Perhaps you should try some spelling variations:
trinh quan » tinh quang, trinh luat, trinh han
hieu tach » hieu cach, chiet tach, chieu sach
trinh cua » tinh cua, trinh luat, trinh luan
dang cong » dung cong
doc hieu » toc thieu, hoc thieu, hoc hien
dan toan » van toan, dan than, manh toan
van than » van thanh, van thang, van tuan

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: doc hieu tach - hanh ((trinh cua) OR (trinh quan)) dang cong ((dan toan) OR (van than)) cau~.
• Adding a wildcard symbol may retrieve word variants: doc hieu tach - hanh ((trinh cua) or (trinh quan)) dang cong ((dan toan) or (van than)) cau*.