Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
mai hoi » mai khoi, dai hoi, lai hoi
hieu va » lieu va, hieu qua
sach ky » sac ky, sach y, sach ty
hieu ve » hieu van
ky tang » ky nang, ky dang, kho tang
cua tre » cua te, cuu tre, cua triet
ma hoi » xa hoi, ma hoa, me hoi
tro va » tao va, tho va, tro ba
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 (mai hoi)). ((hieu ve) or (hieu va)) cac tro 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 (mai hoi)). ((hieu ve) OR (hieu va)) cac tro 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 (mai hoi)). ((hieu ve) or (hieu va)) cac tro va dan vi cua tre*".