https://github.com/yanckst/search-nuget-v3/blob/master/search.linq

<Query Kind="Program">
  <NuGetReference>NuGet.PackageManagement</NuGetReference>
  <NuGetReference>NuGet.Packaging</NuGetReference>
  <Namespace>System.Threading.Tasks</Namespace>
  <Namespace>NuGet.Protocol.Core.Types</Namespace>
  <Namespace>NuGet.Configuration</Namespace>
  <Namespace>NuGet.ProjectManagement</Namespace>
  <Namespace>NuGet.PackageManagement</Namespace>
</Query>

NuGet.Protocol.Core.Types.SourceRepository sourceRepository;

async Task Main()
{
    InitializeNugetDependencies();
    var jsonNugetPackages = await SearchTestPackage("Newtonsoft.Json");
    jsonNugetPackages.Dump();
}

private void InitializeNugetDependencies() 
{
    List<Lazy<INuGetResourceProvider>> providers = new List<Lazy<INuGetResourceProvider>>();
    providers.AddRange(Repository.Provider.GetCoreV3());

    PackageSource packageSource = new PackageSource("https://api.nuget.org/v3/index.json");
    this.sourceRepository = new NuGet.Protocol.Core.Types.SourceRepository(packageSource, providers);
}


private async Task<IEnumerable<IPackageSearchMetadata>> SearchTestPackage(string packageName)
{
    var searchResource = await this.sourceRepository.GetResourceAsync<PackageSearchResource>();
    var supportedFramework = new[] { ".NETFramework,Version=v4.6" };
    var searchFilter = new SearchFilter(true)
    {
        SupportedFrameworks = supportedFramework,
        IncludeDelisted = false
    };

    return await searchResource.SearchAsync(packageName, searchFilter, 0, 10, null, CancellationToken.None);
}

C# 调用NuGet 实现获取包的顶级依赖

using System;
using static NuGet.Frameworks.FrameworkConstants;
using static NuGet.Protocol.Core.Types.Repository;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using NuGet.Common;
using NuGet.Packaging.Core;
using NuGet.Protocol;
using NuGet.Protocol.Core.Types;
//using NuGet.Test.Utility;
using NuGet.Versioning;
using NuGet.PackageManagement;
namespace NuGet_Remote_develop
{
    internal class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
            Console.WriteLine("!!!!");
            // Set up
            var packageIdentityA100 = new PackageIdentity("a", NuGetVersion.Parse("1.0.0"));
            Console.WriteLine("%%%%%");
            var packageIdentityB100 = new PackageIdentity("b", NuGetVersion.Parse("1.0.0"));
            var packageIdentityC100 = new PackageIdentity("c", NuGetVersion.Parse("1.0.0"));
            var packageIdentityC110 = new PackageIdentity("c", NuGetVersion.Parse("1.1.0"));
            var packageIdentityD100 = new PackageIdentity("d", NuGetVersion.Parse("1.0.0"));


            var packageDependencyInfos = new List<PackageDependencyInfo>();
            //制造关于A的依赖图
            var packageDependencyInfoA = new PackageDependencyInfo(packageIdentityA100,
                new PackageDependency[] {
                    new PackageDependency(packageIdentityB100.Id, VersionRange.Parse(packageIdentityB100.Version.OriginalVersion)),
                    new PackageDependency(packageIdentityC100.Id, VersionRange.Parse(packageIdentityC100.Version.OriginalVersion)),
                });
            var packageDependencyInfoB = new PackageDependencyInfo(packageIdentityB100,
                new PackageDependency[] {
                    new PackageDependency(packageIdentityD100.Id, VersionRange.Parse(packageIdentityD100.Version.OriginalVersion)),
                });
            var packageDependencyInfoC = new PackageDependencyInfo(packageIdentityC110, Enumerable.Empty<PackageDependency>());
            var packageDependencyInfoD = new PackageDependencyInfo(packageIdentityD100, Enumerable.Empty<PackageDependency>());

            //增加所有的依赖关系图
            packageDependencyInfos.Add(packageDependencyInfoA);
            packageDependencyInfos.Add(packageDependencyInfoB);
            packageDependencyInfos.Add(packageDependencyInfoC);
            packageDependencyInfos.Add(packageDependencyInfoD);

            // Act————》》获取依赖图
            var packageWithDependants = PackageGraphAnalysisUtilities.GetPackagesWithDependants(packageDependencyInfos);
            Console.WriteLine(packageWithDependants);
            Console.WriteLine("*****");
            foreach (var package in packageWithDependants)
            {
                switch (package.Identity.Id)
                {
                    case "a":
                        {
                            //看他是不是没有其他的依赖项
                            Console.WriteLine(package.DependantPackages.Count);
                            Console.WriteLine(package.IsTopLevelPackage);
                            break;
                        }
                    case "b":
                        {
                            //看他是不是只有一个依赖项，而且这个依赖项是A。并且他不是直接依赖
                            Console.WriteLine( package.DependantPackages.Count);
                            Console.WriteLine(package.DependantPackages.Single().Id);
                            Console.WriteLine(package.IsTopLevelPackage);
                            break;
                        }
                    case "c":
                        {
                            Console.WriteLine(package.DependantPackages.Count);
                            Console.WriteLine(package.IsTopLevelPackage);
                            break;
                        }
                    case "d":
                        {
                            Console.WriteLine( package.DependantPackages.Count);
                            Console.WriteLine( package.DependantPackages.Single().Id);
                            Console.WriteLine(package.IsTopLevelPackage);
                            break;
                        }
                    default:
                        {
                            Console.WriteLine($"Unexpected package {package.Identity}");
                            break;
                        }
                }
            }
            Console.ReadKey();
        }
    }
}