全文获取类型
收费全文 | 4616篇 |
免费 | 522篇 |
国内免费 | 185篇 |
专业分类
电工技术 | 47篇 |
综合类 | 365篇 |
化学工业 | 2394篇 |
金属工艺 | 157篇 |
机械仪表 | 67篇 |
建筑科学 | 183篇 |
矿业工程 | 170篇 |
能源动力 | 52篇 |
轻工业 | 683篇 |
水利工程 | 31篇 |
石油天然气 | 178篇 |
武器工业 | 31篇 |
无线电 | 106篇 |
一般工业技术 | 345篇 |
冶金工业 | 423篇 |
原子能技术 | 54篇 |
自动化技术 | 37篇 |
出版年
2024年 | 12篇 |
2023年 | 49篇 |
2022年 | 100篇 |
2021年 | 119篇 |
2020年 | 128篇 |
2019年 | 116篇 |
2018年 | 78篇 |
2017年 | 135篇 |
2016年 | 152篇 |
2015年 | 127篇 |
2014年 | 267篇 |
2013年 | 279篇 |
2012年 | 329篇 |
2011年 | 334篇 |
2010年 | 258篇 |
2009年 | 242篇 |
2008年 | 194篇 |
2007年 | 284篇 |
2006年 | 288篇 |
2005年 | 250篇 |
2004年 | 219篇 |
2003年 | 173篇 |
2002年 | 181篇 |
2001年 | 152篇 |
2000年 | 137篇 |
1999年 | 108篇 |
1998年 | 118篇 |
1997年 | 75篇 |
1996年 | 73篇 |
1995年 | 53篇 |
1994年 | 53篇 |
1993年 | 36篇 |
1992年 | 31篇 |
1991年 | 32篇 |
1990年 | 23篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1959年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有5323条查询结果,搜索用时 31 毫秒
131.
湿法磷酸脱硫(SO4^2—)净化研究 总被引:5,自引:0,他引:5
针对云南湿法磷酸进行了脱除硫酸根的实验研究,考察了沉淀剂用量,反应时间及温度等因素对硫酸根去除率的影响 相似文献
132.
Zhang Fenge Hao Guizheng Gu PingHe Bei Institute of Architectural Engineering Tian Jin University 《河北建筑工程学院学报》1997,(3)
高锰酸钾具有氧化助凝作用,用它替代预氯化氧化地表水中有机物,使加氯点后移,降低三氯甲浣生成量。高锰酸钾投量与水中三氯甲浣生成量有着密切联系。 相似文献
133.
Philip M. Stone Yong-Ki Kim 《Journal of research of the National Institute of Standards and Technology》2004,109(5):505-515
Cross sections for electron impact excitation of atoms are important for modeling of low temperature plasmas and gases. While there are many experimental and theoretical results for excitation to the first excited states, little information is available for excitation to higher states. We present here calculations of excitations from the ground state to the np levels of sodium (n = 3 through 11) and potassium (n = 4 through 12). We also present a calculation for a transition from the excited sodium level 3p to 3d to show the generality of the method. Scaling formulas developed earlier by Kim [Phys. Rev. A 64, 032713 (2001)] for plane-wave Born cross sections are used. These formulas have been shown to be remarkably accurate yet simple to use. We have used a core polarization potential in a Dirac-Fock wave function code to calculate target atom wave functions and a matching form of the dipole transition operator to calculate oscillator strengths and Born cross sections. The scaled Born results here for excitation to the first excited levels are in very good agreement with experimental and other theoretical data, and the results for excitation to the next few levels are in satisfactory agreement with the limited data available. The present results for excitation to the higher levels are believed to be the only data available. 相似文献
134.
本文介绍了铜锍吹炼主要工艺方案 ,重点分析并对比了PS转炉、闪速吹炼炉工艺技术的先进性、可靠性、环境保护、操作实践以及运行情况 ,得出了基本结论 ,为金隆扩建改造工程吹炼工艺方案的选择提供了依据。 相似文献
135.
Alkali activated foams (known also as “geopolymer foams”) are formed by the adding of a foaming agent, such as Al powder or H2O2, to an alkali activated matrix which can be based on, for example, fly ash, slag or meta-kaolin. The foaming agent decomposes and reacts inside the matrix, resulting in the release of gasses which form pores within the structure. Such pores have to be created before the alkali activated foams harden. In order to prevent the escape of these gasses from the foam, a stabilizing agent can be added to the foam mixture. This paper presents the results of tests involving the pore-foaming process in the case of highly porous, alkali activated, fly-ash based foams. Between 0.5 and 1.5 mass % of H2O2 was added to the fly ash precursor as a foaming agent, as well as different amounts (varying from 0.1 to 4.0 mass %) of the selected stabilizing agent, which is known as SDS - sodium dodecyl sulfate. The physical, mechanical, and microstructural properties of the hardened alkali-activated foams were determined. Their pore structures were characterised by SEM, as well as by a three-dimensional (3D) technique, X-ray computed micro-tomography. The advantage of the latter method is that a better insight can be obtained into the characteristics of the hardened pore structure, including information about its homogeneity and the pore size distribution. The influence of the amount of the added foaming agent, as well as that of the amount of the stabilization agent, was evaluated, and optimal addition mass percentages were determined. In the case of the best mixtures, the investigated hardened pore structures showed relatively good mechanical properties, and could therefore be used for various applications in the building industry. 相似文献
136.
Valuable metal extraction technology from thermal power plant fly ash is limited. In the present study, aluminium is extracted from fly ash as highly pure aluminium sulphate (>99.0%) by leaching with sulphuric acid, followed by pre-concentration and successive crystallization. Two types of fly ashes from different sources, i.e., Talcher Thermal Power Station (TTPS) and Vedanta Aluminium Company Limited (VAL) were chosen for comparative study on the extraction of aluminium as aluminium sulphate. The product is characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Purity of aluminium sulphate was also investigated by inductively coupled plasma–optical emission spectrometry (ICP–OES). The extraction efficiency of aluminium depends on the varied solid-to-liquid ratio (fly ash : 18 mol/L H2SO4, g/mL) and particle size of fly ashes. Physico-chemical analysis indicates that the obtained product is Al2(SO4)3·18H2O, having low iron content (0.08%). 相似文献
137.
Wooram Kim Younja Kwon Young Min Jo Young Chul Park 《Journal of Energetic Materials》2017,35(1):44-52
Potassium sulfamate (PS) is an efficient starting material for the nitration reaction used in the synthesis of ammonium dinitramide (ADN), which is an environmentally friendly high-energy oxidizer for propellants that does not release chlorine-based compounds. PS is a core structure to form dinitramide, -N(NO2)2, by taking NO2? from nitric acid. In this work, five test batches of PS were prepared using a few solvents including ethanol, methanol, acetone, isopropanol, and their mixtures. The lab-made PSs matched well with the commercial PS in terms of the chemical structure. The use of acetone led to a high recovery of PS up to 97 w/w% and ultimately contributed to the formation of high-purity and (99.2%) and a high yield (57.3%) that are greater than those for commercial PS (87.3% purity and 31.3% yield). Therefore, we proved that the crystallinity and homogeneity of PS influenced the properties of ADN and the synthesis efficiency. 相似文献
138.
139.
140.
B. Widyartha Y. Setiyorini F. Abdul T.J. Subakti S. Pintowantoro 《Materialwissenschaft und Werkstofftechnik》2020,51(6):750-757
To address the issue of high energy employment and un-green processing in limonitic laterites extraction, selective reduction using Na2SO4 additive with the introduction of different fluxes including quicklime, dolomite, and limestone followed by magnetic separation was studied. The objective of the research was to find out the influence of fluxes in optimizing ferronickel product of reduction. The reduction process was carried out at 1400 °C for 6 hours and the obtained product was characterized by scanning electron microscopy (SEM), emission dispersive x-ray (EDX), and x-ray diffraction (XRD) to image the morphology, determine the composition, and examine the mineralogical structure. Result showed that the employment of fluxes exhibited positive effect in improving the product. The highest nickel grade was 21.68 % using limestone flux, while the most promising recovery was 93.73 % utilizing dolomite flux. Meanwhile, mineralogical assessment also proved that the ascending of nickel content is due to the formation of troilite (FeS) as the result of synergy between Na2SO4 additives and carbonate minerals from fluxes. This result exhibits a notable performance of fluxes for improving the product of selective reduction. 相似文献