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   49463篇
  免费   6523篇
  国内免费   3893篇
电工技术   5013篇
综合类   4915篇
化学工业   6752篇
金属工艺   3332篇
机械仪表   3309篇
建筑科学   3810篇
矿业工程   1692篇
能源动力   1368篇
轻工业   5020篇
水利工程   1461篇
石油天然气   1715篇
武器工业   848篇
无线电   5430篇
一般工业技术   4930篇
冶金工业   1874篇
原子能技术   922篇
自动化技术   7488篇
  2024年   188篇
  2023年   1044篇
  2022年   2253篇
  2021年   3108篇
  2020年   2141篇
  2019年   1566篇
  2018年   1693篇
  2017年   1800篇
  2016年   1570篇
  2015年   2603篇
  2014年   2960篇
  2013年   3366篇
  2012年   4019篇
  2011年   4279篇
  2010年   3882篇
  2009年   3753篇
  2008年   3707篇
  2007年   3276篇
  2006年   2893篇
  2005年   2412篇
  2004年   1720篇
  2003年   1219篇
  2002年   1266篇
  2001年   1111篇
  2000年   789篇
  1999年   384篇
  1998年   169篇
  1997年   134篇
  1996年   111篇
  1995年   92篇
  1994年   69篇
  1993年   50篇
  1992年   27篇
  1991年   34篇
  1990年   24篇
  1989年   30篇
  1988年   16篇
  1987年   16篇
  1986年   21篇
  1985年   4篇
  1984年   3篇
  1983年   7篇
  1982年   4篇
  1981年   10篇
  1980年   19篇
  1979年   7篇
  1965年   1篇
  1960年   1篇
  1959年   11篇
  1951年   15篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
High-k oxide dielectric films have attracted intense interest for thin-film transistors (TFTs). However, high-quality oxide dielectrics were traditionally prepared by vacuum routes. Here, amorphous high-k alumina (Al2O3) thin films were prepared by the simple sol-gel spin-coating and post-annealing process. The microstructure and dielectric properties of Al2O3 dielectric films were systematically investigated. All the Al2O3 thin films annealed at 300–600?°C are in amorphous state with ultrasmooth surface (RMS ~ 0.2?nm) and high transparency (above 95%) in the visible range. The leakage current of Al2O3 films gradually decreases with the increase of annealing temperature. Al2O3 thin films annealed at 600?°C showed the low leakage current density down to 3.9?×?10?7 A/cm2 at 3?MV/cm. With the increase of annealing temperature, the capacitance first decreases then increases to 101.1?nF/cm2 (at 600?°C). The obtained k values of Al2O3 films are up to 8.2. The achieved dielectric properties of Al2O3 thin films are highly comparable with that by vapor and solution methods. Moreover, the fully solution-processed InZnO TFTs with Al2O3 dielectric layer exhibit high mobility of 7.23?cm2 V?1 s?1 at the low operating voltage of 3?V, which is much superior to that on SiO2 dielectrics with mobility of 1.22?cm2/V?1 s?1 at the operating voltage of 40?V. These results demonstrate that solution-processed Al2O3 thin films are promising for low-power and high-performance oxide devices.  相似文献   
93.
Supercapacitors are a kind of novel energy storage devices with long cycle stability and high power density. Electrode materials selection is one of the key factors that affect the properties of supercapacitors. Biomass-derived electrode materials – being low cost, renewable and environmentally friendly – are therefore attracting researchers’ attention. In this work, we adopted a simple process of carbonization and activation with rice plant soot, a common biomass material, as carbon source, and finally obtained the nanoscale porous carbon electrode (NPCE) materials. Then, the electrochemical properties of the as-prepared NPCE materials were tested in 6 M KOH, and the results indicated that the specific capacitance could reach 216?Fg?1. Therefore, this low-cost, highly efficient technique is a significant milepost towards environmentally sustainable and commercially feasible fabrication of carbon electrode materials from biomass sources.  相似文献   
94.
Introducing graphene into polymer matrix is an effective way to enhance performances of anion exchange membrane (AEM). However, utilizing the advantages of graphene by physical approach is limited due to the weak interface interaction between graphene and polymer matrix. Herein, we report an effective strategy to covalently bond graphene with polymer matrix to improve the interface interaction and further to improve the properties of AEM. A series of cross-linked quaternized graphene-based hybrid AEM were fabricated by covalently bonding poly (vinylbenzyl chloride) grafted graphene (GN-g-PVBC) copolymer with chloromethyl functionalized poly (styrene-b-isobutylene-b-styrene) (SIBS) through the cross-linker (N,N,N′,N′-tetramethyl-1,6-hexanediamine) by in-situ synthetic approach. The interface interaction between graphene and QSIBS is greatly enhanced according to micromorphology characterization of the hybrid membrane. The cross-linked quaternized hybrid AEM containing 0.55 wt% of GN-g-PVBC exhibits obviously improved dynamical mechanical properties (storage modulus: 418 MPa), ion conductivity (1.81 × 102 S cm?1), methanol barrier property (5.19 × 10?7 cm2 s?1), selectivity (3.49 × 104 S s cm?3) at 60 °C and especially a comparably excellent chemical stability to that of Nafion 115 due to the enhanced interface interaction between graphene and the polymer matrix.  相似文献   
95.
孙锐  张睿 《水泥工程》2018,31(5):21-23
很多熟料库在设计时未注意清库门的设置,或者是设计的清库门不合理从而给施工和后期的实际使用造成很多麻烦。本文介绍了几种熟料清库门的几种设计方案,对比了其设计方式,设计要点及优缺点,为熟料库设计提供了有益的思路。  相似文献   
96.
韩瑞 《水泥工程》2018,31(5):56-56
我厂共有3台CRM4622型立式磨机生产矿渣粉,分别为#3,#4,#5立磨。其中#3,#4立磨(#3立磨投产于2010年,#4立磨投产于2012年)于2014年4月相继出现磨盘刮料架整体脱落情况。经过更换螺栓,情况得到暂时缓解。一段时间后,刮料架再次脱落。为了彻底解决刮料架脱落问题,决定对刮料架的固定方式进行改进,以提高刮料架的稳定性。  相似文献   
97.
采用种子乳液聚合法,以丙烯酸丁酯为核层单体、甲基丙烯酸甲酯为壳层单体、甲基丙烯酸烯丙酯为交联剂制备了抗冲ACR树脂。考察了不同加料方式对ACR乳液粒径及对PVC冲击性能的影响,结果表明:连续滴加方式可实现乳液粒径的稳定控制,并能得到性能优异的抗冲ACR树脂。  相似文献   
98.
分析Zr-4合金板材真空退火过程中的传热方式,计算锆合金板材径向传热系数,利用ABAQUS对Zr-4合金板材退火温度场进行数值模拟,分析工装夹具对锆合金板材退火的影响,结果表明,工装夹具能改善锆合金板材温度场分布均匀性,使锆合金板材温度分布的最高温差由70 ℃降低至35 ℃,升温过程更加稳定,并且数值模拟结果与实测结果有较好的一致性。  相似文献   
99.
100.
The practical application of lithium–sulfur (Li–S) batteries is hindered by the “shuttle” of lithium polysulfides (LiPS) and sluggish Li–S kinetics issues. Herein, a synergistic strategy combining mesoporous architecture design and defect engineering is proposed to synthesize multifunctional defective 3D ordered mesoporous cobalt sulfide (3DOM N‐Co9S8?x) to address the shuttling and sluggish reaction kinetics of polysulfide in Li–S batteries. The unique 3DOM design provides abundant voids for sulfur storage and enlarged active interfaces that reduce electron/ion diffusion pathways. Meanwhile, X‐ray absorption spectroscopy shows that the surface defect engineering tunes the CoS4 tetrahedra to CoS6 octahedra on Co9S8, endowing abundance of S vacancies on the Co9S8 octahedral sites. The ever‐increasing S vacancies over the course of electrochemical process further promotes the chemical trapping of LiPS and its conversion kinetics, rendering fast and durable Li–S chemistry. Benefiting from these features, the as‐developed 3DOM N‐Co9S8?x/S cathode delivers high areal capacity, superb rate capability, and excellent cyclic stability with ultralow capacity fading rate under raised sulfur loading and low electrolyte content. This design strategy promotes the development of practically viable Li–S batteries and sheds lights on the material engineering in related energy storage application.  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