全文获取类型
收费全文 | 6052篇 |
免费 | 48篇 |
国内免费 | 35篇 |
专业分类
航空 | 3048篇 |
航天技术 | 2077篇 |
综合类 | 78篇 |
航天 | 932篇 |
出版年
2021年 | 45篇 |
2018年 | 80篇 |
2017年 | 70篇 |
2016年 | 47篇 |
2015年 | 46篇 |
2014年 | 116篇 |
2013年 | 151篇 |
2012年 | 131篇 |
2011年 | 235篇 |
2010年 | 175篇 |
2009年 | 225篇 |
2008年 | 323篇 |
2007年 | 181篇 |
2006年 | 156篇 |
2005年 | 165篇 |
2004年 | 136篇 |
2003年 | 188篇 |
2002年 | 124篇 |
2001年 | 178篇 |
2000年 | 121篇 |
1999年 | 160篇 |
1998年 | 172篇 |
1997年 | 146篇 |
1996年 | 154篇 |
1995年 | 199篇 |
1994年 | 180篇 |
1993年 | 114篇 |
1992年 | 154篇 |
1991年 | 76篇 |
1990年 | 69篇 |
1989年 | 145篇 |
1988年 | 63篇 |
1987年 | 52篇 |
1986年 | 59篇 |
1985年 | 187篇 |
1984年 | 157篇 |
1983年 | 116篇 |
1982年 | 127篇 |
1981年 | 172篇 |
1980年 | 57篇 |
1979年 | 64篇 |
1978年 | 58篇 |
1977年 | 41篇 |
1976年 | 39篇 |
1975年 | 65篇 |
1974年 | 39篇 |
1972年 | 56篇 |
1971年 | 37篇 |
1969年 | 38篇 |
1967年 | 41篇 |
排序方式: 共有6135条查询结果,搜索用时 109 毫秒
971.
Recent developments in the physics input for iron core collapse models of type II supernovae are reviewed. The effect of these developments on collapse calculations is also discussed. The inner core collapses homologously, with little change in specific entropy, bounces in the neighborhood of nuclear density, and sets up an outward moving shock. In adiabatic models an explosion may result. The Inclusion of neutrino effects may produce substantial shock damping. Current results indicate that core collapse, bounce and shock propagation does not produce an explosion when neutrino effects are included. 相似文献
972.
The behavior of nitromethane under the action of a plane shock wave presenting local overpressures is experimentally analysed. The role of hot spots and the successive activation of new reaction sites are clearly evidenced. The optical observations made during the build-up to detonation and the measured shock sensitivities support a model of initiation for heterogeneous explosives. 相似文献
973.
974.
The planetary radio astronomy experiment will measure radio spectra of planetary emissions in the range 1.2 kHz to 40.5 MHz. These emissions result from wave-particle-plasma interactions in the magnetospheres and ionospheres of the planets. At Jupiter, they are strongly modulated by the Galilean satellite Io.As the spacecraft leave the Earth's vicinity, we will observe terrestrial kilometric radiation, and for the first time, determine its polarization (RH and LH power separately). At the giant planets, the source of radio emission at low frequencies is not understood, but will be defined through comparison of the radio emission data with other particles and fields experiments aboard Voyager, as well as with optical data. Since, for Jupiter, as for the Earth, the radio data quite probably relate to particle precipitation, and to magnetic field strength and orientation in the polar ionosphere, we hope to be able to elucidate some characteristics of Jupiter auroras.Together with the plasma wave experiment, and possibly several optical experiments, our data can demonstrate the existence of lightning on the giant planets and on the satellite Titan, should it exist. Finally, the Voyager missions occur near maximum of the sunspot cycle. Solar outburst types can be identified through the radio measurements; when the spacecraft are on the opposite side of the Sun from the Earth we can identify solar flare-related events otherwise invisible on the Earth. 相似文献
975.
R.B. Stoltzfus S.A. Bowhill L.G. Smith 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(6):143-146
The Langmuir-probe technique for measurement of electron concentration in the mesosphere is capable of excellent altitude resolution, of order 1 m. Measurements from nine rocket flights frequently show small-scale ionization structures in the altitude region 60–90 km. These are believed to be identical with regions of strong coherent backscatter seem by VHF radars at Jicamarca, Peru and Urbana, Illinois. They are believed to represent intermittent turbulence attributable to nonlinear interaction of waves in the mesosphere. Parameters of the turbulent regions are estimated. 相似文献
976.
lt is possible that usable combination codes can be obtained if Barker and Huffman sequences are chosen as the inner and outer codes. lt is shown that an improvement in either energy efficiency or time sidelobe structure will result either from a modification of a Huffman sequence or from a modification of a Barker sequence. Results are given for a combination code of length 91, with inner and outer codes of length 7 and 13. 相似文献
977.
Charles F. Lillie Charles W. Hord Kevin Pang David L. Coffeen James E. Hansen 《Space Science Reviews》1977,21(2):159-181
The Voyager Photopolarimeter Experiment is designed to determine the physical properties of particulate matter in the atmospheres of Jupiter, Saturn, and the Rings of Saturn by measuring the intensity and linear polarization of scattered sunlight at eight wavelengths in the 2350–7500 Å region of the spectrum. The experiment will also provide information on the texture and probable composition of the surfaces of the satellites of Jupiter and Saturn and the properties of the sodium cloud around Io. During the planetary encounters a search for optical evidence of electrical discharges (lightning) and auroral activity will also be conducted. 相似文献
978.
An implementation of the multidimensional modified LMS algorithm is provided from its relationship to a recently developed class of lhyperstable adaptive filters. 相似文献
979.
Frederick L. Scarf 《Space Science Reviews》1974,15(6):933-950
A study has been carried out to identify the controlled space physics and plasma physics experiments that can be performed from the space shuttle on sortie missions of 7 to 30-day duration. An experiment facility of this type appears to be well-matched to the sortie missions capability, and a technically feasible laboratory can provide a base for an extensive and significant research program to be carried out during the 1980–1990 time period. The laboratory, known as PPEPL, consists of a 33-ft pallet of instruments connected to a 25-ft pressurized control module. Two deployable 50-m booms, two subsatellites, a high power transmitter, a multipurpose high-power accelerator array, a set of deployable canisters for releases, and a gimbaled platform for pointing instruments are the primary systems mounted on the pallet. 相似文献
980.
M.J. Hagyard R.L. Moore A.G. Emslie 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):71-80
We present observational results and their physical implications garnered from the deliberations of the FBS Magnetic Shear Study Group on magnetic field shear in relation to flares. The observed character of magnetic shear and its involvement in the buildup and release of flare energy are reviewed and illustrated with emphasis on recent results from the Marshall Space Flight Center vector magnetograph. It is pointed out that the magnetic field in active regions can become sheared by several processes, including shear flow in the photosphere, flux emergence, magnetic reconnection, and flux submergence. Modeling studies of the buildup of stored magnetic energy by shearing are reported which show ample energy storage for flares. Observational evidence is presented that flares are triggered when the field shear reaches a critical degree, in qualitative agreement with some theoretical analyses of sheared force-free fields. Finally, a scenario is outlined for the class of flares resulting from large-scale magnetic shear; the overall instability driving the energy release results from positive feedback between reconnection and eruption of the sheared field. 相似文献