Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hanh tai » thanh tai, hang tai, han tai
kho tang » cao tang
thuc dan » thuc hanh, hoc dan, thuc vat
hieu van » hieu va, thien van, lieu va
tai cua » thai cua, tai cuc, tri cua
van cam » van nam, van lam, van cau
ky tang » ky nang, ky dang, ky trong
tuc va » thuc va, truc va, tuc xa
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 ((ky tang) or (kho tang)) xa hoi. hieu van cam ((tuc va) or (thuc dan)) hanh tai cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky tang) OR (kho tang)) xa hoi. hieu van cam ((tuc va) OR (thuc dan)) hanh tai cua te.
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky tang) or (kho tang)) xa hoi. hieu van cam ((tuc va) or (thuc dan)) hanh tai cua te*.