全文获取类型
收费全文 | 112152篇 |
免费 | 12571篇 |
国内免费 | 8201篇 |
专业分类
电工技术 | 10141篇 |
技术理论 | 4篇 |
综合类 | 10864篇 |
化学工业 | 14566篇 |
金属工艺 | 7365篇 |
机械仪表 | 8275篇 |
建筑科学 | 8458篇 |
矿业工程 | 4448篇 |
能源动力 | 3323篇 |
轻工业 | 10189篇 |
水利工程 | 3449篇 |
石油天然气 | 4960篇 |
武器工业 | 1780篇 |
无线电 | 12399篇 |
一般工业技术 | 9725篇 |
冶金工业 | 4185篇 |
原子能技术 | 1808篇 |
自动化技术 | 16985篇 |
出版年
2024年 | 461篇 |
2023年 | 1789篇 |
2022年 | 4048篇 |
2021年 | 5347篇 |
2020年 | 3900篇 |
2019年 | 2808篇 |
2018年 | 3295篇 |
2017年 | 3625篇 |
2016年 | 3183篇 |
2015年 | 5121篇 |
2014年 | 6511篇 |
2013年 | 7647篇 |
2012年 | 9342篇 |
2011年 | 9789篇 |
2010年 | 9184篇 |
2009年 | 8615篇 |
2008年 | 8981篇 |
2007年 | 8582篇 |
2006年 | 7333篇 |
2005年 | 5957篇 |
2004年 | 4329篇 |
2003年 | 2923篇 |
2002年 | 2624篇 |
2001年 | 2326篇 |
2000年 | 1839篇 |
1999年 | 1013篇 |
1998年 | 482篇 |
1997年 | 362篇 |
1996年 | 312篇 |
1995年 | 290篇 |
1994年 | 218篇 |
1993年 | 148篇 |
1992年 | 121篇 |
1991年 | 80篇 |
1990年 | 63篇 |
1989年 | 53篇 |
1988年 | 37篇 |
1987年 | 36篇 |
1986年 | 24篇 |
1985年 | 13篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 14篇 |
1980年 | 26篇 |
1979年 | 15篇 |
1966年 | 2篇 |
1965年 | 2篇 |
1959年 | 16篇 |
1951年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
2.
Peiying Wang Juanli Zhao Yun Fan Wei Zhang Yuanyuan Cui Liangmiao Zhang Bin Liu Hongqiang Nian Yiran Li 《Ceramics International》2021,47(11):15023-15029
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
3.
Chenchen Zhou Jia Man Haibo Yu He Xia Luming Man Bin Qi Jianfeng Li 《Ceramics International》2021,47(8):10866-10872
Ceramic microparticles have great potentials in various fields such as materials engineering, biotechnology, microelectromechanical systems, etc. Morphology of the microparticle performs an important role on their application. To date, it remains difficult to find an effective and controllable way for fabricating nonspherical ceramic microparticles with 3D features. This work demonstrates a method that combines UV light lithography and single emulsion opaque-droplet-templated microfluidic molding to prepare the crescent-shaped ceramic microparticles. By tailoring the intensity of UV light and flow rate of fluid, the shapes of microparticles are accordingly tuned. Therefore, varieties of crescent-shaped microparticles and their variations have been fabricated. After sintering, the crescent-shaped alumina ceramic microparticles were obtained. Benefitting from the light absorption and scattering behavior of most ceramic nanoparticles, this system can serve as a general platform to produce crescent-shaped microparticles made from different materials, and hold great potentials for applications in microrobotics, structural materials in MEMS, and biotechnology. 相似文献
6.
7.
深入浅出阐释智慧调峰泵站的基本组成与工作原理,论述有效调峰的基本内涵、实现方法及重要性,给出智慧调峰泵站的设计案例并指出其应用优势,就今后研究设计工作的重点内容给出建议。 相似文献
8.
9.
针对伊拉克米桑油田盐膏层巨厚、钻井液密度窗口窄、存在高压盐水层,储层段漏塌同层导致复杂时效高等问题,通过对比分析国内外盐膏层和窄压力窗口地层钻井技术,总结了米桑油田钻井面临的主要技术难点,从井身结构优化、钻井提速和复杂预防等方面入手,研究形成了适合米桑油田的钻井关键技术,并进行了现场试验应用,取得了显著的效果.伊拉克米桑油田钻井关键技术对该地区钻井技术方案设计和钻井提速提效具有较强的借鉴和指导作用. 相似文献
10.
In this study, a kind of Ni-based superalloy specially designed for additive manufacturing (AM) was investigated. Thermo-Calc simulation and differential scanning calorimetry (DSC) analysis were used to determine phases and their transformation temperature. Experimental specimens were prepared by laser metal deposition (LMD) and traditional casting method. Microstructure, phase constitution and mechanical properties of the alloy were characterized by scanning electron microscopy (SEM), transmission scanning electron microscopy (TEM), X-ray diffraction (XRD) and tensile tests. The results show that this alloy contains two basic phases, γ/γ', in addition to these phases, at least two secondary phases may be present, such as MC carbides and Laves phases. Furthermore, the as-deposited alloy has finer dendrite, its mean primary dendrite arm space (PDAS) is about 30-45 μm, and the average size of γ' particles is 100-150 nm. However, the dendrite size of the as-cast alloy is much larger and its PDAS is 300-500 μm with secondary and even third dendrite arms. Correspondingly, the alloy displays different tensile behavior with different processing methods, and the as-deposited specimen shows better ultimate tensile stress (1,085.7±51.7 MPa), yield stress (697±19.5 MPa) and elongation (25.8%±2.2%) than that of the as-cast specimen. The differences in mechanical properties of the alloy are due to the different morphology and size of dendrites, γ', and Laves phase, and the segregation of elements, etc. Such important information would be helpful for alloy application as well as new alloy development. 相似文献