全文获取类型
收费全文 | 395篇 |
免费 | 1篇 |
国内免费 | 2篇 |
专业分类
航空 | 154篇 |
航天技术 | 81篇 |
综合类 | 3篇 |
航天 | 160篇 |
出版年
2021年 | 3篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 16篇 |
2012年 | 7篇 |
2011年 | 38篇 |
2010年 | 15篇 |
2009年 | 31篇 |
2008年 | 19篇 |
2007年 | 19篇 |
2006年 | 19篇 |
2005年 | 11篇 |
2004年 | 7篇 |
2003年 | 17篇 |
2002年 | 9篇 |
2001年 | 5篇 |
2000年 | 15篇 |
1999年 | 9篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1991年 | 4篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1968年 | 6篇 |
1967年 | 7篇 |
1966年 | 3篇 |
1965年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有398条查询结果,搜索用时 14 毫秒
361.
The geomagnetic signal contains an enormous temporal range—from geomagnetic jerks on time scales of less than a year to the evolution of Earth’s dipole moment over billions of years. This review compares observations and numerical models of the long-term range of that signal, for periods much larger than the typical overturn time of Earth’s core. On time scales of 105–109 years, the geomagnetic field reveals the control of mantle thermodynamic conditions on core dynamics. We first briefly describe the general formalism of numerical dynamo simulations and available paleomagnetic data sets that provide insight into paleofield behavior. Models for the morphology of the time-averaged geomagnetic field over the last 5 million years are presented, with emphasis on the possible departures from the geocentric axial dipole hypothesis and interpretations in terms of core dynamics. We discuss the power spectrum of the dipole moment, as it is a well-constrained aspect of the geomagnetic field on the million year time scale. We then summarize paleosecular variation and intensity over the past 200 million years, with emphasis on the possible dynamical causes for the occurrence of superchrons. Finally, we highlight the geological evolution of the geodynamo in light of the oldest paleomagnetic records available. A summary is given in the form of a tentative classification of well-constrained observations and robust numerical modeling results. 相似文献
362.
Blinn John C. Campbell James P. 《IEEE transactions on aerospace and electronic systems》1966,(5):585-590
This paper discusses the results of an analytic study of the feasibility of using microwave radiometry as a technique for navigation data sensing in Army aircraft. The study included a review of Army aircraft characteristics and navigation requirements. Various means of sensing passively aircraft velocity, altitude, and velocity-altitude ratio were considered. While there appears to be no practical method for direct measurement of either velocity or altitude separately, it does appear possible to measure velocity-altitude ratio by comparing radiometric signals received from the terrain along the aircraft ground track. When combined with a radar altimeter, such a sensor could yield navigation data compatible with Army aircraft requirements. Microwave radiometry may also be the basis for direction sensing (to known landmarks) in high-flying aircraft or satellites. 相似文献
364.
John B. Rogerson Jr. 《Space Science Reviews》1963,2(5):621-652
A review is presented of the Orbiting Astronomical Observatories Program together with a detailed of the OAO spacecraft and the four astronomical instruments currently being developed for the first three observations. 相似文献
365.
D'Antonio R. A. Gaffney John E. 《IEEE transactions on aerospace and electronic systems》1968,(5):728-732
This paper describes a radio interferometer that can be employed for beaming and attitude determination. It differs from conventional interferometers in that it employs a carrier modulated by a pseudonoise sequence. This enables it to provide an unambiguous angular resolution of the signal source. 相似文献
366.
Kovaly John J. Miller Stephen N. 《IEEE transactions on aerospace and electronic systems》1967,(3):518-526
The performance of a uniformly spaced phased-steered line array with element channel superlimiting is studied for far-field sources consisting of 1) two sinusoidal signals with different frequencies and angular locations, and 2) a sinusoid and a noise signal at different angular locations. Attention is focused on the nonlinear case where internal noise is negligible compared to both input signals. The analysis for the two-sinusoid case gives the precise frequencies, positions, and amplitudes of all apparent sources. In addition to the two active sources, the array output has an array of images arranged symmetrically in sine space about the larger input, at intervals equal to the spacing between the two active sources. For the case of a separated sinusoid and a noise source, the analysis shows that the angular positions and average powers of the array outputs duplicate the double-sinusoid results, but the images have noise-like spectra. The analyses are confirmed by experimental results obtained with a 60-element superlimiting X-band array. 相似文献
367.
Robert C. Singleterry Steve R. Blattnig Martha S. Clowdsley Garry D. Qualls Chris A. Sandridge Lisa C. Simonsen Tony C. Slaba Steven A. Walker Francis F. Badavi Jan L. Spangler Aric R. Aumann E. Neal Zapp Robert D. Rutledge Kerry T. Lee Ryan B. Norman John W. Norbury 《Acta Astronautica》2011,68(7-8):1086-1097
OLTARIS (On-Line Tool for the Assessment of Radiation In Space) is a space radiation analysis tool available on the World Wide Web. It can be used to study the effects of space radiation for various spacecraft and mission scenarios involving humans and electronics. The transport is based on the HZETRN transport code and the input nuclear physics model is NUCFRG. This paper describes the tools behind the web interface and the types of inputs required to obtain results. Typical inputs are mission parameters and slab definitions or vehicle thickness distributions. Radiation environments can be chosen by the user. This paper describes these inputs as well as the output response functions including dose, dose equivalent, whole body effective dose equivalent, LET spectra and detector response models. 相似文献
368.
369.
370.
Rodger I. Thompson Jill Bechtold Daniel Eisenstein Xiaohui Fan David Arnett Carlos Martins Robert Kennicutt John Black 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Many theoretical models of dark energy invoke rolling scaler fields which in turn predict time varying values of the fundamental constants. Establishing the value of the fundamental constants at various times in the universe can probe and test the various dark energy theories. One of the constants that is predicted to vary is the ratio of the electron to proton mass μ. It was established early on that molecular spectra are sensitive to the value of μ and can be used as probes of that value. This article describes the use of the spectrum of molecular hydrogen in high redshift Damped Lyman Alpha systems (DLAs) as a sensitive probe of the time evolution of μ. 相似文献