Perhaps you should try some spelling variations:
"tu cach tam than do thi" » "tu cach lam than do thi", "tu cach ta than do thi", "tu canh tam than do thi", "tu cach ban than do thi", "tu cac tam than do thi", "tu cach tam than doc thi", "tu cach tam thanh do thi", "tu cach tam than vo thi"
"so sach ky thuat do khi" » "so sach ky thuat o khi", "bo sach ky thuat do khi", "co sach ky thuat do khi", "hoc sach ky thuat do khi", "so sac ky thuat do khi", "so sach y thuat do khi", "so sach ty thuat do khi", "so sach ky thuat doi khi", "so sach ky thuat co khi", "so sach ky thuat bo khi"
"so sanh ky thuat do khi" » "so sanh ky thuat o khi", "do sanh ky thuat do khi", "so hanh ky thuat do khi", "so sang ky thuat do khi", "so nganh ky thuat do khi", "so sanh ky thuat doi khi", "so sanh ky thuat co khi", "so sanh ky thuat bo 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 sach ky thuat do khi") OR ("so sanh ky thuat do khi"))) or ("tu cach tam than do thi"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("so sach ky thuat do khi") OR ("so sanh ky thuat do khi"))) OR ("tu cach tam than do thi")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"so sach ky thuat do khi\") OR (\"so sanh ky thuat do khi\"))) or (\"tu cach tam than do thi\"))".
• Removing quotes may allow a broader search: (((( so sach ky thuat do khi ) OR ( so sanh ky thuat do khi ))) or ( tu cach tam than do thi )).
• Adding a wildcard symbol may retrieve word variants: (((("so sach ky thuat do khi") OR ("so sanh ky thuat do khi"))) or ("tu cach tam than do thi"))*.