<input type="text" onkeydown="javascript:return isNumber(event,value);"/>

js部分：

<script>
isNumber = function (e,s) {
	var t = 0;
	//只能输入一个小数点 
	if(s.indexOf(".") != -1){
		t = 1;
	}
	
	if(t==1&&((event.keyCode == 190)||(event.keyCode == 110))){
		return false;
	}

	//IE浏览器 
    if ($.browser.msie) {
       if ( ((event.keyCode > 47) && (event.keyCode < 58)) ||  ((event.keyCode > 95) && (event.keyCode < 106)) || 
             (event.keyCode == 8 || (event.keyCode == 190) || (event.keyCode == 110))) { 
           return true;  
       } else {  
           return false;  
       }  
    }else {
        if ( ((e.which > 47) && (e.which < 58)) || ((e.which > 95) && (e.which < 106)) ||
              (e.which == 8)||(e.which == 110)||(e.which == 190)) {  
            return true;  
        } else {  
           return false;  
        }  
    } 
	return true;
}
</script>