全文获取类型
收费全文 | 5520篇 |
免费 | 335篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 38篇 |
综合类 | 1篇 |
化学工业 | 1002篇 |
金属工艺 | 85篇 |
机械仪表 | 87篇 |
建筑科学 | 162篇 |
矿业工程 | 7篇 |
能源动力 | 91篇 |
轻工业 | 1014篇 |
水利工程 | 68篇 |
石油天然气 | 18篇 |
无线电 | 229篇 |
一般工业技术 | 828篇 |
冶金工业 | 1445篇 |
原子能技术 | 14篇 |
自动化技术 | 770篇 |
出版年
2024年 | 7篇 |
2023年 | 42篇 |
2022年 | 54篇 |
2021年 | 116篇 |
2020年 | 109篇 |
2019年 | 135篇 |
2018年 | 190篇 |
2017年 | 201篇 |
2016年 | 219篇 |
2015年 | 179篇 |
2014年 | 233篇 |
2013年 | 448篇 |
2012年 | 347篇 |
2011年 | 331篇 |
2010年 | 251篇 |
2009年 | 249篇 |
2008年 | 240篇 |
2007年 | 223篇 |
2006年 | 120篇 |
2005年 | 102篇 |
2004年 | 115篇 |
2003年 | 98篇 |
2002年 | 106篇 |
2001年 | 80篇 |
2000年 | 71篇 |
1999年 | 85篇 |
1998年 | 546篇 |
1997年 | 301篇 |
1996年 | 196篇 |
1995年 | 100篇 |
1994年 | 79篇 |
1993年 | 78篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 22篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 20篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 19篇 |
1976年 | 28篇 |
1970年 | 1篇 |
排序方式: 共有5859条查询结果,搜索用时 15 毫秒
221.
Margarita Garc��a-Hern��ndez Antonieta Garc��a-Murillo Felipe de J. Carrillo-Romo David Jaramillo-Vigueras Genevi��ve Chadeyron Elder De la Rosa Damien Boyer 《International journal of molecular sciences》2009,10(9):4088-4101
Transparent BaTiO3:Eu3+ films were prepared via a sol-gel method and dip-coating technique, using barium acetate, titanium butoxide, and polyvinylpyrrolidone (PVP) as modifier viscosity. BaTiO3:Eu3+ films ~500 nm thick, crystallized after thermal treatment at 700 ºC. The powders revealed spherical and rod shape morphology. The optical quality of films showed a predominant band at 615 nm under 250 nm excitation. A preliminary luminescent test provided the properties of the Eu3+ doped BaTiO3. 相似文献
222.
Lanthanum-containing Y (LaY) zeolites were prepared by ionic exchange from NaY parent zeolite. The LaY zeolites were de-aluminated by steaming. De-aluminated zeolites presented different Si/Al ratio. The physicochemical properties of these catalysts were characterized by X-ray diffraction, pyridine and xenon adsorption, infrared spectroscopy and 29Si, 27Al, 129Xe, 139La solid-state nuclear magnetic resonance spectroscopy. Furthermore, a fractal geometry approach was adopted to describe the evolution in the texture as a consequence of de-alumination. The catalytic properties of materials were evaluated in the n-hexane cracking reaction. The catalyst with the highest catalytic activity was the zeolite highest de-aluminated (Si/Al ratio of 3.7). Such performance was attributed on the one hand, to active extra-framework aluminum species hosted in the large cavities of zeolites and, on the other hand to redistribution of lanthanum species into the zeolite as a consequence of de-alumination. 相似文献
223.
Mercedes Aleman Carla Daniela Nuchi Ricard Bou Alba Tres Javier Polo Francesc Guardiola Rafael Codony 《European Journal of Lipid Science and Technology》2010,112(7):761-769
Bakery products such as biscuits, cookies, and pastries represent a good medium for iron fortification in food products, since they are consumed by a large proportion of the population at risk of developing iron deficiency anemia, mainly children. The drawback, however, is that iron fortification can promote oxidation. To assess the extent of this, palm oil added with heme iron and different antioxidants was used as a model for evaluating the oxidative stability of some bakery products, such as baked goods containing chocolate. The palm oil samples were heated at 220°C for 10 min to mimic the conditions found during a typical baking processing. The selected antioxidants were a free radical scavenger (tocopherol extract (TE), 0 and 500 mg/kg), an oxygen scavenger (ascorbyl palmitate (AP), 0 and 500 mg/kg), and a chelating agent (citric acid (CA), 0 and 300 mg/kg). These antioxidants were combined using a factorial design and were compared to a control sample, which was not supplemented with antioxidants. Primary (peroxide value and lipid hydroperoxide content) and secondary oxidation parameters (p‐anisidine value, p‐AnV) were monitored over a period of 200 days in storage at room temperature. The combination of AP and CA was the most effective treatment in delaying the onset of oxidation. TE was not effective in preventing oxidation. The p‐AnV did not increase during the storage period, indicating that this oxidation marker was not suitable for monitoring oxidation in this model. 相似文献
224.
Simple Heat Treatment for Production of Hot-Dip Galvanized Dual Phase Steel Using Si-Al Steels 总被引:1,自引:0,他引:1
F. Equihua-Guillén A. M. García-Lara C. R. Muñíz-Valdes J. C. Ortíz-Cuellar J. E. Camporredondo-Saucedo 《Journal of Materials Engineering and Performance》2014,23(1):268-274
This work presents relevant metallurgical considerations to produce galvanized dual phase steels from low cost aluminum-silicon steels which are produced by continuous strip processing. Two steels with different contents of Si and Al were austenized in the two-phase field ferrite + austenite (α + γ) in a fast manner to obtain dual phase steels, suitable for hot-dip galvanizing process, under typical parameters of continuous annealing processing line. Tensile dual phase properties were obtained from specimens cooled from temperature below Ar3, held during 3 min, intermediate cooling at temperature above Ar1 and quenching in Zn bath at 465 °C. The results have shown typical microstructure and tensile properties of galvanized dual phase steels. Finally, the synergistic effect of aluminum, silicon, and residual chromium on martensite start temperature (M s), critical cooling rate (C R), volume fraction of martensite, and tensile properties has been studied. 相似文献
225.
The oxidation behavior in air of a physical vapor-deposited (PVD) Mg–10.6Zr (wt. %) alloy was studied in the 325–450°C temperature range. The oxidation rate of this alloy remains low at temperatures below 375°C. However, at higher temperatures, the alloy experienced extremely high oxidation rates, which can even lead to disintegration of the sample. Oxidation is controlled by fast inward oxygen transport along the open boundaries of the alloy, leading to the formation of cracks throughout the sample, and subsequent formation of a thin MgO at crack interfaces. The MgO layer remains protective while coarsening of zirconium precipitates at the open boundaries does not take place. Thickening of Zr precipitates over a critical size induces impairment of the MgO layer at crack interfaces, facilitating inward oxygen diffusion. The volume increase resulting from the formation of new oxide at open boundaries favors decohesion of open boundaries, leading to accelerated oxidation. 相似文献
226.
Cristian Covarrubias Rafael García Jorge Yánez Renán Arriagada 《Journal of Porous Materials》2008,15(4):491-498
The preparation of organomodified zeolites with different framework structures (FAU, LTA and MOR) using N-cetylpyridinium bromide (CPB) as tailoring agent was studied. The sorption properties of CPB-modified zeolites were evaluated
in the removal of tannery contaminants from aqueous solution. The CPB-modified FAU-type zeolite presented the highest Cr(VI)
retention capacity (37 mmol/kg) due to the higher Cr(VI) retention of its unmodified form (larger pore opening) and its high
CPB sorption capacity. CPB-modified FAU zeolite also exhibited high thermal stability as consequence of special interactions
between the CPB molecules and the zeolite surface. In addition, the intrinsic Cr(III) exchange capacity of FAU zeolite increased
with CPB loading (162–527 mmol/kg), which appear to be due to an additional retention mechanism provided by the sorbed cetylpyridinium
surfactant layer. On other hand, CPB-modified FAU zeolite also exhibited high toluene retention capacity (62 mmol/kg) due
to of the hydrophobic character of its surfactant-modified surface and toluene adsorption on internal sorption sites of FAU
zeolite. Thus, CPB-modified FAU zeolite appears as a promising adsorbent for simultaneous removal of Cr(III), Cr(VI) and toluene
contaminants from aqueous solution. 相似文献
227.
Alba Poerio Alessandra Bendini Lorenzo Cerretani Matteo Bonoli‐Carbognin Giovanni Lercker 《European Journal of Lipid Science and Technology》2008,110(4):368-372
Several studies have suggested that the phenolic fraction plays an important role during storage and therefore in the shelf life of virgin olive oil. This investigation examines the effect of freezing olives (–18 °C) before processing into oil on the transfer of the phenolic compounds into the subsequent oil, and the consequential changes in oxidative stability. Oil samples obtained from frozen olives (24 h at –18 °C), crushed with and without preliminary thawing, were compared to a control sample; both oils were obtained using a two‐phase low‐scale mill. The oxidative stability in different samples was assessed in terms of primary and secondary oxidation products as measured by peroxide values and oxidative stability index times, respectively. The quality of the oil samples was also checked through the percentage of free acidity and the phenolic content. Phenols were determined by both spectrophotometric assays (total phenols and o‐diphenols) and HPLC‐DAD/MSD. The antiradical capacity of the phenolic fraction was determined by DPPH and ABTS spectrophotometric tests. These analyses showed that thawing of olives before oil extraction led to a significant loss of oxidative stability and phenols; in contrast, samples obtained from frozen olives that were not thawed before crushing showed qualitative characteristics similar to control samples. 相似文献
228.
Aranzazu García Manuel Brenes Mª Carmen Dobarganes Concepción Romero Ma Victoria Ruiz‐Méndez 《European Journal of Lipid Science and Technology》2008,110(12):1136-1141
Triterpenic acids are natural compounds present in plants and foods with beneficial properties for human health and thus they are desirable in the food, cosmetics and pharmaceutical industries. Pomace olive is considered a good source of these substances. In this study, oleanolic and maslinic acids were found to be the main triterpenic acids identified in pomace olive oil obtained from stored “Alpeorujo”. Determination of the two acids was achieved by a new procedure that consists of extracting the acids from the oil with a mixture of methanol/ethanol, and then separating and quantifying them by HPLC. Results showed that their concentration increased up to 16 g/kg of oil during storage of the pomace in large ponds for 7 months. The concentration of both triterpenic acids was similar in the pomace olive oil obtained by using the centrifugation system. By contrast, a much lower concentration of maslinic than oleanolic acid was detected in pomace olive oils obtained by solvent extraction from the previously centrifugated “Alpeorujo” paste. These triterpenic acids also contributed to the acidity of the crude oil. Likewise, the oil of the pomace paste was enriched in other substances such as 4‐ethylphenol and aliphatic alcohols during the storage of the paste in large ponds. Consequently, crude pomace olive oil can be considered a good source of triterpenic acids when obtained from a stored olive paste. 相似文献
229.
The decolorisation and mineralisation of a model mixture of reactive dyes, under Fenton and photo‐Fenton conditions, have been investigated. A kinetic study was performed and rate constants and half‐life times determined from batch experimental data according to a pseudo‐first‐order degradation kinetic model. Moreover, the use of natural or artificial light, as well as the effect of temperature, was evaluated with the aim of finding the best Fenton process to promote the efficient degradation of the standard trichromatic system. The experimental results showed that the Fenton process run under solar light was the most effective. It is suggested that Fenton‐ and photo‐Fenton‐type reactions are viable techniques for the treatment of these types of dye mixtures, according to the high levels of colour, chemical oxygen demand and total organic carbon removal. 相似文献
230.
L. Melo G. Giannetto L. Cardozo A. Llanos L. García P. Magnoux M. Guisnet F. Alvarez 《Catalysis Letters》1999,60(4):217-222
Acetone transformation into methyl isobutyl ketone (MIBK) was studied using a fixed-bed dynamic reactor at 160°C, 1 atm pressure
and acetone/H2 molar ratio=3. The reaction was carried out over Pt/HMFI bifunctional catalysts, with 0.30 wt% of platinum which was supported
over three aluminosilicates (Si/Al ratio=40, 95 and 160) and a borosilicate (Si/B ratio=44) with similar dispersion. The results
show that catalytic properties depend greatly on density and strength of the acidic sites of the catalysts. Moreover, the
limiting step of the MIBK synthesis reaction (aldolization of two acetone molecules) is carried out over the acidic sites
of the aluminosilicates, but not over those of the borosilicate, which considerably affects reaction selectivity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献