Perhaps you should try some spelling variations:
hieu cac » hieu luc, hieu va, hieu van
cac chat » cao chat, cac thuat, cac nha
dinh dai » dinh dat, sinh dai, dinh dao
tu sach » thu sach, su sach, te sach
ky lang » ky dang, ky tang, tay lang
dai hoa » dai khoa, dai hoc, dai hoi
soc va » hoc va, loc va, goc va
doc va » duoc va, hoc va, duc va

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 lang) or (ky nang)) xa hoi. hieu cac chat ((soc va) OR (doc va)) dinh dai hoa viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ((ky lang) OR (ky nang)) xa hoi. hieu cac chat ((soc va) OR (doc va)) dinh dai hoa viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ((ky lang) or (ky nang)) xa hoi. hieu cac chat ((soc va) OR (doc va)) dinh dai hoa viet".
• Adding a wildcard symbol may retrieve word variants: tu sach ((ky lang) or (ky nang)) xa hoi. hieu cac chat ((soc va) OR (doc va)) dinh dai hoa viet*.