Perhaps you should try some spelling variations:
cac thuc » cach thuc, can thuc, cay thuc
vat doan » van doan, van doanh, vay doanh
tu sach » thu sach, su sach, te sach
tang ma » mang may, tang van
hieu ve » hieu van
hieu va » lieu va, hieu qua
cac thu » cach thuc, cac thoi
doan vi » doan va, don vi, doan thi
cua tre » cua te, cuu tre, cua triet
y tang » ky tang, 6 tang, 7 tang
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: tu sach y tang ma hoa. ((hieu ve) or (hieu va)) ((cac thuc) or (cac thu)) vat doan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y tang ma hoa. ((hieu ve) OR (hieu va)) ((cac thuc) OR (cac thu)) vat doan vi cua tre.
• Adding a wildcard symbol may retrieve word variants: tu sach y tang ma hoa. ((hieu ve) or (hieu va)) ((cac thuc) or (cac thu)) vat doan vi cua tre*.