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221.
William P. Bishop 《Space Policy》1986,2(4):322-341
This article reviews the revolution in remote sensing which has taken place over the past 25 years. This revolution could not have occurred without the closest cooperation among government agencies, industry and academia. International cooperation is shown to be essential in carrying out the bold missions planned for the next decade. The article reviews the history of the NASA-NOAA relationship, and the history of international partnerships with emphasis on development of the operational METSAT system. The government-industry partnership is also reviewed, with case studies to examine the evolution of METSAT sensor design, LANDSAT commercialization, and the NOAA Administrator's new initiative to facilitate development of a commercial Ocean Color Instrument. Government interaction with academia, in the form of National Science Foundation programmes and government-university ‘cooperative institutes’, is reviewed. The author concludes by showing how plans for integrating research and operations on Space Station platforms can only succeed through an alliance of all the remote-sensing players. 相似文献
222.
Brian J. Anderson Mario H. Acuña David A. Lohr John Scheifele Asseem Raval Haje Korth James A. Slavin 《Space Science Reviews》2007,131(1-4):417-450
The Magnetometer (MAG) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission is a low-noise,
tri-axial, fluxgate instrument with its sensor mounted on a 3.6-m-long boom. The boom was deployed on March 8, 2005. The primary
MAG science objectives are to determine the structure of Mercury’s intrinsic magnetic field and infer its origin. Mariner
10 observations indicate a planetary moment in the range 170 to 350 nT R
M3 (where R
M is Mercury’s mean radius). The uncertainties in the dipole moment are associated with the Mariner 10 trajectory and variability
of the measured field. By orbiting Mercury, MESSENGER will significantly improve the determination of dipole and higher-order
moments. The latter are essential to understanding the thermal history of the planet. MAG has a coarse range, ±51,300 nT full
scale (1.6-nT resolution), for pre-flight testing, and a fine range, ±1,530 nT full scale (0.047-nT resolution), for Mercury
operation. A magnetic cleanliness program was followed to minimize variable and static spacecraft-generated fields at the
sensor. Observations during and after boom deployment indicate that the fixed residual field is less than a few nT at the
location of the sensor, and initial observations indicate that the variable field is below 0.05 nT at least above about 3 Hz.
Analog signals from the three axes are low-pass filtered (10-Hz cutoff) and sampled simultaneously by three 20-bit analog-to-digital
converters every 50 ms. To accommodate variable telemetry rates, MAG provides 11 output rates from 0.01 s−1 to 20 s−1. Continuous measurement of fluctuations is provided with a digital 1–10 Hz bandpass filter. This fluctuation level is used
to trigger high-time-resolution sampling in eight-minute segments to record events of interest when continuous high-rate sampling
is not possible. The MAG instrument will provide accurate characterization of the intrinsic planetary field, magnetospheric
structure, and dynamics of Mercury’s solar wind interaction. 相似文献
223.
We discuss the rationale for a semi-permanent all-sky X-ray monitor, and investigate a variety of options for its implementation. We conclude that the Space Station offers an excellent opportunity for hosting such a monitor, and that a set of pinhole cameras can be configured to provide an effective and economical monitor system. A baseline of six independent pinhole modules, each of which requires approximately one cubic foot, 30 pounds, 2 watts, and 100 bits per second, can provide full sky coverage with scientifically interesting sensitivities. No other resources or special accommodation (such as detailed alignment registration, time-tagging or on-orbit servicing) would be required. The baseline system can locate bright sources to a few arc min, and can simultaneously measure each of the several hundred sources in the sky brighter than a few thousandths the intensity of the Crab nebula every day for decades. 相似文献
224.
Peter H. Schultz Carolyn M. Ernst Jennifer L. B. Anderson 《Space Science Reviews》2005,117(1-2):207-239
The NASA Discovery Deep Impact mission involves a unique experiment designed to excavate pristine materials from below the
surface of comet. In July 2005, the Deep Impact (DI) spacecraft, will release a 360 kg probe that will collide with comet
9P/Tempel 1. This collision will excavate pristine materials from depth and produce a crater whose size and appearance will
provide fundamental insights into the nature and physical properties of the upper 20 to 40 m. Laboratory impact experiments
performed at the NASA Ames Vertical Gun Range at NASA Ames Research Center were designed to assess the range of possible outcomes
for a wide range of target types and impact angles. Although all experiments were performed under terrestrial gravity, key
scaling relations and processes allow first-order extrapolations to Tempel 1. If gravity-scaling relations apply (weakly bonded
particulate near-surface), the DI impact could create a crater 70 m to 140 m in diameter, depending on the scaling relation
applied. Smaller than expected craters can be attributed either to the effect of strength limiting crater growth or to collapse
of an unstable (deep) transient crater as a result of very high porosity and compressibility. Larger then expected craters
could indicate unusually low density (< 0.3 g cm−3) or backpressures from expanding vapor. Consequently, final crater size or depth may not uniquely establish the physical
nature of the upper 20 m of the comet. But the observed ejecta curtain angles and crater morphology will help resolve this
ambiguity. Moreover, the intensity and decay of the impact “flash” as observed from Earth, space probes, or the accompanying
DI flyby instruments should provide critical data that will further resolve ambiguities. 相似文献
225.
Meteoroids and orbital debris pose a serious damage threat to all spacecraft. The effects of a meteoroid/orbital debris (M/OD) impact depend on a variety of factors, including where the M/OD impact occurs, the size, composition, and speed of the impacting object, and the function of the impacted spacecraft system. These effects can be minimal, can degrade a functional spacecraft component, or can compromise spacecraft functionality, even to the point of mission loss or loss of life. To minimize the damage threat from the meteoroid/orbital debris environment, it is often necessary to install protective shielding around critical spacecraft systems. If a system cannot be shielded, operational constraints may need to be imposed to reduce the damage threat. This paper presents an overview of the research and development activities performed since the late 1950s with an aim of increasing the level of protection afforded satellites and spacecraft operating in the M/OD environment and ultimately mitigating the mechanical and structural effects of an M/OD impact. 相似文献
226.
Tewell J. Robert Tobey William H. 《IEEE transactions on aerospace and electronic systems》1966,(3):346-352
One purpose of the GEMINI program is to study the problem of and establish techniques associated with acquisition, tracking, and photography of terrestrial objects from the orbiting spacecraft. This paper describes a ground-based simulation which was performed to obtain a realistic understanding of this problem and to provide the astronauts with preflight experience. The results presented evaluate the test subjects' performance in terms of tracking-rate errors, position errors, and fuel consumption for various orbital altitudes and target offsets. 相似文献
227.
Cosmogenic argon isotopes are produced in feldspars via nuclear reactions between cosmic rays and Ca and K atoms within the lattice. These cosmogenic isotopes can be used as proxies for K and Ca, much like nuclear reactor-derived 39Ar and 37Ar are used as proxies for K and Ca, respectively, in 40Ar/39Ar geochronology. If Ca and K are uniformly distributed, then the ratio of radiogenic 40Ar (40Ar?) to cosmogenic 38Ar or 36Ar (38Arcos or 36Arcos) is proportional to the difference between the radioisotopic and exposure ages, as well as the K/Ca ratio of the degassing phase. Thus cosmogenic, radiogenic, and trapped Ar isotopes, all of which can be measured remotely and are stable over geologic time, are sufficient to generate an isochron-like diagram from which the isotopic composition of the trapped component may be inferred. Such data also provide a means to assess the extent to which the system has remained closed with respect to 40Ar?, thereby mitigating otherwise unquantifiable uncertainties that complicate the conventional K–Ar dating method. 相似文献
228.
Abramovich Y.I. Spencer N.K. Anderson S.J. Gorokhov A.Y. 《IEEE transactions on aerospace and electronic systems》1998,34(4):1271-1292
This paper considers the use of spatio-temporal adaptive array processing in over-the-horizon radar (OTHR) and airborne radar applications in order to remove nonstationary multipath interference, known as “hot clutter”. Since the spatio-temporal properties of hot clutter cannot be assumed constant over the coherent processing interval (CPI), conventional adaptive techniques fail to provide effective hot-clutter mitigation without simultaneously degrading the properties of the backscattered radar signals, known as “cold clutter”. The approach presented incorporates multiple “stochastic” (data-dependent) constraints to achieve effective hot-clutter suppression, while maintaining distortionless output cold-clutter post-processing stationarity 相似文献
229.
Mavroides William G. Dennett Lancer G. Dorr Leon S. 《IEEE transactions on aerospace and electronic systems》1966,(3):323-331
A height-finding technique utilizing the relative phase between a series of point sources of a traveling-wave array is described. The point sources in the focal region of a torus antenna are used to control the phase of the antenna elevation pattern in space. Signals received from a given beam angle will arrive at each terminal of the traveling-wave feed with a different phase. By comparing this phase with a reference phase, the angular direction of an arriving plane wave can be measured with considerable accuracy. Thus a radar system with a single antenna and feed structure can be employed to yield instantaneous height coverage along with the usual range data. 相似文献
230.
David Auslander Joshua Cermenska Gregory Dalton Mauricio de la Pena C. K. H. Dharan William Donokowski Robert Duck Jonghak Kim David Pankow Alec Plauche Mustapha Rahmani Stephen Sulack Tien Fak Tan Paul Turin Tyler Williams 《Space Science Reviews》2008,141(1-4):185-211
The five “Time History of Events and Macroscale Interactions during Substorms” (THEMIS) micro-satellites launched on a common carrier by a Delta II, 7925 heavy, on February 17, 2007. This is the fifth launch in the NASA MeDIum class EXplorer (MIDEX) program. In the mission proposal the decision was made to have the University of California Berkeley Space Sciences Laboratory (UCB-SSL) mechanical engineering staff provide all of the spacecraft appendages, in order to meet the short development schedule, and to insure compatibility. This paper describes the systems engineering, design, development, testing, and on-orbit deployment of these boom systems that include: the 1 and 2 meter carbon fiber composite magnetometer booms, the 40 and 50 m tip to tip orthogonal spin-plane wire boom pairs, and the 6.3 m dipole stiff axial booms. 相似文献