全文获取类型
收费全文 | 1774篇 |
免费 | 116篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 20篇 |
综合类 | 1篇 |
化学工业 | 488篇 |
金属工艺 | 61篇 |
机械仪表 | 74篇 |
建筑科学 | 43篇 |
矿业工程 | 4篇 |
能源动力 | 63篇 |
轻工业 | 362篇 |
水利工程 | 24篇 |
石油天然气 | 10篇 |
无线电 | 79篇 |
一般工业技术 | 316篇 |
冶金工业 | 131篇 |
原子能技术 | 40篇 |
自动化技术 | 176篇 |
出版年
2024年 | 7篇 |
2023年 | 25篇 |
2022年 | 78篇 |
2021年 | 90篇 |
2020年 | 59篇 |
2019年 | 88篇 |
2018年 | 78篇 |
2017年 | 69篇 |
2016年 | 75篇 |
2015年 | 61篇 |
2014年 | 92篇 |
2013年 | 113篇 |
2012年 | 119篇 |
2011年 | 133篇 |
2010年 | 115篇 |
2009年 | 105篇 |
2008年 | 81篇 |
2007年 | 77篇 |
2006年 | 53篇 |
2005年 | 40篇 |
2004年 | 34篇 |
2003年 | 31篇 |
2002年 | 31篇 |
2001年 | 24篇 |
2000年 | 18篇 |
1999年 | 21篇 |
1998年 | 38篇 |
1997年 | 32篇 |
1996年 | 28篇 |
1995年 | 22篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1892条查询结果,搜索用时 15 毫秒
31.
Ana C. Gonalves Jos David Flores-Flix Paula Coutinho Gilberto Alves Luís R. Silva 《International journal of molecular sciences》2022,23(6)
Plant-derived products and their extracted compounds have been used in folk medicine since early times. Zimbro or common juniper (Juniperus communis) is traditionally used to treat renal suppression, acute and chronic cystitis, bladder catarrh, albuminuria, leucorrhea, and amenorrhea. These uses are mainly attributed to its bioactive composition, which is very rich in phenolics, terpenoids, organic acids, alkaloids, and volatile compounds. In the last few years, several studies have analyzed the huge potential of this evergreen shrub, describing a wide range of activities with relevance in different biomedical discipline areas, namely antimicrobial potential against human pathogens and foodborne microorganisms, notorious antioxidant and anti-inflammatory activities, antidiabetic, antihypercholesterolemic and antihyperlipidemic effects, and neuroprotective action, as well as antiproliferative ability against cancer cells and the ability to activate inductive hepato-, renal- and gastroprotective mechanisms. Owing to these promising activities, extracts and bioactive compounds of juniper could be useful for the development of new pharmacological applications in the treatment of several acute and chronic human diseases. 相似文献
32.
Zinc Oxide Nanoparticles: Synthesis,Antimicrobial Activity and Food Packaging Applications 总被引:2,自引:0,他引:2
Paula Judith Perez Espitia Nilda de Fátima Ferreira Soares Jane Sélia dos Reis Coimbra Nélio José de Andrade Renato Souza Cruz Eber Antonio Alves Medeiros 《Food and Bioprocess Technology》2012,5(5):1447-1464
Zinc oxide (ZnO) is an inorganic compound widely used in everyday applications. ZnO is currently listed as a generally recognized
as safe (GRAS) material by the Food and Drug Administration and is used as food additive. The advent of nanotechnology has
led the development of materials with new properties for use as antimicrobial agents. Thus, ZnO in nanoscale has shown antimicrobial
properties and potential applications in food preservation. ZnO nanoparticles have been incorporated in polymeric matrices
in order to provide antimicrobial activity to the packaging material and improve packaging properties. This review presents
the main synthesis methods of ZnO nanoparticles, principal characteristics and mechanisms of antimicrobial action as well
as the effect of their incorporation in polymeric matrices. Safety issues such as exposure routes and migration studies are
also discussed. 相似文献
33.
Carnot Leal Nogueira 《Cement and Concrete Research》2011,41(11):1185-1195
Ultrasonic pulse velocity has been used for decades to detect localized damage and to estimate concrete properties. More recent applications aim at diffuse damage characterization, such as environmental and mechanical damage. In most applications the methodology to calculate pulse speed is a very important issue. This work, applying continuous wavelet transform (CWT) to construct time-frequency signal representations, calculates frequency-dependent velocity of longitudinal and transverse ultrasonic pulses using wavelet scales. The method is applied to a total of 14 specimens of 5 different mixes and frequency-dependent velocities are calculated using four wavelet families. The CWT capability to decompose the inquiring pulse spectrum and analyze phase velocities is discussed with regard to wavelet, pulse type, and mixture. Frequency-dependent velocity of longitudinal pulses at lower frequencies (from 100 kHz up to 250 kHz) was proven to be much more sensitive to mix proportions than transverse pulses. 相似文献
34.
Magalhaes KD Costa LS Fidelis GP Oliveira RM Nobre LT Dantas-Santos N Camara RB Albuquerque IR Cordeiro SL Sabry DA Costa MS Alves LG Rocha HA 《International journal of molecular sciences》2011,12(5):3352-3365
In the present study, six families of sulfated polysaccharides were obtained from seaweed Dictyopteris delicatula by proteolytic digestion, followed by acetone fractionation and molecular sieving on Sephadex G-100. Chemical analyses demonstrated that all polysaccharides contain heterofucans composed mainly of fucose, xylose, glucose, galactose, uronic acid, and sulfate. The fucans F0.5v and F0.7v at 1.0 mg/mL showed high ferric chelating activity (~45%), whereas fucans F1.3v (0.5 mg/mL) showed considerable reducing power, about 53.2% of the activity of vitamin C. The fucan F1.5v presented the most prominent anticoagulant activity. The best antiproliferative activity was found with fucans F1.3v and F0.7v. However, F1.3v activity was much higher than F0.7v inhibiting almost 100% of HeLa cell proliferation. These fucans have been selected for further studies on structural characterization as well as in vivo experiments, which are already in progress. 相似文献
35.
Peres M Magalhães S Fellmann V Daudin B Neves AJ Alves E Lorenz K Monteiro T 《Nanoscale research letters》2011,6(1):378
Undoped self-assembled GaN quantum dots (QD) stacked in superlattices (SL) with AlN spacer layers were submitted to thermal annealing treatments. Changes in the balance between the quantum confinement, strain state of the stacked heterostructures and quantum confined Stark effect lead to the observation of GaN QD excitonic recombination above and below the bulk GaN bandgap. In Eu-implanted SL structures, the GaN QD recombination was found to be dependent on the implantation fluence. For samples implanted with high fluence, a broad emission band at 2.7 eV was tentatively assigned to the emission of large blurred GaN QD present in the damage region of the implanted SL. This emission band is absent in the SL structures implanted with lower fluence and hence lower defect level. In both cases, high energy emission bands at approx. 3.9 eV suggest the presence of smaller dots for which the photoluminescence intensity was seen to be constant with increasing temperatures. Despite the fact that different deexcitation processes occur in undoped and Eu-implanted SL structures, the excitation population mechanisms were seen to be sample-independent. Two main absorption bands with maxima at approx. 4.1 and 4.7 to 4.9 eV are responsible for the population of the optically active centres in the SL samples. 相似文献
36.
Ana Teresa SerraAna A. Matias Ana P.C. AlmeidaM.R. Bronze Paula M. Alves Hermínio C. de SousaCatarina M.M. Duarte 《The Journal of Supercritical Fluids》2011,55(3):1007-1013
In the last years, there has been a growing interest in the recovery of bioactive compounds from natural sources for the development of novel functional foods.In this study, natural extracts, previously obtained by fractioned high pressure extraction from “Saco” cherry culls, were characterized in terms of anticancer activity. The product derived from CO2:EtOH (90:10, v/v) extraction after a pre-treatment of raw material with supercritical CO2 during 1 h, exhibited the highest antiproliferative activity in human HT29 colon cancer cells. In addition, when compared with doxorubicin, cherry extracts induced cell cycle arrest in a different cell cycle checkpoint.In order to obtain extracts with enhanced antiproliferative activity, the extraction process was further explored. Using highly pure CO2 and EtOH 96% the inhibition of cancer cell growth was significantly enhanced by 16-fold. In addition, the incorporation of a conventional extraction step with MetOH or EtOH:H2O (50:50, v/v) prior to fractioned process allowed to obtain cherry extracts more concentrated in antiproliferative compounds. Perillyl alcohol present in cherry extracts was pointed to be one of the major responsible for anticancer properties of cherry extracts. 相似文献
37.
Moacir Fernandes Ferreira Júnior Elaine Angélica Ribeiro Mundim Guimes Rodrigues Filho Carla da Silva Meireles Daniel Alves Cerqueira Rosana Maria Nascimento de Assunção Marcos Marcolin Mara Zeni 《Polymer Bulletin》2011,66(3):377-389
Cellulose, obtained both from sugarcane bagasse and mango seeds, was used for synthesizing cellulose acetate in order to produce asymmetric membranes. These were compared to membranes of commercial cellulose acetate (Rhodia). All produced membranes were asymmetric, characterized by the presence of a dense skin and a porous support. Differences regarding the morphology of the surfaces as well as of the porous support can be noticed. Scanning Electron Microscopy (SEM) showed that the morphology of the superficial layer, responsible for transport, depends on the different lignin content of the starting material and also on the viscosity average molecular weight of the cellulose acetates produced from sugarcane bagasse, mango seed, and Rhodia’s commercial cellulose acetate. 相似文献
38.
Measurements of horizontal three‐phase solid‐liquid‐gas slug flow: Influence of hydrate‐like particles on hydrodynamics 下载免费PDF全文
Luis M. M. Rosas Carlos L. Bassani Rafael F. Alves Fábio A. Schneider Moisés A. Marcelino Neto Rigoberto E. M. Morales Amadeu K. Sum 《American Institute of Chemical Engineers》2018,64(7):2864-2880
Gas hydrate formation is a main flow assurance concern in oil and gas production. Understanding the effects of the introduction of solid particles in the slug flow is essential to improve the efficiency and safety of multiphase production. The purpose of the present work is the experimental characterization of solid‐liquid‐gas slug flow with the presence of dispersed hydrate‐like particles. Experimental tests were carried out with inert polyethylene particles of 0.5‐mm diameter with density similar to gas hydrates (938 kg/m3). The test section comprised a 26‐mm ID, 9‐m length horizontal duct of transparent Plexiglas. High Speed Imaging and resistivity sensors was used to analyze the slug flow unit cell behavior due to the introduction of the solid particles and to measure the unit cell translational velocity, the slug flow frequency, the bubble and slug lengths, and the phase fractions. Two distinct concentrations of solid particles were tested (6 and 8 g/dm3). © 2018 American Institute of Chemical Engineers AIChE J, 64: 2864–2880, 2018 相似文献
39.
The XANES (X-ray absorption near edge structure) technique was used to study Pd and Mo catalysts deposited on supported Al2O3/SiO2 and Al2O3/Si-MCM-41 in the form of monometallic and bimetallic systems. The results indicate that Pd has stronger chemical stability when in the presence of Mo and is always in the metallic form, which is surprising, because the samples were not subjected to reducing conditions prior to the measurements. The increased stability was attributed to the formation of a core-shell structure with a Pd rich core and a Mo rich surface. 相似文献
40.
Paula de Miranda Costa Maria Inês Bruno Tavares André L. B. S. Bathista Emerson O. da Silva José S. Nogueira 《应用聚合物科学杂志》2007,105(2):973-977
The nuclear magnetic resonance spectroscopy (NMR) studies of starches obtained by fruit seeds such as melon and watermelon were carried out as an analytical methodology to understand the molecular dynamic behavior. This study was also accompanied by the conventional X‐ray diffraction and thermal analysis. The NMR results give us a complete behavior of the samples at the molecular level. Thus, the information obtained from NMR will complement the data obtained from X‐ray and thermal analysis allowing us having responses on samples structure and dynamical behavior. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献