Perhaps you should try some spelling variations:
xanh dai » vanh dai, xanh di, xanh tai
hieu van » hieu va, thien van, lieu va
cua viet » ca viet, hoa viet, cua vat
sach ky » sac ky, sach y, sach kem
van dau » van dao, phan dau
sach ty » sach y, sach tu, sach thu
truc va » thuc va, trung va
nang o » nang co, nang ho, nang ro
o hoi » co hoi, o hoc, o hai

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: thu ((sach ky) OR (sach ty)) nang o hoi. hieu van dau ((truc va) OR (thuc vat)) xanh dai cua viet~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu ((sach ky) or (sach ty)) nang o hoi. hieu van dau ((truc va) OR (thuc vat)) xanh dai cua viet~".
• Adding a wildcard symbol may retrieve word variants: thu ((sach ky) or (sach ty)) nang o hoi. hieu van dau ((truc va) OR (thuc vat)) xanh dai cua viet*.