Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
van pham » san pham, van phan, van phat
tan hanh » tan thanh, tang hanh, toan hanh
tu sach » thu sach, su sach, te sach
sach ky » sac ky, sach y, sach ty
nang xa » nang x, lang xa, ang xa
mang xa » lang xa, mang may, dang xay
nang ma » tang ma, sang ma, nang cao
su viet » so viet
vi su » va su, ve su, ki 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 ky ((((nang xa) or (mang xa))) or (nang ma)) hoi. hieu van pham duc tan hanh vi su viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky ((((nang xa) OR (mang xa))) OR (nang ma)) hoi. hieu van pham duc tan hanh vi su viet.
• Adding a wildcard symbol may retrieve word variants: tu sach ky ((((nang xa) or (mang xa))) or (nang ma)) hoi. hieu van pham duc tan hanh vi su viet*.