Perhaps you should try some spelling variations:
khan thong » khap thong, khau thong, nhan thong
sach tren » sach tien, sach tranh
tren thuc » trien thuc, tron thuc, trinh thuc
thuc cach » thuoc sach, truoc cach, thuc hanh
cach hoan » cac khoan, hach toan, sach han
hoan phan » hoa phan, toan phan, doan phan
phan tong » phan trong, phan cong, han tong
sach tri » sach tai, sach truc, sach bai
tue cach » tu cach, ve cach, cuu cach
cach kho » bach khoa, cach thoi, cach pha
kho khan » khoa kham, khoa than
so sach » so sanh, bo sach, co sach
tu sach » thu sach, su sach, te sach

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( so sach tri tue cach kho khan thong ) or ( tu sach tren thuc cach hoan phan tong ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( so sach tri tue cach kho khan thong ) OR ( tu sach tren thuc cach hoan phan tong )).
• Adding a wildcard symbol may retrieve word variants: (( so sach tri tue cach kho khan thong ) or ( tu sach tren thuc cach hoan phan tong ))*.