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   87231篇
  免费   7273篇
  国内免费   3637篇
电工技术   4743篇
技术理论   12篇
综合类   5513篇
化学工业   15159篇
金属工艺   5111篇
机械仪表   5325篇
建筑科学   7201篇
矿业工程   2515篇
能源动力   2621篇
轻工业   5568篇
水利工程   1516篇
石油天然气   6079篇
武器工业   595篇
无线电   9409篇
一般工业技术   10888篇
冶金工业   4437篇
原子能技术   957篇
自动化技术   10492篇
  2024年   343篇
  2023年   1487篇
  2022年   2415篇
  2021年   3375篇
  2020年   2675篇
  2019年   2296篇
  2018年   2626篇
  2017年   2875篇
  2016年   2574篇
  2015年   3287篇
  2014年   4302篇
  2013年   5163篇
  2012年   5514篇
  2011年   5948篇
  2010年   5198篇
  2009年   4959篇
  2008年   4813篇
  2007年   4687篇
  2006年   4817篇
  2005年   4173篇
  2004年   2753篇
  2003年   2492篇
  2002年   2207篇
  2001年   2059篇
  2000年   2171篇
  1999年   2407篇
  1998年   1921篇
  1997年   1567篇
  1996年   1435篇
  1995年   1257篇
  1994年   1033篇
  1993年   740篇
  1992年   588篇
  1991年   441篇
  1990年   397篇
  1989年   272篇
  1988年   240篇
  1987年   148篇
  1986年   132篇
  1985年   92篇
  1984年   69篇
  1983年   42篇
  1982年   44篇
  1981年   31篇
  1980年   26篇
  1979年   12篇
  1978年   5篇
  1975年   3篇
  1974年   3篇
  1959年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
李伟东  江霞  杨华云 《广东化工》2015,42(1):131+136
从独立学院"应用型专业人才"的培养目标出发,结合我院近年来开展《环境监测实验》课程积累的经验,对本实验课程的教学内容、教学方法和课程评价体系等进行了改革。强调理论与实验内容有机结合,通过激发学生的学习兴趣,提高学生的实践应用能力,以满足社会对环境科学与工程专业应用型专业人才的需求。  相似文献   
22.
The evaluation of cell's weatherability is of practical interest. To further improve the soluble lead flow battery's weatherability, physiochemical properties of electrolytes containing fluoborate, perchlorate, methanesulfonate and trifluoromethanesulfonate are investigated from ?60 to 50 °C. Activities of CF3SO3H and HClO4 are poor in trifluoromethanesulfonate and perchlorate solutions due to common anion effect. The solubility of lead salt can be improved by increasing temperature, but worsened by increasing acid's content. With the temperature increasing, the conductivity is enhanced, and the viscosity is lowered for four solutions. The same results have been found by increasing acid's content except for CF3SO3H. The high energy efficiency can be achieved for cells over ?40–0 °C using fluoborate and perchlorate solutions, 73.2% at ?40 °C and 78.1% at ?30 °C respectively. Over the temperature range of 20–50 °C, the cells with methanesulfonate and trifluoromethanesulfonate solutions have good performance, 77.4% and 73.7% at 50 °C respectively.  相似文献   
23.
Core–shell structures have been proposed to improve the electrical properties of negative-temperature coefficient (NTC) thermistor ceramics. In this work, Al2O3-modified Co1.5Mn1.2Ni0.3O4 NTC thermistor ceramics with adjustable electrical properties were prepared through citrate-chelation followed by conventional sintering. Co1.5Mn1.2Ni0.3O4 powder was coated with a thin Al2O3 shell layer to form a core–shell structure. Resistivity (ρ) increased rapidly with increasing thickness of the Al2O3 layer, and the thermal constant (B) varied moderately between 3706 and 3846 K. In particular, Co1.5Mn1.2Ni0.3O4@Al2O3 ceramic with 0.08 wt% Al2O3 showed the increase of ρ double, and the change in its B was less than 140 K. The Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics showed high stability, and their grain size was relatively uniform due to the protection offered by the shell. The aging coefficient of the ceramic was less than 0.2% after aging for 500 hours at 125°C. Taken together, the results indicate that as-prepared Co1.5Mn1.2Ni0.3O4@Al2O3 NTC ceramics with a core–shell structure may be promising candidates for application as wide-temperature NTC thermistor ceramics.  相似文献   
24.
25.
Based on the potential therapeutic value in targeting mitochondria and the fluorophore tracing ability, a fluorescent mitochondria-targeted organic arsenical PDT-PAO-F16 was fabricated, which not only visualized the cellular distribution, but also exerted anti-cancer activity in vitro and in vivo via targeting pyruvate dehydrogenase complex (PDHC) and respiratory chain complexes in mitochondria. In details, PDT-PAO-F16 mainly accumulated into mitochondria within hours and suppressed the activity of PDHC resulting in the inhibition of ATP synthesis and thermogenesis disorder. Moreover, the suppression of respiratory chain complex I and IV accelerated the mitochondrial dysfunction leading to caspase family-dependent apoptosis. In vivo, the acute promyelocytic leukemia was greatly alleviated in the PDT-PAO-F16 treated group in APL mice model. Our results demonstrated the organic arsenical precursor with fluorescence imaging and target-anticancer efficacy is a promising anticancer drug.  相似文献   
26.
Wei  Mengnan  Ban  Boyuan  Li  Jingwei  Sun  Jifei  Li  Feifei  Jiang  Xuesong  Chen  Jian 《SILICON》2020,12(2):327-338
Silicon - A novel green cationic surfactant Poly (propylene glycol) bis (2-aminopropyl ether) (PEA) with multiple amine groups was utilized as a collector for flotation separation of quartz from...  相似文献   
27.
28.
通过分析A公司在研发项目范围管理中所存在问题,提出研发项目范围管理的方法及其在C产品的应用实例,通过运用研发项目范围管理的工具和方法,改善产品开发流程,从而缩短新产品开发周期,提高响应市场的速度,并提高企业研发项目的管理能力。  相似文献   
29.
30.
The effect of Li2O on the crystallization properties of CaO-Al2O3-SiO2-Li2O-Ce2O3 slags was investigated. With increasing the Li2O content, LiAlO2 and CaCeAlO4 were the main crystalline phases. LiAlO2 formed for the charge compensating of Li+ ions to [AlO45?]-tetrahedrons, and CaCeAlO4 formed as a result of the charge balance of Ce3+ ions, Ca2+ ions, and [AlO69?]-octahedrons. Increasing the content of Li2O to 10%, the crystallization temperature was the highest, and the incubation time was the shortest. The crystallization ability was strong due to the three factors of strengthening the interaction between ions and ion groups, decreasing the polymerization degree, and increasing the melting temperature. Further increasing the content of Li2O, the crystallization performance was obviously suppressed, because the melting temperature and the force between the cations and the anion groups decreased.  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