全文获取类型
收费全文 | 12223篇 |
免费 | 1115篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 76篇 |
综合类 | 8篇 |
化学工业 | 4767篇 |
金属工艺 | 127篇 |
机械仪表 | 299篇 |
建筑科学 | 454篇 |
矿业工程 | 17篇 |
能源动力 | 323篇 |
轻工业 | 3155篇 |
水利工程 | 108篇 |
石油天然气 | 70篇 |
无线电 | 466篇 |
一般工业技术 | 1687篇 |
冶金工业 | 542篇 |
原子能技术 | 35篇 |
自动化技术 | 1213篇 |
出版年
2024年 | 35篇 |
2023年 | 127篇 |
2022年 | 602篇 |
2021年 | 1018篇 |
2020年 | 418篇 |
2019年 | 428篇 |
2018年 | 475篇 |
2017年 | 499篇 |
2016年 | 546篇 |
2015年 | 444篇 |
2014年 | 576篇 |
2013年 | 874篇 |
2012年 | 831篇 |
2011年 | 939篇 |
2010年 | 715篇 |
2009年 | 667篇 |
2008年 | 610篇 |
2007年 | 574篇 |
2006年 | 445篇 |
2005年 | 336篇 |
2004年 | 292篇 |
2003年 | 253篇 |
2002年 | 236篇 |
2001年 | 145篇 |
2000年 | 95篇 |
1999年 | 130篇 |
1998年 | 107篇 |
1997年 | 107篇 |
1996年 | 101篇 |
1995年 | 70篇 |
1994年 | 59篇 |
1993年 | 60篇 |
1992年 | 66篇 |
1991年 | 46篇 |
1990年 | 39篇 |
1989年 | 34篇 |
1988年 | 33篇 |
1987年 | 31篇 |
1986年 | 42篇 |
1985年 | 35篇 |
1984年 | 26篇 |
1983年 | 23篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 19篇 |
1979年 | 19篇 |
1978年 | 21篇 |
1977年 | 13篇 |
1976年 | 7篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
991.
María C. Caracoche Jorge A. Martinez Patricia C. Rivas Fernanda Andreola Federica Bondioli Anna Maria Ferrari Tiziano Manfredini 《Journal of the American Ceramic Society》2008,91(7):2357-2359
This paper deals with the phase stability of an aqueous suspension of tetragonal Zr0.9 Pr0.1 O2 (20 wt%/vol%) at room temperature as a function of the aging time. The suspension is investigated in situ using the highly localized Perturbed Angular Correlations technique. The results indicate that an almost fully reversible degradation process toward monoclinic zirconia takes place through a first-order reaction of rate constant k =0.7 day−1 . Two successive diffusion mechanisms are observed that are interpreted as OH− ions' migration in the grain surface and then, as proton defects' diffusion into the bulk. 相似文献
992.
993.
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
994.
Francesca Giuffrida Frédéric Destaillats Maria Herrero Egart Bernadette Hug Pierre-Alain Golay Leif H. Skibsted Fabiola Dionisi 《Food chemistry》2007,101(3):1108-1114
Heat flux differential scanning calorimetry (DSC) and electron spin resonance spectroscopy (ESR) were used to assess the activity and the thermal stability of antioxidants in four vegetable oils. Sunflower oil (SO) and high oleic sunflower oil (HOSO), both rich in diunsaturated fatty acids (FA), low trans oil (LT) and partially hydrogenated palm oil (PHPO), both containing monounsaturated FA, were analyzed by isothermal heat flux DSC, with or without 300 mg/kg of antioxidant: ascorbyl palmitate (AP), α-tocopherol (αT), δ-tocopherol (δT) and propyl gallate (PG). DSC experiments showed that δT is the most effective antioxidant for SO and PG for the less unsaturated oils. SO and PHPO were also analyzed by ESR at 120 and 145 °C, respectively. ESR results confirm the strongest antioxidant activity of δT and PG for SO and PHPO, respectively. Therefore, the present study demonstrates that DSC and ESR are valuable technologies to study activity and stability of antioxidants at high temperature. Moreover, experiments performed in the presence of the spin-trap N-tert-butyl-α-phenylnitrone (PBN), suggest that δT delay lipid oxidation through a different reaction mechanism when compared to αT. A different mechanism between tocopherols isomers in delaying lipid oxidation has been hypotized. 相似文献
995.
Wheat flour from the Hermosillo Hard Red Spring cultivar in Sonora, Mexico was fortified with various levels of lysine and methionine. The effects of added amino acids on the rheological properties were measured by the Brabender Farinograph and the Chopin Alveograph. Nutritional characteristics were measured by Protein Efficiency Ratio (PER). Dough development and stability times were not significantly different between control and fortified flours. Water absorption and Alveograph results indicated differences between samples. PERs were significantly improved by fortification. Overall bread acceptability was not significantly different from unfortified samples. 相似文献
996.
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
997.
The stability of some heterocyclic poly(amide imide)s in acidic and alkaline medium was compared to the structurally related polyimide and poly(amide imide)s without other heterocyclic groups. All the polymers have high stability in acidic medium. The introduction of additional heterocycles such as 1,3,4-0xadiazole or phenylquinoxaline into the macromolecular chain of a poly(amide imide) increases substantially the resistance to alkaline medium. Polyamides containing imide rings only in the side chain are more stable to hydrolysis than related polyamide having imide units in the main chain. 相似文献
998.
Nivia Maria Streit Luisa Helena Rychecki Hecktheuer Marta Weber do Canto Carlos Augusto Mallmann Letícia Streck Thaylise Vey Parodi Liana Pedrolo Canterle 《Food chemistry》2007,102(3):560-564
Erva-mate (Ilex paraguariensis St. Hil.) is a native species from temperate regions of South America, such as Brazil, Paraguay, and Argentina, that is consumed as a beverage known as mate. The objective of this research was to determine the content of caffeic acid, catechin, chlorogenic acid, caffeine, and gallic acid in mate to explain their influence in beverage taste and sensory differences between native and reforested plants, as well as between beverages from plants of different regions of Brazil (Santa Catarina and Rio Grande do Sul states). Compounds were determined by HPLC and results were related to a sensory evaluation performed by trained tasters. Tasters considered the beverage from reforested plants to be more bitter than the beverage from native plants. Beverages from reforested plants had significantly higher caffeic acid and lower catechin, chlorogenic acid, caffeine, and gallic acid content than native plants. Beverages from plants of Santa Catarina state had significantly higher catechin, caffeine, and gallic acid content than plants from Rio Grande do Sul state. 相似文献
999.
Alfonso Ranalli Gabriella De Mattia & Maria L. Ferrante 《International Journal of Food Science & Technology》1997,32(4):289-297
To evaluate the level of quality of the olive oil given by a new processing system we compared it with the percolation oil, which is known to be of high quality. The new product was characterized by the following: (i) higher contents of tocopherols, tyrosol- and hydroxytyrosol-aglycones, volatile aromatic substances, sterols, triterpene alcohols and lipochromes, and higher values of 1,2-diglycerides/1,3-diglycerides and campesterol/stigmasterol ratios, colour indices and turbidity; (ii) lower contents of waxes and triterpene dialcohols, and lower values for spectrophotometric indices, carbonyl index, Wolff's ratio (K232 /K270 ), acidity, and peroxide number; (iii) similar contents of phenols, o- diphenols, free tyrosol, free hydroxytyrosol, triglycerides, stigmastadienes, and aliphatic alcohols, similar sensory score, and similar value of resistance to autoxidation, alcohol index, overall quality indices, and fatty acid composition. 相似文献
1000.
José Ortiz-Landeros Maria Eugenia Contreras-García Heriberto Pfeiffer 《Journal of Porous Materials》2009,16(4):473-479
Macroporous ZrO2–Al2O3 mixed oxides with mesoporous walls were synthesized. The three-dimensional interconnected macroporous structures, of inorganic
zirconia–alumina mixed oxides containing different alumina compositions (25, 50, 100 wt%), were prepared by sol–gel method
from inorganic precursors and using polystyrene microspheres with diameters of 685 and 1520 nm as templates. The final porous
arrays with controllable pore size in the submicrometer range could be obtained by calcination of the organic template. The
structural characteristics are discussed. The physicochemical characterization of the samples was carried out by N2 physisorption (SBET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and transmission
electron microscopy (TEM). The shrinkage of pore diameter was approximately 35%, and the wall thickness of inorganic framework
varied between 135 and 154 nm. The specific surface areas, of the samples, were between 123 and 287 m2/g, obtaining the largest surface area with the highest alumina contents and the smallest templates. 相似文献