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   306篇
  免费   16篇
  国内免费   1篇
化学工业   46篇
金属工艺   2篇
机械仪表   4篇
建筑科学   5篇
能源动力   4篇
轻工业   230篇
水利工程   11篇
石油天然气   9篇
无线电   1篇
一般工业技术   6篇
冶金工业   1篇
原子能技术   1篇
自动化技术   3篇
  2022年   4篇
  2021年   6篇
  2020年   11篇
  2019年   5篇
  2018年   8篇
  2017年   8篇
  2016年   4篇
  2015年   5篇
  2014年   14篇
  2013年   24篇
  2012年   18篇
  2011年   25篇
  2010年   27篇
  2009年   27篇
  2008年   14篇
  2007年   24篇
  2006年   19篇
  2005年   15篇
  2004年   10篇
  2003年   13篇
  2002年   9篇
  2001年   6篇
  2000年   9篇
  1999年   5篇
  1998年   1篇
  1997年   4篇
  1996年   2篇
  1993年   3篇
  1991年   2篇
  1984年   1篇
排序方式: 共有323条查询结果,搜索用时 31 毫秒
1.
Herring gulls (Larus argentatus) are used as ecological indicators of the coastal Lake Superior ecosystem in Pukaskwa National Park, Ontario, Canada. Their populations have declined by 70 % over the last 40 years, suggesting changes in the park ecosystem. Previous studies highlighted declining prey abundance as a possible contributing factor to population declines. Here, we assess herring gull diets via stable isotope (nitrogen, carbon) and fatty acid indicators to investigate how diet may influence population trends through effects on physiology (stress-related hormones), reproduction (egg size) and behavior (nest attentiveness). Diets were variable among individual herring gulls. Gulls utilizing anthropogenic food sources exhibited reduced levels of stress-associated hormones, increased egg size, and increased nest attentiveness. Anthropogenic food sources are likely buffering the impacts of declines in aquatic food availability; however, populations are still declining. Understanding factors contributing to population trends in ecological indicator species is critical for species management and for identifying stressors that are likely affecting the broader ecosystem. Herring gulls are archetypal examples of the “canary in a coalmine” indicator but in an ecosystem context. Changes in their diets and in variables associated with their physiology, reproduction, and behavior point to very significant changes occurring in the Lake Superior ecosystem. Integrated research across the Great Lakes is required to understand the extent of this change and its implications for the sustainability of wildlife populations.  相似文献   
2.
蛋盒型结构是一种新型的周期性单胞轻质结构,该结构具有低密度、高比强度和吸能能力强等特性。本文通过有限元法建立了平面蛋盒型夹芯板与曲面蛋盒型夹心板的落锤冲击模型,对比分析了其抗冲击特性,并且对不同条件下的蛋盒型结构的动态压缩力学性能进行对比分析。结果表明:受到冲击时的夹芯板会经历三个阶段,其中压缩阶段为主要的吸能阶段,通过将冲击动能转变为夹芯板的塑性耗散能来达到缓冲吸能的目的,同时这些特性依赖于成型高度以及上下面板厚度等结构参数,单胞结构成型高度为6mm、单胞周期为20mm、上下面板板厚为0.5mm、曲率半径为400mm时,复合蛋盒型夹芯板具有更好地力学性能。  相似文献   
3.
The objective of this research was to investigate and compare the effect of different treatments including gaseous ozone (6-ppm/4-min), ultrasound (450 W/4 min) and coating of shellac, lysozyme–chitosan (L-C) on fresh eggs internal quality during storage for six weeks at ambient temperature. The internal quality attributes such as weight loss (WL), albumen viscosity, Haugh unit (HU), yolk index, total soluble solids, albumen and yolk's pH were monitored. Control groups had the worst HU (50.04), WL (8.35%), albumen pH (9.27) and viscosity (7.72 mPa·s) values after storage. The best interior qualities were obtained by shellac coating [HU (72.37), WL (1.37) and viscosity (30.10 mPa·s)] and sonication (albumen pH: 8.22). Thus, the shellac-coated eggs maintained all the internal quality parameters at the highest values, while the ozone and ultrasound only helped to keep the internal quality and enhance the shelf life of eggs.  相似文献   
4.
Europium doped calcium orthosilicate (Ca2SiO4) phosphors have been synthesized by the conventional high temperature solid-state reaction method in various concentrations from agricultural waste (egg shell as a CaO and rice husk as a SiO2). These phosphors structure from X-ray diffraction and morphology from scanning electron microscopy have been examined. Concentration dependent Eu3+ ions luminescent properties in Ca2SiO4 phosphors have been studied from the excitation, emission and decay curves analysis. The 5D07FJ transitions observed in luminescence spectrum allows to determine the site symmetry of the Eu3+ ion. A charge transfer band (CTB) at around 260?nm which is due to the Eu–O interaction in the host along with the 4f – 4f excitation bands due to Eu3+ ions in UV and blue regions are observed. The color co-ordinates determined from emission spectra varies with concentrations of Eu3+ ions and are found to fall in the red region. The decay curves show single exponential behavior for all concentrations of Eu3+ ions (0.01–0.4?mol%) and the lifetimes varied from 2.67 to 2.78?ms. It is worth noting that the present material is found to be far better than many red phosphors synthesized by using agricultural waste as raw materials.  相似文献   
5.
Egg shell waste was used as an activation agent directly for the manufacture of a biomass-derived porous carbon,which possessed a surface area of 626 m~2·g~(-1) and was rich in nitrogen, sulfur and oxygen functionalities. The activation mechanism was proposed, and the carbon showed its potential to act as an adsorbent for the adsorptive removal of various contaminants from both aqueous and non-aqueous solutions, possessing maximum adsorption capacities of 195.9, 185.1, 125.5 and 44.6 mg·g~(-1) for sulfamethoxazole, methyl orange, diclofenac sodium and dibenzothiophene, respectively. Through the utilization of egg shell waste as a sustainable activation agent, this work may help to make the widely applied biomass-derived porous carbons more economical and ecological.  相似文献   
6.
Two alcohols, ethanol and butanol, with different water contents were evaluated for phospholipids (PL) sequential extraction from drum dried egg yolk flakes. It showed that butanol was more effective in extracting total yolk lipids compared to ethanol, but the PL in the extract had the same concentration as in the original yolk total lipid. The use of aqueous ethanol of 95 and 75% resulted in lipid extracts with higher PL concentration during the initial stages of the sequential extraction. When ethanol was further diluted to a concentration of 55%, the solvent lost its PL extraction ability, and the total lipid recovery also decreased dramatically. When both the PL purity and recovery were considered, 75% ethanol was the most effective aqueous alcohol for PL extraction and enrichment from the yolk flakes. In the first stage of extraction using such a solvent, 67% of the total PL in the original yolk was recovered in a lipid fraction with a PL purity of 75%. This study identified the optimal ethanol concentration for PL extraction from dried egg yolk. With this information, the best solid:solvent ratio can be designed to extract and enrich the polar lipids from lipid-bearing materials with known moisture content using a renewable or “green” solvent, ethanol.  相似文献   
7.
The effect of ultraviolet processing (10.6 and 63.7 kJ m(-2)) on selected properties of egg white (absorbance, particle size, protein fractions, free sulfhydryl content, immunoreactivity, viscosity, gelling and foaming properties) was investigated. Ultraviolet exposure induced the development of browning, the formation of large protein aggregates by disulfide exchange, and protein backbone cleavage. However, egg white proteins were differently sensitive to UV radiation. No changes in immunoreactivity, gelling temperature and gel firmness were observed. Independently on the UV dose, light treated egg white produced foams with higher stability. This effect was attributed to protein aggregates jamming in the fluid interstices between bubbles and/or to the higher viscosity of the aqueous phase. The latter was also associated to higher foam volume.  相似文献   
8.
Effects of ozone on functional properties of proteins   总被引:1,自引:0,他引:1  
The present study investigates whether the ozone treatment could be an alternative to improve some functional properties of proteins. Ozone treatment was applied on whey protein isolate and egg white proteins which have been extensively used in food products to improve textural, functional and sensory attributes. Ozone treatment of proteins was performed either in aqueous solutions or as gas ozonation of pure protein powders. Foam formation and foam stability of proteins were enhanced extensively. The solubility of proteins were reduced as influenced from the aqueous and gas ozonation medium. The reduction was more pronounced in egg white proteins. Ozone treatment affected emulsion activity of whey protein isolate negatively and reduced the emulsion stability.  相似文献   
9.
The goal of this contribution was to determine the impact of HIUS on the thermal aggregation, gelation, foaming and emulsifying properties of egg white (EW) proteins.  相似文献   
10.
Meringues are characterized by a predominant air phase and their overall quality is intimately related with microstructure. The formation of meringues microstructure relies on the capacity of egg white (EW) proteins to form voluminous and stable foams and it is ultimately related with the chemical properties of proteins and with the addition of ingredients such as sugars, salts, acids and surfactants.The study aimed at assessing the influence of sugar/EW ratio, citric acid and EW type on the microstructural and mechanical properties of meringues. Meringues prepared with different sugar/EW, citric acid level and different EW type were subjected to microstructural analysis by X-ray microtomography and to mechanical assessment by compression tests.Results demonstrate the ability of X-ray microtomography to reconstruct the 3D microstructure of meringues allowing the measurement of porosity, size, shape and distribution of pores. Citric acid, sugar concentration and EW type play a fundamental role on meringues microstructural parameters and mechanical properties. Low sugar/EW ratios as well as increasing citric acid levels increase the air phase and result in a softer texture of meringues. Moreover, low sugar/EW ratios and increasing citric acid in the meringue result in a reduction of pore size and also influence the shape of pores. Meringues microstructural and mechanical properties are affected by the EW quality: fresh and pasteurized EWs and EWs stored at refrigerated temperatures scored the highest structural and mechanical performances, while powdered and frozen EWs and albumens from old eggs showed the worst results. Not only the balance among ingredients but also the choice of raw materials can strongly affect the final quality of meringues.  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