Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
hanh lam » thanh lap, hanh kem, hanh va
vat hanh » vat thanh, van hanh, va hanh
pham duy » pham duc
van pham » san pham, van phan, van phat
hieu van » hieu va, thien van, lieu va
lam cua » nam cua, lam chat
cua tre » cua te, cuu tre, cua triet
sach ty » sach y, sach tu, sach thu
nang ma » tang ma, sang ma, nang cao
rang ma » tang ma, sang ma, rang va
xang ma » tang ma, sang ma, xquang ma

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ty ((((xang ma) or (rang ma))) or (nang ma)) hoi. hieu van pham duy vat hanh lam cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ty ((((xang ma) OR (rang ma))) OR (nang ma)) hoi. hieu van pham duy vat hanh lam cua tre.
• Adding a wildcard symbol may retrieve word variants: doc sach ty ((((xang ma) or (rang ma))) or (nang ma)) hoi. hieu van pham duy vat hanh lam cua tre*.