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