Perhaps you should try some spelling variations:
hieu sau » hieu su, hieu suat, tieu su
sau pham » san pham, su pham, cau pham
van hanh » van thanh, ban hanh, van ban
su triet » su viet, su tien, ve triet
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, mang xa
nang ma » tang ma, sang ma, nang cao
van anh » van thanh, tuan anh, van minh

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 xa) OR (nang ma)) hoi. hieu sau pham duc ((van hanh) or (van anh)) va su triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky ((nang xa) OR (nang ma)) hoi. hieu sau pham duc ((van hanh) OR (van anh)) va su triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky ((nang xa) OR (nang ma)) hoi. hieu sau pham duc ((van hanh) or (van anh)) va su triet".
• Adding a wildcard symbol may retrieve word variants: tu sach ky ((nang xa) OR (nang ma)) hoi. hieu sau pham duc ((van hanh) or (van anh)) va su triet*.