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排序方式: 共有273条查询结果,搜索用时 15 毫秒
91.
92.
以苯酚、乙酰氯为原料,直接反应合成乙酸苯酯,研究了反应温度、反应时间、原料配比、溶剂用量等条件对合成反应的影响,确定了合成乙酸苯酯的最佳工艺条件是:苯酚和乙酰氯反应温度20℃,反应时间5 h;n(苯酚):n(乙酰氯)=1:1.2,溶剂用量为40 mL(相对于0.15 mol苯酚).在此条件下,乙酸苯酯的产品收率达到95.55%,产品纯度达到98.5% 相似文献
93.
探索腐竹中残留甲醛的提取及测定方法。磷酸酸化条件下对腐竹样品进行蒸馏,采用乙酰丙酮分光光度法测定甲醛残留量。试验了腐竹中甲醛的提取条件和光度法测定的显色条件,在选定条件下所得线性回归方程为y=0.2319x+0.0263(R2=0.9994),样品回收率为92.0%~94.4%。该方法测定腐竹中残留甲醛具有稳定性好,准确度高以及操作简单等特点。 相似文献
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95.
Experiments 1 and 2 address the controversy regarding the reliability of methamphetamine effects on interval timing. A temporal discrimination procedure was used, in which the rats were reinforced for pressing the left or the right levers after short and long signals, respectively. Methamphetamine (0.5 mg/kg sc) severely disrupted operant performance at 20-100 min after injection, which disabled the measurement of drug effects on temporal perception (Experiment 1). The same dose of methamphetamine shifted the psychometric function to the left at 100-180 min after injection, indicating an increase in subjective durations (Experiment 2). Although these results confirm the role of dopamine in interval timing, that a change in the speed of a neural clock mediates the methamphetamine-induced change in temporal perception is still a working hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
96.
Twelve maize genotypes, were agronomically evaluated and their stover hydrothermally pretreated in a temperature range of 210–225 °C to assess the effects of genotype and pretreatment severity on stover recalcitrance toward bioethanol conversion. Maize genotypes exhibited significant variation for biomass yield and all agronomic evaluated, while among all cell wall constituents measured in the unpretreated stover, only ash content showed differences among genotypes. The pretreatment severities assayed impacted most stover compositional traits, and the glucose recovered after enzymatic hydrolysis displayed a similar profile among genotypes with similar genetic background. Harsher pretreatment conditions maximized the potential cellulosic bioethanol production (208–239 L/t), while the mildest maximized the bioethanol from the hemicellulosic hydrolysates (137–175 L/t). Consequently, when both pentose and hexose sugars were considered, the total potential bioethanol produced at the lowest and highest pretreatment temperatures was similar in all genotypes (292–358 L/t), indicating that the lowest temperature (210 °C) was the optimal among all assayed. Importantly, the ranking of genotypes for bioethanol yield (L/ha) closely resembled the ranking for stover yield (t/ha), indicating that breeding for biomass yield would increase the bioethanol production per hectare regardless of the manufacturing process. Similarly, the genetic regulation of corn stover moisture is possible and relevant for efficient energy production as biomass moisture has a potential impact on stover transportation, storage and processing requirements. Overall, these results indicate that local landrace populations are important genetic resources to improve cultivated crops, and that simultaneous breeding for production of grain and stover bioethanol is possible in corn. 相似文献
97.
The 4‐ulose and the 3‐ulose, both derived in two steps from the α‐methyl glycoside of N‐acetyl‐D ‐glucosamine (GlcNAc), act as organocatalysts in the asymmetric epoxidation of alkenes, with unprecedented complementary enantioselectivity. The best results are found with α,β‐unsaturated esters as substrates, with enantiomeric ratios up to 90:10 and 11:89, respectively. 相似文献
98.
甲醛成为现在环境空气中的重要检测项目之一.酚试剂分光光度法和乙酰丙酮分光光度法都可以用于对环境空气中甲醛的测定.通过理论和实验数据对两种方法进行分析比较,两种方法测定甲醛含量的结果,是一致的. 相似文献
99.
William R. Swindell Manpreet Randhawa Geovani Quijas Krzysztof Bojanowski Ratan K. Chaudhuri 《International journal of molecular sciences》2021,22(16)
Tetrahexyldecyl Ascorbate (THDC) is an L-ascorbic acid precursor with improved stability and ability to penetrate the epidermis. The stability and transdermal penetration of THDC, however, may be compromised by the oxidant-rich environment of human skin. In this study, we show that THDC is a poor antioxidant that degrades rapidly when exposed to singlet oxygen. This degradation, however, was prevented by combination with acetyl zingerone (AZ) as a stabilizing antioxidant. As a standalone ingredient, THDC led to unexpected activation of type I interferon signaling, but this pro-inflammatory effect was blunted in the presence of AZ. Moreover, the combination of THDC and AZ increased expression of genes associated with phospholipid homeostasis and keratinocyte differentiation, along with repression of MMP1 and MMP7 expression, inhibition of MMP enzyme activity, and increased production of collagen proteins by dermal fibroblasts. Lastly, whereas THDC alone reduced viability of keratinocytes exposed to oxidative stress, this effect was completely abrogated by the addition of AZ to THDC. These results show that AZ is an effective antioxidant stabilizer of THDC and that combination of these products may improve ascorbic acid delivery. This provides a step towards reaching the full potential of ascorbate as an active ingredient in topical preparations. 相似文献
100.
Novel carboxymethyl derivatives of chitin and chitosan materials and their biomedical applications 总被引:1,自引:0,他引:1
R. Jayakumar M. Prabaharan S. Tokura N. Selvamurugan 《Progress in Materials Science》2010,55(7):675-1993
Chitin and chitosan are natural biopolymers that are non-toxic, biodegradable and biocompatible. In the last decade, chitin and chitosan derivatives have garnered significant interest in the biomedical and biopharmaceutical research fields with applications as biomaterials for tissue engineering and wound healing and as excipients for drug delivery. Introducing small chemical groups to the chitin or chitosan structure, such as alkyl or carboxymethyl groups, can drastically increase the solubility of chitin and chitosan at neutral and alkaline pH values without affecting their characteristics; substitution with carboxyl groups can yield polymers with polyampholytic properties. Carboxymethyl derivatives of chitin and chitosan have shown promise for adsorbing metal ions, as drug delivery systems, in wound healing, as anti-microbial agents, in tissue engineering, as components in cosmetics and food and for anti-tumor activities. This review will focus on the preparative methods and applications of carboxymethyl and succinyl derivatives of chitin and chitosan with particular emphasis on their uses as materials for biomedical applications. 相似文献