如果一个四边形绕对角线的交点旋转90°,所得的四边形与原来的四边形重合,那么这个

题型:填空题

问题:

如果一个四边形绕对角线的交点旋转90°,所得的四边形与原来的四边形重合,那么这个四边形是______.

考点:正方形,正方形的性质,正方形的判定图形旋转
题型:填空题

90°射频脉冲激发后,组织中将产生宏观横向磁化矢量,射频脉冲关闭后,由于主磁场的不均匀造成了质子群失相位,组织中的宏观横向磁化矢量逐渐衰减。到TE/2时刻,施加一个180°聚相脉冲,质子群逐渐聚相位,组织中宏观横向磁化矢量逐渐增大;到了TE时刻,质子群得以最大程度聚相位,组织中宏观横向磁化矢量达到最大值,从此时刻开始,质子群又逐渐失相位,组织中的横向宏观磁化矢量又逐渐衰减。

该序列中90°脉冲的作用是()

A.产生失相位

B.产生横向磁化

C.产生回波

D.相位重聚

E.翻转磁化矢量

题型:填空题

语法填空

     In the international business there is always a great need for creative talents.On the other hand creative

people are also searching for areas  1._____ they can put their talents to use.A talent to be noticed

nowadays is much  2._____ (easy) than it used to be in the old times.In the early days,for example,if one

wanted to be a singer,he or she had to have a great amount of talent in singing.That was the only way they

could promote  3._____ and be recognized.Now sources like the Internet help a great deal in promoting

oneself.The Internet is like a global village.4._____ (seat) in your home you are capable  5._____ finding a

lot of sources.People with  6._____ (vary) of talents can be recognized through the Internet.7._____,the

Internet is  8._____ opportunity to put forward one's talents,creativity,and powers in order to be noticed.

Keeping in mind  9._____ a talent unexposed is the talent unfound.Now we are lucky enough to show

our  10._____ (hide) talents,without trying very hard and just by sitting at home.

题型:填空题
如图所示,AB是一质量为m的均匀细直杆,A端靠在光滑的竖直墙壁上,B端置于水平地面上,杆身与竖直方向夹角为θ,杆与地面的摩擦系数为μ,保持平衡,则此时杆与地面的摩擦力为(  )

A.mgtgθ

B.mgsinθ

C.μmg

D.μmg

题型:填空题

当科学理论遇到问题时,一般的辩护策略是把问题转嫁给()

A.观察。

B.背景理论。

C.辅助性假定。

D.亦A亦B亦C。

题型:填空题

服毒后的洗胃处理,下列哪项不恰当

A.一般在服毒后6h内洗胃有效
B.超过6h多数洗胃已无必要
C.惊厥患者不宜插管洗胃
D.吞服强腐蚀性毒物者,不宜洗胃
E.昏迷患者插胃管易致吸入性肺炎,洗胃应慎重

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