Perhaps you should try some spelling variations:
khan thong » khap thong, khau thong, nhan thong
thuc cach » thuoc sach, truoc cach, thuc hanh
sach tren » sach tien, sach tranh
tren thuc » trien thuc, tron thuc, trinh thuc
cach khoa » bach khoa, cac khoa, cac khoan
sach tri » sach tai, sach truc, sach bai
tri thuc » tri tue
cach kho » bach khoa, cach thoi, cach pha
kho khan » khoa kham, khoa than
khoa han » khoa than, hoa han, khoa can
tu sach » thu sach, su sach, te sach
tong » cong, dong, song

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 tri thuc cach kho khan thong ) or ( tu sach tren thuc cach khoa han tong ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( tu sach tri thuc cach kho khan thong ) OR ( tu sach tren thuc cach khoa han tong )).
• Adding a wildcard symbol may retrieve word variants: (( tu sach tri thuc cach kho khan thong ) or ( tu sach tren thuc cach khoa han tong ))*.