首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   92440篇
  免费   488篇
  国内免费   389篇
化学   26875篇
晶体学   912篇
力学   6874篇
数学   32316篇
物理学   16458篇
无线电   9882篇
  2023年   56篇
  2022年   131篇
  2021年   145篇
  2020年   171篇
  2019年   156篇
  2018年   11923篇
  2017年   11571篇
  2016年   7147篇
  2015年   1034篇
  2014年   556篇
  2013年   764篇
  2012年   4458篇
  2011年   11931篇
  2010年   7015篇
  2009年   6958篇
  2008年   7408篇
  2007年   9821篇
  2006年   383篇
  2005年   1708篇
  2004年   1860篇
  2003年   2263篇
  2002年   1178篇
  2001年   313篇
  2000年   346篇
  1999年   195篇
  1998年   229篇
  1997年   189篇
  1996年   245篇
  1995年   151篇
  1994年   114篇
  1993年   144篇
  1992年   117篇
  1991年   106篇
  1990年   98篇
  1989年   119篇
  1988年   105篇
  1987年   103篇
  1986年   99篇
  1985年   116篇
  1984年   102篇
  1983年   82篇
  1982年   92篇
  1981年   96篇
  1980年   96篇
  1979年   94篇
  1978年   80篇
  1977年   70篇
  1976年   72篇
  1975年   60篇
  1974年   54篇
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
1.
Wireless Personal Communications - In the present scenario, there is a boom in the demand of the users to achieve increased capacity, high data, low latency, and high-performance rates. 5G New...  相似文献   
2.

In this paper, we propose to use Artificial Bee Colony (ABC) optimization to solve the joint mode selection, channel assignment, and power allocation (JMSCPA) problem to maximize system throughput and spectral efficiency. JMSCPA is a problem where the allocation of channel and power depends on the mode selection. Such problems require two step solution and are called bi-level optimization problems. As bi-level optimization increases the complexity and computational time, we propose a modified version of single-level ABC algorithm aided with the adaptive transmission mode selection algorithm to allocate the cellular, reuse, and dedicated modes to the DUs along with channel and power allocation based on the network traffic load scenarios. A single variable, represented by the users (CUs and DUs) is used to allocate mode selection, and channel allocation to solve the JMSCPA problem, leading to a simpler solution with faster convergence, and significant reduction in the computational complexity which scales linearly with the number of users. Further, the proposed solution avoids premature stagnation of conventional ABC into local minima by incorporating a modification in its update procedure. The efficacy of the ABC-aided approach, as compared to the results reported in the literature, is validated by extensive numerical investigations under different simulation scenarios.

  相似文献   
3.
Wireless Personal Communications - This article presents a microstrip-fed octagonal shaped monopole antenna with dual band notched characteristics for UWB applications. Partial ground plane has...  相似文献   
4.
In the paper, the authors establish several integral representations for the generating functions of the large and little Schröder numbers and for the large and little Schröder numbers.  相似文献   
5.
Mesoscopic modeling at the pore scale offers great promise in exploring the underlying structure transport performance of flow through porous media. The present work studies the fluid flow subjected to capillarity-induced resonance in porous media characterized by different porous structure and wettability. The effects of porosity and wettability on the displacement behavior of the fluid flow through porous media are discussed. The results are presented in the form of temporal evolution of percentage saturation and displacement of the fluid front through porous media. The present study reveals that the vibration in the form of acoustic excitation could be significant in the mobilization of fluid through the porous media. The dependence of displacement of the fluid on physicochemical parameters like wettability of the surface, frequency along with the porosity is analyzed. It was observed that the mean displacement of the fluid is more in the case of invading fluid with wetting phase where the driving force strength is not so dominant.  相似文献   
6.
7.
We prove that the group of diffeomorphisms of the interval [0, 1] contains surface groups whose action on (0, 1) has no global fix point and such that only countably many points of the interval (0, 1) have non-trivial stabiliser.  相似文献   
8.
9.
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号