to derive a unified UV radiation scale. 相似文献
845.
M.E. Gelman A.J. Miller R.M. Nagatani H.D. Bowman 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(10):159-162
Since Autumn of 1978, the National Meteorological Center of the United States National Weather Service has been archiving in a single, unique data set, global, daily synoptic analyses and computer gridded fields of geopotential height and temperature at 18 pressure levels from 1000 to 0.4 mb. The paper discusses the fields, with special emphasis on data and analysis procedures used for the stratospheric fields, along with estimates of uncertainties. Results are presented for the mean zonal wind and temperature patterns for each January of the four PMP-1 winters 1978/79 to 1981/82. The Preparatory MAP (Middle Atmosphere Program) Project for coordinated study of the behavior of the middle atmosphere is called PMP-1. 相似文献
846.
The problem of scheduling radar tracking pulses in a dense target environment where the position estimation error must be constrained to avoid false return with track correlations is considered. The problem is to schedule n fixed energy pulses such that the rangerate error is minimized at some final time subject to the constraint that the position error will be smaller than some value for the whole time interval. For a fixed time interval, the problem of finding the minimum number of radar measurements required to satisfy the position estimation error constraint is solved. A closed-form solution for the optimum schedule is given in the case where the number of pulses is equal to the minimum number of pulses. For cases where one extra pulse is available, a solution method is described and an algorithm is derived. 相似文献
847.
Current and projected system requirements for inertial reference assemblies emphasize high accuracy, long life, and low power. An inertial reference assembly ( IRA) which embodies the aforementioned characteristics was developed recently. Pulse rebalanced gas-bearing gyroscopes were used to attain high accuracy and long life. Temperature compensation of gyroscope parameters (in lieu of temperature control) and dual voltage spinmotor operation helped achieve low-power operation. The latter two items represent an advancement in the state of the art and form the subject of this paper. These techniques were used in the construction of a three-axis IRA with an operating power less than 50 watts. It has achieved 0.1 percent scale factor accuracy over a 60°F range. 相似文献
848.
849.
850.
H E Ross 《Acta Astronautica》1981,8(9-10):1051-1058
It is often assumed that weight judgements depend primarily on the effort experienced in lifting an object against a 1-G force. Changes in effort and in other weight-cues certainly alter apparent heaviness; but there is a tendency towards mass-constancy when such changes are unrelated to mass. Under water or altered G, both the observer's body and other objects change their effective weight: the change in the former probably provides a cue to the latter. Mass-constancy increases with opportunity for adaptation to the change, leaving a negative aftereffect on return to normal circumstances. The discrimination of weight or mass also deteriorates with sudden changes in arm weight, just as it does with other types of maladaptation and with a reduction in sensory cues. The relative importance of arm weight and other factors has not been precisely measured, but experiments in prolonged spaceflight should help to elucidate the issue. 相似文献