Perhaps you should try some spelling variations:
nang ro » nang co, nang ra, nang rong
hieu ve » hieu va, hieu van
sach ty » sach tu, sach thu, xach tay
cua tre » cua te, cuu tre, cua triet
nang ho » nang hoc, nang co, tang ho
ve cac » va cac, vien cac
cac tu » cac thu, cach tu, cac du
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: thu ((sach ty) OR (sach y)) ((nang ho) or (nang ro)) hoi. hieu ve cac tu va dan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu ((sach ty) OR (sach y)) ((nang ho) OR (nang ro)) hoi. hieu ve cac tu va dan vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu ((sach ty) OR (sach y)) ((nang ho) or (nang ro)) hoi. hieu ve cac tu va dan vi cua tre".
• Adding a wildcard symbol may retrieve word variants: thu ((sach ty) OR (sach y)) ((nang ho) or (nang ro)) hoi. hieu ve cac tu va dan vi cua tre*.