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β-内酰胺类抗生素的构效关系与哪项不符 A. β-内酰胺环是抗菌作用的必要结构,β-内酰胺环并合六元的氢化噻嗪环可显著提高抗菌活性 B. 6-氨基或7-氨基的酰化侧链影响抗菌强度,抗菌谱,耐青霉素酶及耐酸性 C. 侧链中引入吸电子基团将增强对酸的稳定性 D.侧链中引入体积较大基团可增强对青霉素酶的稳定性 E.头孢菌素类的3-位取代基的改变,主要影响化合物的药物动力学特性
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【简答题】阅读理解。 Catherine comes from Australia. She's very smart. She has studied in Sydney University for about 4 years. When vacations come, she usually returns to the town where she was born. She loves teac...
【单选题】She has studied in this school _______ she was seven years old. [ ]
A.
since
B.
if
C.
until
D.
after
【单选题】Which of the following is not true?
A.
She has studied hard all week.
B.
This is the woman’s first term of school.
C.
The man wishes her good luck.
D.
She has failed in a test.
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