Perhaps you should try some spelling variations:
cac thuc » cach thuc, cac thu, can thuc
tu sach » thu sach, su sach, te sach
cua tre » cua te, cua triet, dua tren
doan vi » doan va, don vi, doan thi
va doan » va doanh, van doan, va dan
thuc va » thuc vat, thuc dan, thuc day
hieu va » lieu va, hieu qua
hieu ve » hieu van
tang ma » mang may, tang van
cuu tre » cau tren, cau treo
sach 7 » sach y, sach 2
ma hoi » mai hoi, xa hoi, ma hoa
7 tang » 6 tang

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 7 tang ma hoi. ((hieu ve) or (hieu va)) cac thuc va doan vi ((cua tre) OR (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach 7 tang ma hoi. ((hieu ve) OR (hieu va)) cac thuc va doan vi ((cua tre) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach 7 tang ma hoi. ((hieu ve) or (hieu va)) cac thuc va doan vi ((cua tre) OR (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: tu sach 7 tang ma hoi. ((hieu ve) or (hieu va)) cac thuc va doan vi ((cua tre) OR (cuu tre))*.