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   263篇
  免费   15篇
  国内免费   6篇
电工技术   1篇
综合类   14篇
化学工业   17篇
机械仪表   4篇
建筑科学   24篇
能源动力   16篇
轻工业   125篇
水利工程   21篇
石油天然气   14篇
无线电   10篇
一般工业技术   8篇
冶金工业   12篇
原子能技术   3篇
自动化技术   15篇
  2024年   2篇
  2023年   2篇
  2022年   5篇
  2021年   8篇
  2020年   4篇
  2019年   4篇
  2018年   8篇
  2017年   9篇
  2016年   7篇
  2015年   8篇
  2014年   15篇
  2013年   16篇
  2012年   18篇
  2011年   24篇
  2010年   11篇
  2009年   22篇
  2008年   21篇
  2007年   7篇
  2006年   12篇
  2005年   6篇
  2004年   9篇
  2003年   6篇
  2002年   6篇
  2001年   8篇
  2000年   9篇
  1999年   2篇
  1998年   5篇
  1997年   3篇
  1996年   7篇
  1995年   6篇
  1994年   8篇
  1993年   2篇
  1988年   2篇
  1987年   1篇
  1985年   1篇
排序方式: 共有284条查询结果,搜索用时 15 毫秒
51.
52.
The Pacific Tracker (PacTrac) is a computer program designed to analyse food intakes of individuals from the Pacific Region. PacTrac’s original output included servings of daily intake of food groups according to the United States Food Guide Pyramid, nutrient intake recommendations, and a comparison to other national nutrition recommendations. PacTrac was made available for public use through the Hawaii Foods website (hawaiifoods.hawaii.edu). PacTrac2 is an updated and expanded version of PacTrac that uses the United States MyPyramid/MyPlate food groups in household units of daily intake, rather than servings. In addition, the PacTrac2 includes a physical activity analysis tool which quantifies minutes of physical activities and their intensities based on energy estimates from the compendium of physical activity and research on children. An Expert System (ES) – a computerised decision tree to guide behaviour change – was developed using information on self-efficacy and stage of readiness to change, and the fruit and vegetable intake and physical activity information from PacTrac2. The ES produces reports for the child, the parent/guardian, and the child’s physician with child-specific strategies, targeted behavioural information, and feedback tailored to the child. PacTrac2-ES was designed for the Pacific Kids DASH for Health (PacDASH) intervention study, conducted in the Kaiser Permanente health care system in Hawaii. The intervention is based on the child’s self-efficacy and stage of readiness to change intake of fruits and vegetables and physical activity, with a goal of maintaining body weight to prevent obesity. The intervention is complemented with stage-based mailers addressing the environment for physical activity and fruit and vegetable intake and newsletters that address related behaviours (sedentary activity and a DASH eating approach). This project is the first to expand the PacTrac to contain children’s foods and physical activities from the Pacific Region and to use current US MyPyramid/MyPlate food and physical activity analysis and guidance systems, and to develop and implement an Expert System for fruits, vegetables and physical activity of 5–8-year-old children. The PacTrac2-ES was used in the PacDASH study and will be used for other programs to promote healthy eating and physical activity of children in the Pacific Region.  相似文献   
53.
Cadmium (Cd), mercury (Hg), arsenic (As), lead (Pb) and tin (Sn) concentrations were determined using ICP-MS in soft tissues (wet wt.) from whole greenshell mussels (Perna canaliculus) collected from Urapukapuka-Rawhiti Island, Opua Marina, Waitangi Bridge and Opua Wharf from the Bay of Islands, northern New Zealand (NZ). All samples had metal concentrations well below the Food Standards Australia and New Zealand (FSANZ) maximum limits and were comparable to, or less than, concentrations observed in previous NZ studies. Based on the average values detected in the current study, the concentrations of heavy metals ingested in a ‘typical diet’ containing greenshell mussels are below the provisional tolerable weekly intake (PTWI). However, Māori (indigenous people of New Zealand), Pacific Islanders and Asians consume a far greater quantity of seafood (and therefore heavy metals) than the general public of New Zealand and could potentially consume enough shellfish to exceed the PTWI for Cd (but not for Hg, As, Pb or Sn). Although our results, based on the current PTWIs, indicate no significant health risk to greenshell mussel consumers in this region, PTWIs change over time; concentrations which were thought to be safe are later found to be harmful. Additionally, differences in individual human susceptibilities to various toxins could increase the risk of harm for consumers with low tolerance to heavy metals. We suggest that a survey of the frequency, amount and species consumed by groups whose diet may be largely shellfish-based is required to enable a more comprehensive risk assessment to be made.  相似文献   
54.
Bullfrogs (Rana catesbeiana), native to eastern North America, were introduced into Oregon in the 1930's. Bullfrogs are highly efficient predators that are known to eat a variety of prey including other amphibians. In laboratory experiments, we investigated whether juvenile Pacific treefrogs (Hyla regilla) recognize adult bullfrogs as a predatory threat. The ability of prey animals to acquire recognition of an introduced predator has important implications for survival of the prey. We found that treefrogs from a population that co-occurred with bullfrogs showed a strong avoidance of chemical cues of bullfrogs. In contrast, treefrogs from a population that did not co-occur with bullfrogs, did not respond to the bullfrog cues. Additional experiments showed that both populations of treefrogs use chemical cues to mediate predation risk. Treefrogs from both populations avoided chemical alarm cues from injured conspecifics.  相似文献   
55.
为研究阿魏酸、绿原酸、咖啡酸三种天然保鲜剂对预制南美白对虾冷藏(4℃)期间品质变化影响,以菌落总数(Total Bacterial Count,TBC)、挥发性盐基氮(Total Volatile Base Nitrogen,TVB-N)、pH、硫代巴比妥酸值(Thiobarbituric Acid Reactive ...  相似文献   
56.
Heat treatment is a convenient way to eliminate the effects of endogenous enzymes on the industrial production of stable products. This study describes the preparation of protein isolates from oysters (OPI and HOPI) and krill (KPI and HKPI) by isoelectric solubilisation/precipitation (ISP) with or without heat pretreatment and comparatively presents their characteristics. The results showed that the solubilities of HOPI (24.08 ± 1.94%) and HKPI (42.29 ± 0.78%) were higher than those of OPI (13.46 ± 0.78%) and KPI (21.71.46 ± 1.51%), and the free and total sulphhydryl (-SH) content and surface hydrophobicity of HOPI and HKPI were higher than those of OPI and KPI, which are related to higher fat content of HOPI (10.37 ± 0.55%) and HKPI (34.89 ± 1.19%). SDS–PAGE and gel chromatography pattern results showed that macromolecular proteins were degraded by endogenous enzymes in OPI and KPI, while they remained unaffected in HOPI and HKPI. The FT-IR spectra showed similar patterns between OPI and HOPI and between KPI and HKPI. While the essential amino acid content was similar for OPI and HOPI (47.06 ± 1.33% and 47.93 ± 1.02%), that of KPI and HKPI (50.89 ± 0.89% and 51.19 ± 1.11%, respectively) was not significantly different.  相似文献   
57.
58.
亚太地区大豆质量标准对比分析   总被引:1,自引:0,他引:1       下载免费PDF全文
大豆是世界各国主要种植的粮食作物之一,因富含脂肪和蛋白质使其成为重要的粮食贸易品种。2018年全球大豆产量已达到3.66亿t,其中美国、巴西、阿根廷3个经济体的大豆产量共占全球总产量80%左右。为推动亚太地区各经济体粮食标准互联互通,促进亚太地区粮食贸易便利化和一体化,对包括中国、美国、澳大利亚、加拿大、日本、韩国、墨西哥、菲律宾、泰国、中国台北等10个亚太经合组织经济体及巴西、阿根廷等2个大豆主产国,共12个经济体的大豆标准进行了系统分析;找出标准适用范围、产品分类、等级划分和等级参数有关质量指标等方面的相同和差异之处,对促进亚太地区大豆标准互联互通提出了建议,可为从事粮食标准化、品质检验、大豆进出口贸易的粮食工作者提供参考。  相似文献   
59.
Editorial     
Automated scanning microphotometry provides an objective assessment of the distribution of metal-bearing (MB) amoebocytes in various tissues of the Pacific oyster, Crassostrea gigas. Silver-staining of these cells in paraffin-embedded sections gave good histochemical enhancement for effective photometric discrimination. Metal-associated pixel fractions (MAPF) for 0.41 mm2 tissue-fields were calculated from the results of microphotometric scans, giving an estimate of the metal content and an expression of the population density of MB cells. Gut-associated MB cells in oysters obtained from two geographically-separate metalliferous estuaries had similar distribution patterns, with MAPF values that correlated with metal concentrations in visceral mass determined by atomic absorption spectrophotometry (AAS). The metal content of other tissues varied by two orders of magnitude, the gill having the highest MAPF values. Intermediate MAPF values were found for digestive diverticula and the lowest values in the gonad. There was little difference between gut-associated MB cell populations in oysters from the two collection sites, despite differences in size, glycogen content and gonadal maturation. This non-destructive method of tissue microanalysis may provide a better way of assessing tissue metal-load in individual organisms, and one that is independent of physiological variables.  相似文献   
60.
本文基于产权主体理论研究了内部人控制的问题,并认为:内部人控制势必会为企业带来较大的公司治理风险,影响企业整体组织利益,不能较好地实现公司持续发展。通过分析内部入控制带来的问题并结合太平洋建设:集团的“严氏试验”案例,对内部人控制问题进行了案例论证,得出了相应的研究结论。  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