Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
doc sach » hoc sach, nuoc sach, dac sac
hanh ly » khanh ly, hanh ky, hang ly
thuc va » thuc vat, thuc dan, thuc day
vu cham » va cham, vu kham, tu cham
tang ma » mang may, tang van
hieu vu » hieu va, hieu ve, hieu su
cua tre » cua te, cuu tre, cua triet
ma hoi » mai hoi, xa hoi, ma hoa
luc va » duc va, tuc va, loc va
y tang » ky tang, 6 tang, 7 tang
ly cua » le cua

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 (doc sach)) y tang ma hoi. hieu vu cham ((luc va) or (thuc va)) hanh ly cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) y tang ma hoi. hieu vu cham ((luc va) OR (thuc va)) hanh ly cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (doc sach)) y tang ma hoi. hieu vu cham ((luc va) or (thuc va)) hanh ly cua tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (doc sach)) y tang ma hoi. hieu vu cham ((luc va) or (thuc va)) hanh ly cua tre*.