Perhaps you should try some spelling variations:
dang khai » dang khoi, quang khai, dang thi
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
dang hai » hang hai, dung hai, dong hai
hieu van » hieu va, thien van, lieu va
van cac » van hac, van cau, van bac
sach ky » sach y, sach ty, sach kem
nang xa » nang x, lang xa, nang ma
sac ky » cac ky, sai ky
cua te » cua tu

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

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