文摘
英文文摘
前言
学位论文独创性声明及学位论文使用授权声明
1. Introduction
2. Grammaticalization
3. The hypothesis of unidirectionality
4. The evidence against unidirectionality
5. The evidence for unidirectionality
6. The explanations for unidirectionality
7. Summary
References:
ACKNOWLEGEMENTS