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   1871篇
  免费   110篇
  国内免费   127篇
电工技术   28篇
综合类   205篇
化学工业   373篇
金属工艺   95篇
机械仪表   50篇
建筑科学   5篇
矿业工程   8篇
能源动力   76篇
轻工业   782篇
石油天然气   12篇
无线电   101篇
一般工业技术   209篇
冶金工业   17篇
原子能技术   4篇
自动化技术   143篇
  2024年   8篇
  2023年   89篇
  2022年   94篇
  2021年   95篇
  2020年   93篇
  2019年   73篇
  2018年   47篇
  2017年   52篇
  2016年   74篇
  2015年   38篇
  2014年   118篇
  2013年   109篇
  2012年   198篇
  2011年   209篇
  2010年   185篇
  2009年   208篇
  2008年   102篇
  2007年   154篇
  2006年   26篇
  2005年   9篇
  2004年   13篇
  2003年   9篇
  2002年   12篇
  2001年   16篇
  2000年   4篇
  1999年   9篇
  1998年   4篇
  1996年   3篇
  1995年   5篇
  1994年   5篇
  1993年   2篇
  1992年   2篇
  1991年   4篇
  1990年   3篇
  1989年   1篇
  1988年   6篇
  1987年   7篇
  1986年   10篇
  1985年   4篇
  1984年   3篇
  1982年   2篇
  1980年   1篇
  1978年   1篇
  1976年   1篇
排序方式: 共有2108条查询结果,搜索用时 15 毫秒
991.
豇豆根瘤中含有大量豆血红蛋白。该蛋白是良好的天然色素,可用于人造肉的着色,本文将携带豇豆血红蛋白Lb II基因的质粒pET-15b转化进入大肠杆菌BL21中表达,并对表达条件进行优化。通过查找NCBI数据库得到一条全长456 bp的豇豆血红蛋白Lb II的序列,以pET-15b作为表达载体,大肠杆菌BL21-CodonPlus (DE3)-R-IL作为重组工程菌进行表达,成功表达出豇豆血红蛋白Lb II,并使用镍柱层析对蛋白进行初步纯化,同时添加抗坏血酸为抗氧化剂。以IPTG浓度、温度、时间为自变量,Lb II表达量为因变量进行单因素实验。结果表明,在IPTG终浓度为1.0 mmol/L、诱导温度为25 ℃,时间为14 h时,重组豆血红蛋白Lb II的表达量最高,经SDS-PAGE凝胶电泳和可见光光谱分析法鉴定为目的蛋白Lb II。经响应面试验优化后,表达量可以达到7.30 μg/mL。本研究为后续使用工程菌发酵生产豆血红蛋白奠定了基础。  相似文献   
992.
《Ceramics International》2022,48(11):15613-15621
To explore the impact of the sintering rate on the microstructure and mechanical properties of cermets, the preparation of (Ti,W)C cermets by ultrafast sintering via spark plasma sintering (SPS) is reported. Compared with a slow heating rate, the electric field produced by an ultrafast heating rate enhances the liquid phase mass transfer of the metal binder phase, thus achieving rapid densification of (Ti,W)C cermets and effectively inhibiting abnormal grain growth. However, an excessive heating rate will lead to an “overflow” phenomenon, which reduces the grain growth difficulty and the bonding strength between grains. The results show that when the heating rate is 500 °C/min, the liquid phase mass transfer is moderate, the densification degree is the highest and the mechanical properties are excellent. The flexural strength, Vickers hardness and fracture toughness are 1340.90 ± 23.55 MPa, 18.42 ± 0.46 GPa and 11.96 ± 0.23 MPa?m1/2, respectively.  相似文献   
993.
《Ceramics International》2022,48(6):8097-8103
ZrB2/SiC, ZrB2/SiC/Si3N4 and ZrB2/SiC/WC ceramic tool materials were prepared by spark plasma sintering technology, and their oxidation resistance was tested at different oxidation temperatures. When the oxidation temperature is 1300 °C, the oxide layer thickness, oxidation weight gain and flexural strength of ZrB2/SiC/Si3N4 ceramic tool material after oxidation are 8.476 μm, 1.436 mg cm?2 and 891.0 MPa, respectively. Compared with ZrB2/SiC ceramic tool materials, the oxide layer thickness and oxidation weight gain are reduced by 8.2% and 11.8%, respectively, and the flexural strength after oxidation is increased by 116.1%. However, the addition of WC significantly reduces the oxidation resistance of the ceramic tool material. A dense oxide film is formed on the surface of ZrB2/SiC/Si3N4 ceramic tool material during oxidation, which effectively prevents oxygen from entering the inside of the material, thereby improving the oxidation resistance of the ceramic tool material.  相似文献   
994.
《Ceramics International》2022,48(9):12317-12323
Transparent conductive oxide (TCO) films have important applications in many areas. Unfortunately, TCOs are usually fabricated using vacuum and high-temperature methods, preventing them from applications in low-cost flexible devices. In this paper, facile low-temperature sol-gel method is described that can be used to fabricate high-quality TCO films. This study uses lightwave (LW) irradiation (at ~280 °C) with indium-tin-oxide (ITO) as a typical example. Both structure and key properties of ITO films are investigated for different LW irradiation conditions. ITO can be formed via LW irradiation after a period as short as 5 min. Furthermore, it is found that LW irradiation can promote the formation of M ? O framework, effectively remove Cl impurities, and facilitate the elimination of hydroxyl oxygen defects - even at temperatures as low as ~280 °C. The optimal ITO films show excellent electronic properties, including low sheet-resistance (14.5 Ω·sq?1) and high conductivity (1.7 × 103 S cm?1). Moreover, ITO films also show high transmittance (above 87%). Overall, our ITO films have a figure of merit (FOM) of 1.72 × 10?2 Ω?1, which is comparable to (or higher than) those of previous ITO films that were produced using conventional vacuum and high-temperature methods. Our LW irradiation method provides facile and effective approach to produce high-performance TCO films at remarkably low cost. This means these films could be used in affordable flexible large-area devices.  相似文献   
995.
为在遥感图像中提取出来道路信息,利用深度学习技术,引入U2-Net模型进行遥感图像道路分割。相比于传统的道路提取方法,基于U2-Net方法可以实现道路的自动化提取。为验证U2-Net模型分割效果,选取U-Net、DeepLabV3+等近几年较为流行的语义分割方法进行对比试验,并进一步分析U2-Net显著图融合模块中卷积核对道路提取效果的影响。试验结果表明,U2-Net模型能较有效地提取出道路信息,模型在测试集上的平均交并比达到了76.49%,Kappa达到了0.701 2,分割精度优于U-Net、DeepLabV3+等语义分割方法。基于U2-Net模型的深度学习方法可以用于解决遥感图像中的道路分割问题,并具有较好的分割效果。  相似文献   
996.
Lv  Xiaoyi  Tan  Rong  Xu  Xiaoyun  Li  Yanping  Geng  Chao  Fang  Yishan  Tan  CongPing  Cui  Bo  Wang  Lishi 《Journal of Applied Electrochemistry》2022,52(5):895-905
Journal of Applied Electrochemistry - In this contribution, a uniformly distributed CuNi active nanoalloys was obtained on the electrode substrate by one-step facile electrodeposition method, and a...  相似文献   
997.
During lactation, goat milk contains colostrum, transitional milk, mature milk, and end milk. The protein present in goat milk during different lactation periods has different characteristics. This study aimed to characterize the protein profile of goat milk samples obtained at different lactation stages and to identify changes in the physicochemical and functional properties of whey protein and casein from goat milk collected at 1, 3, 15, 100, and 200 d after calving. The results demonstrated that the lactation period had a great influence on the physicochemical and functional properties of goat milk whey protein and casein, especially the protein properties of colostrum on the first day after delivery. The denaturation temperature, hydrophobicity, and turbidity of whey protein were significantly higher on the first day postpartum than at other lactation periods. Correspondingly, the colostrum whey protein also had better functional properties, such as emulsification, oil holding capacity, and foaming properties on the first day postpartum than at other lactation periods. For casein, the turbidity, particle size, water holding capacity, and foaming properties on the first day after delivery were significantly higher than those at other lactation periods, whereas the denaturation temperature, oil holding capacity, and emulsification followed the opposite trend. For both whey protein and casein, the 2 indicators of emulsifying properties, namely, emulsifying activity index and the emulsion stability, also followed an opposite trend relative to lactation stage, whereas the changes in foaming capacity with the lactation period were completely consistent with the change of foaming stability. These findings could provide useful information for the use of goat milk whey protein and casein obtained during different lactation stages in the dairy industry.  相似文献   
998.
The production of an intense beam of polarized hydrogen ions with an ECR ionizer has been investigated. A deuteron tensor polarization of up to 85% of the theoretical value has been observed. The intensity is significantly improved compared to an electron beam ionizer.  相似文献   
999.
固态发酵技术的研究应用现状   总被引:2,自引:0,他引:2  
首先介绍了固态发酵的技术、特点及其优越性,并与液态发酵进行了对比;简要介绍了其最新研究状况及其在食品加工业、资源环境等各领域中的应用;描述了其发展趋势及应用前景。  相似文献   
1000.
PAE为活性高分子树脂,固含量越高,稳定性越难控制。该文探讨了一种固含量为35%、低成本PAE的制备方法及与市售增强剂进行比较。结果表明,选择胺/酸摩尔比为1:1~1:1.05,聚酰胺预聚体反应温度为170℃左右,环氧化反应后得到黏度为50~60s的聚酰胺树脂,其干抗张强度优于市售PAE,湿抗张强度相当,保存时间为6个月。  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