Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
hieu van » hieu va, thien van, lieu va
cau thuc » cau truc, cuu thuc, can thuc
thuc day » thuc dan, thuc vat
day hanh » day nhanh, day thanh, dao hanh
hanh tai » thanh tai, hang tai, han tai
sach ty » sach y, sach tu, sach thu
nang xa » lang xa, nang ma, mang xa
van cau » van dau, van hau, van chat
cuc te » cua te, cuc thue, cuc tieu

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

• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ty ((nang xa) OR (nang x)) hoi. hieu van cau thuc day hanh tai cuc te~.
• Adding a wildcard symbol may retrieve word variants: doc sach ty ((nang xa) or (nang x)) hoi. hieu van cau thuc day hanh tai cuc te*.