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   326篇
  免费   27篇
  国内免费   1篇
电工技术   2篇
化学工业   112篇
金属工艺   3篇
机械仪表   1篇
建筑科学   10篇
能源动力   4篇
轻工业   114篇
水利工程   4篇
石油天然气   2篇
无线电   8篇
一般工业技术   44篇
冶金工业   14篇
自动化技术   36篇
  2024年   1篇
  2023年   5篇
  2022年   12篇
  2021年   15篇
  2020年   7篇
  2019年   11篇
  2018年   13篇
  2017年   12篇
  2016年   13篇
  2015年   11篇
  2014年   11篇
  2013年   27篇
  2012年   18篇
  2011年   29篇
  2010年   17篇
  2009年   20篇
  2008年   13篇
  2007年   14篇
  2006年   7篇
  2005年   4篇
  2004年   7篇
  2003年   6篇
  2002年   3篇
  2001年   4篇
  2000年   11篇
  1999年   6篇
  1998年   9篇
  1997年   6篇
  1996年   5篇
  1995年   8篇
  1994年   2篇
  1993年   3篇
  1990年   4篇
  1989年   2篇
  1984年   1篇
  1983年   1篇
  1978年   1篇
  1974年   1篇
  1973年   2篇
  1971年   1篇
  1970年   2篇
  1968年   1篇
  1966年   1篇
  1965年   3篇
  1964年   1篇
  1962年   1篇
  1961年   2篇
排序方式: 共有354条查询结果,搜索用时 0 毫秒
31.
32.
The bioavailability of iron from milk-based infant formulas was estimated by an in vitro system including enzymatic digestion, iron uptake by Caco-2 cells and ferritin determination via an enzymoimmunoassay (ELISA). Positive correlations (p < 0.01) were found between the Fe(II) added to Caco-2 cells and ferritin synthesis and between the amount of dialyzed iron added to the cell culture and ferritin synthesis. The comparison of the bioavailability of iron from different milk-based formulas showed that adapted formulas having the same composition but differing in the iron salts added yielded similar ferritin levels. The same happened with follow-up formulas differing only in the presence or absence of bifidobacterium added. However, significant differences in the amount of ferritin synthesized were recorded between the two analyzed toddler formulas. Such differences could be attributed firstly to the ascorbic acid content and perhaps also to the manufacturing process involved, because one formula was in liquid form while the other was powdered.  相似文献   
33.
Fiber crops constitute a good alternative to wood fiber for manufacturing pulp and paper. In fact, fiber plants like flax surpass wood fiber in some technical respects and also in the environmental benignity of their processing. In this work, flax fiber was subjected to environmentally friendly bleaching sequences in order to obtain a high-quality pulp. The totally chlorine-free sequences (TCF) used for this purpose (LE and LRE) included an enzyme treatment with laccase in the presence of HBT as mediator (L stage), an alkaline extraction (E stage) and a reductive treatment with NaBH4 (R stage). The operating conditions for the L stage (laccase and HBT doses, reaction time and oxygen pressure) were optimised by using a sequential statistical plan to assess their influence on pulp properties after the E stage.Mathematical models accurately predicting brightness and kappa number in terms of the previous four variables were developed based on which the most influential factors were the laccase and HBT rates, and treatment time. By contrast, oxygen pressures of 0.2–0.6 MPa in the reactor had no effect on brightness or kappa number. The flax pulp obtained contained some oxidized cellulose that was partially degraded in the alkaline extraction step and reduced viscosity as a result. The viscosity loss associated with the presence of oxidized cellulose in the control and enzyme-treated pulp samples was efficiently recovered by using a reductive stage with sodium borohydride. Effluent was also analysed in order to assess the environmental impact of the process.  相似文献   
34.
Oil and triglyceride contents and fatty acid composition were determined for seeds in nine taxa belonging to the genusCoincya (Brassicaceae) on the Iberian Peninsula (Spain and Portugal). The oil content ranges from 11.1 to 24.6%, triglycerides from 68.7 to 88.5%. The major fatty acids were erucic (24.6–30.5%), linolenic (17.7–27.7%), linoleic (13.9–24.6%) and oleic acid (12.3–21.8%).  相似文献   
35.
An alternative approach for the interpretation of the residence time distribution (RTD) curves is proposed. The method has semiempirical basis, supported upon a gross fit of the tracer curve area by two triangles in order to obtain a single parameter (φ index) that indicates whether the system tends to a completely mixed or to a plug flow hydraulic behavior. In order to verify its applicability, 28 experiments were carried out in a laboratory tank (138 L). In these experiments, the influence of aeration, packing, and number of baffles on the tank hydraulic behavior was assessed using the index as well as conventional models. The general results obtained in the laboratory tank experiments showed that mixed tanks tend to have a larger dead volume fraction (DVF) than plug-flow tanks and that packed tanks tend to have a smaller DVF than nonpacked tanks. This index provides a reliable, quick, and simple method for the interpretation of the RTD curves when hydraulic behavior trends or tank modifications for hydraulic improvements are evaluated.  相似文献   
36.
Turnip roots, which are readily available in Mexico, are a good source of peroxidase, and because of their kinetic and biochemical properties have a high potential as an economic alternative to horseradish peroxidase (HRP). The efficiency of using turnip peroxidase (TP) to remove several different phenolic compounds as water‐insoluble polymers from synthetic wastewater was investigated. The phenol derivatives studied included phenol, 2‐chlorophenol, 3‐chlorophenol, o‐cresol, m‐cresol, 2,4‐dichlorophenol and bisphenol‐A. The effect of pH, substrate concentration, amount of enzyme activity, reaction time and added polyethylene glycol (PEG) was investigated in order to optimize reaction conditions. A removal efficiency ≥85% was achieved for 0.5 mmol dm?3 phenol derivatives at pH values between 4 and 8, after a contact time of 3 h at 25 °C with 1.28 U dm?3 of TP and 0.8 mmol dm?3 H2O2. Addition of PEG (100–200 mg dm?3) significantly reduced the reaction time required (to 10 min) to obtain >95% removal efficiency and up to 230% increase in remaining TP activity. A relatively low enzyme activity (0.228 U dm?3) was required to remove >95% of three phenolic solutions in the presence of 100–200 mg dm?3 PEG. TP showed efficient and fast removal of aromatic compounds from synthetic wastewaters in the presence of hydrogen peroxide and PEG. These results demonstrate that TP has good potential for the treatment of phenolic‐contaminated solutions. © 2002 Society of Chemical Industry  相似文献   
37.
The popularity of herbal products, especially plant food supplements (PFS) and herbal medicine is on the rise in Europe and other parts of the world, with increased use in the general population as well as among specific subgroups encompassing children, women or those suffering from diseases such as cancer. The aim of this paper is to examine the PFS market structures in European Community (EC) Member States as well as to examine issues addressing methodologies and consumption data relating to PFS use in Europe. A revision of recent reports on market data, trends and main distribution channels, in addition an example of the consumption of PFS in Spain, is presented. An overview of the methods and administration techniques used to assess individual food consumption as a starting point, including their uses and limitations, as well as some examples of studies that collect Food Supplement (FS) information, including herbal/botanical/plant-derived products are also discussed. Additionally, the intake estimation process of food nutrients is described and used to propose the PFS ingredients intake estimation process. Nationally representative PFS consumption data is scarce in Europe. The majority of studies have been conducted in Scandinavia and the UK. However the heterogeneity of definitions, study design and objectives make it difficult to compare results and extrapolate conclusions.  相似文献   
38.
BACKGROUND: The protein isolate obtained from safflower meal by aqueous extraction and ultrafiltration was evaluated for its physicochemical and functional properties. RESULTS: Protein, ash and moisture contents of the safflower protein isolate were 901, 51 and 45 g kg?1 respectively. Its water and oil absorption capacities were 2.22 mL H2O g?1 protein and 2.77 mL oil g?1 protein respectively. Least gelation concentration was 20 g kg?1 at pH 2, 6, 8 and 10 but 100 g kg?1 at pH 4. Emulsifying properties were also affected by the pH: emulsifying activity and emulsion stability at pH 6 were 82.5 and 100% respectively. The highest foaming capacity (126%) occurred at pH 2; however, it increased by 104% with the addition of 0.25 g glucose g?1 protein to the foam system. CONCLUSION: In the light of its functional properties found in this study, safflower protein isolate produced by ultrafiltration is recommended for use as an ingredient in food products such as salad dressing, meat products, mayonnaise, cakes, ice cream and desserts. Copyright © 2010 Society of Chemical Industry  相似文献   
39.
The synthesis of a difunctional P-heterocycle combining phosphonate and ester moieties in a six-membered ring is described. Using trifluoromethane sulfonic acid HOTf as organocatalyst, ring-opening with neopentyl alcohol readily occurs with complete selectivity for O-acyl bond cleavage. In turn, ring-opening polymerization proceeds in a controlled manner when an excess of P-heterocycle is used. Copolymerization with ϵ-caprolactone is also reported and semi-batch conditions are shown to enable regular incorporation of the phosphonate moieties along the polymer chains.  相似文献   
40.
Incubation experiments in order to study the influence of some parameters in the fluorescence products formation have been carried out. It has been observed a greater efficiency with the relation linoleic acid hydroperoxide:glutathione, 2:1, and a temperature of 37 °C. The complex formed working with labelled linoleic acid has been separated in two main fractions. The first one (without radioactivity) is fluorescent with excitation and emission maxima at 350 nm and 440 nm, respectively. It has been confirmed that this fraction consists of a complex of glutathione and short chain aldehydes. The fluorescence of the complex did not decrease by treatment with NaBH4 or with pH. The NH2 and SH groups take part in the lipid-peptide complex formation. The second, highly radioactive fraction includes free hydroperoxides and short chain hydroxy fatty acids.  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