Perhaps you should try some spelling variations:
co sach » bo sach, cuon sach, hoc sach
sach ty » sach y, sach tu, sach thu
thu xac » thau xay
hieu ve » hieu va, hieu van
nang ma » tang ma, sang ma, nang cao
ty nang » ky nang, ty xang, ty hang
thu xa » thu ha, thu xe, thu ba
ve cac » va cac, vien cac
lai so » dai so, tai so, hai so

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: co sach ty nang ma hoa. hieu ve cac ((thu xa) OR (thu xac)) hanh ((lai so) OR (lai su)) viet~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "co sach ty nang ma hoa. hieu ve cac ((thu xa) or (thu xac)) hanh ((lai so) OR (lai su)) viet~".
• Adding a wildcard symbol may retrieve word variants: co sach ty nang ma hoa. hieu ve cac ((thu xa) or (thu xac)) hanh ((lai so) OR (lai su)) viet*.