Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
tu sach » thu sach, su sach, te sach
qua cam » qua cham, qua cac, qua ca
duc van » duc tan, duc manh, duc phan
hang di » hang doi, hang vi, hang dien
cua tre » cua te, cuu tre, cua triet
di cua » dai cua, doi cua, de cua
x hoi » xa hoi, o hoi, x ho

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 nang x hoi. hieu qua cam ((duc van) OR (duc va)) hang di cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (toc sach)) ky nang x hoi. hieu qua cam ((duc van) OR (duc va)) hang di cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (toc sach)) ky nang x hoi. hieu qua cam ((duc van) OR (duc va)) hang di cua tre".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (toc sach)) ky nang x hoi. hieu qua cam ((duc van) OR (duc va)) hang di cua tre*.