Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cac nuoc » cap nuoc, hoc nuoc, dat nuoc
cua viet » ca viet, cua vat, cua dieu
nang xa » nang x, lang xa, nang ma
hieu ve » hieu va, hieu van
sach ky » sac ky, sach y, sach ty
cac toc » cac toi, cac thoi
va dau » va dao
dau vi » dau ve, dau va, dat vi

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach ky nang xa hoi. hieu ve ((cac nuoc) or (cac toc)) va dau vi ((cua viet) or (hoa viet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky nang xa hoi. hieu ve ((cac nuoc) OR (cac toc)) va dau vi ((cua viet) OR (hoa viet)).
• Adding a wildcard symbol may retrieve word variants: toc sach ky nang xa hoi. hieu ve ((cac nuoc) or (cac toc)) va dau vi ((cua viet) or (hoa viet))*.