ISO体系认证证书有没有有效期有效期是多久？

<!--360分析--> <script> (function(b,a,e,h,f,c,g,s){b[h]=b[h]||function(){(b[h].c=b[h].c||[]).push(arguments)}; b[h].s=!!c;g=a.getElementsByTagName(e)[0];s=a.createElement(e); s.src="//s.union.360.cn/"+f+".js";s.defer=!0;s.async=!0;g.parentNode.insertBefore(s,g) })(window,document,"script","_qha",366917,false); </script> <script> var _hmt = _hmt || []; (function() { var hm = document.createElement("script"); hm.src = "https://hm.baidu.com/hm.js?4c355d10edd5484d8a235161ce34a89b"; var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(hm, s); })(); </script> <!--商务通--> <script> var _hmt = _hmt || []; (function() { var hm = document.createElement("script"); hm.src = "https://hm.baidu.com/hm.js?726fbe5925292dc7f7b8c4ec07ada508"; var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(hm, s); })(); </script>