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   103403篇
  免费   13052篇
  国内免费   4608篇
电工技术   9193篇
技术理论   4篇
综合类   9581篇
化学工业   12836篇
金属工艺   6422篇
机械仪表   7461篇
建筑科学   8723篇
矿业工程   3686篇
能源动力   3158篇
轻工业   9567篇
水利工程   2955篇
石油天然气   4416篇
武器工业   1413篇
无线电   11821篇
一般工业技术   9293篇
冶金工业   3920篇
原子能技术   1464篇
自动化技术   15150篇
  2025年   471篇
  2024年   2175篇
  2023年   2185篇
  2022年   3578篇
  2021年   4461篇
  2020年   3723篇
  2019年   2792篇
  2018年   2876篇
  2017年   3136篇
  2016年   2909篇
  2015年   4262篇
  2014年   5442篇
  2013年   6135篇
  2012年   7449篇
  2011年   7697篇
  2010年   7264篇
  2009年   7083篇
  2008年   7354篇
  2007年   6667篇
  2006年   6255篇
  2005年   5114篇
  2004年   4021篇
  2003年   3488篇
  2002年   4124篇
  2001年   3510篇
  2000年   2138篇
  1999年   1335篇
  1998年   695篇
  1997年   546篇
  1996年   466篇
  1995年   389篇
  1994年   326篇
  1993年   203篇
  1992年   170篇
  1991年   141篇
  1990年   94篇
  1989年   82篇
  1988年   50篇
  1987年   44篇
  1986年   40篇
  1985年   13篇
  1984年   14篇
  1983年   8篇
  1982年   15篇
  1981年   22篇
  1980年   24篇
  1979年   16篇
  1959年   24篇
  1953年   4篇
  1951年   29篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Many cables containing 1.3-/spl mu/m zero-dispersion single-mode (SM) optical fibers are installed in trunk and access networks. Recently, there have been a number of studies on wavelength-division-multiplexing (WDM) systems designed to increase transmission capacity and flexibility. If we can construct WDM systems using SM optical-fiber cable networks designed to transmit using wavelengths in the 1.3-/spl mu/m window (O-band), this will prove very effective in reducing construction costs. It is therefore important to examine the wavelength dependence of the transmission characteristics of SM optical-fiber cables and networks that have already been installed and in which several optical fibers are joined. In this paper, we describe the measured optical characteristics of SM optical-fiber cables and installed optical-fiber cable networks at various wavelengths. The optical characteristics were stable in the 1.46 to 1.625-/spl mu/m wavelength range and we confirmed that the installed SM optical-fiber cable networks could be used for WDM system applications.  相似文献   
2.
提出了一种新的铝液夹杂物快速检测方法。导出了该法的检测原理方程。分析并试验研究了影响检测重复性和分辨率的因素。试验选择了较好的检测参数,并获得了较好的检测结果。  相似文献   
3.
4.
In this study, 16 cases of unilateral alveolar cleft with cleft lip and palate were repaired with autografts of cancellous bone (13 cases) or hydroxyapatite (3 cases). The grafts were covered by reflected mucoperiosteal flaps and a mucosal flap from the upper lip. Twelve of the thirteen cases were followed up for 1-5 years. Nine of whom using cancellous bone had bony continuity of the maxilla and 7 cases erupted permanent maxillary canines within the area of autografts. None of the 3 cases using hydroxyapatite erupted a canine tooth. The results showed that autograft was better than hydroxyapatite in terms of maxillary canine eruption.  相似文献   
5.
医患和谐与建筑设计   总被引:6,自引:0,他引:6  
谷建 《建筑创作》2005,(12):30-35
我们经常会发现,同样一位医护人员在医院工作场所和在其它地方会表现出不同的性格特质,无论是多么和善的人,到了那种医院环境有时就表现得面目可憎。其实,倒不是个人特质有所改变,而是医疗机构流程的流水线和环境造成的,恶劣的医患关系也因此而愈发不可调和。  相似文献   
6.
A simplified formula for the dispersion limit of single-mode-fiber intensity modulation/direct detection (IM/DD) systems is derived for arbitrary given normalized pulse width U, eye opening penalty X and source linewidth enhancement factor α. From the comparison with published theoretical analyses, computer simulation and experimental data, its validity and the limits of existing formulae are shown. Using this simple and general formula, one can easily obtain the dispersion limit of various fiber types under different working conditions in IM/DD systems  相似文献   
7.
Based on controls of structural style and the position in coalbed methane(CBM)development,we used a method of curvatures to study its relations with CBM development parameters.We calculated structural curvatures of contours of the No.3coal seam floor of the Shanxi Formation in the Zaoyuan block of the Qinshui Basin and analyzed its relations with development parameters of coalbed methane wells.The results show that structural curvature is negatively related to coal reservoir pressure,while positively related to permeability.With an increase in structural curvature,the average production of coalbed methane wells increases at first and then decreases,reaching the highest production at 0.02 m-1 of structural curvature.Therefore,structural curvature can be an important index for potential evaluation of coalbed methane development and provide a basis for siting coalbed methane wells.  相似文献   
8.
A new type of high temperature energy storage material was obtained through the melt infiltration method, using compounding SiC ceramic foam as matrix and Na2SO4 as phase change material. The resulting composite material was measured by XRD, SEM, TG-DSC methods. The experimental results indicate that the composite is composed of silicon carbide, sodium sulfate and square quartz, and no chemical reactions occurs between Na2SO4 and SiC matrix. Na2SO4 has a good bonding with the SiC ceramic foam matrix. As the composite material is characterized by high thermal energy storage density and high thermal conductivity, it is suit for energy storage under high temperature. Funded by the “863” Hi-Tech Research and Development Program of China (2008AA05Z418)  相似文献   
9.
Xia  Bin  Bai  Yuxuan  Yin  Junjie  Li  Yun  Xu  Jian 《Information Systems Frontiers》2021,23(2):285-298
Information Systems Frontiers - System logs that trace system states and record valuable events comprise a significant component of any computer system in our daily life. Each log contains...  相似文献   
10.
Jia  Wei  Gao  Jian  Xia  Wei  Zhao  Yang  Min  Hai  Lu  Jing-Ting 《国际自动化与计算杂志》2021,18(1):18-44

Palmprint recognition and palm vein recognition are two emerging biometrics technologies. In the past two decades, many traditional methods have been proposed for palmprint recognition and palm vein recognition, and have achieved impressive results. However, the research on deep learning-based palmprint recognition and palm vein recognition is still very preliminary. In this paper, in order to investigate the problem of deep learning based 2D and 3D palmprint recognition and palm vein recognition in-depth, we conduct performance evaluation of seventeen representative and classic convolutional neural networks (CNNs) on one 3D palmprint database, five 2D palmprint databases and two palm vein databases. A lot of experiments have been carried out in the conditions of different network structures, different learning rates, and different numbers of network layers. We have also conducted experiments on both separate data mode and mixed data mode. Experimental results show that these classic CNNs can achieve promising recognition results, and the recognition performance of recently proposed CNNs is better. Particularly, among classic CNNs, one of the recently proposed classic CNNs, i.e., EfficientNet achieves the best recognition accuracy. However, the recognition performance of classic CNNs is still slightly worse than that of some traditional recognition methods.

  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