Perhaps you should try some spelling variations:
"cuon sach ky thuat o khi" » "duong sach ky thuat o khi", "cuoc cach ky thuat o khi", "co sach ky thuat o khi", "cuon sach ky thuat do khi", "cuon sach y thuat o khi", "cuon sach ty thuat o khi", "cuon sach kem thuat o khi", "cuon sach ky thuat bo khi"
"su sac ky thuat co khi" » "su sac ky thuat do khi", "su sach ky thuat co khi", "su cac ky thuat co khi", "su xac ky thuat co khi", "su sai ky thuat co khi", "su sac ky thuat cbo khi"
"so sanh ky thuat o khi" » "do sanh ky thuat o khi", "so hanh ky thuat o khi", "so sang ky thuat o khi", "so nganh ky thuat o khi", "so sanh ky thuat do khi", "so sanh ky thuat bo khi"

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 ky thuat o khi") or ("cuon sach ky thuat o khi"))) or ("su sac ky thuat co khi"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("so sanh ky thuat o khi") OR ("cuon sach ky thuat o khi"))) OR ("su sac ky thuat co khi")).
• Removing quotes may allow a broader search: (((( so sanh ky thuat o khi ) or ( cuon sach ky thuat o khi ))) or ( su sac ky thuat co khi )).
• Adding a wildcard symbol may retrieve word variants: (((("so sanh ky thuat o khi") or ("cuon sach ky thuat o khi"))) or ("su sac ky thuat co khi"))*.