Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
hoc sach » hoc sinh, hoc cac, hoc anh
hanh lai » hanh lam, hanh tai, thanh lap
pham duy » pham duc
van pham » san pham, van phan, van phat
hieu van » hieu va, thien van, lieu va
lai cua » dai cua, hai cua, lai chau
va hanh » van hanh, va thanh, va danh
cua tre » cua te, cuu tre, cua triet
nang ma » tang ma, sang ma, nang cao
xang ma » tang ma, sang ma, rang ma
duy va » duy vat, duy van, day va

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((toc sach) OR (hoc sach)) ty ((xang ma) or (nang ma)) hoi. hieu van pham duy va hanh lai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sach)) ty ((xang ma) OR (nang ma)) hoi. hieu van pham duy va hanh lai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (hoc sach)) ty ((xang ma) or (nang ma)) hoi. hieu van pham duy va hanh lai cua tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (hoc sach)) ty ((xang ma) or (nang ma)) hoi. hieu van pham duy va hanh lai cua tre*.