Perhaps you should try some spelling variations:
thanh tung » thanh cong
thong cong » trong cong, tong cong, thong thong
hieu cua » hieu qua, dieu cua, bieu cua
va thong » va thuong, va phuong, he thong
dan than » dan chan, ban than, van than
hieu ca » hieu cac, hieu va, hieu xa
tung va » trung va, tuong va, dung va

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 ca) OR (hieu cua)) - thanh tung va thong cong ((xuan toan) OR (dan than)) cau~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc ((hieu ca) OR (hieu cua)) - thanh tung va thong cong ((xuan toan) or (dan than)) cau~".
• Adding a wildcard symbol may retrieve word variants: doc ((hieu ca) OR (hieu cua)) - thanh tung va thong cong ((xuan toan) or (dan than)) cau*.