Perhaps you should try some spelling variations:
hieu quan » lieu quan, thien quan, lien quan
cua viet » ca viet, hoa viet, cua vat
thuc dan » thuc hanh, hoc dan, thuc vat
nam thuc » nam thuoc, am thuc, nam thu
sach lo » sach dao, sach doi, sach hoi
hanh di » hanh de, hang di, danh di
tu sach » thu sach, su sach, te sach
nang ma » tang ma, sang ma, nang cao
lo nang » ho nang, ly nang, loai nang
ma hoi » mai hoi, xa hoi, ma hoa

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 lo nang ma hoi. ((hieu quan) or (hieu qua)) nam thuc dan ((hanh di) OR (hanh vi)) cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach lo nang ma hoi. ((hieu quan) OR (hieu qua)) nam thuc dan ((hanh di) OR (hanh vi)) cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach lo nang ma hoi. ((hieu quan) or (hieu qua)) nam thuc dan ((hanh di) OR (hanh vi)) cua viet".
• Adding a wildcard symbol may retrieve word variants: tu sach lo nang ma hoi. ((hieu quan) or (hieu qua)) nam thuc dan ((hanh di) OR (hanh vi)) cua viet*.