普通话早期儿童趋向动词习得个案研究——以“上、下”两组趋向动词为例
보통화조기인동추향동사습득개안연구——이“상、하”량조추향동사위례
A Case Study of the Acquisition of Directional Verbs by a Pūtōnghuà Speaking Child ——with shàng and xià types as examples