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   713901篇
  免费   28374篇
  国内免费   13093篇
电工技术   24831篇
技术理论   56篇
综合类   19590篇
化学工业   109799篇
金属工艺   33579篇
机械仪表   33508篇
建筑科学   33027篇
矿业工程   12831篇
能源动力   20824篇
轻工业   45979篇
水利工程   9393篇
石油天然气   29908篇
武器工业   2616篇
无线电   83509篇
一般工业技术   118888篇
冶金工业   91928篇
原子能技术   12210篇
自动化技术   72892篇
  2023年   5582篇
  2022年   8839篇
  2021年   15136篇
  2020年   12378篇
  2019年   11241篇
  2018年   15023篇
  2017年   16284篇
  2016年   14922篇
  2015年   15733篇
  2014年   22136篇
  2013年   38491篇
  2012年   31188篇
  2011年   37223篇
  2010年   30999篇
  2009年   31636篇
  2008年   31454篇
  2007年   30662篇
  2006年   30225篇
  2005年   26837篇
  2004年   20494篇
  2003年   19182篇
  2002年   17295篇
  2001年   16505篇
  2000年   16166篇
  1999年   18359篇
  1998年   31478篇
  1997年   22630篇
  1996年   18343篇
  1995年   14584篇
  1994年   12487篇
  1993年   11236篇
  1992年   8362篇
  1991年   7484篇
  1990年   7029篇
  1989年   6393篇
  1988年   5905篇
  1987年   4953篇
  1986年   4721篇
  1985年   5033篇
  1984年   4566篇
  1983年   4098篇
  1982年   3765篇
  1981年   3773篇
  1980年   3504篇
  1979年   3357篇
  1978年   3326篇
  1977年   3746篇
  1976年   4866篇
  1975年   2852篇
  1973年   2712篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
夏敏浩  赵万剑  王骏 《中州煤炭》2022,(7):189-194,200
为了提高配电网差异化节能降耗效果,解决现有潜力评估方法存在的应用性能差的问题,提出碳中和背景下配电网差异化节能降耗潜力优化评估方法。根据配电网的空间结构,构建相应的等值电路模型。在该模型下,从设备损耗和运行附加损耗2个方面计算配电网的损耗量。根据损耗量计算结果,确定配电网差异化碳中和节能降耗方式。从静态和动态2个角度设置潜力评估指标,通过指标数据处理、指标权重求解等步骤,得出配电网差异化节能降耗潜力的综合量化评估结果。将设计潜力评估方法应用到配电网的差异化节能降耗改造工作中,能够有效降低配电网的实际线损量、降低区域损耗费用,并具有较高的应用价值。  相似文献   
3.
Journal of Materials Science: Materials in Electronics - The Co1?xZnxFe2O4 (Co–Zn) ferrite nanoparticles with x varying from 0.0 to 0.4 have been manufactured by facile chemical...  相似文献   
4.
Journal of Materials Science: Materials in Electronics - The ZnO and TiO2 nanopowders have been prepared by means of the pulsed laser reactive ablation of metallic (Zn, Ti) targets. The Structural,...  相似文献   
5.
Journal of Materials Science: Materials in Electronics - Non-volatile organic memory devices were fabricated using polystyrene sulfonate (PSS)?+?nitrogen-doped multi-walled carbon...  相似文献   
6.
Journal of Materials Science: Materials in Electronics - In the recent years, metal oxides have attracted more interest for researchers because of their applications in energy and...  相似文献   
7.
Journal of Materials Science: Materials in Electronics - A mixed solution of 2-aminopyridine and succinic acid, with a 1:1 molar ratio, was kept at room temperature to develop a 2-aminopridinium...  相似文献   
8.

The non-centrosymmetric space group organic nonlinear optical single crystal of 4-chloro-2-nitroaniline (4Cl2NA) was developed by slow evaporation method at 40 °C. Grown 4Cl2NA was monoclinic structure with Pc space group which was recognized by single-crystal XRD analysis. An intermolecular contact of 4Cl2NA was visually analysed by Hirshfeld surface analysis. Active functional groups and their respective vibrations were identified by FTIR and FT-Raman spectral analysis. Optical properties were evaluated by UV–Visible spectral analysis. Thermal TG/DTA thermogram analysis and mechanical Vickers hardness analysis revealed that the synthesis material was thermally stable up to 115 °C and mechanical work hardness coefficient (n?=?2.98) confirmed the grown crystal was soft material. Laser beam-irradiated LDT analysis expressed the laser utility limitation of the 4Cl2NA crystal. The NLO second harmonic generation efficiency was tested by Kurtz Perry powder method.

  相似文献   
9.

Cr doped ZnAl2O4 spinel samples were prepared by the traditional solid state reaction and co-precipitation synthetic route, and the results suggest that the co-precipitation method has some superiority in contrast to the solid state reaction method. XRD, FT-IR, and XPS spectra confirmed that the well-crystallized spinel cubic phase of ZnAl2O4: Cr3+ samples were successfully formed. The morphology of the samples was investigated by FE-SEM and FE-TEM, and the results show that the samples by the co-precipitation route can generate a smaller size of particles compared to the solid state reaction. Photoluminescence excitation spectra monitored at 686 nm are comprised of two broad excitation bands near 530 nm and 395 nm, and the emission spectra show emissions ranging from 640 to 780 nm, due to the 2E?→?4A2 spin-forbidden transition of Cr3+ ions in spinel lattices. The optimized concentration monitored at 686 nm is 1%, while at 693 nm is 3.5%. Compared with the samples by solid state reaction method, the samples by co-precipitation method show preferable luminescent properties, such as the higher photoluminescence intensity and higher quantum efficiency. Several phosphor-converted LEDs were to investigate the applicability of the prepared samples. The results confirm that the phosphor has potential applications in plant growth and supplementing the red region in white-LEDs and the phosphors prepared by co-precipitation are more suitable to be used in phosphor-converted LED devices due to their preferable luminescent properties.

  相似文献   
10.
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