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   4950篇
  免费   623篇
  国内免费   120篇
电工技术   38篇
综合类   199篇
化学工业   1124篇
金属工艺   720篇
机械仪表   126篇
建筑科学   385篇
矿业工程   365篇
能源动力   185篇
轻工业   462篇
水利工程   111篇
石油天然气   59篇
武器工业   9篇
无线电   182篇
一般工业技术   979篇
冶金工业   623篇
原子能技术   77篇
自动化技术   49篇
  2024年   27篇
  2023年   142篇
  2022年   148篇
  2021年   203篇
  2020年   222篇
  2019年   175篇
  2018年   188篇
  2017年   172篇
  2016年   189篇
  2015年   170篇
  2014年   238篇
  2013年   484篇
  2012年   262篇
  2011年   348篇
  2010年   223篇
  2009年   239篇
  2008年   205篇
  2007年   260篇
  2006年   247篇
  2005年   186篇
  2004年   172篇
  2003年   157篇
  2002年   141篇
  2001年   104篇
  2000年   99篇
  1999年   113篇
  1998年   80篇
  1997年   54篇
  1996年   51篇
  1995年   53篇
  1994年   45篇
  1993年   36篇
  1992年   52篇
  1991年   41篇
  1990年   36篇
  1989年   23篇
  1988年   8篇
  1987年   13篇
  1986年   11篇
  1985年   29篇
  1984年   19篇
  1983年   14篇
  1982年   3篇
  1980年   1篇
  1979年   1篇
  1978年   2篇
  1976年   1篇
  1975年   6篇
排序方式: 共有5693条查询结果,搜索用时 15 毫秒
51.
Four sites in the Detroit River/Lake Erie western basin were evaluated for their toxicity. The evaluation was based on 1) bulk chemical characterization of the sediments, 2) chemical composition of the sediment elutriates, and 3) toxicity of the elutriates to ultraplankton and microplankton/net plankton. A sequence of decreasing contamination was determined from the chemical composition of the elutriates based on the elutriation release of metals such as Zn, Mn, Cd, Ni, and Co. Bioassessment of elutriate toxicity was determined by carbon-14 Algal Fractionation Bioassays (AFB's) which were conducted with various dilutions of standard and Chelex-100 treated elutriates. Site A (near Windsor, Ontario) and Site D (western Lake Erie) were found to be toxic to ultraplankton. The observed toxicity was attributed to the bioavailability and synergistic impact of elutriated metals on ultraplankton production. A direct relationship between the water soluble metal fraction and toxicity was observed. These results confirmed that sediment toxicity should not be evaluated solely on bulk chemical composition of the sediments. The AFB's have been proven useful in the bioassessment of sediments due to their rapidity/sensitivity and hence could be routinely used for the screening and early detection of contaminants affecting fast growing organisms which form the basis of the aquatic food chain.  相似文献   
52.
从含有机物的金废料中提取纯金的研究   总被引:1,自引:0,他引:1  
李世鸿 《黄金》1998,19(5):42-43
物料的经蒸发、燃烧和焙烧除去有机物。焙渣用硝酸浸出可溶性杂质,金富集在渣中。用正水溶解金。金溶液用H2SO4和NaOH进行纯化处理,用亚硫酸钠沉积金。金粉洗至无Cl^-反应后,加稀硝酸煮沸30 ̄60min,得到纯度99.95%以上的海锦金。  相似文献   
53.
In this work a treatment for surface preparation to improve mechanical resistance in adhesive bonding of plastic composites reinforced with fibres and metallic material, has been performed using an excimer laser. The following couplings have been selected to reproduce joints commonly used in the aerospace and automotive industry: CFC (carbon fibre composite) with CFC, CFC with Al 2024T3, Al 99% with Al 99%, GFC (glass fibre composite) with zinc-coated sheet in low carbon steel FeP01. The surfaces have been prepared using an excimer laser, adopting several values of laser parameters. The obtained surfaces have been examined by optical and scanning electron microscope: comparative measures of wetting and roughness have been performed to obtain an accurate characterisation and to select the proper finishes suitable to improve the mechanical resistance of the joints. The results obtained show that laser treatment always improves the final resistance of the joint; notable increases, and no significant surface damages have been highlighted. Better results have been obtained with the Al 99% with Al 99% joints which, with a low number of pulses treatment, have shown an increase of mechanical resistance up to the 70%.  相似文献   
54.
A new discharge system for resistive self-heating has been constructed for the measurement of accurate thermophysical properties. A constant-current pulse is used to heat metals over a time interval of 50 to 100 s, reaching temperatures up to the boiling point. New techniques have been developed to obtain sound speeds in the pulse-heated sample, emissivities, and vapor pressure. A new pyrometer allows the extension of the measured temperature range down to the melting point of copper.  相似文献   
55.
A universal curve relating the maximum of thermal conductivity and its respective temperature with the residual electrical resistivity has been proposed for metals and dilute alloys. Based on the equation of that curve, a comparative analysis of selected literature data of thermal conductivity of metals, which have residual electrical resistivity in the range 10–11<0<10–5. cm, have been performed. Using the data for 33 metals, confirmation of the Wiedemann-Franz law for the impurity component/T of thermal conductivity was obtained, which means that th/el1, where th and el are the parameters of the electron-lattice defect interaction obtained from measurements of thermal and electrical conductivity, respectively. Examples of the failure of the Wiedemann-Franz law are also presented, exhibiting the values of th/el in the range 0.16 to 25. Measurements of thermal conductivity in the range 2 to 20 K and determination of the residual electrical resistivity for the samples of Cd doped with Zn and quenched were performed, resulting in values th/el1.  相似文献   
56.
钱东强  刘时杰 《贵金属》1996,17(3):25-27
介绍了减压蒸馏脱硫,熔炼富集,高温悬浮氯气浸出处理热滤渣的工艺。其综合利用好,元素硫脱除率〉92%,贱金属浸出率〉95%,贵金属回收率〉99%。贵金属富集物可并入贵金属精炼分离工段处理。  相似文献   
57.
主要介绍在面临环境保护要求不断提升,废气排放指标不断降低的情况下,使用臭氧氧化+液碱脱硝技术对稀贵卡尔多炉和旋转顶吹炉生产回收金、银、硒、碲、铅、铋等金属产出的烟气的治理。治理后二氧化硫指标小于50mg/m3、氮氧化合物小于60mg/m3、尘指标小于10mg/m3,满足A类企业环保要求,同时其他重金属指标都满足国家国控指标要求,达到超低排放要求。  相似文献   
58.
张立  孙宝琦 《硬质合金》1994,11(2):71-73
本文研究了配碳量、粘结相中镍含量和温度对WC-Co-Ni硬质合会热扩散事的影响。结果表明,合金的热扩散率随配碳量、粘结相中谋含量增加而增加,随温度升高而降低.  相似文献   
59.
贵金属的化学发光分析   总被引:8,自引:1,他引:8  
耿征 《贵金属》1992,13(1):66-72
介绍化学发光分析的基本原理和测试技术,及其应用于测定贵金属的几种化学发光反应,并展望其前景。  相似文献   
60.
设计并制造了一套半固态铝合金触变成形的实验装置,对实验结果与模拟仿真计算进行了对比,其二者的拟合度很好。  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