首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2254篇
  免费   13篇
  国内免费   10篇
航空   1092篇
航天技术   817篇
综合类   10篇
航天   358篇
  2021年   22篇
  2018年   38篇
  2017年   21篇
  2016年   26篇
  2014年   48篇
  2013年   57篇
  2012年   49篇
  2011年   91篇
  2010年   64篇
  2009年   90篇
  2008年   97篇
  2007年   52篇
  2006年   43篇
  2005年   57篇
  2004年   70篇
  2003年   72篇
  2002年   37篇
  2001年   57篇
  2000年   39篇
  1999年   47篇
  1998年   67篇
  1997年   42篇
  1996年   67篇
  1995年   79篇
  1994年   55篇
  1993年   49篇
  1992年   64篇
  1991年   30篇
  1990年   19篇
  1989年   49篇
  1988年   23篇
  1987年   20篇
  1986年   21篇
  1985年   85篇
  1984年   53篇
  1983年   53篇
  1982年   60篇
  1981年   72篇
  1980年   21篇
  1979年   26篇
  1978年   26篇
  1977年   26篇
  1976年   20篇
  1975年   20篇
  1974年   20篇
  1973年   11篇
  1972年   14篇
  1970年   18篇
  1969年   19篇
  1967年   10篇
排序方式: 共有2277条查询结果,搜索用时 15 毫秒
361.
362.
363.
    
The National Space Research Institute (INPE) is developing the first Brazilian Scientific Microsatellite (SACI-1) based on the vanguard technology and on the experience acquired through projects developed by Brazilian Space Program. The SACI-1 is a 750km polar orbit satellite. The spacecraft will combine spin stabilization with geomagnetic control and has a total mass of 60 kg. The overall dimensions are 640×470×470 mm. The SACI-1 satellite shall be launched together with CBERS (China-Brazil Earth Resource Satellite). Its platform is being designed for multiple mission applications. The Brazilian Academy of Sciences has selected four scientific payloads that characterize the mission. The scientific experiments are: ORCAS (Solar and Anomalous Cosmic Rays Observation in the Magnetosphere), PLASMEX (Study of Plasma Bubbles), FOTSAT (Airglow Photometer), and MAGNEX (Geomagnetic Experiment).  相似文献   
364.
Whether the endolymph of the semicircular canal passes the cupular partition or not was examined using the lateral semicircular canal system of adult pigeons (Columba livia). By applying various pressures by means of injection of a dye solution through the membranous canal, it was found that the dye solution, was seen to pass the cupula even under very low pressures when the pressure was increased gradually. When pulled by a magnet, the ultrafine particles of the dextran magnetite contained in the injected fluid were found to pass through the subcupular space without evident increase of the ampullary pressure.  相似文献   
365.
    
The Infrared Space Observatory (ISO), a fully approved and funded project of ESA, will operate at wavelengths from 3–200 microns. The satellite essentially consists of a large cryostat containing about 2300 litres of superfluid helium to maintain the telescope (primary mirror diameter of 60 cm) and the scientific instruments at temperatures between 2K and 8K. A pointing accuracy of a few arc seconds is provided by a three-axis-stabilisation system. ISO's instrument complement consists of four instruments, namely: an imaging photo-polarimeter (3–200 microns), a camera (3–17 microns), a short wavelength spectrometer (3–45 microns) and a long wavelength spectrometer (45–180 microns). ISO's scheduled launch date is May 1993 and it will be operational for at least 18 months. In keeping with ISO's role as an observatory, two-thirds of its observing time will be made available to the general astronomical community via several Calls for Observing Proposals.  相似文献   
366.
367.
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   
368.
    
Ergun  R.E.  Carlson  C.W.  Mozer  F.S.  Delory  G.T.  Temerin  M.  McFadden  J.P.  Pankow  D.  Abiad  R.  Harvey  P.  Wilkes  R.  Primbsch  H.  Elphic  R.  Strangeway  R.  Pfaff  R.  Cattell  C.A. 《Space Science Reviews》2001,98(1-2):67-91
We describe the electric field sensors and electric and magnetic field signal processing on the FAST (Fast Auroral SnapshoT) satellite. The FAST satellite was designed to make high time resolution observations of particles and electromagnetic fields in the auroral zone to study small-scale plasma interactions in the auroral acceleration region. The DC and AC electric fields are measured with three-axis dipole antennas with 56 m, 8 m, and 5 m baselines. A three-axis flux-gate magnetometer measures the DC magnetic field and a three-axis search coil measures the AC magnetic field. A central signal processing system receives all signals from the electric and magnetic field sensors. Spectral coverage is from DC to 4 MHz. There are several types of processed data. Survey data are continuous over the auroral zone and have full-orbit coverage for fluxgate magnetometer data. Burst data include a few minutes of a selected region of the auroral zone at the highest time resolution. A subset of the burst data, high speed burst memory data, are waveform data at 2×106 sample s–1. Electric field and magnetic field data are primarily waveforms and power spectral density as a function of frequency and time. There are also various types of focused data processing, including cross-spectral analysis, fine-frequency plasma wave tracking, high-frequency polarity measurement, and wave-particle correlations.  相似文献   
369.
The performance of the half-bridge (HB) zero-current-switched (ZCS) quasi-resonant converter (QRC) and zero-voltage-switched (ZVS) multiresonant converter (MRC) is compared with respect to their efficiency, input voltage range, semiconductor stresses, power density, and reliability. The efficiency of the HB ZVS-MRC at a given nominal input is shown to be highly dependent on the range of the input voltage, and it suffers when the converter has to be designed to cover a wide range. However, this is not the case for the HB ZCS-QRC. Experimental versions of the HB ZCS-QRC and HB ZVS-MRC were designed for the input voltage range from 150 to 350 V and a maximum output power of 100 W, under the same constraints, to facilitate their comparison  相似文献   
370.
    
Krymskii  A.M.  Breus  T.K.  Ness  N. F  AcuÑa  M.H. 《Space Science Reviews》2000,92(3-4):535-564
The Mars Global Surveyor mission has revealed that localized crustal paleomagnetic anomalies are a common feature of the Southern Hemisphere of Mars. The magnetometer measured small-scale magnetic fields associated with many individual magnetic anomalies have magnitudes ranging from hundreds to thousands nT at altitude above 120 km. That makes Mars globally different from both Venus and Earth. The data collected by Lunar Prospector near the Moon were interpreted as evidence that above regions of inferred strong surface magnetic fields on the Moon the SW flow is deflected, and a small-scale mini-magnetosphere exists under some circumstances. With a factor of 100 stronger magnetic fields at Mars and a lower SW dynamic pressure, those conditions offer the opportunity for a larger size of small `magnetospheres' which can be formed by the crustal magnetic fields. Outside the regions of the magnetic anomalies, the SW/Mars interaction is Venus-like. Thus, at Mars the distinguishing feature of the magnetic field pile-up boundary most likely varies from Venus-like to Earth-like above the crustal magnetic field regions. The observational data regarding the IMF pile-up regions near Venus and the Earth are initially reviewed. As long as the SW/Mars interaction remains like that at Venus, the IMF penetrates deep into the Martian ionosphere under the `overpressure' conditions. Results of numerical simulations and theoretical expectations regarding the temporal evolution of the IMF inside the Venus ionosphere and appearance of superthermal electrons are also reviewed and assessed.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号