Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
dau tren » dau tien, dat tren, dau tieng
sach ky » sac ky, sach y, sach ty
cac dau » cac dan, cac du, cac dai
dan cac » dan cach, dang cac, dan ca
cam tuc » cam xuc, cam tu, nam thuc
tu sach » thu sach, su sach, te sach
hieu ve » hieu va
cao hoc » co hoc, cho hoc, chat hoc
tuc va » thuc va, truc va, tuc xa
va dan » ca dan, va dao, va dau
co hoi » co hoc, co loi

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 ((co hoi) or (cao hoc)). ((hieu ve) OR (hieu van)) cam tuc va dan cac dau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ky nang ((co hoi) OR (cao hoc)). ((hieu ve) OR (hieu van)) cam tuc va dan cac dau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ky nang ((co hoi) or (cao hoc)). ((hieu ve) OR (hieu van)) cam tuc va dan cac dau tren".
• Adding a wildcard symbol may retrieve word variants: tu sach ky nang ((co hoi) or (cao hoc)). ((hieu ve) OR (hieu van)) cam tuc va dan cac dau tren*.