Interesting question. You'd have to look back to see when he was there the full year. From 1998 on...
1998- Took a a little bit of time off after the Royal Rumble, and then at the end of the year when he was buried alive in December. Not sure what his return date for his WM14 match was, but I imagined he missed a month's worth of action in it all.
1999- From mid-September to the end of the year, he was out
2000- Was out until May
2001- This is the one year I can remember him being there for all of it full-time
2002- Was out the last couple of months of the year
2003- Returned in late January and took a break or two in between that and getting buried alive by Vince, and at that point he was out the rest of the year
2004- Came back at Mania, and for the remainder of the year he took a short leave or two from what I recall
2005- I think he took a break after Mania (?), returned at some point during the draft, and then was gone between No Mercy and Survivor Series
2006- Came back at the Rumble, was there through his feuds with Henry and Khali... although I can't recall if he took a break after his loss at Judgement Day or not? If not, I think he was there almost the whole year
2007- Title reign was cut short due to his injury and he took off between May and September
2008- Was off between June and August, but outside of that, that might've been it
2009- Worked through to Mania, took off between April and August, feuded with Punk, and was there for the rest of the year as champion.
2010- Worked through to Mania, came back for a couple of one-off matches, came back for Summerslam-Bragging Rights for the Kane feud, and then left after.
2011- Only competed in one match/only a handful of appearances through to Mania. Didn't appear at all after
2012- Same as 2011, except he also appeared for Raw 1000
2013- Came back in March, did Mania, and stuck around to do a mini feud with The Shield before being taken out by them and leaving the rest of the year
2014- So far, only a few appearances and Mania, and that's it.
2008 he was there on SD for most of the year. From No Way Out-Summerslam, he was in the main feud with Edge.