首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   537篇
  免费   14篇
  国内免费   1篇
电工技术   4篇
化学工业   103篇
金属工艺   7篇
机械仪表   3篇
建筑科学   27篇
能源动力   19篇
轻工业   102篇
水利工程   2篇
石油天然气   6篇
无线电   16篇
一般工业技术   61篇
冶金工业   96篇
原子能技术   2篇
自动化技术   104篇
  2024年   2篇
  2023年   6篇
  2022年   13篇
  2021年   20篇
  2020年   4篇
  2019年   12篇
  2018年   14篇
  2017年   11篇
  2016年   8篇
  2015年   5篇
  2014年   18篇
  2013年   24篇
  2012年   28篇
  2011年   39篇
  2010年   20篇
  2009年   29篇
  2008年   19篇
  2007年   27篇
  2006年   23篇
  2005年   24篇
  2004年   24篇
  2003年   16篇
  2002年   15篇
  2001年   2篇
  2000年   10篇
  1999年   3篇
  1998年   11篇
  1997年   9篇
  1996年   9篇
  1995年   10篇
  1994年   10篇
  1993年   10篇
  1992年   7篇
  1991年   3篇
  1990年   3篇
  1989年   2篇
  1988年   4篇
  1986年   4篇
  1985年   4篇
  1984年   5篇
  1983年   5篇
  1982年   6篇
  1981年   3篇
  1980年   4篇
  1979年   6篇
  1978年   6篇
  1977年   3篇
  1976年   3篇
  1972年   3篇
  1955年   1篇
排序方式: 共有552条查询结果,搜索用时 15 毫秒
81.
The study evaluated the effects of waxing, irradiation dose and post‐irradiation storage time on the essential oils in orange peel. Mature oranges (Maroc late) waxed or unwaxed were treated with 1 or 2 kGy radiation and stored for 9 weeks at 20 °C and 40–50% RH. Essential oils from the peel were extracted and analysed by GC. Results showed that D ‐limonene was significantly lower in waxed oranges; levels in samples treated with 2 kGy were higher than those in non‐irradiated or treated with 1 kGy. Linalool, methyl anthranilate and 3,7‐dimethyl‐2,6‐octadienal decreased as the dose increased. Levels of linalool increased with storage time but D ‐limonene was unaffected. These results may aid in guaranteeing the quality of orange essential oils during storage time. Copyright © 2004 Society of Chemical Industry  相似文献   
82.
83.
The greenhouse gas mitigation potential of different economic sectors in three world regions are estimated using a bottom-up approach. These estimates provide updates of the numbers reported in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). This study is part of a larger project aimed at comparing greenhouse gas mitigation potentials from bottom-up and top-down approaches. The sectors included in the analysis are energy supply, transport, industry and the residential and service sector. The mitigation potentials range from 11 to 15 GtCO2eq. This is 26–38% of the baseline in 2030 and 47–68% relative to the year 2000. Potential savings are estimated for different cost levels. The total potential at negative costs is estimated at 5–8% relative to the baseline, with the largest share in the residential and service sector and the highest reduction percentage for the transport and industry sectors. These (negative) costs include investment, operation and maintenance and fuel costs and revenues at moderate discount rates of 3–10%. At costs below 100 US$/tCO2, the largest potential reductions in absolute terms are estimated in the energy supply sector, while the transport sector has the lowest reduction potential.  相似文献   
84.
Biogas plants enable power to be generated in a flexible way so that variable, renewable energy sources can be integrated into the energy system. In Germany, the Renewable Energy Sources Act promotes flexible power generation in biogas plants. Two existing biogas plants in flexible operation were analyzed with respect to economic viability and greenhouse gas (GHG) emissions to assess the feasibility of flexible operation. To do this, a biogas technology simulation model was developed to reproduce the technical design of both biogas plants and to link this design with twelve flexibilization scenarios. The evaluation of the economic viability is based on a discounting method of investment appraisal. For assessing the level of GHG emissions, the life cycle assessment method has been applied. The results show that the profitability of flexibilization is contingent upon premium payments promoting flexibility and direct sales resulting from a higher electrical efficiency of new or additionally installed combined heat and power units. Overall, with respect to profitability, the results of the flexible power generation scenarios are dependent upon the properties of the technical plant, such as its power generation and gas storage capacities. Relative GHG emissions from flexible biogas plants show significantly lower values than for referenced fossil gas–steam power stations. Among the various scenarios, the results reveal that the level of GHG emissions especially depends on the number of operating hours of the additional combined heat and power unit(s). The results of the analyzed biogas plants showed no direct correlation between GHG emissions and the economic benefits. Overall, a flexible power generation of biogas plants may improve the economic viability as well as result in lower GHG emissions in comparison with a conventional base load operation. © 2016 The Authors. International Journal of Energy Research published by John Wiley & Sons Ltd.  相似文献   
85.
In recent years, research on biopolymer based-coating containing natural antimicrobial agents is developing significantly. The objective of this study was to evaluate the antimicrobial efficiency of six formulations containing pre-selected natural antimicrobial compounds against Listeria monocytogenes, Escherichia coli O 157:H7, Salmonella typhimurium, the total bacteria and total yeasts and molds in cauliflower. Each formulation was subjected to a sensory test in parallel to microbiological analysis and the efficiency during storage at 5 ℃ was evaluated for the two best formulations, based on their ability to eliminate the target microorganisms. Both formulations were able to reduce all pathogens and total flora below detectable levels after 24 h of storage at 5 ℃. Using washing or spraying treatments, the two formulations were able to reduce Listeria to undetectable levels for 3 d. This efficiency was extended to 7 d when the formulations were incorporated into an edible coating. Washing treatment with the two formulations was also able to limit the growth of yeast and molds at levels lower than 2 log, for more than 7 d. The population of E. coli was reduced to below the detection limit during 14 d of storage, after washing treatment with the two formulations. The spraying treatment of cauliflower with the formulations allowed the use of very small amounts of antimicrobials while maintaining a fairly good efficiency, greatly reducing the potential costs of implementing this method in the industry. Future research may focus on development of nanoemulsion of antimicrobial formulations based on the developed antimicrobial formulations in this study to improve the better coating efficiency.  相似文献   
86.
The use of dietary supplements is increasing globally and this includes the use of plant food supplements (PFS). A variety of factors may be influencing this increased consumption including the increasing number of older people in society, mistrust in conventional medicine and the perception that natural is healthy. Consumer studies in this area are limited, with a focus on dietary supplements in general, and complicated by the use of certain plant food supplements as herbal medicines. Research indicates that higher use of dietary supplements has been associated with being female, being more educated, having a higher income, being white and being older, however the drivers for consumption of supplements are complex, being influenced by both demographic and health-related factors. The aim of this paper is to provide an overview of current knowledge about the users and the determinants of usage of plant food supplements. With growing consumption of these products, the need for effective risk-benefit assessment becomes ever more important and an insight into who uses these types of products and why is an important starting point for any future science-based decisions made by policy makers, PFS manufacturers and ultimately by consumers themselves.  相似文献   
87.
The effect of cranberry extracts and juices during cranberry juice processing on the antiproliferative properties against colon cancer cells was investigated. Two colon cancer cell lines HT-29 and LS-513 were treated with different concentrations of cranberry phenolic extracts from fruits, puree, depectinised puree and pomace and different concentration of three juices (raw, filtered and concentrated juices). The phenolic extracts consisted of water-soluble phenolic compounds, apolar phenolic compounds and anthocyanins. These phenolic extracts and juices were tested against two cell lines at pH 2.5 (natural juice pH) and at pH 7.0 (physiological pH). All cranberry extracts and juices could inhibit the growth of both cell lines with the IC50 values (the concentration of phenolic content required to inhibit 50% the growth of cancer cells) varied from 3.8 to 179.2 μg gallic acid equivalent/ml. It was found that three types of extracts from fruit at pH 7.0 were the most effective at inhibiting the growth of HT-29 cell line. Extracts containing anthocyanins from fruit and from pomace were the most and the least efficient, respectively, in inhibiting the growth of both cancer cell lines. Further, three juices at natural pH (pH 2.5) were more effective at inhibiting the growth of two cell lines as compared to juices at pH 7.0. Concentrated juice at both pH values was the most effective at growth inhibition of two cancer cell lines compared to two other juices.  相似文献   
88.
Lactobacillus sakei is a meat-borne lactic acid bacterium species exhibiting a wide genomic diversity. We have investigated the diversity of response to various oxidative compounds, between L. sakei strains, among a collection representing the genomic diversity. We observed various responses to the different compounds as well as a diversity of response depending on the aeration conditions used for cell growth. A principal component analysis revealed two main phenotypic groups, partially correlating with previously described genomic clusters. We designed strains mixes composed of three different strains, in order to examine the behavior of each strain, when cultured alone or in the presence of other strains. The strains composing the mixtures were chosen as diverse as possible, i.e. exhibiting diverse responses to oxidative stress and belonging to different genomic clusters. Growth and survival rates of each strain were monitored under various aeration conditions, with or without heme supplementation. The results obtained suggest that some strains may act as “helper” or “burden” strains depending on the oxidative conditions encountered during incubation. This study confirms that resistance to oxidative stress is extremely variable within the L. sakei species and that this property should be considered when investigating starter performance in the complex meat bacterial ecosystems.  相似文献   
89.
Fibroblast growth factors (FGFs) are involved in paracrine control of follicle development. It was previously demonstrated that FGF10 decreases estradiol (E(2)) secretion in granulosa cell culture and that theca cell FGF10 mRNA expression is decreased in healthy follicles from abattoir ovaries. The main objectives of this study were to evaluate FGF10 and FGFR2b mRNA expression during follicular development in vivo, to evaluate the effect of FGF10 on follicle growth using Bos taurus taurus cows as a model, and to gain more insight into the mechanisms through which FGF10 inhibits steroidogenesis. Messenger RNA encoding both FGF10 and FGFR2b (main FGF10 receptor) was significantly more expressed in subordinate follicles (SFs) than in dominant follicles (DFs). The intrafollicular injection of FGF10 into the largest growing follicle at 7-8?mm in diameter interrupted the DF growth in a dose-dependent manner (11±0.4, 8.3±1 and 5.9±0.3?mm for 0, 0.1, and 1?μg/ml FGF10, respectively, at 72?h after treatment; P<0.05). In a third experiment, follicles were obtained 24?h after FGF10 (1?μg/ml) or PBS treatment through ovariectomy. In theca cells, FGF10 treatment did not affect mRNA encoding steroidogenic enzymes, LHCGR and IGFBPs, but significantly upregulated FGF10 mRNA expression. The expression of CYP19A1 mRNA in granulosa cells was downregulated by FGF10 treatment, which was accompanied by a 50-fold decrease in E(2) production, and decreased cyclin D2 mRNA. These results have shown that FGF10 and its receptor FGFR2b are more expressed in SFs and provide solid in vivo evidence that FGF10 acts as an important regulator of follicular growth in cattle.  相似文献   
90.
A novel cheese product developed based on the incorporation of various polyphenolic compounds was evaluated for its texture characteristics. Single phenolic compounds including catechin, epigallocatechin gallate (EGCG), tannic acid, homovanillic acid, hesperetin and flavone, along with natural crude compounds such as grape extract, green tea extract and dehydrated cranberry powder, were added as functional ingredients during the cheese-making process. Cheese curds containing polyphenolic compounds at a concentration of 0.5 mg/mL showed a decrease of curd moisture content (CMC) while the gel strength (GS) was not affected. Structural differences were observed when crude polyphenolic compounds were added to the cheese, resulting in rough and granular structures. Physical properties of the cheese product were evaluated after adding bioactive phenolic compounds to the cheese curd. We fully expect to apply this approach to other dairy products in the future.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号