Perhaps you should try some spelling variations:
thien van » thi van
toc sach » hoc sach, doc sach, thuoc sach
hieu van » hieu va, lieu va, hieu ve
dan vanh » dan canh, dan hanh, dang hanh
vanh dai » van dai, vanh tai, lanh dao
tu sach » thu sach, su sach, te sach
ky lang » ky nang, ky dang, ky tang
lang xa » lang ha, dang xay, lang van
thu dan » thuc dan, thu dang, thu ban
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: ((tu sach) or (toc sach)) ky lang xa hoi. ((hieu van) OR (thien van)) nam thu dan vanh dai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (toc sach)) ky lang xa hoi. ((hieu van) OR (thien van)) nam thu dan vanh dai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (toc sach)) ky lang xa hoi. ((hieu van) OR (thien van)) nam thu dan vanh dai cua tre".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (toc sach)) ky lang xa hoi. ((hieu van) OR (thien van)) nam thu dan vanh dai cua tre*.