全文获取类型
收费全文 | 6142篇 |
免费 | 17篇 |
国内免费 | 33篇 |
专业分类
航空 | 2938篇 |
航天技术 | 2213篇 |
综合类 | 20篇 |
航天 | 1021篇 |
出版年
2021年 | 49篇 |
2019年 | 40篇 |
2018年 | 111篇 |
2017年 | 68篇 |
2016年 | 61篇 |
2014年 | 123篇 |
2013年 | 170篇 |
2012年 | 156篇 |
2011年 | 215篇 |
2010年 | 151篇 |
2009年 | 246篇 |
2008年 | 319篇 |
2007年 | 166篇 |
2006年 | 141篇 |
2005年 | 186篇 |
2004年 | 170篇 |
2003年 | 215篇 |
2002年 | 121篇 |
2001年 | 184篇 |
2000年 | 121篇 |
1999年 | 158篇 |
1998年 | 187篇 |
1997年 | 137篇 |
1996年 | 175篇 |
1995年 | 222篇 |
1994年 | 191篇 |
1993年 | 113篇 |
1992年 | 165篇 |
1991年 | 74篇 |
1990年 | 59篇 |
1989年 | 147篇 |
1988年 | 52篇 |
1987年 | 53篇 |
1986年 | 59篇 |
1985年 | 176篇 |
1984年 | 151篇 |
1983年 | 121篇 |
1982年 | 156篇 |
1981年 | 155篇 |
1980年 | 61篇 |
1979年 | 53篇 |
1978年 | 44篇 |
1977年 | 41篇 |
1976年 | 37篇 |
1975年 | 47篇 |
1974年 | 46篇 |
1973年 | 35篇 |
1972年 | 33篇 |
1970年 | 32篇 |
1969年 | 32篇 |
排序方式: 共有6192条查询结果,搜索用时 31 毫秒
281.
K Baltschukat G Horneck H Bucker R Facius M Schafer 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(11):109-115
Using spores of two Bacillus subtilis strains differing in repair capacity, we have studied repair and mutation induction in the spores after irradiation with very heavy ions up to uranium with specific particle energies up to 18.6 MeV/u. The results indicate that repair and mutation induction after heavy ion irradiation are closely related to each other and that both phenomena strongly depend on the atomic number and specific energy of the ions. The effects are discussed in comparison with results obtained after X-irradiation. 相似文献
282.
283.
284.
285.
Space Science Reviews - We summarize our model of galactic cosmic-ray (GCR) origin and acceleration, wherein a mixture of interstellar and/or circumstellar gas and dust is accelerated by a... 相似文献
286.
287.
V. A. Sorokin N. N. Zakharov M. S. Sharov L. S. Yanovskii 《Russian Aeronautics (Iz VUZ)》2010,53(3):295-302
The results of experimental investigations of gasodynamic characteristics of a combustion chamber model in the integrated power plant (IPP) with an asymmetric air intake are presented. The influence of an angle of air supply into the chamber model on hydraulic losses and the flow structure is shown at different air flowrates, relative values of the minimal flow section area of the feeding air intake pipes, under changes of the flowrate of gas simulating gas generation products and geometric model parameters. A technique for measuring the concentration of carbon dioxide simulating IPP gas generation products in the combustion chamber air flow and the results of experimental investigations of a mixture formation process in the combustion chamber model are described. 相似文献
288.
H.S. Ahluwalia R.C. Ygbuhay 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
For six decades, the global network of neutron monitors (NMs) has provided a continuous stream of very valuable data to the heliophysics community, leading to many insights into the myriad modes of charged particle transport in the tangled magnetic fields that permeate the 3D heliosphere. Earlier, Ahluwalia and Ygbuhay (2012) reported on the drifts in some high latitude NM counting rates in the American zone. We continue our enquiry by testing the stability of the counting rate baselines of some NMs operating in Europe, Africa, and Asia. The data from these detectors have been extremely valuable for the short-term time variation studies, but caution is advised in using the data for long-term studies from NMs with baselines that are drifting for cause(s) unknown. 相似文献
289.
The goal of the Kinelite Project is to develop a space qualified motion analysis system to be used in space by the scientific community, mainly to support neuroscience protocols. The measurement principle of the Kinelite is to determine, by triangulation mean, the 3D position of small, lightweight, reflective markers positioned at the different points of interest. The scene is illuminated by Infra Red flashes and the reflected light is acquired by up to 8 precalibrated and synchronized CCD cameras. The main characteristics of the system are: Camera field of view: 45 degrees; Number of cameras: 2 to 8; Acquisition frequency: 25, 50, 100, or 200 Hz; CCD format: 256 x 256; Number of markers: up to 64; 3D accuracy: 2mm; Main dimensions: 45 cm x 45 cm x 30 cm; Mass: 23 kg; Power consumption: less than 200 W. The Kinelite will first fly aboard the NASA Spacelab; it will be used, during the NEUROLAB mission (4/98), to support the "Frames of References and Internal Models" (Principal Investigator: Pr. A. Berthoz, Co Investigators: J. McIntyre, F. Lacquaniti). 相似文献
290.
Image exploitation technology approaches have generally focused on the detection and spatial analysis of stationary groups of objects on the ground using various sensors. While spatial arrangement is clearly necessary in analyzing military formations, it is usually not sufficient. Typically the arrangement must be examined within some context in order to interpret a pattern of deployment. For moving objects the spatial arrangement of the group relative to the direction of motion is key to recognizing the formation. By examining ground moving target indicator (MTI) radar data over time, motion can be inferred and used to establish a context for interpreting the spatial arrangement of the data. New techniques that exploit the multitemporal nature of MTI data are described. The first is a space-time clustering technique that locates compact groups of objects that persist in time. The technique Is an application of Marr and Hildreth's edge detection methodology to the dual problem of region segmentation, or more accurately, volumetric segmentation of space-time. The second technique is based on the use of the Hough transform for recognizing moving formations such as columns, wedges, and lines abreast by analyzing the shape of clustered MTI detections (specifically the orientation of linear arrangements within the group) with respect to their direction of motion. Preliminary results from simulated MTI data sets are presented 相似文献