Perhaps you should try some spelling variations:
mach khien » mach dien, cach thien
sach tien » sach thieu
sach tren » sach tranh
chai khoa » thai khoa, chi khoa, pham khoa
khien hoc » nhiet hoc, dien hoc
khoa hoc » hoa hoc
hoc khoa » hoc pho
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: (( te ((sach tien) OR (sach tren)) chai khoa hoc ) or ( tu mach khien hoc khoa hoc ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( te ((sach tien) OR (sach tren)) chai khoa hoc ) OR ( tu mach khien hoc khoa hoc ))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( te ((sach tien) OR (sach tren)) chai khoa hoc ) or ( tu mach khien hoc khoa hoc ))*".