Perhaps you should try some spelling variations:
vai thiet » va thiet, tai thiet, van thiet
hieu cua » hieu qua, dieu cua, bieu cua
va thanh » ban thanh, va tinh, le thanh
tu sach » thu sach, te sach, tu cach
su sach » so sach, vu sach
ly nang » ky nang, ly hang, ly vang
nang ma » tang ma, sang ma, nang cao
cac duc » cac du, cao duc, cac dac
va vai » va bai, va van, va dai

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 (su sach)) ly nang ma hoa. hieu cua cac duc ((va thanh) OR (gia thanh)) va vai thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (su sach)) ly nang ma hoa. hieu cua cac duc ((va thanh) OR (gia thanh)) va vai thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) or (su sach)) ly nang ma hoa. hieu cua cac duc ((va thanh) OR (gia thanh)) va vai thiet".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) or (su sach)) ly nang ma hoa. hieu cua cac duc ((va thanh) OR (gia thanh)) va vai thiet*.