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   337323篇
  免费   27543篇
  国内免费   14350篇
电工技术   19271篇
技术理论   29篇
综合类   23305篇
化学工业   55617篇
金属工艺   19128篇
机械仪表   21434篇
建筑科学   26104篇
矿业工程   10477篇
能源动力   9260篇
轻工业   23953篇
水利工程   5753篇
石油天然气   21429篇
武器工业   2689篇
无线电   37506篇
一般工业技术   39244篇
冶金工业   17499篇
原子能技术   3351篇
自动化技术   43167篇
  2024年   1046篇
  2023年   5248篇
  2022年   8500篇
  2021年   13220篇
  2020年   10357篇
  2019年   8683篇
  2018年   9633篇
  2017年   10732篇
  2016年   9761篇
  2015年   13202篇
  2014年   16942篇
  2013年   20050篇
  2012年   21715篇
  2011年   23875篇
  2010年   20902篇
  2009年   19846篇
  2008年   19648篇
  2007年   18516篇
  2006年   19007篇
  2005年   16321篇
  2004年   11159篇
  2003年   9597篇
  2002年   8791篇
  2001年   7793篇
  2000年   7913篇
  1999年   8744篇
  1998年   7180篇
  1997年   5877篇
  1996年   5486篇
  1995年   4554篇
  1994年   3652篇
  1993年   2530篇
  1992年   2015篇
  1991年   1589篇
  1990年   1231篇
  1989年   997篇
  1988年   747篇
  1987年   463篇
  1986年   360篇
  1985年   267篇
  1984年   188篇
  1983年   149篇
  1982年   155篇
  1981年   125篇
  1980年   115篇
  1979年   66篇
  1978年   42篇
  1977年   28篇
  1976年   57篇
  1973年   26篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
支婷  刘颖  周华春  张宏科 《电子学报》2021,49(8):1653-1664
随着互联网规模的不断扩大以及应用场景的多元化,传统网络无法很好地满足新业务的动态多样化需求,因此国内外对未来网络展开了深入研究.本文首先介绍了未来互联网体系架构的研究现状.其次,介绍了具备"三层、两域"特征的智慧标识网络(Smart Identifier NETwork,SINET)体系架构,然后重点阐述了SINET服务机理在服务的命名与解析、路由机制、服务缓存、移动性、传输控制机制、可扩展性、绿色节能等关键技术方面取得的研究进展,并进一步详细分析了SINET服务机理的安全性.最后总结了SINET面临的挑战,对SINET服务机理在大规模场景部署中可能存在的问题做出讨论.  相似文献   
12.
13.
14.
15.
16.
Zhang  Nan  Zhao  Man  Liu  Guangfa  Wang  Jiaoyang  Chen  Yunzhi  Zhang  Zhengjian 《Journal of Materials Science》2022,57(19):8687-8700
Journal of Materials Science - A green modification method for effectively enhancing toughness of PLA was established. Herein, alkaline lignin (LG) was firstly alkylated with dodecane, and then...  相似文献   
17.
18.
A appropriate size with three-dimension(3 D) channels for lithium diffusion plays an important role in constructing highperforming LiNi_(0.5)Mn_(1.5)O_4(LNMO) cathode materials, as it can not only reduce the transport path of lithium ions and electrons, but also reduce the side effects and withstand the structural strain in the process of repetitive Li~+ intercalation/deintercalation. In this work, an e fficient method for designing the hollow LNMO microsphere with 3 D channels structure by using polyethylene oxide(PEO) as soft template agent assisted solvothermal method is proposed. Experimental results indicate that PEO can make the reagents mingle evenly and nucleate slowly in the solvothermal process, thus obtaining a homogeneous distribution of carbonate precursors. In the final LNMO products, the hollow 3 D channels structure obtained by the decomposition of PEO and carbonate precursor in the calcination can provide abundant electroactive zones and electron/ion transport paths during the charge/discharge process, which benefits to improve the cycling performance and rate capability. The LNMO prepared by adding 1 g PEO possesses the most outstanding electrochemical performance, which presented an excellent discharge capacity of 143.1 mAh g~(-1) at 0.1 C and with a capacity retention of 92.2% after 100 cycles at 1 C. The superior performance attributed to the 3 D channels structure of hollow microspheres, which provide uninterrupted conductive systems and therefore achieve the stable transfer for electron/ion.  相似文献   
19.
A digital light processing (DLP) technology has been developed for 3D printing lead-free barium titanate (BTO) piezoelectric ceramics. By comparing the curing and rheological properties of slurries with different photosensitive monomer, a high refractive index monomer acryloyl morpholine (ACMO) was chosen, and a design and preparation method of BTO slurry with high solid content, low viscosity and high curing ability was proposed. By further selecting the printing parameters, the single-layer exposure time was reduced and the forming efficiency has been greatly improved. Sintered specimens were obtained after a nitrogen-air double-step debinding and furnace sintering process, and the BTO ceramics fabricated with 80 wt% slurry shows the highest relative density (95.32 %) and piezoelectric constant (168.1 pC/N). Furthermore, complex-structured BTO ceramics were prepared, impregnated by epoxy resin and finally assembly made into hydrophones, which has significance for the future design and manufacture of piezoelectric ceramic-based composites that used in functional devices.  相似文献   
20.
To provide a basis for the high-temperature oxidation of ultra-high temperature ceramics (UHTCs), the oxidation behavior of Zr3[Al(Si)]4C6 and a novel Zr3[Al(Si)]4C6-ZrB2-SiC composite at 1500 °C were investigated for the first time. From the calculation results, the oxidation kinetics of the two specimens follow the oxidation dynamic parabolic law. Zr3[Al(Si)]4C6 exhibited a thinner oxide scale and lower oxidation rate than those of the composite under the same conditions. The oxide scale of Zr3[Al(Si)]4C6 exhibited a two-layer structure, while that of the composite exhibited a three-layer structure. Owing to the volatilization of B2O3 and the active oxidation of SiC, a porous oxide layer formed in the oxide scale of the composite, resulting in the degradation of its oxidation performance. Furthermore, the cracks and defects in the oxide scale of the composite indicate that the reliability of the oxide scale was poor. The results support the service temperature of the obtained ceramics.  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