全文获取类型
收费全文 | 300篇 |
免费 | 12篇 |
国内免费 | 9篇 |
专业分类
航空 | 156篇 |
航天技术 | 100篇 |
综合类 | 9篇 |
航天 | 56篇 |
出版年
2021年 | 4篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2016年 | 4篇 |
2014年 | 14篇 |
2013年 | 9篇 |
2012年 | 14篇 |
2011年 | 23篇 |
2010年 | 12篇 |
2009年 | 14篇 |
2008年 | 15篇 |
2007年 | 6篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 12篇 |
2002年 | 19篇 |
2001年 | 17篇 |
2000年 | 6篇 |
1999年 | 11篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1969年 | 4篇 |
1968年 | 2篇 |
1967年 | 3篇 |
1965年 | 2篇 |
排序方式: 共有321条查询结果,搜索用时 62 毫秒
181.
N Tranquille J J Emeis D de Chambure R Binot C Tamponnet 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(11):167-170
Groups of five rats were fed for sixteen weeks a slightly deficient diet, supplemented with 0-40% of a dried preparation of the blue-green alga Spirulina as a protein source. Control groups were fed a normal rat diet. No significant differences between groups were found in food intake, growth rate or carbon dioxide production. All animals remained apparently healthy, and had similar organ weights. The study suggests that Spirulina may be used as a protein source in rat diets. 相似文献
182.
H. G. van Bueren E. van den Heuvel C. de Jager H. Kallmann-Bijl 《Space Science Reviews》1964,3(5-6):856-858
183.
EXOSAT observations of the Seyfert galaxy NGC 4151 over the period July 1983 to April 1984 have revealed a decreasing flux in the 2 –10 keV band. In accord with previous measurements a power law spectrum attenuated with a simple column of cold gas does not provide a satisfactory spectral fit below 3 keV, where a lower relative opacity is required. Inclusion of additional low energy data from the EXOSAT telescopes allows the modelling of the absorbing column to be improved and reveals a second, separate, soft X-ray spectral component. 相似文献
184.
185.
J. Cacho M. Gil M.J. Sainz de Aja L.F. Alberca 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(4):37-40
Using daily temperature data available from radio-sonde measurements over Barajas (Madrid), La Coruña and Palma de Mallorca stations, for the time span 1971–1982 and an altitude range 100-30 mb, a study is made comparing temperatures at differents levels with the 10.7 cm flux in order to check whether radiation variability must be included in lower stratospheric models. At the latitude studied, stratospheric temperatures are uninfluenced by sudden warming phenomena avoiding difficulties of masking found in previous studies. 相似文献
186.
A method is presented for reducing trajectory sensitivity and achieving robust asymptotic tracking for linear feedback systems when there are parameter perturbations and disturbance inputs. The controller consists of a servocompensator containing the modes of the reference signals and disturbance inputs, a stabilizing feedback loop, and a feedforward compensator. Application of the method to the design of a vertical takeoff and landing (VTOL) aircraft flight control system is discussed. The use of a precompensator allows performance maneuvers such that the aircraft tracks desired trajectories and the feedforward and feedback signals aid in reducing the trajectory sensitivity to variations of parameters due to change in airspeed and to wind gust. Simulation results are presented to show the robust tracking, disturbance rejection, and sensitivity reduction capabilities of the flight control system. 相似文献
187.
R.D. Gehrz E.E. Becklin I. de Pater D.F. Lester T.L. Roellig C.E. Woodward 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is a joint US/German Project to develop and operate a gyrostabilized 2.5-m telescope in a Boeing 747-SP. This observatory will allow astronomical observations from 0.3 μm to sub-millimeter wavelengths at stratospheric altitudes as high as 45,000 ft where the atmosphere is not only cloud-free, but largely transparent at infrared wavelengths. The dynamics and chemistry of interstellar matter, and the details of embedded star formation will be key science goals. In addition, SOFIA’s unique portability will enable large-telescope observations at sites required to observe transient phenomena and location specific events. SOFIA will offer the convenient accessibility of a ground-based telescope for servicing, maintenance, and regular technology upgrades, yet will also have many of the performance advantages of a space-based telescope. Initially, SOFIA will fly with nine first-generation focal plane instruments that include broad-band imagers, moderate resolution spectrographs that will resolve broad features from dust and large molecules, and high resolution spectrometers capable of studying the chemistry and detailed kinematics of molecular and atomic gas. First science flights will begin in 2010, leading to a full operations schedule of about 120 8–10 h flights per year by 2014. The next call for instrument development that can respond to scientifically exciting new technologies will be issued in 2010. We describe the SOFIA facility and outline the opportunities for observations by the general scientific community with cutting edge focal plane technology. We summarize the operational characteristics of the first-generation instruments and give specific examples of the types of fundamental scientific studies these instruments are expected to make. 相似文献
188.
189.
190.
H.S. Sawant J.R. Cecatto H. Mészárosová C. Faria F.C.R. Fernandes M. Karlický M.C. de Andrade 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The digital, decimetric (950–2500 MHz) Brazilian Solar Spectroscope (BSS, Sawant, H.S., Subramanian, K.R., Faria, C., et al. Brazilian Solar Spectroscope (BSS). Solar Phys. 200, 167–176, 2001) with high time (10–1000 ms) and frequency (1–10 MHz) resolution is in regular operation since April, 1998, at the National Space Research Institute (INPE) at São José dos Campos, Brazil. The BSS has now been upgraded with a new digital data acquisition and data processing system. The new version of the BSS has improved the observational possibilities with the capability to record up to 200 frequency channels available in the selectable frequency range 950–2500 MHz. The GPS receiver permits the acquisition of data with time accuracy in the order of 0.1 ms. The software system of the BSS is composed by two distinct modules: the first, data acquisition system provides a flexible Graphical User Interface (GUI) that allows one to choose the observational parameters. The second module is the real time visualization system that permits real time visualization of the observed dynamic spectrum and additionally allows procedures for visualization and preliminary analysis of the recorded solar spectra. Using the new visualization system, we have realized two new types of dm-radio fine structures: narrow band type III bursts with positive as well as negative group frequency drift and dots emissions arranged in zebra-like and fiber-like chains. Furthermore, we have found flare generated fast wave trains according to their tadpole signature in wavelet power spectra for a decimetric type IV radio event (June 6, 2000 flare). 相似文献