Toaru Majutsu no Index: New Testament - Volume 9, Chapter 6: Shifting and Fluctuating World. Version_Alpha.

A small skeleton in the undead world inadvertently passed through to the end of the world. His limited IQ found that his boss seemed to be weak. As a good value, he decided to protect the boss first. When he was annoyed, he would do it directly. Turn the boss to his own position. Gao Shuo inadvertently encountered a strange encounter. At first, he used this skeleton as a combat partner to raise it. Until one day, this skeleton became a man, and Gao Shuo made a new decision. Don’t hesitate to rush to eat. Meng pet sweet text! ! ! (Little Skeleton) The Lord is accepted by the Lord! ! ! The important thing is that the protagonist can be transformed between the monks and the people three times.

- Description from Novelupdates

A scientific genius named Thomas Harrier was transmigrated to an imperial prince body after a car accident that took his life. He found out that he is in a world similar to our own with a timeline akin to early twentieth century. The body that he is occupying was the imperial prince of a failing empire who suddenly rose to power after a successful assassination attempt of his father. Unaware that the attack is just the beginning of what is to come. He faces many challenges throughout. Will Thomas Harrier be able to live his second life in peace while running an empire and getting it back to its former glory? Or will he succumb into a conspiracy lurking within the country's borders?

Expect some:

Cold war era techs.

Super battleship with advanced electronics, propulsion, and fire control systems?
Helicopters?
Missiles?
Modern medicines and equipment?
AC-130?
A nuke?
Challenger or Abrams or Leopard?
F-4 Phantom or MIG-21?
Colored TV's.

Everything!!!

PS. Cover not mine, I just found it on google.

Ye Yun traveled to the Star Railway World and obtained the “Shop of All Worlds” system.Through this system, Ye Yun can sell items from across different worlds and invite guests from other realms to visit the Star Rail.His first encounter is with a space traveler named Stelle, and soon... many new experiences begin to unfold.Each time the shop's turnover reaches a certain amount, Ye Yun receives a reward from the system.

“From today onwards, you will become the Envoy of one of the Main Gods in the Dimensions of Gods. You will travel from one world to another and through that, you will attain what others will never obtain in their entire life.”

The moment these words echoed in Fang Li’s head, Fang Li’s life was destined to be extraordinary…

- Description from novelupdates