全文获取类型
收费全文 | 4430篇 |
免费 | 23篇 |
国内免费 | 7篇 |
专业分类
航空 | 2337篇 |
航天技术 | 1195篇 |
综合类 | 12篇 |
航天 | 916篇 |
出版年
2021年 | 30篇 |
2019年 | 27篇 |
2018年 | 179篇 |
2017年 | 155篇 |
2016年 | 77篇 |
2015年 | 45篇 |
2014年 | 68篇 |
2013年 | 85篇 |
2012年 | 118篇 |
2011年 | 235篇 |
2010年 | 205篇 |
2009年 | 252篇 |
2008年 | 265篇 |
2007年 | 215篇 |
2006年 | 78篇 |
2005年 | 141篇 |
2004年 | 96篇 |
2003年 | 113篇 |
2002年 | 70篇 |
2001年 | 126篇 |
2000年 | 73篇 |
1999年 | 83篇 |
1998年 | 106篇 |
1997年 | 70篇 |
1996年 | 95篇 |
1995年 | 131篇 |
1994年 | 102篇 |
1993年 | 67篇 |
1992年 | 91篇 |
1991年 | 34篇 |
1990年 | 39篇 |
1989年 | 86篇 |
1988年 | 43篇 |
1987年 | 37篇 |
1986年 | 35篇 |
1985年 | 96篇 |
1984年 | 92篇 |
1983年 | 82篇 |
1982年 | 82篇 |
1981年 | 90篇 |
1980年 | 27篇 |
1979年 | 27篇 |
1978年 | 29篇 |
1977年 | 27篇 |
1976年 | 19篇 |
1975年 | 35篇 |
1974年 | 25篇 |
1973年 | 18篇 |
1972年 | 33篇 |
1971年 | 18篇 |
排序方式: 共有4460条查询结果,搜索用时 968 毫秒
331.
Z. Peeters D. Vos I.L. ten Kate F. Selch C.A. van Sluis D.Yu. Sorokin G. Muijzer H. Stan-Lotter M.C.M. van Loosdrecht P. Ehrenfreund 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Halophilic archaea are of interest to astrobiology due to their survival capabilities in desiccated and high salt environments. The detection of remnants of salty pools on Mars stimulated investigations into the response of haloarchaea to martian conditions. Natronorubrum sp. strain HG-1 is an extremely halophilic archaeon with unusual metabolic pathways, growing on acetate and stimulated by tetrathionate. We exposed Natronorubrum strain HG-1 to ultraviolet (UV) radiation, similar to levels currently prevalent on Mars. In addition, the effects of low temperature (4, −20, and −80 °C), desiccation, and exposure to a Mars soil analogue from the Atacama desert on the viability of Natronorubrum strain HG-1 cultures were investigated. The results show that Natronorubrum strain HG-1 cannot survive for more than several hours when exposed to UV radiation equivalent to that at the martian equator. Even when protected from UV radiation, viability is impaired by a combination of desiccation and low temperature. Desiccating Natronorubrum strain HG-1 cells when mixed with a Mars soil analogue impaired growth of the culture to below the detection limit. Overall, we conclude that Natronorubrum strain HG-1 cannot survive the environment currently present on Mars. Since other halophilic microorganisms were reported to survive simulated martian conditions, our results imply that survival capabilities are not necessarily shared between phylogenetically related species. 相似文献
332.
G. Stratta A. Pozanenko J.L. Atteia A. Klotz S. Basa B. Gendre F. Verrecchia M. Boër S. Cutini M. Henze S. Holland M. Ibrahimov F. Ienna I. Khamitov S. Klose V. Rumyantsev V. Biryukov F. Vachier S. Arnouts D. Perley 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The detection of a bright optical emission measured with good temporal resolution during the prompt phase makes GRB 060111B a rare event that is especially useful for constraining theories of the prompt optical emission. Comparing this burst with other GRBs with evidence of optical peaks, we find that the optical peak epoch (tp) is anti-correlated with the high energy burst energetic assuming an isotropic energy release (Eiso) in agreement with Liang et al. (2009), and that the steeper is the post-peak afterglow decay, the less is the agreement with the correlation. GRB 060111B is among the latters and it does not match the correlation. The Cannonball scenario is also discussed and we find that this model cannot be excluded for GRB 060111B. 相似文献
333.
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
334.
D. Perrone R. O. Dendy I. Furno R. Sanchez G. Zimbardo A. Bovet A. Fasoli K. Gustafson S. Perri P. Ricci F. Valentini 《Space Science Reviews》2013,178(2-4):233-270
Understanding transport of thermal and suprathermal particles is a fundamental issue in laboratory, solar-terrestrial, and astrophysical plasmas. For laboratory fusion experiments, confinement of particles and energy is essential for sustaining the plasma long enough to reach burning conditions. For solar wind and magnetospheric plasmas, transport properties determine the spatial and temporal distribution of energetic particles, which can be harmful for spacecraft functioning, as well as the entry of solar wind plasma into the magnetosphere. For astrophysical plasmas, transport properties determine the efficiency of particle acceleration processes and affect observable radiative signatures. In all cases, transport depends on the interaction of thermal and suprathermal particles with the electric and magnetic fluctuations in the plasma. Understanding transport therefore requires us to understand these interactions, which encompass a wide range of scales, from magnetohydrodynamic to kinetic scales, with larger scale structures also having a role. The wealth of transport studies during recent decades has shown the existence of a variety of regimes that differ from the classical quasilinear regime. In this paper we give an overview of nonclassical plasma transport regimes, discussing theoretical approaches to superdiffusive and subdiffusive transport, wave–particle interactions at microscopic kinetic scales, the influence of coherent structures and of avalanching transport, and the results of numerical simulations and experimental data analyses. Applications to laboratory plasmas and space plasmas are discussed. 相似文献
335.
Olivier Mousis Eric Chassefière Jérémie Lasue Vincent Chevrier Megan E. Elwood Madden Azzedine Lakhlifi Jonathan I. Lunine Franck Montmessin Sylvain Picaud Frédéric Schmidt Timothy D. Swindle 《Space Science Reviews》2013,174(1-4):213-250
Thermodynamic conditions suggest that clathrates might exist on Mars. Despite observations which show that the dominant condensed phases on the surface of Mars are solid carbon dioxide and water ice, clathrates have been repeatedly proposed to play an important role in the distribution and total inventory of the planet’s volatiles. Here we review the potential consequences of the presence of clathrates on Mars. We investigate how clathrates could be a potential source for the claimed existence of atmospheric methane. In this context, plausible clathrate formation processes, either in the close subsurface or at the base of the cryosphere, are reviewed. Mechanisms that would allow for methane release into the atmosphere from an existing clathrate layer are addressed as well. We also discuss the proposed relationship between clathrate formation/dissociation cycles and how potential seasonal variations influence the atmospheric abundances of argon, krypton and xenon. Moreover, we examine several Martian geomorphologic features that could have been generated by the dissociation of extended subsurface clathrate layers. Finally we investigate the future in situ measurements, as well as the theoretical and experimental improvements that will be needed to better understand the influence of clathrates on the evolution of Mars and its atmosphere. 相似文献
336.
The results of the comprehensive numerical analysis for dynamics of intrachamber processes that appear at nozzleless solid propellant rocket engine (SPRE) actuation are presented. A complete cycle of rocket engine operation is analyzed. We solve a conjugate problem involving the igniter actuation; heating, ignition and following combustion of a solid propellant charge; a combustion product flow in the combustion chamber; depressurization of the combustion chamber, and the subsequent motion of the rocket engine blank; variation of the combustion surface geometry at the expense of the gradual and nonuniform burnout of solid propellant web. 相似文献
337.
This report is an initial review of plans for a extensive program to survey and develop the Moon and to explore the planet Mars during the 21st century. It presents current typical plans for separate, associated and fully integrated programs of Lunar and Martian research, exploration and development, and concludes that detailed integrated plans must be prepared and be subject to formal criticism. Before responsible politicians approve a new thrust into space they will demand attractive, defensible, and detailed proposals that explain the WHEN, HOW and WHY of each stage of an expanded program of 21st century space research, development and exploration. In particular, the claims of daring, innovative, but untried systems must be compared with the known performance of existing technologies. The time has come to supersede the present haphazard approach to strategic space studies with a formal international structure to plan for future advanced space missions under the aegis of the world's national space agencies, and supported by governments and the corporate sector. 相似文献
338.
The nature of the changes of resistance to infection seems to be very important. Our studies indicate that different functions of natural killers could be depressed after the spaceflight. The decrease of the percentage of the lymphocytes that can bind target cells lead to the lowering of the “active” NK level and this can be resulted in the depression of total NK activity and lowering of resistance to viral and tumor antigens. The investigation of natural killer cells in cosmonauts before and after short and long-term spaceflights also revealed the important role of spaceflight duration, stress and individual immune reactivity. 相似文献
339.
V. V. Kalegaev W. O. Barinova I. N. Myagkova V. E. Eremeev D. A. Parunakyan M. D. Nguyen O. G. Barinov 《Cosmic Research》2018,56(1):32-37
An empirical model of the high-latitude boundary of the outer Earth’s radiation belt (ERB) has been presented, which is based on the measurement data of electron fluxes on the polar low-orbit CORONAS-Photon, Meteor-M1, and Meteor-M2 satellites. The boundary was determined by a sharp decrease to the background level of the flux of trapped electrons with energies of 100 or 200 keV in the polar part of the profile of the outer radiation belt. A numerical algorithm has been implemented to determine the time moment, when the fastest flux changes are recorded. The primary search was carried out, first, on 30 s averaged data, then repeated on data with a higher resolution. A functional dependence was obtained in order to approximate the obtained set of intersections of the boundary by elliptical curve. The empirical model constructed using the CORONAS-Photon measurement data in the epoch of anomalously low geomagnetic activity reflects the longitude structure of the high-latitude boundary of the outer radiation belt associated with the internal Earth’s magnetic field (MF), as well as its dependence on the universal time. Based on the data of intersections of the high-latitude boundary of the outer ERB (OERB) in the epoch of 2014–2016, the latitudinal shift of the boundary to the equator dependent on geomagnetic activity has been determined, as well as the nightside shift of the boundary due to the diurnal rotation of the Earth. 相似文献
340.
G. L. Gdalevich N. I. Izhovkina V. D. Ozerov N. Bankov S. Chapkanov L. Todorieva 《Cosmic Research》2006,44(5):419-424
The results of the satellite low-latitude and mid-latitude measurements of the disturbed plasma concentration, electron temperature, and quasi-stable electric field at heights of ~900 km after sunset are discussed. It is shown that the sharp fronts of changes in the electron temperature and plasma density observed in the experiment onboard the Intercosmos-Bulgaria-1300 satellite in the low-latitude (and equatorial) outer ionosphere can be related to damping of the oscillations of plasma electrons at local decreases of the plasma density (plasma “pits”) and formation of the vortex plasma structures at density and temperature gradients, which promotes conservation of ionosphere irregularities and makes the fronts of concentration variations steeper. Nonmonotonic variations in the plasma conductivity for the ionosphere currents in unstable plasma can be a cause of observed nonmonotonic disturbances of the vertical component of the “constant” electric field. 相似文献