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191.
基于剪切应力传输(SST)k-ω湍流模型,对考虑结构误差情况下的弹箭模型进行数值模拟计算。首先采用CFD和工程经验公式相结合的方法,得到了不同马赫数、不同转速情况下无结构误差模型的多种气动特性参数。通过与实验数据对比,阻力、法向力、俯仰力矩、压心位置误差在10%以内,验证了该方法的可行性和准确性。然后,建立了考虑结构误差即质量分布不对称、弹体不同轴和无结构误差模型,并分别进行了气动特性模拟计算。结果表明,质量偏心对滚转阻尼力矩系数、马格努斯力矩系数影响很大;弹体不同轴对法向力系数导数、俯仰力矩系数导数、马格努斯力矩系数导数和压心位置都产生很大影响。结构误差使模型的多种气动特性参数产生很大变化,将影响其飞行弹道和稳定性。 相似文献
192.
Data Association and Track Management for the Gaussian Mixture Probability Hypothesis Density Filter 总被引:6,自引:0,他引:6
Panta K. Clark D.E. Ba-Ngu Vo 《IEEE transactions on aerospace and electronic systems》2009,45(3):1003-1016
The Gaussian mixture probability hypothesis density (GM-PHD) recursion is a closed-form solution to the probability hypothesis density (PHD) recursion, which was proposed for jointly estimating the time-varying number of targets and their states from a sequence of noisy measurement sets in the presence of data association uncertainty, clutter, and miss-detection. However the GM-PHD filter does not provide identities of individual target state estimates, that are needed to construct tracks of individual targets. In this paper, we propose a new multi-target tracker based on the GM-PHD filter, which gives the association amongst state estimates of targets over time and provides track labels. Various issues regarding initiating, propagating and terminating tracks are discussed. Furthermore, we also propose a technique for resolving identities of targets in close proximity, which the PHD filter is unable to do on its own. 相似文献
193.
SWE,a comprehensive plasma instrument for the WIND spacecraft 总被引:1,自引:0,他引:1
K. W. Ogilvie D. J. Chornay R. J. Fritzenreiter F. Hunsaker J. Keller J. Lobell G. Miller J. D. Scudder E. C. Sittler Jr. R. B. Torbert D. Bodet G. Needell A. J. Lazarus J. T. Steinberg J. H. Tappan A. Mavretic E. Gergin 《Space Science Reviews》1995,71(1-4):55-77
The Solar Wind Experiment (SWE) on the WIND spacecraft is a comprehensive, integrated set of sensors which is designed to investigate outstanding problems in solar wind physics. It consists of two Faraday cup (FC) sensors; a vector electron and ion spectrometer (VEIS); a strahl sensor, which is especially configured to study the electron strahl close to the magnetic field direction; and an on-board calibration system. The energy/charge range of the Faraday cups is 150 V to 8 kV, and that of the VEIS is 7 V to 24.8 kV. The time resolution depends on the operational mode used, but can be of the order of a few seconds for 3-D measurements. Key parameters which broadly characterize the solar wind positive ion velocity distribution function will be made available rapidly from the GGS Central Data Handling Facility. 相似文献
194.
Ueno K. Itanami T. Kumazawa H. Ohtomo I. 《IEEE transactions on aerospace and electronic systems》1995,31(2):600-607
Feasibility studies on a multiband communication satellite antenna system and the key technologies involved in devising this system are described. The proposed multiband communication satellite utilizes four frequency bands: Ka (30/20 GHz), Ku (14/12 GHz), C (6/4 GHz), and S (2.6/2.5 GHz). It has six beam configurations, three multibeam and three shaped-beam. The following key technologies are presented: (1) a low-loss frequency selective subreflector (FSR) for compact feeds, (2) a low-loss and broadband frequency selective surface (FSS), and (3) a highly accurate and reliable mesh reflector 相似文献
195.
用高纯α-Fe在GLEEBLE-1500热模拟机上率进行了热压缩试验。变形温度分别为550℃,700℃,800℃和900℃,应变速率分别为0.001s~(-1),0.01s~(-1),0.1s~(-1),1s~(-1)和10s~(-1)。对其热压缩过程中的显微结构变化及真应力-真应变曲线进行的研究结果表明,形变温度的增加和应变速率降低有利于动态再结晶的进行;对动态再结晶与Z参数关系的研究结果表明,在一定的Z参数范围内即25<1nZ<37,高纯α-Fe可以发生动态再结晶,并给出动态再结晶图。 相似文献
196.
Novel wideband multimode hybrid interferometer system 总被引:3,自引:0,他引:3
Pasala K. Penno R. Schneider S. 《IEEE transactions on aerospace and electronic systems》2003,39(4):1396-1406
In this paper, a novel hybrid of a three-element interferometer comprised of multimode antennas is analyzed. The phase ambiguities associated with the long baselines of the interferometer are resolved using the "coarse" angle estimates provided by the multimode antenna. This results in the elimination of the short baseline interferometers of the conventional five-element interferometer. It is shown here that the signal-to-noise ratio (SNR) must be above a threshold value to resolve the phase ambiguities with a high degree of probability. An expression that shows the dependence of this threshold SNR on the interferometer spacing and the variance of the angle estimates provided by the multimode antenna is derived. A single three-element wideband multimode antenna interferometer can replace several five-element conventional interferometers, each covering a separate frequency band. 相似文献
197.
R. H. Brown K. H. Baines G. Bellucci J.-P. Bibring B. J. Buratti F. Capaccioni P. Cerroni R. N. Clark A. Coradini D. P. Cruikshank P. Drossart V. Formisano R. Jaumann Y. Langevin D. L. Matson T. B. Mccord V. Mennella E. Miller R. M. Nelson P. D. Nicholson B. Sicardy C. Sotin 《Space Science Reviews》2004,115(1-4):111-168
The Cassini visual and infrared mapping spectrometer (VIMS) investigation is a multidisciplinary study of the Saturnian system. Visual and near-infrared imaging spectroscopy and high-speed spectrophotometry are the observational techniques. The scope of the investigation includes the rings, the surfaces of the icy satellites and Titan, and the atmospheres of Saturn and Titan. In this paper, we will elucidate the major scientific and measurement goals of the investigation, the major characteristics of the Cassini VIMS instrument, the instrument calibration, and operation, and the results of the recent Cassini flybys of Venus and the Earth–Moon system.This revised version was published online in July 2005 with a corrected cover date. 相似文献
198.
R. Srama T. J. Ahrens N. Altobelli S. Auer J. G. Bradley M. Burton V. V. Dikarev T. Economou H. Fechtig M. Görlich M. Grande A. Graps E. Grün O. Havnes S. Helfert M. Horanyi E. Igenbergs E. K. Jessberger T. V. Johnson S. Kempf A. V. Krivov H. Krüger A. Mocker-Ahlreep G. Moragas-Klostermeyer P. Lamy M. Landgraf D. Linkert G. Linkert F. Lura J. A. M. McDonnell D. Möhlmann G. E. Morfill M. Müller M. Roy G. Schäfer G. Schlotzhauer G. H. Schwehm F. Spahn M. Stübig J. Svestka V. Tschernjawski A. J. Tuzzolino R. Wäsch H. A. Zook 《Space Science Reviews》2004,114(1-4):465-518
The Cassini-Huygens Cosmic Dust Analyzer (CDA) is intended to provide direct observations of dust grains with masses between 10−19 and 10−9 kg in interplanetary space and in the jovian and saturnian systems, to investigate their physical, chemical and dynamical properties as functions of the distances to the Sun, to Jupiter and to Saturn and its satellites and rings, to study their interaction with the saturnian rings, satellites and magnetosphere. Chemical composition of interplanetary meteoroids will be compared with asteroidal and cometary dust, as well as with Saturn dust, ejecta from rings and satellites. Ring and satellites phenomena which might be effects of meteoroid impacts will be compared with the interplanetary dust environment. Electrical charges of particulate matter in the magnetosphere and its consequences will be studied, e.g. the effects of the ambient plasma and the magnetic field on the trajectories of dust particles as well as fragmentation of particles due to electrostatic disruption.The investigation will be performed with an instrument that measures the mass, composition, electric charge, speed, and flight direction of individual dust particles. It is a highly reliable and versatile instrument with a mass sensitivity 106 times higher than that of the Pioneer 10 and 11 dust detectors which measured dust in the saturnian system. The Cosmic Dust Analyzer has significant inheritance from former space instrumentation developed for the VEGA, Giotto, Galileo, and Ulysses missions. It will reliably measure impacts from as low as 1 impact per month up to 104 impacts per second. The instrument weighs 17 kg and consumes 12 W, the integrated time-of-flight mass spectrometer has a mass resolution of up to 50. The nominal data transmission rate is 524 bits/s and varies between 50 and 4192 bps.This revised version was published online in July 2005 with a corrected cover date. 相似文献
199.
The proposed KAAD (knowledge-based automated air defense) system demonstrates a man-machine environment for airspace defense systems. When the unknown aircraft is hostile, a threat rating and response methods are generated by the system. It serves as a double-check decision-making system for a war control center. In addition to this application, the KAAD system can also be a useful tool as a training program for the war controller. The capabilities of the system are limited due to the shortage of knowledge resources. It requires communications among war controllers and air fighter pilots to organize a practical knowledge base. It is shown that the KAAD system can be combined with an automated ATC (air traffic control) system to become a practical system for air defense applications 相似文献
200.
H. M. Fischer J. D. Mihalov L. J. Lanzerotti G. Wibberenz K. Rinnert F. O. Gliem J. Bach 《Space Science Reviews》1992,60(1-4):79-90
The Energetic Particles Investigation (EPI) instrument operates during the pre-entry phase of the Galileo Probe. The major science objective is to study the energetic particle population in the innermost regions of the Jovian magnetosphere — within 4 radii of the cloud tops — and into the upper atmosphere. To achieve these objectives the EPI instrument will make omnidirectional measurements of four different particle species — electrons, protons, alpha-particles, and heavy ions (Z > 2). Intensity profiles with a spatial resolution of about 0.02 Jupiter radii will be recorded. Three different energy range channels are allocated to both electrons and protons to provide a rough estimate of the spectral index of the energy spectra. In addition to the omnidirectional measurements, sectored data will be obtained for certain energy range electrons, protons, and alpha-particles to determine directional anisotropies and particle pitch angle distributions. The detector assembly is a two-element telescope using totally depleted, circular silicon surfacebarrier detectors surrounded by a cylindrical tungsten shielding with a wall thickness of 4.86 g cm-2. The telescope axis is oriented normal to the spherical surface of the Probe's rear heat shield which is needed for heat protection of the scientific payload during the Probe's entry into the Jovian atmosphere. The material thickness of the heat shield determines the lower energy threshold of the particle species investigated during the Probe's pre-entry phase. The EPI instrument is combined with the Lightning and Radio Emission Detector (LRD) such that the EPI sensor is connected to the LRD/EPI electronic box. In this way, both instruments together only have one interface of the Probe's power, command, and data unit. 相似文献