Perhaps you should try some spelling variations:
dan thanh » dang thanh, danh thanh, ban thanh
dan hanh » dang hanh, dan khanh, ban hanh
hieu van » hieu va, thien van, lieu va
su sach » so sach, vu sach
hoi cua » hoi chuc
cua tre » cua te, cuu tre, cua triet
nang ma » tang ma, sang ma, nang cao
van am » van nam, van lam, van dam

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach y ((mang may) or (nang ma)) hoi. hieu van am thuc ((dan hanh) OR (dan thanh)) hoi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach y ((mang may) OR (nang ma)) hoi. hieu van am thuc ((dan hanh) OR (dan thanh)) hoi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach y ((mang may) or (nang ma)) hoi. hieu van am thuc ((dan hanh) OR (dan thanh)) hoi cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach y ((mang may) or (nang ma)) hoi. hieu van am thuc ((dan hanh) OR (dan thanh)) hoi cua tre*.