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   54836篇
  免费   3797篇
  国内免费   1832篇
电工技术   2050篇
技术理论   11篇
综合类   3063篇
化学工业   17365篇
金属工艺   3355篇
机械仪表   1202篇
建筑科学   2726篇
矿业工程   1144篇
能源动力   2913篇
轻工业   5647篇
水利工程   443篇
石油天然气   2515篇
武器工业   200篇
无线电   2960篇
一般工业技术   9980篇
冶金工业   3345篇
原子能技术   449篇
自动化技术   1097篇
  2025年   649篇
  2024年   2048篇
  2023年   1754篇
  2022年   1939篇
  2021年   2073篇
  2020年   2302篇
  2019年   2076篇
  2018年   1796篇
  2017年   1988篇
  2016年   2085篇
  2015年   1886篇
  2014年   2728篇
  2013年   2945篇
  2012年   3558篇
  2011年   3725篇
  2010年   2761篇
  2009年   2767篇
  2008年   2223篇
  2007年   2820篇
  2006年   2739篇
  2005年   2258篇
  2004年   1921篇
  2003年   1749篇
  2002年   1435篇
  2001年   1074篇
  2000年   965篇
  1999年   750篇
  1998年   656篇
  1997年   476篇
  1996年   424篇
  1995年   369篇
  1994年   320篇
  1993年   223篇
  1992年   188篇
  1991年   143篇
  1990年   139篇
  1989年   79篇
  1988年   55篇
  1987年   64篇
  1986年   45篇
  1985年   63篇
  1984年   53篇
  1983年   46篇
  1982年   27篇
  1981年   6篇
  1980年   16篇
  1977年   3篇
  1976年   5篇
  1959年   6篇
  1951年   27篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
碳纳米管高温热稳定性与结构的关系   总被引:7,自引:5,他引:7  
使用分子动力学方法对单壁碳纳米管高温下的结构进行了计算机模拟。对扶手椅结构(10,10)和(20,20)的单壁碳纳米管进行了模拟,结果表明,碳纳米管开关端由于能量弛豫过程,直径比内部略大,在温度逐渐升高之后,构成纳米管的碳原子逐渐偏离晶格位置,小直径的碳纳米管在3000K温度之下结构是稳定的;直径小的碳纳米管的高温热稳定性比直径大的碳纳米管要好。  相似文献   
62.
煤基碳纳米材料的研究进展   总被引:2,自引:0,他引:2  
以煤基碳纳米管和煤基活性炭为代表,介绍了煤基碳纳米材料在生长机理、制备工艺和应用领域等方面的研究进展。提出研究开发煤基碳纳米管是实现低成本、大批量制备碳纳米管的重要途径;煤基活性炭在储能超级电容器中的使用拓展了其应用范围。  相似文献   
63.
This paper proposes an instance?learning?based intrusion?detection system (IL?IDS) for wireless sensor networks (WSNs). The goal of the proposed system is to detect routing attacks on a WSN. Taking an ...  相似文献   
64.
Black teas manufactured in Darjeeling and Assam were analysed for various macrominerals such as P, K, Ca, Mg and microminerals such as Mn, Fe and Cu. A considerable amount of minerals, eg K (40-46 mg), Mg (2.7-3.0 mg), Ca (0.48-0.66 mg) and traces of Mn (0.28-0.40 mg), Fe (0.16-0.20 mg), P (29-41 μg) and Cu (12-22 μg) were found in a cup of black tea brew. Black teas manufactured from the leaf coming from a pruned section and fine portion usually showed higher mineral content than tea manufactured from unpruned sections and coarse grade teas of Darjeeling. Assam CTC tea was found to be richer in mineral content compared to Darjeeling orthodox tea.  相似文献   
65.
Stress-strain relationships were determined for heated egg white gels. Compressive strain at failure was independent of protein concentration, while stress at failure increased with protein concentration. Between the length ratios of 1.6 and 2.4 before and after compression, the heated egg white gels followed the Mooney Rivlin model. In stress relaxation, the asymptotic hypothetical equilibrium modulus increased with protein concentration.  相似文献   
66.
通过对CS-444碳硫分析仪空白的来源、测量和计算广阔支及空白值与助熔剂、坩埚、助燃气体和分析气路等因素的的研讨,提出了降低和稳定空白值的一些具体方法。  相似文献   
67.
The effect of prereduction on CO oxidation activity of unsupported copper-chromite oxide catalysts was examined. Results were found to be in good agreement with two mechanisms for a surface copper enrichment due to CO prereduction which produced an activity increase in the copper-chromite catalyst.  相似文献   
68.
An enzymatic approach to assess the stability of organic matter extracted from organic fertilizers and amendments is proposed. The use of 0.1M NaOH plus 0.1M Na4P2O7 previously suggested as a suitable extractant solution for soil organic matter was also found satisfactory for the extraction of organic matter from organic fertilizers and amendments, especially when the temperature was raised to 65°C. The presence of nonhumified compounds in the extracts from organic fertilizers may interfere considerably during fractionation of organic carbon. An enzymatic hydrolysis with lipase, lysozyme and pronase, added sequentially to the extracts, led to an appreciable reduction in the interference. The interference was further reduced by carrying out a successive acid hydrolysis with 3N H2SO4; in this case the DH values (percentage of humified fractions with respect to total extractable carbon) were reduced to less than 10% in all organic fertilizers, but remained higher than about 70% in organic amendments.  相似文献   
69.
A semiconducting single-walled carbon nanotubes (s-SWCNTs) interlayer between poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and n-Si was used for high performance organic-Si hybrid photovoltaic (PV) devices. The s-SWCNTs films with different thickness were utilized to investigate the PV effect on PEDOT:PSS/Si device performance. The surface potential of Si substrate with s-SWCNTs was dramatically reduced, which increased the compatibility between Si and PEDOT:PSS. In addition, s-SWCNTs with good semiconducting properties, guaranteed the charge transfer between Si and PEDOT:PSS. Therein, the electrical contact was dramatically improved with addition of s-SWCNTs interlayer, which led to increased fill factor. A power conversion efficiency (PCE) of 12.14% was achieved with an optimized thickness of s-SWCNTs layer. The s-SWCNTs interface layer was fabricated by a simple solution processed method, which was easily coupled with organic-Si solar cells to enhance the PCE.  相似文献   
70.
本文根据线光源高压汞灯的特点设计了一个用于光动力疗法的光反应室 ,它输出的光功率连续可调 ,波段选择简单灵活  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