全文获取类型
收费全文 | 3606篇 |
免费 | 239篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 13篇 |
综合类 | 2篇 |
化学工业 | 1558篇 |
金属工艺 | 48篇 |
机械仪表 | 59篇 |
建筑科学 | 88篇 |
矿业工程 | 6篇 |
能源动力 | 82篇 |
轻工业 | 686篇 |
水利工程 | 17篇 |
石油天然气 | 16篇 |
无线电 | 137篇 |
一般工业技术 | 542篇 |
冶金工业 | 151篇 |
原子能技术 | 11篇 |
自动化技术 | 430篇 |
出版年
2024年 | 6篇 |
2023年 | 75篇 |
2022年 | 409篇 |
2021年 | 358篇 |
2020年 | 125篇 |
2019年 | 124篇 |
2018年 | 138篇 |
2017年 | 150篇 |
2016年 | 136篇 |
2015年 | 108篇 |
2014年 | 157篇 |
2013年 | 214篇 |
2012年 | 232篇 |
2011年 | 240篇 |
2010年 | 173篇 |
2009年 | 181篇 |
2008年 | 172篇 |
2007年 | 147篇 |
2006年 | 115篇 |
2005年 | 97篇 |
2004年 | 76篇 |
2003年 | 61篇 |
2002年 | 59篇 |
2001年 | 34篇 |
2000年 | 29篇 |
1999年 | 34篇 |
1998年 | 34篇 |
1997年 | 29篇 |
1996年 | 25篇 |
1995年 | 19篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 3篇 |
1991年 | 7篇 |
1989年 | 4篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1971年 | 4篇 |
1969年 | 2篇 |
1934年 | 1篇 |
排序方式: 共有3846条查询结果,搜索用时 15 毫秒
31.
Claudio Alimonti Mara Lombardi Monica Cardarilli Elena Soldo 《Water Resources Management》2017,31(6):1745-1758
The quantification of soil variability is one of the most important aspects in the geo-engineering context. The uncertainty analysis is the main part of the reliability assessment for which a quantitative evaluation was performed in this study. The Reliability Index and the Probability of Failure using the First-Order Reliability Method (FORM) represents both, an effective method which is easy to implement at the same time. This work analyzes possible effects of compaction induced into the aquifer of the Scarlino Plain, caused by the extension of the hydraulic barrier for groundwater remediation. The currently implemented vertical barrier is composed of 12 wells which reach the depth of 10 m. The improvement of the project involves the construction of a further 40 clusters, each consisting of a doublet which intercepts different depths (10 and 18 m). The models of the subsoil stratigraphy and of the groundwater were built using a numerical model. The groundwater flow and the piezometric surface in the current configuration of the barrier were studied and the project configuration was evaluated. Using the Aquitard drainage model, the land subsidence was estimated to calculate the maximum admissible displacement related to exhibited goods, the so called territorial vulnerability. The evaluation analysis was performed using a traditional deterministic approach, followed by a reliability method based on probabilistic models. Finally, the respective results were reported in a soil mapping with overlapping layers. 相似文献
32.
Elena R. Andrievskaya Lidiya M. Lopato 《Journal of the American Ceramic Society》1992,75(11):3026-3032
Phase equilibria in the system HfO2 –Y2 O3 –CaO were studied in the temperature range 1250° to 2850°C by both experimental methods (X-ray phase analysis at 20° to 2000°C, petrography, annealing and quenching, differential thermal analysis in He at temperatures to 2500°C, thermal analysis in air using a solar furnace at temperatures to 3000°C, and electron microprobe X-ray analysis) and theoretical means (development of a mathematical model for the liquidus surface by means of the reduced polynomial method). Phase equilibria were determined by the structure of the restricting binary systems. No ternary compounds were found. The liquidus was characterized by the presence of six four-phase, invariant equilibria. Solid solutions were based on monoclinic (M), tetragonal (T), and cubic (F) modifications of HfO2 ; C and H forms of Y2 O3 ; CaO; and CaHfO3 that crystallized in two polymorphous modifications, namely, the cubic and rhombic perovskite-type structure. 相似文献
33.
The genesis of polyaniline nanotubes 总被引:1,自引:0,他引:1
Aniline has been oxidized with ammonium peroxydisulfate in 0.4 M acetic acid. Protons are produced in the course of oxidation and the pH decreases as the reaction proceeds. The oxidation had two subsequent phases: (1) the oxidation of the neutral aniline molecules and the initially produced low-molecular weight aniline oligomers at low acidity, followed by (2) the oxidation of the anilinium cation after the acidity became higher. The two phases of oxidation gave different products, aniline oligomers with mixed ortho- and para-coupling of aniline molecules, and polyaniline nanotubes, respectively.The aniline oligomers are produced at first at low acidity, pH > 4, some of them as rod-like crystals. The molecular weight of the oligomers has been assessed by gel-permeation chromatography to be of several thousands. The 2-3 wt.% content of sulfur in deprotonated samples suggests that the oxidation products are partly sulfonated. The oxidation of ortho-coupled anilines combined with intramolecular cyclization produces phenazine units or their blocks, as indicated by FTIR spectra. A high-molecular weight polyaniline is produced at pH < 2. The protonation of the intermediate pernigraniline form of polyaniline is a prerequisite for the polymerization.The nano-sized oligomer crystallites serve as starting templates for the nucleation of PANI nanotubes. Further growth of nanotubes proceeds by the self-organization of the phenazine units or their blocks located at the ends of the PANI chains. Polyaniline nanotubes have a typical outer diameter of 100-200 nm, with a wall thickness of 50-100 nm, an inner diameter of 0-100 nm, and a length extending to several micrometres. 相似文献
34.
Valerii S. Kozlov Elena P. Yausheva Svetlana A. Terpugova Mikhail V. Panchenko Dmitriy G. Chernov Vladimir P. Shmargunov 《International journal of remote sensing》2014,35(15):5722-5741
A comprehensive experiment on the study of dynamics of optical and microphysical characteristics of submicron aerosols in the near-ground air layer was carried out in June–August of 2012 under conditions of extremely strong smoke haze originating from vast forest fires in Siberia. Variations of the spectral angular scattering coefficients and the degree of linear polarization in the visible wavelength range are studied, as well as the mass concentrations of dry fractions of aerosol and black carbon, relative content of black carbon (BC fraction), single scattering albedo, particle size distribution function, complex refractive index of the particulate matter, and parameter of condensation activity of aerosol. Peculiarities of differences between optical and microphysical characteristics of near-ground aerosol in smoke haze and under smokeless conditions are revealed. This study is important for validation of results of remote sensing of the composition of smoke haze and background atmosphere obtained from satellite data and sun photometric measurements at the Aerosol Robotic Network (AERONET). 相似文献
35.
Urs T. Gonzenbach ré R. Studart David Steinlin Elena Tervoort Ludwig J. Gauckler 《Journal of the American Ceramic Society》2007,90(11):3407-3414
Direct foaming of colloidal suspensions is a simple and versatile approach for the fabrication of macroporous ceramic materials. Wet foams produced by this method can be stabilized by long-chain surfactants or by colloidal particles. In this work, we investigate the processing of particle-stabilized wet foams into crack-free macroporous ceramics. The processing steps are discussed with particular emphasis on the consolidation and drying process of wet foams. Macroporous alumina ceramics prepared using different consolidation and drying methods are compared in terms of their final microstructure, porosity, and compressive strength. Consolidation of the wet foam by particle coagulation before drying resulted in porous alumina with a closed-cell structure, a porosity of 86.5%, an average cell size of 35 μm, and a remarkable compressive strength of 16.3 MPa. On the other hand, wet foams consolidated via gelation of the liquid within the foam lamella led to porous structures with interconnected cells in the size range from 100 to 150 μm. The tailored microstructure and high mechanical strength of the macroporous ceramics can be of interest for the manufacture of bio-scaffolds, thermal insulators, impact absorbers, separation membranes, and light weight ceramics. 相似文献
36.
Stability of a learning algorithm with respect to small input perturbations is an important property, as it implies that the derived models are robust with respect to the presence of noisy features and/or data sample fluctuations. The qualitative nature of the stability property enhardens the development of practical, stability optimizing, data mining algorithms as several issues naturally arise, such as: how “much” stability is enough, or how can stability be effectively associated with intrinsic data properties. In the context of this work we take into account these issues and explore the effect of stability maximization in the continuous (PCA-based) k-means clustering problem. Our analysis is based on both mathematical optimization and statistical arguments that complement each other and allow for the solid interpretation of the algorithm’s stability properties. Interestingly, we derive that stability maximization naturally introduces a tradeoff between cluster separation and variance, leading to the selection of features that have a high cluster separation index that is not artificially inflated by the features variance. The proposed algorithmic setup is based on a Sparse PCA approach, that selects the features that maximize stability in a greedy fashion. In our study, we also analyze several properties of Sparse PCA relevant to stability that promote Sparse PCA as a viable feature selection mechanism for clustering. The practical relevance of the proposed method is demonstrated in the context of cancer research, where we consider the problem of detecting potential tumor biomarkers using microarray gene expression data. The application of our method to a leukemia dataset shows that the tradeoff between cluster separation and variance leads to the selection of features corresponding to important biomarker genes. Some of them have relative low variance and are not detected without the direct optimization of stability in Sparse PCA based k-means. Apart from the qualitative evaluation, we have also verified our approach as a feature selection method for $k$ -means clustering using four cancer research datasets. The quantitative empirical results illustrate the practical utility of our framework as a feature selection mechanism for clustering. 相似文献
37.
Unai Diaz-Orueta Aitziber Etxaniz Mari Feli Gonzalez Cristina Buiza Elena Urdaneta Javier Yanguas 《Universal Access in the Information Society》2014,13(1):89-97
The complexity of new information technologies (IT) may limit the access of elderly people to the information society, exacerbating what is known as “the digital divide,” as they appear to be too challenging for elderly citizens regardless of the integrity of their cognitive status. This study is an attempt to clarify how some cognitive functions (such as attention or verbal memory) may determine the interaction of cognitively impaired elderly people with technology. Twenty participants ranging from mild cognitive impairment to moderate Alzheimer’s disease were assessed by means of a neuropsychological and functional battery and were asked to follow simple commands from an avatar appearing on a TV by means of a remote control, such as asking the participant to confirm their presence or to respond Yes/No to a proposal to see a TV program. The number of correct answers and command repetitions required for the user to respond were registered. The results show that participants with a better cognitive and functional state in specific tests show a significantly better performance in the TV task. The derived conclusion is that neuropsychological assessment may be used as a useful complementary tool for assistive technology developers in the adaptation of IT to the elderly with different cognitive and functional profiles. Further studies with larger samples are required to determine to what extent cognitive functions can actually predict older users’ interaction with technology. 相似文献
38.
Despite significant advances in water based surface coating technology, the presence of surfactants in emulsion polymer binders leads to loss of performance after prolonged immersion in water, relative to solvent based coatings that are free of surfactant impurities. This study begins with water uptake evaluation of a range of emulsion polymer binders. A carboxylated styrene butadiene rubber latex (c-SBR) performed best in the latter evaluations and was selected for the formulation of an exterior grade paint and construction of a mathematical model to predict water uptake of the dry film. The c-SBR was then compounded with a range of inorganic fillers and water uptake and tensile properties were evaluated. Talc was found to be the best performing filler, and was used in a three factorial central composite design study where the simultaneous effects of talc, titanium dioxide and phenolic stabiliser on water up take were evaluated and fitted to response equations. A quadratic model was found to provide the most accurate prediction of effects associated with interactions between talc and TiO2. Certain combinations of talc and titanium dioxide were found to be synergistic in reducing the water uptake. This was considered to be associated with a packing effect stemming from the vast difference in particle size between talc and titanium dioxide particles. An optimised formulation was finally prepared to meet one of the final formulation objectives; i.e., minimised water uptake. Preparation of such a formulation showed that the predicted and measured water uptake responses were in excellent agreement. This study illustrates the effectiveness of statistical experimental design methods in predicting the water uptake characteristics of water-based coatings. 相似文献
39.
Michail V. Kozlov Junwei Zhu Peter Philipp Wittko Francke Elena L. Zvereva Bill S. Hansson Christer Löfstedt 《Journal of chemical ecology》1996,22(3):431-454
The fifth abdominal segment of femaleEriocrania semipurpurella (Stephens) andE. sangii (Wood) contains a pair of exocrine glands. Hexane extracts of this segment were prepared from both species and analyzed by gas chromatography with simultaneous flame ionization and electroantennographic detection (EAD). For both species, the EAD active peaks were identified as nonan-2-one, (Z)-6-nonen-2-one, and (Z)-6-nonen-2-ol by means of mass spectrometry and comparison of retention indices with those of synthetic standards. Enantiomeric separation of chiral alcohols from the female extracts was achieved by gas chromatographic analysis on a cyclodextrin column. InE. semipurpurella, a mixture of (2S,6Z)-nonen-2-ol and (2R,6Z)-nonen-2-ol (2: I) was found, whereas inE. sangii (2S,6Z)-nonen-2-ol was the predominant enantiomer and only traces of theR enantiomer were indicated by the antennal response. In field tests, a blend of the three compounds was not attractive to conspecific males. A subtractive assay showed that the alcohol in various enantiomeric mixtures was the only attractive compound, whereas addition of (Z)-6-nonen-2-one to the alcohol completely inhibited the attraction of both species. A trapping experiment including a wide range of ratios between theR andS enantiomers showed that baits containing 95–100% of theS enantiomer were attractive to maleE. sangii, whereas males ofE. semipurpurella were attracted to all tested ratios of the enantiomers. However, the response profiles of maleE. semipurpurella differed between populations from southern Sweden, south Finland, and the Kola Peninsula in Russia. In south Sweden males were maximally attracted to a racemic mixture of the alcohols. At the Kola PeninsulaE. semipurpurella was attracted to baits containing 95–100% of theR enantiomer. In south Finland all tested ratios between 0 and 100%R enantiomer trappedE. semipurpurella, but the trap catches appeared to be bimodally distributed with peaks around 15 and 70%R enantiomer. The trapping results suggest the existence of pheromone races or sibling species among the specimens identified asE. semipurpurella.Dedicated to Prof. H. J. Bestmann on the occasion of his 70th birthday. 相似文献
40.
Amanda Baker Michael Lanagan Clive Randall Elena Semouchkina George Semouchkin Khalid Z. Rajab Richard Eitel Khalid Z. Rajab Raj Mittra Sorah Rhee Peter Geggier Claus Duschl Günter Fuhr 《International Journal of Applied Ceramic Technology》2005,2(6):514-520
At the Keck Smart Materials Integration Laboratory at Penn State University, low-temperature co-fired ceramic (LTCC) material systems have been used to fabricate a number of devices for a variety of applications. This article presents an overview of the integration of the concepts and materials that we have used to achieve miniaturization and unique device function. Examples of microwave filters, metamaterial antennas, and a dielectrophoretic cell sorter will be presented, with emphasis on device modeling and design, prototype construction methods, and test results. 相似文献