Perhaps you should try some spelling variations:
hieu quan » lieu quan, thien quan, lien quan
nang mai » nang ma, nang tai, lang mai
nam thuc » nam thuoc, am thuc, nam thu
cua viet » ca viet, hoa viet, cua vat
ho nang » thi nang, kha nang, cao nang
mai hoi » mai khoi, dai hoi, lai hoi
su sach » so sach, vu sach
thuc va » thuc vat, thuc dan, thuc day
va hanh » van hanh, va thanh, va danh
tu sach » thu sach, te sach, tu cach
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: ((tu sach) OR (su sach)) ho nang mai hoi. ((hieu quan) or (hieu qua)) nam thuc va hanh vi cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((tu sach) OR (su sach)) ho nang mai hoi. ((hieu quan) OR (hieu qua)) nam thuc va hanh vi cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((tu sach) OR (su sach)) ho nang mai hoi. ((hieu quan) or (hieu qua)) nam thuc va hanh vi cua viet".
• Adding a wildcard symbol may retrieve word variants: ((tu sach) OR (su sach)) ho nang mai hoi. ((hieu quan) or (hieu qua)) nam thuc va hanh vi cua viet*.