Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
cua viet » ca viet, hoa viet, cua dieu
sach ty » sach tu, sach thu, xach tay
cao hoi » cau hoi, co hoi, cao hoc
van cac » van hac, van cau, van bac
cac day » cac dan, cac dai, cac cay
va hanh » van hanh, va thanh, va danh

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: te ((sach ty) OR (sach y)) nang cao hoi. hieu van cac day va hanh vi ((cua viet) OR (cua vat))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "te ((sach ty) or (sach y)) nang cao hoi. hieu van cac day va hanh vi ((cua viet) OR (cua vat))~".
• Adding a wildcard symbol may retrieve word variants: te ((sach ty) or (sach y)) nang cao hoi. hieu van cac day va hanh vi ((cua viet) OR (cua vat))*.