Perhaps you should try some spelling variations:
sach thu » sach thue, sach thieu, sach tham
cac lop » cac hop, cac loai
sach ty » sach y, sach tu, xach tay
hieu va » hieu qua
nang xa » nang x, lang xa, nang ma
cua tre » cua te, cuu tre, cua triet
lop va » lap va, hop va, nop va
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 thu)) nang xa hoi. ((hieu va) or (lieu va)) cac lop va dan vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu ((sach ty) OR (sach thu)) nang xa hoi. ((hieu va) OR (lieu va)) cac lop va dan vi cua tre.
• Adding a wildcard symbol may retrieve word variants: thu ((sach ty) or (sach thu)) nang xa hoi. ((hieu va) or (lieu va)) cac lop va dan vi cua tre*.