Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
nam thuc » nam thuoc, am thuc, nam thu
hieu van » hieu va, thien van, lieu va
cau treo » cau theo, cau tren, cau triet
doc sach » hoc sach, nuoc sach, dac sac
ky lang » ky nang, ky tang, tay lang
ky dang » ky nang, ky danh
thuc va » thuc vat, thuc dan, thuc day
va dao » ca dao
dao va » dao van, tao va, do va
va cau » van cau, va cac, va dau

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)) ((ky lang) OR (ky dang)) xa hoi. hieu van nam thuc va dao va cau treo~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (doc sach)) ((ky lang) OR (ky dang)) xa hoi. hieu van nam thuc va dao va cau treo".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (doc sach)) ((ky lang) OR (ky dang)) xa hoi. hieu van nam thuc va dao va cau treo*.