onto

1. His soup spoon dropped onto the ground.
   他的汤勺掉到了地上。
2. A miner's lamp is fixed onto his helmet.
   矿灯固定在矿工的头盔上。
3. I reached the gate that opened onto the lake.
   我走到临湖而开的那扇门前。
4. He jumped onto the table.
   他跳上了桌子。

on.to

prep.（介词）
On top of; to a position on; upon:
到…之上：在…顶端；在一位置上；在…上面：
例句：
The dog jumped onto the chair.See Usage Note at on
这条狗跳到了椅子上面参见 on

Informal Fully aware of; informed about:
【非正式用语】 知晓：非常熟悉；了解：
例句：
The police are onto the robbers` plans.
警察局都清楚抢劫犯的阴谋

adj.Mathematics （形容词）【数学】
Of, relating to, or being a mapping such that every element of the set referred to is the image of an element in another.
映成的：一集合中的每一元素，经映象后为另一集合至少一元素的象的；与之有关的；或成为象的