Perhaps you should try some spelling variations:
thanh dat » thanh san, thanh van, thanh ha
thanh hai » thanh phan, thanh hoa, thanh san
hieu van » hieu va, thien van, lieu va
sach ky » sac ky, sach y, sach ty
cao hoi » cau hoi, co hoi, cao hoc
van cau » van dau, van hau, van chat
truc va » thuc va, thuc vat, trung va
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 cau truc va ((thanh dat) OR (thanh hai)) 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 cau truc va ((thanh dat) OR (thanh hai)) 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 cau truc va ((thanh dat) OR (thanh hai)) cua tre".
• Adding a wildcard symbol may retrieve word variants: tu ((sach ky) or (cac ky)) nang cao hoi. hieu van cau truc va ((thanh dat) OR (thanh hai)) cua tre*.