Perhaps you should try some spelling variations:
tang mai » tang ma, tang tai, lang mai
tu sach » thu sach, su sach, te sach
mai hoi » mai khoi, dai hoi, lai hoi
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
y tang » ky tang, 6 tang, 7 tang
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 y tang mai hoi. ((hieu ve) or (hieu qua)) cac tro va dan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach y tang mai hoi. ((hieu ve) OR (hieu qua)) cac tro va dan vi cua tre*.