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   962篇
  免费   48篇
电工技术   17篇
综合类   1篇
化学工业   219篇
金属工艺   15篇
机械仪表   17篇
建筑科学   35篇
矿业工程   7篇
能源动力   39篇
轻工业   33篇
水利工程   3篇
石油天然气   2篇
无线电   74篇
一般工业技术   255篇
冶金工业   102篇
原子能技术   7篇
自动化技术   184篇
  2023年   5篇
  2022年   14篇
  2021年   21篇
  2020年   14篇
  2019年   27篇
  2018年   24篇
  2017年   23篇
  2016年   30篇
  2015年   27篇
  2014年   28篇
  2013年   60篇
  2012年   40篇
  2011年   80篇
  2010年   53篇
  2009年   80篇
  2008年   42篇
  2007年   54篇
  2006年   53篇
  2005年   53篇
  2004年   40篇
  2003年   14篇
  2002年   29篇
  2001年   16篇
  2000年   12篇
  1999年   19篇
  1998年   25篇
  1997年   16篇
  1996年   11篇
  1995年   13篇
  1994年   9篇
  1993年   8篇
  1992年   3篇
  1991年   6篇
  1990年   7篇
  1989年   4篇
  1988年   4篇
  1986年   3篇
  1985年   3篇
  1984年   2篇
  1981年   5篇
  1980年   4篇
  1979年   3篇
  1978年   2篇
  1977年   4篇
  1976年   2篇
  1975年   3篇
  1974年   3篇
  1966年   2篇
  1943年   1篇
  1942年   1篇
排序方式: 共有1010条查询结果,搜索用时 15 毫秒
91.
在IEEE标准802.15.4组织和ZigBee联盟的努力下,未来的家庭、工厂、办公室和零售商店都不需要很多缆线.连接传感器和开关到照明、保安、HVAC和工业控制设备的缆线大约占一般大楼缆线的三分之一.如果用802.15.4无线开关取代传统的缆线式开关,承建商就能够在新的建筑工程中把劳动和材料等两方面的成本削减大约三分之一;如果采用更现代化的设备对大楼进行翻新,所节省的成本甚至更多.  相似文献   
92.
A series of ZSM-5 samples with similar SiO2/Al2O3 ratio was synthesised using different aluminum sources and by including varying amounts of calcium hydroxide during the synthesis. The samples were subsequently ion-exchanged with Cu-ions, and evaluated with respect to deNOx activity in the absence and presence of water. The choice of aluminum source and the presence of calcium hydroxide during the zeolite synthesis affected the lean deNOx activity of Cu-ZSM-5.  相似文献   
93.
X-ray peak broadening has been used to study the milling behaviour of a number of commercial alumina powders. It is shown that the milling behaviour is dependent upon the original particle size, internal defects in particles and the milling liquid used. Peak-broadening studies allow the effects of milling upon reduction of crystallite size and increase in stored energy to be separated. The effect of these two parameters was separated using the Cauchy correction method. Measurement of the particle size of the unmilled alumina powders in the transmission electron microscope was used to determine that the Cauchy method gave the most correct estimation of crystallite size. Both alumina crystallite size and stored energy are expected to enhance sintering of the powder to a high density. Attempts are made to predict the sintering ability of the materials studied in terms of the above parameters.  相似文献   
94.
The load-following capability of a proton exchange membrane fuel cell was studied by measuring the cell voltage response to a sinusoidal current load with large amplitude and varying frequency. A mathematical model was developed, incorporating mass transport and capacitive effects as well as the membrane resistance. The model was capable of separating the faradaic and capacitive currents and predicting the observed hysteresis. At frequencies of the sinusoidal current load below 1 Hz, no appreciable hysteresis in the polarisation curve was observed. When increasing the frequency above 1 Hz, a hysteresis appeared at current densities below 0.2 A cm?2. The model related this hysteresis to capacitive effects. When using air as the cathode feed, hysteresis in the current density range 0.5 A cm?2 and higher appeared above 1 Hz compared to 100 Hz for pure oxygen. The model revealed that hysteresis observed in this current density range was caused by oxygen transport limitations.  相似文献   
95.
Electroconductive papers were produced by coating commercial base papers with blends of poly(3,4‐ethylenedioxythiophene)/poly(4‐styrenesulfonate) (PEDOT:PSS) and organic solvents. The bulk conductivities of the coated papers were measured using a four‐probe technique. One‐sided and two‐sided coating gave comparable conductivity levels. The presence of sorbitol and isopropanol in the PEDOT:PSS blends did not enhance the bulk conductivity of the coated paper, and with increasing concentrations of these solvents, the conductivity decreased due to dilution of the conducting component. Samples coated with PEDOT:PSS blends containing N‐methylpyrrolidone (NMP) or dimethyl sulfoxide (DMSO) exhibited a higher conductivity than those coated with pure PEDOT:PSS because of their plasticizing effect and conformational changes of PEDOT molecules indicated by the red shift and disappearance of the shoulder peak at about 1442 cm?1 in the Raman spectra of the coated samples. EDS imaging showed that PEDOT:PSS is distributed throughout the thickness direction of the paper. Contact angle measurements were made to monitor the hydrophilicity of the paper surface and total sulfur analysis was used to determine the amount of PEDOT:PSS deposited onto the paper. The tensile strength of all the paper samples increased slightly after treatment. Thus, it is demonstrated that enhanced bulk conductivity in the order of 10?3 S/cm can be achieved by using organic conductive materials and surface treatment techniques. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   
96.
Conduction properties of nanoscale contacts can be studied using first-principles simulations. Such calculations give insight into details behind the conductance that is not readily available in experiments. For example, we may learn how the bonding conditions of a molecule to the electrodes affect the electronic transport. Here we describe key computational ingredients and discuss these in relation to simulations for scanning tunneling microscopy (STM) experiments with C60 molecules where the experimental geometry is well characterized. We then show how molecular dynamics simulations may be combined with transport calculations to study more irregular situations, such as the evolution of a nanoscale contact with the mechanically controllable break-junction technique. Finally we discuss calculations of inelastic electron tunnelling spectroscopy as a characterization technique that reveals information about the atomic arrangement and transport channels.  相似文献   
97.
A novel technology to mitigate the climate changes and improve energy security is Pressurized Entrained flow High Temperature Black Liquor Gasification (PEHT-BLG) in combination with an efficient fuel synthesis using the resulting syngas. In order to optimise the technology for use in a pulp and paper mill based biorefinery, it is of great importance to understand how the operational parameters of the gasifier affect the product gas composition. The present paper is based on experiments where gas samples were withdrawn from the hot part of a 3 MW entrained flow pressurized black liquor gasifier of semi industrial scale using a high temperature gas sampling system. Specifically, the influence of process conditions on product gas composition (CO2, CO, H2, CH4, H2S, and COS) were examined by systematically varying the operational parameters: system pressure, oxygen to black liquor equivalence ratio, black liquor flow rate to pressure ratio and black liquor pre-heat temperature. Due to the harsh environment inside the gasification reactor, gas sampling is a challenging task. However, for the purpose of the current study, a specially designed high temperature gas sampling system was successfully developed and used. The results, obtained from two separate experimental campaigns, show that all of the investigated operational parameters have a significant influence on the product gas composition and present valuable information about to the process characteristics.  相似文献   
98.
The aim of this study was to explore how acid deposition may affect the concentration and quality of dissolved organic matter (DOM) in soil-water. This was done by a small-scale acidification experiment during two years where 0.5 × 0.5 m(2) plots were artificially irrigated with water with different sulfuric acid content, and soil-water was sampled using zero-tension lysimeters under the O-horizon. The DOM was characterized using absorbance, fluorescence, and size exclusion chromatography analyses. Our results showed lower mobility of DOM in the high acid treatment. At the same time, there was a significant change in the DOM quality. Soil-water in the high acid treatment exhibited DOM that was less colored, less hydrophobic, less aromatic, and of lower molecular weight, compared to the low acid treatment. This supports the hypothesis that reduction in sulfur deposition is an important driver behind the ongoing brownification of surface waters in many regions.  相似文献   
99.
Changes, over a period of 8 years, in the chemical composition and morphology of deposit and lining materials in a production rotary kiln for iron ore pellet manufacture are described. The following have been studied: two types of refractory brick used as lining material; deposited chunk materials from the lining; the interaction zones between deposits and linings. Morphological changes at the deposit/lining interface, and the active chemical reactions, are established. Larger hematite grains in the deposit material (5–50 μm) primarily remain at the original deposit/lining interface. The remainder penetrates fissures, voids and brick joints, forms a laminar structure with corundum from the bricks, and migrates in grains in the lining material. Potassium penetrates more deeply into the bricks than hematite, resulting in the formation of kalsilite, leucite and potassium β-alumina, which contribute to degradation of the lining.  相似文献   
100.
This paper focuses on the application of principal component analysis (PCA) to thoroughly analyse and interpret multidimensional data from a cold rolling process. The analysis includes the effects of variables on the final properties of strips in a cold rolling mill. Unscrambler software was used to analyse and identify hidden variables. Variable correlations were also used to derive correlations between the control parameters. The results of this research will be used to improve the selection of material in order to reduce the occurrence of defects in the cold rolling process and to improve the adjustment of the set points that are performed in every pass or section of the cold rolling process. The hot rolled strips that enter the cold rolling mill are made of different materials and are produced by different strip manufacturers. Some strips break during the thickness reduction process in the cold rolling mill. This paper focuses on two possible causes of breakage: non-uniform strip material properties and failures in the rolling mill process. Two types of rolled strips (those that break and those that do not break) were compared to identify causes of breakage. The results indicate that breakages are caused by material or process failures. PCA was applied to the dataset in order to identify and analyse the relationships between the variables in the process. This information was used to interpret and diagnose the process behaviour. Swarm analysis and relating observations to process behaviour were able to distinguish between different start-up conditions, and between desirable and undesirable process conditions.  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