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   3668篇
  免费   365篇
  国内免费   166篇
电工技术   156篇
综合类   171篇
化学工业   482篇
金属工艺   706篇
机械仪表   206篇
建筑科学   267篇
矿业工程   56篇
能源动力   95篇
轻工业   118篇
水利工程   59篇
石油天然气   42篇
武器工业   15篇
无线电   591篇
一般工业技术   774篇
冶金工业   195篇
原子能技术   60篇
自动化技术   206篇
  2024年   9篇
  2023年   143篇
  2022年   121篇
  2021年   143篇
  2020年   179篇
  2019年   109篇
  2018年   116篇
  2017年   174篇
  2016年   148篇
  2015年   112篇
  2014年   233篇
  2013年   242篇
  2012年   220篇
  2011年   255篇
  2010年   188篇
  2009年   190篇
  2008年   136篇
  2007年   158篇
  2006年   175篇
  2005年   128篇
  2004年   113篇
  2003年   114篇
  2002年   89篇
  2001年   95篇
  2000年   88篇
  1999年   68篇
  1998年   73篇
  1997年   55篇
  1996年   37篇
  1995年   28篇
  1994年   34篇
  1993年   26篇
  1992年   25篇
  1991年   24篇
  1990年   38篇
  1989年   29篇
  1988年   11篇
  1987年   8篇
  1986年   10篇
  1985年   9篇
  1984年   6篇
  1983年   5篇
  1982年   9篇
  1981年   6篇
  1980年   4篇
  1979年   2篇
  1977年   1篇
  1976年   2篇
  1975年   9篇
  1974年   1篇
排序方式: 共有4199条查询结果,搜索用时 29 毫秒
1.
东北地区是我国粮食的主产区和最重要的流出区域。东北地区粮食外运中,受原粮产后储藏条件、设施装备、运输方式、品质监测、储粮生态区域变化等因素限制,存在原粮损失偏高、颗粒破损、虫害发展、表面结露、局部发热、储藏品质和食味品质下降甚至霉变等质量问题,建议推进粮食分类分级、品质检测、绿色储粮工艺、运粮通道物流设施完善、提高“四散化”运输率和集装箱运输率、粮食物流信息服务、粮食食用及加工需求产销对接、粮食品质监测追溯等技术应用,加强保质流通标准体系建设,为我国粮食保质运输提供技术参考。  相似文献   
2.
目的:提高工业环境下樱桃分级分拣工作的效率。方法:提出了基于Faster R-CNN框架改进的樱桃缺陷识别分拣模型。结果:通过对比VGG16、MobileNet-V2和ResNet50网络,主干网络为ResNet50的效果最优,改进后的Faster R-CNN模型对樱桃裂口、双生、刺激生长、霉变、褐变腐烂和完好果的检测精度分别为97.75%,99.77%,98.90%,97.56%,96.67%,98.80%,平均检测精度达98.24%,高于其他模型,检测速度为31.16帧/s。结论:试验方法对樱桃缺陷类别的检测具有较高的识别精度。  相似文献   
3.
随着大家对汽车外观表面的更多需求,亚光清漆也逐渐被使用。本文主要结合极星汽车厂的第一代跑车 -Polestar 1的亚光清漆应用经验,对亚光清漆的作用机理,工艺流程和常见问题进行分析,完成亚光清漆的顺利投产。相较于高光清漆的应用,亚光清漆对洁净度和修补手法要求更高。  相似文献   
4.
针对目前涡流无损检测尚存在检测精度低、反演识别难的问题,利用理论仿真分析,设计了励磁均匀性较好的励磁线圈和阵列隧道磁阻(TMR)传感器探头,基于阵列探头提出了等空间间隔插值成像缺陷检测方法,搭建试验系统,并进行缺陷检测试验。结果表明,提出的方法可有效地避免探头速度对成像结果的影响,从而实现不同形状尺寸缺陷的轮廓成像检测,为后续导电材料缺陷的涡流智能检测提供支持。  相似文献   
5.
3D food printing has recently attracted significant attention, both from academic and industrial researchers, due to its ability to manufacture customized products in such terms as size, shape, texture, color, and nutrition to meet demands of individual consumers. 4D printing, which is a technique that allows evolution of various characteristics/properties of 3D printed objects over time through external stimulation, has also been gaining more attention. In order to produce defect-free printed objects via both 3D and 4D printing, it is necessary to first identify the causes of defects and then their mitigation strategies. Comprehensive review on these important issues is nevertheless missing. The purpose of this review is to investigate causes and characteristics of defects occurring during and/or after 3D food printing, with a focus on how different factors affect the printing accuracy. Various techniques that can potentially minimize or eliminate printing defects and produce high-quality 3D/4D printed food products without the need for time-consuming trial and error printing experiments are critically discussed. Guidelines to avoid defects to improve the efficiency of future 3D/4D printed food production are given.  相似文献   
6.
《Ceramics International》2022,48(14):20000-20009
Zinc oxide (ZnO) offers a major disadvantage of asymmetry doping in terms of reliability, stability, and reproducibility of p-type doping, which is the main hindrance in realization of optoelectronic devices. The problem is even more complicated due to formation of various native defects in unintentionally doped n-type ZnO. The realization of p-type conductivity in doped ZnO requires an in-depth understanding of the formation of an effective shallow acceptor, as well as donor-acceptor compensation. Photophysical properties such as photoconductivity along with photoluminescence (PL) studies have unprecedentedly and effectively been utilized in this work to monitor the evolution of various in-gap defects. Phosphorus (P) doped ZnO thin films have been grown by RF magnetron sputtering under various Ar to O2 gas ratios to investigate the effect of O2 on the donor-acceptor compensation by comprehensive photoconductivity measurements supported by the PL studies. Initial elemental analyses indicate presence of abundant zinc vacancies (VZn) in O-rich ambience. The results predict that P sits in the zinc (Zn) site rather than the oxygen (O) site causing the formation of PZn–2VZn acceptor-like defects, which compensates the donor defects in P doped ZnO films. Photocurrent spectra uniquely reveal presence of more oxygen vacancies (VO) defects states in lower O2 flow, which gets compensated with an increase in the O2 flow. Successive photocurrent transients indicate probable presence of more VO in the films grown with lower O2 flow and more VZn in higher O2 flow. Overall the photosensitivity measurements clearly present that O-rich ambience expedites the formation of acceptor defects which are compensated, thereby lowering the dark current and enhancing the ultraviolet photosensitivity.  相似文献   
7.
In this work, the composition-dependent point defect types and formation energies of RE2Hf2O7 (RE = La, Ce, Pr, Nd, Pm, Sm, Eu and Gd) as well as the oxygen diffusion behavior are systematically investigated by first-principles calculations. The possible defect reactions and dominant defect complexes under stoichiometric and non-stoichiometric conditions are revealed. It is found that O Frenkel pairs are the predominant defect in stoichiometric pyrochlore hafnates. Hf-RE cation anti-site defects, accompanied by RE vacancies and/or oxygen interstitials, are stable in the non-stoichiometric case of HfO2 excess. On the other hand, RE-Hf anti-site defects together with oxygen vacancies and/or RE interstitials are preferable in the case of RE2O3 excess. The energy barriers for the migration along the VO48f - VO48f pathway of pyrochlore hafnates were calculated to be between 0.81 eV and 0.89 eV. Based on these results, a defect engineering strategy is proposed and the pyrochlore hafnates investigated here are predicted to exhibit potential oxygen ionic conductivity.  相似文献   
8.
针对垂直线生产可锻铸铁管件出现的较严重的气孔、夹渣、缩松缺陷,分析缺陷产生原因,并通过优化浇注系统、排气方式及增设集渣包等改进措施实施,解决了可锻铸铁管件气孔、夹渣、缩松缺陷。  相似文献   
9.
基于断裂力学理论对铝合金型材对搭接搅拌摩擦焊接头中Hook缺陷进行安全评定,并通过疲劳试验进行验证。金相显示Hook缺陷的本质是搭接面在搅拌头剧烈搅拌作用下向上迁移的结果,显现为裂纹的形式。将Hook缺陷归一化为延伸到焊缝内部的单边裂纹,裂纹扩展速率线性拟合得出应力强度因子幅度门槛值ΔKth为2.509 MPa·m1/2。依据裂纹扩展条件,得到评定Hook缺陷疲劳扩展的缺陷尺寸-应力幅关系曲线。疲劳试验结果与理论Hook缺陷临界扩展应力幅值有一定的误差,误差平均值为9.4%,整体趋势与理论曲线吻合度较好,可以将该理论公式应用到Hook缺陷疲劳扩展临界应力幅的预测中,对不同工作应力幅下接头中Hook缺陷进行安全评定。  相似文献   
10.
In this study, we developed a unique defect healing method for 3D printed ceramic compact via cold isostatic pressing (CIP) after debinding, and typical features of interlayer interface defects of 3D-printed zirconia compact were characterized and found to be reduced significantly. The characteristic sintering kinetics window and microstructure evolution of the healed sintered bodies were systematically investigated, which was found to be quite different from conventional shaping methods. The three sintering stages are probed by their feature microstructure details such as the mechanically flattening surface at the early sintering stage, the heterogeneous microstructure and high porosity in the interlayer interface region at the middle stage, and the slightly ripple-like structural features combined with the healed interlayer defects at the final stage. The evolution of the pore structure of the healed 3D printed bodies were traced and the mechanical properties such as the Young's modulus, hardness, and fracture toughness were measured to understand the significance of the heal effect.  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