全文获取类型
收费全文 | 46818篇 |
免费 | 4004篇 |
国内免费 | 1970篇 |
专业分类
电工技术 | 1449篇 |
技术理论 | 1篇 |
综合类 | 2179篇 |
化学工业 | 13800篇 |
金属工艺 | 5545篇 |
机械仪表 | 914篇 |
建筑科学 | 1152篇 |
矿业工程 | 2450篇 |
能源动力 | 4010篇 |
轻工业 | 3125篇 |
水利工程 | 279篇 |
石油天然气 | 991篇 |
武器工业 | 92篇 |
无线电 | 2638篇 |
一般工业技术 | 7253篇 |
冶金工业 | 5859篇 |
原子能技术 | 448篇 |
自动化技术 | 607篇 |
出版年
2024年 | 171篇 |
2023年 | 892篇 |
2022年 | 1487篇 |
2021年 | 1813篇 |
2020年 | 1691篇 |
2019年 | 1587篇 |
2018年 | 1515篇 |
2017年 | 1597篇 |
2016年 | 1660篇 |
2015年 | 1570篇 |
2014年 | 2460篇 |
2013年 | 2733篇 |
2012年 | 3081篇 |
2011年 | 3736篇 |
2010年 | 2799篇 |
2009年 | 2588篇 |
2008年 | 2195篇 |
2007年 | 2743篇 |
2006年 | 2466篇 |
2005年 | 1971篇 |
2004年 | 1755篇 |
2003年 | 1552篇 |
2002年 | 1422篇 |
2001年 | 1159篇 |
2000年 | 1070篇 |
1999年 | 815篇 |
1998年 | 723篇 |
1997年 | 592篇 |
1996年 | 532篇 |
1995年 | 446篇 |
1994年 | 386篇 |
1993年 | 274篇 |
1992年 | 283篇 |
1991年 | 201篇 |
1990年 | 198篇 |
1989年 | 161篇 |
1988年 | 112篇 |
1987年 | 62篇 |
1986年 | 39篇 |
1985年 | 52篇 |
1984年 | 41篇 |
1983年 | 21篇 |
1982年 | 44篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
系统分析了新钢公司一钢厂转炉入炉铁水温度低的原因及铁水温度对炼钢的影响,提出了提高铁水温度的措施及转炉应对低温铁水的办法。 相似文献
102.
103.
The molten iron allocation problem (MIAP) is to allocate molten iron from blast furnaces to steel-making furnaces. The allocation needs to observe the release times of the molten iron defined by the draining plan of the blast furnaces and the transport time between the iron-making and steel-making stages. Time window constraints for processing the molten iron must be satisfied to avoid freezing. The objective is to find a schedule with minimum total weighted completion time. This objective reflects the practical consideration of improving steel-making efficiency and reducing operation cost caused by the need for reheating. Such a problem can be viewed as a parallel machine scheduling problem with time windows which is known to be NP-hard. In this paper, we first formulate the molten iron allocation problem as an integer programming model and then reformulate it as a set partitioning model by applying the Dantzig–Wolfe decomposition. We solve the problem using a column generation-based branch-and-price algorithm. Since the subproblem of column generation is still NP-hard, we propose a state-space relaxation-based dynamic programming algorithm for the subproblem. Computational experiments demonstrate that the proposed algorithm is capable of solving problems with up to 100 jobs to optimality within a reasonable computation time. 相似文献
104.
Akbar Eslami Simin Nasseri Bahram Yadollahi Alireza Mesdaghinia Foroogh Vaezi Ramin Nabizadeh Shahrokh Nazmara 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(11):1447-1453
BACKGROUND: Over the past several decades methyl tert‐butyl ether (MTBE) as additive to gasoline, intended to either boost ratings of fuel or to reduce air pollution, has been accepted worldwide. Since MTBE has high water solubility, the occurrence of fuel spills or leaks from underground storage tanks or transferring pipeline has led to the contamination of natural waters. In this study the degradation of aqueous MTBE at relatively high concentrations was investigated by a UV‐visible/ZnO/H2O2 photocatalytic process. The effects of important operational parameters such as pH, amount of H2O2, catalyst loading and irradiation time were also investigated. Concentration of MTBE and intermediates such as tert‐butyl formate and tert‐butyl alcohol were measured. RESULTS: Time required for complete degradation increased from 20 to 150 min when the initial concentration was increased from 10 to 500 mg L?1. The first‐order rate constants for degradation of MTBE were estimated to be 0.183–0.022 min?1 as the concentration increased from 10 to 500 mg L?1. Study of the overall mineralization monitored by total organic carbon analysis showed that at an initial concentration of 100 mg L?1 MTBE complete mineralization was obtained after 100 min under UV‐visible/ZnO/H2O2 photocatalysis. CONCLUSION: The data presented in this paper clearly indicated that UV‐visible/ZnO/O2 as an advanced oxidation process provides an efficient treatment alternative for the remediation of MTBE‐contaminated waters. Copyright © 2008 Society of Chemical Industry 相似文献
105.
Cu-Cr合金高温氧化行为分析 总被引:3,自引:0,他引:3
该文用热分析天平,结合金相、X射线衍射(XRD)、扫描电镜(SEM)和能谱(EXD)研究了Cu—Cr合金在不同温度下的氧化行为。结果表明,Cu—Cr合金在700℃-900℃氧化符合抛物线规律,其最外层氧化膜为CuO,内层为Cu2O和Cr2O3,铬有助于提高合金的抗氧化能力。 相似文献
106.
低工作温度的氧化钨气敏材料 总被引:3,自引:0,他引:3
本文报道了一种可以在100℃左右工作的氢化钨气敏材料,它对氢气和一氧化氮有很高的灵敏度和良好的选择性,并可对空气中的一氧化氮进行探测 相似文献
107.
化学模式识别法在钢铁工业中的若干应用 总被引:1,自引:0,他引:1
本文涉及一种崭新的非函数数据处理法及其在工业诊断和优化中的应用。并对其进行要因分析和优化决策的原理作了介绍。结合钢铁工业生产中的实例进行了分析。还探讨了该方法在钢铁工业中应用的意义。 相似文献
108.
为提高抽油机减速器齿轮铸件的机械性能,提出以Sn代替Mo作为合金元素,并通过试验确定了合理的Si、Cu、Sn的加入量。指出Si加入量应控制在1.9%-2.1%范围内,同时加入0.36%~0.9%的Cu和0.025%~0.07%的Sn,可保证球铁的强度和延伸率都满足QT700-2的要求。鉴于试件与实际铸件的表面硬度有一定的差值,为提高铸件表面硬度,进行了余热正火试验,并给出了铸件在铸型内的时间-冷却温度曲线。最后根据球铁化学成分的选择结果,进行了齿轮生产试验。 相似文献
109.
大型离心复合球墨铸铁轧辊的生产 总被引:1,自引:0,他引:1
简述了我公司为舞阳铜厂试制4200mm厚板轧机离心复合球墨铸铁轧辊的性能要求、内外层双重金属铸造工艺参数的选择及整个铸造生产工艺过程。 相似文献
110.
Zakaria Chajar Michel Primet Hélène Praliaud Michèle Chevrier Catherine Gauthier Frédéric Mathis 《Catalysis Letters》1994,28(1):33-40
The role of nitrogen dioxide in the selective reduction of NO by propane over a Cu-MFI zeolite is investigated. NO2 and NO reductions were carried out under similar conditions of reaction. In the presence of oxygen, the reduction of NO by C3H8 does not differ significantly from that of NO2. In the absence of oxygen, the reduction of NO2 by propane occurs with a partial decomposition of the nitric dioxide molecule. Such a decomposition leads to the formation of oxygen, which is responsible for the increase in catalytic activity by comparison with the same reaction performed with NO. NO2 formed and released in the gas phase during the reduction of NO by propane in the presence of oxygen does not play a predominant role in the catalytic process. 相似文献