Perhaps you should try some spelling variations:
can thiet » dan thiet, cac thiet, cad thiet
thu sach » tu sach, thuat sach, thuoc sach
hieu sau » hieu su, hieu suat, tieu su
sau cham » cau cham, sau chan, va cham
va thanh » gia thanh, ban thanh, va tinh
van hanh » van thanh, ban hanh, van anh
sach ky » sac ky, sach y, sach ty
nang ma » sang ma, nang cao, mang may
tang ma » mang may, tang van
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: thu sach ky ((nang ma) OR (tang ma)) hoi. hieu sau cham soc ((va thanh) or (van hanh)) vi can thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ky ((nang ma) OR (tang ma)) hoi. hieu sau cham soc ((va thanh) OR (van hanh)) vi can thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ky ((nang ma) OR (tang ma)) hoi. hieu sau cham soc ((va thanh) or (van hanh)) vi can thiet".
• Adding a wildcard symbol may retrieve word variants: thu sach ky ((nang ma) OR (tang ma)) hoi. hieu sau cham soc ((va thanh) or (van hanh)) vi can thiet*.