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   157585篇
  免费   13097篇
  国内免费   6960篇
电工技术   8761篇
技术理论   3篇
综合类   8385篇
化学工业   25133篇
金属工艺   8565篇
机械仪表   10176篇
建筑科学   9479篇
矿业工程   3327篇
能源动力   5305篇
轻工业   11213篇
水利工程   2812篇
石油天然气   4953篇
武器工业   1287篇
无线电   22284篇
一般工业技术   21774篇
冶金工业   9918篇
原子能技术   2179篇
自动化技术   22088篇
  2024年   483篇
  2023年   1825篇
  2022年   3513篇
  2021年   5262篇
  2020年   3884篇
  2019年   3457篇
  2018年   3966篇
  2017年   4430篇
  2016年   4587篇
  2015年   5553篇
  2014年   7489篇
  2013年   9834篇
  2012年   10678篇
  2011年   12229篇
  2010年   10763篇
  2009年   10633篇
  2008年   10471篇
  2007年   9745篇
  2006年   9038篇
  2005年   7354篇
  2004年   5865篇
  2003年   4996篇
  2002年   4838篇
  2001年   3987篇
  2000年   3339篇
  1999年   2732篇
  1998年   3177篇
  1997年   2263篇
  1996年   1875篇
  1995年   1508篇
  1994年   1128篇
  1993年   1018篇
  1992年   712篇
  1991年   671篇
  1990年   555篇
  1989年   528篇
  1988年   397篇
  1987年   339篇
  1986年   310篇
  1985年   257篇
  1984年   221篇
  1983年   182篇
  1982年   172篇
  1981年   154篇
  1980年   147篇
  1979年   112篇
  1978年   101篇
  1977年   136篇
  1976年   170篇
  1975年   88篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
面部运动单元检测旨在让计算机从给定的人脸图像或视频中自动检测需要关注的运动单元目标。经过二十多年的研究,尤其是近年来越来越多的面部运动单元数据库的建立和深度学习的兴起,面部运动单元检测技术发展迅速。首先,阐述了面部运动单元的基本概念,介绍了已有的常用面部运动单元检测数据库,概括了包括预处理、特征提取、分类器学习等步骤在内的传统检测方法;然后针对区域学习、面部运动单元关联学习、弱监督学习等几个关键研究方向进行了系统性的回顾梳理与分析;最后讨论了目前面部运动单元检测研究存在的不足以及未来潜在的发展方向。  相似文献   
62.
Phytoalexins are inducible secondary metabolites possessing antimicrobial activity against phytopathogens. Rice produces a wide array of phytoalexins in response to pathogen attacks and environmental stresses. With few exceptions, most phytoalexins identified in rice are diterpenoid compounds. Until very recently, flavonoid sakuranetin was the only known phenolic phytoalexin in rice. However, recent studies have shown that phenylamides are involved in defense against pathogen attacks in rice. Phenylamides are amine-conjugated phenolic acids that are induced by pathogen infections and abiotic stresses including ultra violet (UV) radiation in rice. Stress-induced phenylamides, such as N-trans-cinnamoyltryptamine, N-p-coumaroylserotonin and N-cinnamoyltyramine, have been reported to possess antimicrobial activities against rice bacterial and fungal pathogens, an indication of their direct inhibitory roles against invading pathogens. This finding suggests that phenylamides act as phytoalexins in rice and belong to phenolic phytoalexins along with sakuranetin. Phenylamides also have been implicated in cell wall reinforcement for disease resistance and allelopathy of rice. Synthesis of phenolic phytoalexins is stimulated by phytopathogen attacks and abiotic challenges including UV radiation. Accumulating evidence has demonstrated that biosynthetic pathways including the shikimate, phenylpropanoid and arylmonoamine pathways are coordinately activated for phenolic phytoalexin synthesis, and related genes are induced by biotic and abiotic stresses in rice.  相似文献   
63.
Evaluation of kinetic distribution and behaviors of nanoparticles in vivo provides crucial clues into their roles in living organisms. Extracellular vesicles are evolutionary conserved nanoparticles, known to play important biological functions in intercellular, inter‐species, and inter‐kingdom communication. In this study, the first kinetic analysis of the biodistribution of outer membrane vesicles (OMVs)—bacterial extracellular vesicles—with immune‐modulatory functions is performed. OMVs, injected intraperitoneally, spread to the whole mouse body and accumulate in the liver, lung, spleen, and kidney within 3 h of administration. As an early systemic inflammation response, increased levels of TNF‐α and IL‐6 are observed in serum and bronchoalveolar lavage fluid. In addition, the number of leukocytes and platelets in the blood is decreased. OMVs and cytokine concentrations, as well as body temperature are gradually decreased 6 h after OMV injection, in concomitance with the formation of eye exudates, and of an increase in ICAM‐1 levels in the lung. Following OMV elimination, most of the inflammatory signs are reverted, 12 h post‐injection. However, leukocytes in bronchoalveolar lavage fluid are increased as a late reaction. Taken together, these results suggest that OMVs are effective mediators of long distance communication in vivo.  相似文献   
64.
65.
66.
67.
68.
Cystoseira hakodatensis is an unutilised brown algae belonging to family Sargassaceae. A crude methanol extract from the algae showed inhibitory effects on the growths of Bacillus cereus and Bacillus licheniformis. To isolate the major antimicrobial agent, a sequential active‐guided isolation procedure was applied: liquid–liquid extraction, column chromatography and bio‐autography. A marked antimicrobial agent (active α) was isolated in hydrophobic fraction and was determined to phenolics without carbohydrates and proteins by phytochemical test. Regarding the antimicrobial potential, the isolated active α showed better inhibitory effects against B. cereus and B. licheniformis at 2 and 4 times of lower concentrations (62.5 and 31.3 μg mL?1) in comparison with epigallocatechin gallate. These results showed that C. hakodatensis is a potential source of antimicrobial agent capable of preventing the growth of the two bacteria.  相似文献   
69.
70.
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