Perhaps you should try some spelling variations:
van viet » san viet, gian viet, tran viet
thuc van » thuc vat, thuc dan, thuc va
nam thuc » nam thuoc, am thuc, nam thu
hanh va » hang va
sach ky » sac ky, sach y, sach ty
su sach » so sach, vu sach
ky dang » ky nang, ky danh
hieu le » hieu ve, hieu he, hieu ly
le nam » ly nam, he nam, le na
me hoi » le hoi

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 dang ((me hoi) or (ma hoa)). hieu le nam thuc van ((hanh va) OR (hanh vi)) van viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach ky dang ((me hoi) OR (ma hoa)). hieu le nam thuc van ((hanh va) OR (hanh vi)) van viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach ky dang ((me hoi) or (ma hoa)). hieu le nam thuc van ((hanh va) OR (hanh vi)) van viet".
• Adding a wildcard symbol may retrieve word variants: su sach ky dang ((me hoi) or (ma hoa)). hieu le nam thuc van ((hanh va) OR (hanh vi)) van viet*.