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   202520篇
  免费   2704篇
  国内免费   649篇
电工技术   4097篇
综合类   127篇
化学工业   27705篇
金属工艺   7597篇
机械仪表   5566篇
建筑科学   4275篇
矿业工程   757篇
能源动力   4814篇
轻工业   14760篇
水利工程   1754篇
石油天然气   2856篇
武器工业   7篇
无线电   27698篇
一般工业技术   38547篇
冶金工业   46134篇
原子能技术   3570篇
自动化技术   15609篇
  2021年   1393篇
  2020年   1068篇
  2019年   1419篇
  2018年   2285篇
  2017年   2249篇
  2016年   2359篇
  2015年   1636篇
  2014年   2841篇
  2013年   8270篇
  2012年   4817篇
  2011年   6565篇
  2010年   5223篇
  2009年   6022篇
  2008年   6471篇
  2007年   6473篇
  2006年   5874篇
  2005年   5513篇
  2004年   5413篇
  2003年   5217篇
  2002年   5042篇
  2001年   5395篇
  2000年   4976篇
  1999年   5483篇
  1998年   15683篇
  1997年   10373篇
  1996年   7976篇
  1995年   5824篇
  1994年   5059篇
  1993年   5059篇
  1992年   3416篇
  1991年   3275篇
  1990年   3230篇
  1989年   3060篇
  1988年   2798篇
  1987年   2248篇
  1986年   2317篇
  1985年   2622篇
  1984年   2322篇
  1983年   2069篇
  1982年   1913篇
  1981年   2051篇
  1980年   1798篇
  1979年   1666篇
  1978年   1660篇
  1977年   2035篇
  1976年   2714篇
  1975年   1427篇
  1974年   1371篇
  1973年   1321篇
  1972年   1125篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
Russian Microelectronics - The recently developed nanomaterials and their production technologies as intellectual property objects (IPOs) are considered. The role of the informational-analytical...  相似文献   
63.
Wireless Personal Communications - The majority of security systems for wireless sensor networks are based on symmetric encryption. The main open issue for these approaches concerns the...  相似文献   
64.
65.
66.
The development of a miniature triaxial apparatus is presented. In conjunction with an X-ray micro-tomography (termed as X-ray μCT hereafter) facility and advanced image processing techniques, this apparatus can be used for in situ investigation of the micro-scale mechanical behavior of granular soils under shear. The apparatus allows for triaxial testing of a miniature dry sample with a size of 8mm×16mm (diameter × height). In situ triaxial testing of a 0.4–0.8 mm Leighton Buzzard sand (LBS) under a constant confining pressure of 500 kPa is presented. The evolutions of local porosities (i.e., the porosities of regions associated with individual particles), particle kinematics (i.e., particle translation and particle rotation) of the sample during the shear are quantitatively studied using image processing and analysis techniques. Meanwhile, a novel method is presented to quantify the volumetric strain distribution of the sample based on the results of local porosities and particle tracking. It is found that the sample, with nearly homogenous initial local porosities, starts to exhibit obvious inhomogeneity of local porosities and localization of particle kinematics and volumetric strain around the peak of deviatoric stress. In the post-peak shear stage, large local porosities and volumetric dilation mainly occur in a localized band. The developed triaxial apparatus, in its combined use of X-ray μCT imaging techniques, is a powerful tool to investigate the micro-scale mechanical behavior of granular soils.  相似文献   
67.
The primary goal of this study is to create and test a lecture‐capture system that can rearrange visual elements while recording is still taking place, in such a way that student performance can be positively influenced. The system we have devised is capable of integrating and rearranging multimedia sources, including learning content, the instructor and students' images, into lecture videos that are embedded in a website for students to review after school. The present study employed a two‐group experimental design, with 153 participants (145 females and 8 males) making up an experimental group in which lecture courses were recorded using the new lecture‐capture system, and 149 participants (140 females and 9 males) forming a control group whose lectures were recorded by traditional means. All participants were in the freshman college and studying Introduction to Computer and Information Science in one of six classes, and were randomly assigned to one of the two groups. The participants' midterm examination and final examination scores were collected as indicators of their academic performance, with their mathematics entrance scores used as a pre‐test. The findings obtained from analysis of covariance (ANCOVA) suggest that appropriate rearrangement of visual elements in lecture videos can significantly impact students' learning performance.  相似文献   
68.
The data on the use of solar photovoltaic plants (PVPs) for providing a reliable and guaranteed power supply to telecommunication systems and cellular communication systems in the conditions prevalent in Uzbekistan are given. The research-based structures developed by OOO MIR SOLAR and the selection of PVP elements ensuring their reliable operation are described. The main influencing factors are discussed, and the use of effective combinations of different types of panels (from monocrystalline and polycrystalline silicon) and a specially developed controller are considered.  相似文献   
69.
The dynamic characteristics of a saw gin as a subsystem with lumped and distributed parameters are considered in the paper. On the basis of investigation of the machine assembly, graphs are drawn that allow establishing the maximum values of the angle of relative rotation and the angle of rotation of the saw cylinder shaft under torsion.  相似文献   
70.
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