全文获取类型
收费全文 | 2687篇 |
免费 | 4篇 |
国内免费 | 7篇 |
专业分类
航空 | 1253篇 |
航天技术 | 943篇 |
综合类 | 9篇 |
航天 | 493篇 |
出版年
2021年 | 20篇 |
2019年 | 17篇 |
2018年 | 60篇 |
2017年 | 36篇 |
2016年 | 41篇 |
2015年 | 12篇 |
2014年 | 63篇 |
2013年 | 92篇 |
2012年 | 63篇 |
2011年 | 94篇 |
2010年 | 77篇 |
2009年 | 127篇 |
2008年 | 144篇 |
2007年 | 66篇 |
2006年 | 68篇 |
2005年 | 69篇 |
2004年 | 66篇 |
2003年 | 89篇 |
2002年 | 46篇 |
2001年 | 96篇 |
2000年 | 49篇 |
1999年 | 67篇 |
1998年 | 72篇 |
1997年 | 67篇 |
1996年 | 68篇 |
1995年 | 94篇 |
1994年 | 86篇 |
1993年 | 44篇 |
1992年 | 51篇 |
1991年 | 17篇 |
1990年 | 24篇 |
1989年 | 51篇 |
1988年 | 32篇 |
1987年 | 23篇 |
1986年 | 31篇 |
1985年 | 81篇 |
1984年 | 75篇 |
1983年 | 43篇 |
1982年 | 73篇 |
1981年 | 68篇 |
1980年 | 20篇 |
1978年 | 32篇 |
1977年 | 12篇 |
1975年 | 24篇 |
1974年 | 18篇 |
1973年 | 16篇 |
1972年 | 17篇 |
1969年 | 13篇 |
1968年 | 12篇 |
1966年 | 11篇 |
排序方式: 共有2698条查询结果,搜索用时 78 毫秒
251.
Kau S. Kumar K.S.P. Granley G.B. 《IEEE transactions on aerospace and electronic systems》1969,(6):906-911
The theory of nonlinear filtering has been applied to the problem of the attitude determination of a satellite. Two approximation methods have been studied with a view to practical implementation. Computer simulation results are included. 相似文献
252.
Logistics support of a long duration space station will dictate a high degree of space flight activity to rotate personnel and transport supplies and equipment. Systems characteristics and mission requirements for space station logistics have been analyzed within the context of a broad spectrum of space missions. Preliminary concepts for a space shuttle system (space transportation) have been developed. This system can support not only a space station program, but a wide variety of space missions for both NASA and the DOD. 相似文献
253.
Richard I. Klein Maxwell T. Sandford II Rodney W. Whitaker 《Space Science Reviews》1980,27(3-4):275-282
Two-dimensional calculations of ionization-shockwave propagation into a curved molecular cloud are presented. Density enhancement occurs due to the combined effects of cloud curvature and radiation flow. The star formation process is expected to be enhanced near the edges of irregularly shaped molecular clouds.Authors listed alphabetically 相似文献
254.
M.B. Vasilyev A.S. Vyshlov M.A. Kolosov A.P. Mesterton N.A. Savich V.A. Samovol L.N. Samoznaev A.I. Sidorenko 《Acta Astronautica》1980,7(3):335-340
The experiment with two-frequency radio occultation measurements of the Venusian nightside ionosphere using the Venera-9 and 10 orbiters is described. The experiment is the first of a kind in which the radio link to one of the spacecraft is used to probe the ionosphere, while the other is measuring the variations in the integral electron number density along the path of radio ray propagation. The experiment has been designed to achieve the maximum possible accuracies in determining the parameters of the probed ionosphere using the bistatic two-frequency radio occultation method. 相似文献
255.
Induced abnormality in Mir- and Earth grown Super Dwarf wheat. 总被引:4,自引:0,他引:4
D L Bubenheim J Stieber W F Campbell F B Salisbury M Levinski V Sytchev I Podolsky L Chernova I Pdolsky 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(1):229-234
Super-dwarf wheat grown on the Mir space station using the Svet "Greenhouse" exhibited morphological, metabolic and reproductive abnormalities compared with Earth-grown wheat. Of prominent importance were the abnormalities associated with reproductive ontogeny and the total absence of seed formation on Mir. Changes in the apical meristem associated with transition from the vegetative phase to floral initiation and development of the reproductive spike were all typical of 'Super-Dwarf' wheat up to the point of anthesis. Observation of ruptured anthers from the Mir-grown plants revealed what appeared to be normally developed pollen. These pollen gains, however, contained only one nuclei, while normal viable pollen is tri-nucleate. A potentially important difference in the flight experiment, compared with ground reference studies, was the presence of a high level of atmospheric ethylene (1,200 ppb). Ground studies conducted by exposing 'Super-Dwarf' wheat to ethylene just prior to anthesis resulted in manifestation of the same abnormalities observed in the space flight samples. 相似文献
256.
S B Curtis E G Luebeck W D Hazelton S H Moolgavkar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):937-944
When applied to the Colorado Plateau miner population, the two-stage clonal expansion (TSCE) model of radiation carcinogenesis predicts that radiation-induced promotion dominates radiation-induced initiation. Thus, according to the model, at least for alpha-particle radiation from inhaled radon daughters, lung cancer induction over long periods of protracted irradiation appears to be dominated by radiation-induced modification of the proliferation kinetics of already-initiated cells rather than by direct radiation-induced initiation (i.e., mutation) of normal cells. We explore the possible consequences of this result for radiation exposures to space travelers on long missions. Still unknown is the LET dependence of this effect. Speculations of the cause of this phenomenon include the suggestion that modification of cell kinetics is caused by a "bystander" effect, i.e., the traversal of normal cells by alpha particles, followed by the signaling of these cells to nearby initiated cells which then modify their proliferation kinetics. 相似文献
257.
The hypothesis that life originated and evolved from linear informational molecules capable of facilitating their own catalytic replication is deeply entrenched. However, widespread acceptance of this paradigm seems oblivious to a lack of direct experimental support. Here, we outline the fundamental objections to the de novo appearance of linear, self-replicating polymers and examine an alternative hypothesis of template-directed coding of peptide catalysts by adsorbed purine bases. The bases (which encode biological information in modern nucleic acids) spontaneously self-organize into two-dimensional molecular solids adsorbed to the uncharged surfaces of crystalline minerals; their molecular arrangement is specified by hydrogen bonding rules between adjacent molecules and can possess the aperiodic complexity to encode putative protobiological information. The persistence of such information through self-reproduction, together with the capacity of adsorbed bases to exhibit enantiomorphism and effect amino acid discrimination, would seem to provide the necessary machinery for a primitive genetic coding mechanism. 相似文献
258.
Duke MB 《Acta Astronautica》2002,50(6):379-383
The Clementine mission has revived interest in the possibility that ice exists in shadowed craters near the lunar poles. Theoretically, the problem is complex, with several possible sources of water (meteoroid, asteroid, comet impact), several possible loss mechanisms (impact vaporization, sputtering, photoionization), and burial by meteorite impact. Opinions of modelers have ranged from no ice to several times 10(16) g of ice in the cold traps. Clementine bistatic radar data have been interpreted in favor of the presence of ice, while Arecibo radar data do not confirm its presence. The Lunar Prospector mission, planned to be flown in the fall of 1997, could gather new evidence for the existence of ice. If ice is present, both scientific and utilitarian objectives would be addressed by a lunar polar rover, such as that proposed to the NASA Discovery program, but not selected. The lunar polar rover remains the best way to understand the distribution and characteristics of lunar polar ice. 相似文献
259.
We describe the formation of hot intergalactic gas along with baryonic remnants in galaxy halos. In this scenario, the mass and metallicity of the hot intracluster and intragroup gas relates directly to the production of baryonic remnants during the collapse of galactic halos. We construct a schematic but self-consistent model in which early bursts of star formation lead to a large remnant population in the halo, and to the outflow of stellar ejecta into the halo and ultimately the Local Group. We consider local as well as high redshift constraints on this scenario. This study suggests that the microlensing objects in the Galactic halo may predominantly be 0.5M white dwarfs, assuming that the initial mass function for early star formation favored the formation of intermediate mass stars with m 1M. However, the bulk of the baryonic dark matter in this scenario is associated with the ejecta of the white dwarf progenitors, and resides in the hot intergalactic medium. 相似文献
260.
The sopite syndrome is a poorly understood response to motion. Drowsiness and mood changes are the primary characteristics of the syndrome. The sopite syndrome can exist in isolation from more apparent symptoms such as nausea, can last long after nausea has subsided, and can debilitate some individuals. It is most likely a distinct syndrome from "regular" motion sickness or common fatigue, and is of potential concern in a variety of situations. The syndrome may be particularly hazardous in transportation settings where other performance challenges (e.g., sleep deprivation) are already present. It is also a potential concern in cases where illnesses such as sleep disorders or depression may interact with the syndrome and confuse diagnosis. 相似文献