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排序方式: 共有2949条查询结果,搜索用时 31 毫秒
41.
Ilaria Serafini Livia Lombardi Claudia Fasolato Manuel Sergi Francesca Di Ottavio Fabio Sciubba 《Natural product research》2019,33(7):1040-1051
AbstractIn this paper, the application of a multi-analytical approach for the characterisation of synthetic and natural dyes in a historical textile is presented. The work is focused on a historical dress of a Sicilian noblewoman, dating from about 1865–1870. Firstly, SERS on fibre was performed, in order to individuate the classes of dyes employed. The SERS spectra suggested the presence of two main dyes: mauveine and orcein. In order to confirm these preliminary results, two different extraction protocols were applied. The extracts obtained were analysed by ESI-MS, MALDI-ToF and UHPCL-MS analyses, confirming the SERS results. In particular, the application of the ammonia mild extraction technique allowed to selectively extract the phenoxazonic dyes, separating them already in the extraction step from the synthetic ones. Thanks to this multi-analytical approach, this dress could be considered as one of the first examples of employment of synthetic dyes in association with natural ones. 相似文献
42.
A New Diterpene Acid from the Flowers of Heteropappus altaicus 总被引:2,自引:0,他引:2
QingHuaLIU JunShanYANG YangLU QiTaiZHENG LiMAO 《中国化学快报》2005,16(7):921-924
A new compound, named heteraltaic acid was isolated from the flowers of Heteropappus altaicus (willd) Novopokr. The compound was elucidated as (5R, 6S, 8aS) -5-[2-(3-furyl) ethyl-5, 6, 8a-trimethyl-4a, 5, 6, 7, 8, 8a -hexahydro-l-naphthalenecarboxylic acid] by the combination of 1D and 2D NMR techniques (HSQC, HMBC) and X-ray analysis. 相似文献
43.
A white substance was got by directly heating TiSi powder on Ti foil, under Ar+O
2 atmosphere. ED, EDX, SEM and HRTEM studies reveal that the white substance consists of amorphous SiO
2 nanowires of smooth surface and uniform diameter (40-90 nm). X-ray-induced luminescent emission experiment shows that two
broad peaks are at 430 and 570 nm. A one-dimensional growth mechanism, on the basis of the one-dimensional thermal flow during
nanowire formation, is discussed. 相似文献
44.
从两二酸二乙酯、氯乙酸乙酯和氯苄出发,经LiAlH4还原,合成新的二元醇,进而合成新的螺环化合物:3,9-二羟乙基-3',9'-二苯甲基-1,5,7,11-四氧杂螺[5,5]十一烷.该化合物的结构由它的氢和碳-13核磁共振谱、红外光谱和元素分析得到证明.该单体在三氟化硼乙醚络合物的作用下进行开环聚合反应.由于环上四个取代基的稳定作用,聚合物的收率比较低(产率10%左右).通过对聚合物的结构分析,提出了这一单体的阳离子开环聚合反应机理.对随聚合温度升高,聚合物中酯基/苯基的克分子比降低,以及本体聚合时得到交联聚合物等一系列现象作了探讨. 相似文献
45.
运用量子化学从头算方法, 在MP2/6-311++G(d,p), MP2/6-311++G(2df,2p), MP2/6-311++G(3df,3pd)和QCISD/6-311++G(d,p)水平上, 研究了CH3F, CH3Cl和CH3Br作为质子给体与Cl-, Br-作为质子接受体形成的氢键CH3…Y. 计算结果表明: 6种复合物中C—H键收缩, 伸缩振动频率增大, 形成蓝移氢键. 分子中原子(Atoms in Molecules, AIM)分析表明, 这些复合物的电子密度拓扑性质与普通氢键有着本质的不同, 在Y…H之间不存在键临界点, 而在Y与C之间存在键临界点, 因此这些相互作用严格地不能称为氢键. 自然键轨道(Natural bond orbital, NBO)分析表明, 在这些复合物中弯曲的CH…Y的特殊结构使得分子间超共轭n(Y)®σ*(C—H)减小到可以忽略; 质子接受体的电子密度没有转移到σ*(C—H)上, 而是转移到了σ*(C—X) (X=F, Cl, Br)上; 存在一定程度的重杂化; 分子内超共轭相互作用减小使得σ*(C—H)的电子密度减少. 这些因素共同导致C—H伸缩振动频率的蓝移. 相似文献
46.
47.
Synthesis of new colloidal formations during the strengthening of different activated hydrated metallurgical slags 总被引:3,自引:0,他引:3
Vsvolod A. Mymrin Haroldo A. Ponte Carlos I. Yamamoto 《Colloids and surfaces. A, Physicochemical and engineering aspects》2003,220(1-3):211-221
This paper reports on a comparison of experimental researches on the hydration hardening of different types of dumped ferrous slag (DFS) (blast furnace, open hearth, electric steel and converter), non-activated and activated with small (2%) additions of Portland cement or lime. Activation was found to accelerate the strengthening processes in the early stages of hydration resulting from the growth of colloidal sol–gel new formations in a more alkaline environment. Over time, these formations became denser and transformed into stone-like amorphous materials with a uniaxial strength of up to 47.6 MPa at 1 year of age. All these types of slag can, therefore, be used in different applications, for example, like traditional binders, such as Portland cement, to different ceramic goods, new construction materials, etc. But till now the results of this research were used only for the preparing of binder materials for natural soils strengthening as road bases in Russia. Highways whose roadbeds were built with these DFS as binder materials have shown excellent performance indices in different parts of Russia, including Siberia and northern regions. 相似文献
48.
49.
《Expositiones Mathematicae》2022,40(1):127-139
We investigate various groupoids associated to an arbitrary inverse semigroup with zero. We show that the groupoid of filters with respect to the natural partial order is isomorphic to the groupoid of germs arising from the standard action of the inverse semigroup on the space of idempotent filters. We also investigate the restriction of this isomorphism to the groupoid of tight filters and to the groupoid of ultrafilters. 相似文献
50.
Sampling Consensus of 2nd-Order Multi-Agent Systems Based on Time-Varying Topology北大核心CSCD 下载免费PDF全文
基于速度一致位移差保持不变的一致性概念,研究了二阶多智能体系统在时变拓扑下的采样一致性问题。首先,引入虚拟领导者,将具有时变拓扑结构的多智能体系统的采样一致性问题转换为误差系统的采样控制稳定性问题。其次,通过预估采样误差,研究采样误差对系统达到一致性的影响。最后,应用Lyapunov稳定性理论,分析所构造的误差系统的稳定性,并给出该误差系统最终稳定的充分条件。数值仿真结果验证了理论分析的有效性和正确性。 相似文献