验证文本框只能输入数字

<input id="txtProjectDates" runat="server" style="width: 29%" type="text" class="border" onkeyup="if(this.value.length==1){this.value=this.value.replace(/[^1-9]/g,'')}else{this.value=this.value.replace(//D/g,'')}" onafterpaste="if(this.value.length==1){this.value=this.value.replace(/[^1-9]/g,'')}else{this.value=this.value.replace(//D/g,'')}" />