Perhaps you should try some spelling variations:
"so sanh ki thuat co khi" » "do sanh ki thuat co khi", "so sanh ki thuat cbo khi"
"tu cach ky thuat o khi" » "tu cac ky thuat o khi", "tu cach ky thuat bo khi"
"te sach ky thuat do khi" » "toc sach ky thuat do khi", "te sac ky thuat do khi", "te sach y thuat do khi", "te sach ty thuat do khi", "te sach ky thuat doi khi", "te sach ky thuat do thi", "te sach ky thuat bo khi", "te sach ky thuat dbo khi"

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("so sanh ki thuat co khi") or ((("tu cach ky thuat o khi") or ("te sach ky thuat do khi"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("so sanh ki thuat co khi") OR ((("tu cach ky thuat o khi") OR ("te sach ky thuat do khi")))).
• Removing quotes may allow a broader search: (( so sanh ki thuat co khi ) or ((( tu cach ky thuat o khi ) or ( te sach ky thuat do khi )))).
• Adding a wildcard symbol may retrieve word variants: (("so sanh ki thuat co khi") or ((("tu cach ky thuat o khi") or ("te sach ky thuat do khi"))))*.