全文获取类型
收费全文 | 2759篇 |
免费 | 6篇 |
国内免费 | 8篇 |
专业分类
航空 | 1277篇 |
航天技术 | 965篇 |
综合类 | 9篇 |
航天 | 522篇 |
出版年
2021年 | 21篇 |
2019年 | 17篇 |
2018年 | 65篇 |
2017年 | 37篇 |
2016年 | 39篇 |
2015年 | 16篇 |
2014年 | 65篇 |
2013年 | 106篇 |
2012年 | 67篇 |
2011年 | 111篇 |
2010年 | 85篇 |
2009年 | 135篇 |
2008年 | 156篇 |
2007年 | 68篇 |
2006年 | 72篇 |
2005年 | 80篇 |
2004年 | 71篇 |
2003年 | 95篇 |
2002年 | 47篇 |
2001年 | 98篇 |
2000年 | 49篇 |
1999年 | 68篇 |
1998年 | 71篇 |
1997年 | 68篇 |
1996年 | 66篇 |
1995年 | 88篇 |
1994年 | 87篇 |
1993年 | 41篇 |
1992年 | 53篇 |
1991年 | 17篇 |
1990年 | 24篇 |
1989年 | 52篇 |
1988年 | 35篇 |
1987年 | 24篇 |
1986年 | 33篇 |
1985年 | 76篇 |
1984年 | 70篇 |
1983年 | 44篇 |
1982年 | 69篇 |
1981年 | 68篇 |
1980年 | 20篇 |
1979年 | 11篇 |
1978年 | 31篇 |
1977年 | 12篇 |
1975年 | 25篇 |
1974年 | 16篇 |
1973年 | 17篇 |
1972年 | 16篇 |
1970年 | 9篇 |
1969年 | 12篇 |
排序方式: 共有2773条查询结果,搜索用时 15 毫秒
871.
A model and a technique for calculating polymer composite materials with an ellipsoid-shaped filler that take into account the influence of system porosity, particle anisodiametry and a boundary layer on the effective heat conduction are proposed. The results of calculations made by numerical methods are in a good agreement with the well-known statistic and Odolevskii, Maxwell, and Dul’nev matrix models. 相似文献
872.
Yarovoy A.G. Ligthart L.P. Matuzas J. Levitas B. 《Aerospace and Electronic Systems Magazine, IEEE》2008,23(5):36-40
UWB radar for detection and positioning of human beings in a complex environment has been developed and manufactured. The novelty of the radar lies in its large operational bandwidth (11.7 GHz at -10 dB level) combined with high time stability. Detection of respiratory movement of a person in laboratory conditions has been demonstrated. Based on experimental results, human being radar return has been analysed in the frequency band from 1 GHz to 12 GHz. The novel principle of human being detection is considered and verified experimentally. 相似文献
873.
M.C. Rabello-Soares B.J. Thompson D. Scherrer C. Morrow 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(8):1206-1211
Education and public outreach (EPO) is one of the four components of the International Heliophysical Year (IHY). It is fundamental in achieving one of IHY’s primary objectives which is to “demonstrate the beauty, relevance and significance of Space and Earth science to the world.” 相似文献
874.
S.P. Seth U.B. Jayanthi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(9):1353-1360
The Accelerometer Experiment (ACC) onboard Mars Global Surveyor (MGS) measured 1600 density profiles in the upper atmosphere of Mars during aerobraking. These measurements reveal large-scale and small-scale structure in the thermosphere of Mars. Here, the measurements of mass density for 115 orbits (#P0670–P0789) from November 1 to 30, 1998, under spring equinox and medium solar activity conditions (average F10.7 ∼ 137) during phase 2 of the aerobraking in the thermosphere of Mars at different altitudes and longitudes are presented for northern mid-latitude (17–42°N) in the dayside atmosphere using ACC onboard MGS. From these mass densities, the neutral densities of different gases are derived from their mixing ratios. Using these neutral densities, the longitudinal distribution of photoionization rates and photoelectron impact ionization rates are calculated at wavelength range 1–102.57 nm due to EUV and soft X-ray radiation under photochemical controlled region using Analytical Yield Spectrum approach (AYS). These conditions are appropriate for MGS Phase 2 aerobraking period from which the accelerometer data is used. Under the photochemical equilibrium condition, the electron density near the peak varies as the square root of the total peak ionization rate. Using this fact, an attempt is being made to estimate the mean primary and secondary peak electron density by averaging the longitudinal variations of total peak ionization rates in the northern mid-latitude (17–42°N) ionosphere of Mars, as there is no radio science measurement at this latitude region by MGS. 相似文献
875.
876.
E J Hall D J Brenner B Worgul L Smilenov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,35(2):249-253
In the context of space radiation, it is important to know whether the human population includes genetically predisposed radiosensitive subsets. One possibility is that haploinsufficiency for ATM confers radiosensitivity, and this defect involves 1-3% of the population. Using knock-out mice we chose to study cataractogenesis in the lens and oncogenic transformation in mouse embryo fibroblasts to assay for effects of ATM deficiency. Radiation induced cataracts appeared earlier in the heterozygous versus wild-type animals following exposure to either gamma rays or 1 GeV/nucleon iron ions. In addition, it was found that embryo fibroblasts of Atm heterozygotes showed an increased incidence of oncogenic transformation compared with their normal litter-matched counterparts. From these data we suggest that Ataxia Telangiectasia heterozygotes could indeed represent a societally significant radio sensitive subpopulation. Knock-out mice are now available for other genes including BRCA1 and 2, and Mrad9. An exciting possibility is the creation of double heterozygotes for pairs of mutated genes that function in the same signal transduction pathway, and consequently confer even greater radiosensitivity. 相似文献
877.
Weiss A.J. Willsky A.S. Levy B.C. 《IEEE transactions on aerospace and electronic systems》1989,25(1):48-55
A polynomial approach for maximum-likelihood (ML) estimation of superimposed signals in time-series problems and array processing was recently proposed. This technique was applied successfully to linear uniform arrays and to uniformly sampled complex exponential signals. However, uniformly spaced arrays are not optimal for minimum variance estimation of bearing, range or position, and uniform sampling of signals is not always possible in practice. The authors make use of the expectation-maximization algorithm to apply the polynomial approach to sublattice arrays and to missing samples in time-series problems 相似文献
878.
Bera R. Paul B.D. Sinha N.B. Guchhait A. Maity G. 《Aerospace and Electronic Systems Magazine, IEEE》2008,23(7):25-27
Fog, mist, and atmospheric dust particles, having the dimension of one micrometer or less, play an important role in the deterioration of visibility, as well as in causing local warming in the atmosphere. With an attempt to reduce the deterioration, a scientific approach has to be taken to determine their origins. A monostatic LIDAR may be one of the best instruments for such work. The authors are tempted to develop such a LIDAR for fog, mist, and dust particle monitoring over River Teesta at Sikkim. LIDAR is an acronym for Light Detection And Ranging. What can we do with LIDAR? Measure distance, measure speed, measure rotation, measure chemical composition and concentration, and measure cross-sections of the targets. The digital technique is always utilized for its development which results in better security, lower power consumption, higher power efficiency, higher reliability, lower transmitter power, lower multipath effect, higher interference suppression as compared to an analog system. The commercial systems like disdometer, rain radar, mobile robot, etc., utilizing LIDAR principles are operational in different parts of the world. The authors are highly motivated for such LIDAR development and their development effort follows. 相似文献
879.
880.
A brief overview is given of the current status of Stirling machine technology. The first commercial device, a Vuilleumier heat pump, is described. Some potential applications of Stirling engines are examined 相似文献