Perhaps you should try some spelling variations:
thuoc sach » hoc sach, nuoc sach, thuat sach
doc sach » hoc sach, toc sach, nuoc sach
van hanh » van thanh, ban hanh, van anh
tai cua » thai cua, tai cuc, tri cua
va hanh » va thanh, va danh, ban hanh
cao tuc » dao tuc, cao duc, cao suc
hieu va » lieu va, hieu qua
ky tang » ky nang, ky dang, kho tang
tang ma » mang may, tang van
va cao » va cac, va co, va dao
ma hoi » mai hoi, xa hoi, ma hoa
cua te » cua tu

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((thuoc sach) or (doc sach)) ky tang ma hoi. hieu va cao tuc ((va hanh) OR (van hanh)) tai cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((thuoc sach) OR (doc sach)) ky tang ma hoi. hieu va cao tuc ((va hanh) OR (van hanh)) tai cua te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((thuoc sach) or (doc sach)) ky tang ma hoi. hieu va cao tuc ((va hanh) OR (van hanh)) tai cua te".
• Adding a wildcard symbol may retrieve word variants: ((thuoc sach) or (doc sach)) ky tang ma hoi. hieu va cao tuc ((va hanh) OR (van hanh)) tai cua te*.