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991.
碳纤维中的单层石墨物相及其对力学性能的影响 总被引:2,自引:0,他引:2
依据碳纤维中各种物相的X射线衍射特性, 确认PAN基碳纤维中除了乱层石墨微晶外, 还存在大量的单层六元环C原子层面物相, 建立起两种非完整结晶物相的定量分析方法. 实验结果表明, 随着退火温度由1350 ℃上升到2400 ℃, Tx-3高强型碳纤维中的单层石墨含量由59.6%下降到34.8%, 乱层石墨含量由40.4%上升为65.2%. 与此同时, 碳纤维的拉伸强度则由3.65 GPa下降到2.05 GPa, 而延伸率也由1.04%下降到0.58%. 并对PAN基碳纤维中单层石墨对其力学性能的影响也进行了初步的探讨. 相似文献
992.
云南重楼中的新甾体皂苷 总被引:3,自引:0,他引:3
从云南重楼Paris polyphylla Sm. var. yunnanensis(France. )Hand.-Mazz.的干燥根茎中分离鉴定了4个甾体皂苷(1~4), 其中化合物1是新化合物, 采用波谱技术鉴定其结构为24-O-β-D-吡喃半乳糖基-(23S,24S)-螺甾-5, 25(27)-二烯-1β,3β,23,24-四醇-1-O-β-D-吡喃木糖基(1→6)-β-D-吡喃葡萄糖基(1→3)[α-L-吡喃鼠李糖基(1→2)]-β-D-吡喃葡萄糖苷. 相似文献
993.
LIU Xiu-dong YU Wei-ting LIN Jun-zhang MA Xiao-jun YUAN Quan 《高等学校化学研究》2007,23(5):579-584
Alginate has been widely used in cell microencapsulation and drug delivery systems in the form of gel beads or microcapsules.Although an alternative novel emulsification-internal gelation technology has been established and both the properties and the potential applications of the beads in drug delivery systems have been studied,the mechanism has not been well understood compared with the traditional droplet method(external gelation technology).On the basis of our previous knowledge that the novel technology is composed of complicatedly consecutive processes with multistep diffusion and reaction,and the diffusion of acetic acid across oil/water interface being the prerequisite that determines the occurrence and rate for the reactions and the structures and properties of final produced gel beads,a special emphasis was placed on the diffusion process.With the aid of diffusion modeling and simple experimental design,the diffusion rate constant and diffusion coefficient of acetic acid across oil/water interface were determined to be in the orders of magnitude of 10-6 and 10-16,respectively.This knowledge will be of particular importance in understanding and interpreting the formation,structure of the gel beads and the relationship between the structure and properties and guiding the preparation and quality control of the gel beads. 相似文献
994.
邻氨基二苯醚类重氮盐的水解及分子内缩合反应 总被引:1,自引:0,他引:1
用邻氨基二苯醚类化合物进行重氮化水解反应制备邻羟基二苯醚类化合物, 对影响氯代邻氨基二苯醚重氮盐水解反应和分子内关环反应的因素进行了系统研究, 讨论了取代基、金属及其离子催化等对两类反应的影响规律, 揭示了在金属离子催化下, 邻氨基二苯醚类化合物重氮盐发生分子内关环反应的规律, 并推测了反应机理. 相似文献
995.
Artificial long-lived radionuclides such as 90Sr and 239,240Pu have been long released into the environment by human nuclear activities, which have a profound impact on the ecological environment. It is of great significance to monitor the concentration of these radionuclides for environmental safety. This paper summarizes and critically discusses the separation and measurement methods for ultra-trace determination of 90Sr, 239Pu, and 240Pu in the environment. After selecting the measurement method, it is necessary to consider the decontamination of the interference from matrix elements and the key elements, and this involves the choice of the separation method. Measurement methods include both radiometric methods and non-radiometric methods. Radiometric methods, including alpha spectroscopy, liquid scintillation spectrometry, etc., are commonly used methods for measuring 239+240Pu and 90Sr. Mass spectrometry, as the representative of non-radiometric measurement methods, has been regarded as the most promising analytical method due to its high absolute sensitivity, low detection limit, and relatively short sample-analysis time. Through the comparison of various measurement methods, the future development trend of radionuclide measurement is prospected in this review. The fully automatic and rapid analysis method is a highlight. The new mass spectrometer with ultra-high sensitivity shows strong analytical capabilities for extremely low concentrations of 90Sr, 239Pu, and 240Pu, and it is expected to develop determination methods with higher sensitivity and lower detection limit. 相似文献
996.
Mengzhou Bi Zhen Guan Tengjiao Fan Na Zhang Jianhua Wang Guohui Sun Lijiao Zhao Rugang Zhong 《Molecules (Basel, Switzerland)》2022,27(6)
Dual-specific tyrosine phosphorylation regulated kinase 1 (DYRK1A) has been regarded as a potential therapeutic target of neurodegenerative diseases, and considerable progress has been made in the discovery of DYRK1A inhibitors. Identification of pharmacophoric fragments provides valuable information for structure- and fragment-based design of potent and selective DYRK1A inhibitors. In this study, seven machine learning methods along with five molecular fingerprints were employed to develop qualitative classification models of DYRK1A inhibitors, which were evaluated by cross-validation, test set, and external validation set with four performance indicators of predictive classification accuracy (CA), the area under receiver operating characteristic (AUC), Matthews correlation coefficient (MCC), and balanced accuracy (BA). The PubChem fingerprint-support vector machine model (CA = 0.909, AUC = 0.933, MCC = 0.717, BA = 0.855) and PubChem fingerprint along with the artificial neural model (CA = 0.862, AUC = 0.911, MCC = 0.705, BA = 0.870) were considered as the optimal modes for training set and test set, respectively. A hybrid data balancing method SMOTETL, a combination of synthetic minority over-sampling technique (SMOTE) and Tomek link (TL) algorithms, was applied to explore the impact of balanced learning on the performance of models. Based on the frequency analysis and information gain, pharmacophoric fragments related to DYRK1A inhibition were also identified. All the results will provide theoretical supports and clues for the screening and design of novel DYRK1A inhibitors. 相似文献
997.
998.
通过4-羟基苯甲醛与2,6-二(4-氯甲基苯基)苯并[1-2,4-5′]二唑之间的Wittig反应,制备了具有蓝色荧光特性的小分子单体2,6-二{4-[2-(4-羟基苯基)乙烯基]苯基}苯并[1-2,4-5′]二唑,在碳酸钾的催化作用下,通过其与4,4′-二氟二苯甲酮的缩聚反应,设计并合成了以均二苯乙烯为共轭母核的可发射蓝光的聚醚醚酮材料(BOE-PEEK),并对其结构进行了表征.测定结果表明,该聚合物的平均分子量(-Mw)为1.38×105,均分散系数(PDI)为4.35,玻璃化温度(Tg)为195℃,热分解温度(Td)为440℃,BOE-PEEK在二甲基乙酰胺(DMA)溶剂中的UV-Vis吸收光谱(λmax)为372 nm,荧光光谱(λmax)为455nm,由导电玻璃/发光层/金属铝电极(ITO/BOE-PEEK/Al)组成的单层器件在电压15 V时,发光亮度达530 cd·cm-2,发光效率为0.36 cd/A. 相似文献
999.
1000.