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   95103篇
  免费   1542篇
  国内免费   1413篇
化学   28391篇
晶体学   856篇
力学   7065篇
综合类   38篇
数学   32629篇
物理学   17517篇
无线电   11562篇
  2023年   220篇
  2022年   267篇
  2021年   320篇
  2020年   296篇
  2019年   341篇
  2018年   12010篇
  2017年   11628篇
  2016年   7251篇
  2015年   1274篇
  2014年   766篇
  2013年   849篇
  2012年   4811篇
  2011年   12281篇
  2010年   7261篇
  2009年   7215篇
  2008年   7642篇
  2007年   10069篇
  2006年   656篇
  2005年   1949篇
  2004年   2022篇
  2003年   2432篇
  2002年   1285篇
  2001年   461篇
  2000年   499篇
  1999年   394篇
  1998年   388篇
  1997年   321篇
  1996年   357篇
  1995年   266篇
  1994年   221篇
  1993年   194篇
  1992年   151篇
  1991年   167篇
  1990年   115篇
  1989年   98篇
  1988年   102篇
  1987年   92篇
  1986年   76篇
  1985年   67篇
  1984年   54篇
  1983年   57篇
  1982年   47篇
  1981年   41篇
  1980年   48篇
  1979年   45篇
  1914年   45篇
  1913年   40篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
用等厚干涉测定液体折射率   总被引:7,自引:0,他引:7  
介绍一种采用等厚干涉原理测定液体折射率的简单可靠的方法。  相似文献   
2.
In this letter, a concise process technology is proposed for the first time to enable the fabrication of good quality three-dimensional (3-D) suspended radio frequency (RF) micro-inductors on bulk silicon, without utilizing the lithography process on sidewall and trench-bottom patterning. Samples were fabricated to demonstrate the applicability of the proposed process technology.  相似文献   
3.
4.
5.
It is explicitly shown that if phase transition occurs at the core of a newborn neutron star with moderately strong magnetic field strength, which populates only the electron’s Landau levels, then in the β -equilibrium condition, the quark core is energetically much more unstable than the neutron matter of identical physical condition.  相似文献   
6.
A novel single-longitudinal-mode (SLM) fiber ring laser that incorporates an equivalent phase-shifted fiber Bragg grating acting as an ultra-narrow bandpass filter in the laser cavity is proposed. The equivalent phase-shifted fiber Bragg grating has an ultra-narrow transmission bandwidth which ensures an SLM lasing. Stable SLM operation without mode hopping is demonstrated.  相似文献   
7.
In this paper, RF noise in 0.18-mum NMOSFETs concerning the contribution of carrier heating and hot carrier effect is characterized and analyzed in detail via a novel approach that modulates the channel carrier heating and number of hot carriers using body bias. We confirm qualitatively a negligible role of hot carrier effect on the channel noise in deep-submicrometer MOSFETs. For a device under reverse body bias (Vb), even though the increase in hot carrier population is clearly characterized by dc measurements, the device high-frequency noise is found to be irrelevant to the increase in the channel hot carriers. Experimental results show that the high-frequency noise is slightly reduced with the increase in |Vb|, and can be qualitatively explained by secondary effects such as the suppression of nonequilibrium channel noise and substrate induced noise. The reduction of NFmin and Rn with the increase in |Vb| may provide a possible methodology to finely adjust the device high-frequency noise performance for circuit design  相似文献   
8.
This paper describes some work carried out in the Scientific Research and Development Branch (SRDB) of the Home Office, intended to contribute to an overall aim of building up internal expertise in the field of expert systems. This was done by carrying out a number of pilot and demonstrator projects, two of which are described in some detail. The plan, which proved successful, was to build as far as possible on the relevant skills already possessed by an OR group in the branch. The lessons learned from these are summarized in the hope that they will be of use to other groups who wish to become involved in this important area.  相似文献   
9.
前言随着电信市场竞争越来越激烈,各种电信业务资费呈下降趋势,因此大客户原来主要采用低速专线来组织其内部通信网的方式也发生变化,逐渐采用高速的2M电路或者LAN专线、VPN等IP电路进行组网。目前大客户主要分布在金融、政府、行政、外企、交通等行业,其采用运营商电路来组织其内部通信网络以满足中心网点与各个分支网点、分支机构的语音、数  相似文献   
10.
It is well known that tile-boundary artifacts occur in wavelet-based lossy image coding. However, until now, their cause has not been understood well. In this paper, we show that boundary artifacts are an inescapable consequence of the usual methods used to choose tile size and the type of symmetric extension employed in a wavelet-based image decomposition system. This paper presents a novel method for reducing these tile-boundary artifacts. The method employs odd tile sizes (2N + 1 samples) rather than the conventional even tile sizes (2N samples). It is shown that, for the same bit rate, an image compressed using an odd tile length low-pass first (OTLPF) convention has significantly less boundary artifacts than an image compressed using even tile sizes. The OTLPF convention can also be incorporated into the JPEG 2000 image compression algorithm using extensions defined in Part 2 of this standard.  相似文献   
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