检波器一般要有阻尼,否则会降低分辩率,但检波器阻尼对振幅特性和相位特性有影响,阻尼太大会导致振荡,阻尼过小会降低探测的灵敏度,因此,最合适的阻尼应是临界值的0.7倍。
参考答案:错
在世界文化遗产中,明清皇家陵寝所分布的省区不包括( )。
A.北京
B.辽宁
C.河北
D.河南
根据下列句子及所给单词的首字母,在答题卷上按题号写出各单词的完全形式(每空限填一词)。
小题1:My grandfather likes to water the f______ in the garden on weekends.
小题2:The boy is too young. So don’t leave him a______ at home.
小题3:If I don’t help my mom do some h______ on weekends, my mother will be very angry with me.
小题4:Last night I didn’t go to bed u______ the TV program was over.
小题5:Last Sunday I w______ a letter to my father.
小题6:I need to look smart for my job i______.
小题7:He f______ his test last week. He should study hard.
小题8:He m______ his teacher in the street yesterday.
小题9:When the little girl saw the big tiger, she felt very s______.
小题10:Last week, I p______ 500 yuan for my new bike.