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71.
Alankrita Isha Mrigakshi Daniel Matthiä Thomas Berger Günther Reitz Robert F. Wimmer-Schweingruber 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The radiation environment in space is a major concern for human spaceflight because of the adverse effects of high levels of radiation on astronauts’ health. Therefore, it is essential to perform radiation risk assessments already during the concept studies of a manned mission. Galactic Cosmic Rays (GCR) have been identified to be one of the primary sources of radiation exposure in space. 相似文献
72.
Esa Kallio Jean-Yves Chaufray Ronan Modolo Darci Snowden Robert Winglee 《Space Science Reviews》2011,162(1-4):267-307
Increased computer capacity has made it possible to model the global plasma and neutral dynamics near Venus, Mars and Saturn??s moon Titan. The plasma interactions at Venus, Mars, and Titan are similar because each possess a substantial atmosphere but lacks a global internally generated magnetic field. In this article three self-consistent plasma models are described: the magnetohydrodynamic (MHD) model, the hybrid model and the fully kinetic plasma model. Chamberlain and Monte Carlo models of the Martian exosphere are also described. In particular, we describe the pros and cons of each model approach. Results from simulations are presented to demonstrate the ability of the models to capture the known plasma and neutral dynamics near the three objects. 相似文献
73.
Gates David F. Haislmaier Robert J. Hill Lemmuel L. 《IEEE transactions on aerospace and electronic systems》1967,(2):303-308
A Doppler radar tracking system has been used successfully to measure impact drag coefficients for several water-entry configurations. Hemisphere-cylinder and cone-cylinder models were launched vertically into a tank of water at velocities between 100 and 200 feet per second. These launchings were evaluation tests for a system to be used in a new facility at the Naval Ordnance Laboratory?the Hydroballistics Tank. Planned launchings in that facility will be at velocities up to 3000 feet per second. Knowledge of the drag coefficient profile (CD versus depth of penetration) is important in the design of high-velocity water-entry weapons. 相似文献
74.
The problem of optimally processing data with unknown focus is investigated. Optimum data processors are found by the method of maximum likelihood under a variety of assumptions that apply to most of the situations arising in practice. The unknown focus may be either an unknown parameter or an unknown random variable; the signal may be of known form or a random function; it is further assumed that the signal is received in additive, white, Gaussian noise. The problems of jointly estimating other unknown parameters and, in the case of a random signal, jointly estimating the signal, are also treated. The asymptotic variance and correlation of the estimators is discussed. Electrooptical realizations of the maximum likelihood computers are given. An iterative method of solution of the likelihood equation is also discussed. The discussion and results are directly applicable to the processing of synthetic aperture radar data. 相似文献
75.
Recent determinations of the primordial He abundance have given significantly different results. We are attempting to identify some of the causes of these differences and propose observational solutions. Here we identify a systematic difference in how the data are interpreted (differences in corrections for the presence of neutral helium) and the importance of a systematic bias towards lower derived helium abundances (underestimating the presence of underlying stellar absorption). 相似文献
76.
Robert J. Ferl Agata Zupanska April Spinale David Reed Susan Manning-Roach George Guerra David R. Cox Anna-Lisa Paul 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Molecular biology experiments on the International Space Station (ISS) continue to face challenges of sample harvesting and sample return to earth for post flight analysis; however, the use of Kennedy Space Center Fixation Tubes filled with RNALater has proven to be a robust solution to many of these challenges. While it is clear that one direction of future spaceflight experimentation may be towards enhanced on-orbit analytical capabilities, the rapid progress of earth-bound analytical capacity dictates that facile return of molecular biology samples from the ISS will continue to be a mainstay of space life sciences research and flight operations. In this paper we present a case study of the successful performance of KFTs and RNALater over a broad set of operational conditions of ascent configuration, on-orbit experiment use, on-orbit storage and sample return configurations that are unique to ISS current operations and constraints. We also provide observations on performance limits and discuss deployment opportunities and scenarios that are consistent with continued successful ISS molecular biology experimentation. 相似文献
77.
Meteor Phenomena and Bodies 总被引:12,自引:0,他引:12
Zdeněk Ceplecha JiřÍ Borovička W. Graham Elford Douglas O. ReVelle Robert L. Hawkes VladimÍr Porubčan Miloš Šimek 《Space Science Reviews》1998,84(3-4):327-471
Meteoroids can be observed at collision with the Earth's atmosphere as meteors. Different methods of observing meteors are
presented: besides the traditional counts of individual events, exact methods yield also data on the geometry of the atmospheric
trajectory; on the dynamics and ablation of the body in the atmosphere; on radiation; on the spectral distribution of radiation;
on ionization; on accompanying sounds; and also data on orbits. Theoretical models of meteoroid interaction with the atmosphere
are given and applied to observational data. Attention is paid to radar observations; to spectroscopic observations; to experiments
with artificial meteors and to different types of meteor sounds. The proposed composition and structure of meteoroids as well
as their orbits link them to meteorites, asteroids and comets. Meteor streams can be observed as meteor showers and storms.
The rate of influx of meteoroids of different sizes onto Earth is presented and potential hazards discussed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
78.
Robert H. Nichols Jr. 《Space Science Reviews》2000,92(1-2):113-122
Variations in the abundances of short-lived radionuclides such as 26Al (τ1/2 ≈ 0.74 Ma) and 53Mn (τ1/2 ≈ 3.7 Ma) in meteoritic solids may be used to infer relative formation intervals of these solids in the nebula at precisions
of less than 1 Ma. In a strict chronometric interpretation of the isotopic variations, whereby criteria such as spatial and
temporal isotopic homogeneity and closed system isotopic evolution are met, solid formation occurred in the nebula for at
least several million years. This is longer than some theoretical and astronomical estimates for the duration of the active
nebula. The evidence for live 41Ca (τ1/2 ≈ 0.10 Ma) in meteoritic inclusions further indicates that the onset of solid formation occurred quite early, perhaps within
a few hundred thousand years after the onset of the collapse of the sun's parent molecular cloud. Failure of the chronometric
interpretation may arise for a variety of reasons, including but not limited to, the late, inhomogeneous injection of material
from a nearby stellar source or the local production of short-lived radionuclides by an energetic particle irradiation, e. g., from T Tauri (X-wind) or galactic cosmic ray sources. Although some isotopic evidence exists that the criteria required
for a strict chronometric interpretation are not met by each of the short-lived chronometers, there is no compelling reason
to shorten the interval of solid formation in the nebula to less than 1 Ma.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
79.
Martin Tluczykont Daniel Hampf Dieter Horns Tanja Kneiske Robert Eichler Rayk Nachtigall Gavin Rowell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The question of the origin of cosmic rays and other questions of astroparticle and particle physics can be addressed with indirect air-shower observations above 10 TeV primary energy. We propose to explore the cosmic ray and γ-ray sky (accelerator sky) in the energy range from 10 TeV to 1 EeV with the new ground-based large-area wide angle (ΔΩ ∼ 0.85 sterad) air-shower detector HiSCORE (Hundred∗i Square-km Cosmic ORigin Explorer). The HiSCORE detector is based on non-imaging air-shower Cherenkov light-front sampling using an array of light-collecting stations. A full detector simulation and basic reconstruction algorithms have been used to assess the performance of HiSCORE. First prototype studies for different hardware components of the detector array have been carried out. The resulting sensitivity of HiSCORE to γ-rays will be comparable to CTA at 50 TeV and will extend the sensitive energy range for γ-rays up to the PeV regime. HiSCORE will also be sensitive to charged cosmic rays between 100 TeV and 1 EeV. 相似文献
80.
James R. Drummond Jiansheng Zou Florian Nichitiu Jayanta Kar Robert Deschambaut John Hackett 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The MOPITT (Measurements of Pollution in the Troposphere) instrument has provided more than nine years of global carbon monoxide (CO) measurements on a continuous basis since its launch aboard the Terra Spacecraft on December 18th, 1999. This paper gives an overview of the core sub-system performance and major issues of the in-flight instrument over the mission period. Some of the instrument anomalies are also discussed. The major successes are: (1) the concept of using a combination of correlation systems such as Length Modulated Cells (LMCs) and Pressure Modulated Cells (PMCs) to retrieve CO profiles in the troposphere; (2) the redundant design in the instrumentation which was crucial for coping with unexpected in-flight anomalies and for continuing the mission in the case of component failure; (3) the thermal environment on orbit that is so stable that some calibration procedures are not necessary; and (4) the recent production of CO total column retrieved from the MOPITT 2.3 μm channel. 相似文献