Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
vien can » vien canh, vien cac, vien cao
thu nang » thi nang, thu hang, thu bang
cua viet » ca viet, cua vat, cua dieu
can quoc » han quoc, dan quoc, cac quoc
sach thu » sach thue, sach thieu, sach tham
va hanh » van hanh, va thanh, va danh
quoc va » nuoc va, duoc va, quoc gia
su sach » so sach, vu sach
dai hoi » dai hoc, dai hai, dai moi
mai hoi » mai khoi, lai hoi, mai doi

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 thu nang ((mai hoi) or (dai hoi)). hieu vien can quoc va hanh vi ((cua viet) OR (hoa viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach thu nang ((mai hoi) OR (dai hoi)). hieu vien can quoc va hanh vi ((cua viet) OR (hoa viet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach thu nang ((mai hoi) or (dai hoi)). hieu vien can quoc va hanh vi ((cua viet) OR (hoa viet))".
• Adding a wildcard symbol may retrieve word variants: su sach thu nang ((mai hoi) or (dai hoi)). hieu vien can quoc va hanh vi ((cua viet) OR (hoa viet))*.