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排序方式: 共有307条查询结果,搜索用时 390 毫秒
291.
针对传统蜂窝共面和异面承载能力差距太大的问题,提出了胞壁弓字形弯折蜂窝、层间组合蜂窝和折叠蜂窝等3种新型蜂窝,建立了新型蜂窝的有限元模型并分析了其变形模式和承载能力。结果表明,在相对密度一致的前提下,与传统正六边形蜂窝相比,这3种新构型蜂窝均缩小了共面和异面方向承载能力的差距。其中胞壁弓字形弯折蜂窝的共面/异面承载比提高了21.3倍;层间组合蜂窝两个共面方向承载能力悬殊,承载能力更强的共面方向与异面的承载比值提高了42倍;折叠蜂窝则提高了21.3倍。研究结果可以为抗多向冲击载荷作用下的蜂窝结构设计提供新思路和参考。 相似文献
292.
Xu LP Gong JR Wan LJ Jiu TG Li YL Zhu DB Deng K 《The journal of physical chemistry. B》2006,110(34):17043-17049
To achieve a controllable and predictable molecular architecture on a two-dimensional (2D) surface, a series of oligothiophenes with carboxylic groups and alkane chains were synthesized. The alkane chains and carboxylic groups, which can form hydrogen bonding, were intentionally designed in different positions of the oligothiophenes. The resulted molecular architectures by using the so-prepared oligothiophenes on a highly oriented pyrolytic graphite (HOPG) surface were investigated by scanning tunneling microscopy (STM) and density functional theory (DFT). It is found that the hydrogen bonding plays an essential role in the formation of the ordered assemblies. A controlled 2D molecular assembly could be fabricated by using hydrogen bondings. 相似文献
293.
A Yb(OTf)_3-catalyzed approach for the synthesis of pyrroles under solvent-free conditions was achieved,which could afford the desired products with yields ranged from moderate to excellent. 相似文献
294.
Abiodun Humphrey Adebayo 《中国化学快报》2009,20(8):945-948
Two novel 4,5-secoeudesmane sesquiterpenoids,oxyphyllones A(1) and B(2) were isolated from the fruits of Alpinia oxyphylla.Their structures were established by spectroscopic methods including 1D and 2D NMR spectra.These two compounds are the first example of naturally occurring sesquiterpenoids with a 4,5-secoeudesmane skeleton in the family of Zingiberaceae and oxyphyllone A(1) is the first 4,5-secoeudesmane type of 13-norsesquiterpenoid.Compounds 1 and 2 exhibited no cytotoxicities against three cancer... 相似文献
295.
差动共焦式纳米级光聚焦探测系统的研究 总被引:5,自引:0,他引:5
为解决纳米级大范围的非接触测量问题 ,提出了基于差动式共焦显微技术的光聚焦探测系统。介绍了系统的工作原理和结构装置 ,对系统中的关键技术进行了优化设计 ,通过对共焦光路的差动设计 ,可以有效地抑制光源的噪声和漂移对测量结果的影响。初步实验结果表明 ,该系统的轴向分辨率可达 2 nm 相似文献
296.
297.
外加极化电位对316L不锈钢微动磨蚀行为的影响 总被引:2,自引:0,他引:2
采用球-平面接触微动磨损试验机考察了轧制固溶316L不锈钢在不同极化状态下的微动磨蚀行为。结果表明:在阳极极化状态下,随着极化电位的升高,腐蚀疲劳微断裂作用增强,促进了微动损伤过程的发展;在阴极保护状态下,摩擦系数随微动过程的变化规律及微动损伤形貌与阳极极化态下的存在显著差异,在阴极极化态下,微动磨擦副之间的粘着导致较高的微动摩擦应力状态,但与阳极极化态相比并未产生严重损伤。 相似文献
298.
In this paper the Cauchy problem for the following nonhomogeneous Burgers’ equation is considered : (1)u
t
+uu
x
=μu
xx
−kx,x ∈R,t > 0, where μ and k are positive constants. Since the nonhomogeneous term kx does not belong to any Lp(R) space, this type of equation is beyond usual Sobolev framework in some sense. By Hopf-Cole transformation, (1) takes the
form (2)ϕ
t
−ϕ
xx
= −x
2
ϕ. With the help of the Hermite polynomials and their properties, (1) and (2) are solved exactly. Moreover, the large time
behavior of the solutions is also considered, similar to the discussion in Hopf’s paper. Especially, we observe that the nonhomogeneous
Burgers’ equation (1) is nonlinearly unstable. 相似文献
299.
Two 4,13‐diaza‐18‐crown‐6 ethers with either two pyrenyl or two carbazolyl groups were synthesized. The two crown ethers can form complexes with methyl viologen in methanol solution. Photoirradiation of the complexes resulted in the electron transfer from the excited states of the chromophores to methyl viologen as demonstrated by the quenching of the chromophore fluorescence and the detection of the absorption spectrum of the generated viologen radical cation. The back electron transfer in these systems was inhibited by the electrostatic repulsion between the positively charged viologen radical cation and the generated chromophore radical cation. Long‐lived charge separation states (up to tens of min) were observed. 相似文献
300.
均三嗪荒氨酸衍生物添加剂在菜籽油中的摩擦学性能研究 总被引:5,自引:0,他引:5
合成了一系列具有不同烷基结构的均三嗪荒氨酸衍生物,采用热重分析对其热稳定性进行了评价,利用四球摩擦磨损试验考察了合成衍生物添加剂在菜籽油中的摩擦学性能。结果表明,这一类添加剂可以大幅度提高菜籽油的极压性能,但是其抗磨减摩作用并不明显。 相似文献