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   7418篇
  免费   1045篇
  国内免费   557篇
电工技术   180篇
综合类   736篇
化学工业   1917篇
金属工艺   77篇
机械仪表   102篇
建筑科学   2128篇
矿业工程   498篇
能源动力   125篇
轻工业   1065篇
水利工程   583篇
石油天然气   692篇
武器工业   7篇
无线电   88篇
一般工业技术   509篇
冶金工业   191篇
原子能技术   26篇
自动化技术   96篇
  2024年   31篇
  2023年   105篇
  2022年   178篇
  2021年   282篇
  2020年   254篇
  2019年   250篇
  2018年   290篇
  2017年   291篇
  2016年   299篇
  2015年   327篇
  2014年   437篇
  2013年   481篇
  2012年   527篇
  2011年   574篇
  2010年   429篇
  2009年   431篇
  2008年   409篇
  2007年   489篇
  2006年   466篇
  2005年   417篇
  2004年   360篇
  2003年   323篇
  2002年   276篇
  2001年   169篇
  2000年   166篇
  1999年   154篇
  1998年   117篇
  1997年   102篇
  1996年   61篇
  1995年   58篇
  1994年   54篇
  1993年   37篇
  1992年   33篇
  1991年   37篇
  1990年   22篇
  1989年   13篇
  1988年   9篇
  1987年   7篇
  1986年   8篇
  1985年   9篇
  1984年   5篇
  1983年   8篇
  1982年   7篇
  1981年   1篇
  1979年   13篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1959年   1篇
排序方式: 共有9020条查询结果,搜索用时 15 毫秒
11.
采用稀土氧化物和无机化合物的复合物(不简称RI-复合物)作为搪瓷釉浆悬浮剂,使之全部或大部分代替粘土,进行了一系列试验,已获得成功,突破了长期来搪瓷工业离不开粘土的传统工艺,并实现了工业化生产。  相似文献   
12.
Evaluating Liquefaction Strength of Partially Saturated Sand   总被引:1,自引:0,他引:1  
A method is presented for evaluating the liquefaction strength of partially saturated sand using the compression wave velocity (P-wave velocity), a new indicator of saturation. Based on laboratory test results, an empirical correlation that relates the liquefaction strength with the pore pressure coefficient B is firstly proposed. The strength is defined as the cyclic stress ratio required to cause liquefaction at a specified number of cycles. With the aid of a theoretical relation between B and the P-wave velocity, an explicit correlation of more interest is then established between the liquefaction strength of sand and its P-wave velocity. A comparison of the predictions using this explicit correlation with laboratory measurements shows a satisfactory agreement. The significance of this method lies in that it makes it possible to evaluate the liquefaction strength of sand as affected by saturation through the measurement of P-wave velocity, which can be made not only in the laboratory but particularly in the field.  相似文献   
13.
用热失重法确定水合粘土水分含量及存在形式   总被引:1,自引:1,他引:0  
文章以蒙脱土为例,采用热失重法定性定量确定了水合粘土中结合水类型、界限及其相对含量,并与等温吸附法结果进行了对比。结果表明,用该方法得到的水合蒙脱土中各种水分的相对含量及总含水量与等温吸附实验结果相一致。热失重(25~250 ℃)分析结果表明,水合蒙脱土中水分子主要存在自由水、松散吸附结合水、紧密吸附水(强吸附结合水)3种状态,分别对应于25~75 ℃、75~120 ℃、120~230 ℃区间里的失水。从热失重(25~250 ℃)规律来看,仍存在两个明显的转折点p/ps=0.9、0.98,它们为粘土-水体系的两个特征湿度,前者为粘土表面强结合水与松散结合水(渗透结合水)之间的界限,后者为松散结合水与自由水之间的界限,这验证了等温吸附法确定的两个特征湿度及对粘土表面结合水界限划分的正确性。  相似文献   
14.
Intercalation of poly[oligo(oxyethylene) methacrylates] onto sodium montmorillonite (MMT) clay has been investigated. A polymer–clay hybrid has been synthesized through intercalation of the monomer followed by its solution free‐radical polymerization. Eight polymer–clay hybrids were prepared using different weight ratios of clay, different oligo(oxyethylene) lengths and different proportions of crosslinker. Evidence of the development of nanostructures is obtained from scanning electron microscopy, and wide‐angle X‐ray diffraction studies support these results which show disappearance of the peak characteristic to d001 spacing. In this hybrid MMT is dispersed homogeneously in the polymer matrix. © 2003 Society of Chemical Industry  相似文献   
15.
为了继承和发扬错金工艺,从其定义出发,探讨了该工艺在中国古代及国外的发展与应用以及笔者对该工艺的实验研究。针对在错金工艺实践过程中出现的问题,在查阅了相关的资料后,对传统错金工艺的实现方法提出了质疑。  相似文献   
16.
对Daleel油田作业5区三分支水平井DL-59井井下复杂情况分析,室内测定了引起复杂情况的Nahr Umr泥页岩地层的矿物组分和粘土矿物含量,优选了适应在该泥页岩地层215.9 mm造斜井段的钻井液配方中的各种处理剂,最后研制出钻井液配方,通过DL-73井应用后,取得了良好的防塌效果.  相似文献   
17.
Z.P. Luo  J.H. Koo 《Polymer》2008,49(7):1841-1852
As the performance of polymer layered silicate nanocomposites strongly depends on their interior layer dispersion, quantification of the layer dispersion degree is needed. In this work, a new methodology was developed to determine the dispersion parameter D0.1, based on the measurement of the free-path spacing distance between the single clay sheets from the transmission electron microscopy (TEM) images. Several examples of exfoliated, intercalated, and immiscible composites were studied. It was found that the exfoliated composites had D0.1 over 8%, while that of intercalated composites were between 4 and 8%. In the case of intercalation, a high frequency peak appeared at a short spacing distance in the histogram, which was a characteristic of the intercalation, distinct from the exfoliation. The main utility of this TEM methodology is for the quantification of exfoliated or intercalated samples with small number of layers with stacks. The dispersion parameter D0.1 below 4% was suggested to classify as immiscible. A unique advantage of the TEM measurement is that the dispersion degree of different fillers can be counted individually.  相似文献   
18.
Samples of chicken meat from spent laying hens were obtained by four different methods: (1) manual deboning of whole carcasses; (2) manual deboning of skinned carcasses; (3) mechanical deboning of whole carcasses; and (4) mechanical deboning of skinned carcasses. The meat was packaged, frozen and stored at ?18 °C for up to 3 months. Functional properties studied were pH, emulsifying capacity (EC) and water‐holding capacity (WHC) and, in addition, pigment concentration was investigated. Sensory properties included aroma, colour, texture and overall acceptability, as judged by a trained panel using a nine‐point hedonic scale. Removal of the skin prior to deboning by either method gave significantly higher values (P < 0.05) for EC, while WHC values were not significantly different among the experimental treatments, despite higher pH values for mechanically‐deboned meat, with and without skin. Pigment concentrations were highest in meat from Treatment 4 and lowest for Treatment 1, but values for both methods of deboning were affected by the presence of skin. There were no significant differences between treatments for any of the sensory properties studied. Changes occurring in the meat during frozen storage are described.  相似文献   
19.
A prediction method for the thermal conductivity of halocarbon refrigerants in the saturated liquid state in the reduced temperature range 0.3 to well above 0.9 is presented in this paper. The aim of the method is to present a very simple calculation of the transport property useful for engineering purposes. The method determines thermal conductivity as a sole function of the reduced temperature and requires the knowledge of a parameter dependent upon easily available physical constants characteristic of each compound. The method is validated against experimental data available in the literature, giving average absolute deviations which are usually less than 5%, with maximum absolute deviations generally less than 10%. An extension of the method to estimate thermal conductivity of binary mixtures is also presented, along with a comparison with the few experimental data available in the literature.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.  相似文献   
20.
以生产润滑油基础油的老三套工艺为基础,开发了改善油品氧化安定性的组合工艺。该工艺的主要特点是包括一步络合脱氮过程。实验证明,该组合工艺既可以有效地提高基础油的氧化安定性,又能降低溶剂精制深度,提高基础油收率。  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