Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
dan hanh » dang hanh, dan khanh, dan thanh
thuc dan » thuc hanh, hoc dan, thuc vat
nam thuc » nam thuoc, am thuc, nam thu
su sach » so sach, vu sach
ca viet » va viet, hoa viet, san viet
co viet » so viet, o viet, hoc viet
sach ky » sac ky, sach y, sach ty
hieu ve » hieu va
sang ma » tang ma, nang ma, sang tao
ky sang » ky nang, ky dang, ky tang
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: su sach ky sang ma hoi. ((hieu ve) or (hieu van)) nam thuc dan hanh vi ((ca viet) OR (co viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky sang ma hoi. ((hieu ve) OR (hieu van)) nam thuc dan hanh vi ((ca viet) OR (co viet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky sang ma hoi. ((hieu ve) or (hieu van)) nam thuc dan hanh vi ((ca viet) OR (co viet))".
• Adding a wildcard symbol may retrieve word variants: su sach ky sang ma hoi. ((hieu ve) or (hieu van)) nam thuc dan hanh vi ((ca viet) OR (co viet))*.