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   264452篇
  免费   4574篇
  国内免费   1968篇
电工技术   5607篇
技术理论   5篇
综合类   1406篇
化学工业   42638篇
金属工艺   11274篇
机械仪表   7970篇
建筑科学   6929篇
矿业工程   1790篇
能源动力   5688篇
轻工业   26014篇
水利工程   2944篇
石油天然气   6267篇
武器工业   264篇
无线电   28190篇
一般工业技术   49612篇
冶金工业   47445篇
原子能技术   5651篇
自动化技术   21300篇
  2021年   2636篇
  2020年   1791篇
  2019年   2221篇
  2018年   3494篇
  2017年   3477篇
  2016年   3790篇
  2015年   2928篇
  2014年   4775篇
  2013年   11570篇
  2012年   7921篇
  2011年   10406篇
  2010年   8313篇
  2009年   8847篇
  2008年   9667篇
  2007年   9737篇
  2006年   8635篇
  2005年   7587篇
  2004年   6777篇
  2003年   6325篇
  2002年   6321篇
  2001年   6422篇
  2000年   6013篇
  1999年   5964篇
  1998年   12928篇
  1997年   9586篇
  1996年   7324篇
  1995年   5590篇
  1994年   5121篇
  1993年   4975篇
  1992年   3971篇
  1991年   3775篇
  1990年   3837篇
  1989年   3788篇
  1988年   3545篇
  1987年   3036篇
  1986年   3056篇
  1985年   3412篇
  1984年   3323篇
  1983年   3074篇
  1982年   2701篇
  1981年   2905篇
  1980年   2643篇
  1979年   2840篇
  1978年   2738篇
  1977年   2841篇
  1976年   3694篇
  1975年   2458篇
  1974年   2290篇
  1973年   2321篇
  1972年   1981篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
The crystallization of Pd40Ni40P20 glass, produced by melt-spinning in air, has been studied by optical metallography. Crystallization is predominantly from the surface and is more prevalent on the wheel-side. The non-uniformity is attributed to variation in quench rate during production. A three-stage anneal permits crystals which have nucleated at the surface to be identified and their size distribution to be analysed. The surface nucleation is heterogeneous and appears to be hindered by mild oxidation. The annealing atmosphere markedly affects the surface crystallization behaviour, as does removal of the original ribbon surface. When nucleation is sparse, partial crystallization causes the development of noticeable relief on the sample surfaces.  相似文献   
983.
The rôle of saponins in the undesirable sensory properties of the dried pea P sativum is reported. The sensory properties of isolated soyasaponin I are defined and described as bitter, astringent and metallic. The distribution of saponin in various air-classified pea flour fractions shows that the protein-rich fraction may contain sufficient saponin to cause undesirable tastes.  相似文献   
984.
Previous studies have found that in American culture high-arousal positive states (HAP) such as excitement are valued more and low-arousal positive states (LAP) such as calm are valued less than they are in Chinese culture. What specific factors account for these differences? The authors predicted that when people and cultures aimed to influence others (i.e., assert personal needs and change others' behaviors to meet those needs), they would value HAP more and LAP less than when they aimed to adjust to others (i.e., suppress personal needs and change their own behaviors to meet others' needs). They test these predictions in 1 survey and 3 experimental studies. The findings suggest that within and across American and Chinese contexts, differences in ideal affect are due to specific interpersonal goals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
985.
986.
Concentration profiles obtained by slicing a cylindrical gel were used to measure diffusion of volatiles in viscous aqueous dextrose solutions. The column length, slice thickness and diffusion time were optimized to maximize the repeatability of measurements, the results being very sensitive to small changes in variables. Coefficients of variation between 5 and 10% were obtained. In the presence of different concentrations of dextrose, the diffusivity of acetone decreased markedly as dextrose concentration increased. However, when the acetone concentration was varied within the range 0·6 to 13·7%, at a constant 50% (w/w) dextrose concentration, its diffusivity did not change significantly. The sliced gel system gave values of diffusivity in close agreement with those obtained by other techniques.  相似文献   
987.
988.
A total of six cows, divided into 3 groups, were fed various amounts of rape cake containing 6 g of goitrin/kg over a period of 7 days. The cows were milked twice a day and the goitrin content of the heated milk samples were determined by a HPLC-method within 2 h. When rape cake was fed at 0.39, 1.9 and 3.9% resp. of the total feed this resulted in medium goitrin values of 37, 163 and 707 micrograms/l milk. These values correspond to a transfer of about 0.1% of the original progoitrin content in the feed. 12 h after the last rape feeding the amount of goitrin in the milk was below the detection limit of 7 ppb. The toxicological significance of these findings are dicussed.  相似文献   
989.
990.
In order to investigate the galvanic anodic protection (GAP) of ferrous metals (such as 410, 304 and 316 stainless steels) in acid solutions by doped polyaniline (PANi), separate doped PANi powder-pressed electrodes with different surface areas (the area ratio of the PANi electrode to stainless steel is between 1:1 and 1:2) have been prepared. These were coupled with ferrous metal in the following solutions: 5 M sulphuric acid, 5 M phosphoric acid and industrial phosphoric acid (containing 5 M phosphoric acid and 0.05% chloride ion) to construct a galvanic cell, in which PANi is cathode while ferrous metal is anode. The results indicate that a PANi electrode with sufficient area can provide corrosion protection to stainless steel in these acidic solutions. A pilot scale coupling experiment was carried out. The results indicate that PANi is a promising material as an electrode for the anodic protection of ferrous metals in acidic solutions in industrial situations.  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