全文获取类型
收费全文 | 1883篇 |
免费 | 392篇 |
国内免费 | 351篇 |
专业分类
航空 | 1273篇 |
航天技术 | 443篇 |
综合类 | 213篇 |
航天 | 697篇 |
出版年
2024年 | 12篇 |
2023年 | 30篇 |
2022年 | 87篇 |
2021年 | 73篇 |
2020年 | 75篇 |
2019年 | 82篇 |
2018年 | 78篇 |
2017年 | 69篇 |
2016年 | 75篇 |
2015年 | 116篇 |
2014年 | 141篇 |
2013年 | 120篇 |
2012年 | 161篇 |
2011年 | 157篇 |
2010年 | 160篇 |
2009年 | 139篇 |
2008年 | 120篇 |
2007年 | 111篇 |
2006年 | 100篇 |
2005年 | 76篇 |
2004年 | 68篇 |
2003年 | 74篇 |
2002年 | 64篇 |
2001年 | 55篇 |
2000年 | 54篇 |
1999年 | 57篇 |
1998年 | 54篇 |
1997年 | 42篇 |
1996年 | 20篇 |
1995年 | 22篇 |
1994年 | 24篇 |
1993年 | 22篇 |
1992年 | 16篇 |
1991年 | 21篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有2626条查询结果,搜索用时 15 毫秒
141.
Qile Zhao Jing Guo Zhigang Hu Chuang Shi Jingnan Liu Hua Cai Xianglin Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The GRACE (Gravity Recovery And Climate Experiment) monthly gravity models have been independently produced and published by several research institutions, such as Center for Space Research (CSR), GeoForschungsZentrum (GFZ), Jet Propulsion Laboratory (JPL), Centre National d’Etudes Spatiales (CNES) and Delft Institute of Earth Observation and Space Systems (DEOS). According to their processing standards, above institutions use the traditional variational approach except that the DEOS exploits the acceleration approach. The background force models employed are rather similar. The produced gravity field models generally agree with one another in the spatial pattern. However, there are some discrepancies in the gravity signal amplitude between solutions produced by different institutions. In particular, 10%–30% signal amplitude differences in some river basins can be observed. In this paper, we implemented a variant of the traditional variational approach and computed two sets of monthly gravity field solutions using the data from January 2005 to December 2006. The input data are K-band range-rates (KBRR) and kinematic orbits of GRACE satellites. The main difference in the production of our two types of models is how to deal with nuisance parameters. This type of parameters is necessary to absorb low-frequency errors in the data, which are mainly the aliasing and instrument errors. One way is to remove the nuisance parameters before estimating the geopotential coefficients, called NPARB approach in the paper. The other way is to estimate the nuisance parameters and geopotential coefficients simultaneously, called NPESS approach. These two types of solutions mainly differ in geopotential coefficients from degree 2 to 5. This can be explained by the fact that the nuisance parameters and the gravity field coefficients are highly correlated, particularly at low degrees. We compare these solutions with the official and published ones by means of spectral analysis. It is found that our solutions are, in general, consistent with others in the spatial pattern. The water storage variations of the Amazon, Chari and Ganges river basins have also been computed. The variations computed with the NPARB approach are closer to those produced by JPL and DEOS solutions, while the variations produced with the NPESS approach are in good agreement with those produced by the CSR and GFZ solutions. A simulation study is implemented with considering realistic noise and low-frequency error. The two approaches are used to recover the true model. The NPESS solution appears closer to the true one. Therefore we are inclined to estimate the nuisance parameters simultaneously with the geopential coefficients. 相似文献
142.
针对卫星控制系统测试数据类型多和数据量大的特点,人工判读方式存在判读时间长和判读精度不够高等不足,分析了卫星控制系统测试数据的变化规律,建立了测试数据的判读规则,在此基础上完成自动判读方法设计和自动判读系统设计,该系统能够按照设置的判读规则进行自动判读,对判读结果进行实时显示和存储,提高了测试效率和判读的准确性. 相似文献
143.
The design of landing gear is complicated due to the numerous considered elements.And the initial elements related to each other can also be influenced by different factors.Landing gear design often involves a very large variety of configurations,especially in the conceptual design phase.However,traditional method costs more time to complete the whole procedure for suitable configurations of landing gears.Therefore,the parametric modeling of component library for landing gear based on computer aided three-dimensional interface application/component application architecutre(CATIA/CAA)is proposed.According to the analysis of the characteristics of landing gear components,a method is presented to extract the primary parameters of landing gear components so that a systematic classification can be established.Further,the related theories and methods,including receiving geometrical parameters of the components and updating the parametrical model,displaying the component parts,are also illustrated.Finally,the development technology for component library is explained.The proposed modeling method can improve the efficiency of the whole design cycle for landing gear. 相似文献
144.
145.
146.
147.
外端壁收缩与单向倾斜组合涡轮导叶的三维气动力研究 总被引:1,自引:0,他引:1
低展弦比涡轮导叶的外端壁收缩与单向正倾斜组合设计是既可减小两端二次流损失又可以满足冲击冷却叶片叶身需平直要求的技术措施。本文简要阐述了组合设计可减小二次流损失的力学机制、流场特征及三维流场设计分析的评价准则。通过三维流场计算 ,详细分析了诸如单向倾斜角度、子午面外端壁轮廓收缩起点、内外曲率半径等主要特征参数对流场品质的影响。给出了组合设计的方法与步骤及评价流场的定性准则。该组合设计方法对低展弦比高温涡轮导向叶片的成功设计具有指导意义。 相似文献
148.
149.
150.