全文获取类型
收费全文 | 55019篇 |
免费 | 1481篇 |
国内免费 | 88篇 |
专业分类
电工技术 | 415篇 |
综合类 | 146篇 |
化学工业 | 12878篇 |
金属工艺 | 1028篇 |
机械仪表 | 1051篇 |
建筑科学 | 1744篇 |
矿业工程 | 121篇 |
能源动力 | 1752篇 |
轻工业 | 9962篇 |
水利工程 | 521篇 |
石油天然气 | 309篇 |
武器工业 | 7篇 |
无线电 | 2451篇 |
一般工业技术 | 7886篇 |
冶金工业 | 8752篇 |
原子能技术 | 331篇 |
自动化技术 | 7234篇 |
出版年
2024年 | 450篇 |
2023年 | 576篇 |
2022年 | 1256篇 |
2021年 | 1842篇 |
2020年 | 1300篇 |
2019年 | 1455篇 |
2018年 | 1778篇 |
2017年 | 1803篇 |
2016年 | 1943篇 |
2015年 | 1455篇 |
2014年 | 1982篇 |
2013年 | 3888篇 |
2012年 | 3174篇 |
2011年 | 3491篇 |
2010年 | 2665篇 |
2009年 | 2571篇 |
2008年 | 2340篇 |
2007年 | 2019篇 |
2006年 | 1648篇 |
2005年 | 1392篇 |
2004年 | 1273篇 |
2003年 | 1205篇 |
2002年 | 1024篇 |
2001年 | 790篇 |
2000年 | 714篇 |
1999年 | 785篇 |
1998年 | 3090篇 |
1997年 | 2014篇 |
1996年 | 1384篇 |
1995年 | 771篇 |
1994年 | 664篇 |
1993年 | 624篇 |
1992年 | 245篇 |
1991年 | 221篇 |
1990年 | 168篇 |
1989年 | 199篇 |
1988年 | 194篇 |
1987年 | 176篇 |
1986年 | 139篇 |
1985年 | 181篇 |
1984年 | 134篇 |
1983年 | 103篇 |
1982年 | 106篇 |
1981年 | 118篇 |
1980年 | 130篇 |
1979年 | 65篇 |
1978年 | 64篇 |
1977年 | 203篇 |
1976年 | 398篇 |
1973年 | 71篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Patricia Garcia‐Herrera Maria‐Luisa Pérez‐Rodríguez Teresa Aguilera‐Delgado Maria‐Jose Labari‐Reyes Begoña Olmedilla‐Alonso Montana Camara Sonia de Pascual‐Teresa 《International Journal of Food Science & Technology》2016,51(10):2290-2300
A fast and reliable method for anthocyanin extraction and identification by HPLC‐DAD‐ESI/MS‐QTOF was used to analyse the anthocyanin composition of commercial red fruit juices (blackberry, redcurrant and pomegranate), purees (strawberry, cherry and raspberry) and concentrates (elderberry, blueberry and red grape). The anthocyanin profile of black carrot juice is also reported. The extraction and analysis method allowed us to detect and quantify a wide range of individual anthocyanins in a simple and rapid way. Pelargonidin‐3‐glucoside was detected in redcurrant for the first time and petunidin‐3‐galactoside quantified for the first time in blueberries. Considering the health benefits that have been associated with anthocyanin consumption, all these fruit and vegetables processed products could appear as a good source of this group of phytochemical compounds for their direct consumption or their use as ingredients for the design of new food product or food supplements. 相似文献
972.
Luis E. Quintero Rodríguez Ramiro Rearte Germán Domínguez R. Luzbel de la Sota Laura V. Madoz Mauricio J. Giuliodori 《Journal of dairy science》2019,102(10):9481-9487
The main objective of this study was to evaluate the risk factors for late embryonic loss (LEL) in supplemented grazing dairy cows. Additional objectives were to assess the incidence of LEL and its association with the reproductive performance of cows. A data set containing productive, reproductive, and health records of 13,551 lactations was used. A retrospective case-control study involving 631 cows with LEL (cases) and 2,524 controls (4 controls per case within each study year) was run. A case of LEL was defined when the embryo had no heartbeat or there was evidence of detached membranes or floating structures including embryo remnants by ultrasonography (US) at 28 to 42 d post-artificial insemination (AI), whereas a non-case was defined as a cow diagnosed with positive pregnancy by US 28 to 42 d post-AI and reconfirmed as pregnant 90 ± 7 d post-AI. Four controls per case were randomly selected from the non-cases with a temporal matching criterion (±3 d around the date of the fecundating AI of the case). Multivariable logistic models were offered with the following predictors: year of LEL (2011 through 2015), season of LEL (summer vs. fall vs. winter vs. spring), parity (1 vs. 2 vs. ≥3), uterine disease (UD), non-uterine disease (NUD), body condition score at parturition, body condition score at 28 to 42 d post-AI (BCS-LEL), days in milk (DIM), and daily milk yield (MY). Statistical significance was set at P < 0.05 and a tendency was set at P ≤ 0.10. We found that 4.7, 22, and 23% of cows had LEL, UD, and NUD, respectively. Cases tended to have higher daily MY than controls (32.5 vs. 31.8 kg); also, cases had much longer calving to pregnancy interval (226 vs. 118 d), lower hazard of pregnancy [hazard ratio = 0.39, 95% confidence interval (CI) = 0.35–0.43], and higher odds for non-pregnancy [odds ratio (OR) = 2.89, 95% CI = 2.37–3.54] than controls. We found that the odds for LEL increased with parity number (OR = 2.48, 95% CI = 1.99–3.08 for parity ≥3) and with BCS-LEL <2.50 (OR = 1.81, 95% CI = 1.33–2.47). Conversely, the odds for LEL decreased with BCS-LEL >3.00 (OR = 0.70, 95% CI = 0.53–0.91). The odds for LEL increased with UD (OR = 1.23, 95% CI = 1.01–1.49), NUD (OR = 1.24, 95% CI = 1.01–1.54), DIM (OR = 1.03, 95% CI = 1.00–1.05), and daily MY (OR = 1.14, 95% CI = 1.04–1.25) in univariable models only. Finally, the odds for LEL were not associated with year, season, DIM, and body condition score at parturition. In conclusion, LEL is associated with extended calving to pregnancy interval, and among its risk factors are parity number and BCS-LEL. 相似文献
973.
974.
975.
Identifying the package and label features that are most relevant for consumer might provide useful information for designing a food package that closely matches consumer needs and expectations. In the present work two groups of 100 milk dessert consumers were asked to elicit package and label features of milk desserts using word association and free listing. Both methodologies were useful, efficient and quick methods to determine package and label features most likely to influence consumer perception of milk desserts. Although some differences were found between them, results related to the design of milk dessert packages were similar and suggested that brand, package shape, colour, and the design of the label might be the most relevant features that should be taken into account during package design of this food product. Cluster analysis of participants enabled the identification of groups of consumers that might be driven by different package features when making their purchase decisions of milk desserts. 相似文献
976.
The aim of this study was to determine the effect of a carotenoid mixture (Capsantal FS-30-NT), containing capsanthin and capsorubin, on growth and aflatoxins (AF) production of AF-producing Aspergillus flavus isolates. 相似文献
977.
Fernando de la Peña Moreno Gracia Patricia Blanch Gema Flores María Luisa Ruiz del Castillo 《Journal of the science of food and agriculture》2010,90(6):989-994
BACKGROUND: Although strawberry aroma is very complex, certain compounds have been described as main contributors, i.e. furanones, aldehydes, alcohols, sulfur compounds and particularly methyl and ethyl esters. In addition, strawberries possess potent antioxidant activity because of their high content of phenolic compounds. Among them, flavonols are highlighted as important antioxidant compounds in strawberry. The objective of this study was to assess the effect of methyl jasmonate (MJ) on the composition of the major contributors to aroma and on the content of certain flavonols in strawberry fruits. RESULTS: The levels of all studied volatile compounds were significantly affected by MJ treatment, though the individual effect differed according to the specific compound considered. Most of them increased significantly (P < 0.05), except methyl butanoate, which always showed higher levels in untreated strawberries. In contrast to aroma compounds, the change in the concentration of flavonols (i.e. myricetin, quercetin and kaempferol) was not significant in MJ‐treated strawberries. Considering the health‐promoting activity of these compounds, further investigations on the experimental conditions related to the treatment are required to control flavonol bioformation by means of MJ. CONCLUSION: The exogenous application of MJ vapour to strawberry enhances, in general, the production of the most relevant aroma‐active compounds. On the contrary, MJ treatment does not appear to influence the levels of myricetin, quercetin and kaempferol. Thus postharvest MJ treatment is proposed as an approach to obtain improved strawberry fruits in terms of sensory quality and health‐promoting properties. Copyright © 2010 Society of Chemical Industry 相似文献
978.
Monica Cavia‐Saiz Maria D Busto Maria Concepción Pilar‐Izquierdo Natividad Ortega Manuel Perez‐Mateos Pilar Muñiz 《Journal of the science of food and agriculture》2010,90(7):1238-1244
BACKGROUND: This study was designed to evaluate and compare antioxidant capacity and radical scavenging activity of naringin and its aglycone by different in vitro assays. The effects of flavanones on lipid peroxidation, glutathione (GSH) oxidation and DNA cleavage were also assessed. RESULTS: The results showed that naringenin exhibited higher antioxidant capacity and hydroxyl and superoxide radical scavenger efficiency than naringin. Our results evidenced that glycosylation attenuated the efficiency in inhibiting the enzyme xanthine oxidase and the aglycone could act like a more active chelator of metallic ions than the glycoside. Additionally, naringenin showed a greater effectiveness in the protection against oxidative damage to lipids in a dose‐dependent manner. Both flavanones were equally effective in reducing DNA damage. However, they show no protective effect on oxidation of GSH. CONCLUSION: The data obtained support the importance of characterizing the ratio naringin/naringenin in foods when they are evaluated for their health benefits. Copyright © 2010 Society of Chemical Industry 相似文献
979.
Amparo Martínez‐Fuentes Carlos Mesejo Carmina Reig Manuel Agustí 《Journal of the science of food and agriculture》2010,90(11):1936-1943
BACKGROUND: In Citrus the inhibitory effect of fruit on flower formation is the main cause of alternate bearing. Although there are some studies reporting the effect on flowering of the time of fruit removal in a well‐defined stage of fruit development, few have investigated the effect throughout the entire fruit growth stage from early fruitlet growth to fruit maturity. The objective of this study was to determine the phenological fruit developmental stage at which the fruit begins its inhibitory effect on flowering in sweet orange by manual removal of fruits, and the role of carbohydrates and nitrogen in the process. RESULTS: Fruit exerted its inhibitory effect from the time it was close to reaching its maximum weight, namely 90% of its final size (November) in the present experiments, to bud sprouting (April). The reduction in flowering paralleled the reduction in bud sprouting. This reduction was due to a decrease in the number of generative sprouted buds, whereas mixed‐typed shoots were largely independent of the time of fruit removal, and vegetative shoots increased in frequency. The number of leaves and/or flowers per sprouted shoot was not significantly modified by fruit load. CONCLUSION: In ‘Valencia’ sweet orange, fruit inhibits flowering from the time it completes its growth. Neither soluble sugar content nor starch accumulation in leaves due to fruit removal was related to flowering intensity, but some kind of imbalance in nitrogen metabolism was observed in trees tending to flower scarcely. Copyright © 2010 Society of Chemical Industry 相似文献