全文获取类型
收费全文 | 493篇 |
免费 | 47篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 170篇 |
金属工艺 | 1篇 |
机械仪表 | 10篇 |
建筑科学 | 12篇 |
能源动力 | 29篇 |
轻工业 | 202篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 11篇 |
一般工业技术 | 37篇 |
冶金工业 | 13篇 |
原子能技术 | 2篇 |
自动化技术 | 50篇 |
出版年
2024年 | 2篇 |
2023年 | 3篇 |
2022年 | 17篇 |
2021年 | 19篇 |
2020年 | 26篇 |
2019年 | 16篇 |
2018年 | 21篇 |
2017年 | 25篇 |
2016年 | 19篇 |
2015年 | 19篇 |
2014年 | 25篇 |
2013年 | 51篇 |
2012年 | 33篇 |
2011年 | 44篇 |
2010年 | 32篇 |
2009年 | 28篇 |
2008年 | 19篇 |
2007年 | 20篇 |
2006年 | 25篇 |
2005年 | 14篇 |
2004年 | 11篇 |
2003年 | 18篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1993年 | 1篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有540条查询结果,搜索用时 15 毫秒
51.
Isabel C.F.R. Ferreira Lillian Barros Maria Elisa Soares Maria Lourdes Bastos José Alberto Pereira 《Food chemistry》2007,103(1):188-195
Olive trees (Olea europaea L. Cv. Cobrançosa) from the northeast of Portugal were sprayed with three different copper formulations [bordeaux mixture (copper sulphate + calcium hydroxide − 20% Cu), copper hydroxide (40% Cu) and copper oxychloride (50% Cu)] to control olive fungal diseases. The residues of copper in olive leaves, harvested at different times, were evaluated by atomic absorption spectrometry. At all the collection times, treated olive leaves had significantly higher copper contents, compared to the control. The different copper amounts in pesticide formulations lowered the leaves contents in total phenols and hence their antioxidant properties. Olive leaves sprayed with copper oxychloride possessed the highest copper levels and the lowest content in phenols, which influenced its antioxidant activity (higher EC50 values for reducing power, scavenging effect on DPPH radicals and inhibition of erythrocyte hemolysis). Leaves without copper residues proved to be a good natural source of antioxidants, giving values comparable to the reference compounds. 相似文献
52.
Maria de Lourdes Mata Bilbao Cristina Andrés-Lacueva Olga Jáuregui Rosa Maria Lamuela-Raventós 《Food chemistry》2007,101(4):1742-1747
Flavonoids are a group of polyphenolic compounds with health-related properties. Citrus fruits are rich in flavonoids and their extracts are being used as functional ingredients for several industrial products. A new high performance liquid chromatography technique with an UV photodiode-array detector was used to analyze flavonoids of an extract of Citrus species. To our knowledge this is the first study that reports isoquercitrin presence at a level of 77.3 mg/100 g in a sample made of Citrus fruits; four other flavonoids were quantified as rutin (326.59 mg/100 g), naringin (338.36 mg/100 g), quercetin (96.35 mg/100 g) and naringenin (2.35 mg/100 g). Identification was confirmed by a liquid chromatography mass spectrometer system. Method validation was achieved, providing an analytical technique that can be used to detect trace amounts of these compounds in Citrus extracts with an extremely rapid sample preparation. 相似文献
53.
Celia Conesa María Carmen Rota María-Dolores Pérez Miguel Calvo Lourdes Sánchez 《European Food Research and Technology》2008,228(2):205-211
The antibacterial activity of human lactoferrin from milk (hLF), recombinant human lactoferrin from Aspergillus awamori (rhLF) and their hydrolysates obtained with pepsin was investigated against Escherichia coli O157:H7, Salmonella Enteritidis and Listeria monocytogenes. The minimum inhibitory concentrations (MIC) and the minimum bactericidal concentrations (MBC) were determined for all the
bacteria and the proteins assayed. Taking into account the MICs found for both lactoferrins studied, we can say that they
behave very similarly, except for L. monocytogenes for which rhLF was more active. We studied the effect that heat treatments exerted on the antibacterial activity of the two
types of lactoferrin and the only heat treatment that had a negative effect on that activity was 85 °C for 10 min. The activity
of hLF and rhLF in UHT milk and whey against E. coli O157:H7 and L. monocytogenes, was also assayed. Our results showed a reduction in the number of viable cells for both microorganisms when were incubated
with rhLF or hLF, but this decrease was lower than in broth media. 相似文献
54.
This paper is a first attempt at documenting efficiency levels in Africa's electricity firms, their evolution and the sources of this evolution. The analysis is based on a sample of 12 operators providing services in the 12 country members of the Southern Africa Power Pool. We focus on the changes in total factor productivity (TFP) of the largest operators in each country between 1998 and 2005. We then rely on a data envelopment analysis (DEA) decomposition to identify the sources of the changes in TFP. The results suggest fairly comparable levels of efficiency in the region and performance levels and evolution quite independent of the degree of vertical integration, the presence of a private actor or the main sources of energy supply. The analysis suggest that although the companies have not made significant improvements during the period of analysis in using their capital and human assets, they have done much better in adopting better technologies and better commercial practices. No clear correlation could be associated with the adoption of reforms during the last decade and data limitations impede a more refined assessment of the impact of reforms on efficiency at this stage. 相似文献
55.
Iñigo Pagola Martín Gastón Carlos Fernández-Peruchena Sara Moreno Lourdes Ramírez 《Renewable Energy》2010,35(12):2792-2798
In this paper, solar radiation obtained from different frequently used databases is compared in some different locations. In the analyzed databases, the data come from ground measurement networks, or from different models and with different resolutions. The proposed methodology assumes the hypothesis that the uncertainty of the databases is approximately the same as the meteorological uncertainty of the location. Therefore the heterogeneity of the observations is due to different observations. A weighted average is proposed taking into account different time and spatial characteristics of each database, and the estimation of standard deviation of weighted observations that derives the meteorological variability expected. 相似文献
56.
Beln García‐Gmez Mª Lourdes Vzquez‐Odriz Nieves Muoz‐Ferreiro Mª ngeles Romero‐Rodríguez Manuel Vzquez 《International Journal of Dairy Technology》2021,74(1):202-214
The aim of this study was to evaluate the consumer acceptance and preference of a novel cheese coagulated with vegetal rennet and microbial transglutaminase (V + TG) as an alternative for lacto‐vegetarian consumers. The evolution of the sensory and instrumental parameters throughout the storage time was studied. Cheese with animal rennnet and microbial transglutaminase (A + TG), vegetal rennet alone (V) and animal rennet alone (A) were also studied as controls. The consumer test showed that the V + TG cheese was preferred and showed high texture and taste acceptance scores. This cheese could be successful for its sensory acceptance and as an alternative for the lacto‐vegetarian market. 相似文献
57.
Elena Molina Mercedes Ramos Lourdes Amigo 《Journal of the science of food and agriculture》2002,82(10):1240-1245
The physicochemical characteristics of Ibérico cheese, a semi‐hard Spanish variety manufactured from mixtures of cow's, ewe's and goat's milk, were studied. The casein fraction and breakdown products of 6‐month‐old cheeses were characterised by various electrophoretic techniques: urea polyacrylamide gel electrophoresis (urea‐PAGE) at alkaline pH, isoelectric focusing (IEF) and two‐dimensional polyacrylamide gel electrophoresis (2DE). Proteins were separated in 2DE according to their charge/mass ratio by urea‐PAGE at alkaline pH in the first dimension and according to their isoelectric point by IEF in the second dimension. Some individual bands considered homogeneous by urea‐PAGE at alkaline pH (ie different grades of phosphorylation of αs1‐casein and αs2‐casein) or by IEF (ie overlapping of several bands of αs2‐casein with γ‐casein bands) were found to be complex mixtures of casein components by 2DE. The two‐dimensional electrophoretic pattern was characteristic of the milk of each animal species included in Ibérico cheese. Capillary electrophoresis (CE) was also used to study the Ibérico cheeses. The high resolution of this technique allowed the identification of the main caseins of the different species (ie para‐κ‐casein, β‐casein, γ2‐casein and γ3‐casein). © 2002 Society of Chemical Industry 相似文献
58.
59.
Peña-Gomar MC González-González ML García-Valenzuela A Antó-Roca J Pérez E 《Applied optics》2004,43(32):5963-5970
We investigate the use of laser reflectometry near the critical angle to monitor particle adsorption onto a flat glass surface. Experimental results show that positive particles are adsorbed onto the glass surface and that their adsorption kinetics depend strongly on the volume fraction occupied by the particles in suspension but not appreciably on the particle size. The reflectance near the critical angle is dominated by the particles on the surface, with the contribution of the particles in suspension being very low. We compare the reflectance change near the critical angle with the change in reflectance near the Brewster angle when particles are adsorbed onto the glass surface. We find that reflectometry near the critical angle is 3000 times more sensitive than it is near the Brewster angle. Some optical images are presented to validate our results. 相似文献
60.
Elahe Nezami Jennifer Unger Sylvia Tan Caitlin Mahaffey Anamara Ritt-Olson Steve Sussman Selena Nguyen-Michel Lourdes Baezconde-Garbanati Stan Azen C Anderson Johnson 《Nicotine & tobacco research》2005,7(2):243-248
Numerous studies have shown associations between smoking and depression, but the generalizability of the relationship across ethnic groups remains unknown. The present study assessed the association between depression and smoking intention and experimentation among adolescents from four ethnic groups in the Los Angeles area-Chinese/Chinese American, Latino/Hispanic, Persian/Iranian, and White. Over 800 7th graders in the Los Angeles area completed measures of depressive symptoms, experimentation with smoking, intention to smoke, and sociodemographic covariates. Chinese/Chinese American students had the lowest levels of depressive symptoms, whereas Latinos/Hispanics had the highest levels. Latinos/Hispanics also were the most likely to intend to smoke in the next year and were the most likely to have started experimenting with cigarette smoking. Depressive symptoms were significantly associated with intention to smoke even after controlling for language use acculturation, socioeconomic status, gender, and ethnicity. The association between depressive symptoms and intention to smoke did not vary significantly across ethnic groups. These results indicate that the association between depressive symptoms and adolescent smoking generalizes across diverse ethnic groups. 相似文献