全文获取类型
收费全文 | 7181篇 |
免费 | 36篇 |
国内免费 | 39篇 |
专业分类
航空 | 3234篇 |
航天技术 | 2650篇 |
综合类 | 30篇 |
航天 | 1342篇 |
出版年
2021年 | 73篇 |
2019年 | 56篇 |
2018年 | 164篇 |
2017年 | 116篇 |
2016年 | 100篇 |
2015年 | 39篇 |
2014年 | 169篇 |
2013年 | 210篇 |
2012年 | 193篇 |
2011年 | 296篇 |
2010年 | 213篇 |
2009年 | 355篇 |
2008年 | 393篇 |
2007年 | 217篇 |
2006年 | 173篇 |
2005年 | 212篇 |
2004年 | 220篇 |
2003年 | 246篇 |
2002年 | 162篇 |
2001年 | 232篇 |
2000年 | 151篇 |
1999年 | 172篇 |
1998年 | 193篇 |
1997年 | 154篇 |
1996年 | 176篇 |
1995年 | 226篇 |
1994年 | 194篇 |
1993年 | 113篇 |
1992年 | 171篇 |
1991年 | 59篇 |
1990年 | 62篇 |
1989年 | 147篇 |
1988年 | 55篇 |
1987年 | 54篇 |
1986年 | 68篇 |
1985年 | 210篇 |
1984年 | 161篇 |
1983年 | 132篇 |
1982年 | 152篇 |
1981年 | 197篇 |
1980年 | 76篇 |
1979年 | 42篇 |
1978年 | 49篇 |
1977年 | 42篇 |
1976年 | 43篇 |
1975年 | 39篇 |
1974年 | 44篇 |
1973年 | 32篇 |
1970年 | 31篇 |
1969年 | 30篇 |
排序方式: 共有7256条查询结果,搜索用时 15 毫秒
971.
T.K. Yeoman H.C. Scoffield D.M. Wright L.J. Baddeley A.N. Vasilyev N.V. Semenova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
A brief review is provided of recent progress in understanding the ionospheric Alfvén resonator (IAR) at high latitude. Firstly, naturally occurring resonances of the IAR as detected by pulsation magnetometers in the auroral zone at Sodankylä and in the polar cap at Barentsburg are considered. The characteristics of the IAR in the two regions are broadly similar, although the effects of solar illumination are less clear at the higher latitudes. Secondly we review recent attempts to stimulate the IAR through high-power radio frequency experiments both in the auroral zone at Tromsø with the European Incoherent SCATter (EISCAT) heater, and within the polar cap at Longyearbyen with the Space Plasma Exploration by Active Radar (SPEAR) facility. In the auroral zone at, Tromsø the stimulated IAR has been observed by ground-based magnetometers, and through electron acceleration observed on the FAST spacecraft. At SPEAR in the polar cap, the stimulated IAR has been investigated, with ground magnetometers, with the first results indicative of a positive detection. 相似文献
972.
B.F. Gordiets Yu.N. Kulikov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(9):113-117
The plausible mechanisms of cooling of the nightside Venus' thermosphere are analysed with the aid of the model of the atmospheric heat budget that incorporates, in addition to thermal conduction and IR radiation in the 15 μ band of CO2, heating and cooling due to global scale winds, eddy turbulence, and IR radiation in the rotational bands of H2O and CO, as well as the 63 μ line of atomic oxygen. The H2O mixing ratio and parameters of turbulence required for cooling of the thermosphere down to the observed low temperatures are evaluated. 相似文献
973.
S. Azouggagh-McBride L.A. Roe M.A. Franzen J.A. Buffington D.W.G. Sears 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Laboratory impact tests have been performed on experimental versions of a proposed robotic sample collector for extraterrestrial samples. The collector consists of a retractable aluminum ring containing an impregnable silicone compound that is pressed into the surface of the body to be sampled. As part of a comprehensive program to evaluate this idea, we have performed tests to determine if the samples embedded in the collector medium can survive the impact forces experienced during direct reentry, such as that of the recent Genesis sample return mission. For the present study, samples of sand, rock, glass, and chalk were subjected to decelerations of 1440–2880 g using drop tests. We found that even the most fragile samples, chosen to be representative of a wide range of the types of materials found on the surface of asteroids that have currently been studied, can withstand impacts of the intensity experienced by a sample return capsule during direct reentry. 相似文献
974.
Basic equations of hydrodynamics in an elastic pipeline that are found using the vectorial notation of Newton’s law for a viscous fluid are presented. An analog of Poiseuille’s formula for the fluid flowrate in the elastic pipeline and the results of the comparative analysis of a viscous flow in elastic and rigid pipelines are given. It is shown that the ratio of the maximal fluid velocity in the pipeline cross section and the section-average velocity is similar for elastic and rigid pipelines. 相似文献
975.
Some experimental data on the process of impulsive ultrasonic machining are presented. Also given are the data on variations in the impulsive vibration frequency of a workpiece and a tool. 相似文献
976.
T Takakura E Goto M Tanaka 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(4-5):255-258
An axis clinostat was constructed to create micro and negative gravity also a rotated flat disk was constructed with different rotation rates to give increased gravity, by centrifugal force up to 48 g. Rice seeds were grown on agar in tubes at the constant air temperature of 20 degrees C under an average light condition of 110 micromol/m2/sec(PPF). Humidity was not controlled but was maintained above 90%. Since the tube containers were not large enough for long cultivation, shoot and root growth were observed every 12 hours until the sixth day from seeding. The lengths of shoots and roots for each individual plant were measured on the last day. The stem lengths were increased by microgravity but the root lengths were not. Under the negative gravity, negative orthogeotropism and under microgravity, diageotropism was observed. No significant effect of increased gravity was observed on shoot and root growth. 相似文献
977.
G Pugacheva A A Gusev U B Jayanthi N G Schuch W N Spjeldvik K T Choque 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(6):1433-1437
The existence of significant fluxes of antiparticles in the Earth magnetosphere has been predicted on theoretical considerations in this article. These antiparticles (positrons or antiprotons) at several hundred kilometers of altitudes, we believe are not of direct extraterrestrial origin, but are the natural products of nuclear reactions of the high energy primary cosmic rays (CR) and trapped protons (TP) confined in the terrestrial radiation belt, with the constituents of terrestrial atmosphere. Extraterrestrial positrons and antiprotons born in nuclear reactions of the same CR particles passing through only 5-7 g/cm2 of interstellar matter, exhibit lower fluxes compared to the antiprotons born at hundreds of g/cm2 in the atmosphere, which when confined in the magnetic field of the Earth (in any other planet), get accumulated. We present the results of the computations of the antiproton fluxes at 10 MeV to several GeV energies due to CR particle interactions with the matter in the interstellar space, and also with the residual atmosphere at altitudes of approximately 1000 km over the Earth's surface. The estimates show that the magnetospheric antiproton fluxes are greater by two orders of magnitude compared to the extraterrestrial fluxes measured at energies <1-2 GeV. 相似文献
978.
979.
G. A. Gusev B. N. Lomonosov K. M. Pichkhadze N. G. Polukhina V. A. Ryabov T. Saito V. K. Sysoev E. L. Feinberg V. A. Tsarev V. A. Chechin 《Cosmic Research》2006,44(1):19-38
An estimate of the feasibility of the ultrahigh-energy cosmic ray and neutrino detection using a lunar satellite-borne radio receiver is presented. The data obtained in the proposed experiment will make resolving the current contradictions in the ultrahigh-energy cosmic ray spectra measured with the major ground-based instruments possible. Moreover, they will enable us to considerably extend the accessible energy range and to check predictions of various models of the origin of the highest-energy particles in the Universe. At the same time the lunar radio detector provides a means of searching for ultrahigh-energy neutrinos with a high sensitivity combined with a very large target effective mass. 相似文献
980.
Understanding properties of solar energetic particle (SEP) events associated with coronal mass ejections has been identified
as a key problem in solar-terrestrial physics. Although recent CME shock acceleration models are highly promising, detailed
agreement between theoretical predictions and observations has remained elusive. Recent observations from ACE have shown substantial
enrichments in the abundances of 3He and He+ ions which are extremely rare in the thermal solar wind plasma. Consequently, these ions act as tracers of their source material,
i.e.,
3He ions are flare suprathermals and He+ ions are interstellar pickup ions. The average heavy ion composition also exhibits unsystematic differences when compared
with the solar wind values, but correlates significantly with the ambient suprathermal material abundances. Taken together
these results provide compelling evidence that CME-driven shocks draw their source material from the ubiquitous but largely
unexplored suprathermal tail rather than from the more abundant solar wind peak. However, the suprathermal energy regime has
many more contributors and exhibits much larger variability than the solar wind, and as such needs to be investigated more
thoroughly. Answers to fundamental new questions regarding the preferred injection of the suprathermal ions, the spatial and
temporal dependence of the various sources, and the causes of their variability and their effects on the SEP properties are
needed to improve agreement between the simulations and observations. 相似文献