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 31 毫秒
761.
T.K. Yeoman H.C. Scoffield D.M. Wright L.J. Baddeley A.N. Vasilyev N.V. Semenova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
A brief review is provided of recent progress in understanding the ionospheric Alfvén resonator (IAR) at high latitude. Firstly, naturally occurring resonances of the IAR as detected by pulsation magnetometers in the auroral zone at Sodankylä and in the polar cap at Barentsburg are considered. The characteristics of the IAR in the two regions are broadly similar, although the effects of solar illumination are less clear at the higher latitudes. Secondly we review recent attempts to stimulate the IAR through high-power radio frequency experiments both in the auroral zone at Tromsø with the European Incoherent SCATter (EISCAT) heater, and within the polar cap at Longyearbyen with the Space Plasma Exploration by Active Radar (SPEAR) facility. In the auroral zone at, Tromsø the stimulated IAR has been observed by ground-based magnetometers, and through electron acceleration observed on the FAST spacecraft. At SPEAR in the polar cap, the stimulated IAR has been investigated, with ground magnetometers, with the first results indicative of a positive detection. 相似文献
762.
R.C. Elphic T.J. Kelly C.T. Russell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(4):131-134
Magnetic field measurements obtained in the nightside magnetosphere by the co-orbiting ISEE-1 and 2 spacecraft have been examined for signatures of field-aligned currents (FAC). Such currents are found on the boundary of the plasma sheet both when the plasma sheet is expanding and when it is thinning. Plasma sheet boundary layer current structure and substorm associated dynamics can be determined using the two spacecraft, although for slow traversals of the FAC sheet the spatial/temporal ambiguity is still an issue. We often find evidence for the existence of waves on the plasma sheet boundary, leading to multiple crossings of the FAC sheet. At times the boundary layer FAC sheet orientation is nearly parallel to the X-Z GSM plane, suggesting ‘protrusions’ of plasma sheet into the lobes. The boundary layer current polarity is, as expected, into the ionosphere in the midnight to dawn local time sector, and outward near dusk. Current sheet thicknesses and velocities are essentially independent of plasma sheet expansion or thinning, having typical values of 1500 km and 20–40 km/s respectively. Characteristic boundary layer current densities are about 10 nanoamps per square meter. 相似文献
763.
C. G. Page 《Space Science Reviews》1985,40(3-4):387-390
The EXOSAT Medium Energy instrument has been used with the new HER6 mode to study the rapid variability of Cygnus X-1. It was found that the fluctuations in the higher energy band (5–14 keV) lagged behind those in the lower band (2–5 keV) by about 6 milliseconds. This confirms predictions of the inverse Compton model and gives an upper limit to the scale-size of the hot gas clouds. 相似文献
764.
E.A. Roth 《Acta Astronautica》1985,12(10):719-730
In this paper the Gaussian equations are derived for the nonsingular equinoctial elements, as they are required for dissipative perturbations of a satellite orbit. As examples, airdrag and solar radiation pressure are considered and the first-order variation of the elements and time after one revolution are given explicitly. 相似文献
765.
Douglas Lynch A.E. Gerard Genello B. Michael Wicks C. 《Aerospace and Electronic Systems Magazine, IEEE》2007,22(1):8-10
This program will develop an automated and unmanned ultra-wide band (UWB) perimeter surveillance sensor designed to provide detection and tracking of personnel and vehicles at the perimeter of critical areas such as military installations and other such facilities. This effort describes the work being done for the protection of high value assets using a compact system which incorporates two technologies to enhance the probability of detection in stressing environments 相似文献
766.
Sorace R. Lee E. Baldauf J. Heffernan P. 《IEEE transactions on aerospace and electronic systems》1998,34(3):947-954
A study of the distribution of gain-to-noise-temperature (G/T) values for the Tracking and Data Relay Satellite (TDRS) satellite is described. The statistics of the G/T values are determined by a Monte Carlo simulation of the orbital geometry of the Sun and Moon, and the gain and noise temperature calculations is included. The results and their underlying assumptions are described 相似文献
767.
768.
T Takakura E Goto M Tanaka 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(4-5):255-258
An axis clinostat was constructed to create micro and negative gravity also a rotated flat disk was constructed with different rotation rates to give increased gravity, by centrifugal force up to 48 g. Rice seeds were grown on agar in tubes at the constant air temperature of 20 degrees C under an average light condition of 110 micromol/m2/sec(PPF). Humidity was not controlled but was maintained above 90%. Since the tube containers were not large enough for long cultivation, shoot and root growth were observed every 12 hours until the sixth day from seeding. The lengths of shoots and roots for each individual plant were measured on the last day. The stem lengths were increased by microgravity but the root lengths were not. Under the negative gravity, negative orthogeotropism and under microgravity, diageotropism was observed. No significant effect of increased gravity was observed on shoot and root growth. 相似文献
769.
770.