the sound of knocking (as on a door or in an engine or bearing);
"the knocking grew louder"
例句
用作名词(n.)
A war came knocking on your door.一个战争受到在你的门上爆震音的影响。
(vbl.)
They found that knocking out the gene in fetal mice whose hematopoietic systems had already formed caused hematopoietic stem cells to disappear.他们发现击昏已经形成造血系统的胚胎小鼠的基因会引起造血干细胞的消失。
