全文获取类型
收费全文 | 151143篇 |
免费 | 15437篇 |
国内免费 | 8989篇 |
专业分类
电工技术 | 11183篇 |
技术理论 | 11篇 |
综合类 | 11736篇 |
化学工业 | 22464篇 |
金属工艺 | 9251篇 |
机械仪表 | 10181篇 |
建筑科学 | 11965篇 |
矿业工程 | 4669篇 |
能源动力 | 4754篇 |
轻工业 | 10187篇 |
水利工程 | 3611篇 |
石油天然气 | 7336篇 |
武器工业 | 1898篇 |
无线电 | 18595篇 |
一般工业技术 | 16593篇 |
冶金工业 | 6470篇 |
原子能技术 | 2187篇 |
自动化技术 | 22478篇 |
出版年
2024年 | 265篇 |
2023年 | 2037篇 |
2022年 | 3900篇 |
2021年 | 5985篇 |
2020年 | 4506篇 |
2019年 | 3762篇 |
2018年 | 4150篇 |
2017年 | 4653篇 |
2016年 | 4315篇 |
2015年 | 6332篇 |
2014年 | 7960篇 |
2013年 | 9528篇 |
2012年 | 10937篇 |
2011年 | 11923篇 |
2010年 | 10949篇 |
2009年 | 10545篇 |
2008年 | 10504篇 |
2007年 | 10083篇 |
2006年 | 9634篇 |
2005年 | 7776篇 |
2004年 | 5764篇 |
2003年 | 4789篇 |
2002年 | 4760篇 |
2001年 | 4145篇 |
2000年 | 3322篇 |
1999年 | 2736篇 |
1998年 | 1971篇 |
1997年 | 1679篇 |
1996年 | 1371篇 |
1995年 | 1159篇 |
1994年 | 871篇 |
1993年 | 717篇 |
1992年 | 518篇 |
1991年 | 417篇 |
1990年 | 292篇 |
1989年 | 285篇 |
1988年 | 207篇 |
1987年 | 137篇 |
1986年 | 137篇 |
1985年 | 91篇 |
1984年 | 52篇 |
1983年 | 50篇 |
1982年 | 53篇 |
1981年 | 53篇 |
1980年 | 37篇 |
1979年 | 29篇 |
1977年 | 24篇 |
1976年 | 22篇 |
1959年 | 18篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
An-guo Wang Zhou-hua Jiang Yan-chun Lou Ji Tang Yun-long Xiong Yan-wu Dong Yan-wu Dong Fu-bin Liu Jing-chang Cheng Rui Chen 《中国铸造》2020,(1):48-55
Electroslag casting(ESC)is an important method to produce high quality castings.In this study,the ESC up-pulling inner mold method(EUPIM)was used to produce hollow cylindrical castings with the multiple consumable electrodes.The radial deformation,the axial and radial internal stress of the inner mold,and the axial internal stress of the slag shell were analyzed using the finite element method(FEM)with the aid of ANSYS software.The ProCAST software was used to calculate the specific heat,heat conductivity and density curve of Cu.Simulation results show that the radial deformation,the axial and radial internal stress of the inner mold,and the axial internal stress of the slag shell near the slag-metal interface of hollow cylndrical casting gradually increase from 0 s to 360 s after the ESC starting(slagging)process but before applying the up-pulling force.The suitable initial up-pulling moment of the inner mold is at around 180-198 s after the starting process. 相似文献
83.
This paper reported an effectiveness of pre-cold rolling-induced{332}\113[twins combined with subsequent isothermal x-phase formation for enhancement of uniform elongation in a b-type Ti–15Mo alloy with high yield strength level.Mechanical{332}\113[twins were induced by cold rolling with an thickness reduction of 5%,which had little effect on x-phase precipitation after aging at 573 K for 3.6 ks.Twinning after the cold rolling was further activated during tensile deformation,even with the presence of isothermal x-phase.This combination of twins and x-phase enhanced uniform elongation from 0 to 9%at yield strength level of 890 MPa.The high yield strength was mainly dominated by dislocation slip due to the isothermal x-phase formation,and early onset of plastic instability after yielding was hindered due to the pre-cold rolling-induced twins.Dynamic microstructural refinement was induced by further twinning activation during deformation,which resulted in high work hardening rate corresponding enhancement of uniform elongation. 相似文献
84.
In this work, the effects of stray alternating current (AC) on the corrosion of coated X70 pipeline steel and the delamination of 3-layer polyethylene (3PE) coatings with defects were investigated using COMSOL Multiphysics simulation, electrochemical impedance spectroscopy and three-dimensional (3D) digital microscope techniques. The results showed that under the same level of AC interference, pits with deeper maximum pit depth were observed at the smaller defect areas than those at larger defect areas. It was consistent with the simulation results that a greater corrosion current density was accompanied on samples with smaller defects. According to 3D digital images, the larger delamination of 3PE coatings was found on samples with smaller defects. With the increase of current density, the impedance of samples with small defects decreased, while that of samples with large defects increased. Additionally, with the same defect size, the maximum pit depth became deeper and the corrosion was more severe. 相似文献
85.
基于深度特征的目标检测方法Faster R-CNN在火焰检测任务上存在检测效率低的问题,因此提出了基于颜色引导的抛锚策略。该策略设计火焰颜色模型来限制锚的生成,即利用火焰颜色约束锚的生成区域,从而减少了初始锚的数量,提升了计算效率。为了进一步提高网络的计算效率,将区域生成网络中的卷积层替换成掩膜卷积。为了验证所提方法的检测效果,采用BoWFire和Corsician数据集进行验证。实验结果表明,该方法实际检测速度相较于原Faster R-CNN提高了10.1%,BoWFire上该方法的火焰检测F值为0.87,Corsician上该方法的准确度可达99.33%。所提方法可以提高火焰检测的效率,并能够准确检测图像中的火焰。 相似文献
86.
Baohua Mao Yang Dai Jun Cai Qingtian Li Chenggong Jiang Yimin Li Jingying Xie Zhi Liu 《Topics in Catalysis》2018,61(20):2123-2128
Lower charge overpotential of sodium–oxygen (Na–O2) batteries makes them a promising electrical storage technology. However, they have an undesirable discharge product, sodium carbonate (Na2CO3), which has widely been found in many previous studies. Whether and how the carbon components in the cathode are involved in the formation of Na2CO3 is still not well understood. Herein, an all solid-state Na–O2 battery was constructed and its charge and discharge cycles were studied using ambient pressure X-ray photoelectron spectroscopy. The operando XPS results clearly demonstrate the formation of Na2CO3 on the cathode during the discharge cycle. A fraction of the carbonate formed can be cycled while charging the battery. Transformation of the carbon-based cathode to Na2CO3 is a potential cause of capacity fading of the Na–O2 battery. 相似文献
87.
A three-dimensional (3D) numerical model is established and validated for cooling performance optimization between a high-level water collecting natural draft wet cooling tower (HNDWCT) and a usual natural draft wet cooling tower (UNDWCT) under the actual operation condition at Wanzhou power plant, Chongqing, China. User defined functions (UDFs) of source terms are composed and loaded into the spray, fill and rain zones. Considering the conditions of impact on three kinds of corrugated fills (Double-oblique wave, Two-way wave and S wave) and four kinds of fill height (1.25 m, 1.5 m, 1.75 m and 2 m), numerical simulation of cooling performance are analysed. The results demonstrate that the S wave has the highest cooling efficiency in three fills for both towers, indicating that fill characteristics are crucial to cooling performance. Moreover, the cooling performance of the HNDWCT is far superior to that of the UNDWCT with fill height increases of 1.75 m and above, because the air mass flow rate in the fill zone of the HNDWCT improves more than that in the UNDWCT, as a result of the rain zone resistance declining sharply for the HNDWCT. In addition, the mass and heat transfer capacity of the HNDWCT is better in the tower centre zone than in the outer zone near the tower wall under a uniform fill layout. This behaviour is inverted for the UNDWCT, perhaps because the high-level collection devices play the role of flow guiding in the inner zone. Therefore, when non-uniform fill layout optimization is applied to the HNDWCT, the inner zone increases in height from 1.75 m to 2 m, the outer zone reduces in height from 1.75 m to 1.5 m, and the outlet water temperature declines approximately 0.4 K compared to that of the uniform layout. 相似文献
88.
Fluorescence‐Activated Cell Sorters: Standing Surface Acoustic Wave (SSAW)‐Based Fluorescence‐Activated Cell Sorter (Small 40/2018) 下载免费PDF全文
89.
基于微电子机械系统(MEMS)工艺,提出一种多层圆片堆叠的THz硅微波导结构及其制作方法。为了验证该结构在制作THz无源器件中的优势,基于6层圆片堆叠的硅微波导结构,设计了一种中心频率365 GHz、带宽80 GHz的功率分配/合成结构,并对其进行了仿真。研究了制作该结构的工艺流程,攻克了工艺过程中的关键技术,包括硅深槽刻蚀技术和多层热压键合技术,并给出了工艺结果。最终实现了多层圆片堆叠功率分配/合成结构的工艺制作和测试。测试结果表明,尽管样品的插入损耗较仿真值增加3 dB左右,考虑到加工误差和夹具损耗等情况,样品主要技术指标与设计值较为一致。 相似文献
90.