Perhaps you should try some spelling variations:
mai khoi » mai khoa, cac khoi, dai khoa
tai khoa » da khoa, noi khoa
su sach » so sach, vu sach
dinh vi » dinh ve, dinh viet, dinh tri
thuc va » thuc vat, thuc dan, thuc day
truc va » thuc vat, trung va
qua ca » qua cac, qua cua, qua cai
sach v » sach va, sach y, sach 2
v nang » va nang, vu nang, van nang
vi va » vi van, vai va, vu va
thiet » thieu

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: su sach v nang ((mai khoi) OR (tai khoa)). hieu qua ca ((truc va) OR (thuc va)) dinh vi va thiet~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach v nang ((mai khoi) OR (tai khoa)). hieu qua ca ((truc va) or (thuc va)) dinh vi va thiet~".
• Adding a wildcard symbol may retrieve word variants: su sach v nang ((mai khoi) OR (tai khoa)). hieu qua ca ((truc va) or (thuc va)) dinh vi va thiet*.