Perhaps you should try some spelling variations:
van hanh » van thanh, ban hanh, van anh
hieu sau » hieu suat, tieu su, hieu va
sach thu » sach thue, sach thieu, sach tham
so sach » so sanh, bo sach, co sach
hieu su » tieu su, hieu so, hieu suat
sang ma » tang ma, nang ma, sang tao
lang ha » long ha
cua tre » cua te, cuu tre, cua triet
ham so » nam so, cham soc
so van » su van, vo van
vi cua » vai cua, di cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach thu ((sang ma) or (lang ha)) hoi. ((hieu su) OR (hieu sau)) ham so van hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach thu ((sang ma) OR (lang ha)) hoi. ((hieu su) OR (hieu sau)) ham so van hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach thu ((sang ma) or (lang ha)) hoi. ((hieu su) OR (hieu sau)) ham so van hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: so sach thu ((sang ma) or (lang ha)) hoi. ((hieu su) OR (hieu sau)) ham so van hanh vi cua tre*.