Perhaps you should try some spelling variations:
trung cong » truong cong, trong cong, trung uong
hieu quan » hieu qua, lieu quan, thien quan
doi hieu » doi chieu, doc hieu, doi hien
tinh cua » trinh cua, tinh chat, tranh cua
sinh cua » manh cua, dinh cuu, sinh va
cong van » cong vang, cong san, song van
van toan » van tuan, van tan, van thanh
toan ban » van ban

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: doi hieu quan - hanh ((((tinh cua) OR (sinh cua))) OR (trinh luat)) trung cong van toan ban~.
• Adding a wildcard symbol may retrieve word variants: doi hieu quan - hanh ((((tinh cua) or (sinh cua))) or (trinh luat)) trung cong van toan ban*.