全文获取类型
收费全文 | 589篇 |
免费 | 25篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 153篇 |
金属工艺 | 2篇 |
机械仪表 | 10篇 |
建筑科学 | 19篇 |
能源动力 | 11篇 |
轻工业 | 88篇 |
石油天然气 | 1篇 |
无线电 | 29篇 |
一般工业技术 | 123篇 |
冶金工业 | 25篇 |
原子能技术 | 6篇 |
自动化技术 | 138篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 20篇 |
2021年 | 20篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 19篇 |
2017年 | 12篇 |
2016年 | 29篇 |
2015年 | 19篇 |
2014年 | 22篇 |
2013年 | 36篇 |
2012年 | 41篇 |
2011年 | 44篇 |
2010年 | 35篇 |
2009年 | 31篇 |
2008年 | 31篇 |
2007年 | 42篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 20篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 11篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有615条查询结果,搜索用时 0 毫秒
51.
The aim of the present work was to evaluate the chemical composition and the radical-scavenging and antioxidant activities of hot pepper fruits (Capsicum annuum L. var. acuminatum) at three maturity stages (small green, green and red). GC–MS analysis of n-hexane and chloroform fractions showed a different composition between the three stages of ripening. The first stage of maturation (small green) showed the highest radical-scavenging activity (IC50 of 129 μg/ml). Using the bovine brain peroxidation assay, the methanolic extract of green pepper showed significant antioxidant activity (IC50 of 522 μg/ml). Addition of methanolic extract of red and green pepper inhibited oxidation of linoleic acid. Methanolic extract of red pepper showed greater antioxidative potency than the others (IC50 of 3 μg/ml). The different composition of lipophilic compounds and the various amount of phenolics, showed in the three stage of ripening of C. annuum var. acuminatum fruits, modifies the antioxidant activity. 相似文献
52.
Antonella De Leonardis Alessandra Aretini Gabriele Alfano Vincenzo Macciola Giancarlo Ranalli 《European Food Research and Technology》2008,226(4):653-659
In this research, a phenol extract of high hydroxytyrosol (OLPE) content was obtained from olive leaves (Olea europaea L.), and subsequently tested under different contexts. The method used to obtain the OLPE basically involved two steps: the
use of strongly-acid aqueous steam, generated from 10% HCl (v/v) at 100°C, to directly hydrolyse the native complex phenols
from integral olive leaves, and OLPE recovery by liquid–liquid extraction with ethyl acetate. Hydrolysis time was 1 h. Finally,
the dried extract was dissolved in distilled water. The OLPE total phenols were determined by Folin–Ciocalteu’s method and
by HPLC analysis. Hydroxytyrosol was about 92% of the total phenols present in OLPE, and the yield was about 0.2% on fresh
leaves. OLPE showed antioxidant effects on different food lipids and did not inhibit lactic acid bacteria growth; however,
it showed cytotoxicity on NIH/3T3 fibroblasts and human umbilical vein endothelial cells at concentrations higher than 0.32 mM
(as hydroxytyrosol). 相似文献
53.
Giancarlo Cravotto Stefano Di Carlo Massimo Curini Vander Tumiatti Carlo Roggero 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2007,82(2):205-208
Microwave (MW) and high‐intensity ultrasound (US) provide innovative techniques for the degradation of persistent organic pollutants (POPs). When Fenton's reagent is used to treat industrial wastes, organic pollutants are degraded by highly reactive hydroxyl radicals (HO·) that can oxidize almost any organic compound to carbon dioxide and water. These reactions, when carried out under US or MW, are faster and much more efficient. The present work assesses the combined effect of US and MW using a new flow reactor developed in our laboratory. In this 5 L pilot reactor the liquid was pumped in parallel through a modified domestic MW oven and through a cell where it was irradiated with two US generators working at 20 and 300 kHz, while MW irradiation took place in a modified domestic oven. We studied the degradation of 2,4‐dibromophenol (0.1 g L?1 in water) by Fenton's reagent, assessing the contribution of each energy source to the overall effect, and found that MW and US‐300 kHz played the main role. A modest amount of oxidant (6 mL 30% H2O2 per 1 L of polluted water) sufficed to achieve complete degradation within 6 h, at which time organic compounds were no longer detectable. Even if no Fenton's reagent was added, about one half of the pollutant was degraded after 3 h irradiation. Copyright © 2007 Society of Chemical Industry 相似文献
54.
Isabella Medeiros Araújo Pedro Capalbo Becalette Elda Sabino da Silva Giancarlo de Souza Dias Michelle da Cunha Abreu Xavier Alex Fernando de Almeida Alfredo Eduardo Maiorano Sergio Andres Villalba Morales Rafael Firmani Perna 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2023,98(2):419-430
55.
Stanley HE Buldyrev SV Franzese G Giovambattista N Starr FW 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2005,363(1827):509-523
The thermodynamic behaviour of water seems to be related to static heterogeneities. These static heterogeneities are related to the local structure of water molecules and, when properly characterized, may offer an economical explanation of thermodynamic data. 'What matters' most in determining some of the unusual properties of liquid water may be the fact that the local geometry of the liquid molecules is not spherical or oblong, but rather tetrahedral. In respect to static heterogeneities, this local geometry is critical. The dynamic behaviour of water seems to be related to dynamic heterogeneities, which seem to explain the dynamics of supercooled liquid water well. 相似文献
56.
Christian Durante Abdirisak Ahmed Isse Giancarlo Sandon Armando Gennaro 《Applied catalysis. B, Environmental》2009,88(3-4):479-489
The reductive dehalogenation of CCl4, CHCl3, CH2Cl2 and CH3Cl has been investigated by cyclic voltammetry and controlled-potential electrolysis at Ag, glassy carbon (GC) and graphite electrodes in dimethylformamide (DMF) + 0.1 M Et4NClO4 in the absence and presence of a proton donor. In particular, the study was focused in the evaluation of the intermediates and final products of the reduction process and how their distribution could be affected by tuning relevant chemical and electrochemical parameters. In general, depending on the value of the applied potential, all polychloromethanes (PCMs) can be partially or completely dechlorinated, methane being exclusively formed in the latter case. The nature of the electrode material and the proton availability of the medium affect drastically the distribution of reduction products. The results point out that at both types of electrode, reduction of PCMs takes place through two competing reaction pathways both leading to methane. One reaction route involves a sequence of reductive dehalogenation steps, with the removal of one chlorine atom at a time, whereas the other is based on hydrogenolysis of carbenes and bypasses the intermediacy of partially dechlorinated PCMs. The presence of a proton source affects substantially the hydrodehalogenation efficiency, enhancing the concentration of intermediate PCMs and the final yield of methane. The silver electrode exhibits an extraordinary electrocatalytic effect resulting in remarkable positive shifts of the reduction potentials of all PCMs with respect to GC. The Ag surface strongly affects the kinetics of the dissociative electron transfer to CHnCl(4−n) (n = 0–3) as well as the reactivity of the intermediate radicals, carbanions and carbenes. 相似文献
57.
Because of the progress in electronic technology and the increasing importance of colour quality control in various branches of industry, over the last decades several colour-measuring instruments have been developed, each one with its own design features; the lack of standardization among them might be an obstacle to the spread of colour quality control as a means for product qualification. Colour-difference measurements taken with 11 different models of spectrophotometers [four with 45 (circumferential)/0 geometry and the others with diffuse geometry] were compared with the aim of analyzing their correlation and dispersion. In order to cover different colour-space regions, measurements were taken on test panels painted with four saturated basic hue (red, yellow, green, and blue) acrylic products gradually modified by adding white or black paint. Basic statistical analyses made on colour-difference values (ΔE*ab, ΔL*, Δa*, and Δb*) resulted in a high correlation among the examined instruments, but a certain variability, particularly as far as certain hues are concerned. 相似文献
58.
Optically active (?)menthylethylfumarate (2) and (?)dimenthylfumarate (3) have been synthesised and free radically copolymerized with N-vinylcarbazole (1). Copolymers of (1) and (2) exhibit a strong tendency to alternation in agreement with earlier conclusions from studies of copolymerization of (1) with diethylfumarate. Surprisingly the much more hindered, but symmetrical fumarate, (3) yields copolymers which always have carbazole monomer contents in excess of the 1:1 alternating ratio. Chiroptical measurements indicate significant induced optical activity in the carbazole chromophores of all the copolymers obtained but, in accord with the predominance of alternating structures, there is no real evidence for any sequence-determined maximum in induced circular dichroism. Fluorescence emission spectra of all copolymer samples exhibit significant asymmetric broadening on the long wavelength (low energy) side of the normal carbazole monomeric emission. This broadening is exhibited even by poly (1-co-2) samples for which the monomer compositions strongly indicate alternating sequences and must, therefore, represent interaction between carbazole segments. Accordingly, and in contrast to widely held assumptions, it is concluded that excimer-like emission may be exhibited by alternating copolymers of N-vinylcarbazole. Further evidence for electronic interactions between non-nearest neighbour carbazole units is provided by u.v. absorption and 1H-n.m.r. spectra of appropriate copolymers. 相似文献
59.
Camila R. Correa Lei Li Giancarlo Aldini Marina Carini C.-Y. Oliver Chen Hye-Kyung Chun Soo-Muk Cho Ki-Moon Park Robert M. Russell Jeffrey B. Blumberg Kyung-Jin Yeum 《Food chemistry》2010
Phytochemical compositions of five varieties of black soybeans (Glycine max) and their stabilities at room temperature, 4 and −80 °C over 14 months were determined by HPLC systems with electrochemical (ECD) and UV detectors. Polyphenol profiling was carried out by a liquid chromatography–electrospray ionisation-mass spectrometry (LC–ESI-MS) with orbitrap as a mass analyser in both positive and negative ion modes, and polyphenols in aglycone forms were quantified by HPLC–ECD. Five different varieties of black soybeans (G. max) contained 249–405 μg/g dry wt of γ-tocopherol and 6.76–14.98 μg/g dry wt of lutein. Major polyphenols in black soybeans (G. max) were daidzein (193–288 μg/g dry wt) and genistein (145–223 μg/g dry wt), mainly present as glucosides and acetyl glucosides. No significant decrease was found in total phenols of black soybeans (G. max) stored at room temperature, 4 or −80 °C for 14 months. On the other hand, lutein and γ-tocopherol degraded significantly within a month of storage at room temperature (p < 0.01), whereas they remained stable up to 6 months at 4 °C and up to 14 months at −80 °C. The current study indicates that black soybeans (G. max) are rich source of γ-tocopherol and phenols (isoflavones, flavonols, flavan-3-ols, proanthocyanidins and anthocyanin) and that the levels vary depending upon varieties. In addition, storage at low temperature is recommended to reduce the loss of fat-soluble phytochemicals in black soybeans (G. max) over an extended period of time. 相似文献
60.
Palmira Mazzaracchio Piergiorgio Pifferi Maddalena Kindt Athanase Munyaneza & Giancarlo Barbiroli 《International Journal of Food Science & Technology》2004,39(1):53-59
The interactions between different glucosidic anthocyanins (pelargonin, cyanin, delphinin, malvin and petunin) and some organic compounds (lactic, galacturonic, tannic, phenolic and sinapic acids; pyrogallol, furfural, pectin, cellulose, hydrolitic lignin) which are present in food‐stuffs were investigated at pH 3.0–4.3 and 25 °C. The interactions were monitored by means of u.v.‐VIS spectra and their different behaviours were highlighted by following changes in absorbance over a range of wavelengths (Δλ and ΔA). Significant effects on absorbance were detected and are discussed in terms of the phenomenon of co‐pigmentation. 相似文献