Perhaps you should try some spelling variations:
sach tranh » canh tranh
mach khien » mach dien, cach thien
sach tren » sach tien
chai khoa » thai khoa, pham khoa, tai khoa
khien chi » khien cho, kien chi, khien khi
khoa hoc » hoa hoc
chi khoa » nhi khoa, chua khoa, thai khoa
tu mach » tu cach, tu manh, tu hach

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( tu ((sach tren) OR (sach tranh)) chai khoa hoc ) or ( tu mach khien chi khoa hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( tu ((sach tren) OR (sach tranh)) chai khoa hoc ) OR ( tu mach khien chi khoa hoc )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( tu ((sach tren) OR (sach tranh)) chai khoa hoc ) or ( tu mach khien chi khoa hoc ))".
• Adding a wildcard symbol may retrieve word variants: (( tu ((sach tren) OR (sach tranh)) chai khoa hoc ) or ( tu mach khien chi khoa hoc ))*.