Perhaps you should try some spelling variations:
tu sach » thu sach, su sach, te sach
doan vi » doan va, don vi, doan thi
va doan » va doanh, van doan, va dan
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va, hieu van
mai hoi » mai khoi, dai hoi, mai doi
lai hoi » dai hoi, lai hoa, lai roi
ky tang » ky nang, ky dang, kho tang
cua tre » cua te, cuu tre, cua triet
tro va » tao va, tho va, tro ba
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 ((mai hoi) OR (lai hoi)). ((hieu ve) or (hieu qua)) cac tro va doan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky tang ((mai hoi) OR (lai hoi)). ((hieu ve) OR (hieu qua)) cac tro va doan vi cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky tang ((mai hoi) OR (lai hoi)). ((hieu ve) or (hieu qua)) cac tro va doan vi cua tre*".