Perhaps you should try some spelling variations:
khan thong » khap thong, khau thong, nhan thong
than thong » than thuong, toan thong, tran thong
sach tren » sach tien, sach tranh
tren thuc » trien thuc, tron thuc, trinh thuc
khoa than » khoa luan, hoa thai, hoa tan
thuc cac » thuc cach, tuc cac, phuc cac
cac khoa » cac khoan, cac khoi, dac khoa
mai thac » mai thach, mai hac, mai khac
thac cac » thoai cac, thanh cac, thuc cach
kho khan » khoa kham
te sach » toc sach
tu bach » vu bach, tu cach, tu bac
cac kho » cac khoi, cac khu, cac ho

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