全文获取类型
收费全文 | 89篇 |
免费 | 0篇 |
专业分类
航空 | 34篇 |
航天技术 | 33篇 |
航天 | 22篇 |
出版年
2021年 | 2篇 |
2019年 | 1篇 |
2018年 | 6篇 |
2017年 | 1篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 2篇 |
2012年 | 6篇 |
2011年 | 6篇 |
2010年 | 2篇 |
2009年 | 2篇 |
2008年 | 4篇 |
2007年 | 1篇 |
2006年 | 6篇 |
2005年 | 1篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2001年 | 3篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1992年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 7篇 |
排序方式: 共有89条查询结果,搜索用时 954 毫秒
1.
A Fekete Gy Rontó M Hegedüs K Módos A Bérces G Kovács H Lammer C Panitz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(8):1306-1310
The main goal of PUR experiment (phage and uracil response) is to examine and quantify the effect of specific space conditions on nucleic acid models. To achieve this an improved method was elaborated for the preparation of DNA and bacteriophage thin films. The homogeneity of the films was controlled by UV spectroscopy and microscopy. To provide experimental evidence for the hypothesis that interplanetary transfer of the genetic material is possible, phage T7 and isolated T7 DNA thin films have been exposed to selected space conditions: intense UVC radiation (lambda=254 nm) and high vacuum (10(-4) Pa). The effects of DNA hydration, conformation and packing on UV radiation damage were examined. Characteristic changes in the absorption spectrum, in the electrophoretic pattern of DNA and the decrease of the amount of PCR products have been detected indicating the photodamage of isolated and intraphage DNA. 相似文献
2.
We present the results from a study of the variations of the cosmic-ray intensity with time, heliographic latitude, and longitude, and for varying interplanetary conditions, using our three-dimensional, time-dependent computer code for cosmic-ray transport in the heliosphere. Our code also produces a solar-wind and interplanetary magnetic field (IMF) configuration which is compared with observations. Because of the fully threedimensional nature of the model calculations, we are able to model time variations which would be expected to be observed along Ulysses's trajectory as it moves to high latitudes. In particular we can model the approximately 13-and 26-day solar-rotation induced variations in cosmic rays, solar wind and IMF, as a function of increasing heliographic latitude, as one moves poleward of the interplanetary current sheet. Our preliminary model results seem to be in general form quite similar to published data, but depend on the physical parameters used such as cosmic-ray diffusion coefficients, boundary conditions, and the nature of the solar wind and IMF and current sheet. 相似文献
3.
The simple tilted dipole picture of Corotating Interaction Regions which prevailed during the first polar pass of Ulysses no longer applies since the Sun entered a more active phase. Recent observations show that CIRs still persist, though the
large polar coronal holes of solar minimum shrink to smaller areas and move to lower latitudes. We present 3-D simulations
for the cosmic-ray intensity variations in a model with non-polar high speed streams. Latitudinal and recurrent time-variations
are discussed, but more detailed and realistic simulations are required before quantitative comparisons with observations
can be made.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
Annual solar UV exposure and biological effective dose rates on the Martian surface. 总被引:4,自引:0,他引:4
M R Patel A Bérces T Kerékgyárto Gy Rontó H Lammer J C Zarnecki 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(8):1247-1252
The ultraviolet (UV) environment of Mars has been investigated to gain an understanding of the variation of exposure throughout a Martian year, and link this flux to biological effects and possible survival of organisms at the Martian surface. To gain an idea of how the solar UV radiation varies between different regions, including planned landing sites of two future Mars surface missions, we modelled the total solar UV surface flux throughout one Martian year for two different dust scenarios. To understand the degree of solar UV stress on micro-organisms and/or molecules essential for life on the surface of Mars, we also calculated the biologically effective dose (BED) for T7 and Uracil in relevant wavelength regions at the Martian surface as a function of season and latitude, and discuss the biological survival rates in the presence of Martian solar UV radiation. High T7/Uracil BED ratios indicate that even at high latitudes where the UV flux is significantly reduced, the radiation environment is still hostile for life due to the persisting UV-C component of the flux. 相似文献
5.
A Lazcano E Díaz-Villagómez T Mills J Oró 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(3):345-356
The most frequently invoked explanation for the origin of metabolic pathways is the retrograde evolution hypothesis. In contrast, according to the so-called "patchwork" theory, metabolism evolved by the recruitment of relatively inefficient small enzymes of broad specificity that could react with a wide range of chemically related substrates. In this paper it is argued that both sequence comparisons and experimental results on enzyme substrate specificity support the patchwork assembly theory. The available evidence supports previous suggestions that gene duplication events followed by a gradual neoDarwinian accumulation of mutations and other minute genetic changes lead to the narrowing and modification of enzyme function in at least some primordial metabolic pathways. 相似文献
6.
7.
López-Valverde Miguel A. Gerard Jean-Claude González-Galindo Francisco Vandaele Ann-Carine Thomas Ian Korablev Oleg Ignatiev Nikolai Fedorova Anna Montmessin Franck Määttänen Anni Guilbon Sabrina Lefevre Franck Patel Manish R. Jiménez-Monferrer Sergio García-Comas Maya Cardesin Alejandro Wilson Colin F. Clancy R. T. Kleinböhl Armin McCleese Daniel J. Kass David M. Schneider Nick M. Chaffin Michael S. López-Moreno José Juan Rodríguez Julio 《Space Science Reviews》2018,214(1):1-31
Space Science Reviews - Time measured by an ideal clock crucially depends on the gravitational potential and velocity of the clock according to general relativity. Technological advances in... 相似文献
8.
9.
Gy Rontó A Bérces A Fekete G Kovács P Gróf H Lammer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(8):1302-1305
Polycrystalline uracil thin layers participate in the phage and uracil response (PUR) experiment, assigned to the biological dosimetry of the extraterrestrial solar radiation on the International Space Station (ISS). In ground based experiments (experiment verification tests), the following space parameters were simulated and studied: temperature, vacuum and short wavelength UV (UV-C, down to 200 nm) radiation. The closed uracil samples proved to be vacuum-tight for 7 days. In the tested temperature range (from -20 to +40 degrees C) the uracil samples are stable. The kinetic of dimer formation (dimerization) and reversion (monomerization) of uracil dimers due to short wavelength UV radiation was detected, the monomerization efficiency of the polychromatic deuterium lamp is higher than that of the germicidal lamp. A mathematical model describing the kinetic of monomerization-dimerization was constructed. Under the influence of UV radiation the dimerization-monomerization reactions occur simultaneously, thus the additivity law of the effect of the various wavelengths is not applicable. 相似文献
10.
J Oró J M Berry 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1987,7(5):23-32
Some of the chemical species which have been detected in comets include H2O, HCN, CH3CN, CO, CO2, NH3, CS, C2 and C3. All of these have also been detected in the interstellar medium, indicating a probable relationship between interstellar dust and gas clouds and comets. Laboratory experiments carried out with different mixtures of these molecules give rise to the formation of the biochemical compounds which are necessary for life, such as amino acids, purines, pyrimidines, monosaccharides, etc. However, in spite of suggestions to the contrary, the presence of life in comets is unlikely. On the other hand, the capture of cometary matter by the primitive Earth is considered essential for the development of life on this planet. The amount of cometary carbon-containing matter captured by the Earth, as calculated by different authors, is several times larger than the total amount of organic matter present in the biosphere (10(18)g). The major classes of reactions which were probably involved in the formation of key biochemical compounds are discussed. Our tentative conclusions are that: 1) comets played a predominant role in the emergence of life on our planet, and 2) they are the cosmic connection with extraterrestrial life. 相似文献