全文获取类型
收费全文 | 5336篇 |
免费 | 25篇 |
国内免费 | 32篇 |
专业分类
航空 | 2607篇 |
航天技术 | 1960篇 |
综合类 | 14篇 |
航天 | 812篇 |
出版年
2021年 | 35篇 |
2019年 | 37篇 |
2018年 | 71篇 |
2017年 | 60篇 |
2016年 | 55篇 |
2014年 | 105篇 |
2013年 | 136篇 |
2012年 | 125篇 |
2011年 | 174篇 |
2010年 | 121篇 |
2009年 | 213篇 |
2008年 | 264篇 |
2007年 | 141篇 |
2006年 | 120篇 |
2005年 | 144篇 |
2004年 | 150篇 |
2003年 | 167篇 |
2002年 | 113篇 |
2001年 | 174篇 |
2000年 | 100篇 |
1999年 | 123篇 |
1998年 | 150篇 |
1997年 | 93篇 |
1996年 | 146篇 |
1995年 | 170篇 |
1994年 | 167篇 |
1993年 | 94篇 |
1992年 | 119篇 |
1991年 | 60篇 |
1990年 | 58篇 |
1989年 | 135篇 |
1988年 | 51篇 |
1987年 | 50篇 |
1986年 | 58篇 |
1985年 | 182篇 |
1984年 | 142篇 |
1983年 | 116篇 |
1982年 | 111篇 |
1981年 | 177篇 |
1980年 | 51篇 |
1979年 | 47篇 |
1978年 | 51篇 |
1977年 | 47篇 |
1976年 | 32篇 |
1975年 | 55篇 |
1974年 | 40篇 |
1973年 | 42篇 |
1972年 | 40篇 |
1970年 | 41篇 |
1969年 | 43篇 |
排序方式: 共有5393条查询结果,搜索用时 171 毫秒
561.
Y Takahashi K Nitta H Ohya M Oguchi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1987,7(4):81-84
The wet-oxidation catalysis of Au, Pd, Pt, Rh or Ru on a ceramic honeycomb carrier was traced in detail by 16 to 20 repetitive batch tests each. As a result, Pt or Pd on a honeycomb carrier was shown to catalyze complete nitrogen gasification as N2. Though the catalysts which realize both complete nitrogen gasification and complete oxidation could not be found, the Ru+Rh catalyst was found to be most promising. Ru honeycomb catalyzed both nitrification and nitrogen gasification. 相似文献
562.
Slattery Richard E. Clay Wallace G. Worthington William C. 《IEEE transactions on aerospace and electronic systems》1968,(2):187-193
Increased sensitivity and dynamic range of the instrumental techniques used in conjunction with experiments on ballistic ranges have brought to the fore many problems arising from contamination in the ranges themselves. This is seldom discussed when experimental results are presented but is frequently the controlling limitation on the accuracy of the measurements. The authors discuss contamination due to dirt and debris resultant from gun operation, gaseous impurities, and projectile-borne impurities as they have occurred at the Re-entry Simulating Range of Lincoln Laboratory. The effects of these contaminants on measurements are discussed and illustrated, and measures for controlling them are outlined. Finally, a particular range operation is described from the standpoint of impurity control. 相似文献
563.
Roy E. Cameron 《Space Science Reviews》1963,2(2):297-312
New frontiers in soil science are currently found in the investigation of soils in harsh, terrestrial and simulated extraterrestrial environments, the development of new methods and probes for soil characterization, and the eventual investigation, characterization, and development of extraterrestrial soil. Current aspects of space science involving soil studies are presented, including a more detailed soil study program involving the microflora of desert soil ecosystems. Basic precepts are given for preparation, investigation, and use of extraterrestrial soil.Contribution from the Bioscience Group of the Chemistry Section, Space Science Division, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California. Presented as an invitational paper before the Synapsis Club, University of California, Riverside, California, December 3, 1962. 相似文献
564.
565.
During the conceptual design of a re-entry vehicle, the vehicle shape and geometry can be varied and its impact on performance can be evaluated. In this study, the shape optimization of two classes of vehicles has been studied: a capsule and a winged vehicle. Their aerodynamic characteristics were analyzed using local-inclination methods, automatically selected per vehicle segment. Entry trajectories down to Mach 3 were calculated assuming trimmed conditions. For the winged vehicle, which has both a body flap and elevons, a guidance algorithm to track a reference heat-rate was used. Multi-objective particle swarm optimization was used to optimize the shape using objectives related to mass, volume and range. The optimizations show a large variation in vehicle performance over the explored parameter space. Areas of very strong non-linearity are observed in the direct neighborhood of the two-dimensional Pareto fronts. This indicates the need for robust exploration of the influence of vehicle shapes on system performance during engineering trade-offs, which are performed during conceptual design. A number of important aspects of the influence of vehicle behavior on the Pareto fronts are observed and discussed. There is a nearly complete convergence to narrow-wing solutions for the winged vehicle. Also, it is found that imposing pitch-stability for the winged vehicle at all angles of attack results in vehicle shapes which require upward control surface deflections during the majority of the entry. 相似文献
566.
567.
While there is great potential for successful use of neural network (NN) algorithms in automatic target recognition (ATR) and other pattern identification/classification applications, significant barriers have been encountered that, to date, defy rigorous use of NNs within feedback control designs. The status of several problems and contradictions involving NNs relating to control and estimation theory applications (and to practical failure detection within INS/GPS navigation systems) are summarized here. To give a positive spin and for a balanced perspective, we also mention many novel laudable NN results obtained by invoking the techniques and results of control and estimation theory 相似文献
568.
Z Han H Suzuki F Suzuki M Suzuki Y Furusawa T Kato Jr. M Ikenaga 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,22(12):1725-1732
We have studied the induction of morphological transformation of Syrian hamster embryo cells by low doses of heavy ions with different linear energy transfer (LET), ranging from 13 to 400 keV/μm. Exponentially growing cells were irradiated with 12C or 28Si ion beams generated by the Heavy Ion Medical Accelerator in Chiba (HIMAC), inoculated to culture dishes, and transformed colonies were identified when the cells were densely stacked and showed a crisscross pattern. Over the LET range examined, the frequency of transformation induced by the heavy ions increased sharply at very low doses no greater than 5 cGy. The relative biological effectiveness (RBE) of the heavy ions relative to 250 kVp X-rays showed an initial increase with LET, reaching a maximum value of about 7 at 100 keV/μm, and then decreased with the further increase in LET. Thus, we confirmed that high LET heavy ions are significantly more effective than X-rays for the induction of in vitro cell transformation. 相似文献
569.
We present the results of processing and analysis of more than 4500 events of radio occultation sounding of the Earth’s atmosphere observed in the course of the COSMIC experiment on the limb path ‘satellite-ionosphere-satellite’. Events observed in December 2011 (when a number of solar flares occurred) and in January 2012 (when a strong solar proton event took place) were analyzed. It is shown that small-scale variations of electron density increase in polar latitudes, equatorial region, and midlatitudes of the southern hemisphere in January 2012. In the same period, an increase of large-scale variations of electron density is observed during daylight hours in the equatorial region and in the southern hemisphere. No noticeable distinctions in comparison with days of quiet Sun were observed in December 2011. 相似文献
570.