全文获取类型
收费全文 | 3157篇 |
免费 | 9篇 |
国内免费 | 14篇 |
专业分类
航空 | 1673篇 |
航天技术 | 1083篇 |
综合类 | 9篇 |
航天 | 415篇 |
出版年
2018年 | 37篇 |
2017年 | 21篇 |
2016年 | 22篇 |
2014年 | 55篇 |
2013年 | 79篇 |
2012年 | 60篇 |
2011年 | 105篇 |
2010年 | 82篇 |
2009年 | 117篇 |
2008年 | 176篇 |
2007年 | 90篇 |
2006年 | 60篇 |
2005年 | 77篇 |
2004年 | 78篇 |
2003年 | 100篇 |
2002年 | 52篇 |
2001年 | 99篇 |
2000年 | 48篇 |
1999年 | 79篇 |
1998年 | 93篇 |
1997年 | 73篇 |
1996年 | 91篇 |
1995年 | 124篇 |
1994年 | 98篇 |
1993年 | 66篇 |
1992年 | 101篇 |
1991年 | 42篇 |
1990年 | 36篇 |
1989年 | 87篇 |
1988年 | 33篇 |
1987年 | 28篇 |
1986年 | 32篇 |
1985年 | 87篇 |
1984年 | 91篇 |
1983年 | 59篇 |
1982年 | 82篇 |
1981年 | 92篇 |
1980年 | 34篇 |
1979年 | 42篇 |
1978年 | 32篇 |
1977年 | 22篇 |
1976年 | 21篇 |
1975年 | 37篇 |
1974年 | 24篇 |
1973年 | 18篇 |
1972年 | 29篇 |
1969年 | 17篇 |
1968年 | 16篇 |
1967年 | 20篇 |
1966年 | 16篇 |
排序方式: 共有3180条查询结果,搜索用时 0 毫秒
361.
C. S. Wu 《Space Science Reviews》1985,41(3-4):215-298
This article reviews the theory of the kinetic (cyclotron an synchroton) maser instabilities. The subject has been extensively developed in recent years by many authors, who have been incited by the research of the auroral kilometric radiation and other applications. The maser mechanism is appealing because it is simple and efficient, and can lead to direct amplification of radiation. Two types of electron distribution functions have been investigated so far. These are the loss-cone and hollow-beam distributions which may exist pervasively in many regions within and beyond the solar system. It is likely that the maser instabilities can have many potentially important applications to numerous radio emission processes observed in astrophysical research. 相似文献
362.
P. Ubertini A. Bazzano L. Boccaccini N.A. Dipper L. Iafrate C. LaPadula M. Mastropietro R. Patriarca V. Polcaro M.L. Urciuoli 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(1):105-108
A new design of position sensitive spectroscopic proportional counter is described, for use in a balloon borne hard x-ray telescope. Initial position and spectral resolution data from a one-dimensional laboratory prototype are reported. With this device, the final telescope will have an angular resolution of better than 10 minutes of arc. 相似文献
363.
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
364.
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
365.
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
366.
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
367.
368.
369.
C. de Jager A. Ollongren Tj. de Graaf B. J. Levin M. Tucker 《Space Science Reviews》1969,9(5):740-742
370.
Arthur C. Clarke 《Space Policy》1986,2(2)
Soviet General Secretary Gorbachev, in his January 1986 speech, expressed a hope that the level of nuclear weapons would before long be greatly reduced. The Soviet Embassy in Sri Lanka invited Arthur C. Clarke to comment on the General Secretary's speech. This article is his response. 相似文献