Perhaps you should try some spelling variations:
can thiet » dan thiet, cac thiet, cad thiet
van hanh » van thanh, ban hanh, van anh
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
nang ma » tang ma, sang ma, mang may
hieu vu » hieu va, hieu ve, hieu su
vu cham » va cham, vu kham, tu cham
va hanh » va thanh, va danh, ban hanh
vi can » voi can, vi van, i can

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 ky ((nang ma) OR (nang cao)) hoi. hieu vu cham soc ((va hanh) or (van hanh)) vi can thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky ((nang ma) OR (nang cao)) hoi. hieu vu cham soc ((va hanh) OR (van hanh)) vi can thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky ((nang ma) OR (nang cao)) hoi. hieu vu cham soc ((va hanh) or (van hanh)) vi can thiet".
• Adding a wildcard symbol may retrieve word variants: tu sach ky ((nang ma) OR (nang cao)) hoi. hieu vu cham soc ((va hanh) or (van hanh)) vi can thiet*.