Perhaps you should try some spelling variations:
manh trung » manh tung, thanh trung, manh hung
hieu sach » chieu sach, hieu cach, dien sach
trung cap » truong cao, trung tam
hieu luc » hieu luat, hieu qua
can cong » cac cong, cao cong, van cong
tan thai » ban thai, tan tai, van thai
tay thai » lay thai, toc thai, y thai
cap can » cap han, cap van, tap can

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: doc ((hieu sach) OR (hieu luc)) - manh trung cap can cong ((tan thai) OR (tay thai)) cao~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "doc ((hieu sach) or (hieu luc)) - manh trung cap can cong ((tan thai) OR (tay thai)) cao~".
• Adding a wildcard symbol may retrieve word variants: doc ((hieu sach) or (hieu luc)) - manh trung cap can cong ((tan thai) OR (tay thai)) cao*.