Perhaps you should try some spelling variations:
hieu sach » chieu sach, hieu cach, dien sach
toan nang » toan mang, toan tang, toan thang
nang dong » nang song, lang dong, nang luong
dong cong » duong cong, dung cong, dang cong
doc hieu » toc thieu, hoc thieu, hoc hien
cong dan » cong san, cong tan, huong dan
toan ban » van ban

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 - tinh toan nang dong cong dan ((toan tap) or (toan ban))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc hieu sach - tinh toan nang dong cong dan ((toan tap) OR (toan ban))*.