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   282307篇
  免费   3091篇
  国内免费   1311篇
电工技术   4846篇
综合类   525篇
化学工业   40983篇
金属工艺   11211篇
机械仪表   8464篇
建筑科学   6656篇
矿业工程   1629篇
能源动力   7082篇
轻工业   22825篇
水利工程   3089篇
石油天然气   5806篇
武器工业   44篇
无线电   33739篇
一般工业技术   57031篇
冶金工业   51975篇
原子能技术   7521篇
自动化技术   23283篇
  2021年   2201篇
  2019年   2101篇
  2018年   3624篇
  2017年   3706篇
  2016年   3943篇
  2015年   2509篇
  2014年   4409篇
  2013年   12213篇
  2012年   7187篇
  2011年   9912篇
  2010年   7696篇
  2009年   8881篇
  2008年   9285篇
  2007年   9307篇
  2006年   7998篇
  2005年   7436篇
  2004年   7354篇
  2003年   7100篇
  2002年   6816篇
  2001年   6920篇
  2000年   6560篇
  1999年   6855篇
  1998年   16422篇
  1997年   11659篇
  1996年   9000篇
  1995年   6911篇
  1994年   6090篇
  1993年   6120篇
  1992年   4458篇
  1991年   4226篇
  1990年   4141篇
  1989年   4122篇
  1988年   3804篇
  1987年   3440篇
  1986年   3441篇
  1985年   3794篇
  1984年   3530篇
  1983年   3264篇
  1982年   3093篇
  1981年   3096篇
  1980年   3079篇
  1979年   2872篇
  1978年   2904篇
  1977年   3176篇
  1976年   4127篇
  1975年   2443篇
  1974年   2406篇
  1973年   2422篇
  1972年   2027篇
  1971年   1790篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Abstract The purpose of this exploratory study was to investigate the influence of two individual characteristics (Web experience and academic focus) of adolescents on the Web perception, using off-line questionnaires (a Lickert response scale) constituted on the basis of a series of interviews. Questions concerned: perceptions about the nature of information found in the Web; 'strategies' of access to the interesting Internet sites and the reliability of different information resources (libraries, television, Web, etc.). Results lead to the assumption that adolescents with high Web experience became more critical, less confident and less enthusiastic than adolescents with low Web experience and that, in some dimensions, perceptions of literature students are different to those of science students. Even if some interesting results were obtained, further research is needed to explore users' perceptions related to individuals' characteristics and to determine the generalisability of the influences identified in this exploratory study.  相似文献   
112.
Su  J. Ritter  P.R. 《Software, IEEE》1991,8(2):26-33
The testing and quality assurance of the Motif 1.0 graphical user-interface software are described. The testing goals, which fell into three general categories (code coverage, defect-density, and defect-arrival rate), and a deliverable formal test suite are examined. The three phases of the testing process-evaluation, test development, and regression testing-and the tools used in testing are discussed  相似文献   
113.
Foreword     
  相似文献   
114.
P. Gallone 《Electrochimica acta》1986,31(12):1485-1490
On 30 October 1786 Luigi Galvani gave the first account, at the Academy of Sciences of Bologna, about his experiments on animal electricity, of which he thought to have obtained evidence from the convulsions shown by a dissected frog, as soon as its hind-limbs were connected with the spinal cord by means of a metallic conductor. The publication of these experiments gave rise to Galvani's controversy with Volta, who denied the existence of animal electricity after discovering that there exists a potential difference between any couple of dissimilar conductors. This was a preliminary step that led Volta to the invention of the voltaic pile. Evidence of animal electricity was given about 1840 by Carlo Matteucci, using the astatic galvanometer invented by Leopoldo Nobili. This fundamental property of living organisms is now a well-advanced field of investigation by electrophysiology and bioelectrochemistry.  相似文献   
115.
The exfiltration of wastewater from sewer systems in urban areas causes a deterioration of soil and possibly groundwater quality. Beside the simulation of transport and degradation processes in the unsaturated zone and in the aquifer the analysis of the potential impact requires the estimation of quantity and temporal variation of wastewater exfiltration. Exfiltration can be assessed by the application of a leakage model. The hydrological approach was originally developed to simulate the interactions between the groundwater and surface water, it was adapted to allow for modelling of interactions between groundwater and sewer system. In order to approximate the exfiltration specific model parameters infiltration specific parameters were used as a basis. Scenario analysis of the exfiltration in the City of Dresden from 1997 to 1999 and during the flood event in August 2002 shows the variation and the extent of exfiltration rates.  相似文献   
116.
Analysis and synthesis of on-chip spiral inductors   总被引:3,自引:0,他引:3  
This paper presents a physically based compact model for estimating high-frequency performance of spiral inductors. The model accurately accounts for skin and proximity effects in the metal conductors as well as eddy current losses in the substrate. The model shows excellent agreement with measured data mostly within 10% across a variety of inductor geometries and substrate dopings up to 20 GHz. A web-based spiral inductor synthesis and analysis tool COILS, which makes use of the compact models, is presented. An optimization algorithm using binary searches speeds up the synthesis of inductor designs.  相似文献   
117.
118.
Comments that a critical element in the final report of the American Psychological Association (APA) Task Force on the Victims of Crime and Violence may be lost simply because of the enormity and complexity of the issues involved. The real nature of the victim's emotional experience is often not directly addressed by researchers or service providers in the mental health community. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
119.
120.
Pull-out experiments have been carried out on single production fibres under carefully controlled conditions. Four parameters were determined. The interfacial yield stresses, of about 9–14 MPa, were very much smaller than the shear strengths of the bulk polymers in the case of an epoxy, whether post-cured or not, and a non-post-cured polyester. Values for the work of fracture of the interface varied from 140 to 300 Jm?2, and again were less than those of the polymer. Interface failure sometimes took place in the epoxy rather than at the fibre surface, whereas with the polyester it always took place at the fibre surface. After interface failure, pull-out was governed by friction, with maximum shear stresses of 7–10 MPa for polyester, and 21–34 MPa for epoxy, the higher values being obtained for the post-cured resins. Average frictional shear stresses were sometimes less than a half of the maximum shear stress, indicating that the fibre Poisson's shrinkage was playing an important role in the pull-out process. A silicone release agent reduced the frictional shear stresses to 2·5 MPa, with both resins.  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