全文获取类型
收费全文 | 31891篇 |
免费 | 2372篇 |
国内免费 | 1723篇 |
专业分类
电工技术 | 818篇 |
综合类 | 1999篇 |
化学工业 | 4417篇 |
金属工艺 | 9353篇 |
机械仪表 | 749篇 |
建筑科学 | 1594篇 |
矿业工程 | 1021篇 |
能源动力 | 672篇 |
轻工业 | 556篇 |
水利工程 | 613篇 |
石油天然气 | 429篇 |
武器工业 | 217篇 |
无线电 | 842篇 |
一般工业技术 | 5369篇 |
冶金工业 | 6759篇 |
原子能技术 | 209篇 |
自动化技术 | 369篇 |
出版年
2024年 | 78篇 |
2023年 | 509篇 |
2022年 | 645篇 |
2021年 | 916篇 |
2020年 | 924篇 |
2019年 | 789篇 |
2018年 | 778篇 |
2017年 | 878篇 |
2016年 | 824篇 |
2015年 | 900篇 |
2014年 | 1479篇 |
2013年 | 1798篇 |
2012年 | 1863篇 |
2011年 | 2487篇 |
2010年 | 1841篇 |
2009年 | 1943篇 |
2008年 | 1728篇 |
2007年 | 2039篇 |
2006年 | 2315篇 |
2005年 | 1754篇 |
2004年 | 1690篇 |
2003年 | 1384篇 |
2002年 | 1099篇 |
2001年 | 903篇 |
2000年 | 805篇 |
1999年 | 615篇 |
1998年 | 473篇 |
1997年 | 458篇 |
1996年 | 376篇 |
1995年 | 333篇 |
1994年 | 272篇 |
1993年 | 211篇 |
1992年 | 181篇 |
1991年 | 142篇 |
1990年 | 125篇 |
1989年 | 83篇 |
1988年 | 39篇 |
1987年 | 55篇 |
1986年 | 47篇 |
1985年 | 25篇 |
1984年 | 33篇 |
1983年 | 25篇 |
1982年 | 29篇 |
1981年 | 21篇 |
1980年 | 18篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
22.
Power transformers are protected by different relays that operate independently. Malfunction of each relay has a major role in reducing the reliability of the protection system. In order to mitigate the main drawbacks of the power transformer relays, an overall protection scheme is presented in this paper. This scheme proposes a novel multi criterion algorithm using decision-making based on fuzzy logic. In this paper the outputs of restricted earth fault relay and a directional check unit, are combined with the output of the differential protection relay. Therefore, problems that are pertaining to independent operation of each relay have been mitigated and the relays cover protection blind spots of each other. The improved power transformer protection (IPTP) scheme enhances the sensitivity and reliability of the power transformer protection. Extensive simulations are used to measure the effectiveness and merit of the proposed IPTP relay. The above efforts result in a multi criteria approach for protection of power transformers. 相似文献
23.
针对四川某稀土矿选矿工艺存在的稀土回收率低的问题,开展了一系列选矿试验研究。试验结果表明,在矿浆质量浓度为30%,粗选NaOH用量为600g/t,水玻璃用量为3000g/t,EF1106用量为3500g/t,起泡剂用量为60g/t情况下,采用一粗、三精、两扫、中矿按顺序返回的选矿流程,可获得稀土REO的品位和回收率分别为66.32%和79.88%的稀土浮选精矿。与该选厂的生产指标相比,稀土回收率提高了13.93%。 相似文献
24.
Iryna Smokovych Manja Krüger Michael Scheffler 《Journal of the European Ceramic Society》2019,39(13):3634-3642
Silica-based coating systems were developed using polymer derived ceramics (PDCs) technology. Ceramic composites on the base of a SiO2 and SiNO matrix and homogeneously distributed Mo5SiB2, SiB6, Si and B fillers were manufactured. The coating systems have low porosity and provide a high oxidation resistance up to 100 h at 800 °C and 1100 °C in air. The influence of temperature and atmosphere of pyrolysis on the polymer precursor, the volume fraction of filler materials on the chemical composition of compacts as well as their high-temperature oxidation protection was investigated. 相似文献
25.
To improve the electrochemical properties of rare-earth–Mg–Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the ... 相似文献
26.
O.N. Kondrateva G.E. Nikiforova A.V. Tyurin M.A. Ryumin V.M. Gurevich A.P. Kritskaya K.S. Gavrichev 《Ceramics International》2018,44(15):18103-18107
The heat capacity of ytterbium orthovanadate was first measured by adiabatic calorimetry in the temperature range T?=?12.28–344.06?K. No obvious anomalies were observed on the curve obtained. The values of standard thermodynamic functions in the temperature range T?=?0–400 K were calculated. Based on low-temperature calorimetry data obtained, previously published data on the high-temperature heat capacity of ytterbium orthovanadate were corrected. The anomalous contribution to heat capacity for YbVO4 was compared with the data known for YbPO4. 相似文献
27.
采用溶胶-凝胶法制备了经稀土元素Ce掺杂改性的Ti/RuO_2-SnO_2-Ce电极,利用SEM、XRD、EDS等分析方法对电极表面的形貌、物相和涂层成分进行了表征,利用CV曲线、LSV曲线等检测手段对电极的电化学性能进行了测试。以Ti/RuO_2-SnO_2-Ce电极为阳极,钛板为阴极,构建电化学氧化反应装置,并采用其对焦化废水进行电解处理。结果表明,Ti/RuO_2-SnO_2电极经稀土Ce改性后极板表面活性位点数量明显增大,金属涂层的结晶化程度明显增强,电极的催化氧化活性显著提高。室温条件下,保持pH值为7.83,在电流密度为30mA/cm~2,电解时间为30min时,焦化废水经电解处理后COD去除率可达91.63%,TOC去除率可达66.22%,UV254值下降到0.921。 相似文献
28.
29.
30.
Timothy Zurrer Kenneth Wong Jonathan Horlyck Emma C. Lovell Joshua Wright Nicholas M. Bedford Zhaojun Han Kang Liang Jason Scott Rose Amal 《Advanced functional materials》2021,31(9):2007624
The vast chemical and structural tunability of metal–organic frameworks (MOFs) are beginning to be harnessed as functional supports for catalytic nanoparticles spanning a range of applications. However, a lack of straightforward methods for producing nanoparticle-encapsulated MOFs as efficient heterogeneous catalysts limits their usage. Herein, a mixed-metal MOF, NiMg-MOF-74, is utilized as a template to disperse small Ni nanoclusters throughout the parent MOF. By exploiting the difference in Ni O and Mg O coordination bond strength, Ni2+ is selectively reduced to form highly dispersed Ni nanoclusters constrained by the parent MOF pore diameter, while Mg2+ remains coordinated in the framework. By varying the ratio of Ni to Mg in the parent MOF, accessible surface area and crystallinity can be tuned upon thermal treatment, influencing CO2 adsorption capacity and hydrogenation selectivity. The resulting Ni nanoclusters prove to be an active catalyst for CO2 methanation and are examined using extended X-ray absorption fine structure and X-ray photoelectron spectroscopy. By preserving a segment of the Mg2+-containing MOF framework, the composite system retains a portion of its CO2 adsorption capacity while continuing to deliver catalytic activity. The approach is thus critical for designing materials that can bridge the gap between carbon capture and CO2 utilization. 相似文献