全文获取类型
收费全文 | 74篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
航空 | 51篇 |
航天技术 | 9篇 |
航天 | 16篇 |
出版年
2018年 | 3篇 |
2017年 | 1篇 |
2014年 | 2篇 |
2012年 | 3篇 |
2011年 | 3篇 |
2009年 | 3篇 |
2008年 | 3篇 |
2007年 | 5篇 |
2006年 | 2篇 |
2005年 | 2篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 1篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 7篇 |
1987年 | 2篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1968年 | 2篇 |
1967年 | 3篇 |
1964年 | 1篇 |
排序方式: 共有76条查询结果,搜索用时 515 毫秒
51.
Flinn ED 《Aerospace America》2003,41(11):22-23
When astronauts first go to Mars, it will be difficult for them to bring everything they need to survive. Even the first tentative explorations could last as long as two years. However, spaceships can carry only limited supplies. "We might have to do what explorers have done for ages: live off the land," says chemical engineer Ken Debelak of Vanderbilt University. It is a meager atmosphere, compared to Earth's, and it is about 95% carbon dioxide. This, however, turns out to be an advantage. The CO2, says Debelak, can be used to harvest almost everything else. 相似文献
52.
Fucci RL Gardner J Hanifin JP Jasser S Byrne B Gerner E Rollag M Brainard GC 《Acta Astronautica》2005,56(9-12):1017-1024
Light is being used as a pre-launch countermeasure to circadian and sleep disruption in astronauts. The effect of light on the circadian system is readily monitored by measurement of plasma melatonin. Our group has established an action spectrum for human melatonin regulation and determined the region of 446-477 nm to be the most potent for suppressing plasma melatonin. The aim of this study was to compare the efficacy of 460 and 555 nm for suppressing melatonin using a within-subjects design. Subjects (N=12) were exposed to equal photon densities (7.18 x 10(12) photons/cm2/s) at 460 and 555 nm. Melatonin suppression was significantly stronger at 460 nm (p<0.02). An extension to the action spectrum showed that 420 nm light at 16 and 32 microW/cm2 significantly suppressed melatonin (p<0.04 and p<0.002). These studies will help optimize lighting countermeasures to circadian and sleep disruption during spaceflight. 相似文献
53.
54.
Microbial life in a liquid asphalt desert 总被引:1,自引:0,他引:1
Schulze-Makuch D Haque S de Sousa Antonio MR Ali D Hosein R Song YC Yang J Zaikova E Beckles DM Guinan E Lehto HJ Hallam SJ 《Astrobiology》2011,11(3):241-258
Pitch Lake in Trinidad and Tobago is a natural asphalt reservoir nourished by pitch seepage, a form of petroleum that consists of mostly asphaltines, from the surrounding oil-rich region. During upward seepage, pitch mixes with mud and gases under high pressure, and the lighter portion evaporates or is volatilized, which produces a liquid asphalt residue characterized by low water activity, recalcitrant carbon substrates, and noxious chemical compounds. An active microbial community of archaea and bacteria, many of them novel strains (particularly from the new Tar ARC groups), totaling a biomass of up to 10(7) cells per gram, was found to inhabit the liquid hydrocarbon matrix of Pitch Lake. Geochemical and molecular taxonomic approaches revealed diverse, novel, and deeply branching microbial lineages with the potential to mediate anaerobic hydrocarbon degradation processes in different parts of the asphalt column. In addition, we found markers for archaeal methane metabolism and specific gene sequences affiliated with facultative and obligate anaerobic sulfur- and nitrite-oxidizing bacteria. The microbial diversity at Pitch Lake was found to be unique when compared to microbial communities analyzed at other hydrocarbon-rich environments, which included Rancho Le Brea, a natural asphalt environment in California, USA, and an oil well and a mud volcano in Trinidad and Tobago, among other sites. These results open a window into the microbial ecology and biogeochemistry of recalcitrant hydrocarbon matrices and establish the site as a terrestrial analogue for modeling the biotic potential of hydrocarbon lakes such as those found on Saturn's largest moon Titan. 相似文献
55.
Edward G. Schmidt 《Space Science Reviews》1980,27(3-4):449-455
Conclusions The discrepancy between the luminosity scale for Cepheids derived from the intermediate band photometry and the presently accepted scale requires further investigation. We have discussed various factors which might affect the previous work and which might affect the present method but we are unable at this time to provide a definite explanation. However, since there is no obvious problem with the intermediate band photometry we should give serious consideration to the possibility that the Cepheid luminosity scale might require some revision. 相似文献
56.
57.
Edward P. J. van den Heuvel 《Space Science Reviews》1981,30(1-4):623-642
Observational evidence suggests that most — if not all — binary X-ray sources are neutron stars. The evolutionary status and possible formation mechanisms of the type I (massive) and type II (low-mass) X-ray binaries are discussed. The difference between the standard massive X-ray binaries and the Be/X-ray binaries is ascribed to a somewhat different evolutionary history and status, and possible reasons for the existence of short- and long — period X-ray pulsars are discussed. Type II X-ray sources in globular clusters were most probably formed by capture processes; their formation rate inferred from the observations indicates that only a small fraction ( 1 to 10 percent) of the originally formed neutron stars have remained in their clusters. Type II sources in the galactic bulge may also have formed from cataclysmic binaries in which a white dwarf was driven over the Chandrasekhar limit by accretion. 相似文献
58.
Edward A. Spiegel 《Space Science Reviews》2009,144(1-4):25-51
59.
The past two decades have witnessed significant changes in our knowledge of long-term solar and solar wind activity. The sunspot number time series (1700-present) developed by Rudolf Wolf during the second half of the 19th century was revised and extended by the group sunspot number series (1610–1995) of Hoyt and Schatten during the 1990s. The group sunspot number is significantly lower than the Wolf series before ~1885. An effort from 2011–2015 to understand and remove differences between these two series via a series of workshops had the unintended consequence of prompting several alternative constructions of the sunspot number. Thus it has been necessary to expand and extend the sunspot number reconciliation process. On the solar wind side, after a decade of controversy, an ISSI International Team used geomagnetic and sunspot data to obtain a high-confidence time series of the solar wind magnetic field strength (\(B\)) from 1750-present that can be compared with two independent long-term (> ~600 year) series of annual \(B\)-values based on cosmogenic nuclides. In this paper, we trace the twists and turns leading to our current understanding of long-term solar and solar wind activity. 相似文献
60.
As an increasing number of fascinating discoveries within the realm of bioastronomy appear in media headlines, participating scientists continue to pursue ways of insuring the long-term success of the scientific discipline. In an effort to foster cross-disciplinary collaboration, communication, and training for scientists involved in bioastronomy research, a team of scientists and science education professionals have developed a survey to assess (1) the degree to which scientists in bioastronomy define themselves as interdisciplinary scientists, (2) the extent to which scientists identify their needs for professional development opportunities to become more effective interdisciplinary collaborators, and (3) what services and infrastructure the bioastronomy community needs to develop for long-term productive interdisciplinary communication, collaboration, research and training. The results of a survey, distributed at the 2004 Astrobiology Science Conference (held at Moffett Field, CA), serve the bioastronomy science community by providing a sound research baseline that informs decisions and targeted efforts to increase cross-disciplinary communication, gathering information about needed professional development opportunities for scientists, and generating insights for training of the next generation of astrobiologists. Results indicate that members of the community feel that interdisciplinary communication and collaboration can best be supported by (1) increased funding opportunities, (2) scheduled time for collaboration at professional meetings, (3) reduction of concurrent sessions at professional meetings, and (4) creation of professional development opportunities for scientists. 相似文献