Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, lieu va
hanh tai » thanh tai, hang tai, han tai
sach ky » sach y, sach ty, sach kem
van cam » van nam, van lam, van cau
so viet » hoc viet
nang xa » nang x, lang xa, nang ma
sac ky » cac ky, sai ky
tai so » tai sao, dai so, tai co
tu xa » tu xay, tu va, tu ma
te xa » te va

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

• Performing a fuzzy search may retrieve terms with similar spellings: so ((sach ky) or (sac ky)) nang xa hoi. hieu van cam ((tu xa) OR (te xa)) hanh tai so viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so ((sach ky) OR (sac ky)) nang xa hoi. hieu van cam ((tu xa) OR (te xa)) hanh tai so viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so ((sach ky) or (sac ky)) nang xa hoi. hieu van cam ((tu xa) OR (te xa)) hanh tai so viet".
• Adding a wildcard symbol may retrieve word variants: so ((sach ky) or (sac ky)) nang xa hoi. hieu van cam ((tu xa) OR (te xa)) hanh tai so viet*.