Perhaps you should try some spelling variations:
thanh hoi » thanh hoai, thanh hoa, thanh hai
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
thuc dan » thuc hanh, hoc dan, thuc vat
thuc day » thuc vat
ky tang » ky nang, ky dang, kho tang
ky lang » ky nang, ky dang, tay lang
hoi cua » hoi chuc
cua tre » cua te, cuu tre, cua triet

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 lang) or (ky tang)) xa hoi. hieu van nam ((thuc day) OR (thuc dan)) thanh hoi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((ky lang) OR (ky tang)) xa hoi. hieu van nam ((thuc day) OR (thuc dan)) thanh hoi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((ky lang) or (ky tang)) xa hoi. hieu van nam ((thuc day) OR (thuc dan)) thanh hoi cua tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ((ky lang) or (ky tang)) xa hoi. hieu van nam ((thuc day) OR (thuc dan)) thanh hoi cua tre*.