Perhaps you should try some spelling variations:
hieu vien » hieu hien, hieu viec, thieu nien
ban duoc » tan duoc, van duoc, ban thuoc
can duoc » tan duoc, can cuoc, van duoc
sach thu » sach thue, sach thieu, sach tham
cua viet » ca viet, hoa viet, cua vat
thu nang » thi nang, thu hang, thu bang
dai hoi » dai hoc, dai hai, dai moi
mai hoi » mai khoi, lai hoi, mai doi
va hanh » van hanh, va thanh, va danh
su sach » so sach, vu sach
vi cua » vai cua, di cua

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 duoc) OR (ban duoc)) va hanh vi cua 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 duoc) OR (ban duoc)) va hanh vi cua 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 duoc) OR (ban duoc)) va hanh vi cua viet".
• Adding a wildcard symbol may retrieve word variants: su sach thu nang ((mai hoi) or (dai hoi)). hieu vien ((can duoc) OR (ban duoc)) va hanh vi cua viet*.