全文获取类型
收费全文 | 1156篇 |
免费 | 18篇 |
国内免费 | 6篇 |
专业分类
航空 | 514篇 |
航天技术 | 511篇 |
综合类 | 15篇 |
航天 | 140篇 |
出版年
2022年 | 5篇 |
2021年 | 15篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 5篇 |
2014年 | 31篇 |
2013年 | 26篇 |
2012年 | 36篇 |
2011年 | 57篇 |
2010年 | 31篇 |
2009年 | 57篇 |
2008年 | 103篇 |
2007年 | 29篇 |
2006年 | 30篇 |
2005年 | 45篇 |
2004年 | 39篇 |
2003年 | 34篇 |
2002年 | 27篇 |
2001年 | 53篇 |
2000年 | 21篇 |
1999年 | 38篇 |
1998年 | 38篇 |
1997年 | 13篇 |
1996年 | 35篇 |
1995年 | 20篇 |
1994年 | 34篇 |
1993年 | 22篇 |
1992年 | 30篇 |
1991年 | 11篇 |
1990年 | 14篇 |
1989年 | 32篇 |
1988年 | 15篇 |
1987年 | 6篇 |
1986年 | 12篇 |
1985年 | 20篇 |
1984年 | 27篇 |
1983年 | 23篇 |
1982年 | 20篇 |
1981年 | 24篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1973年 | 3篇 |
1970年 | 3篇 |
1969年 | 4篇 |
排序方式: 共有1180条查询结果,搜索用时 500 毫秒
121.
To cancel clutter, both medium-PRF waveforms which are ambiguous in both range and Doppler and high-PRF waveforms which are ambiguous in range but unambiguous in ambiguities, a previous paper has shown that superior results for a single target can be achieved by using a clustering algorithm. Here, the problem of multiple targets is considered. A maximum likelihood (ML) technique which incorporates the clustering algorithm is developed for the multiple target problem. Simulation results show that four targets which have the same speed but are at different ranges can be resolved by using a medium-PRF waveform and employing the ML resolution technique 相似文献
122.
Y. Lin S.F. Martin O. Engvold L.H.M. Rouppe van der Voort M. van Noort 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
High resolution Hα images and magnetograms (0.2 arc s) of an active region were obtained in alternating time series at 42 s cadences using the Swedish 1-m Solar Telescope on 2004 August 21. The Hα filtergrams reveal an active region filament and surges consisting of thread-like structures which have widths similar to the widths of chromospheric fibrils, both recorded down to the resolution limit in the best images. All observed structures in the active region appear highly dynamic. Fibrils show counterstreaming strongly resembling the counterstreaming threads in filaments. 相似文献
123.
Hyoung Joong Kim Gyu-in Jee Jang Gyu Lee 《IEEE transactions on aerospace and electronic systems》1996,32(2):607-612
A tree network consisting of communicating processors is considered. The objective is to minimize the processing time by distributing the processing load to other nodes. The effect of the order of load distribution on the processing time is addressed. An algorithm which optimally determines the order of load distribution is developed. It is shown that the order depends only on the channel capacity between nodes but not on the computing capability of each node 相似文献
124.
Y. Tanaka 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(3):81-89
Tenma, the second X-ray astronomy satellite of Japan launched in February 1983, is outlined. The main instrument of Tenma is a large-area gas scintillation proportional counter array. Some of the highlights of the results thus far obtained are briefly discussed. 相似文献
125.
V Switzer RC rdBogo G A Mickley 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):443-451
Application of the degeneration sensitive, cupric-silver staining method to brain sections of male Sprague-Dawley rats irradiated 4 days before sacrifice with 155 Mev protons, 2-8 Gy at 1 Gy/min (N=6) or 22-l0lGy at 20 Gy/min (N=16) or with 18.6 Mev electrons, 32-67 Gy at 20 Gy/min (N=20), doses which elicit behavioral changes (accelerod or conditioned taste aversion), resulted in a display of degeneration of astrocyte-like cell profiles which were not uniformly distributed. Plots of 'degeneration scores' (counts of profiles in 29 areas) vs. dose for the proton and electron irradiations displayed a linear dose response for protons in the range of 2-8 Gy. In the 20-100 Gy range, for both electrons and protons the points were distributed in a broad band suggesting a saturation curve. The dose range in which these astrocyte-like profiles becomes maximal corresponds well with the dose range for the X-ray eradication of a subtype of astrocytes, 'beta astrocytes'. 相似文献
126.
S. Namazov S. Nikolaishvili Y. Romanovsky V. Ivanov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(12):123-126
The evolution of a barium ion cloud formed in the MR-20 rocket experiment in the low-latitude ionosphere is considered using data of Doppler multifrequency sounding. 相似文献
127.
An analysis of the relationship between a linear amplifier chain and an analog-to-digital converter (ADC) in a digital microwave receiver, with respect to sensitivity and dynamic range issues, is presented. The effects of gain, third-order intermodulation products and ADC characteristics on the performance of the receiver are illustrated and design criteria for the linear amplifier chain (given a specified ADC) are developed. A computer program is included which calculates theoretical receiver performance based on gain and third-order intermodulation product selections. Experimental results are also presented and compared with theoretical values 相似文献
128.
A.A Trotman A.M Almazan A.D Alexander P.A Loretan X Zhou J.Y Lu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,18(12):269
Many challenges are presented by biological degradation in a bioregenerative Controlled Ecological Life Support System as envisioned by the U.S. National Aeronautics and Space Administration. In studies conducted with biodegradative microorganisms indigenous to sweetpotato fields, it was determined that a particle size of 75 microns and incubation temperature of 30°C were optimal for degradation. The composition of the biomass and characterization of plant nutrient solution indicated the presence of potential energy sources to drive microbial transformations of plant waste. Selected indigenous soil isolates with ligno-cellulolytic or sulfate-reducing ability were utilized in biological studies and demonstrated diversity in their ability to reduce sulfate in solution and to utilize alternative carbon sources: a lignin analog 4-hydroxy, 3-methoxy cinnamic acid, cellulose, arabinose, glucose, sucrose, mannitol, galactose, ascorbic acid. 相似文献
129.
Y Kitaya A Tani M Kiyota I Aiga 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(11):281-284
In order to obtain basic data for construction of a plant cultivation system incorporating a mushroom cultivation subsystem in the CELSS, plant growth and atmospheric CO2 balance in the system were investigated. The plant growth was promoted by a high level of CO2 which resulted from the respiration of the mushroom mycelium in the system. The atmospheric CO2 concentration inside the system changed significantly due to the slight change in the net photosynthetic rate of plants and/or the respiration rate of the mushroom when the plant cultivation system combined directly with the mushroom cultivation subsystem. 相似文献
130.
Y Uchihori E Benton J Moeller G Bendrick 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,32(1):41-46
The risks to aircrew health posed by prolonged exposure to low levels of ionizing radiation at aircraft altitudes have recently received renewed attention. Civil and military aircraft currently on the drawing board are expected to operate at higher altitudes (>12 km) and fly longer ranges than do existing aircraft, thereby exposing their crews to higher levels of ionizing radiation, for longer periods of time. We are currently carrying out dosimetric measurements of the ionizing radiation environment at approximately 20 km altitude using portable Si detectors aboard NASA's two ER-2 high altitude research aircraft. The instruments, Liulin-4J, have been extensively calibrated at several particle accelerators. With these instruments, we can measure not only absorbed dose, but also variation of the absorbed dose as a function of time. We report radiation dose measurements as function of time, altitude, and latitude for several ER-2 missions. 相似文献