python爬虫为什么不能抓取亚马逊页面？

这是我要搜的地址：https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=wireless+mouse
这是我写的爬虫代码：
import urllib2
content = urllib2.urlopen('https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=wireless+mouse').read()
print "content:", content
这是搜索结果报错：
PS C:\Users\xypcx\desktop\x-man\crawler> python crawlertest2.py
Traceback (most recent call last):
File "crawlertest2.py", line 2, in <module>
content = urllib2.urlopen('https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=wireless+mouse').read()
File "C:\python27\lib\urllib2.py", line 154, in urlopen
return opener.open(url, data, timeout)
File "C:\python27\lib\urllib2.py", line 437, in open
response = meth(req, response)
File "C:\python27\lib\urllib2.py", line 550, in http_response
'http', request, response, code, msg, hdrs)
File "C:\python27\lib\urllib2.py", line 475, in error
return self._call_chain(*args)
File "C:\python27\lib\urllib2.py", line 409, in _call_chain
result = func(*args)
File "C:\python27\lib\urllib2.py", line 558, in http_error_default
raise HTTPError(req.get_full_url(), code, msg, hdrs, fp)
urllib2.HTTPError: HTTP Error 503: Service Unavailable
试了好几次都不行
这是为什么？