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排序方式: 共有3038条查询结果,搜索用时 171 毫秒
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Jeffrey Buenaflor Parker Sommerville Hang Qian Christine Luscombe 《Macromolecular chemistry and physics.》2020,221(2)
A comparative study involving bimetallic nickel catalysts designed from disubstituted N,N,N′,N′‐tetra(diphenylphosphanylmethyl)benzene diamine bridging ligands is reported. Catalyst behavior is explored in the Kumada catalyst‐transfer polymerization (KCTP) using poly(3‐hexylthiophene) (P3HT) as the model system. The success of a controlled polymerization is monitored by analyzing monomer conversion, degree of polymerization, end‐group identity, and molecular weight distribution. The characterization of P3HT obtained from KCTP initiated with the bimetallic catalysts shows chain‐growth behavior; however, the presence of Br/Br end‐groups and broader molecular weight distribution reveals a reduced controlled polymerization compared to the commonly employed Ni(dppp)Cl2. The observed increase in intermolecular chain transfer and termination processes in KCTP initiation with the bimetallic catalysts can be attributed to a weaker Ni(0)‐π‐aryl complex interaction, which is caused by increased steric crowding of the coordination sphere. 相似文献
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Color Stability of Dry Earth Pigmented Maxillofacial Silicone A-2186 Subjected to Microwave Energy Exposure 总被引:2,自引:0,他引:2
Sudarat Kiat-amnuay DDS MS ; Dennis A. Johnston PhD ; John M. Powers PhD ; Rhonda F. Jacob DDS MS 《Journal of prosthodontics》2005,14(2):91-96
PURPOSE: The purpose of this study was to measure spectrophotometrically the color stability of pigmented A-2186 silicone maxillofacial elastomer with 10% by volume of titanium white dry earth opacifier before and after exposure to microwave energy over a simulated 1.5-year period of microwave sterilization. Materials AND METHODS: A-2186 silicone elastomer opacified with titanium white dry earth pigment, pigmented with 5 cosmetic dry earth pigment colors [no pigment (control) group (Pc), red (Pr), yellow ochre (Py), burnt sienna (Po), and a mixture of Pr + Py + Po color group (P3)], was used in this study. Each of the 5 experimental groups consisted of 5 specimens. All specimens were placed in a 250 ml glass beaker filled with 150 ml of water (replenished for each microwave exposure). An exposure of 6 minutes was used 18 times (simulating 1.5 years of microwave sterilization with one 6 minute exposure monthly). Reflectance values were measured by spectrophotometer. Three- and two-way analyses of variance with repeated measures were performed for the color difference (DeltaE*) with the factors of group/color/months, and group/months, respectively. Means were compared by Tukey Honest Significant Difference (HSD) multiple range test calculated at the 0.05 level of significance using SPSS. RESULTS: The trained human eye can detect color changes (DeltaE*) greater than 1.0. Most DeltaE* values of the red pigment group at all intervals and the mixed pigment group at 15- and 18- month intervals increased significantly greater than 1.0 (p < 0.001) compared with the control group. Yellow and burnt sienna groups remained the most color stable over time with DeltaE* values below 0.35. CONCLUSIONS: Lack of color stability of red dry earth pigmented A-2186 silicone maxillofacial elastomers was clinically significant after 12-month exposure to microwave energy as compared with yellow, burnt sienna, and opacified A-2186 dry earth pigments. 相似文献
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嵌体与全冠治疗牙间食物嵌塞的临床应用比较 总被引:3,自引:0,他引:3
目的:比较嵌体与全冠治疗牙间食物嵌塞的临床操作及修复效果.方法:对纳入标准的78例患者随机分组,分别用嵌体和全冠进行修复并进行随访观察,并对两种方法的临床应用效果进行比较.结果:在对牙龈及牙周保护方面,嵌体与全冠有显著性差异;在边缘密合、重塑邻接关系及牙齿敏感方面,二者无显著性差异.结论:嵌体较全冠修复牙间食物嵌塞临床操作简便省时,更有利于保护牙髓及牙周组织健康,美观经济. 相似文献
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Hiroshi Asanuma Hiroyuki Satoh Seiichiro Shishido 《International journal of urology》2007,14(1):43-47
OBJECTIVE: Tubularized incised plate urethroplasty has become a popular technique for repairing distal and proximal hypospadias in many institutions. Dorsal inlay graft urethroplasty has been used in our institution since 2003 to reduce the risk of meatal stenosis. In the present study, we evaluated the results of the dorsal inlay graft procedure. METHODS: A total of 28 patients with no deep groove and no severe curvature underwent one-stage urethroplasty using an inner preputial-based dorsal inlay graft. The medical records of all patients were retrospectively reviewed with regard to complication rate and cosmetic appearance. RESULTS: Mean patient age at surgery was 21 months (range, 14 months to 4.6 years). Preoperatively the urethral meatus was coronal in two cases, distal shaft in 17, proximal shaft in six and penoscrotal in three. Nine patients required testosterone therapy before surgery. Mean operative time was 200 min (range, 154-249 min). Mean length of inlay graft was 20.9 mm (range, 12-30 mm). In all patients, a straight penis was achieved without dorsal plication of the corposa cavernosa, and the neomeatus with a slit-like appearance was positioned at the glans tip. At a mean of 22 months of follow up, a urethrocutaneous fistula developed in only one patient (3.6%), requiring repair surgery 6 months after urethroplasty. No patient had meatal stenosis, neourethral stricture or urethral diverticulum along the inlay graft. CONCLUSION: Dorsal inlay graft urethroplasty is an effective method for hypospadiac repair and leads to good cosmetic outcome with low risk of complications. 相似文献
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细胞标记用大粒径羧化彩色高分子微球的研制 总被引:1,自引:0,他引:1
制备一种普通光学显微镜下可见的细胞标记用大粒径彩色高分子微球。以苯乙烯及丙烯酰胺为原料,在体系中加入电解质,有机溶剂及油溶性染料,采用无乳化剂乳液聚合法制备彩色高分子微球,并通过酰肼化和羧化两步反应在微球表现衍生出羧基。 相似文献
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以ESR、UV和IR表征Cu(2+)离子与PVAC的配位反应。根据CUCl2·2H2O乙醇溶液与PVAc-CuCl2·2H2O乙醇溶液的电导率差值随Cu(2+)离子摩尔浓度变化的明显转析点得知,1个Cu(2+)离子大约能与PVAc4个链节单元配位。证实MMA在Cu(Ⅱ)-PVAc配合物/Na2SO3体系的聚合体是无规PMMA,得率为70%。讨论了MMA在Cu(Ⅱ)-PVAc配合物/Na2SO3体系络合催化引发下的游离基反应历程。 相似文献