Perhaps you should try some spelling variations:
trien khat » trien khai, trien thuat, trien nha
sach trien » sach tren, sach thieu, cach thien
sach tien » sach tren, sach thieu
chai khoa » thai khoa, chi khoa, pham khoa
khat khoa » khuan khoa, pham khoa, vat khoa
sach xin » sach kinh, sach xa, vac xin
khoa hoc » hoa hoc
su sach » so sach, vu sach

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

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