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   1417022篇
  免费   24233篇
  国内免费   6884篇
电工技术   33898篇
综合类   6332篇
化学工业   267502篇
金属工艺   62804篇
机械仪表   39159篇
建筑科学   44587篇
矿业工程   11235篇
能源动力   50281篇
轻工业   100547篇
水利工程   13990篇
石油天然气   37238篇
武器工业   129篇
无线电   193694篇
一般工业技术   268348篇
冶金工业   118496篇
原子能技术   33691篇
自动化技术   166208篇
  2021年   15633篇
  2020年   11858篇
  2019年   14636篇
  2018年   13940篇
  2017年   13089篇
  2016年   20464篇
  2015年   17267篇
  2014年   28679篇
  2013年   87814篇
  2012年   33019篇
  2011年   43837篇
  2010年   40542篇
  2009年   49574篇
  2008年   41483篇
  2007年   38076篇
  2006年   42715篇
  2005年   36844篇
  2004年   39484篇
  2003年   39552篇
  2002年   38992篇
  2001年   35074篇
  2000年   33994篇
  1999年   32272篇
  1998年   30442篇
  1997年   30501篇
  1996年   29682篇
  1995年   27400篇
  1994年   26178篇
  1993年   26098篇
  1992年   25335篇
  1991年   22231篇
  1990年   22696篇
  1989年   21751篇
  1988年   20209篇
  1987年   18609篇
  1986年   17911篇
  1985年   21262篇
  1984年   21860篇
  1983年   19841篇
  1982年   18958篇
  1981年   19030篇
  1980年   17576篇
  1979年   18211篇
  1978年   17459篇
  1977年   16593篇
  1976年   16472篇
  1975年   15781篇
  1974年   15326篇
  1973年   15375篇
  1972年   12864篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
Trust is the key element of commerce, both for traditional models and — more recently — for eCommerce. Unlike its traditional counterpart, eCommerce relies on trust being created and maintained with the help of digital devices and services. Convergence brings significant changes to the way people interact through digital media by offering ubiquitous and seamless communication. This has a significant impact on the way trust is established and maintained, with consequent impact upon eCommerce. This paper identifies a number of the most important challenges to trust in eCommerce as well as trust-related aspects of key enablers of eCommerce. From this perspective, the paper studies an impact of convergence on trust within eCommerce to identify several positive relationships.  相似文献   
33.
34.
It was found that vanadyl porphyrin complexes synthesized from petroleum metal porphyrin concentrates stimulated epoxidation during the olefin oxygenation process. The yields of obtained oxiranes turned out to be 38–75%, depending on the olefin structure. An epoxidation mechanism that suggests the formation of a protonated dioxygen adduct as an intermediate during oxygenation of olefins in the presence of vanadyl porphyrin complexes was proposed. An analogy is drawn between the epoxide formation reaction upon the catalytic oxygenation of olefins and the Prilezhaev reaction.  相似文献   
35.
Presented here are details of the development of a novel membrane integrated circuit (IC) probe card structure based on microsystems technology. The device design allows probing of both solder bumps and pads. A self-limiting sensor was integrated to prolong device lifetime. Comparison with and discussion of the use of modelling is made. Possible enhancements to the probing structure are discussed to improve alignment and measurements. Also shown is data using our microsystems probe card to access a simple IC device. Our device has a contact resistance of less than 0.5 Ω for a force of 0.004 N. A method to implement our probing structure for commercial application and the potential developments which can be made to improve its ease of use are then discussed.  相似文献   
36.
The Magnitogorsk Metallurgical Combine has conducted a study of the effect of technological factors on the hydrogen content of chromium-nickel-molybdenum steel after vacuum degassing. It was established that the most important factor is the hydrogen content of the steel before the degassing operation. The study also determined the effects of the circulation coefficient, the duration of the degassing operation, and the vacuum used in the treatment. __________ Translated from Metallurg, No. 7, pp. 68–69, July, 2006.  相似文献   
37.
38.
Kowalik  J. 《Computer》2006,39(3):104-103
Isolating applied mathematics from computer science harms the profession and those who depend on it.  相似文献   
39.
The homogenization of Ni in powder metal (PM) steel compacts is usually difficult even after high-temperature sintering at 1250°C. An earlier study by the authors demonstrated that this problem can be alleviated through the addition of 0.5 wt pct Cr in the form of stainless steel powders. To further improve the microstructure and mechanical properties of Ni-containing PM steels and to understand the mechanisms, an attempt was made in this study using the Fe-3Cr-0.5Mo prealloyed powder as the base material. The results showed that the distribution of the Ni additives was significantly improved. As a result, the tensile strength of the Fe-3Cr-0.5Mo-4Ni-0.5C compact sintered at 1250°C reached 1323 MPa. The elongation was higher than 1 pct. These sinter-hardened properties, which were attained using a slow furnace cooling rate, were comparable to those of the sinter-hardened alloys reported in the literature using accelerated cooling and were equivalent to those of the best quenched-and-tempered alloys registered in the Metal Powder Industries Federation (MPIF) standards. These improvements were attributed to the positive effect of Cr addition on alloy homogenization due to the reduction of the repelling effect between Ni and C, as was demonstrated through the thermodynamic analysis using the Thermo-Calc program.  相似文献   
40.
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