全文获取类型
收费全文 | 4446篇 |
免费 | 291篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 53篇 |
综合类 | 5篇 |
化学工业 | 1011篇 |
金属工艺 | 101篇 |
机械仪表 | 64篇 |
建筑科学 | 185篇 |
矿业工程 | 6篇 |
能源动力 | 172篇 |
轻工业 | 346篇 |
水利工程 | 40篇 |
石油天然气 | 15篇 |
无线电 | 381篇 |
一般工业技术 | 887篇 |
冶金工业 | 780篇 |
原子能技术 | 28篇 |
自动化技术 | 667篇 |
出版年
2023年 | 63篇 |
2022年 | 129篇 |
2021年 | 195篇 |
2020年 | 118篇 |
2019年 | 123篇 |
2018年 | 158篇 |
2017年 | 139篇 |
2016年 | 161篇 |
2015年 | 128篇 |
2014年 | 201篇 |
2013年 | 285篇 |
2012年 | 254篇 |
2011年 | 310篇 |
2010年 | 219篇 |
2009年 | 197篇 |
2008年 | 208篇 |
2007年 | 192篇 |
2006年 | 165篇 |
2005年 | 114篇 |
2004年 | 125篇 |
2003年 | 84篇 |
2002年 | 93篇 |
2001年 | 45篇 |
2000年 | 37篇 |
1999年 | 62篇 |
1998年 | 127篇 |
1997年 | 78篇 |
1996年 | 52篇 |
1995年 | 48篇 |
1994年 | 41篇 |
1993年 | 32篇 |
1992年 | 28篇 |
1991年 | 14篇 |
1990年 | 26篇 |
1989年 | 25篇 |
1988年 | 16篇 |
1987年 | 15篇 |
1985年 | 26篇 |
1984年 | 25篇 |
1983年 | 26篇 |
1982年 | 26篇 |
1981年 | 33篇 |
1980年 | 13篇 |
1979年 | 26篇 |
1978年 | 24篇 |
1977年 | 24篇 |
1976年 | 37篇 |
1975年 | 19篇 |
1974年 | 20篇 |
1971年 | 12篇 |
排序方式: 共有4741条查询结果,搜索用时 15 毫秒
91.
Keran Su Kim Huey Ee Jingcan Sun Shao Quan Liu Benjamin Lassabliere Ulrich Feiter Yunle Huang Rui Min Vivian Goh Aileen Pua Bin Yu 《International Journal of Food Science & Technology》2022,57(3):1666-1678
The structural diversity of polyphenols and the inherent limitations of current extraction techniques pose a challenge to extract polyphenols using a simple and green method. Hence, in this study, a method was developed to simultaneously fractionate multiple classes of polyphenols by only varying ethanol-water solutions. Honeybush tea, which is rich in polyphenols, was selected as a model for this study. Solvent extraction followed by solid-phase extraction (SPE) was developed to obtain a polyphenol-rich fraction from six honeybush samples. Based on a gradient elution programme (10%, 30%, 50%, 70% and 90% (v/v) ethanol-water solution) of SPE, the Strata X cartridge showed a better recovery of most targeted polyphenols under 0.9 mL of the drying volume and 1 mL min−1 of the dispensing speed. The elution programme for fractionating most polyphenols was as follows: single elution with 50% ethanol, followed by twice elution with 70% ethanol. The antioxidant capacity was used to analyse the differences among the polyphenol-rich fractions from six honeybush samples. Principal component analysis (PCA) revealed that unfermented C. genistoides (GG) has the greatest antioxidant capacity among the honeybush species studied. Additionally, mangiferin, isomangiferin and vicenin-2 were the main contributors to the antioxidant capacity in six honeybush fractions according to the correlation study. 相似文献
92.
The aim of this study was to evaluate the short- and long-term effects of initial serum total protein (STP) concentration, average starter feed intake (SI) during the last week of the preweaning period, and average daily gain (ADG) on the growth, fertility, and performance of Holstein heifers during their first lactation. Eighty-four female Holstein dairy calves were weaned at d 56 of age and then the study continued until the end of the first lactation. Growth performance, including body weight, ADG, withers height, and its change were analyzed monthly from 3 to 450 d of life, and reproduction data and performance in the first lactation of primiparous dairy heifers over a 4-yr period (2015 to 2019) were recorded. In the first 24 h of life, calves received 4 L of colostrum (<2 h and <12 h after birth); on d 2 and 3: 2 feedings/d of 2 L of transition milk; from d 4 to 49: 6 L/d of milk replacer (150 g of powder/L as-fed) in 3 feedings; and from d 50 to 56: 2 L/d of milk replacer in 1 feeding. The calves were fed pelleted starter feed from d 4 to 56, and after that from 8 wk until 3 mo of age, a dry total mixed ration with an 85:15 ratio of weaning pelleted starter to straw. From 3 to 7 mo and from 8 mo of age to calving, the total mixed ration contained 16.9% and ~14.0% crude protein, respectively, on a dry matter basis and ~2.40 Mcal of metabolizable energy/kg on a dry matter basis. The results of the current study showed that the initial STP concentration of primiparous dairy heifers was associated with improved growth performance, especially greater body weight and withers height. In addition, with increasing levels of initial STP concentration, age at first estrus, artificial insemination (AI) service, pregnancy, and calving was decreased by 16, 18, 25, and 25 d, respectively. Initial STP concentration was positively correlated with milk production and increased total milk yield and yield of energy-corrected milk by about 1,558 kg and 1,149 kg during first lactation. Calves with higher average starter feed intake during the last week of the preweaning period had better growth performance, which in turn was positively associated with fertility parameters, accelerated first estrus (by 17 d), and reduced age at AI service (by 13 d). Preweaning ADG was favorably associated with fertility performance of heifers, with faster occurrence of first estrus and a reduction in age at AI service, pregnancy, and calving. Also, increasing preweaning ADG increased milk yield, energy-corrected milk, and 4% fat-corrected milk at 305 DIM by about 829, 754, and 763 kg at first lactation of primiparous heifers. These results indicate that in the rearing period, particular attention should be paid to the initial STP concentration, average SI during the last week of this period, and rearing ADG to increase growth, fertility, and performance in the first lactation of primiparous dairy heifers. 相似文献
93.
94.
Two proprietary biocides were compounded and extruded at three concentrations, respectively, into high density polyethylene-maple wood flour lumber (HDPE-MWL) and evaluated for their efficacy to control fungal colonization and discoloration using the ASTM Standard G 21-96. Although the silver biocide used in this study did not control fungal colonization and discoloration of HDPE-MWL, statistically significant difference was observed between the highest silver biocide concentration and those of the two lower silver biocide concentrations. The latter exhibited no significant difference with the controls. In contrast, the three levels of zinc biocides showed significant difference from each other with respect to their efficacy against fungal colonization and discoloration of HDPE-MWL. Overall, only the zinc biocide was efficacious against fungal colonization and discoloration. The biocide containing zinc as an active biocidal agent was most efficacious at 1% (by weight) concentration. 相似文献
95.
Quirós L Jarque S Lackner R Fernández P Grimalt JO Piña B 《Environmental science & technology》2007,41(14):5154-5160
Cytochrome p450 1A (CYP1A) gene expression in fish liver increases upon exposure to a variety of chemical compounds, including organochlorine compounds (OCs) and polycyclic aromatic hydrocarbons (PAHs). To use this physiological response as a marker of environmental impact, we developed and validated a set of primers to quantify CYP1A expression by qRT-PCR in the brown trout, Salmo trutta. These primers were used to explore the natural variability of CYP1A expression in 8 isolated populations (65 samples) from European remote lakes, in a geographical distribution encompassing the Tyrolean Alps, Pyrenees, Rila, Tatras, and Norwegian and Scottish mountains. CYP1A expression values varied more than 2 orders of magnitude among samples, with strong variations within each population. CYP1A expression values were significantly elevated in Tatras and Pyrenees fish populations, whereas the lowest median values were found in populations from the Tyrolean Alps and Rila. These values correlated with the content of different environmentally relevant pollutants in the sediments of the lakes harboring each fish population, particularly with HCB and 4,4'-DDE contents. To our knowledge, this works represents a first report of a physiological response linked to persistent organic pollutants in fish from mountain lakes. 相似文献
96.
Benjamin D. Tanner 《中国纤检》2010,(2):79-82
引言
如果你的公司设计、生产或销售抗菌织物.那么你首先要知道这些产品能带给顾客的特性。你不得不花费时间和精力去了解抗茵的知识.并且在这个过程中极有可能获得大量的有关微生物和实验室测试的知识。毫无疑问.你也会感谢这些高性能织物带来的商业潜力。 相似文献
97.
Lofts S Chapan PM Dwyer R McLaughlin MJ Choeters I Sheppard SC Adams WJ Alloway BJ Antunes PM Campbell PG Davies B Degryse F De Vries W Farley K Garrett RG Green A Jan Groenenberg B Hale B Harrass M Hendershot WH Keller A Lanno R Liang T Liu WX Ma Y Menzie C Moolenaar SW Piatkiewicz W Reimann C Rieuwerts JS Santore RC Sauvé S Schuetze G Schlekat C Skeaff J Smolders E Tao S Wilkins J Zhao FJ 《Environmental science & technology》2007,41(18):6326-6331
98.
Influence of yeast on the yield of fermentation and volatile profile of ‘Węgierka Zwykła’ plum distillates 下载免费PDF全文
Katarzyna Pielech‐Przybylska Maria Balcerek Agnieszka Nowak Piotr Patelski Urszula Dziekońska‐Kubczak 《Journal of the Institute of Brewing》2016,122(4):612-623
The character of plum brandies depends on a unique aroma profile of the plum and the microbiota present on the surface of the fruits, as well as yeast used for fermentation. In this study, an evaluation of the effect of microorganisms applied for the fermentation of W?gierka Zwyk?a var. plum mashes and processing temperature (18 °C, 30 °C) on its efficiency and volatile profile, as well as taste and flavour of distillates obtained was performed. An estimation of the odour activity values (OAVs) of the volatile compounds was also conducted. Regardless of whether the fermentation was carried out using Saccharomyces bayanus wine yeast or by native microflora present on plums as well as raisins, the efficiency of this process was high and ranged between 91.7 and 96.7% of the theoretical efficiency. Especially rich in esters (among others ethyl acetate and isoamyl acetate) was the distillate derived after fermentation with the microflora of plums and raisins, at 18 °C. An evaluation of the individual aromatic effect of chemical compounds present in tested distillates, in terms of their OAVs, revealed that the highest OAVs were reached with isovaleraldehyde. Other compounds that showed aroma values >1 and possibly had an effect on the overall aroma of tested plum distillates were the following: hexanal, benzaldehyde, ethyl acetate, isoamyl acetate, ethyl benzoate, ethyl hexanoate, 1‐propanol, 2‐methyl‐1‐butanol, 3‐methyl‐1‐butanol and 1‐hexanol. The performed sensory ranking showed that the best rated distillate was the one obtained after fermentation with the indigenous microflora of plums and raisins, at 18 °C. Copyright © 2016 The Institute of Brewing & Distilling 相似文献
99.
100.