Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
sach ky » sac ky, sach y, sach ty
dao voi » da voi, dao noi, do voi
cac toc » cac toi, cac nuoc, cac thoi
cuu tre » cua tre, cau tren, cau treo
cac tuc » cac tu, cac tac, cac nuoc
hieu ve » hieu va, hieu van
nang ma » tang ma, sang ma, nang cao
dao vi » dao ve, dao va, dao li
ma hoi » mai hoi, xa hoi, ma hoa

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 nang ma hoi. hieu ve ((cac tuc) OR (cac toc)) va ((dao vi) or (dao voi)) cuu tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky nang ma hoi. hieu ve ((cac tuc) OR (cac toc)) va ((dao vi) OR (dao voi)) cuu tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky nang ma hoi. hieu ve ((cac tuc) OR (cac toc)) va ((dao vi) or (dao voi)) cuu tre".
• Adding a wildcard symbol may retrieve word variants: toc sach ky nang ma hoi. hieu ve ((cac tuc) OR (cac toc)) va ((dao vi) or (dao voi)) cuu tre*.