Er 3+ doped transparent oxyfluoride glass ceramics containing LaF_3 nanocrystals were prepared and the up-con- version and near infrared luminescence behavior o
一、选择题:本大题共8小题,每小题5分,满分40分. 1. 设集合M={-1,0,1},N={x|x2≤x},则M∩N=( ) A. {0} B. {0,1} C. {-1,1} D. {-1,0} 2. 已知复数z1=2 i,z1·z2=2-i,则复数z2=( ) A. i B. --i C. -i D. - i 3. 已知平面向量=(x1,y1),=(x2,y2),若||=2,||