全文获取类型
收费全文 | 7586篇 |
免费 | 29篇 |
国内免费 | 23篇 |
专业分类
航空 | 3889篇 |
航天技术 | 2648篇 |
综合类 | 33篇 |
航天 | 1068篇 |
出版年
2021年 | 52篇 |
2019年 | 53篇 |
2018年 | 99篇 |
2017年 | 64篇 |
2016年 | 59篇 |
2014年 | 138篇 |
2013年 | 180篇 |
2012年 | 163篇 |
2011年 | 228篇 |
2010年 | 166篇 |
2009年 | 259篇 |
2008年 | 343篇 |
2007年 | 188篇 |
2006年 | 184篇 |
2005年 | 187篇 |
2004年 | 171篇 |
2003年 | 248篇 |
2002年 | 147篇 |
2001年 | 255篇 |
2000年 | 152篇 |
1999年 | 189篇 |
1998年 | 233篇 |
1997年 | 160篇 |
1996年 | 209篇 |
1995年 | 273篇 |
1994年 | 251篇 |
1993年 | 150篇 |
1992年 | 183篇 |
1991年 | 99篇 |
1990年 | 92篇 |
1989年 | 198篇 |
1988年 | 88篇 |
1987年 | 88篇 |
1986年 | 88篇 |
1985年 | 253篇 |
1984年 | 206篇 |
1983年 | 180篇 |
1982年 | 192篇 |
1981年 | 231篇 |
1980年 | 81篇 |
1979年 | 61篇 |
1978年 | 68篇 |
1977年 | 69篇 |
1976年 | 49篇 |
1975年 | 87篇 |
1974年 | 53篇 |
1973年 | 53篇 |
1972年 | 75篇 |
1971年 | 56篇 |
1970年 | 54篇 |
排序方式: 共有7638条查询结果,搜索用时 15 毫秒
71.
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
72.
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
73.
Loran-C is a pulsed, hyperbolic radio aid for long-range marine, air, and land navigation. The worldwide expansion of Loran-C, especially in Europe, has focused attention on carrier-wave interference to the system. The effects of a multiplicity of carrier-wave interferers (CWIs) on receiver timing measurement accuracy are considered. Both the phase tracking and the cycle-selection performance of receivers are quantified in terms of the probabilities that they will operate correctly within the arbitrarily set error limits. Characteristic functions (CFs) are used to compute these probabilities. Analyses and results are presented for typical situations. The relative sensitivity of the phase tracking and cycle-selection functions to interfering signals are discussed 相似文献
74.
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
75.
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
76.
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
77.
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
78.
An electric vehicle (EV) energy management system (EMS) developed to accurately predict and extend the usable driving range and the life of the battery pack is discussed. The EMS monitors and records battery state of charge, vehicle performance, power consumption of key components, and driver's actions. Convenient drive inputs in conjunction with memorized energy consumption profiles allow accurate prediction of driving range and selection of appropriate recharging profiles. EV range extension is accomplished by identifying inefficient use of energy, resulting in EMS modification of energy usage by offending subsystems or EMS suggestion to the driver of improved driving habits or vehicle use. Factors affecting the accuracy of range prediction and the amount of range extension are described 相似文献
79.
The design of fault-tolerant distributed control systems is discussed. The application described is a generic flight control system (FCS) for a fighter aircraft. The system is designed for high redundancy and expandability to meet various requirements. The communication network is based on the fiber distributed data interface (FDDI), which provides a high level of electromagnetic interference resistance and reliability. The choice of fiber optic media also provides an extremely high bandwidth and tremendous growth capability for future communications needs. This study is not specific to FDDI or flight control systems. The methods and configurations presented should be applicable to many real-time control implementations 相似文献
80.