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   31935篇
  免费   3936篇
  国内免费   1525篇
电工技术   975篇
综合类   1897篇
化学工业   6586篇
金属工艺   5171篇
机械仪表   2004篇
建筑科学   1239篇
矿业工程   1343篇
能源动力   1128篇
轻工业   1447篇
水利工程   439篇
石油天然气   3216篇
武器工业   233篇
无线电   2296篇
一般工业技术   4990篇
冶金工业   3332篇
原子能技术   512篇
自动化技术   588篇
  2024年   60篇
  2023年   873篇
  2022年   878篇
  2021年   1255篇
  2020年   1376篇
  2019年   1320篇
  2018年   1035篇
  2017年   1213篇
  2016年   1183篇
  2015年   1159篇
  2014年   1755篇
  2013年   2044篇
  2012年   2221篇
  2011年   2143篇
  2010年   1554篇
  2009年   1602篇
  2008年   1418篇
  2007年   1873篇
  2006年   1835篇
  2005年   1686篇
  2004年   1351篇
  2003年   1374篇
  2002年   1109篇
  2001年   906篇
  2000年   830篇
  1999年   645篇
  1998年   535篇
  1997年   392篇
  1996年   388篇
  1995年   301篇
  1994年   240篇
  1993年   178篇
  1992年   142篇
  1991年   110篇
  1990年   93篇
  1989年   81篇
  1988年   41篇
  1987年   32篇
  1986年   23篇
  1985年   31篇
  1984年   33篇
  1983年   26篇
  1982年   16篇
  1981年   5篇
  1980年   4篇
  1979年   3篇
  1978年   3篇
  1977年   4篇
  1975年   4篇
  1951年   8篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
为提高海洋平台结构的抗冰能力,提出一种新型中空夹层金属管混凝土导管腿构件。通过理论分析、数值模拟和试验相结合,研究不同外钢管材料(Q345钢、奥氏体304级不锈钢和T6061铝合金)对中空夹层钢管混凝土构件的影响。通过单次冲击和连续冲击两种加载方式进行加载,并与钢质空心导管腿进行对比,试验结果发现:组合构件抗冲击性能优于空管构件,铝合金组合构件整体抗冲击能力较差,不锈钢单次冲击作用下极限承载能量高达18.83 kJ以上,小能量连续冲击作用下承载冲击次数最多,不锈钢组合构件抗冲击力学性能最好。结合有限元ABAQUS软件,对单次冲击构件建模并得出计算结果,与试验结果基本吻合。  相似文献   
92.
The appearance of heavy metals in wastewater brings a major burden to wastewater treatment plants, due to the high toxicity to microorganisms. Several commonly used heavy metals, including Zn(II), Cd(II), Hg(II), and Pb(II) were adopted to clear the individual and joint toxicity to the completely autotrophic nitrogen removal over nitrite (CANON) process in six sequencing batch reactors. The obtained results suggested that the nitrogen removal performances were transiently inhibited, but rapidly recovered. The restoration period under the stress of Hg(II) and Pb(II) was shorter than that under Zn(II), Cd(II), and the joint heavy metals. During the long-term exposure, Cd(II) in 1mg L−1 slightly inhibited the nitrogen removal, while Zn(II), Hg(II), Pb(II), and mixture showed a negligible impact on CANON process. The defense of extracellular polymeric substances (EPS), the good adaptability of functional bacteria, and the inducement of resistant genera by heavy metals all contributed to the robustness and stability of CANON process. Therefore, it is feasible to treat nitrogenous wastewater containing low heavy metals using CANON process. © 2020 Society of Chemical Industry  相似文献   
93.
Tandem organic light-emitting diodes (OLEDs) have been studied to improve the long-term stability of OLEDs for 10 years. The key element in a tandem OLEDs is the charge generation layer (CGL), which provides electrons and holes to the adjacent sub-OLED units. Among different types of CGLs, n-doped electron transporting layer (ETL)/transition metal oxide (TMO)/hole transporting layer (HTL) has been intensively studied. Past studies indicate that this kind of CGL can achieve the desired efficiency enhancement, however, its long-term stability was reported not good and sometime even poor than a single OLED. This issue was not well addressed over the past 10 years. Here, for the first time, we found that this is caused by the unwanted diffusion of TMO into the underlying n-doped ETL layer and can be well resolved by introducing an additional diffusion suppressing layer (DSL) between them. Our finding will fully release the potential of TMO-based CGL in tandem OLEDs.  相似文献   
94.
The formation of IrB2, IrB1.35, IrB1.1 and IrB monoboride phases in the Ir–B ceramic nanopowder was confirmed during mechanochemical reaction between metallic Ir and elemental B powders. The Ir–B phases were analysed after 90 h of high energy ball milling and after annealing of the powder for 72 h at 1050°C in vacuo. The iridium monoboride (IrB) orthorhombic phase was synthesised experimentally for the first time and identified by powder X-ray diffraction. Additionally, the ReB2 type IrB2 hexagonal phase was also produced for the first time and identified by high resolution transmission electron microscope. Ir segregation along disordered domains of the boron lattice was found to occur during high temperature annealing. These nanodomains may have useful catalytic properties.  相似文献   
95.
本文讲述空调复杂空间曲面钣金件的设计思路及分析方法。主要从设计方法、模拟分析、零件测量比对等方面分析空间复杂曲面钣金件的设计思路,以满足结构使用要求、强度刚度以及经济要求。  相似文献   
96.
The Amyloid Precursor Protein (APP) has been extensively studied for its role as the precursor of the β-amyloid protein (Aβ) in Alzheimer’s disease (AD). However, our understanding of the normal function of APP is still patchy. Emerging evidence indicates that a dysfunction in APP trafficking and degradation can be responsible for neuronal deficits and progressive degeneration in humans. We recently reported that the Y682 mutation in the 682YENPTY687 domain of APP affects its binding to specific adaptor proteins and leads to its anomalous trafficking, to defects in the autophagy machinery and to neuronal degeneration. In order to identify adaptors that influence APP function, we performed pull-down experiments followed by quantitative mass spectrometry (MS) on hippocampal tissue extracts of three month-old mice incubated with either the 682YENPTY687 peptide, its mutated form, 682GENPTY687 or its phosphorylated form, 682pYENPTY687. Our experiments resulted in the identification of two proteins involved in APP internalization and trafficking: Clathrin heavy chain (hc) and its Adaptor Protein 2 (AP-2). Overall our results consolidate and refine the importance of Y682 in APP normal functions from an animal model of premature aging and dementia. Additionally, they open the perspective to consider Clathrin hc and AP-2 as potential targets for the design and development of new therapeutic strategies.  相似文献   
97.
Exploring the reinforcing role of carbon nanotubes to obtain materials (polymers, metals, ceramics) with enhanced properties has been often attempted, but the success is strongly limited by the dispersing degree of carbon nanotubes. Here we report on an innovative colloidal approach to disperse the carbon nanotubes in the powders mixture of the precursor materials in order to profit from their reinforcing potential and obtain a new class of closed-cell metal foams. The feasibility of the proposed approach was demonstrated for aluminium foams reinforced with multi-walled carbon nanotubes. These nanocomposite metal foams synergistically combine the remarkable properties of both metal foams and carbon nanotubes. The results indicate that the tubular structure of carbon nanotubes is preserved throughout the entire the process. The carbon nanotubes are individually dispersed, stretched and randomly aligned in the aluminium-matrix of these closed-cell foams, thus potentiating their homogeneous 3D reinforcing role. Accordingly, the Vickers micro-hardness of the closed-cell foams was greatly enhanced.  相似文献   
98.
Ultrasonic treatment could decrease the viscosity of heavy oil and previous study on had focused on one heavy oil sample and involved less on the influence of asphaltene content. This study examined the effect of asphaltene content on viscosity reduction rate by ultrasonication. A comparison on samples with various asphaltene content and vibration parameter was made. The results showed that the optimal vibration frequency might decrease as the asphaltene content increased, whereas the optimal vibration intensity and the optimal treatment time were suggested to be enlarged. A semi-quantitative correlation was matched, which helped for numerical simulation about ultrasonic treatment.  相似文献   
99.
Rational design of oxygen evolution reaction (OER) electrocatalysts with advance nanostructures and composition superiority is an urgent need to promote electrocatalytic property. In this research, we fabricate Fe–NiCoP/NiCoP/NF electrocatalyst for OER via the interfacial scaffolding strategy with Prussian-blue-analogue (PBA) followed by low-temperature phosphating. The cube-on-sheet multimetallic-TMPs-based nanoarchitecture of Fe–NiCoP/NiCoP/NF exhibits outstanding OER performance, which only requires the overpotential of 201 mV to achieve a current density of 10 mA cm−2 and possesses good durability up to 50 h in 1.0 M KOH solution. The superior OER property of Fe–NiCoP/NiCoP/NF is mainly characteristic to the rich composition that optimizes the electronic structure and the cube-on-sheet multimetallic-TMPs-based nanoarchitecture which can facilitate more effective active sites exposure and ultimately promote charge transfer at the same time. This research provides a new strategy for the construction of advanced nanoarrays structure and the improvement of the electrocatalytic performance of polymetallic phosphides, which offers its promising applications especially in energy storage and conversion technology.  相似文献   
100.
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