共 6 条
- [2] Ohl R., 1948, U.S. Patent, Patent No. [2, 443,542, 2443542]
- [3] OHL RS, 1946, Patent No. 2402839
- [4] OHL RS, 1952, BELL SYSTEM TECH JAN
- [5] Ohl RS., 1946, United States Pat off, Patent No. 2402662
- [6] SCAFF JH, 1949, T AM I MIN MET ENG, V185, P383