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41.
金刚石砂轮的精密修整是脆硬材料镜面磨削的关键技术之一,为了保证磨轮起到足够数量微小磨削刃的作用,以使脆硬材料镜面磨削得到较好的面形精度,超微粒金刚石砂轮精密修整技术是目前国内外研究的一个课题。这里介绍了目前国内外修整金刚石砂轮的各种技术方法,并提出采用碗形碳化硅修整器和在线电解修整法,可获得较理想的修整效果。 相似文献
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Zhaohui Tang Xuesi Chen Qizhi Liang Xinchao Bian Lixin Yang Longhai Piao Xiabin Jing 《Journal of polymer science. Part A, Polymer chemistry》2003,41(13):1934-1941
An amino isopropoxyl strontium (Sr‐PO) initiator, which was prepared by the reaction of propylene oxide with liquid strontium ammoniate solution, was used to carry out the ring‐opening polymerization (ROP) of cyclic esters to obtain aliphatic polyesters, such as poly(ε‐caprolactone) (PCL) and poly(L ‐lactide) (PLLA). The Sr‐PO initiator demonstrated an effective initiating activity for the ROP of ε‐caprolactone (ε‐CL) and L‐lactide (LLA) under mild conditions and adjusted the molecular weight by the ratio of monomer to Sr‐PO initiator. Block copolymer PCL‐b‐PLLA was prepared by sequential polymerization of ε‐CL and LLA, which was demonstrated by 1H NMR, 13C NMR, and gel permeation chromatography. The chemical structure of Sr‐PO initiator was confirmed by elemental analysis of Sr and N, 1H NMR analysis of the end groups in ε‐CL oligomer, and Fourier transform infrared (FTIR) spectroscopy. The end groups of PCL were hydroxyl and isopropoxycarbonyl, and FTIR spectroscopy showed the coordination between Sr‐PO initiator and model monomer γ‐butyrolactone. These experimental facts indicated that the ROP of cyclic esters followed a coordination‐insertion mechanism, and cyclic esters exclusively inserted into the Sr–O bond. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1934–1941, 2003 相似文献
43.
ConsiderneutraldifferentialdiffereflceequatinwhereTE(0,co),ae[0,co),Q(t)EC[[t.,co),R ].In1988,G.Ladaspresentedanopenprobleminprivatecommuni(:ationandthenin[1].Theproblemisasfollowing:Assumethatfi:Q(s)ds=co,showthateverynonoscillatorysollltioTIot'equation(… 相似文献
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In this paper, we give a definition of pseudo almost periodic sequence and study the existence of pseudo almost periodic sequence to difference equation. Based on these, we investigate the existence of pseudo almost periodic solutions to differential equations with piecewise constant arguments which was considered by K. L. Cooke & J. Wiener and found applications in certain biomedical problems. 相似文献
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Xiu-Rong Huang Yu-Mei Zhang Ting-Biao Wan Piao Zhang Xiu-Xiu Zhang Fang-Ming Wang Defeng Xu Mei-Hua Shen Hua-Dong Xu 《Tetrahedron》2019,75(45):130336
Functionalized 1,2-oxazinanes are interesting and valuable heterocycles with potential applications in synthetic and medicinal chemistry. A straightforward strategy for quick access to unprecedented trans-4-hydroxyl-5-azido/cyano/amino 1,2-oxazinanes are developed: N-COR 3,6-dihydro- 1,2-oxazine oxides are prepared with ease from related dihydro- 1,2-oxazines and opened by nucleophiles TMSN3, TMSCN and aryl/alkyl amines. Appropriate Lewis acid catalysts are found playing a vital role for both reaction rate and regioselectivity. The N-COR group can be removed under mild conditions to provide highly desirable NH 1,2-oxazinanes inaccessible via previous methods. 相似文献
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Journal of Radioanalytical and Nuclear Chemistry - The migration of iodine on Beishan granite was studied by the dynamic column method using an UV detector. Migration parameters, such as... 相似文献