全文获取类型
收费全文 | 74577篇 |
免费 | 7668篇 |
国内免费 | 4712篇 |
专业分类
电工技术 | 4503篇 |
技术理论 | 2篇 |
综合类 | 7703篇 |
化学工业 | 5408篇 |
金属工艺 | 2296篇 |
机械仪表 | 5773篇 |
建筑科学 | 10213篇 |
矿业工程 | 1497篇 |
能源动力 | 1879篇 |
轻工业 | 1255篇 |
水利工程 | 1075篇 |
石油天然气 | 2479篇 |
武器工业 | 780篇 |
无线电 | 7490篇 |
一般工业技术 | 3965篇 |
冶金工业 | 1939篇 |
原子能技术 | 330篇 |
自动化技术 | 28370篇 |
出版年
2024年 | 168篇 |
2023年 | 1027篇 |
2022年 | 1656篇 |
2021年 | 2140篇 |
2020年 | 2212篇 |
2019年 | 1776篇 |
2018年 | 1547篇 |
2017年 | 1919篇 |
2016年 | 2159篇 |
2015年 | 2654篇 |
2014年 | 4606篇 |
2013年 | 4121篇 |
2012年 | 4980篇 |
2011年 | 6039篇 |
2010年 | 4542篇 |
2009年 | 4887篇 |
2008年 | 5114篇 |
2007年 | 5814篇 |
2006年 | 4985篇 |
2005年 | 4495篇 |
2004年 | 3689篇 |
2003年 | 3412篇 |
2002年 | 2527篇 |
2001年 | 2140篇 |
2000年 | 1731篇 |
1999年 | 1247篇 |
1998年 | 937篇 |
1997年 | 755篇 |
1996年 | 604篇 |
1995年 | 567篇 |
1994年 | 458篇 |
1993年 | 385篇 |
1992年 | 308篇 |
1991年 | 246篇 |
1990年 | 160篇 |
1989年 | 166篇 |
1988年 | 126篇 |
1987年 | 84篇 |
1986年 | 71篇 |
1985年 | 89篇 |
1984年 | 90篇 |
1983年 | 58篇 |
1982年 | 34篇 |
1981年 | 26篇 |
1980年 | 25篇 |
1979年 | 25篇 |
1978年 | 17篇 |
1977年 | 22篇 |
1975年 | 18篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
1.
2.
《International Journal of Hydrogen Energy》2022,47(77):33014-33026
The present study investigates the combined influence of Channel to Rib Width (CRW) ratio and clamping pressure on the structure and performance of High Temperature-Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC) using a three-dimensional numerical model developed previously. It also considers the impact of interfacial contact resistance between the Gas Diffusion Layer (GDL) and Bipolar Plate (BPP). The structural analysis of the single straight channel HT-PEMFC geometry shows that the von-Mises stress greatly increases in the GDL under the ribs as the CRW ratio increases resulting in considerably high deformation. The cell performance analysis depicts the significance of ohmic resistance and concentration polarization for different CRW ratios, particularly at higher operating current densities. However, in low to medium current density regions, the CRW ratio has little influence on cell performance. A substantial impact on the species, overpotential, and current distributions is observed. The findings also reveal that the CRW ratio significantly affects the temperature distribution in the cell. 相似文献
3.
4.
资源型产业发展为推进国家经济增长和工业化进程提供了重要保障。为深入了解资源型产业的研究情况,以CNKI数据库为数据源,搜集2000—2020年关于资源型产业的核心及以上期刊论文,利用CiteSpace软件从发文作者与研究机构分布、关键词共现网络和时区图谱等方面,绘制知识图谱,进行可视化分析。研究发现:资源型产业领域的研究成果愈加丰富,但研究群体间联系合作较少,且现有的合作研究主要集中在所处地域资源富集和具有学科优势的研究机构及学者;资源型产业领域的研究热点可概括为产业发展、资源型城市、产业集群、产业结构、产业链和产业集聚等方面;针对资源型产业领域未来可从资源型产业相关理论研究、创新发展模式和可持续发展等方面深入展开。 相似文献
5.
6.
Software is a central component in the modern world and vastly affects the environment’s sustainability. The demand for energy and resource requirements is rising when producing hardware and software units. Literature study reveals that many studies focused on green hardware; however, limited efforts were made in the greenness of software products. Green software products are necessary to solve the issues and problems related to the long-term use of software, especially from a sustainability perspective. Without a proper mechanism for measuring the greenness of a particular software product executed in a specific environment, the mentioned benefits will not be attained. Currently, there are not enough works to address this problem, and the green status of software products is uncertain and unsure. This paper aims to identify the green measurements based on sustainable dimensions in a software product. The second objective is to reveal the relationships between the elements and measurements through empirical study. The study is conducted in two phases. The first phase is the theoretical phase, where the main components, measurements and practices that influence the sustainability of a software product are identified. The second phase is the empirical study that involved 103 respondents in Malaysia investigating current practices of green software in the industrial environment and further identifying the main sustainability dimensions and measurements and their impact on achieving green software products. This study has revealed seven green measurements of software product: Productivity, Usability, Cost Reduction, Employee Support, Energy Efficiency, Resource Efficiency and Tool Support. The relationships are statistically significant, with a significance level of less than 0.01 (p = 0.000). Thus, the hypothesised relationships were all accepted. The contributions of this study revolve around the research perspectives of the measurements to attain a green software product. 相似文献
7.
Yumin An Yi Yang Yongna Jia Wenbo Han Yehong Cheng 《Journal of the American Ceramic Society》2022,105(4):2385-2391
Biomimetic Bouligand architecture is constructed in the ceramic to improve its toughness. Firstly, unidirectional carbon fiber-reinforced ZrB2-SiC ceramic films are achieved through a vacuum-assisted filtration method using graphene oxide. Then, ceramic films are helically assembled at a fixed angle of 30° in the graphite die based on the fiber orientation. Finally, the spark plasma sintering method was utilized to densify helical assembly carbon fiber/ceramic films. By constructing Bouligand structure, high fracture toughness (7.4 MPa·m0.5) and work of fracture (∼1055 J/m2) are achieved in ZrB2-based ceramic. The toughening mechanisms mainly are crack deflection, twisting and branching, carbon fiber pulling out, and bridging. 相似文献
8.
Rodrigo Montoya Allan G. Ruiz-García Alma Ortiz-Ozuna Blanca Ramírez-Barat Juan Genesca 《工业材料与腐蚀》2021,72(7):1259-1269
The electrochemical interactions between aluminum alloy 7075 and low-carbon steels under gelled electrolytes were studied. Such electrolytes provided the opportunity to investigate both thick and thin electrolyte systems. The electrolyte was chemically modified to visually track the acidic fronts during the anodic reaction and the subsequent hydrolysis process. Two mathematical models were validated for both thick and ultrathin electrolytes. The acidification of thick electrolytes was extended some millimeters beyond the aluminum alloy surface, whereas the acidic front was localized next to the metallic joint using ultrathin electrolytes. The combination of both numerical and experimental results allows proving (and explaining why) that the acidification process is more aggressive under dilute than under concentrated electrolytes. 相似文献
9.
Form selection of concomitant polymorphs: A case study informed by crystallization kinetics modeling
Weiwei Tang Yufeng Quan Junbo Gong Jingkang Wang Qiuxiang Yin Tonglei Li 《American Institute of Chemical Engineers》2021,67(4):e17129
Molecular mechanisms and process kinetics of crystallizing concomitant polymorphs remain poorly understood. Solvent-mediated phase transformation and concomitant crystallization are difficult to be distinguished in practice, as multiple forms can be detected at the same time. Herein, we developed a population balance model to simulate a concomitant crystallization process of two polymorphs of tolfenamic acid. Our kinetic modeling aims to understand concomitant crystallization and help guide form selection of such a molecular system. Crystallization kinetics of ethanolic solutions were uncovered from induction time measurements, as well as seeded and unseeded crystallization experiments. Experimental and simulation results demonstrate that the stable form I crystallizes concomitantly with the metastable form II. The faster growing form II results in an intermediate decline in the composition of form I in crystallized samples, a characteristic feature of the concomitantly crystallized system. A four-quadrant scheme of attainable polymorph outcome was simulated under various crystallization conditions. 相似文献
10.