全文获取类型
收费全文 | 45389篇 |
免费 | 5009篇 |
国内免费 | 4034篇 |
专业分类
电工技术 | 2187篇 |
技术理论 | 1篇 |
综合类 | 4915篇 |
化学工业 | 7747篇 |
金属工艺 | 4396篇 |
机械仪表 | 5506篇 |
建筑科学 | 3932篇 |
矿业工程 | 2361篇 |
能源动力 | 1156篇 |
轻工业 | 2987篇 |
水利工程 | 1080篇 |
石油天然气 | 2916篇 |
武器工业 | 632篇 |
无线电 | 2179篇 |
一般工业技术 | 4946篇 |
冶金工业 | 1714篇 |
原子能技术 | 256篇 |
自动化技术 | 5521篇 |
出版年
2024年 | 508篇 |
2023年 | 1411篇 |
2022年 | 2424篇 |
2021年 | 2430篇 |
2020年 | 1939篇 |
2019年 | 1517篇 |
2018年 | 1360篇 |
2017年 | 1536篇 |
2016年 | 1664篇 |
2015年 | 1652篇 |
2014年 | 2430篇 |
2013年 | 2193篇 |
2012年 | 2916篇 |
2011年 | 3142篇 |
2010年 | 2465篇 |
2009年 | 2698篇 |
2008年 | 2248篇 |
2007年 | 3029篇 |
2006年 | 2827篇 |
2005年 | 2365篇 |
2004年 | 1886篇 |
2003年 | 1771篇 |
2002年 | 1439篇 |
2001年 | 1177篇 |
2000年 | 1032篇 |
1999年 | 852篇 |
1998年 | 707篇 |
1997年 | 531篇 |
1996年 | 462篇 |
1995年 | 391篇 |
1994年 | 360篇 |
1993年 | 226篇 |
1992年 | 178篇 |
1991年 | 170篇 |
1990年 | 119篇 |
1989年 | 90篇 |
1988年 | 78篇 |
1987年 | 35篇 |
1986年 | 28篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 21篇 |
1979年 | 8篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1959年 | 4篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
金属Ni包覆于陶瓷粉体的表面,可以促进其烧结、提高导电性或赋予新的功能性质.本文采用旋转化学气相沉积法(RCVD),利用二茂镍(NiCp_2)前驱体的热分解,借助载体氢气对反应的催化促进作用,在Al_2O_3粉体表面包覆了均匀分散的Ni纳米粒子,并研究了包覆温度和原料供应速率对反应产物物相、粒度和形貌的影响规律.研究表明,在包覆温度为450~550℃、前驱体二茂镍(NiCp_2)供给速率为(0.6~2.0)×10~(-6)kg/s条件下,通过对反应过程中镍纳米粒子的包覆温度和前驱体二茂镍(NiCp_2)供给速率调控可对镍纳米粒子的粒径大小和包覆层数进行调控.结合实验结果,分析了载体氢气对二茂镍反应的催化促进作用,阐述了旋转化学气相沉积条件下Ni纳米粒子在Al_2O_3粉体表面均匀包覆的过程与机制.通过调控包覆温度和原料供应速率,可以影响前驱体二茂镍的分解行为,从而调控镍纳米粒子在Al_2O_3粉体表面的包覆状态. 相似文献
992.
Guang Feng Qiuzu Liu Wenliang Guo Yupeng Xin Qunlong Liang 《Materials and Manufacturing Processes》2018,33(9):1030-1035
Nanogrinding experiments are performed to investigate the processing characteristics and material removal mechanism of reaction-bonded silicon carbide (RB-SiC) wafers on an ultraprecision grinder using the cup wheel. #120, #600 diamond wheels are used as coarse and semifinished grinding wheels, while #2000 and #12000 diamond wheels are selected as fine and finish grinding wheels, respectively. The experimental results indicate that an ultrasmooth surface with roughness value Ra less than 3?nm and groove depth about 5?nm can be achieved using a diamond wheel whose mesh size exceeds 2000. In addition, Ra less than 1?nm and groove depth about 2?nm will be obtained with a #12000 diamond wheel. The present study reveals the feasibility of ultraprecision grinding RB-SiC materials in the ductile regime and provides technological insights into nanogrinding of hard materials with an ultrasmooth surface. 相似文献
993.
Reinforcement in Al Matrix Composites: A Review of Strengthening Behavior of Nano‐Sized Particles
下载免费PDF全文
![点击此处可从《Advanced Engineering Materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
994.
Mechanical Properties and Interlaminar Fracture Toughness of Glass‐Fiber‐Reinforced Epoxy Composites Embedded with Shape Memory Alloy Wires
下载免费PDF全文
![点击此处可从《Advanced Engineering Materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Li‐Dan Xu Ming‐Fang Shi Xiao‐Yu Sun Zhen‐Qing Wang Bin Yang 《Advanced Engineering Materials》2018,20(3)
995.
Tensile Strength Evolution and Damage Mechanisms of Al–Si Piston Alloy at Different Temperatures
下载免费PDF全文
![点击此处可从《Advanced Engineering Materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Meng Wang Jianchao Pang Yu Qiu Haiquan Liu Shouxin Li Zhefeng Zhang 《Advanced Engineering Materials》2018,20(2)
996.
《材料科学技术学报》2019,35(5):917-925
The tribological behavior of Al0.25CoCrFeNi high-entropy alloy (HEA) sliding against Si3N4 ball was investigated from room temperature to 600 ℃. The microstructure of the alloys was characterized by simple FCC phase with 260 HV. Below 300 ℃, with increasing temperature, the wear rate increased due to high temperature softening. The wear rate remained stabilized above 300 ℃ due to the anti-wear effect of the oxidation film on the contact interface. The dominant wear mechanism of HEA changed from abrasive wear at room temperature to delamination wear at 200 ℃, then delamination wear and oxidative wear at 300 ℃ and became oxidative above 300 ℃. Moreover, the adhesive wear existed concomitantly below 300 ℃. 相似文献
997.
《材料科学技术学报》2019,35(11):2705-2713
In this study, the Zn-0.5 wt%Zr (Zn-Zr) alloy was treated by laser surface remelting (LSR), and then the microstructure and degradation mechanism of the remelting layer were investigated and compared with the original as-cast alloy. The results reveal that after LSR, the bulky Zn22Zr phase in the original Zn-Zr alloy is dissolved and the coarse equiaxed grains transform into fine dendrites with a secondary dendrite arm space of about 100 nm. During the degradation process in simulated body fluid (SBF), the corrosion products usually concentrate at some certain areas in the original alloy, while the corrosion products distribute uniformly and loosely in the LSR-treated surface. After removing the corrosion products, it was found that the former suffers obvious pitting corrosion and then localized corrosion. The proposed mechanism is that corrosion initiates at grain boundaries and develops into the depth at some locations, and then leads to localized corrosion. For the LSR-treated sample, corrosion initiates at some active sites and propagates in all directions, corrosion takes place in the whole surface with distinctly uniform thickness reduction, while the localized corrosion and peeling of bulky Zn22Zr particles were eliminated. The electrochemical results also suggest the uniform corrosion of LSR-treated sample and localized corrosion of original sample. Based on the results, a new approach to regulate the corrosion mode of the biodegradable Zn alloy is proposed. 相似文献
998.
采用真空熔覆技术在45钢表面制备Ni +WC复合熔覆层并进行阶段性取样,研究镍基复合涂层的形成机制。结果表明:在45钢表面生成与基体冶金熔合、WC硬质颗粒分布均匀的Ni基复合熔覆层。整个熔覆层由4 mm厚的复合层、1 mm厚的过渡层、20 μm厚的扩散熔合区以及250 μm厚的扩散影响区组成。复合层区由WC和分解形成的富W复相碳化物包围在Ni颗粒周围组成;复合熔覆层的主要组成相有γ-Ni固溶体、Cr7C3、Ni2.9Cr0.7Fe0.36、Cr23C6、Ni3Fe、Ni3Si、Ni3B、W2C以及C等;真空熔覆过程包括:镍基合金颗粒达到熔点(900℃)前升温阶段颗粒间微烧结颈的形成、升温达到熔点(1020℃)开始的镍基合金颗粒熔融以及保温阶段(1060℃)的熔合扩散与WC颗粒微区位置的调整。 相似文献
999.
Quanzhao Yue Lin Liu Wenchao Yang Chuang He Dejian Sun Taiwen Huang Jun Zhang Hengzhi Fu 《材料科学技术学报》2019,35(5):752-763
Elevated temperature creep behaviors at 1100℃ over a wide stress regime of 120–174 MPa of a thirdgeneration Ni-based single crystal superalloy were studied. With a reduced stress from 174 to 120 MPa,the creep life increased by a factor of 10.5, from 87 h to 907 h, presenting a strong stress dependence.A splitting phenomenon of the close-(about 100 nm) and sparse-(above 120 nm) spaced dislocation networks became more obvious with increasing stress. Simultaneously, a_0010 superdislocations with low mobilities were frequently observed under a lower stress to pass through γ'precipitates by a combined slip and climb of two a_0110 superpartials or pure climb. However, a_0110 superdislocations with higher mobility were widely found under a higher stress, which directly sheared into γ'precipitates.Based on the calculated critical resolved shear stresses for various creep mechanisms, the favorable creep mechanism was systematically analyzed. Furthermore, combined with the microstructural evolutions during different creep stages, the dominant creep mechanism changed from the dislocation climbing to Orowan looping and precipitates shearing under a stress regime of 137–174 MPa, while the dislocation climbing mechanism was operative throughout the whole creep stage under a stress of 120 MPa, resulting a superior creep performance. 相似文献
1000.
在陀螺经纬仪校准过程中,需要将陀螺经纬仪中心与天文定向时的观测中心对中,此对中精度直接影响其寻北精度的测量结果。本文设计了一种基于两个平行光管的双目标精确对中方法,经实验验证,该方法可实现被检陀螺经纬仪中心与天文定向时的观测中心的高精度对中,成功提高了陀螺经纬仪校准的准确性;为配合该方法的使用,设计了陀螺经纬仪对中调整机构,该机构可以实现陀螺经纬仪水平二维位移调整和高低姿态调整,通过姿态调整,可以与天文定向时的观测中心高精度对心,提高测量精度,并满足不同型号陀螺经纬仪校准需求。 相似文献