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   870篇
  免费   41篇
  国内免费   3篇
电工技术   13篇
综合类   1篇
化学工业   232篇
金属工艺   19篇
机械仪表   20篇
建筑科学   15篇
能源动力   29篇
轻工业   102篇
水利工程   7篇
石油天然气   7篇
无线电   116篇
一般工业技术   162篇
冶金工业   61篇
原子能技术   9篇
自动化技术   121篇
  2024年   4篇
  2023年   18篇
  2022年   50篇
  2021年   53篇
  2020年   47篇
  2019年   47篇
  2018年   43篇
  2017年   38篇
  2016年   34篇
  2015年   37篇
  2014年   50篇
  2013年   59篇
  2012年   55篇
  2011年   48篇
  2010年   37篇
  2009年   31篇
  2008年   27篇
  2007年   28篇
  2006年   20篇
  2005年   17篇
  2004年   12篇
  2003年   9篇
  2002年   15篇
  2001年   6篇
  2000年   11篇
  1999年   12篇
  1998年   9篇
  1997年   9篇
  1996年   11篇
  1995年   7篇
  1994年   7篇
  1993年   14篇
  1992年   7篇
  1991年   5篇
  1990年   3篇
  1989年   2篇
  1988年   5篇
  1987年   2篇
  1986年   3篇
  1985年   2篇
  1983年   3篇
  1982年   3篇
  1981年   4篇
  1980年   2篇
  1979年   4篇
  1977年   1篇
  1975年   1篇
  1967年   1篇
  1966年   1篇
排序方式: 共有914条查询结果,搜索用时 0 毫秒
901.
BACKGROUND: Methionine (Met) being the first limiting amino acid in maize/soybean‐based quail diets, its supplementation provides scope for improvement of protein quality and reduction of dietary protein concentration. The question remains to what extent it can be incorporated in the diet of genetically improved quails. Therefore the effect of dietary Met level was assessed on growth performance and immune response in growing Japanese quails (n = 400) divided equally into 20 groups. Five dietary treatments (~230 g kg?1 crude protein and 12.14 MJ kg?1 metabolisable energy) were formulated with 3.5, 4.5, 5.0, 5.5 and 6.0 g kg?1 Met respectively, and each was offered to four groups of birds from 0 to 35 days of age. RESULTS: Live weight at day 35 increased (P < 0.0001) up to 5.0 g kg?1 dietary Met level but did not improve further at higher Met levels (5.5 and 6.0 g kg?1). Improved (P < 0.039) feed conversion ratio was achieved at 5.5 g kg?1 Met level, which was statistically similar to that at 5.0 g kg?1 Met level during 0–14 days of age. Cellular (phytohaemagglutinin from Phaseolus vulgaris) immune response increased (P < 0.0001) with increasing dietary Met concentration, whereas humoral (sheep red blood cells) immune response did not differ. CONCLUSION: The optimal requirement of Met was 5.0 g kg?1 for growth and 5.5 g kg?1 for maximum cellular immune response. Copyright © 2009 Society of Chemical Industry  相似文献   
902.
With an ever-increasing demand for clean label products, there is a greater need for efficient and environmentally friendly processes to compete the conventional thermal or chemical treatments. For instance, high-pressure processing (HPP) has been widely studied in the fruit industry from the last two decades. HPP can inactivate or activate different enzymes in fruit juices, pulp, and purées. HPP treatment inactivates the enzymes by the alterating the conformation of the protein structure and the active site. Depending on the enzyme, pressure, pH, temperature and treatment time, HPP can increase enzyme activity due to the release of membrane-bound enzymes and also due to changes in protein conformation and active site that facilitate interaction with the substrate. Furthermore, the combination of high pressure, temperature and reduced treatment times offered greater inactivation of enzymes in fruit beverages. This study aimed to investigate the inactivation kinetics of endogenous enzymes in fruit beverages.  相似文献   
903.
3-Monochloropropane-1,2-diol (3-MCPD) as a main source of food contamination has always been known as a carcinogenic agent. Kidney, liver, testis, and heart seem to be the main target organs for 3-MCPD. Because oxidative stress and mitochondrial dysfunction have been realized to be involved in 3-MCPD-induced cytotoxicity, the present study aimed to investigate the probable toxicity mechanisms of 3-MCPD in isolated mitochondria, HEK-293 cell line, and cell isolated from the rats’ liver and kidney through measuring multiparametric oxidative stress assay. Based on the data indicating no significant difference between 3-MCPD-treated groups and control group, metabolites of 3-MCPD have a key role in organ toxicity caused by them. To further investigating the suggested hypothesis, the effect of 3-MCPD toxicity on HEK-293 cell line was examined. Although the proliferation declined after exposure to a low dose of 3-MCPD (10 to 200 µM), controversial responses in higher concentration (2 to 10 mM) have led to studies on the effect of oxidative stress and cell death signaling on isolated kidney and liver cells. Treatment of the isolated kidney and liver cells with 3-MCPD resulted in an increase in the level of reactive oxygen species (ROS), the collapse of mitochondrial membrane potential (MMP), and activation of cell death signaling without creating any significant difference in the amount of reduced glutathione. In fact, 3-MCPD can disrupt the mitochondrial electron transfer in isolated cells, which is correlated with the impairment of mitochondrial oxidative phosphorylation system, the rise of ROS level, and the failure of MMP, leading to the release of cytochrome c from mitochondria to cytosol and finally the activation of cell death signaling.  相似文献   
904.
Grapefruit juice was investigated using pulsed electric fields (PEF) with (electric field strengths: 0, 5, 10, 15, 20 and 25 kV cm?1; flow rate: 80 mL min?1; pulse frequency: 1 kHz at 40 °C for 600 μs). Total phenolics, DPPH, total antioxidant capacity (TAC), total anthocyanins, total carotenoids, sugars and physicochemical properties of grapefruit juice were studied. In addition, the effect of PEF treatment on micro‐organisms was also observed. Results indicated that no significant change was observed in pH, Brix, titratable acidity, sugars, total anthocyanins and colour attributes with the increase in pulsed electric strength as compared to control treatment. However, significant decrease in nonenzymatic browning (NEB) and viscosity while an increase in cloud value, DPPH, TAC, total phenolics and total carotenoids, while reduction in the activity of micro‐organisms, was also observed with the increase in pulsed electric strength as compared to control treatment. This study suggested that PEF at 25 kV cm?1 could improve the quality of grapefruit juice.  相似文献   
905.
Biogenic amine formation and bacterial growth of vacuum‐packed European anchovy treated with 1% lemon balm (LB) or lavender (LD) ethanol extracts was investigated. The treated samples were stored at 2 ± 1 °C for 11 d and analyzed for biogenic amines, total viable count, fecal coliform count, and lactic acid bacterial count. The analyses were done on 0, 4, 7, 9, and 11 d of storage. Both LB and LD extracts proved effective in reducing most biogenic amines, with histamine reduced by 3‐fold compared to control. The calculated biogenic amine index showed that LB extract was the most effective in inhibiting the biogenic amine formation. The reduction in total viable count was low and the bacterial contamination reached more than 7 log cfu/g at the end of the storage period for all the samples. Moreover, the reduction in fecal coliform and lactic acid bacterial count by LB and LD extracts was below 1 log cfu/g. Treatment of European anchovy with LB and LD extracts proved to be a very effective preservation technique to reduce the biogenic amine formation and lower the risk of histamine fish poisoning but is not effective in reduction of bacterial load. Consequently, LB and LD extracts could be used to reduce the biogenic amine formation which provides additional safety prior to spoilage for histamine sensitive fish species.  相似文献   
906.
The effect of residual (built up in continued fertilizer experiments) and applied P in Fatehpur loamy sand and Jodhan sandy loam soils of two long term experiments on its availability and uptake by wheat (Triticum aestivum L.) was studied using32P in greenhouse experiment. Dry matter yield increased significantly with carry over P. Response in the absence of residual P was observed up to a direct application of 134 kg P ha?1, whereas, in the presence of carry over P, the response was confined upto 67 kg P ha?1 at site A. The response was however, observed up to 67 kg P ha?1 irrespective of carry over P at site B. Total P uptake by wheat was significantly increased at all levels of residual P. However, it did not differ signficantly among levels of residual P when these were high. The uptake of soil P (residual) increased signficantly with increase in the dose of directly applied P, indicating that addition of inorganic P fertilizer tends to mobilize the native soil P. Per cent utilization of fertilizer P was enhanced in soils having residual P from continuous application of both inorganic and organic P sources.  相似文献   
907.
Journal of Materials Science: Materials in Electronics - Combination nanostructures of metal, semiconductor oxides and carbon materials pursued well in optical and electrical devices. Here we...  相似文献   
908.
Journal of Computational Electronics - LiXH3 (X?=?Cr, Fe, Co, &amp; Zn) hydride type perovskites have been studied by applying density functional theory (DFT), and their structural,...  相似文献   
909.
Rana S  Cho JW 《Nanotechnology》2011,22(27):275609
Core-shell nanowires having multiwalled carbon nanotubes (MWNT) as a core and polypyrrole (PPy) as a shell were synthesized using Cu(I)-catalyzed azide-alkyne cycloaddition click chemistry. According to transmission electron microscopy measurements, the uniform PPy layers of 10-20 nm in thickness were formed well on the MWNT's surface. In particular 'grafting from' click coupling was more effective in obtaining uniform and stable core-shell nanowires as well as in the reaction yield, compared to 'grafting to' click coupling. This is due to chemical bond formation between PPy and MWNT in equal intervals along the longitudinal direction of the MWNT, achieved by 'grafting from' click coupling. As a result, the core-shell nanowires were very stable even in the sonication of nanowires and showed an enhanced electrical conductivity of 80 S cm(-1), due to the synergetic interaction between MWNTs and PPy, which is higher than the conductivity of pure MWNTs and pure PPy. In addition, the core-shell nanowires could show better NO2 gas sensing properties compared to pure MWNTs and pure PPy as well as MWNT/PPy composites prepared by in situ polymerization. The synthesized core-shell nanowires would play an important role in preparing electrical and sensing devices.  相似文献   
910.
This article describes citric acid cross-linked amphiphilic poly(ethylene oxide) (PEO) macroporous open cell polyester amphigel, optimally synthesized using response surface methodology by applying central composite design to screen significant reaction parameters for maximizing percent water sorption. The chemical structure of the amphigel was confirmed by proton nuclear magnetic resonance (1H NMR), FT-IR and the thermal behavior was studied using thermo-gravimetric and DSC. Due to amphiphilic nature, the amphigels also showed high chloroform (1151.33%–1193.33%) and water (755.33%–865%) absorption capacity. Thermal analysis revealed that amphigels are less thermal stability as compared to PEO, however, the degradation process was found to be multi step. The amphigel was effectively used as a carrier for easy loading of a hydrophobic pesticide and showed a slow release of the same.  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