全文获取类型
收费全文 | 3256篇 |
免费 | 687篇 |
国内免费 | 590篇 |
专业分类
航空 | 2169篇 |
航天技术 | 849篇 |
综合类 | 563篇 |
航天 | 952篇 |
出版年
2024年 | 20篇 |
2023年 | 39篇 |
2022年 | 99篇 |
2021年 | 140篇 |
2020年 | 135篇 |
2019年 | 98篇 |
2018年 | 99篇 |
2017年 | 97篇 |
2016年 | 103篇 |
2015年 | 127篇 |
2014年 | 162篇 |
2013年 | 169篇 |
2012年 | 204篇 |
2011年 | 222篇 |
2010年 | 239篇 |
2009年 | 198篇 |
2008年 | 251篇 |
2007年 | 203篇 |
2006年 | 154篇 |
2005年 | 149篇 |
2004年 | 103篇 |
2003年 | 110篇 |
2002年 | 100篇 |
2001年 | 117篇 |
2000年 | 105篇 |
1999年 | 143篇 |
1998年 | 147篇 |
1997年 | 113篇 |
1996年 | 107篇 |
1995年 | 78篇 |
1994年 | 87篇 |
1993年 | 91篇 |
1992年 | 71篇 |
1991年 | 65篇 |
1990年 | 52篇 |
1989年 | 34篇 |
1988年 | 20篇 |
1987年 | 33篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1965年 | 2篇 |
排序方式: 共有4533条查询结果,搜索用时 921 毫秒
951.
Liu JiaFu Fu Yu Zhang Liang Luo Na Wang Weiwei Zhao Dan Wu ZhiGang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(4):1333-1349
Reflectors are very critical space elements and can be used not only as solar collectors/reflectors, telecommunication radio antennas and telescopes but also for dual-usage such as solar sails and solar concentrators to probe and sublimate materials from asteroids when actively controlling the surface shape. In this paper, the surface shape of a slack reflector with negligible elastic deformations will be controlled to be a paraboloid by actively modulating the solar radiation pressure (SRP) force using reflectivity control devices (RCDs) across the reflector. Nonlinear static equilibrium equations for an arbitrary infinitesimal within the reflector along the radial, circumferential and transverse directions are established considering the external modulated SRP force and internal tensions respectively. The coupled radial stress differential governing equation and reflectivity algebraic equation are obtained for the paraboloid reflector by the help of the formulation of an inverse problem based on equilibrium equations previously established. Some analytical and numerical analysis for reflectors with ideal and non-perfect SRP force models are performed respectively. The conclusions concerning about how to control the reflector’s surface shape successfully using allowed reflectivity, resulting in reasonable stress range, moreover, how to get the feasible solutions influenced by the reflector’s size parameters, are all based on the presented analytical and numerical analysis. 相似文献
952.
Tong Xu Yanli Hu Jian Wu Zhensen Wu Chunbin Li Zhenwen Xu Yucheng Suo 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The seismo-ionospheric coupling is a hot topic of modern scientific research. One of the most reasonable mechanisms is the hypothesis of quasistatic electric field. With a preliminary analytical method, electric field in F2-region before Wenchuan earthquake was derived from the five lower latitude ground-based ionosondes: Lhasa (29.63°N, 91.17°E), Chongqing (29.50°N, 106.40°E), Kunming (25.00°N, 102.70°E), Guangzhou (23.15°N, 113.35°E) and Haikou (23.15°N, 110.35°E). The results show that there was an anomalous enhancement of electric field in F2-region close to the epicenter with maximal amplitude ∼2 mV/m (about 10 times of the background) at 15:00 LT on 9 May, which is in line with the amplitudes of anomalous electric field related to some previous earthquakes observed by satellites. 相似文献
953.
954.
Three-dimensional(3D)carbon networks have been explored as promising capacitive materials thanks to their unique structural features such as large ion-accessible surface area and interconnected porous networks,thus enhancing both ions and electrons transport.Here,sustainable bacterial cellulose(BC)is used both precursor and template for facile synthesis of free-standing N,S-codoped 3Dcarbon networks(a-NSC)by the pyrolysis and activation of polyrhodanine coated BC.The synthesized a-NSC shows highly conductive interconnected porous networks(24S·cm~(-1)),large surface area(1 420m~2·g~(-1))with hierarchical meso-microporosity,and high-level heteroatoms codoping(N:3.1%in atom,S:3.2%in atom).Benefitting from these,a-NSC as binder-free electrode exhibits an ultrahigh specific capacitance of 340F·g~(-1)(24μF·cm~(-2))at the current density of 0.5A·g~(-1)in 6MKOH electrolyte,high-rate capability(71%at 20A·g~(-1))and excellent cycle stability.Furthermore,the assembled symmetrical supercapacitor displays a much short time constant of 0.35sin 1MTEABF4/AN electrolyte,obtaining a maximum energy density of 32.1W·h·kg~(-1 )at power density of 637W·kg~(-1).The in situ multi-heteroatoms doping enables biocellulose-derived carbon networks to exploit its full potentials in energy storage applications,which can be extended to other dimensional carbon nanostructures. 相似文献
955.
956.
957.
Hong Wu Congli Huang Keping Zhang Yeqing Sun 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Cauliflower and sprout broccoli are widely planted vegetables particularly in Fujian Province, China. To study the mutation in these two types of vegetables induced from spaceflight, we flew the seeds on the 20th Chinese recoverable satellite which orbited the Earth for 18 days. After returning to the Earth, the cauliflower seeds were planted for two generations and the sprout broccoli seeds for one generation at the Xiamen Agriculture Research Institute. Of the 12 cauliflowers planted for the first generation, two showed significant phenotypical changes in both the size of the plant and the weight of the flower head. In addition, most of the space flown plants were found to be resistant to the black rot attack in the field. Cauliflowers planted for the second generation from the seeds in one of the two plants that displayed phenotypical changes in the first generation showed similar mutations. For the first generation of sprout broccoli, the rate of emergence from the flown seeds was lower than that of the control by 30%. No significant changes in the phenotype between the sprout broccolis planted from the flown seeds and the control were observed except one of the mutated sprout broccolis showed a change in the appearance in the lesser bud of the chief flower head. Results of the study demonstrated that DNA damages in some of the genes may have occurred in the seeds flown in space, and some of the changes in the genes may have inherited from the first to the second generation. The improved resistance to the black rot attack and increased size of the flower head are apparently beneficial. 相似文献
958.
整体叶盘片光饰抛光试验及发展应用探析 总被引:1,自引:0,他引:1
介绍了整体叶盘叶片利用机械光饰机进行的抛光试验,根据叶片试验取得的数据,分析了该种加工方法所具有的特点,以及应用时应采取的一些措施,为该种方法的应用提供了一定的借鉴经验. 相似文献
959.
A kind of wireless sensor was previously developed,which is powered and transmit signals wirelessly instead of using an electrical connection to the embedded reinforcement.Based on this technique,the relationship between diameters of corroded sensing steel wires and corrosion levels of steel bars is established by experiments.Quadratic function is utilized to fit the experiment results,and the correlation coefficients are all larger than 0.95.Estimated corrosion levels of commonly used steel bars are given for different diameters of corroded sensing steel wires fractured due to corrosion. 相似文献
960.