全文获取类型
收费全文 | 3906篇 |
免费 | 15篇 |
国内免费 | 8篇 |
专业分类
航空 | 1748篇 |
航天技术 | 1451篇 |
综合类 | 11篇 |
航天 | 719篇 |
出版年
2021年 | 31篇 |
2018年 | 63篇 |
2017年 | 53篇 |
2016年 | 51篇 |
2015年 | 22篇 |
2014年 | 74篇 |
2013年 | 109篇 |
2012年 | 93篇 |
2011年 | 164篇 |
2010年 | 113篇 |
2009年 | 156篇 |
2008年 | 202篇 |
2007年 | 115篇 |
2006年 | 85篇 |
2005年 | 113篇 |
2004年 | 127篇 |
2003年 | 127篇 |
2002年 | 81篇 |
2001年 | 119篇 |
2000年 | 61篇 |
1999年 | 86篇 |
1998年 | 107篇 |
1997年 | 77篇 |
1996年 | 72篇 |
1995年 | 109篇 |
1994年 | 125篇 |
1993年 | 65篇 |
1992年 | 76篇 |
1991年 | 32篇 |
1990年 | 42篇 |
1989年 | 68篇 |
1988年 | 32篇 |
1987年 | 27篇 |
1986年 | 38篇 |
1985年 | 125篇 |
1984年 | 115篇 |
1983年 | 94篇 |
1982年 | 79篇 |
1981年 | 157篇 |
1980年 | 32篇 |
1979年 | 35篇 |
1978年 | 37篇 |
1977年 | 34篇 |
1976年 | 29篇 |
1975年 | 34篇 |
1974年 | 29篇 |
1973年 | 31篇 |
1972年 | 41篇 |
1971年 | 22篇 |
1970年 | 23篇 |
排序方式: 共有3929条查询结果,搜索用时 0 毫秒
971.
972.
Sabiha Tunçel Güçtekin Selçuk Bilir Salih Karaali Olcay Plevne Serap Ak 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(3):1360-1373
We used the ugr magnitudes of 1437467 F-G type main-sequence stars with metal abundance dex and estimated radial and vertical metallicity gradients for high Galactic-latitude fields, and , of the Milky Way Galaxy. The radial metallicity gradient dex kpc?1 estimated for the stars with kpc is attributed to the thin-disc population. While, the radial gradients evaluated for stars at higher vertical distances are close to zero indicating that the thick disc and halo have not undergone a radial collapse phase at least at high Galactic latitudes. The vertical metallicity gradients estimated for stars with three different Galactic latitudes, and do not show a strong indication for Galactic latitude dependence of our gradients. The thin disc, kpc, with a vertical metallicity gradient dex kpc?1, is dominant only in galactocentric distance interval kpc, while the thick disc ( kpc) could be observed in the intervals and kpc with compatible vertical metallicity gradients, i.e. dex kpc?1 and dex kpc?1. Five vertical metallicity gradients are estimated for the halo ( kpc) in three galactocentric distance intervals, and kpc. The first one corresponding to the interval kpc is equal to dex kpc?1, while the others at larger galactocentric distances are close to zero. We derived synthetic vertical metallicity gradients for 2,230,167 stars and compared them with the observed ones. There is a good agreement between the two sets of vertical metallicity gradients for the thin disc, while they are different for the thick disc. For the halo, the conspicuous difference corresponds to the galactocentric distance interval kpc, while they are compatible at higher galactocentric distance intervals. 相似文献
973.
E. Amata G. Bellucci V. Formisano 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(12):263-266
Observations of comet Halley through CCD and Schmidt plates have been performed at Catania Observatory (Italy) from October 1985 through April 1986. Preliminary results are presented concerning the spatial structures for different spectral ranges of cometary light. 相似文献
974.
G.G. Pavlov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
A review is given of recent developments in the theory of emission from a magnetized plasma for accreting neutron star conditions. Some observational data on X-ray pulsars are discussed, and present problems are indicated. 相似文献
975.
A. G. Sattarov 《Russian Aeronautics (Iz VUZ)》2008,51(4):452-456
A method and the results of calculating the temperature field distribution for a three-focus plasma formation are presented; the calculation is made by the numerical method with the use of the theoretical Glumb and Krier model. It is proposed that multi-phase plasma formations consisting of solid laser sparks should be used in the absorption chamber of a laser rocket engine (LRE). 相似文献
976.
977.
Specific features of propagation of a wideband rectangular pulse along the route spacecraft-Martian surface-spacecraft caused by the influence of the planetary ionosphere are considered as applied to the problem of radio pulse sounding of the subsurface Martian soil from the Mars-Express satellite. The night Martian ionosphere considerably reduces the energy of the pulse, but does not lead to degradation of its envelope or uncertainty function. When sounding a two-layer surface, the influence of the ionosphere is also manifested in limitation from below of the thickness of the upper layer accessible for measurement, which is more essential than when sounding with the use of a wideband Gaussian pulse. It is demonstrated that the surface sounding is possible through the dayside planet ionosphere at the parameters of operating pulse of the MARSIS radar. 相似文献
978.
This paper describes an approach to the realization of a VLF loop-type antenna system. The theoretical analysis is applied to a four-loop system for Loran-C reception. 相似文献
979.
980.
Terrestrial planets are accreted in a disk orbiting a central star. The basic challenge of their formation consists of assembling micron-sized or smaller dust grains to bodies with over 104 km in diameter. This formation process, ultimately based on collisions, occurs in three very different physical regimes depending upon the size of the bodies present: 1) Early on, micron- to mm-sized dust grains, chondrules and chondrites are strongly coupled to the gas. 2) As they grow larger, gravity increases the collisional cross section allowing runaway growth to occur. 3) After this runaway phase stops from exhaustion of matter in the immediate surroundings of the protoplanets, further growth occurs on timescales typical of mutual gravitational perturbations. The emphasis of this book is on the timescales corresponding to these formation phases as well as the characteristic chemical and isotopic composition of the bodies involved. This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献