Perhaps you should try some spelling variations:
cac thuc » cach thuc, cac thu, can thuc
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
hieu ve » hieu van
tang ma » mang may, tang van
cua tre » cua te, cuu tre, cua triet
y tang » ky tang, 6 tang, 7 tang
ma hoi » mai hoi, xa hoi, ma hoa
dan vi » doan vi, don vi, gan vi
dan va » doan va, dan ca, ban va

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 hoi. ((hieu ve) or (hieu va)) cac thuc vat ((dan vi) OR (dan va)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y tang ma hoi. ((hieu ve) OR (hieu va)) cac thuc vat ((dan vi) OR (dan va)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach y tang ma hoi. ((hieu ve) or (hieu va)) cac thuc vat ((dan vi) OR (dan va)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu sach y tang ma hoi. ((hieu ve) or (hieu va)) cac thuc vat ((dan vi) OR (dan va)) cua tre*.