Perhaps you should try some spelling variations:
thu sach » thuat sach, thuoc sach, thu hoach
tu sach » su sach, te sach, tu cach
doan vi » doan va, don vi, doan thi
va doan » va doanh, van doan, va dan
hieu va » lieu va, hieu qua
hieu ve » hieu van
tang ma » mang may, tang van
ky tang » ky nang, ky dang, kho tang
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa
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) OR (thu sach)) ky tang ma hoi. ((hieu ve) or (hieu va)) cac tro va doan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (thu sach)) ky tang ma hoi. ((hieu ve) OR (hieu va)) cac tro va doan vi cua tre*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) OR (thu sach)) ky tang ma hoi. ((hieu ve) or (hieu va)) cac tro va doan vi cua tre*".