全文获取类型
收费全文 | 2393篇 |
免费 | 178篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 44篇 |
综合类 | 2篇 |
化学工业 | 684篇 |
金属工艺 | 72篇 |
机械仪表 | 85篇 |
建筑科学 | 57篇 |
矿业工程 | 5篇 |
能源动力 | 86篇 |
轻工业 | 477篇 |
水利工程 | 16篇 |
石油天然气 | 30篇 |
无线电 | 146篇 |
一般工业技术 | 298篇 |
冶金工业 | 219篇 |
原子能技术 | 12篇 |
自动化技术 | 340篇 |
出版年
2024年 | 20篇 |
2023年 | 28篇 |
2022年 | 89篇 |
2021年 | 148篇 |
2020年 | 88篇 |
2019年 | 102篇 |
2018年 | 132篇 |
2017年 | 120篇 |
2016年 | 105篇 |
2015年 | 68篇 |
2014年 | 94篇 |
2013年 | 199篇 |
2012年 | 145篇 |
2011年 | 149篇 |
2010年 | 133篇 |
2009年 | 130篇 |
2008年 | 100篇 |
2007年 | 73篇 |
2006年 | 55篇 |
2005年 | 53篇 |
2004年 | 39篇 |
2003年 | 32篇 |
2002年 | 32篇 |
2001年 | 21篇 |
2000年 | 35篇 |
1999年 | 35篇 |
1998年 | 64篇 |
1997年 | 52篇 |
1996年 | 38篇 |
1995年 | 31篇 |
1994年 | 18篇 |
1993年 | 31篇 |
1992年 | 12篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 11篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有2573条查询结果,搜索用时 0 毫秒
101.
Andre L. M. Freitas Dereck N. F. Muche Edson R. Leite Flavio L. Souza 《Journal of the American Ceramic Society》2020,103(12):6833-6846
This work addresses the role of different modifiers on the overall photocurrent response, which allowed a dual material insertion, increasing the charge separation without compromise the surface catalysis. Sn-addition onto nanoceramic hematite photoelectrodes clearly increased flat band potential, promoting a good charge separation, and shifting the onset to a higher potential, attributed to the surface-trapping state created by this modification. Notoriously, Sn-hematite photoelectrodes loaded with NiFeOx exhibited the highest photocurrent density, suggesting a partially recovered surface-trapping states created during the electrode designing. The well-known cocatalyst acted in the overall photoelectrocatalytic response with no significant effect on the turn-on voltage, in other words, with minor effect related to catalytic efficiency. The dual modification contributes to understand the role of different modifiers allowing to satisfactorily improve charge separation while maintaining the conductivity attributed to IV-group ions. 相似文献
102.
Daniel T. Payne Mandeep K. Chahal V clav B&rcaron ezina Whitney A. Webre Katsuhiko Ariga Francis D Souza Jan Labuta Jonathan P. Hill 《Frontiers of Chemical Science and Engineering》2020,14(1):28
Chiral 1,1’-binaphthyl-linked diporphyrin ‘tweezers’ (R)-1/(S)-1 and the corresponding zinc(II) complexes (R)-2/(S)-2 were prepared as chiral host molecules, and their utility for chiral analyses (especially enantiomeric excess (ee) determinations) were evaluated. Tris(1-n-dodecyl)porphyrins were used for the first time as the interacting units. Host capabilities of the diporphyrin tweezers were investigated by titrations with (R,R)- and (S,S)-cyclohexane-1,2-diamine (CHDA). The host molecules could be used as multichannel probes of ee by using UV-vis, circular dichroism (CD), fluorescence emission and 1H nuclear magnetic resonance (1H-NMR) methods. Chiral configurations could also be differentiated using CD or 1H-NMR spectroscopy. All three optical techniques give good resolution of ee with reasonable sensitivity considering the low concentrations used (ca. 10−6 mol·L−1). The ee determination of CHDA enantiomers using NMR spectroscopy is also possible because of the reasonably well separated resonances in the case of (R,R)- and (S,S)-CHDA. Non-metallated (R)-1/(S)-1 hosts could not be used to detect chiral information in a strongly acidic chiral guest. This work demonstrates the utility of 1,1’-binapthyl-linked chiral hosts for chiral analysis of ditopically interacting enantiomers. 相似文献
103.
This work presents useful composites for oil spill cleanup processes. These systems are composed of a polyester matrix loaded with coffee ground powder and maghemite. They were prepared by in situ polymerization. The aliphatic monomers proportion—castor oil and glycerin—was studied with the aim of understanding the effect of feed ratio on the product properties. The materials were studied using several techniques, including Fourier Transform Infrared Spectroscopy, Ultraviolet‐visible Spectrophotometry, and Wide Angle X‐ray Scattering, with magnetic force tests used for the characterization of materials. Density tests showed the presence of coffee grounds causes an important reduction in the density values of composites, improving their flotation. The interaction between composites and petroleum is more than twice that between composites and water. Moreover, for all magnetizable composites, the removal capability was (25.1 ± 1.2) g/g (petroleum/composite), allowing us to state that this is a promising material for use in oil spill cleanup processes. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43127. 相似文献
104.
M.A. Souza 《Thin》1987,5(6):411-423
The effects of initial imperfection and support conditions which change during the loading process on the vibration of structural elements liable to buckling are discussed. Typical experimental results reported in the literature are presented. Simplified one-degree-of-freedom models which reproduce stability characteristics of columns, plates and cylindrical shells are used. Damping is not included in the analysis. 相似文献
105.
Fernando G. Souza Jr Marcos T. D. Orlando Ricardo C. Michel José Carlos Pinto Tainá Cosme Geiza E. Oliveira 《应用聚合物科学杂志》2011,119(5):2666-2673
Pressure‐sensitive polymers that simultaneously present reasonable electrical conducting properties, useful thermosetting behavior, and softness are hard to develop. To combine these properties into a single material, a cardanol‐based phenolic resin was prepared and blended in situ with polyaniline (PAni). The final polymer blend was composed of a soft solid material that could not be dissolved in ordinary solvents. Samples were characterized through X‐ray scattering, Fourier transform infrared (FTIR) spectroscopy, and electrical conductivity and pressure sensitivity measurements. FTIR results indicate that the insertion of PAni into the blends did not change the chemical nature of the resin. According to wide‐angle X‐ray scattering results, PAni was dispersed homogeneously in the final polymer samples; this improved the sensitivity of the electrical conductivity to pressure variations, as confirmed through electromechanical tests. Pressure sensitivity and electromechanical analyses indicated that the produced blends could be used as pressure‐sensing materials. Among the tested materials, the blends containing 5 wt % PAni·H2SO4 presented the largest compression sensitivity values. Finally, it was shown for the first time through XRD analyses under pressure that PAni chains were considerably disturbed by compressive stresses. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
106.
In this study, we present the experimental results for the crosslinking process of a commercial polyester resin based on measurements of the spin lattice relaxation time T1 of protons, as function of the crosslinking time evolution. Multiexponential decomposition of the evolution of magnetization measured in inversion‐recovery experiments is performed. The population of “rigid” and “mobile” nuclear spin sites was estimated as function of time evolution. In analogy to the usual monomer conversion u, site conversion from “mobile” to “rigid” sites uM were also estimated as a function of time evolution and initial concentrations of the reagents. The multiexponential decomposition approach of T1 relaxation data allows one to follow crosslinking processes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
107.
Zero‐Modified Geometric INAR(1) Process for Modelling Count Time Series with Deflation or Inflation of Zeros 下载免费PDF全文
Wagner Barreto‐Souza 《时间序列分析杂志》2015,36(6):839-852
In this article, we propose a first‐order integer‐valued autoregressive [INAR(1)] process for dealing with count time series with deflation or inflation of zeros. The proposed process has zero‐modified geometric marginals and contains the geometric INAR(1) process as a particular case. The proposed model is also capable of capturing underdispersion and overdispersion, which sometimes are caused by deflation or inflation of zeros. We explore several statistical and mathematical properties of the process, discuss point estimation of the parameters and find the asymptotic distribution of the proposed estimators. We also propose a test based on our model for checking if the count time series considered is deflated or inflated of zeros. Two empirical illustrations are presented in order to show the potential for practice of our zero‐modified geometric INAR(1) process. This article contains a Supporting Information. 相似文献
108.
Optimization of alcohol‐free beer production by lager and cachaça yeast strains using response surface methodology 下载免费PDF全文
Cláudia Puerari Jan Strejc Angélica C. Souza Marcel Karabín Rosane F. Schwan Tomáš Brányik 《Journal of the Institute of Brewing》2016,122(1):69-75
Alcohol‐free beers (AFBs) are an attractive segment of the beer market both for the brewing industry and for consumers. While AFBs produced by arrested/limited fermentation often suffer from a lack of volatile compounds, beer flavour can be improved by yeast selection and optimization of fermentation conditions. The yeast selection strategy was demonstrated by comparing traditional lager yeast with selected cachaça yeast strains. Correspondingly, response surface methodology was used to enhance the formation of the flavour‐active volatile compounds by optimization of the fermentation conditions (original wort extract, fermentation temperature, pitching rate). Statistical analysis of the experimental data revealed the relative significance of process variables and their interactions. The developed quadratic model describing the responses of total esters and higher alcohols to changes in process variables was used to predict the ideal fermentation conditions in terms of flavour formation. The predicted conditions were experimentally verified and alternative strategies of AFB production are suggested. Copyright © 2016 The Institute of Brewing & Distilling 相似文献
109.
Physical properties of spray dried acerola pomace extract as affected by temperature and drying aids
Germano Éder Gadelha Moreira Arthur Cláudio Rodrigues de Souza Maria de Fátima Dantas de Medeiros 《LWT》2009,42(2):641-645
The objective of this study was to assess the impact of some processing parameters on moisture content, flowability, hygroscopicity and water solubility of spray dried acerola pomace extract using maltodextrin and cashew tree gum as drying aids. The experiment was conducted according to Response Surface Methodology, with the independent variables being: inlet temperature (170-200 °C), drying aid/acerola ratio (2:1-5:1), and percent replacement of maltodextrin by cashew tree gum (0-100%). Higher inlet temperatures favored the desired physical properties of the powders, decreasing their moisture contents and hygroscopicity, and increasing flowability. The drying aids decreased the powder hygroscopicity, especially cashew tree gum (CTG), which also enhanced the powder flowability. The best processing conditions to obtain a free-flowing and least hygroscopic acerola pomace extract powder by spray drying were: inlet temperature above 194 °C; drying aid/acerola solid ratio, 4:1; percent replacement of maltodextrin by CTG, at least 80%. 相似文献
110.
Vinicius Câmara Costa Wesley Nascimento Guedes Antonio de Santana Santos Madson Moreira Nascimento 《Food Analytical Methods》2018,11(7):2004-2012
The current study describes a fast and efficient procedure of ultrasound-assisted extraction for determination of Ca, Mg, K, Na, Cu, Zn, Mn, and Al in tea leaves by inductively coupled plasma optical emission spectrometry (ICP OES). The variables of procedure were optimized using the Box–Behnken design and the conditions selected were nitric acid concentration (1.0 mol L?1), sonication time (7 min), and sonication temperature (75 °C). The extraction efficiency was calculated using the analyte concentration obtained by a total digestion procedure as reference. Accuracy was confirmed by analysis of certified reference material of apple leaves (NIST 1515) and spinach leaves (NIST 1570a) using the procedure proposed. A statistical evaluation using Student’s t test showed that there is no significant difference between the value obtained with the proposed procedure and the certified value, at 95% confidence level. The proposed procedure was successfully applied and is a good alternative to conventional acid digestion procedure and can be applied to routine analysis for determination of Ca, Mg, K, Na, Zn, Mn, Cu, and Al in tea leaves used for the preparation of infusions. 相似文献