Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hanh lam » thanh lap, hanh kem, hanh va
pham duy » pham duc
hieu van » hieu va, thien van, lieu va
van pham » san pham, van phan, van phat
va hanh » van hanh, va thanh, va danh
nang ma » tang ma, sang ma, nang cao
xang ma » tang ma, sang ma, rang ma
cua tre » cuu tre, cua triet, dua tren
duy va » duy vat, duy van, day va
cua te » cua tu

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