| 年份 | 单位：% |
| 2012 | 购买后可见 » |
| 2011 | 购买后可见 » |
| 2010 | 购买后可见 » |
| 2009 | 购买后可见 » |
| 2008 | 购买后可见 » |
| 2007 | 购买后可见 » |
| 2006 | 购买后可见 » |
| 2005 | 购买后可见 » |
| 2004 | 购买后可见 » |
| 2003 | 购买后可见 » |
| 2002 | 4.70 |
| 2001 | 3.80 |
| 2000 | 5.30 |
| 1999 | 3.60 |
| 1998 | 4.00 |
| 1997 | 4.50 |
| 1996 | 6.90 |
| 1995 | 7.80 |
| 1994 | 9.10 |
| 1993 | 8.90 |
| 1992 | 9.10 |
| 1991 | 4.40 |
| 1990 | 0.10 |
| 1989 | 2.10 |
| 1988 | 7.50 |
| 1987 | 2.50 |
| 1986 | 5.20 |
| 1985 | 5.50 |
| 1984 | 4.70 |
| 1983 | 4.70 |
| 1982 | 1.90 |
| 1981 | 0.80 |
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