图甲是回旋加速器的示意图,其核心部分是两个“D”形金属盒,在加速带电粒子时,两金

题型:选择题

问题:

图甲是回旋加速器的示意图,其核心部分是两个“D”形金属盒,在加速带电粒子时,两金属盒置于匀强磁场中,并分别与高频电源两极相连。带电粒子在磁场中运动的动能Ek随时间t的变化规律如图乙所示,若忽略带电粒子在电场中的加速时间,则下列说法正确的是

A.在Ek—t图中应有(t2-t1)>(t3-t2)>(t4-t3)>……(tn-tn-1

B.高频电源的变化周期应该等于tn-tn-1

C.要使粒子获得的最大动能增大,可以增大“D”形盒的半径

D.在磁感应强度B、“D”形盒半径R、粒子的质量m及其电荷量q不变的情况下,粒子的加速次数越多,粒子的最大动能一定越大

考点:回旋加速器质谱仪
题型:选择题
已知向量
a
=(1,n),
b
=(-1,n-2),若
a
b
共线.则n等于(  )
A.1B.
2
C.2D.4
题型:选择题

One Sunday morning in June 1959 my mother walked into my room. “Surprise!” she said, proudly holding up a yellow dress. “I made it just for you. What do you think?”

I bit my tongue. How could I tell Mom it was the ugliest dress I had ever seen?

“It’s perfect for church,” my mother continued delightedly.“I wish someone had made a dress like this for me.”

Too bad you can’t wear it, I thought. But I knew Mom had spent a lot of time on the dress. No one should refuse.

Unwillingly I put it on.

All through church I prayed(祈祷),Lord, let me get out of here without anyone seeing me. Especially Dennis Pearce, the boy I had a crush on, one of the coolest boys at Neptune High School. Although we were in some of the same classes, Dennis had never taken any notice of me. Every time I got near him, I became tongue-tied.

At the end of the service I rushed for the door. But I had to wait on the steps while my parents chatted with their friends. Just a little while longer…Then out of the corner of my eye I saw the Pearces coming near. Before I could escape, Dennis was right beside me.

I started talking, hoping if I kept it up he wouldn’t notice my ugly dress. “I’m going to college in September,” I said.

“That’s great,” Dennis replied “I got accepted to police academy(学院).”

“Wow!” I said. Somehow I kept the conversation going. The next thing I knew Dennis had asked me out on a date!

We courted(恋爱)through college, and eventually got married. Months after our wedding I asked Dennis if he remembered the day he had first asked me out.

“Certainly I do,” he said.“You were always quiet in school. I didn’t think you’d be much fun. But you were so lively when we talked on the church steps, I wanted to get to know you better.” Maybe that yellow dress wasn’t what I would have chosen, but that day it was the perfect dress for me.

小题1:Why did she accept such a dress?

A.She was fond of its new pattern.

B.Her Mom just brought it for her.

C.It was proper to go to church in it.

D.She understood her Mom’s love.小题2:The author tried to carry the dialog on,hoping        .

A.she would catch other boys’ attention

B.Dennis would get her out for a date

C.Dennis wouldn’t take notice of her dress

D.she could be noticed by Dennis’s parents小题3:The underlined part“had a crush on’’ in Paragraph 6 probably means:“     ”.

A.10ved deeply

B.met by chance

C.100ked down on

D.worried about小题4:What would be the best title for the text?

A.An Ugly Dress

B.A Perfect Dress

C.A Dress for the Church

D.A Dress for the Date

题型:选择题

现代较有影响的课程理论有哪些?其代表人物和观点是什么?

题型:选择题

下列不属于并开药名的是()

A.二母

B.龙牡

C.茯神木

D.白蒺藜

E.猪茯苓

题型:选择题

亚非国家第一次在没有西方殖民国家参加下,自行召开的会议是( )。

A.第一次不结盟国家和政府首脑会议

B.万隆会议

C.六方会谈

D.维也纳会议

更多题库