Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, am thuc, nam thu
hoc cac » hoc cao
ky lang » ky nang, ky dang, ky tang
lang xa » lang ha, dang xay, lang van
thuc va » thuc vat, thuc dan, thuc day
vai cau » va cau, vai cac, lai chau
van cau » van dau, van hau, van chat
va dao » ca dao

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