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   274篇
  免费   28篇
电工技术   2篇
化学工业   104篇
机械仪表   1篇
建筑科学   9篇
能源动力   3篇
轻工业   60篇
水利工程   3篇
无线电   11篇
一般工业技术   39篇
冶金工业   45篇
原子能技术   1篇
自动化技术   24篇
  2024年   2篇
  2023年   12篇
  2022年   25篇
  2021年   26篇
  2020年   8篇
  2019年   14篇
  2018年   8篇
  2017年   11篇
  2016年   11篇
  2015年   14篇
  2014年   6篇
  2013年   22篇
  2012年   9篇
  2011年   16篇
  2010年   8篇
  2009年   5篇
  2008年   10篇
  2007年   19篇
  2006年   9篇
  2005年   5篇
  2004年   7篇
  2003年   3篇
  2002年   6篇
  2001年   5篇
  2000年   2篇
  1999年   3篇
  1998年   5篇
  1997年   5篇
  1996年   3篇
  1995年   4篇
  1994年   4篇
  1992年   2篇
  1991年   1篇
  1990年   6篇
  1986年   2篇
  1984年   1篇
  1982年   1篇
  1980年   1篇
  1975年   1篇
排序方式: 共有302条查询结果,搜索用时 13 毫秒
101.
Magnetic Resonance Materials in Physics, Biology and Medicine - To investigate the effects of a range of parameter settings on T1 measurement stability in the portal vein using the T1-mapping...  相似文献   
102.
Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) have been identified as metabolites of PBDEs, and also as compounds of natural origin in the marine environment; however, there has only been very limited study of their presence in the abiotic environment. In the present study, OH-PBDEs were determined in samples of surface water and precipitation (rain and snow) collected from sites in Ontario, Canada. OH-PBDEs were detected in all the samples analyzed, although half of the observed peaks did not correspond to any of the 18 authentic standards available. Fluxes of sigmaOH-PBDEs ranged from 3.5 to 190 pg/m2 in snow and from 15 to 170 pg/m2/day in rain, and those were higher at three of the southern Ontario locations relative to a single northern remote site. Concentrations of sigmaOH-PBDEs ranged from 2.2 to 70 pg/L in water and from < 1 to 420 pg/g in particulate organic carbon (POC), and higher values were found near sewage treatment plant (STP) outfalls in Lake Ontario. Partition coefficients (log K(oc)) for OH-PBDEs ranged from 4.0 to 5.1. The results in this study suggest that OH-PBDEs are ubiquitous in the abiotic environment and most likely are produced through reaction of PBDEs with atmospheric OH radicals. As well, they may be present in surface waters near STPs due to oxidation of PBDEs and inflows from metabolism by humans and animals.  相似文献   
103.
Recent spikes in world food and energy prices have fostered renewed momentum for agricultural investment in lower and middle-income countries. Governments in some food-importing countries are promoting the acquisition of land overseas as a means to ensure long-term national food security. Businesses are recognizing new opportunities for strong returns from international investments in agriculture for food, fuel and other agricultural commodities. Dubbed ‘land grabs’ in the media, land-based investments have kindled much international debate, in which strong positions are taken on the impacts of such investments on environment, rights, sovereignty, livelihoods, development and conflict at local, national and international levels. Depending on how they are structured, agricultural investments may deliver local benefits and include small-scale producers in value chains, or carry environmental and social risks that fall disproportionately on local people. Vigorous public debate in recipient countries, effective screening of proposed investments, including robust environmental and social impact assessments, secure local land and resource rights, local voice in decision-making, skillfully negotiated and regulated contracts and effective policy incentives for business models that favor working with local farmers over large plantations can help make the renewed momentum in agricultural investment work for development.  相似文献   
104.
Abstract: The growth of bifidobacteria that are employed in the production of functional food is often slow or limited, even on synthetic media. In this study, we investigated whether a peptide hydrolyzate (functional animal protein [FAP]), from poultry bones and meat trimmings, could be a potential source of growth stimulators. The bifidogenic activity of FAP on 18 strains of Bifidobacterium species was assessed via 2 different techniques: turbidimetric measurements and a direct count by fluorescence microscopy. Growth experiments were performed in B12 broth as the basal medium, B12 broth supplemented with N‐acetylglucosamine, and B12 broth supplemented with FAP. FAP supplementation yielded the highest maximum optical density (OD) and count values. The use of the microscopic fluorescence counts allowed for better evaluation of the extent of growth and assessment of the viability of cells. FAP from poultry bones and meat trimmings has potential as a growth stimulator for different bifidobacteria of human origin. FAP is a promising ingredient for inclusion in industrial media that are used to culture probiotic strains, including bifidobacteria, because it supports growth very well and maintains cells at a high level of viability. Practical Application: Proteinaceous hydrolyzate can be considered a promising ingredient for industrial media that are used to culture probiotic strains, including bifidobacteria, because it improves bacterial growth and maintains cells at a high level of viability.  相似文献   
105.
Flavour development and overall eating quality of pork semimembranosus were investigated with regard to different raw meat qualities (feeding/fasting strategy; control/low glycogen level, gender; castrate/female, slaughter live-weight; 84 kg/110 kg) combined with frying temperature (150 °C/240 °C). It was further investigated whether the precursor levels of glycogen, IMP, inosine, and hypoxanthine in the raw meat were correlated to the raw meat quality and fried/grilled attributes. Pork schnitzels were fried on a pan (155 °C) or grill–pan (240–250 °C) to a core temperature of 70 °C. Frying temperature was the one factor with greatest influence on the sensory attributes, and pan-grilled schnitzels had significantly higher scores in fried/grilled attributes regardless of meat quality compared to pan-fried schnitzels. Texture was not appreciably influenced by any treatment. There was no correlation between precursor levels and raw meat qualities or fried sensory attributes. Gender and slaughter live-weight had no pronounced influence on flavour and overall eating quality.  相似文献   
106.
107.
In this article, we characterize in terms of analytic tableaux the repairs of inconsistent relational databases, that is databases that do not satisfy a given set of integrity constraints. For this purpose we provide closing and opening criteria for branches in tableaux that are built for database instances and their integrity constraints. We use the tableaux based characterization as a basis for consistent query answering, that is for retrieving from the database answers to queries that are consistent with respect to the integrity constraints.  相似文献   
108.
Data collected over a 3-year study of a high arctic watershed and lake are used to understand the fate of organochlorine compounds (OCs) and form the basis of a mass balance contaminant fate model. The model uses the fugacity/aquivalence approach to describe OC dynamics between air, stream inflows and outflow, the water column, and surficial sediments. The steady-state model results indicate that stream inflows contributed from 96 to >99% of total chemical loadings, but 57-98% of total loadings were lost from the lake via the outlet, the percentage of which is controlled by the hydrologic regime of the high arctic lake. Conversely, only 0.4-3.4% of loadings were retained within the sediments due to the high export rate, minimal scavenging from the water column and low organic carbon fraction of the sediments. Using the unsteady-state model, which includes year-round processes, degradation was estimated to account for losses of 7-32% for the more persistent OCs and 42-50% for the less persistent OCs (alpha-HCH, gamma-HCH, and endosulfan I). If loadings were eliminated, water column concentrations would decline with half-lives <1 year for less persistent OCs and 1-2 years for the more persistent OCs, whereas the half-lives for OCs in sediment are 8-25 years.  相似文献   
109.
The use of agro-industrial waste for food enrichment can be limited, due to taste, odour, colour and other unpleasant characteristics. Trub (brewing waste) has important nutrients, such as proteins and carbohydrates, and phytochemical compounds; however, its applications are hindered by the astringent flavour. In order to reduce the bitterness of trub, aqueous extractions were realized at high temperature (100 °C per 1 h) in five steps. Two fractions were obtained; a liquid fraction (containing bitter compounds) and a solid fraction (the trub after the extraction process; TAP). Both fractions and the trub before the extraction process (TBP) were evaluated. The bitterness of TBP was significantly reduced in TAP while the protein content increased; TAP presented a branched network and changes in its structure. The reduction in bitterness and the high protein content allows the use of trub in the food industry.  相似文献   
110.
Annually averaged concentrations and enantiomeric compositions of organochlorine pesticides (OCPs) in air were determined in 2000/2001 at 40 stations across North America using XAD-based passive samplers. Absolute concentration differences acrossthe continent, the skewness and kurtosis of the concentration distribution, the relative abundance of parent compound and metabolites, and the chiral signatures can identify regional sources of OCP to the atmosphere. Specifically, air samples collected in the southeastern United States had elevated concentrations of chlordane-related compounds, higher ratios of trans- to cis-chlordane and heptachlor to heptachlor epoxide, as well as higher enantiomeric fractions of trans-chlordane as compared to other regions, suggesting continued release of microbially unprocessed chlordane to the regional atmosphere. Similarly, greatly elevated concentrations of p,p'-DDT, low relative abundance of the metabolite DDE, and a racemic composition of o,p'-DDT in samples from southern Mexico and Belize indicate recent use of DDT in these regions. Belize is also a potential source region for dieldrin. Reflecting its continued use in North America, endosulfan is now one of the most abundant and ubiquitous OCPs in the continental atmosphere. In contrast to these OCPs, air concentrations of penta- and hexachlorobenzene vary only by factors of 2-4 across the continent, reflecting a long atmospheric residence time and few primary sources. Atmospheric levels of the chlorobenzenes, alpha-endosulfan, and p,p'-DDE increase with elevation in the Canadian Rocky Mountains. Empirical travel distances for the OCPs derived from latitudinal concentration profiles are in good agreementwith model-derived indicators of long-range transport potential and, in particular, lead to a similar categorization of the OCPs. Large-scale passive air sampling networks are suitable for monitoring compliance with, and effectiveness of, regulatory control measures and for establishing experimentally the atmospheric long-range transport behavior of organic air pollutants.  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