Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
van hanh » van thanh, ban hanh, van anh
doc sach » hoc sach, nuoc sach, dac sac
chat huu » pham huu
chat cua » nhat cua, chat va, ca cua
hieu ve » hieu va, hieu van
tu nano » truc nano
cua tre » cua te, cuu tre, cua triet
va hoi » xa hoi, va hoc, va hoa
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: ((toc sach) OR (doc sach)) tu nano va hoi. hieu ve ((chat cua) or (chat huu)) van hanh vi cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) tu nano va hoi. hieu ve ((chat cua) OR (chat huu)) van hanh vi cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (doc sach)) tu nano va hoi. hieu ve ((chat cua) or (chat huu)) van hanh vi cua tre".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (doc sach)) tu nano va hoi. hieu ve ((chat cua) or (chat huu)) van hanh vi cua tre*.