C#中@字符d是个什么意思

string str = @"C:\Windows";

string str = "C:\\Windows";

string str = @"<script type=""text/javascript"">
    <!--
    -->
</script>";

string fileName = "D:\\文本文件\\text.txt";

string fileName = @"D:\文本文件\text.txt";

    string strSQL = "SELECT * FROM HumanResources.Employee AS e"
   + " INNER JOIN Person.Contact AS c"
   + " ON e.ContactID = c.ContactID"
   + " ORDER BY c.LastName";

    string strSQL = @"SELECT * FROM HumanResources.Employee AS e
                INNER JOIN Person.Contact AS c
                ON e.ContactID = c.ContactID
                ORDER BY c.LastName";

    public static void @static(int @int)
 {
            if (@int > 0)
            {
                System.Console.WriteLine("Positive Integer");
            }
            else if (@int == 0)
            {
                System.Console.WriteLine("Zero");
            }
            else
            {
                System.Console.WriteLine("Negative Integer");
            }
}