全文获取类型
收费全文 | 2509篇 |
免费 | 2篇 |
国内免费 | 6篇 |
专业分类
航空 | 1237篇 |
航天技术 | 998篇 |
综合类 | 5篇 |
航天 | 277篇 |
出版年
2021年 | 14篇 |
2019年 | 14篇 |
2018年 | 41篇 |
2017年 | 34篇 |
2016年 | 26篇 |
2015年 | 11篇 |
2014年 | 52篇 |
2013年 | 60篇 |
2012年 | 50篇 |
2011年 | 88篇 |
2010年 | 65篇 |
2009年 | 106篇 |
2008年 | 152篇 |
2007年 | 64篇 |
2006年 | 51篇 |
2005年 | 62篇 |
2004年 | 71篇 |
2003年 | 92篇 |
2002年 | 46篇 |
2001年 | 102篇 |
2000年 | 45篇 |
1999年 | 87篇 |
1998年 | 85篇 |
1997年 | 62篇 |
1996年 | 63篇 |
1995年 | 88篇 |
1994年 | 97篇 |
1993年 | 37篇 |
1992年 | 59篇 |
1991年 | 22篇 |
1990年 | 28篇 |
1989年 | 60篇 |
1988年 | 20篇 |
1987年 | 35篇 |
1986年 | 19篇 |
1985年 | 74篇 |
1984年 | 42篇 |
1983年 | 46篇 |
1982年 | 55篇 |
1981年 | 77篇 |
1980年 | 26篇 |
1979年 | 24篇 |
1978年 | 22篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1975年 | 18篇 |
1974年 | 12篇 |
1972年 | 17篇 |
1969年 | 13篇 |
1966年 | 8篇 |
排序方式: 共有2517条查询结果,搜索用时 531 毫秒
411.
US Army helicopters that will allow single-crewmember operability in tactical environments require a high degree of automation. A tightly integrated flight control and navigation system has been studied. An architecture is discussed which meets anticipated flight control and navigation requirements, at an acceptable weight, using techniques of functional and physical integration. The architecture maximizes the sharing of sensor and computational resources in a flight critical environment and uses modular equipment packaging, dual fault-tolerant tetrad ring-laser-gyro inertial measurement units, and triplex self-checking processor pair-based flight critical processing channels 相似文献
412.
Stark L. Tendick F. Kim W. Anderson R. Hisey M. Mills B. Matsunaga K. An Nguyen Ramos C. Tyler M. Zahalak G. Amick M. Baker B. Brown N. Brown T. Chang J. Jyh-Horng Chen Chik J. Cohen D. Cox D. Dubey J. Ellis K. Engdahl E. Frederickson C. Halamka J. Hauser R. Jacobs J. Lee C. Lee D. Liu A. Ninomiya R. Rudolph J. Schafer S. Schendel E. So G. Takeda M. Tam L. Thompson M. Wood E. Woodruff T. 《IEEE transactions on aerospace and electronic systems》1988,24(5):542-551
With major emphasis on simulation, a university laboratory telerobotics facility permits problems to be approached by groups of graduate students. Helmet-mounded displays provide realism; the slaving of the display to the human operator's viewpoint gives a sense of `telepresence' that may be useful for prolonged tasks. Using top-down 3-D model control of distant images allows distant images to be reduced to a few parameters to update the model used for display to the human operator in a preview model to circumvent, in part, the communication delay. Also, the model can be used as a format for supervisory control and permit short-term local autonomous operations. Image processing algorithms can be made simpler and faster without trying to construct sensible images from the bottom. Control studies of telerobots lead to preferential manual control modes and, in this university environment, to basic paradigms for human motion and thence, perhaps, to redesign of robotic control, trajectory path planning, and rehabilitation prosthetics. Speculation as to future industrial drives for this telerobotic field suggests efficient roles for government agencies such as NASA 相似文献
413.
A brief survey is presented of trends in work reported at four International Stirling Engine Conferences held during the 1980s. The discussion covers international participation, publication sources and types, engine types, specialized engines, sponsoring institutions and observed trends 相似文献
414.
It is shown that synthetic-aperture radar (SAR) motion can be compensated by using an antenna-mounted strapdown inertial measurement unit (IMU) as the motion sensing system, but sensor and system errors affect SAR image quality. A strapdown IMU consists of three accelerator channels and three gyro channels. Strapdown IMU errors include gyro-scale and accelerometer-scale factor and bias errors, velocity error, platform tilt, and errors induced by limited inertial sensor bandwidth. The effects of these errors on the SAR image quality are presented in terms of the SAR impulse response. IMU errors that cause low-frequency phase errors (less than one cycle per array time) are categorized in terms of quadratic and cubic phase errors. IMU errors that cause high-frequency phase errors (greater than one cycle per array time) are categorized in terms of the integrated sidelobe ratio and peak sidelobe ratio. A motion compensation system conceptualization is described wherein a strapdown IMU is attached to an antenna and transfer-aligns to the aircraft's master navigator 相似文献
415.
T.C. Forbes 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(7):53-56
The resistive MHD equations are numerically solved in two dimensions for an initial-boundary-value problem which simulates reconnection between an emerging magnetic flux region and an overlying coronal magnetic field. The solution involves both ideal-MHD and resistive-MHD processes, and the solution shows an evolution which is remarkably suggestive of the preflare, impulsive, and main phases of the flare-cycle. 相似文献
416.
Sekine M. Ohatani S. Musha T. Irabu T. Kiuchi E. Hagisawa T. Tomita Y. 《IEEE transactions on aerospace and electronic systems》1982,(6):729-730
It is shown that the Weibull-distributed ground clutter obeys a Weibull distribution after processing by the double canceler moving target indicator (MTI). 相似文献
417.
B.N. Khare C. Sagan W.R. Thompson E.T. Arakawa F. Suits T.A. Callcott M.W. Williams S. Shrader H. Ogino T.O. Willingham B. Nagy 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(12):59-68
A dark reddish organic solid, called tholin, is synthesized from simulated Titanian atmospheres by irradiation with high energy electrons in a plasma discharge. The visible reflection spectrum of this tholin is found to be similar to that of high altitude aerosols responsible for the albedo and reddish color of Titan. The real (n) and imaginary (k) parts of the complex refractive index of thin films of Titan tholin prepared by continuous D.C. discharge through a 0.9 N2/0.1 CH4 gas mixture at 0.2 mb is determined from x-ray to microwave frequencies. Values of n (1.65) and k (0.004 to 0.08) in the visible are consistent with deductions made by ground-based and spaceborne observations of Titan. Many infrared absorption features are present in k(λ), including the 4.6 μm nitrile band. Molecular analysis of the volatile component of this tholin was performed by sequential and non-sequential pyrolytic gas chromatography/mass spectrometry. More than one hundred organic compounds are released; tentative identifications include saturated and unsaturated aliphatic hydrocarbons, substituted polycyclic aromatics, nitriles, amines, pyrroles, pyrazines, pyridines, pyrimidines, and the purine, adenine. In addition, acid hydrolysis produces a racemic mixture of biological and non-biological amino acids. Many of these molecules are implicated in the origin of life on Earth, suggesting Titan as a contemporary laboratory environment for prebiological organic chemistry on a planetary scale. 相似文献
418.
419.
K.-P. Wenzel R. Reinhard T.R. Sanderson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(3):105-108
ISEE-3 observations of a long-lasting low-energy proton intensity increase during the 25 September 1978 shock event are presented as an example for interplanetary particle acceleration in association with shock waves. The observations are discussed in the light of current models for particle acceleration. The particular shape of the time intensity behaviour of the particle intensity increase, the existence of a shock spike and the observed particle distributions indicate that the particles are accelerated at the shock by the induced electric field . 相似文献
420.
Brewster L.T. Stigall P.D. 《IEEE transactions on aerospace and electronic systems》1988,24(6):682-692
Aircraft vertical profile simulation is realized using a demand-driven minimal-calculation directed graph structure to reduce calculation time and to force synchronization of the performance measurement functions with the system state variables. Performance-directed model adaptation makes dynamic vertical profile path corrections, in the presence of fixed drag variations, possible. Drag variations ranging from +10% to -10% yielded fuel consumption improvements of less than 1% in the majority of the cases. Calculation time improvement for path simulation ranges from a factor of 1.19 in the worst case to 1.5 in the best case 相似文献