Perhaps you should try some spelling variations:
dong trong » duong trong, dung trong, cong trong
lang trong » dung trong, cong trong
hieu sach » chieu sach, dien sach, hieu cac
hieu cach » hieu cac, chieu sach, hieu ca
nang cong » nang song, dang cong, bang cong
cong van » cong vang, cong san, song van
van tan » van tuan, van ban, van tai
tan cau » toan cau, van cau, tan ca

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc ((hieu sach) OR (hieu cach)) - ((lang trong) or (dong trong)) chuc nang cong van tan cau~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc ((hieu sach) OR (hieu cach)) - ((lang trong) OR (dong trong)) chuc nang cong van tan cau.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc ((hieu sach) OR (hieu cach)) - ((lang trong) or (dong trong)) chuc nang cong van tan cau".
• Adding a wildcard symbol may retrieve word variants: doc ((hieu sach) OR (hieu cach)) - ((lang trong) or (dong trong)) chuc nang cong van tan cau*.