Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
van hanh » van thanh, ban hanh, van anh
phan dau » phan tu, hang dau
dau van » dao van, dam van, dau va
va phan » van phan, va phat, va phap
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
nang ma » tang ma, sang ma, nang cao
mang xa » lang xa, mang may, dang xay
vi su » va su, ki su, oi su
ve su » va su

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