Perhaps you should try some spelling variations:
hoc sach » hoc sinh, hoc cac, hoc anh
hieu van » thien van, lieu va, hieu ve
bo sach » co sach
va hanh » van hanh, va thanh, va danh
thuc va » thuc vat, thuc dan, thuc day
hieu va » lieu va, hieu qua
sang ma » tang ma, nang ma, sang tao
ty sang » ty xang, ty hang, duy sang
ca viet » va viet, co viet, hoa viet
ma hoi » mai hoi, xa hoi, ma hoa
vi ca » vit ca, li ca, va ca

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((bo sach) OR (hoc sach)) ty sang ma hoi. ((hieu va) or (hieu van)) am thuc va hanh vi ca viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((bo sach) OR (hoc sach)) ty sang ma hoi. ((hieu va) OR (hieu van)) am thuc va hanh vi ca viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((bo sach) OR (hoc sach)) ty sang ma hoi. ((hieu va) or (hieu van)) am thuc va hanh vi ca viet".
• Adding a wildcard symbol may retrieve word variants: ((bo sach) OR (hoc sach)) ty sang ma hoi. ((hieu va) or (hieu van)) am thuc va hanh vi ca viet*.