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   308476篇
  免费   4333篇
  国内免费   1341篇
电工技术   5127篇
综合类   575篇
化学工业   46720篇
金属工艺   11689篇
机械仪表   8968篇
建筑科学   8212篇
矿业工程   1654篇
能源动力   7775篇
轻工业   24892篇
水利工程   3311篇
石油天然气   5935篇
武器工业   46篇
无线电   35719篇
一般工业技术   61965篇
冶金工业   55834篇
原子能技术   7695篇
自动化技术   28033篇
  2021年   2807篇
  2020年   2102篇
  2019年   2621篇
  2018年   4248篇
  2017年   4306篇
  2016年   4741篇
  2015年   3252篇
  2014年   5328篇
  2013年   13766篇
  2012年   8601篇
  2011年   11696篇
  2010年   8945篇
  2009年   10130篇
  2008年   10729篇
  2007年   10668篇
  2006年   9153篇
  2005年   8387篇
  2004年   8214篇
  2003年   7834篇
  2002年   7565篇
  2001年   7365篇
  2000年   6978篇
  1999年   7272篇
  1998年   16805篇
  1997年   12023篇
  1996年   9369篇
  1995年   7274篇
  1994年   6418篇
  1993年   6470篇
  1992年   4763篇
  1991年   4419篇
  1990年   4393篇
  1989年   4367篇
  1988年   4012篇
  1987年   3667篇
  1986年   3663篇
  1985年   4031篇
  1984年   3713篇
  1983年   3455篇
  1982年   3255篇
  1981年   3244篇
  1980年   3195篇
  1979年   3010篇
  1978年   3032篇
  1977年   3281篇
  1976年   4217篇
  1975年   2550篇
  1974年   2487篇
  1973年   2488篇
  1972年   2079篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
We propose a method of fabricating surface barrier diodes with overlapped metal junction, which provides for a significant decrease in the reverse currents and an increase in the breakdown voltage.  相似文献   
82.
Fiber cross sections for use in textiles and composites are becoming more and more complex. Shape impacts fiber or filaments properties and therefore the yarn and fabric characteristics. This paper presents the influence of the fiber cross section on the fabric surface characteristics. The material used was polyester staple fibers, of four different shapes: round, scalloped oval, cruciform and hexachannel. All fibers had the same cut length with different fineness. Yarns obtained from these fibers had nominally the same yarn count, torsion value and structure. Plain jersey fabrics were knitted from each of the yarns under identical conditions and then relaxed prior to testing. Friction behavior was evaluated and a roughness-friction criterion developed. An indirect measurement of the real area of contact was obtained in order to provide roughness and friction properties. The influence of fiber cross section on yarn bending rigidity and on the state of the knitted fabric surface was characterized.  相似文献   
83.
The material properties of maraging steels are greatly affected by the alloy and inclusion content and hence by the production route. This paper describes various past and current production routes at Böhler Edelstahl GmbH and the effect of these routes on the specified element (alloy) and non-specified element (inclusion) contents. Non-metallic inclusions were investigated by EDX analysis. The effects of various alloying and tramp elements on the material properties are presented as a statistical evaluation of previous melts. Nitrogen solubility was calculated with Thermo–Calc for maraging steel Mat.-No. 1.6354 and the precipitation of nitrides is discussed. A proposal is made for the production of melts with improved properties.  相似文献   
84.
New thermodynamic data for the In–Sb system are obtained and compared with calculation results available in the literature. An isothermal vacuum cell and a procedure for electrolyte preparation are described which ensure high measurement accuracy.  相似文献   
85.
The operation of a torsional oscillator for detection, of flow-driven textural transitions in, 3He-A is described. The detection technique, tracking the shift of the resonant frequency of the torsional oscillator, allows us to observe textural changes and the presence of vortices in zero magnetic field. It relies on. the anisotropic superfluid density of 3He-A and its change due to reorientation of the Î-texture caused by counterflow.  相似文献   
86.
A high-gain ballistic hot-electron device is described. The GaAs-AlGaAs heterostructure device, with a 21-mm-thick pseudomorphic In 0.12Ga0.88As base, had a current gain of 27 at 77 K and 41 at 4.2 K. As characteristically seen in ballistic devices, transfer into the L valley limited the maximum gain. The Γ-L valley separation in the strained In0.12Ga0.88As was estimated to be about 380 meV  相似文献   
87.
88.
89.
A newly developed membrane performance enhancer (MPE) was used to prevent membrane fouling in a membrane bioreactor (MBR) process. It transpired that 1,000 mg/l of MPE reduced polysaccharide levels from 41 mg/I to 21 mg/I on average under the experimental condition. Repeated experiments also confirmed that 50-1,000 mg/l of MPE could reduce membrane fouling significantly and increase the intervals between membrane cleanings. Depending on MPE dosages and experimental conditions, trans-membrane pressure (TMP) increase was suppressed for 20-30 days, while baseline TMP surged within a few days. In addition, MPE allowed MBR operation even at 50,000 mg/l of total solid and reduced permeate COD. However, no evidence of toxicity for sludge was found from respiratory works.  相似文献   
90.
The biochemical composition can be seen as a good indicator of both the biodegradability and the methane potential of a given waste. The work presented here is an attempt to elaborate a typology of wastes and to compare it to the anaerobic degradation characteristics. The first data indicate that there is a link between the ligno-cellulosic content of the waste and the biodegradability. When dealing with application to anaerobic digestion processes, having a tool to predict the ability of the waste to be degraded could be of the greatest interest for preventing failures, estimating biogas production, methane content, or for the management of co-digestion processes.  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