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   812830篇
  免费   11889篇
  国内免费   2450篇
电工技术   14821篇
综合类   825篇
化学工业   121861篇
金属工艺   29762篇
机械仪表   23141篇
建筑科学   21105篇
矿业工程   2936篇
能源动力   22223篇
轻工业   75097篇
水利工程   7354篇
石油天然气   10699篇
武器工业   49篇
无线电   97217篇
一般工业技术   153278篇
冶金工业   160139篇
原子能技术   14249篇
自动化技术   72413篇
  2021年   6655篇
  2020年   4821篇
  2019年   6132篇
  2018年   10299篇
  2017年   10120篇
  2016年   10729篇
  2015年   7871篇
  2014年   12917篇
  2013年   37873篇
  2012年   21084篇
  2011年   29565篇
  2010年   23177篇
  2009年   26062篇
  2008年   27119篇
  2007年   27036篇
  2006年   23928篇
  2005年   21991篇
  2004年   21197篇
  2003年   20900篇
  2002年   19962篇
  2001年   19970篇
  2000年   18537篇
  1999年   19775篇
  1998年   49547篇
  1997年   35181篇
  1996年   27178篇
  1995年   20768篇
  1994年   18217篇
  1993年   17782篇
  1992年   12858篇
  1991年   12254篇
  1990年   11798篇
  1989年   11448篇
  1988年   10788篇
  1987年   9390篇
  1986年   9242篇
  1985年   10802篇
  1984年   10096篇
  1983年   8866篇
  1982年   8305篇
  1981年   8385篇
  1980年   7931篇
  1979年   7733篇
  1978年   7337篇
  1977年   8892篇
  1976年   11969篇
  1975年   6291篇
  1974年   5988篇
  1973年   5977篇
  1972年   4870篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Heat resistant coatings are required primarily for stacks, exhaust pipes, reactors, space crafts and similar equipments that are permanently or occasionally exposed to elevated temperatures. High-temperature coatings are generally based on silicone resin with ceramic and metallic pigments. In this study, iron oxide, cobalt oxide (thermo chromic compound) and aluminum oxide are used for the preparation of four new types of coloured pigments. The thermal resistant characteristics of these ceramic pigments were studied by differential thermal analysis, thermo gravimetric analysis and differential scanning calorimetric analysis. These ceramic pigments are found to be thermally stable up to 400 °C.  相似文献   
992.
Summary The effect of the addition of four commercial pectolytic preparations on the visual characteristics (colour and turbidity) of red wines has been evaluated. The effect of both clarifying and colour extracting enzymes and the effect of different doses used, were evaluated and compared. All the red wines treated enzymatically, independent of the type of enzyme and dose, present chromatic characteristics which can be considered better than those of the control wines. Also, those wines treated with enzymes had greater stability during 2 years storage in bottles, in particular the turbidity was better than untreated wines.  相似文献   
993.
A hybrid technology for the realization of three-dimensional (3-D) miniaturized power inductors is presented. Our devices consist of planar Cu coils on polyimide substrates, and mm-size ferrite magnetic cores, obtained by three-dimensional micro-patterning of ferrite wafers using powder blasting. The coils are realized using an in-house developed high-resolution polyimide spinning and Cu electroplating process. Winding widths down to 5 /spl mu/m have been obtained and total device volumes are ranging between 1.5 and 10 mm/sup 3/. Inductive and resistive properties are characterized as a function of frequency; inductance values in the 100 /spl mu/H range have been obtained.  相似文献   
994.
From visual data exploration to visual data mining: a survey   总被引:8,自引:0,他引:8  
We survey work on the different uses of graphical mapping and interaction techniques for visual data mining of large data sets represented as table data. Basic terminology related to data mining, data sets, and visualization is introduced. Previous work on information visualization is reviewed in light of different categorizations of techniques and systems. The role of interaction techniques is discussed, in addition to work addressing the question of selecting and evaluating visualization techniques. We review some representative work on the use of information visualization techniques in the context of mining data. This includes both visual data exploration and visually expressing the outcome of specific mining algorithms. We also review recent innovative approaches that attempt to integrate visualization into the DM/KDD process, using it to enhance user interaction and comprehension.  相似文献   
995.
ABSTRACT: Herring byproducts were stored at 2 and 15 °C for up to 72 h. Over time, significant increases of total volatile bases (TVB), histamine, putrescine, cadaverine, and tyramine were detected. However, only tyramine and TVB levels were temperature-dependent. The level of total polyunsaturated fatty acids (PUFAs) was constant. Longer byproducts storage gave rise to an oil with higher levels of free fatty acids, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and total PUFAs, while fluorescent compounds were lower. A higher storage temperature led to oil higher in α-tocopherol and EPA levels and lower in anisidine value. Surprisingly, the oil with the highest content of PUFAs was not produced from the freshest byproducts, and oil with low oxidation products can be extracted from stored byproducts.  相似文献   
996.
997.
The cooling and solidification of melted drops during their movement in an immiscible cooling medium is widely employed for granulation in the chemical industry, and a study of these processes to provides a basis for the design of the granulation tower height and the temperature of the cooling medium is reported. A physical model of the cooling and solidification of the drop is established and the numerical calculation is performed. The influences of the key factors in the solidification, i.e., Bi number, drop diameter, temperature of the cooling medium, etc. are presented. The cooling and solidification during wax granulation in a water‐cooling tower and during urea granulation in an air‐cooling tower (spraying tower) are described in detail. Characteristics of the solidification and temperature distribution within the particle at different times are shown. The model and calculations can be used for structure design of the granulation tower and optimization of the operation parameters.  相似文献   
998.
As a result of shrinking fossil fuels, biomass as a regenerative energy source gains importance. To realize biomass projects it is essential to investigate in convenient thermal procedures. On this evidence an analysis and evaluation of diverse gasification technologies with different boundary conditions and diverse biomasses are indispensable. Form and kind of the biomass as well as the type of the gasification plant cause different compositions of the product gas. The gasifiers show advantages and disadvantages concerning the biomass and the produced gas quality, depending on reactor type, kind of heat supply, gasification medium, and the pressure ratio in the reactor. As the ideal gasifier for different biomass is presently not available, it will be shown, which biomass is suitable for fixed bed or fluidized bed gasifiers.  相似文献   
999.
1000.
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