Perhaps you should try some spelling variations:
thanh dat » thanh san, thanh hai, thanh van
hieu van » hieu va, thien van, lieu va
van doan » van doanh, van toan, van hoan
thuc va » thuc vat, thuc dan, thuc day
dat cua » dai cua, day cua, mat cua
truc va » thuc vat, trung va
sach ky » sac ky, sach y, sach ty
cao hoi » cau hoi, co hoi, cao hoc
cua tre » cua te, cuu tre, cua triet

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

• Performing a fuzzy search may retrieve terms with similar spellings: tu ((sach ky) or (cac ky)) nang cao hoi. hieu van doan ((truc va) OR (thuc va)) thanh dat cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu ((sach ky) OR (cac ky)) nang cao hoi. hieu van doan ((truc va) OR (thuc va)) thanh dat cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu ((sach ky) or (cac ky)) nang cao hoi. hieu van doan ((truc va) OR (thuc va)) thanh dat cua tre".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) or (cac ky)) nang cao hoi. hieu van doan ((truc va) OR (thuc va)) thanh dat cua tre*.