全文获取类型
收费全文 | 7286篇 |
免费 | 36篇 |
国内免费 | 39篇 |
专业分类
航空 | 3329篇 |
航天技术 | 2650篇 |
综合类 | 30篇 |
航天 | 1352篇 |
出版年
2021年 | 73篇 |
2019年 | 56篇 |
2018年 | 214篇 |
2017年 | 135篇 |
2016年 | 102篇 |
2015年 | 42篇 |
2014年 | 169篇 |
2013年 | 212篇 |
2012年 | 193篇 |
2011年 | 304篇 |
2010年 | 218篇 |
2009年 | 357篇 |
2008年 | 395篇 |
2007年 | 220篇 |
2006年 | 173篇 |
2005年 | 213篇 |
2004年 | 222篇 |
2003年 | 246篇 |
2002年 | 162篇 |
2001年 | 236篇 |
2000年 | 151篇 |
1999年 | 172篇 |
1998年 | 193篇 |
1997年 | 154篇 |
1996年 | 176篇 |
1995年 | 226篇 |
1994年 | 194篇 |
1993年 | 114篇 |
1992年 | 172篇 |
1991年 | 59篇 |
1990年 | 62篇 |
1989年 | 147篇 |
1988年 | 55篇 |
1987年 | 54篇 |
1986年 | 68篇 |
1985年 | 210篇 |
1984年 | 161篇 |
1983年 | 132篇 |
1982年 | 152篇 |
1981年 | 197篇 |
1980年 | 76篇 |
1979年 | 42篇 |
1978年 | 49篇 |
1977年 | 42篇 |
1976年 | 43篇 |
1975年 | 39篇 |
1974年 | 44篇 |
1973年 | 32篇 |
1970年 | 31篇 |
1969年 | 30篇 |
排序方式: 共有7361条查询结果,搜索用时 468 毫秒
881.
We examine X-ray maps of the whole sky covering energies from 0.1 to 6 keV. We model Loop I X-ray emission as being caused by an old supernova that exploded into an already warm interstellar medium. After comparison with Loop III we deduce that there may be a general temperature gradient in the gas as we move away from the plane in the northern galactic hemisphere. 相似文献
882.
A.H. Manson C.E. Meek M. Massebeuf J.L. Fellous W.G. Elford R.A. Vincent R.L. Craig R.G. Roper S. Avery B.B. Balsley G.J. Fraser M.J. Smith R.R. Clark S. Kato T. Tsuda A. Ebel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(7):135-144
During the last decade a large number of radars (~12) have been developed, which have produced substantial quantities of tidally-corrected mean winds data. The distribution of the radars is not global, but many areas are well covered: the Americas with Poker Flat (65°N), Saskatoon (52°N), Durham (43°N), Atlanta (34°N), Puerto Rico (18°N); Europe with Kiruna (68°), Garchy (47°N) and Monpazier (44°N); and Oceania with Christchurch (44°S), Adelaide (35°S), Townsville (20°S), and Kyoto (35°N). Zonal and meridional wind height-time cross-sections from km (MF/Meteor Radar) to ~110 km have been prepared for the last 5–6 years. They are compared with cross-sections from CIRA-72 for zonal winds, and Groves (1969) for meridional winds.It is shown that while CIRA-72 is still a useful model for many purposes, significant differences exist between it and the new radar data. The latter demonstrate important seasonal, latitudinal, longitudinal and hemispheric variations. The new meridional cross-sections are of great value. The common features with Groves (1969) are the equatorward cells in summer near 85 km; however their strength (~10 ms?1) and size are less. Systematic and somewhat different variations emerge at higher (?52°N) and middle (35–44°) latitudes. 相似文献
883.
M.R. Ananthasayanam R. Narasimha 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(7):145-154
Motivated by the need in many aerospace applications for a meaningful reference atmosphere characteristic of the whole of the tropics in both the northern and southern hemispheres of the globe, a proposal is made here for such an atmosphere upto an altitude of 80 km. The proposal is based on balloonsonde, rocketsonde and grenade and falling sphere data, respectively, in the range of about 0–20, 20–50 and 50–80 km height. The final proposal consists of six linear segments in the temperature distribution, with temperature values in degrees Centigrade of 27, ?9, ?74, ?5, ?5, ?74 and ?74 at altitudes of 0, 9, 16, 46, 52, 75 and 80 km respectively. The sea level pressure is taken as 1010 mb, and abridged tables of quantities of interest in meteorological and aerospace applications are provided. 相似文献
884.
Patrick J. Cannon Robert M. Enderson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(1):17-20
After over twenty years there is a new film introduced in the United States for fabricating scientific balloons. The film was developed by Raven and is designated Astrofilm.The film is a result of a critical selection of both the resin and extruding parameters. The film's physical properties and results of a test flight are reported. Also reported are a proposed design modification and failure analysis. 相似文献
885.
M Casolino V Bidoli E De Grandis M P De Pascale G Furano A Morselli L Narici P Picozza E Reali R Sparvoli A Galper M Korotkov Y Ozerov A Popov G Mazzenga M Ricci G Castellini S Avdeev M Boezio W Bonvicini A Vacchi N Zampa P Spillantini P Carlson C Fuglesang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(1):135-140
In this work we present preliminary results of nuclear composition measurements on board space station MIR obtained with SILEYE-2 particle telescope. SILEYE-2 was placed on MIR in 1997 and has been working since then. It consists of an array of 6 active silicon strip detectors which allow nuclear and energetic identification of cosmic rays in the energy range between approximately 30 and 200 MeV/n. The device is attached to an helmet and connected to an eye mask which shields the cosmonaut eyes from light and allow studies of the Light Flashes (LF) phenomenon. In addition to the study of the causes of LF, the device is used to perform real time long term radiation environment monitoring inside the MIR, performing measurements in solar quiet and active days. 相似文献
886.
H.S. Sawant J.A.C.F. Neri F.C.R. Fernandes J.R. Cecatto M.R. Sankararaman C. Faria S. Stephany R.R. Rosa M.C. Andrade E.M.B. Alonso E. Lüdke K.R. Subramanian R. Ramesh M.S. Sundararajan S. Ananthakrishnan G. Swarup J.W.V. Boas L.C.L. Botti C.E. Moron J.H. Saito 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,32(12):2715-2720
We present the technical characteristics of a low-cost radio telescope for solar/non solar observations at decimetric (1200–1700 MHz) and centimetric (2700 and 5000 MHz) wavelengths known as Brazilian Decimetric Array (BDA). The technical specifications of the antenna, tracking system, log-periodic feed, preamplifier and the frequency-synthesised receiver with a Single Side Band (SSB) video output of 2.5 MHz are given. 相似文献
887.
888.
The 2003 Columbia accident demonstrated that spaceflight remains a risky and dangerous human endeavor, yet there have been few ‘unofficial’ investigations into astronaut safety. This report summarizes the findings of one such study by George Washington University's Space & Advanced Communications Research Institute—e.g. that simplicity of design may be better than complexity, that cargo missions would be better carried out robotically and that all new space transportation systems should be developed to common international standards—before examining ways that international cooperation can advance the cause of space safety. In establishing future space safety standards input from a wider range of participants (industry, universities and private research institutes, as well as space agencies, etc.) will need to be sought. 相似文献
889.
Space Science Reviews - 相似文献
890.
This paper describes one solution to the problem of providing Perimeter Intruder Detection, (PIDS), for sites whose boundary includes direct access from uncontrolled water. Two surveillance heads were proposed, each consisting of a TI camera and a Colour CCTV camera mounted on a pan and tilt unit 相似文献