Perhaps you should try some spelling variations:
cac thuc » cach thuc, cac thu, can thuc
hieu van » hieu va, thien van, lieu va
su sach » so sach, vu sach
dinh vi » dinh ve, dinh viet, dinh tri
va dinh » van dinh, va kinh, va tinh
thuc va » thuc vat, thuc dan, thuc day
van cac » van hac, van cau, van bac
cua tre » cua te, cuu tre, cua triet
tang ma » mang may, tang van
nang ma » sang ma, nang cao, mang may
so sanh » do sanh
vi cua » vai cua, di cua

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: ((su sach) OR (so sanh)) y ((nang ma) OR (tang ma)) hoi. hieu van cac thuc va dinh vi cua tre~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) or (so sanh)) y ((nang ma) OR (tang ma)) hoi. hieu van cac thuc va dinh vi cua tre~".
• Adding a wildcard symbol may retrieve word variants: ((su sach) or (so sanh)) y ((nang ma) OR (tang ma)) hoi. hieu van cac thuc va dinh vi cua tre*.