全文获取类型
收费全文 | 6275篇 |
免费 | 54篇 |
国内免费 | 34篇 |
专业分类
航空 | 3107篇 |
航天技术 | 1913篇 |
综合类 | 81篇 |
航天 | 1262篇 |
出版年
2021年 | 49篇 |
2018年 | 188篇 |
2017年 | 172篇 |
2016年 | 79篇 |
2015年 | 61篇 |
2014年 | 117篇 |
2013年 | 138篇 |
2012年 | 154篇 |
2011年 | 336篇 |
2010年 | 266篇 |
2009年 | 326篇 |
2008年 | 366篇 |
2007年 | 268篇 |
2006年 | 138篇 |
2005年 | 209篇 |
2004年 | 140篇 |
2003年 | 172篇 |
2002年 | 114篇 |
2001年 | 158篇 |
2000年 | 117篇 |
1999年 | 137篇 |
1998年 | 154篇 |
1997年 | 127篇 |
1996年 | 134篇 |
1995年 | 164篇 |
1994年 | 146篇 |
1993年 | 109篇 |
1992年 | 120篇 |
1991年 | 66篇 |
1990年 | 60篇 |
1989年 | 111篇 |
1988年 | 59篇 |
1987年 | 46篇 |
1986年 | 52篇 |
1985年 | 171篇 |
1984年 | 122篇 |
1983年 | 117篇 |
1982年 | 110篇 |
1981年 | 157篇 |
1980年 | 45篇 |
1979年 | 46篇 |
1978年 | 50篇 |
1977年 | 42篇 |
1976年 | 37篇 |
1975年 | 53篇 |
1974年 | 39篇 |
1972年 | 45篇 |
1970年 | 34篇 |
1969年 | 38篇 |
1967年 | 30篇 |
排序方式: 共有6363条查询结果,搜索用时 99 毫秒
981.
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
982.
V A Sarychev V V Sazonov A S Zlatorunsky S F Khlopina A D Egorov V I Somov 《Acta Astronautica》1980,7(6):719-730
The problem considered in this paper is the investigation of the properties of a mass-meter, i.e. the device for determining the mass of cosmonaut's body under zero-gravity conditions. The estimates of accuracy of mass measurement by this device are given, and the results of measuring the masses of cosmonauts' bodies on the Salyut 5 and 6 orbital stations are presented. 相似文献
983.
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
984.
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
985.
986.
Kenneth R. Lang Robert F. Willson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(11):91-100
We present observations of flaring active regions with the Very Large Array (V.L.A. at 6 cm and 20 cm wavelengths) and the Westerbork Synthesis Radio Telescope (W.S.R.T. at 6 cm wavelength). These are compared with photospheric magnetograms (Meudon) and with Hα and offband Hα photographs (Big Bear and Ottawa River Solar Observatories). The 6 cm radiation of these active regions marks the legs of dipolar loops which have their footpoints in lower-lying sunspots. The intense, million degree radiation at 6 cm lies above sunspot umbrae in coronal regions where the longitudinal magnetic field strength H? = 600 Gauss and the height above the sunspot umbrae h = 3.5±0.5 × 109 cm. Circularly polarized horseshoe structures at 6 cm ring the sunspot umbrae. The high degree of circular polarization (?c = 95%) of the horseshoes is attributed to gyroresonant emission above sunspot? penumbrae. The 20 cm radiation of these active regions exhibits looplike coronal structures which extend across regions of opposite magnetic polarity in the underlying photosphere. The 20 cm loops are the radio wavelength counterparts of the X-ray coronal loops. We infer semilengths L = 5 × 109 cm, maximum electron temperatures Te(max) = 3 × 106 K, emission measures ∫Ne2d = 1028 cm?5, and electron densities Ne = 109 cm?3 (or pressures p = 1 dyn cm?2) for the 20 cm bremsstrahlung. A total of eight solar bursts were observed at 6 cm or 20 cm wavelength with second-of-arc angular resolution. The regions of burst energy were all resolved with angular sizes between 5″ and 30″, brightness temperatures between 2 × 107 K and 2 × 108 K, and degrees of circular polarization between 10% and 90%. The impulsive phase of the radio bursts are located near the magnetic neutral lines of the active regions, and between the flaring Hα kernels which mark the footpoints of magnetic loops. In one case there was preburst heating in the coronal loop in which a burst occurred. Snapshot maps at 10 s intervals reveal interesting burst evolution including rapid changes of circular polarization and an impulsive burst which was physically separated from both the preburst radio emission and the gradual decay phase of the burst. 相似文献
987.
Approximate equations are developed for converting geodetic coordinates to a local north-east-down (NED) Cartesian coordinate system, and it is shown that good accuracy can be obtained if the ellipsoidal shape of the Earth is taken into account. 相似文献
988.
The application of importance sampling to the efficient simulation of low-probability events is discussed. Several examples are given to illustrate how the technique works for processes involving single and multiple statistical inputs. A procedure is also given for handling the case of multiple inputs where each is from a different statistical process. 相似文献
989.
M.G. Kivelson K.W. Behannon T.E. Cravens I. de Pater T.V. Johnson D.L. Matson H. Masursky D.J. Southwood V.M. Vasyliunas 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(3):5-14
A was presented in conjunction with the Twenty-fourth Plenary Meeting of the Committee on Space Research. This paper summarizes the talks presented and places the remaining papers of this volume in context. 相似文献
990.
J Kiefer S Rase F Schopfer E Schneider K Weber G Kraft 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1983,3(8):115-125
The action of heavy ions (Ar to U) accelerated to specific energies up to about 10 MeV/u (u=atomic mass unit) on different functions of yeast cells was studied. Ribosomal-RNA synthesis is inhibited according to a single-hit mechanism. Inactivation cross-sections were linearly related to the ratio of the squares of the effective charge Z* and the velocity of the ions. It is concluded from the analysis that the range of the most energetic delta-electrons is larger than previously assumed. There is no such dependence for survival and induction of mutants. In both cases cross-sections increase with the ion's specific-energy indicating an important contribution of long-range delta-electrons. The analysis shows that diploid yeast is not killed by a single-hit mechanism even by very heavy ions if the track width is too small. The relative importance of the penumbral region is even more pronounced with the more sensitive strains. 相似文献