| 年份 | 单位：% |
| 2010 | 93.30 |
| 2009 | 92.60 |
| 2008 | 93.70 |
| 2007 | 92.60 |
| 2006 | 93.60 |
| 2005 | 91.30 |
| 2004 | 91.00 |
| 2003 | 92.10 |
| 2002 | 93.20 |
| 2001 | 93.30 |
| 2000 | 94.00 |
| 1999 | 94.70 |
| 1998 | 95.20 |
| 1997 | 94.60 |
| 1996 | 73.00 |
| 1995 | 84.90 |
| 1994 | 86.80 |
| 1993 | 84.90 |
| 1992 | 56.40 |
| 1991 | 59.10 |
| 1990 | 61.70 |
| 1989 | 61.00 |
| 1988 | 60.70 |
| 1987 | 59.70 |
| 1986 | 59.40 |
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