共查询到20条相似文献，搜索用时 78 毫秒
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研究了正戊醇和水形成的两相体系混合溶剂中,蔗糖和乙酸乙烯酯在游离态脂肪酶的催化作用下,发生转酯化反应合成蔗糖酯,确定了合成反应的各工艺参数。即当蔗糖为1.0g,水体积含量为60%,温度在40℃,缓冲液的pH值为8.0,脂肪酶用量为0.3g,蔗糖与乙酸乙烯酯的比例为1∶4,反应时间24h时,蔗糖的转化率为54.8%。通过红外光谱确定了生成主要的产物是蔗糖-6-乙酸酯。 相似文献
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刘小英 《泉州师范学院学报》2006,24(2):29-31
试验了腰果酚醛铁聚合物(PC-Fe)对乙酸-正丁醇酯化反应的催化性能.结果表明,腰果酚醛铁聚合物具有催化合成乙酸丁酯的性能;乙酸与正丁醇反应的最佳条件:n(乙酸)∶n(正丁醇)=1.1∶1,反应温度为112℃~122℃,PC-Fe用量占0.79%(摩尔分数),反应时间4 h,酯得率达到84.3%.yh 相似文献
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β-环糊精增敏荧光猝灭法测定水中微量银离子 总被引：1，自引：0，他引：1
银离子和盐酸萘乙二胺(NNE)的活性氨基有很好的配位络合作用,在pH=5.80的乙酸-乙酸钠缓冲溶液中可形成金属配合物NNE-Ag导致荧光强度发生猝灭,因其降低NNE分子的极性,有利于分子中的萘环进入β-环糊精的疏水空腔中,使体系的荧光强度猝灭更加明显。据此建立β-环糊精增敏NNE荧光猝灭测定银离子的方法。考察了pH值、反应介质、反应时间和β-环糊精用量等条件对体系的荧光强度影响。结果表明,在β-环糊精存在条件下,银离子可以使NNE的荧光强度发生较明显的猝灭,荧光猝灭程度与Ag离子的浓度在0-28μmol/L范围内呈良好线性,回归方程为I0/I=0.99363+0.01108C(C的单位为μmol/L),r=0.9985,检出限为2.35×10-4mol/L。将该方法用于水样中银离子的测定,得到较满意的结果。 相似文献
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合成对羟基苯甘氨酸乙二醇酯盐酸盐时,对羟基苯甘氨酸∶乙二醇∶氯化亚砜=1∶1.5∶1.5,在-10℃～0℃下酰化8 h,pH=6,将20 mL CH2Cl2直接加入作溶剂,20 mL CH2Cl2与氯化亚砜混合后滴加,滴加时间为2 h～3 h,反应总收率为96%. 相似文献
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目的:β-葡萄糖苷酶活性是新生儿坏死性小肠结肠炎早期诊断和药用植物有效成分改变的重要指标。现有活性检测方法操作时间长,试剂消耗大,且需要昂贵的仪器设备和专业的技术人员,不利于β-葡萄糖苷酶的快速、实时检测。本文尝试构建一种基于血糖仪的酶活性检测方法,为实际样品中β-葡萄糖苷酶活性的快速检测提供科学依据。创新点:首次将便携式血糖仪引入β-葡萄糖苷酶活性检测中,通过酶反应条件优化、方法学考察、实际样品中的应用以及现有方法的比较,建立β-葡萄糖苷酶活性检测新方法。方法:采用单因素试验,以酶反应溶液、pH值、反应温度、反应时间和底物浓度为指标,优化酶活性测定条件;通过考察精密度、稳定性、重复性、加样回收率、专一性等指标验证方法的可行性;通过实际样品中新方法的应用以及与现有二硝基水杨酸(DNS)法和4-硝基苯基-β-D-吡喃葡萄糖苷(pN PG)法的比较,研究新方法在实际样品检测中的适用性。结论:酶活性测定最优条件为以柠檬酸-柠檬酸钠缓冲液(0.05 mol/L,pH 5.0)为反应溶液,0.03 g/mL水杨苷为底物,在50°C条件下,反应30 min。新方法具有良好的精密度、准确性、重复性、稳定性和耐用性,且不受β-葡聚糖酶、蜗牛酶、β-半乳糖苷酶、半纤维素酶和葡萄糖醛酸的影响,专一性较强。β-葡萄糖苷酶在缓冲液和大鼠血清中线性关系良好,线性范围分别为0.0873～1.5498U/m L和0.4076～2.9019U/m L。该方法已成功应用于苦杏仁、燀苦杏仁、酶制剂以及黑曲霉培养的一系列β-葡萄糖苷酶活性检测中,结果与现有方法所测的基本相符。 相似文献
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《实验室研究与探索》2017,(6):18-20
通过对脂质体内外水相pH梯度的制备方法的探讨,采用凝胶过滤层析技术将脂质体外水相的pH4.0柠檬酸缓冲液替换成pH 7.2磷酸盐缓冲液,在脂质体内外水相形成pH梯度。在药脂比为1∶5、1∶10、1∶15和1∶20(质量比)时,阿霉素在pH梯度的驱动下从脂质体外水相穿越脂质双分子膜进入内水相,包封率分别达到96.7%、98.7%、96.8%和95.1%,其中药脂比1∶10时包封率达到最高。药脂比1∶10制备的阿霉素脂质体在37℃,12 h内阿霉素泄漏均低于1.0%;48 h内药物泄露率低于5.0%。通过该实验,使学生们能够观测到如何采用凝胶过滤层析技术调节pH梯度,以及pH梯度在阿霉素脂质体主动载药过程中的重要性,为脂质体递释系统的课堂理论教学奠定了良好的实验基础。 相似文献
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异硫氰酸酯的抗癌活性与结构的关系 总被引：4，自引：0，他引：4
给出了异硫氰酸β-苯基乙基酯(PEITC)、异硫氰酸苄基酯(BITC)、异硫氰酸1-萘基酯(NITC)及异硫氰酸丙烯基酯(AITC)的结构信息含量指数(SIC)与抗癌活性(IC50)的关系即：IC50=20.41-24.90SIC，其相关性R=-0．9425，计算了其他异硫氰酸酯的IC50值。对于R—(CH2)n—NCS而言，其中R=Me，Ph或其他基团，IC50值随着n值的增加而增大。 相似文献
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《海外英语》2007,(5):10-11
Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help? 相似文献
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罗艳萍 《读与写:教育教学刊》2008,5(6)
The communication of people partially is the communication of cultures. Culture has a direct effect on international commercial activities in all aspects. Different conceptions about time, space, equality, law and the like, lead people to deal with things in different ways. So to know cultures of the counterpart is to facil-itate our enterprises so as to have a smooth and successful communication in commercial activity. 相似文献
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《海外英语》2007,(4):36
There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love. 相似文献
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Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject. 相似文献
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Richard Denner 《海外英语》2007,(4):14-15
Rosco and I wait for the fishermen to return.I sit at a wooden bench near the store at Mt.Baker Resort and watch the clouds change shape. Rosco has my belt around his neck and an eight foot tow chain hooked to a tree. Dogs must be on a leash. Ducks and rabbits are loose. 相似文献
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Given a graph G,a subgraph C is called a clique of G if C is a complete subgraph of G maximal under inclusion and |C|≥2. A clique-transversal set S of G is a set of vertices of G such that S meets all cliques of G. The clique-transversal number, denoted as TC (G), is the minimum cardinality of a clique-transversal set in G. The clique-graph of G, denoted as K (G), is the graph obtained by taking the cliques of G as vertices, and two vertices are adjacent if and only if the corresponding cliques in G have nonempty intersection. Let F be a class of graphs G such that F={G|K(G) is a tree}. In this paper the graphs in F having independent clique-transversal sets are shown and thus TC (G)/|G|≤1/2 for all G ∈ F. 相似文献
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Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities. 相似文献