Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
cac duc » cac du, cao duc, cac dac
hieu ve » hieu va, hieu van
v nang » va nang, vu nang, van nang
va anh » van anh, va danh, va hanh
ve cac » va cac, vien cac
x hoi » xa hoi, o hoi, x ho
vi su » va su, ve su, oi su
ki su » ky su

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 ((v nang) or (cam nang)) x hoi. hieu ve cac duc va anh ((vi su) OR (ki su)) tien~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ((v nang) OR (cam nang)) x hoi. hieu ve cac duc va anh ((vi su) OR (ki su)) tien*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ((v nang) or (cam nang)) x hoi. hieu ve cac duc va anh ((vi su) OR (ki su)) tien*".