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61.
Alan Title 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(8):67-74
Solar physics is about to undergo a revolution in the amount and quality of undistorted high resolution filter-grams and spectra available for study. Spacelab 2 will obtain UV and visible data comparable to the best obtained on Earth, but free of both blurring and image distortion. The goals of the Spacelab 2 flight are to collect data on the evolution of the solar magnetic and velocity fields on time scales of seconds to days. In the first part of the next decade, the 1.3 meter aperture Solar Optical Telescope will have sufficient spatial resolution to collect data on the scale of the solar density scale height [~ 100 km] which should be sufficient to study the basic physical processes in the solar atmosphere. 相似文献
62.
Grigoriadis K.M. Watson J.T. Jr. 《IEEE transactions on aerospace and electronic systems》1997,33(4):1326-1338
Necessary and sufficient conditions are derived for the existence of a solution to the continuous-time and discrete-time reduced-order H/sub /spl infin// and L/sub 2/-L/sub /spl infin// filtering problems. These conditions are expressed in terms of linear matrix inequalities (LMIs) and a coupling nonconvex matrix rank constraint. Convex LMI problems are obtained for the full-order and the zeroth-order filtering. An explicit parametrization of all reduced-order filters that correspond to a feasible solution is derived in terms of a contractive matrix, and iterative algorithms are proposed to solve the reduced-order filtering problems using alternating projections. 相似文献
63.
The Mercury Dual Imaging System on the MESSENGER Spacecraft 总被引:1,自引:0,他引:1
S. Edward Hawkins III John D. Boldt Edward H. Darlington Raymond Espiritu Robert E. Gold Bruce Gotwols Matthew P. Grey Christopher D. Hash John R. Hayes Steven E. Jaskulek Charles J. Kardian Jr. Mary R. Keller Erick R. Malaret Scott L. Murchie Patricia K. Murphy Keith Peacock Louise M. Prockter R. Alan Reiter Mark S. Robinson Edward D. Schaefer Richard G. Shelton Raymond E. Sterner II Howard W. Taylor Thomas R. Watters Bruce D. Williams 《Space Science Reviews》2007,131(1-4):247-338
The Mercury Dual Imaging System (MDIS) on the MESSENGER spacecraft will provide critical measurements tracing Mercury’s origin
and evolution. MDIS consists of a monochrome narrow-angle camera (NAC) and a multispectral wide-angle camera (WAC). The NAC
is a 1.5° field-of-view (FOV) off-axis reflector, coaligned with the WAC, a four-element refractor with a 10.5° FOV and 12-color
filter wheel. The focal plane electronics of each camera are identical and use a 1,024×1,024 Atmel (Thomson) TH7888A charge-coupled
device detector. Only one camera operates at a time, allowing them to share a common set of control electronics. The NAC and
the WAC are mounted on a pivoting platform that provides a 90° field-of-regard, extending 40° sunward and 50° anti-sunward
from the spacecraft +Z-axis—the boresight direction of most of MESSENGER’s instruments. Onboard data compression provides capabilities for pixel
binning, remapping of 12-bit data into 8 bits, and lossless or lossy compression. MDIS will acquire four main data sets at
Mercury during three flybys and the two-Mercury-solar-day nominal mission: a monochrome global image mosaic at near-zero emission
angles and moderate incidence angles, a stereo-complement map at off-nadir geometry and near-identical lighting, multicolor
images at low incidence angles, and targeted high-resolution images of key surface features. These data will be used to construct
a global image base map, a digital terrain model, global maps of color properties, and mosaics of high-resolution image strips.
Analysis of these data will provide information on Mercury’s impact history, tectonic processes, the composition and emplacement
history of volcanic materials, and the thickness distribution and compositional variations of crustal materials. This paper
summarizes MDIS’s science objectives and technical design, including the common payload design of the MDIS data processing
units, as well as detailed results from ground and early flight calibrations and plans for Mercury image products to be generated
from MDIS data. 相似文献
64.
We report Ariel V(SSI) observations of three X-ray pulsars A0535+26, 2S1145-619 and GX301-2 (2S1223-624). These sources exhibit X-ray outbursts which appear, on the basis of observations extending over 5 years, to have recurrence periods of 110 days, 187.5 days and 41.4 days respectively. If these periods are orbital in origin, the observed X-ray modulation may be explained in terms of an appreciable orbital eccentricity giving rise to time variable accretion. (In the case of GX301-2 published pulse timing data already provide independent evidence for a 41.4 day orbital period and an eccentricity e 0.4). The optical counterparts are all early-type stars; A0535+26 and 2S1145-619 are identified with Be main sequence stars and GX301-2 with a B2 supergiant which also shows an emission line spectrum. The implications of the observations in relation to possible mass transfer mechanisms in such systems are discussed. 相似文献
65.
A direct fusion drive for rocket propulsion 总被引:1,自引:0,他引:1
Yosef S. Razin Gary Pajer Mary Breton Eric Ham Joseph Mueller Michael Paluszek Alan H. Glasser Samuel A. Cohen 《Acta Astronautica》2014
The Direct Fusion Drive (DFD), a compact, anuetronic fusion engine, will enable more challenging exploration missions in the solar system. The engine proposed here uses a deuterium–helium-3 reaction to produce fusion energy by employing a novel field-reversed configuration (FRC) for magnetic confinement. The FRC has a simple linear solenoid coil geometry yet generates higher plasma pressure, hence higher fusion power density, for a given magnetic field strength than other magnetic-confinement plasma devices. Waste heat generated from the plasma?s Bremsstrahlung and synchrotron radiation is recycled to maintain the fusion temperature. The charged reaction products, augmented by additional propellant, are exhausted through a magnetic nozzle. A 1 MW DFD is presented in the context of a mission to deploy the James Webb Space Telescope (6200 kg) from GPS orbit to a Sun–Earth L2 halo orbit in 37 days using just 353 kg of propellant and about half a kilogram of 3He. The engine is designed to produce 40 N of thrust with an exhaust velocity of 56.5 km/s and has a specific power of 0.18 kW/kg. 相似文献
66.
Liz Watson 《航空制造技术》2005,(3):56
IAE国际航空发动机公司是由美国普惠公司、英国罗·罗公司、日本航空发动机公司和德国航空发动机公司这4家全球优秀的飞机发动机制造商组成,具有当今航空航天领域先进的技术。V2500系列的涡轮风扇发动机是IAE公司1983年开始研制和生产的。IAEV2500发动机目前的额定推力值为22000-33000磅,为快速增长的150座级飞机市场提供了动力装置。V2500发动机有3大主要特点:宽弦空心的风扇叶片、"浮壁"燃烧室、高效的燃油率。V2500最引人注目的特点之一就是它的风扇叶片,采用的是由罗·罗公司设计和发展的无凸台宽弦空心叶 相似文献
67.
John F. Cavanaugh James C. Smith Xiaoli Sun Arlin E. Bartels Luis Ramos-Izquierdo Danny J. Krebs Jan F. McGarry Raymond Trunzo Anne Marie Novo-Gradac Jamie L. Britt Jerry Karsh Richard B. Katz Alan T. Lukemire Richard Szymkiewicz Daniel L. Berry Joseph P. Swinski Gregory A. Neumann Maria T. Zuber David E. Smith 《Space Science Reviews》2007,131(1-4):451-479
The Mercury Laser Altimeter (MLA) is one of the payload science instruments on the MErcury Surface, Space ENvironment, GEochemistry,
and Ranging (MESSENGER) mission, which launched on August 3, 2004. The altimeter will measure the round-trip time of flight
of transmitted laser pulses reflected from the surface of the planet that, in combination with the spacecraft orbit position
and pointing data, gives a high-precision measurement of surface topography referenced to Mercury’s center of mass. MLA will
sample the planet’s surface to within a 1-m range error when the line-of-sight range to Mercury is less than 1,200 km under
spacecraft nadir pointing or the slant range is less than 800 km. The altimeter measurements will be used to determine the
planet’s forced physical librations by tracking the motion of large-scale topographic features as a function of time. MLA’s
laser pulse energy monitor and the echo pulse energy estimate will provide an active measurement of the surface reflectivity
at 1,064 nm. This paper describes the instrument design, prelaunch testing, calibration, and results of postlaunch testing. 相似文献
68.
James A. Blake Paul Chote Don Pollacco William Feline Grant Privett Andrew Ash Stuart Eves Arthur Greenwood Nick Harwood Thomas R. Marsh Dimitri Veras Christopher Watson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(1):360-370
Recent anomalies exhibited by satellites and rocket bodies have highlighted that a population of faint debris exists at geosynchronous (GEO) altitudes, where there are no natural removal mechanisms. Despite previous optical surveys probing to around 10–20 cm in size, regular monitoring of faint sources at GEO is challenging, thus our knowledge remains sparse. It is essential that we continue to explore the faint debris population using large telescopes to better understand the risk posed to active GEO satellites. To this end, we present photometric results from a survey of the GEO region carried out with the 2.54 m Isaac Newton Telescope in La Palma, Canary Islands. We probe to 21st visual magnitude (around 10 cm, assuming Lambertian spheres with an albedo of 0.1), uncovering 129 orbital tracks with GEO-like motion across the eight nights of dark-grey time comprising the survey. The faint end of our brightness distribution continues to rise until the sensitivity limit of the sensor is reached, suggesting that the modal brightness could be even fainter. We uncover a number of faint, uncatalogued objects that show photometric signatures of rapid tumbling, many of which straddle the limiting magnitude of our survey over the course of a single exposure, posing a complex issue when estimating object size. This work presents the first instalment of DebrisWatch, an ongoing collaboration between the University of Warwick and the Defence Science and Technology Laboratory (UK) investigating the faint population of GEO debris. 相似文献
69.
Alan F. M. Moorwood 《Space Science Reviews》1996,77(3-4):303-366
Bursts of massive star formation can temporarily dominate the luminosity of galaxies spanning a wide range of morphological types. This review is concerned primarily with such events in the central 1 kpc region of spiral galaxies which result from bar driven inflows of gas triggered by interactions or mergers. Most of the stellar radiant luminosity of such bursts is absorbed by dust and re-emitted in the far-infrared and is accompanied by radio and X-ray emission from supernova remnants which can also act collectively to drive galaxy scale outflows. Both evolutionary stellar models and estimates of the gas depletion times are consistent with typical burst durations of 107–8 yr. Spatially-resolved studies of nearby starburst galaxies reveal that the activity is distributed over many individual star forming complexes within rings and other structures organized by interactions between bars and the disc over a range of scales. More distant and extreme examples associated with mergers of massive spirals have luminosities > 1013
L
and molecular gas masses > 1010
M
implying star formation rates > 1000 M
yr–1 which can only be sustained for 107 yr. In the most luminous merging systems, however, the relative importance of starburst and AGN activity and their possible evolutionary connection is still a hotly debated issue. Also controversial are suggestions that starbursts in addition to a black hole are required to account for the properties of AGNs or that starbursts alone may be sufficient under certain conditions. In a wider context, starbursts must clearly have played an important role in galaxy formation and evolution at earlier times. Recent detections of high redshift galaxies show that star formation was underway at z 4 but do not support a continuing increase of the strong evolution in the co-moving star formation density seen out to z l. Primeval starburst pre-cursors of spheroidal systems also remain elusive. The most distant candidates are radio galaxies and quasars at z = 4–5 and a possible population of objects responsible for an isotropic sub-mm wave background tentatively claimed to have been detected by the COBE satellite. 相似文献
70.
Alan M. Levine Hale Bradt Edward H. Morgan Ron Remillard The MIT/GSFC ASM Team 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2970-2975
Selected results from the Rossi X-ray Timing Explorer All-Sky Monitor are presented to illustrate the phenomenology of the light curves. The sensitivity to periodic intensity variations is indicated by the folded light curve of AM Her. The gray line between transient and persistent sources is emphasized. Light curves of a range of systems comprising black holes or neutron stars and low and high mass companion stars show that the behavior of these systems is often, but not always, characteristic. 相似文献