全文获取类型
收费全文 | 6062篇 |
免费 | 476篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 46篇 |
综合类 | 4篇 |
化学工业 | 1211篇 |
金属工艺 | 78篇 |
机械仪表 | 96篇 |
建筑科学 | 270篇 |
矿业工程 | 12篇 |
能源动力 | 129篇 |
轻工业 | 1287篇 |
水利工程 | 89篇 |
石油天然气 | 26篇 |
无线电 | 275篇 |
一般工业技术 | 836篇 |
冶金工业 | 1284篇 |
原子能技术 | 25篇 |
自动化技术 | 872篇 |
出版年
2024年 | 9篇 |
2023年 | 58篇 |
2022年 | 68篇 |
2021年 | 145篇 |
2020年 | 138篇 |
2019年 | 154篇 |
2018年 | 251篇 |
2017年 | 238篇 |
2016年 | 232篇 |
2015年 | 187篇 |
2014年 | 260篇 |
2013年 | 474篇 |
2012年 | 390篇 |
2011年 | 380篇 |
2010年 | 300篇 |
2009年 | 263篇 |
2008年 | 271篇 |
2007年 | 274篇 |
2006年 | 191篇 |
2005年 | 136篇 |
2004年 | 126篇 |
2003年 | 108篇 |
2002年 | 95篇 |
2001年 | 94篇 |
2000年 | 66篇 |
1999年 | 90篇 |
1998年 | 516篇 |
1997年 | 277篇 |
1996年 | 187篇 |
1995年 | 100篇 |
1994年 | 84篇 |
1993年 | 79篇 |
1992年 | 27篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 16篇 |
1988年 | 20篇 |
1987年 | 25篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 6篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 11篇 |
1977年 | 11篇 |
1976年 | 20篇 |
1975年 | 5篇 |
排序方式: 共有6540条查询结果,搜索用时 15 毫秒
951.
Anuraag Gaddam Amarnath R. Allu Hugo R. Fernandes George E. Stan Catalin C. Negrila Atul P. Jamale François O. Méar Lionel Montagne José M.F. Ferreira 《Journal of the American Ceramic Society》2021,104(6):2495-2505
The structural role of V in 28Li2O–72SiO2 (in mol%) lithium silicate glass doped with 0.5 mol% V2O5 was assessed using 29Si and 51V Nuclear Magnetic Resonance (NMR), Fourier-transform infrared (FTIR), and X-ray photoelectron (XPS) spectroscopy techniques. Despite the low amount of V2O5 used, the structural information obtained or deduced from the statistical analysis of the NMR data could explain the evolution of glass properties after V2O5 addition. The XPS results indicated that all vanadium exists in 5+ oxidation state. Both the 29Si NMR and FTIR data point toward an increase in the polymerization of the silicate network, caused by the V2O5 acting as network former, capable to form various tetrahedral units (for n = 0, 1, and 2) in the glasses. These units, which are similar to phosphate units, scavenge the Li+ ions and cause the silicate network to polymerize. However, in an overall balance, the entire glass network is depolymerized due to the additional nonbridging oxygens contributed by the vanadium polyhedra. The addition of vanadium causes the network to expand and increases the ionic conductivity. 相似文献
952.
Hendrix JA Shimshock SJ Shutske GM Tomer JD Kapples KJ Palermo MG Corbett TJ Vargas HM Kafka S Brooks KM Laws-Ricker L Lee DK de Lannoy I Bordeleau M Rizkalla G Owolabi J Kamboj RK 《Chembiochem : a European journal of chemical biology》2002,3(10):999-1009
A new class of potent dopamine D(4) antagonists was discovered with selectivity over dopamine D(2) and the alpha-1 adrenoceptor. The lead compound was discovered by screening our compound collection. The structure-activity relationships of substituted isoindoline rings and the chirality about the hydroxymethyl side chain were explored. The isoindoline analogues showed modest differences in potency and selectivity. The S enantiomer proved to be the more potent enantiomer at the D(4) receptor. Several analogues with greater than 100-fold selectivity for D(4) over D(2) and the alpha-1 adrenoreceptor were discovered. Several selective analogues were active in vivo upon oral or intraperitoneal administration. A chiral synthesis starting from either D- or L-O-benzylserine is also described. 相似文献
953.
954.
Francesc Valls Ernesto Redondo David Fonseca Ricardo Torres-Kompen Sergi Villagrasa Nuria Martí 《Telematics and Informatics》2018,35(4):1039-1052
The configuration of urban projects using Information and Communication Technologies is an essential aspect in the education of future architects. Students must know the technologies that will facilitate their academic and professional development, as well as anticipating the needs of the citizens and the requirements of their designs. In this paper, a data mining approach was used to outline the strategic requirements for an urban design project in an architecture course using a Project-Based Learning strategy. Informal data related to an award-winning public space (Gillett Square in London, UK) was retrieved from two social networks (Flickr and Twitter), and from its official website. The analysis focused on semantic, temporal and spatial patterns, aspects generally overlooked in traditional approaches. Text-mining techniques were used to relate semantic and temporal data, focusing on seasonal and weekly (work-leisure) cycles, and the geographic patterns were extracted both from geotagged pictures and by geocoding user locations. The results showed that it is possible to obtain and extract valuable data and information in order to determine the different uses and architectural requirements of an urban space, but such data and information can be challenging to retrieve, structure, analyze and visualize. The main goal of the paper is to outline a strategy and present a visualization of the results, in a way designed to be attractive and informative for both students and professionals – even without a technical background – so the conducted analysis may be reproducible in other urban data contexts. 相似文献
955.
Martínez-Morales José Quej-Cosgaya Héctor Lagunas-Jiménez José Palacios-Hernández Elvia Morales-Saldaña Jorge 《中国科学:技术科学(英文版)》2019,62(6):1055-1064
Science China Technological Sciences - A multilayer perceptron (MLP) artificial neural network (ANN) model has been optimized by the multi-objective ant colony optimization (MOACO) algorithm, which... 相似文献
956.
Thermal and fire behavior of isophorone diisocyanate based polyurethane foams containing conventional flame retardants
下载免费PDF全文
![点击此处可从《应用聚合物科学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
I. Eceiza A. Barrio L. Martín M. A. Veganzones M. J. Fernández‐Berridi L. Irusta 《应用聚合物科学杂志》2018,135(10)
This work reports on the fire behavior of isophorone diisocyanate‐based polyurethane foams containing different conventional flame retardants (FRs) such as melamine, ammonium polyphosphate, aluminum hydroxide, expandable graphite, and their combinations. The foams were obtained in a laboratory scale and characterized in terms of their morphology, density, thermal stability, and fire behavior. According to atomic force microscopy, the incorporation of FRs decreased the phase separated domain size. The cellular structure of the foams was examined qualitatively by scanning electron microscopy while the quantitative analysis of the surrounding skin was performed by optical microscopy and Image J. The FR containing foams showed more and smaller cells. The thermogravimetric analysis showed that the FRs had no influence in the initial degradation temperature of the foams. However, the obtained residue values were higher than the theoretical ones, indicating that there was some type of interaction between the FRs and the foams. The fire behavior of polyurethane foams was studied by the cone calorimeter and the data showed that the introduction of expandable graphite and combinations of ammonium polyphosphate/melamine to the reference foam gave rise to a significant reduction in the total heat release. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45944. 相似文献
957.
Impedance spectroscopy of bismuth sodium titanate: Barium titanate ceramics with manganese doping
下载免费PDF全文
![点击此处可从《Journal of the American Ceramic Society》网站下载免费的PDF全文](/ch/ext_images/free.gif)
V. Hugo Schmidt Noah Archer Chi‐Shun Tu 《Journal of the American Ceramic Society》2018,101(2):713-722
In this work we use Impedance Spectroscopy (IS) to study lead‐free ceramics of perovskite structure (Bi1/2Na1/2TiO3)0.925(BaTiO3)0.075 with Mn doping of 0, 0.2, 1.0, and 2.0 at.%. We compare our IS results with permittivity results, using dielectric to resistivity transformation equations which allow us to display results either as permittivity or as resistivity. We observe ionic conductivity dominating at lower temperatures, giving way to electronic conductivity at higher temperatures. The permittivity shows deviations from Curie‐Weiss behavior characteristic of relaxor ferroelectrics. The 0.2% Mn samples show the highest ionic resistivity, which will reduce heating for high voltage piezoelectric applications. They also have the highest Curie‐Weiss temperature and Burns temperature. 相似文献
958.
Selective hydrogenation of cinnamaldehyde using Pd catalysts supported on Mg/Al mixed oxides: Influence of the Pd incorporation method
下载免费PDF全文
![点击此处可从《加拿大化工杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
María J. Martínez‐Ortiz Miguel A. de la Rosa‐Guzmán Jorge R. Vargas‐García Jorge L. Flores‐Moreno Nancy Castillo Ariel Guzmán‐Vargas Sara Morandi Rosa M. Pérez‐Gutiérrez 《加拿大化工杂志》2018,96(1):297-306
A series of hydrotalcite‐like compounds was synthesized by varying Mg/Al molar ratio with values of 2, 3, and 4. After thermal treatment at 823 K, the corresponding mixed oxides were obtained and used as catalytic supports. The incorporation of a Pd metallic phase (0.5 g/g loading), was carried out by two methods: 1) in situ vapour phase thermal decomposition, and 2) impregnation by organic method. Fresh and calcined samples were characterized by XRD and N2 sorption experiments. The basic and metal functions were analyzed by CO2‐TPD and H2‐TPR. The Pd‐support interaction was studied by FTIR spectroscopy using CO as a probe molecule while the morphology of Pd nanoparticles on the catalysts was studied by SEM, HRTEM, and theoretical simulation using the Fast Fourier Transform (FFT) method. Finally, the catalytic activity results showed a higher conversion towards hydrocinnamaldehyde in the cinnamaldehyde hydrogenation reaction for the catalysts prepared by vapour phase thermal decomposition, compared with those prepared by organic method, showing the significant dependence on the catalytic activity and the Pd incorporation method. 相似文献
959.
Growth Hormone Secretagogue (A233) Improves Growth and Changes the Tissue Fatty Acid Profile in Juvenile Tilapia (Oreochromis niloticus)
下载免费PDF全文
![点击此处可从《Lipids》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Rebeca Martínez Carmen Morales Amilcar Arenal Antonio Morales Fidel Herrera Víctor González Mario Pablo Estrada 《Lipids》2018,53(4):429-436
Growth hormone (GH) release is a process that is well regulated by several factors, including GH secretagogues. GH can mediate the regulation of the fatty acid level and composition. The aim of this study was to determine the effect of a synthetic GH secretagogue peptide (A233) on the growth and fatty acid composition in tilapia (Oreochromis niloticus). To address this objective, we administrated a diet supplemented with A233 to juvenile tilapia for 60 days. The group fed with a diet supplemented with 600 μg of A233 per kg of feed increased in weight (4.81 ± 0.09 g) and specific growth rate (2.49 ± 0.03%/day) compared to the control diet group (3.63 ± 0.08 g, 2.07 ± 0.04%/day; respectively) (p < 0.001). In the muscle, the total lipids for the control diet group were higher than that in the group fed with 600 μg of A233 per kg feed; however, no differences were detected in the liver. In both tissues, the patterns of fatty acid composition and content were generally similar, with some exceptions. Tilapia fed with 600 μg of A233 per kg of feed showed, in liver and muscle, a significantly higher composition and content of n‐3 polyunsaturated fatty acids (such as 20:5n‐3, 22:5n‐3, 22:6n‐3) and n‐3/n‐6 PUFA than animals fed with the control diet. To our knowledge, this is the first report on the the effects of natural or synthetic GH secretagogues (GHS) on fatty acid composition, implying an increase in the nutritional quality of the tilapia. 相似文献
960.
Jagannathan Ramesh Ahmad Salman Shaul Mordechai Shmuel Argov Jed Goldstein Igor Sinelnikov Shlomo Walfisch Hugo Guterman 《Subsurface Sensing Technologies and Applications》2001,2(2):99-117
Fourier-Transform Infrared Spectroscopy (FTIR) employs a unique approach tooptical diagnosis of tissue pathology based on the characteristic molecularvibrational spectra of the tissue. The biomolecular changes in the cellularand sub-cellular levels developing in abnormal tissue, including a majorityof cancer forms, manifest themselves in different optical signatures, whichcan be detected in infrared microspectroscopy. This report has two parts. Inthe first part, we report studies on normal, premalignant (polyp) andmalignant human colonic tissues from three patients with different stages ofmalignancy. Our method is based on microscopic infrared study (FTIR-microscopy)of thin tissue specimens and a direct comparison with traditional histopathologicalanalysis, which serves as a gold reference. The limited dataavailable showed normal colonic tissue has a stronger absorption thanpolypoid tumor and cancerous types over a wide region in a total of 100measurements. Detailed analysis showed that there is a significant decreasein total carbohydrate, phosphate and possibly creatine contents for polyp andcancerous tissue types in comparison to the controls. The same trend is maintainedin seven other patients studied. The second part consists of an analysis showingthe influence of various independent factors such as age, sex and grade of malignancy. Ourpreliminary results suggest that among the above three factors, age and gradeof malignancy have significant effect on the metabolites level, but sex has onlyminor effect on the measured spectra. Initial results on Linear DiscriminantAnalysis (LDA) showed good classification between normal and malignant cellsof human colonic tissues. 相似文献