Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, nam thu, nam tu
su sach » so sach, vu sach
sach va » sach xa, sach ha, sach dao
va nang » van nang, da nang, cam nang
cao hoi » cau hoi, co hoi, cao hoc
hanh di » hanh de, hang di, danh di
thiet » thieu

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

• Performing a fuzzy search may retrieve terms with similar spellings: su sach va nang cao hoi. hieu van ((am thuc) or (nam thuc)) va ((hanh di) OR (hanh vi)) va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach va nang cao hoi. hieu van ((am thuc) OR (nam thuc)) va ((hanh di) OR (hanh vi)) va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach va nang cao hoi. hieu van ((am thuc) or (nam thuc)) va ((hanh di) OR (hanh vi)) va thiet".
• Adding a wildcard symbol may retrieve word variants: su sach va nang cao hoi. hieu van ((am thuc) or (nam thuc)) va ((hanh di) OR (hanh vi)) va thiet*.