Perhaps you should try some spelling variations:
thanh dai » thanh hai, thanh tai, thanh dat
vat thanh » dat thanh, gat thanh, tat thanh
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, am thuc, nam thu
cua viet » hoa viet, cua vat, cua dieu
hoc sac » hoc sach, hoc cac, hoc mac
ca viet » va viet, co viet, hoa viet
sac ky » cac ky, sai ky
ma hoi » mai hoi, xa hoi, me hoi

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: hoc sac ky nang ((ma hoi) or (ma hoa)). hieu van nam thuc vat thanh dai ((cua viet) OR (ca viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: hoc sac ky nang ((ma hoi) OR (ma hoa)). hieu van nam thuc vat thanh dai ((cua viet) OR (ca viet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "hoc sac ky nang ((ma hoi) or (ma hoa)). hieu van nam thuc vat thanh dai ((cua viet) OR (ca viet))".
• Adding a wildcard symbol may retrieve word variants: hoc sac ky nang ((ma hoi) or (ma hoa)). hieu van nam thuc vat thanh dai ((cua viet) OR (ca viet))*.