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   1481521篇
  免费   27466篇
  国内免费   6919篇
电工技术   34323篇
综合类   6370篇
化学工业   268915篇
金属工艺   64124篇
机械仪表   41920篇
建筑科学   45722篇
矿业工程   11423篇
能源动力   50259篇
轻工业   109845篇
水利工程   14881篇
石油天然气   37672篇
武器工业   134篇
无线电   195962篇
一般工业技术   280277篇
冶金工业   151726篇
原子能技术   34021篇
自动化技术   168332篇
  2021年   15500篇
  2020年   11848篇
  2019年   14599篇
  2018年   15597篇
  2017年   14886篇
  2016年   21283篇
  2015年   17387篇
  2014年   28699篇
  2013年   87988篇
  2012年   34714篇
  2011年   46973篇
  2010年   42309篇
  2009年   50844篇
  2008年   44039篇
  2007年   41179篇
  2006年   44041篇
  2005年   38922篇
  2004年   40951篇
  2003年   40842篇
  2002年   40113篇
  2001年   36620篇
  2000年   35151篇
  1999年   33980篇
  1998年   40463篇
  1997年   36820篇
  1996年   33785篇
  1995年   29881篇
  1994年   28083篇
  1993年   27965篇
  1992年   26022篇
  1991年   23074篇
  1990年   23430篇
  1989年   22571篇
  1988年   21096篇
  1987年   19299篇
  1986年   18661篇
  1985年   22015篇
  1984年   22277篇
  1983年   20241篇
  1982年   19250篇
  1981年   19346篇
  1980年   17954篇
  1979年   18471篇
  1978年   17752篇
  1977年   17474篇
  1976年   18314篇
  1975年   16034篇
  1974年   15491篇
  1973年   15581篇
  1972年   13076篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
841.
The effect of Co addition on the formation of Ni-Ti clusters in maraging stainless steel was studied by three dimensional atom probe (3DAP) and first-principles calculation. The cluster analysis based on the maximum separation approach showed an increase in size but a decrease in density of Ni-Ti clusters with increasing the Co content. The first-principles calculation indicated weaker Co-Ni (Co-Ti) interactions than Co-Ti (Fe-Ti) interactions, which should be the essential reason for the change of distribution characteristics of Ni-Ti clusters in bcc Fe caused by Co addition.  相似文献   
842.
843.
844.
A previously designed and developed 12-step total synthesis that includes [1,1′-biphenyl]-2-amine and carbazole intermediates and that ultimately produces the carbazole alkaloid carbazomycin G was exploited as a screening compound library with the goal of identifying potential lead compound(s) with cytotoxic effect. These compounds were investigated by using in-vitro tests involving the two human cell lines HL-60 and MOLM-13, which both model acute myeloid leukaemia (AML). The in-vitro biological test results were used together with the molecular structures of the various intermediates in a concise SAR analysis. Several of the intermediates revealed cytotoxicity (IC50<10−4 M), although the final natural product carbazomycin G did not reveal cytotoxicity versus the two said human cell lines.  相似文献   
845.
Ferrites may contain single domain particles which gets converted into super-paramagnetic state near critical size. To explore the existence of these characteristic feature of ferrites, we have performed magnetization(M-H loop) and Mössbauer spectroscopic studies of Ni2+ substitution effect in Co1-xNixFe2O4 (where x?=?0, 0.25, 0.5, 0.75 and 1) nanoparticles were fabricated by solution combustion route using mixture of carbamide and glucose as fuels for the first time. As prepared samples exhibit spinel cubic structure with lattice parameters which decreases linearly with increase in Ni2+ concentration. The M-H loops reveals that saturation magnetization(Ms), coercive field(Hc) remanence magnetization(Mr) and magnetron number(ηB) decreases significantly with increasing Ni2+ substitution. The variation of saturation magnetization has been explained on the basis of Neel's molecular field theory. The coercive field(Hc) is found strongly dependent on the concentration of Ni2+ and decrease of coercivity suggests that the particles have single domain and exhibits superparamagnetic behavior. The Mössbauer spectroscopy shows two ferrimagnetically relaxed Zeeman sextets distribution at room temperature. The dependence of Mössbauer parameters such as isomer shift, quadru pole splitting, line width and hyperfine magnetic field on Ni2+ concentration have been discussed. Hence our results suggest that synthesized materials are potential candidate for power transformer application.  相似文献   
846.
847.
848.
849.
850.
Consumer studies and market reports show an increase in consumption of ready‐to‐eat (RTE) foods. Although conventional processing technologies can in most cases produce safe products, they can also lead to the degradation of nutritional compounds and negatively affect quality characteristics. Consumers strongly prefer food that is minimally processed with the maximum amount of health‐promoting substances. Novel processing technologies as pre‐ or post‐treatment decontamination methods or as substitutes of conventional technologies have the potential to produce foods that are safe, rich in nutrient content and with superior organoleptic properties. Combining novel with conventional processes can eliminate potential drawbacks of novel technologies. This review examines available scientific information and critically evaluates the suitability and efficiency of various novel thermal and nonthermal technologies in terms of microbial safety, quality as well as nutrient content on the production of RTE meals, meats and pumpable products.  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