Perhaps you should try some spelling variations:
trinh vat » trinh luat, sinh vat, trinh han
trinh van » trinh han, trinh quan, trinh toan
dung cong » dung trong
nam sach » ngan sach, nam danh, nam sao
san toan » van toan, dan toan, manh toan
toan cau » toan cao, toan ban, toan tap
he nam » ha nam, nghe nam

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

• If you are trying to use Boolean operators, they must be ALL CAPS: he nam sach - hanh ((trinh vat) OR (trinh van)) ((dang cong) OR (dung cong)) san toan cau~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "he nam sach - hanh ((trinh vat) or (trinh van)) ((dang cong) OR (dung cong)) san toan cau~".
• Adding a wildcard symbol may retrieve word variants: he nam sach - hanh ((trinh vat) or (trinh van)) ((dang cong) OR (dung cong)) san toan cau*.