全文获取类型
收费全文 | 362914篇 |
免费 | 30918篇 |
国内免费 | 17649篇 |
专业分类
电工技术 | 21595篇 |
技术理论 | 57篇 |
综合类 | 44647篇 |
化学工业 | 53335篇 |
金属工艺 | 14932篇 |
机械仪表 | 17511篇 |
建筑科学 | 48969篇 |
矿业工程 | 17787篇 |
能源动力 | 11305篇 |
轻工业 | 24526篇 |
水利工程 | 15861篇 |
石油天然气 | 14907篇 |
武器工业 | 3009篇 |
无线电 | 27860篇 |
一般工业技术 | 32848篇 |
冶金工业 | 20384篇 |
原子能技术 | 3622篇 |
自动化技术 | 38326篇 |
出版年
2024年 | 1250篇 |
2023年 | 4104篇 |
2022年 | 7447篇 |
2021年 | 8649篇 |
2020年 | 9178篇 |
2019年 | 7870篇 |
2018年 | 7485篇 |
2017年 | 9144篇 |
2016年 | 10515篇 |
2015年 | 11536篇 |
2014年 | 20268篇 |
2013年 | 19103篇 |
2012年 | 24523篇 |
2011年 | 26078篇 |
2010年 | 20506篇 |
2009年 | 21373篇 |
2008年 | 19651篇 |
2007年 | 25553篇 |
2006年 | 24398篇 |
2005年 | 21147篇 |
2004年 | 18000篇 |
2003年 | 16087篇 |
2002年 | 13353篇 |
2001年 | 11139篇 |
2000年 | 9329篇 |
1999年 | 7619篇 |
1998年 | 5761篇 |
1997年 | 4978篇 |
1996年 | 4507篇 |
1995年 | 3845篇 |
1994年 | 3373篇 |
1993年 | 2564篇 |
1992年 | 2212篇 |
1991年 | 1654篇 |
1990年 | 1409篇 |
1989年 | 1192篇 |
1988年 | 913篇 |
1987年 | 671篇 |
1986年 | 469篇 |
1985年 | 424篇 |
1984年 | 400篇 |
1983年 | 305篇 |
1982年 | 244篇 |
1981年 | 173篇 |
1980年 | 165篇 |
1979年 | 116篇 |
1978年 | 63篇 |
1977年 | 77篇 |
1976年 | 59篇 |
1975年 | 59篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
综述了铁素体与铁素体异种金属焊缝(dissimilar metal welds,DMWs)接头界面组织及其影响。结果表明,在焊后热处理或运行温度下的铁素体钢DMWs接头的不均匀界面组织中,通常会形成脱碳层和增碳层。在铁素体钢DMWs焊接接头界面组织影响因素中,焊缝金属的化学成分有重要影响;焊后热处理规范(温度和时间)、工作温度下运行时间的影响较为突出;焊接工艺参数的影响亦不可忽略。异种钢接头界面处近缝区裂纹的产生,以及接头的蠕变强度随Larson Miller 参数增大而下降等不利影响,均为异种钢界面碳迁移行为所导致。焊缝成分控制法是接头界面组织控制或改善的必要条件,而脱碳层部位转移法能有效防止裂纹发生,亦是接头安全运行的重要工艺措施之一。 相似文献
32.
《Advanced Powder Technology》2022,33(6):103628
The charge sources, as well as the charging mechanism of the contact electrification (CE) of polymers, are still debatable. Since CE is accompanied by destruction, it is considered that “hard contacting” via ball milling can induce covalent bond scission and produce naked-activated-charge sources. Regarding “soft contacting” via nano-scale sliding, which does not induce covalent bond scission, a frontier-electron, “f-electron,” of the naked-activated-charge source is crucial to electron transfer among the naked-activated-charge sources. Here, we configure naked-activated-charge-source models, naked-activated-mechano-anion, and naked-activated-mechano-cation, which are produced by mechanical energy induced heterogeneous covalent bond scission, as well as naked-activated-mechano-radicals that are produced by homogeneous covalent bond scission. Regarding “soft contacting” among naked-activated-charge sources in a vacuum, f-electron can be transferred from a donor to an acceptor if the energy level of the donor is higher than that of the acceptor. The net amount of the normalized transferred-f-electrons is obtained by adopting settings in which the average energy level of the naked-activated-charge sources (as the donors) is higher than that of the sources employed as acceptors. Thus, the surfaces comprising the donors and acceptors will exhibit positive and negative net surface charges, respectively. We conclude that net surface charges depend on the average energy level of naked-activated-charge sources. Further, we observe that the alignment of polyethylene (PE)-polyvinyl chloride (PVC)-polytetrafluoroethylene (PTFE) to the average energy level is identical to that of the triboelectric series. 相似文献
33.
《Advanced Powder Technology》2022,33(8):103663
In this work, a new type of FeSi/FeNi soft magnetic powder core (SMPC) was successfully fabricated by coating FeNi nanoparticles on the surface of FeSi micrometer powder. The effects of different contents of FeNi nanoparticles on the micromorphology, internal structures, and soft magnetic properties of SMPCs were studied. The results show that FeNi nanoparticles adhere to the surface of FeSi powder, which can effectively fill the air gap between FeSi powder and is beneficial to the compaction of the powder cores during the pressing process. Thus, the density of the SMPCs is increased. Compared to FeSi SMPCs, the comprehensive soft magnetic properties of FeSi/FeNi SMPCs have been greatly improved. When adding 15 wt% FeNi nanoparticles, the SMPCs exhibit excellent magnetic properties with high effective permeability (increased by 43.8 %) and low core loss (decreased by 22.1 %). The high performance FeSi/FeNi SMPCs prepared in this work are expected to be widely used in power choke coils, uninterruptible power supplies, and boosts and inverter inductors. 相似文献
34.
35.
36.
Against the background of smart manufacturing and Industry 4.0, how to achieve real-time scheduling has become a problem to be solved. In this regard, automatic design for shop scheduling based on hyper-heuristics has been widely studied, and a number of reviews and scheduling algorithms have been presented. Few studies, however, have specifically discussed the technical points involved in algorithm development. This study, therefore, constructs a general framework for automatic design for shop scheduling strategies based on hyper-heuristics, and various state-of-the-art technical points in the development process are summarized. First, we summarize the existing types of shop scheduling strategies and classify them using a new classification method. Second, we summarize an automatic design algorithm for shop scheduling. Then, we investigate surrogate-assisted methods that are popular in the current algorithm field. Finally, current problems and challenges are discussed, and potential directions for future research are proposed. 相似文献
37.
38.
《Ceramics International》2021,47(21):30298-30309
The novel Al4O4C–(Al2OC)1-x(AlN)x–Zr2Al3C4–Al2O3 refractories with ultra-low carbon content have been successfully prepared by constructing the core-shell structure of aluminum at 1300–1700°C in nitrogen. The phase composition, microstructure, and properties of the novel refractories are deeply investigated. The cracking temperature on the core-shell structure of aluminum is further explored and the reaction mechanism of Zr2Al3C4 has also added explanation. The results show that the novel refractories have excellent physical properties and cannot be corroded by molten iron. There exist two different Al2OC solid solutions in the novel refractories, Al2OC-rich (Al2OC)1-x(AlN)x and AlN-rich (Al2OC)1-x(AlN)x. The temperatures affect their relative content. When temperatures are less than 1600°C, the relative content of Al2OC-rich (Al2OC)1-x(AlN)x is more than that of AlN-rich (Al2OC)1-x(AlN)x. When temperatures are above 1700°C, the relative content of AlN-rich (Al2OC)1-x(AlN)x is more than that of Al2OC-rich (Al2OC)1-x(AlN)x. The core-shell structure of aluminum fully ruptures at about 1200°C. Zr2Al3C4 begins to form at about 1000°C and generates in large at 1200°C. 相似文献
39.
《International Journal of Hydrogen Energy》2022,47(62):25880-25898
Hydrogen as an energy carrier can play a significant role in reducing environmental emissions if it is produced from renewable energy resources. This research aims to assess hydrogen production from wind energy considering environmental, economic, and technical aspect for the East Azerbaijan province of Iran. The economic assessment is performed by calculation of payback period, levelized cost of hydrogen, and levelized cost of electricity. Since uncertainty in the power output of wind turbines may affect the payback period, all calculations are performed for four different turbine degradation rates. While it is common in the literature to choose the wind turbine based on a single criterion, this study implements Multi-Criteria Decision-Making (MCDM) techniques for this purpose. The results of Step-wise Weight Assessment Ratio Analysis illustrates that economic issue is the most important criterion for this research. The results of Weighted Aggregated Sum Product Assessment shows that Vestas V52 is the most suitable wind turbine for Ahar and Sarab cities, while Eovent EVA120 H-Darrieus is a better choice for other stations. The most suitable location for wind power generation is found to be Ahar, where it is estimated to annually generate 2914.8 kWh of electricity at the price of 0.045 $/kWh, and 47.2 tons of hydrogen at the price of 1.38 $/kg, which result in 583 tons of CO2 emission reduction. 相似文献
40.
《Ceramics International》2022,48(16):23504-23509
KTaO3 and KTa0.9M0.1O3-α (M = Ti, Hf, Zr) were prepared by solid state reaction at 1330 °C for 2 h and characterized by x-ray diffraction. The AC impedance technique was used to analyze the sintered solid electrolytes in 1%H2/Ar and dry air atmosphere. Among KTa0.9M0.1O3-α (M = Ti, Hf, Zr), KTa0.9Zr0.1O3-α displays the highest conductivity in 1%H2/Ar atmosphere. The carriers transport numbers of solid electrolytes were measured by concentration cell method. The results show KTa0.9Zr0.1O3-α is a pure proton conductor below 525 °C. Stability tests show that KTa0.9Zr0.1O3-α has good chemical stability against CO2 and H2O. 相似文献