共查询到20条相似文献，搜索用时 109 毫秒
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核酸中的碱基分两类:嘧啶碱基和嘌呤碱基。嘌呤碱基是母体化合物嘌呤衍生而来的,DNA和RNA所含的两种嘌呤碱基完全相同,即腺嘌呤(A)和鸟嘌呤(G)。嘧啶碱基是母体化合物嘧啶的衍生物,核酸中常见的嘧啶有三类:胞嘧啶(C)、尿嘧啶(U)和胸腺嘧啶(T)。其中胞嘧啶(C)为DNA和RNA共有;尿嘧啶(U)只存在于RNA中;胸腺嘧啶(T)一般存在于DNA中,但是tRNA中也有少量存在[1]。tRNA(转运RNA)约占细胞RNA总量的15%,由核内形成并迅速加工后进入细胞质,主要作用是将氨 相似文献
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采用胶束电动毛细管色谱法（MEKC）分离8种3,4-二氢嘧啶-2-酮衍生物,研究了电泳缓冲液的pH值、组成及浓度和分离电压等对分离效果的影响。得到了优化的实验条件：缓冲溶液组成为10 mmol/LNa2HPO4-75 mmol/L十二烷基硫酸钠（SDS）-5 mmol/L脱氧胆酸钠（SDC）,pH=9.0,压力进样（3 447.4Pa）5 s,25℃,分离电压20 kV。8种分离物中其中6种分析物达到基线分离。 相似文献
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观察了不同浓度pH、葡萄糖、NaCl、KCl、MgCl2和CaCl2对翘嘴红鲌(Erythroculter ilishaeformis)精于激活等级的影响.结果表明:pH在5.5 ～8.5时,精于活力无显著差异,最适合翘嘴红鲌精子运动的pH在8.5附近.翘嘴红鲌精子的激活等级受葡萄糖、Na+、K+,Mg2+,Ca2+的影响,最适于翘嘴红鲌精子激活率的葡萄糖、KCl、MgCl2、和CaCl2溶液浓度分别为1g/L、0.9mmol/L、1 mmol/L和20mmol/L.Na+组精于激活等级均低于对照组,是翘嘴红鲌精子激活等级的抑制因子.低浓度K+能促进翘嘴红鲌精于活力,K+是提高翘嘴红鲌精子激活等级的主要因子. 相似文献
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利用在线推扫富集技术建立了毛细管电色谱测定新药那格列奈中痕量杂质的方法．考察了缓冲溶液pH值、SDS浓度、运行电压以及进样时间对富集效果的影响．结果表明，那格列奈中的痕量组分富集和检测的最佳缓冲溶液组成为16mmol／L NaH2PO4 6mmol／L Na2B4O7 60mmol／L SDS(pH=7．14)，进样时间为200秒．在最佳条件下对那格列奈进行了痕量杂质测定，那格列奈中的杂质总含量为0．56％．本方法可用于药物的质量控制。 相似文献
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运用移动反应界面理论建立奶粉中三聚氰胺的毛细管电泳富集分离体系。与传统的毛细管电泳相比,体系中引入了富集缓冲溶液(富集相)和分离缓冲溶液(分离相)。优化的条件:样品缓冲溶液为50mmol/L甲酸-甲酸钠(pH2.60),富集相为20mmol/L甲酸钠-甲酸pH8.00),分离缓冲溶液为50mmol/L～50mmol/L甲酸-甲酸钠(pH2.60);样品压力进样50mbar×40s,富集相压力进样50mbar×20s,紫外检测波长232nm,电压30kv。该方法比常规电泳灵敏度高近20倍。 相似文献
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DNA分子具有独特的双螺旋结构。它的内涵相当的丰富，概括起来，有如下几点：一、每一条DNA链都有两条脱氧核著酸链组成在“转录”的过程中．只有一条能够“转录”称反斗链，另一条不能“转录”的称有义链；每条脱氧核音酸链都有许多个脱氧核音酸组成；每个脱氧核音酸都由1分子的脱氧核糖，五分子的含氮碱基，l分子的磷酸组成。二、DNA分子有四种碱基腺嘌吟（A）、鸟嘌呤（G）、胞嘧啶（C）、胸腺嘧啶（T），因此它们可以组成四种不同的脱氧核苷酸：腺嘌吟脱氧核糖核酸、鸟嘌吟脱氧核糖核糖核酸、胞嘧啶脱氧核糖核酸、胸腺嘧啶脱氧核… 相似文献
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利用铋膜修饰电极对胞嘧啶的电化学行为进行了研究．结果表明,在0．1mol/L 的PBS 缓冲溶液（ pH6.64）中,胞嘧啶于-0．23 V电位处有一良好的氧化峰,峰电流与胞嘧啶在4．98×10-6～3．38×10-5 mol/L浓度范围内呈良好的线性关系,检出限为5．6×10-7 mol/L．实验显示,铋膜修饰电极性质稳定,对胞嘧啶的测定具有良好的选择性． 相似文献
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用SDS法提取了苜蓿基因组DNA的模板。从100个10bp的随机引物中筛选出了12条能在11个苜蓿品种中均能扩增出清晰的片段的引物。应用L16(45)正交表,研究了DNA、dNTPs、Mg2 、Taq酶和引物的浓度对扩增迁移率重现性的影响。用这种方法建立的苜蓿RAPD-PCR优化反应体系为:20μL体系中含DNA模板的浓度是5.0mg/L、dNTPs浓度是0.175mmol/L、Mg2 浓度是1.25mmol/L、Taq酶在20μL的体系中是1.00U、引物浓度是0.40μmol/L。 相似文献
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枇杷属植物RAPD反应体系的优化与应用 总被引：2，自引：0，他引：2
采用CTAB—蛋白酶K法提取了48份枇杷种质的DNA,以西班牙枇杷品种Ullera为模板DNA,对枇杷属植物RAPD反应体系进行优化研究,结果表明:25μL反应体系中,Taq DNA聚合酶、Mg2+、引物、模板DNA和dNTPs等5种主要成分的适宜浓度或用量分别是:Mg2+为2.0 mmol/L,Taq DNA聚合酶为1.0 U,引物为0.25"mol/L,dNTPs为0.100—0.125 mmol/L,模板DNA为25—30 ng。利用该优化体系对48份枇杷种质进行RAPD随机扩增,经琼脂糖电泳获得了清晰的扩增图谱。 相似文献
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邱崇丙 《唐山师范学院学报》2014,(1):21-23
汉字的六书,《说文》对“转注”一类,语焉不详。后世学者提及转注,也仅限于许慎所举出的例字。《汉字例说》一文,作者从转注的角度综合考虑,对部分现代常用字作了分析,跟传统的解释有所不同。希望能抛砖引玉,互相切磋,以推进学术研究。 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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Rachel Zupek 《海外英语》2007,(11):40-41
我们绝大部分人都同意一件事情——我们喜欢金钱。但是你对金钱的喜欢之情足够到让你创立一份事业么?.财富通常被人忽视,主要在于人们不能真正了 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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YANGShiguo 《重庆大学学报(英文版)》2004,3(1):86-88
The problem on the geometrc inequalities involving an n-dimensional simplex and its inscribed simplex is studied. Aninequality is established, which reveals that the difference between the squared circumradius of the n-dimensional simplex andthe squared distance between its circumcenter and barycenter times the squared circumradius of its inscribed simplex is not lessthan the 2(n-1)th power of n times its squared inradius, and is equal to when the simplex is regular and its inscribed siplex is atangent point one. Deduction from this inequality reaches a generalization of n-dimensional Euler inequality indicating that thecircumradius of the simplex is not less than the n-fold inradius. Another inequality is derived to present the relationship betweenthe circumradius of the n-dimensional simplex and the circumradius and inradius of its pedal simplex. 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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GUO Bao-feng Xiao Da-wei 《重庆大学学报(英文版)》2005,4(3):129-133
Using virtual reality for interactive design gives a designer an intuitive vision of a design and allows the designer to achieve a viable, optimal solution in a timely manner. The article discusses the process of making the Virtual Reality System of the Humble Administrator＇s Garden. Translating building data to the Virtual Reality Modeling Language （VRML） is by far unsatisfactory. This creates a challenge for computer designers to do optimization to meet requirements. Five different approaches to optimize models have been presented in this paper. The other methods are to optimize VRML and to reduce the file size. This is done by keeping polygon counts to a minimum and by applying such techniques as object culling and level-ofdetail switching. 相似文献