全文获取类型
收费全文 | 9131篇 |
免费 | 59篇 |
国内免费 | 44篇 |
专业分类
航空 | 4230篇 |
航天技术 | 3155篇 |
综合类 | 91篇 |
航天 | 1758篇 |
出版年
2021年 | 94篇 |
2019年 | 51篇 |
2018年 | 176篇 |
2017年 | 144篇 |
2016年 | 123篇 |
2015年 | 73篇 |
2014年 | 218篇 |
2013年 | 273篇 |
2012年 | 256篇 |
2011年 | 405篇 |
2010年 | 299篇 |
2009年 | 421篇 |
2008年 | 480篇 |
2007年 | 285篇 |
2006年 | 231篇 |
2005年 | 259篇 |
2004年 | 228篇 |
2003年 | 275篇 |
2002年 | 205篇 |
2001年 | 287篇 |
2000年 | 191篇 |
1999年 | 224篇 |
1998年 | 250篇 |
1997年 | 177篇 |
1996年 | 216篇 |
1995年 | 266篇 |
1994年 | 262篇 |
1993年 | 158篇 |
1992年 | 198篇 |
1991年 | 82篇 |
1990年 | 77篇 |
1989年 | 188篇 |
1988年 | 85篇 |
1987年 | 79篇 |
1986年 | 81篇 |
1985年 | 247篇 |
1984年 | 191篇 |
1983年 | 155篇 |
1982年 | 154篇 |
1981年 | 272篇 |
1980年 | 70篇 |
1979年 | 65篇 |
1978年 | 75篇 |
1977年 | 59篇 |
1976年 | 48篇 |
1975年 | 78篇 |
1974年 | 55篇 |
1972年 | 64篇 |
1971年 | 59篇 |
1970年 | 50篇 |
排序方式: 共有9234条查询结果,搜索用时 15 毫秒
101.
Stratton D.A. Stengel R.F. 《IEEE transactions on aerospace and electronic systems》1993,29(4):1185-1194
Severe low-altitude wind shear is a threat to aviation safety. Newly developed airborne sensors measure the radial component of wind along a line directly in front of an aircraft. The authors use optimal estimation theory to define a detection algorithm to warn of hazardous wind shear from these sensors. To achieve robustness, a wind shear detection algorithm must distinguish threatening wind shear from less hazardous gustiness, despite variations in wind shear structure. Statistical analysis methods to refine wind shear detection algorithm robustness are presented. Computational methods predict the ability to warn of severe wind shear and avoid false warning. Comparative capability of the detection algorithm as a function of its design parameters is determined, identifying designs that provide robust detection of severe wind shear 相似文献
102.
Intersecting spheres are useful in the design of pressure vessels for weight limited situations as in the case of space or ocean applications. This paper treats the general problem of N intersecting spheres demonstrating that mass reduction can be achieved in relation to the single sphere that encloses the same internal volume. It is shown that this reduction approaches asymptotically the value of 39.5%. 相似文献
103.
Fisher H.L. Musser K.L. Shuster M.D. 《IEEE transactions on aerospace and electronic systems》1993,29(1):22-26
Attitude estimation algorithms for the Thrusted Vector Mission which determine attitude based on Sun sensor and very coarse albedo sensor measurements are presented. On the basis of these measurements, it has been demonstrated by comparison with more accurate gyro-based attitude that it is possible to estimate three-axis attitude with an average error per axis of 11 deg. Most of this error is about the Sun direction. Both deterministic quick-look and optimal estimates are examined 相似文献
104.
R D Govorun I V Koshlan N A Koshlan E A Krasavin N L Shmakova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):885-890
The induction of HPRT-mutations and survival of Chinese hamster cells (line B11ii-FAF28, clone 431) were studied after irradiation by 4He and 12C-ions of various LET (20-360 keV/micrometers), produced by the U-200 heavy ion accelerator. The RBE increases with LET up to the maximum at 100-200 keV/micrometers and then decreases. Cytogenetic analysis was performed on the HPRT-mutant subclones selected from unirradiated Chinese hamster V-79 cells and from HPRT-mutant subclones that arose after exposure to gamma-rays, 1 GeV protons and 14N-ions (LET-77 keV/micrometers), produced by the synchrophasotron and the U-400M heavy ion accelerator. Slow growing mutant subclones were observed. The cytogenetic properties of individual clones were highly heterogeneous and chromosome instability was observed in both spontaneous and radiation-induced mutants. Chromosome instability was highest among spontaneous mutants and decreased with increasing LET. 相似文献
105.
V. Koblik E. Polyakhova L. Sokolov A. Shmyrov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,29(12):4431-2088
We present results of numerical simulations of trajectories of a space probe with a flat solar sail which moves from a circular Earth orbit to near-Sun regions. We consider the upper limit of the sail temperature as the basic restriction. We also examine the planar (ecliptic) solar sail transfer with gravity-assist flybys around planets. 相似文献
106.
D. L. Judge H. S. Ogawa D. R. McMullin P. Gangopadhyay J. M. Pap 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,29(12):502-1968
The SOHO Solar EUV Monitor has been in operation since December 1995 onboard the SOHO spacecraft. This instrument is a highly stable transmission grating solar extreme ultraviolet spectrometer. It has made nearly continuous full disk solar irradiance measurements both within an 8 nm bandpass centered at 30.4 nm and throughout the 0.1 to 50 nm solar flux region since launch. The 30.4 nm flux, the 0.1 to 50 nm flux and the extracted soft X-ray (0.1 to 5 nm) flux are presented and compared with the behavior of solar proxies. 相似文献
107.
F A Cucinotta L W Townsend J W Wilson M J Golightly M Weyland 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):661-670
The solar particle events (SPE) will contain a primary alpha particle component, representing a possible increase in the potential risk to astronauts during an SPE over the often studied proton component. We discuss the physical interactions of alpha particles important in describing the transport of these particles through spacecraft and body shielding. Models of light ion reactions are presented and their effects on energy and linear energy transfer (LET) spectra in shielding discussed. We present predictions of particle spectra, dose, and dose equivalent in organs of interest for SPE spectra typical of those occurring in recent solar cycles. The large events of solar cycle 19 are found to have substantial increase in biological risk from alpha particles, including a large increase in secondary neutron production from alpha particle breakup. 相似文献
108.
109.
A. Sh. Dzhabrailov Yu. V. Klochkov S. S. Marchenko A. P. Nikolaev 《Russian Aeronautics (Iz VUZ)》2007,50(2):115-120
We demonstrate that it is possible to express each component of the displacement vector for the interior point of the finite element (FE) through all components of nodal unknowns in curvilinear coordinates. The effectiveness of the valid technique of vector approximation for displacement fields has been verified on an example. 相似文献
110.
The characteristics of the insulator wear process in the discharge chamber of a stationary plasma thruster (SPT) are analyzed. The results of studying the erosion resistance to ionic spraying of different ceramic compositions are presented. It is shown experimentally that the integral characteristics (the value of thrust and thrust efficiency) as well as the SPT lifetime can be improved in changing from the conventional hot-pressed boron silicate (BN + SiO2) ceramics to the BN + Si3N4 ceramic compositions. 相似文献