全文获取类型
收费全文 | 66956篇 |
免费 | 6729篇 |
国内免费 | 3628篇 |
专业分类
电工技术 | 4391篇 |
技术理论 | 5篇 |
综合类 | 5236篇 |
化学工业 | 10819篇 |
金属工艺 | 3620篇 |
机械仪表 | 4367篇 |
建筑科学 | 5756篇 |
矿业工程 | 2150篇 |
能源动力 | 1935篇 |
轻工业 | 5322篇 |
水利工程 | 1270篇 |
石油天然气 | 2943篇 |
武器工业 | 520篇 |
无线电 | 7916篇 |
一般工业技术 | 7974篇 |
冶金工业 | 2972篇 |
原子能技术 | 856篇 |
自动化技术 | 9261篇 |
出版年
2024年 | 307篇 |
2023年 | 1158篇 |
2022年 | 2083篇 |
2021年 | 2899篇 |
2020年 | 2167篇 |
2019年 | 1859篇 |
2018年 | 2004篇 |
2017年 | 2240篇 |
2016年 | 2089篇 |
2015年 | 2717篇 |
2014年 | 3436篇 |
2013年 | 4111篇 |
2012年 | 4441篇 |
2011年 | 4579篇 |
2010年 | 4309篇 |
2009年 | 3997篇 |
2008年 | 3821篇 |
2007年 | 3564篇 |
2006年 | 3481篇 |
2005年 | 2993篇 |
2004年 | 2165篇 |
2003年 | 2333篇 |
2002年 | 2811篇 |
2001年 | 2481篇 |
2000年 | 1752篇 |
1999年 | 1551篇 |
1998年 | 1048篇 |
1997年 | 919篇 |
1996年 | 833篇 |
1995年 | 708篇 |
1994年 | 572篇 |
1993年 | 378篇 |
1992年 | 322篇 |
1991年 | 251篇 |
1990年 | 174篇 |
1989年 | 158篇 |
1988年 | 124篇 |
1987年 | 79篇 |
1986年 | 65篇 |
1985年 | 46篇 |
1984年 | 25篇 |
1983年 | 19篇 |
1982年 | 25篇 |
1981年 | 17篇 |
1980年 | 33篇 |
1979年 | 19篇 |
1977年 | 10篇 |
1962年 | 42篇 |
1961年 | 39篇 |
1960年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Wei-Li Xie Xiao-Dong Zhang Wen-Hui Liu Qi Xie Guang-Wu Wen Xiao-Xiao Huang Jian-Dong Zhu Fei-Xiang Ma 《稀有金属(英文版)》2019,(3)
SiC nano wires were fabricated on the silicon substrate dipped with a layer of Ni catalyst at 900 ℃ by gas pressure annealing processing. The morphologies and crystal structures were determined by scanning electron microscopy(SEM), transmission electron microscopy(TEM)and X-ray diffraction(XRD). The results show that the assynthesized nanowires are β-SiC single crystalline with diameter range of 50-100 nm, and length of tens of micron by directly annealing at 900 ℃. The SiC nano wires grow along the [111] direction with highly uniform morphology. And the possible growth mechanism of SiC nano wires is proposed.The present work provides an efficient strategy for the production of high-quality SiC nano wires. 相似文献
33.
34.
Wen Cao Zhonghua Zhou Chenyu Li Qun Wang Yue Huang Shirley Shen 《Ceramics International》2021,47(2):1807-1818
Sodalime float (SF) glass is widely used in our societies and industries. Hydrothermal corrosion method is one of the effective ways to prepare a superhydrophobic glass, but there is still lack of knowledge about hydrothermal corrosion behavior and mechanism of SF glass. We have hydrothermally treated SF glass at 180 °C for different time, and tried to reveal the aqueous corrosion process of SF glass. We have characterized the morphologies and chemical compositions of samples, and found that (1) the two sides of SF glass have different corrosion resistances, and (2) a multilayer structural coating with a nanoflake layer (Mg-rich gel layer), a nanowire layer (Ca-rich gel layer), and a porous layer (etched layer) is formed on the air-side of SF glass. Based on the experimental results, we have proposed an aqueous corrosion mechanism of SF glass. The insights of the hydrothermal corrosion behaviors and mechanism provide helpful guidelines to glass surface structural control and functionalization. 相似文献
35.
针对多角度下车辆出现一定的尺度变化和形变导致很难被准确识别的问题,提出基于多尺度双线性卷积神经网络(MS-B-CNN)的车型精细识别模型。首先,对双线性卷积神经网络(B-CNN)算法进行改进,提出MS-B-CNN算法对不同卷积层的特征进行了多尺度融合,以提高特征表达能力;此外,还采用基于中心损失函数与Softmax损失函数联合学习的策略,在Softmax损失函数基础上分别对训练集每个类别在特征空间维护一个类中心,在训练过程中新增加样本时,网络会约束样本的分类中心距离,以提高多角度情况下的车型识别的能力。实验结果显示,该车型识别模型在CompCars数据集上的正确率达到了93.63%,验证了模型在多角度情况下的准确性和鲁棒性。 相似文献
36.
37.
Abdul Rahman Mohtasebzadeh Longfei Ye Thomas M. Crawford 《International journal of molecular sciences》2015,16(8):19769-19779
We study magnetic-field directed self-assembly of magnetic nanoparticles onto templates recorded on perpendicular magnetic recording media, and quantify feature width and height as a function of assembly time. Feature widths are determined from Scanning Electron Microscope (SEM) images, while heights are obtained with Atomic Force Microscopy (AFM). For short assembly times, widths were ~150 nm, while heights were ~14 nm, a single nanoparticle on average with a 10:1 aspect ratio. For long assembly times, widths approach 550 nm, while the average height grows to 3 nanoparticles, ~35 nm; a 16:1 aspect ratio. We perform magnetometry on these self-assembled structures and observe the slope of the magnetic moment vs. field curve increases with time. This increase suggests magnetic nanoparticle interactions evolve from nanoparticle–nanoparticle interactions to cluster–cluster interactions as opposed to feature–feature interactions. We suggest the aspect ratio increase occurs because the magnetic field gradients are strongest near the transitions between recorded regions in perpendicular media. If these gradients can be optimized for assembly, strong potential exists for using perpendicular recording templates to assemble complex heterogeneous materials. 相似文献
38.
Study on the relationship between the particle size distribution and the effectiveness of the K‐powder fire extinguishing agent 下载免费PDF全文
The relationship between the particle size distribution and the extinguishing effectiveness of the new K‐powder fire extinguishing agent has been studied experimentally, to explore the reason of the great extinguishing efficiency exhibited by the new K‐powder fire extinguishing agent on Class B fire (liquid fuel fire). The results of the experiment showed that the extinguishing effectiveness increased along with the decrease of the particle size distribution. In addition, a sharp discontinuity appeared around the limiting size, about 40 μm. The powder with the particle size below 40 μm exhibited highly effective extinguishing with the minimum effective extinguishing concentration Cxr = 23 g·m?3, while the powder with the particle size above 40 μm exhibited little fire extinguishing efficiency. Compared with other fire extinguishing agents produced by different substances, the new K‐powder fire extinguishing has the bigger limiting size. That means, in the same particle size distribution, the new K‐powder fire extinguishing agent contains more highly effective powder than others contain, and is more effective. 相似文献
39.
40.
Tao Li Zehui Du Nobumichi Tamura Mao Ye Saikumar Inguva Wei Lu Xierong Zeng Shanming Ke Haitao Huang 《Journal of the European Ceramic Society》2018,38(4):1488-1497
(1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 ((1-x)PZN-xPT in short) is one of the most important piezoelectric materials. In this work, we extensively investigated (1-x)PZN-xPT (x = 0.07–0.11) ferroelectric single crystals using in-situ synchrotron μXRD, complemented by TEM and PFM, to correlate microstructures with phase transitions. The results reveal that (i) at 25 °C, the equilibrium state of (1-x)PZN-xPT is a metastable orthorhombic phase for x = 0.07 and 0.08, while it shows coexistence of orthorhombic and tetragonal phases for x = 0.09 and x = 0.11, with all ferroelectric phases accompanied by ferroelastic domains; (ii) upon heating, the phase transformation in x = 0.07 is Orthorhombic → Monoclinic → Tetragonal → Cubic. The coexistence of ferroelectric tetragonal and paraelectric cubic phases was in-situ observed in x = 0.08 above Curie temperature (TC), and (iii) phase transition can be explained by the evolution of the ferroelectric and ferroelastic domains. These results disclose that (1-x)PZN-xPT are in an unstable regime, which is possible factor for its anomalous dielectric response and high piezoelectric coefficient. 相似文献