Perhaps you should try some spelling variations:
thuc dan » thuc hanh, hoc dan, thuc vat
hieu van » thien van, lieu va, hieu ve
bo sach » co sach, hoc sach
sach ty » sach y, sach tu, sach thu
thuc va » thuc vat, thuc day
ca viet » va viet, co viet, hoa viet
hieu va » lieu va, hieu qua
sang ma » tang ma, nang ma, sang tao
ty sang » ty xang, ty hang, duy sang
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 ty sang ma hoi. ((hieu va) or (hieu van)) am ((thuc va) OR (thuc dan)) hanh vi ca viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: bo sach ty sang ma hoi. ((hieu va) OR (hieu van)) am ((thuc va) OR (thuc dan)) hanh vi ca viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "bo sach ty sang ma hoi. ((hieu va) or (hieu van)) am ((thuc va) OR (thuc dan)) hanh vi ca viet".
• Adding a wildcard symbol may retrieve word variants: bo sach ty sang ma hoi. ((hieu va) or (hieu van)) am ((thuc va) OR (thuc dan)) hanh vi ca viet*.