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   4846247篇
  免费   333605篇
  国内免费   186150篇
电工技术   263746篇
技术理论   150篇
综合类   269617篇
化学工业   688666篇
金属工艺   233749篇
机械仪表   262248篇
建筑科学   276460篇
矿业工程   114893篇
能源动力   135867篇
轻工业   394769篇
水利工程   100932篇
石油天然气   149786篇
武器工业   36724篇
无线电   524331篇
一般工业技术   591824篇
冶金工业   568862篇
原子能技术   64622篇
自动化技术   688756篇
  2023年   42820篇
  2022年   93129篇
  2021年   141936篇
  2020年   106096篇
  2019年   87768篇
  2018年   105388篇
  2017年   116182篇
  2016年   106694篇
  2015年   127158篇
  2014年   173032篇
  2013年   274965篇
  2012年   284436篇
  2011年   322356篇
  2010年   288759篇
  2009年   288087篇
  2008年   294242篇
  2007年   285651篇
  2006年   261024篇
  2005年   219196篇
  2004年   157992篇
  2003年   123183篇
  2002年   114798篇
  2001年   102936篇
  2000年   98564篇
  1999年   84300篇
  1998年   145661篇
  1997年   103855篇
  1996年   86352篇
  1995年   69667篇
  1994年   60449篇
  1993年   52945篇
  1992年   35815篇
  1991年   32028篇
  1990年   31298篇
  1989年   30038篇
  1988年   27708篇
  1987年   24622篇
  1986年   23783篇
  1985年   25414篇
  1984年   21963篇
  1983年   20103篇
  1982年   19025篇
  1981年   19372篇
  1980年   18571篇
  1979年   16628篇
  1978年   16100篇
  1977年   22728篇
  1976年   33598篇
  1975年   13992篇
  1974年   12870篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
Journal of Materials Science: Materials in Electronics - Gum kondagogu (GK), a natural biopolymer was successfully employed in the synthesis of trimetallic (AgAuPd) nanocomposites and characterized...  相似文献   
42.

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   
43.
Journal of Materials Science: Materials in Electronics - The influences of the selenium (Se) growth condition on the electronic level structure including deep defects and further on the...  相似文献   
44.
Journal of Materials Science: Materials in Electronics - 0.95(Li0.02Na0.50K0.48)(Nb0.95Sb0.05)O3–0.05AgTaO3@BaZrO3 (LNKNbSAT@BZ) lead-free ceramics were prepared via a sol–gel...  相似文献   
45.
Journal of Materials Science: Materials in Electronics - Layered transition metal dichalcogenides hold tunable and promising photoelectrochemical properties. MoSe2 is a potential candidate of the...  相似文献   
46.
Journal of Materials Science: Materials in Electronics - In this study, Mn3O4 thin films were grown by Successive Ionic Layer Adsorption and Reaction Technique (SILAR) with 20 and 50...  相似文献   
47.

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   
48.
Journal of Materials Science: Materials in Electronics - Pure PVDF has higher breakdown strength but low dielectric and ferroelectric properties. Thus, we synthesized the LaFeO3 and GdFeO3...  相似文献   
49.
周忠彬  高金霞  袁宝慧 《爆破器材》2022,51(5):20-23,30
针对压制成型的PBX炸药装药,选择CT无损检测、巴西实验和扫描电镜检测等技术,对比研究了室温和加热两种温度下压制成型的炸药装药内部质量、静态力学性能和细观破坏形式。结果表明,加热压制有利于改善炸药装药的内部质量,可避免产生初始损伤,且提高了装药的力学性能。细观尺度上,室温压制成型的装药主要发生界面脱黏破坏,加热压制成型装药的主要破坏形式是穿晶断裂。  相似文献   
50.
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