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991.
992.
设 a、b、c、k是适合 a+b=ck,gcd(a,b) =1 ,c∈ { 1 ,2 ,4} ,k>1且 k在 c=1或 2时为奇数的正整数 ;又设 ε=(a + - b) / c ,ε=(a - - b) / c .本文证明了 :当 (a,b,c,k)≠ (1 ,7,4,2 )或 (3,5,4,2 )时 ,至多有 1个大于 1的正奇数 n适合 |(εn-εn) / (ε-ε) |=1 ,而且如此的 n必为满足 n<1 +(2 logπ) / logk+2 563.43(1 +(2 1 .96π) / logk)的奇素数 . 相似文献
993.
Rhodium‐Catalyzed Synthesis of 4‐Bromo‐1,2‐dihydroisoquinolines: Access to Bromonium Ylides by the Intramolecular Reaction of a Benzyl Bromide and an α‐Imino Carbene 下载免费PDF全文
Jun He Yinping Shi Wanli Cheng Zengming Man Dongdong Yang Prof. Dr. Chuan‐Ying Li 《Angewandte Chemie (International ed. in English)》2016,55(14):4557-4561
Highly functionalized 4‐bromo‐1,2‐dihydroisoquinolines were synthesized from readily available 4‐(2‐(bromomethyl)phenyl)‐1‐sulfonyl‐1,2,3‐triazoles. A bromonium ylide is proposed as the key intermediate, which can be formed by the intramolecular nucleophilic attack of the benzyl bromide on the α‐imino rhodium carbene formed in the presence of the rhodium catalyst. 相似文献
994.
Juna Bae Jung Cho Jeong Hwan Lee Dr. Sung Man Seo Prof. Suk Bong Hong 《Angewandte Chemie (International ed. in English)》2016,55(26):7369-7373
Zeolite EU‐12, the framework structure of which has remained unsolved during the past 30 years, is synthesized at a specific SiO2/Al2O3 ratio using choline as an organic structure‐directing agent, with both Na+ and Rb+ ions present. Synchrotron powder X‐ray diffraction and Rietveld analyses reveal that the EU‐12 structure has a two‐dimensional 8‐ring channel system. Among the two distinct 8‐ring (4.6×2.8 and 5.0×2.7 Å) channels along c axis, the smaller one interconnects with the sinusoidal 8‐ring (4.8×3.3 Å) channel along a axis. The other large one is simply linked up with the sinusoidal channel by sharing 8‐rings (4.8×2.6 Å) in the ac plane. The proton form of EU‐12 was found to show a considerably higher ethene selectivity in the low‐temperature dehydration of ethanol than H‐mordenite, the best catalyst for this reaction. 相似文献
995.
Man Kyu Shim Dr. Hong Yeol Yoon Dr. Ju Hee Ryu Dr. Heebeom Koo Dr. Sangmin Lee Dr. Jae Hyung Park Dr. Jong‐Ho Kim Dr. Seulki Lee Dr. Martin G. Pomper Dr. Ick Chan Kwon Dr. Kwangmeyung Kim 《Angewandte Chemie (International ed. in English)》2016,55(47):14698-14703
Recently, metabolic glycoengineering with bioorthogonal click reactions has focused on improving the tumor targeting efficiency of nanoparticles as delivery vehicles for anticancer drugs or imaging agents. It is the key technique for developing tumor‐specific metabolic precursors that can generate unnatural glycans on the tumor‐cell surface. A cathepsin B‐specific cleavable substrate (KGRR) conjugated with triacetylated N‐azidoacetyl‐d ‐mannosamine (RR‐S‐Ac3ManNAz) was developed to enable tumor cells to generate unnatural glycans that contain azide groups. The generation of azide groups on the tumor cell surface was exogenously and specifically controlled by the amount of RR‐S‐Ac3ManNAz that was fed to target tumor cells. Moreover, unnatural glycans on the tumor cell surface were conjugated with near infrared fluorescence (NIRF) dye‐labeled molecules by a bioorthogonal click reaction in cell cultures and in tumor‐bearing mice. Therefore, our RR‐S‐Ac3ManNAz is promising for research in tumor‐specific imaging or drug delivery. 相似文献
996.
Jinbai Huang Hu Yue Shufang Lv Zhanzhan Hao Man Wang 《Journal of Macromolecular Science: Physics》2016,55(4):361-371
The thermal degradation behavior of polybenzoxazine based on bisphenol-S/allylamine was studied by Fourier transform–infrared spectroscopy and thermogravimetry–mass spectrometry. The reaction proceeded through detaching of Schiff bases and cleavage of aromatic C–S bonds and the Mannich bridge structures; the scission temperature of the aromatic C–S bond was lower than those of C–N and C–C bonds. The activation energy of the thermal degradation was evaluated with the Flynn–Wall–Ozawa method. 相似文献
997.
Shi Yan Dongbai Sun Yu Gong Yuanyuan Tan Xueqing Xing Guang Mo Zhongjun Chen Quan Cai Zhihong Li Hongying Yu Zhonghua Wu 《Journal of synchrotron radiation》2016,23(3):718-728
Silver nanoparticles were synthesized with a chemical reduction method in the presence of polyvinylpyrrolidone as stabilizing agent. The thermal stability behavior of the silver nanoparticles was studied in the temperature range from 25 to 700°C. Thermal gravimetric analysis was used to measure the weight loss of the silver nanoparticles. Scanning electron microscopy and high‐resolution transmission electron microscopy were used to observe the morphology and the change in shape of the silver nanoparticles. In situ temperature‐dependent small‐angle X‐ray scattering was used to detect the increase in particle size with temperature. In situ temperature‐dependent X‐ray diffraction was used to characterize the increase in nanocrystal size and the thermal expansion coefficient. The results demonstrate that sequential slow and fast Ostward ripening are the main methods of nanoparticle growth at lower temperatures (<500°C), whereas successive random and directional coalescences are the main methods of nanoparticle growth at higher temperatures (>500°C). A four‐stage model can be used to describe the whole sintering process. The thermal expansion coefficient (2.8 × 10?5 K?1) of silver nanoparticles is about 30% larger than that of bulk silver. To our knowledge, the temperature‐driven directional coalescence of silver nanocrystals is reported for the first time. Two possible mechanisms of directional coalescence have been proposed. This study is of importance not only in terms of its fundamental academic interest but also in terms of the thermal stability of silver nanoparticles. 相似文献
998.
An effective capillary electrophoretic technique for separating samples of negatively charged, polydisperse, water-soluble gold monolayer-protected cluster (Au MPC) protected by monolayers of N-acetyl-L-cysteine has been developed. The separation mechanisms of the Au MPC in CZE suggest that the larger core sizes Au MPC emerge first from the capillary. The electrophoretic separation depends on pH, buffer concentration, and organic modifiers. The addition of aliphatic alcohols to the run buffer can improve the separation of Au MPC by reducing the EOF and changing the selectivity between the Au MPCs. The enhancement of resolution is attributed to the more significant difference in the charge-to-size ratio between the Au MPCs. The run buffer containing 20 v/v % ethanol provides the best separation for water-soluble Au MPC. Our proposed CE method provides a powerful tool to evaluate and separate the water-soluble Au MPC products. 相似文献
999.
Man Singh 《Surface and interface analysis : SIA》2008,40(2):76-80
Interfacial tension (IFT) (γift, N m?1) of benzene‐water; and surface tensions (γ, N m?1) and viscosities (η, N s m?2) of solvents methanol, ethanol, glycerol, ethyl acetate, n‐hexane, diethyl ether, chloroform, benzene, carbon tetrachloride [CCl4], formic acid, Acetonitril, and dimethylformamide [DMF] were measured with Survismeter‐IFT. The ± 1.1 × 10?5 N m?1, ± 1.3 × 10?5 N m?1, and ± 1.1 × 10?5 N s m?2 deviations in respective values were noted. It has 10 times better accuracy than those of individual methods. The survismeter is inexpensive minimizing 2/3 each of consumables, human efforts, time, and infrastructure, cutting down 80% of the waste disposed the environment. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
1000.
采用2-氯-5-(氯甲基)吡啶和2-氯-5-(氯甲基)噻唑为原料, 经过叠氮化, 与乙酰乙酸乙酯环化, 水解, 酰氯化, 然后与异硫氰酸钾反应生成相应的异硫氰酸酯5, 最后与2-氨基-4,6-二取代嘧啶加成, 合成了10种未见文献报道的目标化合物, 其结构经IR, 1H NMR, MS和元素分析确证, 初步的生物活性测定结果表明, 部分目标化合物在100 mg/L浓度下显示出良好的除草活性. 相似文献