C# 无法解析Microsoft.EntityFrameworkCore.SqlServer依赖项

我正在尝试在VS 2015更新3中安装Entity Framework Core，这样我就可以从现有数据库中对EF模型进行反向工程。我正在按照Microsoft的指示进行操作，这里：

但是，一旦将此行添加到my project.json文件中：

    "Microsoft.EntityFrameworkCore.SqlServer":  "1.1.0" 

我的引用中出现“包还原失败”错误，表示无法解决依赖关系。无论指定哪个版本，我都会收到相同的错误

下面是我的package.json文件的全部内容——我添加的唯一一行就是上面提到的那一行。当我从“新ASP.NET核心Web应用程序”模板创建项目时，默认情况下，所有其余的都在那里

我已尝试添加对Microsoft.EntityFrameworkCore的引用，如下所示：，但我收到了与该引用相关的相同错误消息（同样，无论我指定的版本如何）

有谁能解释问题是什么，以及一个人应该如何从提供的最少信息中找出这个问题

{
    "dependencies": {
        "Microsoft.NETCore.App": {
            "version": "1.0.1",
            "type": "platform"
        },
        "Microsoft.ApplicationInsights.AspNetCore": "1.0.0",
        "Microsoft.AspNetCore.Diagnostics": "1.0.0",
        "Microsoft.AspNetCore.Mvc": "1.0.1",
        "Microsoft.AspNetCore.Razor.Tools": {
            "version": "1.0.0-preview2-final",
            "type": "build"
        },
        "Microsoft.AspNetCore.Routing": "1.0.1",
        "Microsoft.AspNetCore.Server.IISIntegration": "1.0.0",
        "Microsoft.AspNetCore.Server.Kestrel": "1.0.1",
        "Microsoft.AspNetCore.StaticFiles": "1.0.0",
        "Microsoft.Extensions.Configuration.EnvironmentVariables": "1.0.0",
        "Microsoft.Extensions.Configuration.Json": "1.0.0",
        "Microsoft.Extensions.Logging": "1.0.0",
        "Microsoft.Extensions.Logging.Console": "1.0.0",
        "Microsoft.Extensions.Logging.Debug": "1.0.0",
        "Microsoft.Extensions.Options.ConfigurationExtensions": "1.0.0",
        "Microsoft.VisualStudio.Web.BrowserLink.Loader": "14.0.0",
        "Microsoft.EntityFrameworkCore.SqlServer":  "1.1.0"
    },

  "tools": {
    "BundlerMinifier.Core": "2.0.238",
    "Microsoft.AspNetCore.Razor.Tools": "1.0.0-preview2-final",
    "Microsoft.AspNetCore.Server.IISIntegration.Tools": "1.0.0-preview2-final"
  },

  "frameworks": {
    "netcoreapp1.0": {
      "imports": [
        "dotnet5.6",
        "portable-net45+win8"
      ]
    }
  },

  "buildOptions": {
    "emitEntryPoint": true,
    "preserveCompilationContext": true
  },

  "runtimeOptions": {
    "configProperties": {
      "System.GC.Server": true
    }
  },

  "publishOptions": {
    "include": [
      "wwwroot",
      "**/*.cshtml",
      "appsettings.json",
      "web.config"
    ]
  },

  "scripts": {
    "prepublish": [ "bower install", "dotnet bundle" ],
    "postpublish": [ "dotnet publish-iis --publish-folder %publish:OutputPath% --framework %publish:FullTargetFramework%" ]
  }
}

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我发现问题出在一个无效的包源上。我在NuGet包管理器中删除了无效的源代码，然后可以添加引用