Perhaps you should try some spelling variations:
sach nganh » sach ngan, sach tranh, cac nganh
sach pham » sach tham, sach phat, sach phap
cong thai » cong hai, cong thanh, cong tac
hong thai » hong ha, hinh thai
so sach » so sanh, bo sach, co sach
su sach » vu sach
y khi » ly khi, ky khi, my khi

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: (( so sach nganh y khi đong luc ) OR ( su sach pham ((cong thai) OR (hong thai)) đong luc ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( so sach nganh y khi đong luc ) or ( su sach pham ((cong thai) OR (hong thai)) đong luc ))~".
• Adding a wildcard symbol may retrieve word variants: (( so sach nganh y khi đong luc ) or ( su sach pham ((cong thai) OR (hong thai)) đong luc ))*.