全文获取类型
收费全文 | 156篇 |
免费 | 45篇 |
国内免费 | 45篇 |
专业分类
航空 | 178篇 |
航天技术 | 23篇 |
综合类 | 19篇 |
航天 | 26篇 |
出版年
2023年 | 3篇 |
2022年 | 9篇 |
2021年 | 12篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 15篇 |
2015年 | 11篇 |
2014年 | 11篇 |
2013年 | 16篇 |
2012年 | 18篇 |
2011年 | 13篇 |
2010年 | 11篇 |
2009年 | 10篇 |
2008年 | 10篇 |
2007年 | 10篇 |
2006年 | 10篇 |
2005年 | 14篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有246条查询结果,搜索用时 15 毫秒
51.
52.
53.
压气机叶片气动阻尼的改善设计 总被引:2,自引:2,他引:0
针对气动阻尼在强迫响应分析中的应用现状,提出了一种在叶型基本确定的条件下进一步设计气动阻尼的方法.该方法只对叶片基元级的积叠轴做微小的调整,这种调整对叶栅流场气动特性和固有频率的影响很小,可以忽略不计.研究了积叠轴调整对叶片气动阻尼的影响,得出在不需要大量流场计算的条件下,即可判断如何调整叶片积叠轴以达到增加气动阻尼目的的结论.在分析中用振型相似度衡量叶片模态振型与气动阻尼比的关系,相似度越小气动阻尼比越大. 相似文献
54.
从增韧改性CE角度出发,介绍了近几年增韧改性氰酸酯树脂的方法,包括纳米粒子(SiO2、SiC)改性、笼型倍半硅氧烷(POSS)改性、热固性树脂(EP、BMI)改性、热塑性树脂改性及其他改性方法,并且着重阐述了增韧机理.. 相似文献
55.
超磁致伸缩作动器(GMA)输入输出之间存在着磁滞非线性关系,当研究其中高频输出特性时,为了降低材料自身迟滞非线性特性的影响,往往选用零点与饱和状态之间线性度较好的不饱和小回线,因此很有必要开展动态不饱和小回线数学模型的研究。首先在综合研究磁致伸缩材料(GMM)和GMA结构动力学特性的基础上结合安培环路定理提出以励磁电流为输入、应变为输出的动态Jiles-Atherton(J-A)模型,然后在引入磁滞回线特性变量的基础上得出J-A模型关键模型参数对其特性的影响规律,根据不饱和小回线仿真与实验波形的偏离特性提出模型参数的修正方法得到不饱和小回线动态J-A模型。最后,在不同频率和不同饱和幅值下通过实验验证该数学模型的正确性。 相似文献
56.
57.
Mehdi Eshagh 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The satellite gravity gradiometric data can be used directly to recover the gravity anomaly at sea level using inversion of integral formulas. This approach suffers by the spatial truncation errors of the integrals, but these errors can be reduced by modifying the formulas. It allows us to consider smaller coverage of the satellite data over the region of recovery. In this study, we consider the second-order radial derivative (SORD) of disturbing potential (Trr) and determine the gravity anomaly with a resolution of 1° × 1° at sea level by inverting the statistically modified version of SORD of extended Stokes’ formula. Also we investigate the effect of the spatial truncation error on the quality of inversion considering noise of Trr. The numerical investigations show satisfactory results when the area of Trr coverage is the same with that of the gravity anomaly and the integral formula is modified by the biased least-squares modification. The error of recovery will be about 6 mGal after removing the regularization bias in the presence of 1 mE noise in Trr measured on the orbit. 相似文献
58.
Investigation on Thermal and Dimensional Stability of Epoxy Resin In-Situ Modified by Cyanate Ester Resin and Polydimethylsiloxane
下载免费PDF全文
![点击此处可从《上海航天》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The thermal and dimensional stability of epoxy resin (EP) in-situ modified by cyanate ester (CE) and polydimethylsiloxane (PDMS) are investigated by means of experiments and numerical simulation. Thermal gravimetric analysis (TGA) and differential scanning calorimeter (DSC) are used to analyze the heat resistance of the modified EP. The dimensional stability is characterized by the volume shrinkage of the series PDMS/CE/EP obtained by the density method. The chemical structure of the PDMS/CE/EP is analyzed by Fourier transform infrared spectroscopy (FTIR). The results of TGA and DSC indicate that the thermal stability of PDMS/CE/EP decreases firstly and then increases with the increase in the amount of CE. The addition of PDMS shows a slight effect on the thermal stability. The 40% CE makes the blending system exhibit the lowest initial decomposition temperature, which reduces by 15.5% and 40.8% compared with pure EP and CE, respectively. The FTIR results suggested that the influence of CE on the thermal stability of the modified EP is mainly ascribed to the generation of oxazolidinone ring with low thermal stability and the increase in the triazine ring with high thermal stability. The volume shrinkage measurement results show that the introduction of CE and PDMS are both beneficial to the improvement of the dimensional stability of the blending systems. The in-situ addition of 80% CE shows the lowest volume shrinkage of 6.11%. The thermal stress distribution of PDMS/CE/EP generated during the solidification process is simulated by the finite element analysis. The results suggested that the introduction of 80% CE into EP results in the lowest thermal stress in the blending system, which indicates that the system has the lowest volume shrinkage, which agrees well with the experimental results. 相似文献
59.
SVM最优分类面相对位置的修正 总被引:1,自引:1,他引:0
通过放宽标准支持向量机(SVM,Support Vector Machines)中类别边界至分类面等间隔的约束,保持两类函数间隔之和不变的条件,在支持向量机思想框架下得出分类面依样本分布进行调整的新型支持向量机,其对偶形式与标准支持向量机完全相同,从而在理论上进一步完善了支持向量机.在此基础上,提出使类别的函数间隔正比于样本标准差的具体算法--方差修正法,达到最优分类面的相对位置依样本方差而调整之目的.从统计意义上来说,方差修正法在分类精度上有所提高,但计算量增加不多. 相似文献
60.
Interconnected Ni(OH)2 nanoflakes and polyether amine(PEA) were deposited on carbon fiber tows via a facial and effective process of chemical bath deposition and dip coating. Based on this, a win–win benefit of simultaneously improvements in interfacial shear strength(IFSS) of carbon fiber/epoxy composites and the electrochemical activity has been achieved. Compared with CF and CF-Ni(OH)2 composites, the IFSS of CF-Ni(OH)2-PEA/epoxy composite respectively increas... 相似文献