全文获取类型
收费全文 | 4955篇 |
免费 | 2篇 |
国内免费 | 11篇 |
专业分类
航空 | 2605篇 |
航天技术 | 1579篇 |
综合类 | 181篇 |
航天 | 603篇 |
出版年
2021年 | 31篇 |
2019年 | 29篇 |
2018年 | 75篇 |
2017年 | 42篇 |
2016年 | 41篇 |
2014年 | 73篇 |
2013年 | 108篇 |
2012年 | 109篇 |
2011年 | 162篇 |
2010年 | 104篇 |
2009年 | 189篇 |
2008年 | 195篇 |
2007年 | 120篇 |
2006年 | 92篇 |
2005年 | 91篇 |
2004年 | 115篇 |
2003年 | 140篇 |
2002年 | 181篇 |
2001年 | 203篇 |
2000年 | 97篇 |
1999年 | 124篇 |
1998年 | 154篇 |
1997年 | 102篇 |
1996年 | 144篇 |
1995年 | 169篇 |
1994年 | 147篇 |
1993年 | 95篇 |
1992年 | 123篇 |
1991年 | 60篇 |
1990年 | 63篇 |
1989年 | 129篇 |
1988年 | 58篇 |
1987年 | 60篇 |
1986年 | 51篇 |
1985年 | 154篇 |
1984年 | 128篇 |
1983年 | 113篇 |
1982年 | 122篇 |
1981年 | 160篇 |
1980年 | 57篇 |
1979年 | 46篇 |
1978年 | 57篇 |
1977年 | 37篇 |
1976年 | 40篇 |
1975年 | 49篇 |
1974年 | 39篇 |
1972年 | 49篇 |
1971年 | 47篇 |
1970年 | 30篇 |
1969年 | 34篇 |
排序方式: 共有4968条查询结果,搜索用时 15 毫秒
291.
Marchi S. Asphaug E. Bell J. F. Bottke W. F. Jaumann R. Park R. S. Polanskey C. A. Prettyman T. H. Williams D. A. Binzel R. Oran R. Weiss B. Russell C. T. 《Space Science Reviews》2022,218(4):1-28
Space Science Reviews - Analysis of Homestake, Gallex and GNO measurements reveals evidence of variability of presumed solar-neutrino-flux measurements. Analysis of Super-Kamiokande neutrino... 相似文献
292.
A.R. Engel K. Beurle A. Bewick P.K.S. Harper J.J. Quenby N.J.C. Spooner A.G. Fenton K.B. Fenton A.B. Giles J.G. Greenhill D.M. Warren I.M. Martin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
Hard X-ray balloon altitude measurements with a 1600 cm2 phoswich array are described. Data from observations on Sco X-1, GX1+4, GX5−1, Nova Oph. 1977, SMC X-1, SS433, IC 4329A and MR 2251-178 are presented. The role of Comptonisation in X-ray production for Sco X-1 and GX1+4 is discussed. 相似文献
293.
G. Hasinger W. Pietsch C. Reppin J. Trümper W. Voges E. Kendziorra R. Staubert 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
The Crab was observed in a balloon flight from Palestine/Texas on 9/28/81 at hard X-ray energies (20–200 keV). The light curve is significantly sharper than reported previously for this energy range. The pulse-averaged as well as the interpulse spectra show breaks in our energy-range. The variation of spectral index across the pulse has an amplitude similar to that found at lower energies by OSO-8 and larger than reported by HEAO-1 A4 at hard X-rays. For a sharp emission line at 77 keV a 99% upper limit of 1.0*10−3 photons/ cm2 sec can be placed, a factor of 4 lower than line fluxes reported previously. Pulse-shape fits to the optical, X-ray, hard X-ray and gamma ray light-curves reveal a consistent picture of the origin of the interpulse and off-pulse emission, the breaks in the spectra and the variation of spectral index, providing arguments against a thermal component and also a polar cap emission model for NP0532. 相似文献
294.
M. Combes V. I. Moroz J. F. Crifo J. P. Bibring N. Coron J. Crovisier T. Encrenaz N. F. Sanko A. Grigoriev D. Bockele-Morvan R. Gispert C. Emerich J. M. Lamarre F. Rocard V. A. Krasnopolsky T. Owen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(12):127-131
Results of the 2.5–5 micron spectroscopic channel of the IKS instrument on Vega are reported and the data reduction process is described. H2O and CO2 molecules have been detected with production rates of 1030 s−1 and 1.5 1028 s−1 respectively. Emission features between 3.3 and 3.7 microns are tentatively attributed to CH - bearing compounds - CO is marginally detected with a mixing ratio CO/H2O 0.2. OH emission and H2O - ice absorption might also be present in the spectra. 相似文献
295.
G. Reitz H. Bücker R. Beaujean W. Enge R. Facius W. Heinrich T. Ohrndorf E. Schopper 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(12):107-113
The experiment was flown in different locations inside BIORACK on the D1 mission. It contained different plastic detectors (cellulose nitrate, Lexan, and CR 39) and emulsions to measure the high LET components of the radiation environment. For low LET measurements thermoluminescence dosimeters (L iF) were used. The paper gives data about total dose, charge, energy, and LET spectra so far obtained. These data are compared with data of previous spaceflights. 相似文献
296.
H. Bücker R. Facius G. Horneck G. Reitz E. H. Graul H. Berger H. Hffken W. Rüther W. Heinrich R. Beaujean W. Enge 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1986,6(12):115-124
The influence of cosmic radiation and/or microgravity on insect development was studied during the 7 day German Spacelab Mission D1. Eggs of Carausius morosus of five stages differing in sensitivity to radiation and in capacity to regeneration were allowed to continue their development in the BIORACK 22°C incubator, either at microgravity conditions or on the 1 g reference centrifuge. Using the Biostack concept - eggs in monolayers were sandwiched between visual track detectors - and the 1 g reference centrifuge, we were able to separate radiation effects from microgravity effects and also from combined effects of these two factors in space. After retrieval, hatching rates, growth kinetics and anomaly frequencies were determined in the different test samples. The early stages of development turned out to be highly sensitive to single hits of cosmic ray particles as well as to the temporary exposure to microgravity during their development. In some cases, the combined action of radiation and microgravity even amplified the effects exerted by the single parameters of space. Hits by single HZE particles caused early effects, such as body anomalies, as well as late effects, such as retarded growth after hatching. Microgravity exposure lead to a reduced hatching rate. A synergistic action of HZE particle hits and microgravity was established in the unexpectedly high frequency of anomal larvae. However, it cannot be excluded, that cosmic background radiation or low LET HZE particles are also causally involved in damage observed in the microgravity samples. 相似文献
297.
描述并确定具有明显纹理粗糙表面均方根斜率的光散射技术(均方根斜率是联合表面轮廓高度和波长特性的混合参数)。称为散射光锥法(The scattered light-conemethod)的该技术是基于激光角散射检测阵列(DALLAS——Defector Array for Laser LishtAngular Scattering),它用于测量粗糙表面散射光角分布的仪器。均方根斜率是从DALLAS光散射图象的角宽得到的。一般可以发现角宽(即估计的均方根斜率)对光的入射角和散射角变化相当大时是不敏感的。这些结果与表面材料无关,并且对正弦和随机粗糙表面都是有效的。介绍了散射光锥法的测量原理、实验、数据分析和几点结论。 相似文献
298.
P. Laurent A. Claret F. Lebrun J. Paul M. Dennis D. Barret L. Bouchet P. Mandrou R. Sunyaev E. Churazov M. Gilfanov N. Khavenson A. Dyachkov B. Novikov R. Kremnev V. Kovtunenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1993,13(12):139-148
After more than two years of operation, the imaging γ-ray SIGMA telescope has accumulated several days of observation toward well known X-ray binaries. Four bright sources falling in this category have been detected so far: The pulsar GX 1+4 near the center of our galaxy, the stellar wind accreting system 4U 1700-377, and the black hole candidates Cygnus X-1 and GX 339-4. Moreover, SIGMA have observed three transients sources, which turned out to be also hard X-ray sources : The burster KS 1731-260, Tra X-1, and the Musca Nova. The properties of these systems in the SIGMA domain will be reviewed and a spectral distinction between black holes and neutron stars will be sketched. 相似文献
299.
基于磨粒分析方法的发动机磨损故障智能诊断技术 总被引:5,自引:1,他引:5
磨粒是研究磨损状态时最直接、最重要的信息元,通过对滑油中的磨粒进行监测与分析来判断机械设备的磨损情况,可以预防并监测机械设备的磨损故障。本文运用显微形态学方法建立了一套磨粒显微特征描述体系,以提取磨粒信息并进行磨损故障的模式识别;并结合摩擦学理论和人工智能方法,实现对发动机磨损故障的智能诊断和预测。 相似文献
300.
含连续/离散变量结构优化中的神经网络与变尺度模拟退火方法 总被引:2,自引:0,他引:2
传统的优化方法难于有效地处理含有连续/离散混合变量优化问题,本文介绍了一种改进的变尺度模拟退火方法并与人工神经网络能量函数模型相结合,用于求解含连续/离散设计变量的工程结构优化问题,较好地解决了模拟退火技术用于工程结构优化时选取具有全局性的初始点困难及迭代次数较多的弱点。算例表明,该方法可以使模拟退火算法从局部最优的陷阱中跳出,最后求出整体最优解。 相似文献