出自:乐山师范学院生物技术

采用重结晶提纯样品,要求杂质含量为((____)) 以下,如果杂质含量太高,可先用 (____),( (____))方法提纯。
(____)是纯化固体化合物的一种手段,它可除去与被提纯物质的蒸汽间有显著差异的不挥发性杂质。
将液体加热至沸腾,使液体变为蒸气,然后使蒸气冷却再凝结为液体,这两个过程的联合操作称为( (____) )。
常用的分馏柱有( )。 A. 球形分馏柱 B. 韦氏(Vigreux)分馏柱 C. 填充式分馏柱 D. 直形分馏柱
在色谱中,吸附剂对样品的吸附能力与( )有关。 A. 吸附剂的含水量 B. 吸附剂的粒度 C. 洗脱溶剂的极性 D. 洗脱溶剂的流速
正丁醚合成实验是通过( )装置来提高产品产量的? A. 熔点管 B. 分液漏斗 C. 分水器 D. 脂肪提取器
水蒸气蒸馏应用于分离和纯化时其分离对象的适用范围为( )。 A. 从大量树脂状杂质或不挥发性杂质中分离有机物 B. 从挥发性杂质中分离有机物 C. 从液体多的反应混合物中分离固体产物
环己酮的氧化所采用的氧化剂为( ) A. 硝酸 B. 高锰酸钾 C. 重铬酸钾
重结晶时,活性炭所起的作用是( )。 A. 脱色 B. 脱水 C. 促进结晶 D. 脱脂
重结晶实验中,加入活性碳的目的是脱色。( )
薄层色谱可用于化合物纯度的鉴定,有机反应的监控,不能用于化合物的分离。( )
在使用分液漏斗进行分液时,上层液体经漏斗的下口放出。(
微量法测定沸点时,当毛细管中有一连串气泡放出时的温度即为该物质的沸点。( )
液体的蒸气压只与温度有关。即液体在一定温度下具有一定的蒸气压。( )
1、已知ci元素电势图: 酸性介质中:EN CIO 碱性介质中:EN CIO,则: A. 碱性介质中 会发生逆歧化反应 B. 碱性介质中会发生歧化反应 C. 酸性介质中 会发生歧化反应 D. 酸性或碱性介质中都不发生歧化反应
偶然误差可以通过以下哪种方法得以减小:( ) A. 引入校正系数进行校正 B. 不加试样,进行空白试验 C. 用标准样进行对照试验 D. 增加平行测定的次数
已知在溶液中,电对的条件电极电势分别为1.44v和0.68v,在此条件下用Ce标准溶液滴定,其化学计量点的电势值为: A. 2.12V B. 0.86V C. 1.06V D. 1.26V
、 测定某矿石中铁的含量时,获得如下数据:79.58%,79.45%,79.47%,79.50%,79.62%,79.38%。置信度P为90%时经Q检验无可疑数据要 舍弃,则标准偏差s为(____);置信度P为90%时平均值的置信区间为(____)。(已知置信度为90%、n=6时,t=2.015
难挥发性非电解质稀溶液蒸汽压下降的原因是(____)。
人只有在理想中才能创造有价值的人生。( )
现实是此岸,理想是彼岸,那么,唯有读书才是联系两者的桥梁。( )
谈谈现代生物技术在食品工业上的应用和发展趋势。
人工种子包括哪几部分?如何制备人工种子?
什么是单细胞蛋白?简述它的几种来源。
谈谈现阶段转基因生物技术的应用及安全性。
什么是人类基因组计划?人类基因组计划对人类生存将产生哪些影响?
函数y=x-1/lnx+16-x的定义域为( ) A.(0,1) B.(0,1)∪(1,4) C.(0,4) D.(0,1)∪(1,4]
∫dx/4+x2= A.arctan1/2 B. π/4 C.1/4 D.1/2arctan1/2
满足方程f.(x)的x是函数y=f(x)的( ). A. 极大值点 B. 极小值点 C. 驻点 D. 间断点
函数y=ln(1+x2)的单调递增区间是( ). A.(-∞,+∞) B.[0,+∞) C.(-∞,0] D. 以上都不对
下列变量中,不是无穷小量的为( ). A.ln1/x(x→0) B.lnx(x→1) C.cosx(x→0) D.x-2/x2-4(x→2)
曲线y=x2与x=y2所围成图形的面积A =( ). A.∫ (x2-x)dx B.∫(x-x2)dx C.-1/3 D.1/3
曲线y=e-x在点(0,1)处的切线方程是y=x+1 ( )
已知x=sint,y=cos2t,则
函数 y=x3当x=2,时的微分dy=0.24( )
You should choose the ONE that best fits into the passage. Then mark the corresponding letter on the answer sheet. Generally speaking, a British is widely regarded as a quiet, shy and conservative person who is 36 only among those with whom he is acquainted. When a stranger is at present, he often seems nervous, 37 embarrassed. You have to take a commuter train any morning or evening to 38 the truth of this. Serious-looking businessmen and women sit reading their newspapers or dozing in a corner; hardly anybody talks, since to do so would be considered quite offensive. 39 , there is an unwritten but clearly understood code of behavior which, 40 broken, makes the offender immediately the object of 41. It has been known as a fact that the British has a 42 for the discussion of their weather and that, if given a chance, he will talk about it 43. Some people argue that it is because the British weather seldom 44 forecast and hence becomes a source of interest and 45 to everyone. This may be so. 46 a British cannot have much 47 in the weathermen, who, after promising fine, sunny weather for the following day, are often proved wrong 48 a cloud over the Atlantic brings rainy weather to all districts! The man in the street seems to be as accurate---or as inaccurate---as the weathermen in his 49. Foreigners may be surprised at the number of references 50 weather that the British make to each other in the course of a single day. Very often conversational greetings are 51 by comments on the weather. “Nice day, isn’t it?” “Beautiful!” may well be heard instead of “Good morning, how are you?” 52 the foreigner may consider this exaggerated and comic, it is worthwhile pointing out that it could be used to his advantage. 53 he wants to start a conversation with a British but is 54 to know where to begin, he could do well to mention the state of the weather. It is a safe subject which will 55 an answer from even the most reserved of the British. 36.