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   4033篇
  免费   53篇
  国内免费   5篇
电工技术   50篇
化学工业   898篇
金属工艺   85篇
机械仪表   52篇
建筑科学   156篇
矿业工程   5篇
能源动力   58篇
轻工业   460篇
水利工程   32篇
石油天然气   12篇
无线电   301篇
一般工业技术   610篇
冶金工业   815篇
原子能技术   50篇
自动化技术   507篇
  2024年   28篇
  2023年   43篇
  2022年   60篇
  2021年   78篇
  2020年   75篇
  2019年   67篇
  2018年   94篇
  2017年   71篇
  2016年   93篇
  2015年   60篇
  2014年   92篇
  2013年   174篇
  2012年   148篇
  2011年   203篇
  2010年   156篇
  2009年   127篇
  2008年   175篇
  2007年   156篇
  2006年   118篇
  2005年   126篇
  2004年   120篇
  2003年   113篇
  2002年   105篇
  2001年   76篇
  2000年   63篇
  1999年   68篇
  1998年   158篇
  1997年   102篇
  1996年   95篇
  1995年   64篇
  1994年   68篇
  1993年   69篇
  1992年   53篇
  1991年   48篇
  1990年   46篇
  1989年   42篇
  1988年   46篇
  1987年   39篇
  1986年   41篇
  1985年   42篇
  1984年   41篇
  1983年   39篇
  1982年   43篇
  1981年   37篇
  1980年   29篇
  1979年   31篇
  1978年   22篇
  1977年   28篇
  1976年   40篇
  1974年   20篇
排序方式: 共有4091条查询结果,搜索用时 15 毫秒
991.
    
In order to meet the requirements of micro cold forming tools, a new co‐spray forming process has been applied to produce graded materials from two different tool steels in this study. The two steel melts were atomized and co‐sprayed simultaneously onto a flat substrate, resulting in a flat graded deposit when the two sprays were overlapped. To eliminate porosity and break up carbide network, the graded deposits were further hot rolled. The resultant graded tool steels were investigated with respect to porosity, element distribution, microstructure, hardness, strength, and toughness. The degree of overlapping of the two sprays determined the concentration gradient of the chemical elements in the deposits. The overlapping of the spray cones also contributed to low porosity in the gradient zone of the deposits. The porosity in the graded deposits could be essentially eliminated by means of hot rolling. The carbides and grain structures of the hot rolled tool steels were fine and homogeneous. By means of combining different tool steels in a single deposit, different microstructures and properties were combined.  相似文献   
992.
    
This work aims at establishing the effect of stress and temperature on the velocity of ultrasonic longitudinal waves in typical engineering polymers, and evaluating the potential of ultrasonic stress measurement in the evaluation of residual stresses in polymer parts. In order to estimate the effect of material morphology, two amorphous and two semicrystalline polymers have been considered. A series of tests are implemented, to determine the acoustoelastic constants and temperature constant of materials, by using the designed transducer fixtures for in situ measurement of longitudinal wave velocity. As expected, the velocity changes linearly with stress and temperature, and the temperature effect is as important as the acoustoelastic effect. It shows that this kind of nondestructive method is a valuable quantitative tool to estimate the residual stress in polymer products, but the material temperature influence must be considered during the estimation.  相似文献   
993.
    
The 2011 US Billion‐Ton Update1 estimates that there are enough agricultural and forest resources to sustainably provide enough biomass to displace approximately 30% of the country's current petroleum consumption. A portion of these resources are inaccessible at current cost targets with conventional feedstock supply systems because of their remoteness or low yields. Reliable analyses and projections of US biofuels production depend on assumptions about the supply system and biorefinery capacity, which, in turn, depend on economics, feedstock logistics, and sustainability. A cross‐functional team has examined optimal combinations of advances in feedstock supply systems and biorefinery capacities with rigorous design information, improved crop yield and agronomic practices, and improved estimates of sustainable biomass availability. Biochemical‐conversion‐to‐ethanol is analyzed for conventional bale‐based system and advanced uniform‐format feedstock supply system designs. The latter involves ‘pre‐processing’ biomass into a higher‐density, aerobically stable, easily transportable format that can supply large‐scale biorefineries. Feedstock supply costs, logistics and processing costs are analyzed and compared, taking into account environmental sustainability metrics. © 2013 Society of Chemical Industry and John Wiley & Sons Ltd  相似文献   
994.
    
This paper presents methods and results from a study where long‐term wind measurements at 10 m above ground level from meteorological stations across Scotland were used to hindcast both average and hour‐by‐hour local wind speeds. For this, Scotland was divided into 21 simulation areas each containing a meteorological station. The Wind Atlas Analysis and Application Program (WAsP) was then used—well outside its specified range for both distance and area slope—to predict the wind climate at 80 m above ground level on a square kilometre basis. With further processing, time series of wind speed were derived for selected locations. Based on wind turbine power curves it was then possible to derive time series of power which were applied in power system analysis and used to study the degree of matching between renewable generation and electricity demand. This paper focuses on the creation of the onshore wind speed and power time series for areas of interest in Scotland. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
995.
    
Probabilities of leakages in piping systems as used in risk studies up to now do not represent the present state of the art. The goal of this investigation is to formulate a new set of probabilities of leakages in piping systems of German pressurized water reactors for the whole range of pipes which are of interest using the operating experience, the principles of the basis safety approach and fracture mechanics studies.  相似文献   
996.
997.
In the context of inline monitoring and controlling of forming processes, the distribution of acting forces on tool and forming machine causing elastic deformation of the clamping surfaces provides fundamental information on the resulting part quality whereas the inline detection is still challenging. This paper presents a novel method using the T-slot geometry as a cognitive area for inline analyzing of the elastic deformation of the tool-clamping surfaces. Using a newly developed sensor device, the elastic deformation state of the T-slot geometry under process forces is detected by strain measuring of a deformation body mounted inside the T-slot. The functionality principle of the sensor device and measuring method for process monitoring are demonstrated by simulation and experiments, demonstrating the potential for process control.  相似文献   
998.
The present study demonstrates the viability of the reductive attachment step of the single walled carbon nanotube (SWCNT) lengthening process in which long SWCNTs are grown from short nanotube seeds. Aryl sulfonate sidewall-functionalized, carboxylate end-functionalized SWCNTs are attached to an inorganic cluster pro-catalyst (FeMoC) via ligand exchange. The SWCNT-FeMoC complex was electrodeposited onto highly ordered pyrolytic graphite (HOPG), heated and exposed to etching conditions. Pre- and post-treatment AFM imaging shows that controlled reductive etching of the SWCNTs is attainable at a variety of pressures and temperatures in hot surface/cold gas and hot surface/hot gas systems.  相似文献   
999.
In this paper, a computationally, inexpensive, size-integration method based on a modified Rayleigh-Plesset model is developed to predict backscatter spectra from groups of bubbles with various size distributions, incident acoustic amplitudes, and driving frequencies. The method was validated using experimentally measured spectra from contrast bubbles of various sizes: Optison, Levovist, ST68 microbubbles, and submicron bubbles. This method provides a computationally inexpensive means of examining backscatter spectrum from multiple bubbles, especially in predicting occurrence and relative amplitude of subharmonics and second harmonics.  相似文献   
1000.
当前,企业的客户服务部门需要进行“整合”,作出飞跃发展,以跟上竞争形势的变化;但不论是进行战略的、执行的或技术的整合,都应因地制宜,量体裁衣  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