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971.
The work is based on photometry of the Moon’s surface during the total lunar eclipse of June 15, 2011. Photometric data are used to retrieve the value of aerosol extinction coefficient in the troposphere above the Earth’s limb in various spectral bands in the optical and near-IR ranges. The results are analyzed in comparison with the data of previous eclipses in 2004–2008. The main result consists in an increased aerosol concentration in the South-East Asia, which is maximum among all eclipses observed in recent years. At the same time, no relationship between eclipse brightness and solar activity is observed, as well as unified latitude dependency of umbra brightness noticed earlier. 相似文献
972.
This paper describes two methods of generating an analog frequency-modulated waveform by the use of a small number of digital samples of the ?chirp? waveform. The number of digital samples required is a function of the time-bandwidth product. For certain values of time-bandwidth product, this type of signal generation becomes extremely efficient. Several proofs are offered which show how to select ?optimum? values of time-bandwidth products. Two hardware implementations are suggested. One is based on the use of modulo arithmetic and a small stored memory table. The second method utilizes the inherent signal symmetries available if ?optimum? time-bandwidth products are selected. The symmetrical signal patterns are stored in recirculating reversible shift registers which can be read out at high speeds. 相似文献
973.
O V Lobachevska O T Demkiv R T Ripetskyj 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(8-9):1141-1144
During the growth and development of the sporophytic capsules of some moss species, negative gravitropism is changed for a positive one. Horizontal clinostat rotation induced unregulated growth of the sporophytes and their twisting; some of sporophytes remained straight, however. It has been established that the change of the gravitropic reaction is related to capsule formation and to the redistribution of amyloplast cells of the sporophyte graviperception zone. 相似文献
974.
For many years Norwegian airports have been equipped with instrument landing system (ILS) localizers of conventional type. Most of the localizers, however, were found not to perform very well on these sites. The course bends were too large and even moderate amounts of snow and ice could cause the localizer to fall out of operation. To overcome these difficulties, the requirements for localizer operation at these airports were analyzed and a new and improved antenna system developed. After a long period of operational testing, during which it was made clear that a substantial improvement in performance had been achieved, the new localizer antenna system is now in operation at 13 Norwegian airports. 相似文献
975.
Pyrhonen J. Niemela M. Kaukonen J. Luukko J. Pyrhonen O. 《Aerospace and Electronic Systems Magazine, IEEE》1998,13(4):23-27
Synchronous motors are important in large drives. The application of the direct flux linkage control (DFLC) in synchronous machine drives is examined. This control method guarantees the best possible dynamics for the drive. Torque steps the height of which correspond to the motor nominal torque are achieved within a few milliseconds 相似文献
976.
977.
A.S. Biryukov O.R. Grigoryan S.N. Kuznetsov A.V. Sinyakov E.D. Tolstaya 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(12):1665-1668
New experimental data obtained on the orbital station ‘MIR’ in 1991 during solar maximum are discussed. Electron fluxes with Ee>75 keV were registered for three different directions as well as for electrons with Ee>300 and 600 keV. Spatial and time distributions of electron fluxes in the trapping region are presented. In the inner radiation belt an additional maximum is observed at L=1.25–1.35, and the fluxes in the 22-05h MLT interval are 2–3 orders of magnitude smaller, than during other local times. In this region a flattening of the electron spectrum is observed. The results obtained were compared with the AE-8 model. 相似文献
978.
The Solar Terrestrial Relations Observatory (STEREO) is primarily a solar and interplanetary research mission, with one of the natural applications being in the area of space weather. The obvious potential for space weather applications is so great that NOAA has worked to incorporate the real-time data into their forecast center as much as possible. A subset of the STEREO data will be continuously downlinked in a real-time broadcast mode, called the Space Weather Beacon. Within the research community there has been considerable interest in conducting space weather related research with STEREO. Some of this research is geared towards making an immediate impact while other work is still very much in the research domain. There are many areas where STEREO might contribute and we cannot predict where all the successes will come. Here we discuss how STEREO will contribute to space weather and many of the specific research projects proposed to address STEREO space weather issues. The data which will be telemetered down in the Space Weather Beacon is also summarized here. Some of the lessons learned from integrating other NASA missions into the forecast center are presented. We also discuss some specific uses of the STEREO data in the NOAA Space Environment Center. 相似文献
979.
Montgomery J.B. Sanderson R.B. Baxley F.O. 《Aerospace and Electronic Systems Magazine, IEEE》1998,13(4):29-35
The use of high speed multicolor imaging sensors provides a valuable tool for characterizing both the infrared signatures of missiles as well as clutter. Over 14 flight hours worth of collections were made of difficult to characterize clutter. This additional data can be utilized to develop and improve missile warning algorithms for better false alarm rates. These analyses show that although a two color staring system could have multiple advantages over a single color system in false alarm rejection, the clutter rejection capabilities can be limited by the relatively low inter-band correlations between the red and blue bands 相似文献
980.
V. Angelopoulos D. Sibeck C. W. Carlson J. P. McFadden D. Larson R. P. Lin J. W. Bonnell F. S. Mozer R. Ergun C. Cully K. H. Glassmeier U. Auster A. Roux O. LeContel S. Frey T. Phan S. Mende H. Frey E. Donovan C. T. Russell R. Strangeway J. Liu I. Mann J. Rae J. Raeder X. Li W. Liu H. J. Singer V. A. Sergeev S. Apatenkov G. Parks M. Fillingim J. Sigwarth 《Space Science Reviews》2008,141(1-4):453-476
THEMIS was launched on February 17, 2007 to determine the trigger and large-scale evolution of substorms. During the first seven months of the mission the five satellites coasted near their injection orbit to avoid differential precession in anticipation of orbit placement, which started in September 2007 and led to a commencement of the baseline mission in December 2007. During the coast phase the probes were put into a string-of-pearls configuration at 100 s of km to 2 RE along-track separations, which provided a unique view of the magnetosphere and enabled an unprecedented dataset in anticipation of the first tail season. In this paper we describe the first THEMIS substorm observations, captured during instrument commissioning on March 23, 2007. THEMIS measured the rapid expansion of the plasma sheet at a speed that is commensurate with the simultaneous expansion of the auroras on the ground. These are the first unequivocal observations of the rapid westward expansion process in space and on the ground. Aided by the remote sensing technique at energetic particle boundaries and combined with ancillary measurements and MHD simulations, they allow determination and mapping of space currents. These measurements show the power of the THEMIS instrumentation in the tail and the radiation belts. We also present THEMIS Flux Transfer Events (FTE) observations at the magnetopause, which demonstrate the importance of multi-point observations there and the quality of the THEMIS instrumentation in that region of space. 相似文献