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   656篇
  免费   5篇
  国内免费   2篇
电工技术   8篇
综合类   1篇
化学工业   179篇
金属工艺   9篇
机械仪表   13篇
建筑科学   11篇
能源动力   27篇
轻工业   49篇
水利工程   1篇
石油天然气   9篇
无线电   78篇
一般工业技术   139篇
冶金工业   36篇
原子能技术   1篇
自动化技术   102篇
  2024年   9篇
  2023年   9篇
  2022年   39篇
  2021年   37篇
  2020年   25篇
  2019年   34篇
  2018年   38篇
  2017年   16篇
  2016年   18篇
  2015年   12篇
  2014年   26篇
  2013年   55篇
  2012年   27篇
  2011年   42篇
  2010年   22篇
  2009年   18篇
  2008年   33篇
  2007年   17篇
  2006年   20篇
  2005年   14篇
  2004年   19篇
  2003年   15篇
  2002年   17篇
  2001年   9篇
  2000年   10篇
  1999年   11篇
  1998年   12篇
  1997年   8篇
  1996年   3篇
  1995年   4篇
  1994年   5篇
  1993年   5篇
  1992年   7篇
  1991年   3篇
  1990年   2篇
  1989年   3篇
  1988年   3篇
  1987年   4篇
  1985年   3篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1979年   1篇
  1975年   1篇
  1974年   1篇
  1973年   1篇
  1972年   1篇
排序方式: 共有663条查询结果,搜索用时 0 毫秒
61.
62.
    
An approach to enhance the sensitivity of the damage index using the prediction errors of autoregressive – autoregressive exogenous models by augmenting Singular Spectrum Analysis (SSA) to detect and locate minor damage is presented. Numerical simulation studies are carried out by considering a simply supported beam with single and multiple cracks. An experimental study on a reinforced cement concrete beam has been carried out to validate the technique using different levels of damage. The studies emphasise that the SSA improves the sensitivity of the damage index for detection and also localisation, handling environmental/operational variability and measurement noise.  相似文献   
63.
The paper proposes a new method for evaluating the tolerance of trees to SO2 pollution stress, and grouping plants as indicators and controllers by tolerance index values. The index is calculated by a new arithmetic formula. The developed model is useful in identifying tolerant and susceptible plants to SO2.  相似文献   
64.
Journal of Inorganic and Organometallic Polymers and Materials - In recent decades, the analysis of nanoparticles is of greater importance for their applications in various fields. This present...  相似文献   
65.
Most plant materials are freely and abundantly available and can be used for the removal of heavy metals from effluents. This study investigates the effects of equilibrium, kinetic, and thermodynamic parameters on biosorption of Co(II) ions onto the plant source Erythrina variegata orientalis leaf powder. The biosorption studies are carried out in a batch process. A significant increase in percentage removal of Co(II) is observed as pH value is increased from 2 to 5 and the percentage removal is maximum at pH = 7. The maximum sorption capacity is 8.3 mg/g in the range of variables investigated. The experimental data are well represented by Freundlich and Langmuir isotherms indicating favorable biosorption. The biosorption follows second-order kinetics. The biosorption is exothermic, irreversible, and spontaneous.  相似文献   
66.
The present study was undertaken to develop a novel and easy practical approach for synthesis of cyclopentanone, a versatile industrial ingredient. Accordingly, ceria–zirconia based nano-oxide catalysts, namely, CexZr1?xO2 and CexZr1?xO2/M (M = SiO2 and Al2O3) were prepared and evaluated for the title reaction. The physicochemical characterization has been achieved using different techniques, namely, XRD, BET surface area, XPS, Raman, OSC, and HREM. The catalytic results revealed that CexZr1?xO2 based nano-oxides are promising heterogeneous catalysts for synthesis of cyclopentanone. Amongst, the CexZr1?xO2/Al2O3 catalyst exhibited ~100% conversion with 75% desired cyclopentanone product selectivity owing to its favorable physicochemical characteristics.  相似文献   
67.
Aloe vera (AV) is one of the medicinal herbs with a well-established spectrum of wound healing, antimicrobial and anti-inflammatory property. AV-mediated therapeutics present significant tissue regenerative activity by modulating the inflammatory and proliferative phases of wound healing. The purpose of the present work was to combine the biological properties of AV and the advantages of electrospun meshes to prepare a potent transdermal biomaterial. The polycaprolactone (PCL) containing 5 and 10 wt % of lyophilized powder of AV was studied for electrospinning into nanoscale fiber mats and compared with PCL/Collagen blend for dermal substitutes. SEM revealed the average diameters of PCL, PCL-AV 5 %, PCL-AV 10 % and PCL/Collagen nanofiber scaffolds in the range of 519 ± 28, 264 ± 46, 215 ± 63 and 249 ± 52 nm, respectively. PCL-AV 10 % nanofiber scaffolds showed finer fiber morphology with improved hydrophilic properties and higher tensile strength of 6.28 MPa with a Young’s modulus of 16.11 MPa desirable for skin tissue engineering. The nanofibers were then used to investigate differences in biological responses in terms of proliferation and cell morphology of mice dermal fibroblasts. It was found that PCL-AV 10 % nanofibrous matrix favored cell proliferation compared to other scaffolds which almost increased linearly by (p ≤ 0.01) 17.79 % and (p ≤ 0.01) 21.28 % compared to PCL on sixth and ninth day. CMFDA dye expression, secretion of collagen and F-actin expression were significantly increased in PCL-AV 10 % scaffolds compared to other nanofibrous scaffolds. The obtained results proved that the PCL-AV 10 % nanofibrous scaffold is a potential biomaterial for skin tissue regeneration.  相似文献   
68.
Acetylation of lecithin improves the fluid properties, water dispersibility and emulsifying properties of a variety of food formulations. Acetylation of lecithin is usually carried out chemically using acetic anhydride in the presence of tertiary amine. In the present study acetylation of soybean lecithin and egg yolk lecithin was carried out using lipozyme IM 20 having 1,3-specificity from Mucor miehei and vinyl acetate at 70–75 °C. Vinyl acetate played a dual role as acetylating agent and also as the solvent medium. This method selectively acetylated phosphatidylethanolamine without effecting phosphatidylinositol since the enzyme employed was 1,3-specific.  相似文献   
69.
Europium doped calcium orthosilicate (Ca2SiO4) phosphors have been synthesized by the conventional high temperature solid-state reaction method in various concentrations from agricultural waste (egg shell as a CaO and rice husk as a SiO2). These phosphors structure from X-ray diffraction and morphology from scanning electron microscopy have been examined. Concentration dependent Eu3+ ions luminescent properties in Ca2SiO4 phosphors have been studied from the excitation, emission and decay curves analysis. The 5D07FJ transitions observed in luminescence spectrum allows to determine the site symmetry of the Eu3+ ion. A charge transfer band (CTB) at around 260?nm which is due to the Eu–O interaction in the host along with the 4f – 4f excitation bands due to Eu3+ ions in UV and blue regions are observed. The color co-ordinates determined from emission spectra varies with concentrations of Eu3+ ions and are found to fall in the red region. The decay curves show single exponential behavior for all concentrations of Eu3+ ions (0.01–0.4?mol%) and the lifetimes varied from 2.67 to 2.78?ms. It is worth noting that the present material is found to be far better than many red phosphors synthesized by using agricultural waste as raw materials.  相似文献   
70.
ZnCl2–aluminosilicate catalysts were prepared via a sol–gel route involving fluoride‐catalyzed hydrolysis of aluminum and silicon alkoxides in the presence of NaF, KF, NH4F and ZnF2. The catalysts were characterized by employing 29Si, 27Al and 19F solid‐state MAS NMR. The dependence of the activities of the catalysts on the nature and amount of fluoride present in the catalysts were investigated using Friedel–Crafts alkylation reaction of benzene with benzyl chloride. This revised version was published online in July 2006 with corrections to the Cover Date.  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