Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
cua tre » cua te, cua triet, dua tren
cac toc » cac toi, cac nuoc, cac thoi
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
hieu ve » hieu van
tang ma » mang may, tang van
ky tang » ky nang, ky dang, kho tang
cuu tre » cau tren, cau treo
ma hoi » mai hoi, xa hoi, ma hoa
toc va » hoc va, toc ta, tuc va
va dan » ca dan, va dao, va dau
dan vi » doan vi, don vi, dan 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 ky tang ma hoi. ((hieu ve) or (hieu va)) cac toc va dan vi ((cua tre) OR (cuu tre))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky tang ma hoi. ((hieu ve) OR (hieu va)) cac toc va dan vi ((cua tre) OR (cuu tre)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky tang ma hoi. ((hieu ve) or (hieu va)) cac toc va dan vi ((cua tre) OR (cuu tre))".
• Adding a wildcard symbol may retrieve word variants: tu sach ky tang ma hoi. ((hieu ve) or (hieu va)) cac toc va dan vi ((cua tre) OR (cuu tre))*.