You need to adjust your robots.txt file in root directory of your website.
This will block indexing any request uri, coming after "?":
Disallow: /qa/*?
Or you can be more specific and block just what you want (but I prefer first solution):
Disallow: /qa/*?show=
Disallow: /qa/*?to=
etc
Also, you have rel="canonical" tag already on every page, which states canonical urls, which tell search engines what page they should index.
This tag can also be used on pagers (/list?page=1, /list?page=2, ..., /list?page=N). As it often happens, there can be duplicate content on these pages, category description for example. SE will crawl all these pages, will index links and will follow them, but if tag will state that /list page is the canonical url, Google will keep only that page in main index without penalties.
And even in your example qa/229/how-can-i-get-high-quality-backlinks?show=224 page has qa/229/how-can-i-get-high-quality-backlinks canonical url.
