全文获取类型
收费全文 | 4313篇 |
免费 | 12篇 |
国内免费 | 8篇 |
专业分类
航空 | 2203篇 |
航天技术 | 1649篇 |
综合类 | 18篇 |
航天 | 463篇 |
出版年
2018年 | 59篇 |
2017年 | 48篇 |
2016年 | 33篇 |
2014年 | 66篇 |
2013年 | 93篇 |
2012年 | 74篇 |
2011年 | 130篇 |
2010年 | 91篇 |
2009年 | 148篇 |
2008年 | 228篇 |
2007年 | 85篇 |
2006年 | 72篇 |
2005年 | 99篇 |
2004年 | 125篇 |
2003年 | 153篇 |
2002年 | 79篇 |
2001年 | 147篇 |
2000年 | 89篇 |
1999年 | 109篇 |
1998年 | 141篇 |
1997年 | 101篇 |
1996年 | 114篇 |
1995年 | 140篇 |
1994年 | 164篇 |
1993年 | 82篇 |
1992年 | 116篇 |
1991年 | 48篇 |
1990年 | 58篇 |
1989年 | 115篇 |
1988年 | 40篇 |
1987年 | 56篇 |
1986年 | 65篇 |
1985年 | 142篇 |
1984年 | 88篇 |
1983年 | 98篇 |
1982年 | 106篇 |
1981年 | 134篇 |
1980年 | 56篇 |
1979年 | 46篇 |
1978年 | 42篇 |
1977年 | 38篇 |
1976年 | 26篇 |
1975年 | 40篇 |
1974年 | 36篇 |
1973年 | 32篇 |
1972年 | 36篇 |
1971年 | 35篇 |
1969年 | 35篇 |
1967年 | 25篇 |
1966年 | 26篇 |
排序方式: 共有4333条查询结果,搜索用时 15 毫秒
111.
Ground performance of air conditioning and water recycle system for a Space Plant Box. 总被引:2,自引:0,他引:2
A Tani T Okuma E Goto Y Kitaya T Saito H Takahashi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(9):1557-1562
Researchers from 5 Japanese universities have developed a plant growth facility (Space Plant Box) for seed to seed experiments under microgravity. The breadboard model of the Space Plant Box was fabricated by assembling subsystems developed for microgravity. The subsystems include air conditioning and water recycle system, air circulation system, water and nutrient delivery system, lighting system and plant monitoring system. The air conditioning and water recycle system is simply composed of a single heat exchanger, two fans and hydrophilic fibrous strings. The strings allow water movement from the cooler fin in the Cooling Box to root supporting materials in the Plant Growth Chamber driven by water potential deficit. Relative humidity in the Plant Growth Chamber can be changed over a wide range by controlling the ratio of latent heat exchange to sensible heat exchange on the cooling fin of the heat exchanger. The transpiration rate was successfully measured by circulating air inside the Plant Growth Chamber only. Most water was recycled and a small amount of water needed to be added from the outside. The simple, air conditioning and water recycle system for the Space Plant Box showed good performance through a barley (Hordeum vulgare L.) growth experiment. 相似文献
112.
J.-P. Delaboudiniere R.A. Stern A. Maucherat F. Portier-Fozzani W.M. Neupert J.B. Gurman R.C. Catura J.R. Lemen L. Shing G.E. Artzner J. Brunaud A.H. Gabriel D.J. Michels J.D. Moses B. Au K.P. Dere R.A. Howard R. Kreplin J.M. Defise C. Jamar P. Rochus J.P. Chauvineau J.P. Marioge F. Clette P. Cugnon E.L. Van Dessel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,20(12):2231-2237
The SOHO (SOlar and Heliospheric Observatory) satellite was launched on December 2nd 1995. After arriving at the Earth-Sun (L1) Lagrangian point on February 14th 1996, it began to continuously observe the Sun. As one of the instruments onboard SOHO, the EIT (Extreme ultraviolet Imaging Telescope) images the Sun's corona in 4 EUV wavelengths. The He II filter at 304 Å images the chromosphere and the base of the transition region at a temperature of 5 − 8 × 104 K; the Fe IX–X filter at 171 Å images the corona at a temperature of 1.3 × 106 K; the Fe XII filter at 195 Å images the quiet corona outside coronal holes at a temperature of 1.6 × 106 K; and the Fe XV filter at 284 Å images active regions with a temperature of 2.0 × 106 K. About 5000 images have been obtained up to the present. In this paper, we describe also some aspects of the telescope and the detector performance for application in the observations. Images and movies of all the wavelengths allow a look at different phenomena present in the Sun's corona, and in particular, magnetic field reconnection. 相似文献
113.
B V Worgul W Krebs J P Koniarek 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(10):315-323
Efforts to assess radiation risk in space have been complicated by the considerable unknowns regarding the biological effects of the heavy ion component (HZE particles) of the cosmic rays. The attention has focused primarily on the assignation of a quality factor (Q) which would take into account the greater effectiveness of heavy ions vis-a-vis other forms of ionizing radiation. If however, as the so-called "Microlesion Theory" allows, the passage of HZE particles through living tissue produces unique biological damage, the traditional use of Q becomes meaningless. Therefore, it is critical to determine if microlesions, in fact, do exist. While the concept does not necessarily require detectable morphological damage, "tunnel-lesions" or holes in ocular tissues have been cited as evidence of microlesions. These data, however, are open to reinterpretation. On-going light, scanning and transmission electron microscopic studies of the corneas, lenses and retinas of rat eyes exposed to 450 MeV/amu 56Fe ions thus far have not revealed tunnel-lesion damage. The morphological effects of the heavy ions have been found to be qualitatively similar to the changes following other kinds of ionizing radiation. 相似文献
114.
R Roots W Holley A Chatterjee E Rachal G Kraft 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(10):45-55
We have aimed to present a comprehensive review of our understanding to date of the formation of DNA strand breaks induced by high LET radiation. We have discussed data obtained from DNA in solution as well as from the formation and "repair" of strand breaks in cell DNA. There is good agreement, qualitatively, between these two systems. Results were evaluated for two parameters: (1) effectivity per particle, the cross section (sigma) in micrometers 2/particle; and (2) the strand break induction frequency as number of breaks per Gy per unit DNA (bp or dalton). A series of biological effects curves (one for each Z-number) is obtained in effectivity versus LET plots. The relationships between induction frequencies of single-strand breaks, or double-strand breaks, or the residual "irrepairable" breaks and LET-values have been evaluated and discussed for a wide spectrum of heavy ions, both for DNA in solution and for DNA in the cell. For radiation induced total breaks in cell DNA, the RBE is less than one, while the RBE for the induction of DSBs can be greater than one in the 100-200 keV/micrometers range. The level of irrepairable strand breaks is highest in this same LET range and may reach 25 percent of the initial break yield. The data presented cover results obtained for helium to uranium particles, covering a particle incident energy range of about 2 to 900 MeV/u with a corresponding LET range of near 16 to 16000 keV/micrometers. 相似文献
115.
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
116.
King CB Butterfield AJ Hypes WD Nealy JE Simonsen LC 《Journal of spacecraft and rockets》1990,27(3):225-226
The space shuttle external tank, which consists of a liquid oxygen tank, an intertank structure, and a liquid hydrogen tank, is an expendable structure used for approximately 8.5 min during each launch. A concept for outfitting the liquid oxygen tank-intertank unit for a 12-person lunar habitat is described. The concept utilizes existing structures and openings for both man and equipment access without compromising the structural integrity of the tank. Living quarters, instrumentation, environmental control and life support, thermal control, and propulsion systems are installed at Space Station Freedom. The unmanned habitat is then transported to low lunar orbit and autonomously soft landed on the lunar surface. Design studies indicate that this concept is feasible by the year 2000 with concurrent development of a space transfer vehicle and manned cargo lander for crew changeover and resupply. 相似文献
117.
Gerald T. Davidson 《Space Science Reviews》1990,53(1-2):45-82
Morningside aurorae at latitudes below about 70° display complex spatial and temporal structures unlike anything seen in the evening or midnight sectors. The morningside structures are believed to be formed by the precipitation of trapped electrons injected in auroral substorms; no significant role has yet been identified in the morningside auroral regions for the large-scale parallel electric fields that dominate the evening side. How those spatial and temporal structures originate has been the subject of much speculation; most theoretical mechanisms focus on the wave-particle interactions that drive pitch-angle diffusion. The principal evidence pertaining to the role of pitch-angle diffusion in the auroral regions is reviewed here. The observational evidence concerns mainly auroral emissions in the atmosphere, energetic particles observed from rockets and satellites, VLF waves at high altitudes, magnetospheric cold plasma, and magnetic pulsations detected on the ground. With the aid of such evidence, plus observations and theories related to the outer permanently trapped radiation belts, several theoretical models for the modulation of VLF wave growth in the equatorial regions have been pieced together. Those models, and the observational data supporting them, are examined to see how well they fit the observational picture and to see where they might lead in future research. The models fall into two categories: those in which the modulations are externally imposed and those in which the modulations are self-excited. For the temporal variations the self-excited mechanisms are now favored. The leading candidate involves a nonlinear relaxation oscillator; the nonlinearity may have important consequences. There are several contenders in both categories for the origin of the spatial structures, none of which agrees fully with inferences from the observations. All the theories involve critical parameters that have not yet been precisely fixed. The critical research needs are listed and discussed. 相似文献
118.
119.
Initial ISEE magnetometer results: magnetopause observations 总被引:15,自引:0,他引:15
The magnetic field profiles across the magnetopause obtained by the ISEE-1 and -2 spacecraft separated by only a few hundred kilometers are examined for four passes. During one of these passes the magnetosheath field was northward, during one it was slightly southward, and in two it was strongly southward. The velocity of the magnetopause is found to be highly irregular ranging from 4 to over 40 km s-1 and varying in less time than it takes for a spacecraft to cross the boundary. Thicknesses ranged from 500 to over 1000 km.Clear evidence for reconnection is found in the data when the magnetosheath field is southward. However, this evidence is not in the form of classic rotational discontinuity signatures. Rather, it is in the form of flux transfer events, in which reconnection starts and stops in a matter of minutes or less, resulting in the ripping off of flux tubes from the magnetosphere. Evidence for flux transfer events can be found both in the magnetosheath and the outer magnetosphere due to their alteration of the boundary normal. In particular, their presence at the time of magnetopause crossings invalidates the usual 2-dimensional analysis of magnetopause structure. Not only are these flux transfer events probably the dominant means of reconnection on the magnetopause, but they may also serve as an important source of magnetopause oscillations, and hence of pulsations in the outer magnetosphere. On two days the flux transfer rate was estimated to be of the order of 2 × 1012 Maxwells per second by the flux transfer events detected at ISEE. Events not detectable at ISEE and continued reconnection after passage of an FTE past ISEE could have resulted in an even greater reconnection rate at these times. 相似文献
120.
L. Zampieri C. Germanà C. Barbieri G. Naletto A. Čadež I. Capraro A. Di Paola C. Facchinetti T. Occhipinti D. Ponikvar E. Verroi P. Zoccarato 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We are developing fast photon-counter instruments to study the rapid variability of astrophysical sources by time tagging photon arrival times with unprecedented accuracy, making use of a Rubidium clock and GPS receiver. The first realization of such optical photon-counters, dubbed AquEYE (the Asiago Quantum Eye), was mounted in 2008 at the 182 cm Copernicus Observatory in Asiago. AquEYE observed the Crab pulsar several times and collected data of extraordinary quality that allowed us to perform accurate optical timing of the Crab pulsar and to study the pulse shape stability on a timescale from days to years with an excellent definition. Our results reinforce the evidence for decadal stability of the inclination angle between the spin and magnetic axis of the Crab pulsar. Future realizations of our instrument will make use of the Galileo Global Navigation Satellite System (GNSS) time signal. 相似文献