Perhaps you should try some spelling variations:
nam trung » nam trong, tai trung, ba trung
dat tren » dat trong, dua tren
nam truc » nam truoc, nam thuc, nam thuoc
sach ky » sac ky, sach y, sach ty
tu sach » thu sach, su sach, te sach
hieu ve » hieu va, hieu van
cao hoc » co hoc, cho hoc, chat hoc
va dan » va dao, va dau, va dap
ca dan » cac dan, ca dao
ca dat » cai dat, ca dao, va dat

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