Perhaps you should try some spelling variations:
tren thuoc » trien thuoc, tren thuc, trung thuoc
khan thong » khap thong, khau thong, nhan thong
sach tren » sach tien, sach tranh
khang kho » khong kho, khong khoa, hang khoa
hoc thong » hoc thuong, hoc trong, hoc hong
kho khan » khoa kham, khoa than
tren hoc » truyen hoc, trung hoc, triet hoc
cac khoa » cac khoan, cac khoi, dac khoa
khoa hoc » hoa hoc
te sach » toc sach
hoc cac » hoc cao

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 tren thuoc khang kho khan thong ) or ( te sach tren hoc cac khoa hoc thong ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( te sach tren thuoc khang kho khan thong ) OR ( te sach tren hoc cac khoa hoc thong )).
• Adding a wildcard symbol may retrieve word variants: (( te sach tren thuoc khang kho khan thong ) or ( te sach tren hoc cac khoa hoc thong ))*.