Perhaps you should try some spelling variations:
doc sach » hoc sach, toc sach, nuoc sach
chat cua » nhat cua, chat va, chat huu
van hanh » van thanh, ban hanh, van anh
lo hang » ly hang, cho hang, le thang
le hang » le hoang, le thang, le hong
hieu ve » hieu va, hieu van
cua tre » cua te, cuu tre, cua triet
vi cua » vai cua, di cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: doc sach ((lo hang) OR (le hang)) xa hoi. hieu ve ((chat cua) or (chao xu)) van hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: doc sach ((lo hang) OR (le hang)) xa hoi. hieu ve ((chat cua) OR (chao xu)) van hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc sach ((lo hang) OR (le hang)) xa hoi. hieu ve ((chat cua) or (chao xu)) van hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: doc sach ((lo hang) OR (le hang)) xa hoi. hieu ve ((chat cua) or (chao xu)) van hanh vi cua tre*.