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
61.
Alves CR Murai IH Ramona P Nicastro H Bechara LR Lancha AH Brum PC Irigoyen MC Gualano B 《Journal of the International Society of Sports Nutrition》2012,9(1):13-4
Background
Exacerbated oxidative stress is thought to be a mediator of arterial hypertension. It has been postulated that creatine (Cr) could act as an antioxidant agent preventing increased oxidative stress. The aim of this study was to investigate the effects of nine weeks of Cr or placebo supplementation on oxidative stress and cardiovascular parameters in spontaneously hypertensive rats (SHR).Findings
Lipid hydroperoxidation, one important oxidative stress marker, remained unchanged in the coronary artery (Cr: 12.6 ± 1.5 vs. Pl: 12.2 ± 1.7 nmol·mg-1; p = 0.87), heart (Cr: 11.5 ± 1.8 vs. Pl: 14.6 ± 1.1 nmol·mg-1; p = 0.15), plasma (Cr: 67.7 ± 9.1 vs. Pl: 56.0 ± 3.2 nmol·mg-1; p = 0.19), plantaris (Cr: 10.0 ± 0.8 vs. Pl: 9.0 ± 0.8 nmol·mg-1; p = 0.40), and EDL muscle (Cr: 14.9 ± 1.4 vs. Pl: 17.2 ± 1.5 nmol·mg-1; p = 0.30). Additionally, Cr supplementation affected neither arterial blood pressure nor heart structure in SHR (p > 0.05).Conclusions
Using a well-known experimental model of systemic arterial hypertension, this study did not confirm the possible therapeutic effects of Cr supplementation on oxidative stress and cardiovascular dysfunction associated with arterial hypertension. 相似文献62.
L. Šiller L. Alves A. C. Brieva Yu. V. Butenko M. R. C. Hunt 《Topics in Catalysis》2009,52(11):1604-1610
We review the currently known methods of producing gold nitride and report on the influence of electrically isolated substrates
on the growth of gold nitride films by reactive ion sputtering (RIS). It is found that isolation of the substrate decreases
grain size and increases nitrogen content, the latter attributed to longer nitrogen ion lifetime on the surface of the growing
film. The chemical reactivity of gold nitride is compared with that of pure gold films using the adsorption of 1-dodecyl mercaptan
(CH3(CH2)11SH) as a model system and it is found that there is no significant difference between gold films and gold nitride in terms
of Au–S binding. However, gold nitride nanoparticles are suggested to be worthy of further investigation in terms of their
catalytic properties.
相似文献
L. ŠillerEmail: |
63.
M.L. Afonso A. Gomes A. Carvalho L.C. Alves F. Wastin A.P. Gonalves 《Electrochimica acta》2009,54(28):7318-7323
The electrochemical behaviour of UCl4 (0.01 mol L−1 up to 0.05 mol L−1) in 0.1 mol L−1 TBAPF6/DMF solution at vitreous carbon was studied, at room temperature, by cyclic voltammetry and potentiostatic techniques. The electrolytic solutions were analyzed by UV spectroscopy (UV), and the electrodeposited films were characterized by Rutherford Backscattering Spectroscopy (RBS) and X-ray diffraction (XRD). The cyclic voltammetric results, at low UCl4 concentrations (0.01 mol L−1), point that the reduction of U(IV) to U(0) occurs in two steps involving mainly U(IV) and U(III) species. The first electron transfer reaction is quasi-reversible and the second irreversible. The diffusion coefficient of U(IV) in DMF and the charge rate constant were determined to be 4.78 × 10−7 cm2 s−1 and 1.93 × 10−3 cm s−1 (at 0.02 V s−1), respectively.RBS data obtained from samples prepared at constant potential (−3.10 V) during 3 h at room temperature, indicated the presence of uranium particles deposited all over the vitreous carbon surface with aggregates in some places, confirming that the second reduction step corresponds to uranium electrodeposition. No crystallographic ordering could be seen by XRD, pointing to an amorphous character of the uranium films. 相似文献
64.
Michele Espinosa da Cunha Laiza Canielas Krause Maria Silvana Aranda Moraes Candice Schmitt Faccini Rosângela Assis Jacques Suelen Rodrigues Almeida Maria Regina Alves Rodrigues Elina Bastos Caramão 《Fuel Processing Technology》2009
In the present work, the process of biodiesel production in a pilot plant has been studied using beef tallow as raw materials with methanol and potassium hydroxide as catalyst. The biodiesel quality is regulated by Brazilian specifications (Resolution 42) by the National Agency of Petroleum (ANP). The alkaline transesterification of animal fat with methanol produces a biodiesel with high quality and also with a good conversion rate. The process is possible but the economical viability must be improved by recovering methanol and glycerin. The obtained results have been used for industrial scale up of the process. 相似文献
65.
66.
Romário Mauricio Urbanetto Nogueira Carlos Enrique Niño Bohórquez Igor Giacomelli Zanella 《Welding International》2017,31(3):161-172
Despite their similarity, the MIG/MAG and Tubular Electrode processes display particular features with regard to arc stability and variability in the characteristics of the beads. Thus, selection of one of these processes for a specific application will have to consider how these particular features affect the quality of the welds. To support this choice, the present study aimed to investigate how changing the average current affects the stability and regularity of metal transfer in welds carried out with constant voltage and pulsed current and compare the variability in the geometry and dilution of these welds. To achieve these aims, automatic welding was carried out, with steel ABNT 1020 as base metal and wire AWS ER70S-6 and AWS E71T-1 as filler metals. Besides the welds with variation in the average current, the tests involved determination of the parameters for occurrence of stable short circuiting, drop and pulsed transfer. The results showed that the voltage that gives the highest stability in short circuiting transfer is independent of the welding speed and increases with the wire speed, and also showed that welds made with hollow wire displayed greater variability compared to solid wire. 相似文献
67.
Fábio G. Melchiades Bruna T. Rego Silvia M. Higa Helton J. Alves Anselmo O. Boschi 《Journal of the European Ceramic Society》2010,30(12):2443-2449
Transparency is an extremely important optical property of several glazes used in the ceramic tile sector. The present work aimed to identify the causes of loss of transparency presented by some ceramic glazes composed of frits with chemical compositions typical of optically transparent glasses. After identifying the causes of low transparency presented by several ceramic glazes based on microstructural analyses, X-ray diffraction and scanning electron microscopy, attempts were made to increase the transparency of these glazes by altering their chemical compositions. The results suggest that the addition of alumina – through distinct mineral sources – may be an interesting alternative to prevent the crystallization of calcium silicates, which reduce the transparency of glazes used in the ceramic tile sector. 相似文献
68.
Gisele Atsuko Medeiros Hirata André Bernardo Everson Alves Miranda 《Powder Technology》2010,197(1-2):54-57
Recent studies on the use of volatile electrolytes such as CO2 in protein precipitation showed that these agents are a promising alternative to the conventional acids. This use of volatile electrolytes prevents protein denaturation due to local pH extremes, and saline effluent generation is greatly reduced, as the volatile electrolyte may be separated and recovered from solution just by pressure release. In this work, insulin was successfully crystallized in the presence of zinc using CO2 as acidifying agent. The crystals obtained were rhombohedral, a common shape for porcine insulin crystals that contain zinc in their structure, and their average size varied with the mixing applied. 相似文献
69.
Lucimara Lopes da Silva Pedro de Alcântara Pessôa Filho Everson Alves Miranda 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2010,85(7):962-967
BACKGROUND: The use of the volatile salt ammonium carbamate in protein downstream processing has recently been proposed. The main advantage of using volatile salts is that they can be removed from precipitates and liquid effluents through pressure reduction or temperature increase. Although previous studies showed that ammonium carbamate is efficient as a precipitant agent, there was evidence of denaturation in some enzymes. In this work, the effect of ammonium carbamate on the stability of five enzymes was evaluated. RESULTS: Activity assays showed that α‐amylase (1,4‐α–D‐glucan glucanohydrolase, EC 3.2.1.1), lysozyme (1,4‐β‐N‐acetylmuramoylhydrolase, EC 3.2.1.17) and lipase (triacyl glycerol acyl hydrolase, EC 3.1.1.3) did not undergo activity loss in ammonium carbamate solutions with concentrations from 1.0 to 5.0 mol kg?1, whereas cellulase complex (1,4‐(1,3:14)‐β‐D‐glucan 4‐glucano‐hydrolase, EC 3.2.1.4) and peroxidase (hydrogen peroxide oxidoreductase, EC 1.11.1.7) showed an average activity loss of 55% and 44%, respectively. Precipitation assays did not show enzyme denaturation or phase separation for α‐amylase and lipase, while celullase and peroxidase precipitated with some activity reduction. Analysis of similar experiments with ammonium and sodium sulfate did not affect the activity of enzymes. CONCLUSION: Celullase and peroxidase were denatured by ammonium carbamate. While more systematic studies are not available, care must be taken in designing a protein precipitation with this salt. The results suggest that the generally accepted idea that salts that denature proteins tend to solubilize them does not hold for ammonium carbamate. Copyright © 2010 Society of Chemical Industry 相似文献