Perhaps you should try some spelling variations:
hieu quan » lieu quan, thien quan, lien quan
sach hoi » sach doi, sach moi, cach thoi
hoi nang » hoi lang, ho nang, hoa nang
nang mai » nang ma, nang tai, lang mai
nam thuc » nam thuoc, am thuc, nam thu
cua viet » ca viet, hoa viet, cua vat
tu sach » thu sach, su sach, te sach
mai hoi » mai khoi, dai hoi, lai hoi
thuc va » thuc vat, thuc dan, thuc day
va hanh » van hanh, va thanh, va danh
vi cua » vai cua, di cua

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: tu sach hoi 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 hoi nang mai hoi. ((hieu quan) or (hieu qua)) nam thuc va hanh vi cua viet*.