Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
tinh may » trinh may, tinh ma, tinh tay
te sach » toc sach
may cua » day cua, may bua, may sua
va tinh » may tinh
cao duc » dao duc, cao suc, giao duc
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
ve cao » va cao, ve bao, ve cac
ma hoi » mai hoi, ma hoa, me hoi
y tang » ky tang, 6 tang, 7 tang

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((te sach) or (doc sach)) y tang ((ma hoi) OR (xa hoi)). hieu ve cao duc va tinh may cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (doc sach)) y tang ((ma hoi) OR (xa hoi)). hieu ve cao duc va tinh may cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) or (doc sach)) y tang ((ma hoi) OR (xa hoi)). hieu ve cao duc va tinh may cua tre".
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (doc sach)) y tang ((ma hoi) OR (xa hoi)). hieu ve cao duc va tinh may cua tre*.