Perhaps you should try some spelling variations:
ban hanh » ban hang
van hanh » van thanh, van anh, van ban
va pham » van pham, va phat, va phap
hieu va » lieu va, hieu qua
sach tu » sach thu, sach ty, sach uu
nang ma » tang ma, sang ma, nang cao
cach tu » cach thuc
su viet » so viet
ki su » ky su

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