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   248篇
  免费   20篇
电工技术   2篇
化学工业   72篇
金属工艺   14篇
机械仪表   5篇
建筑科学   4篇
能源动力   7篇
轻工业   46篇
水利工程   2篇
石油天然气   2篇
无线电   12篇
一般工业技术   34篇
冶金工业   38篇
原子能技术   5篇
自动化技术   25篇
  2023年   3篇
  2022年   11篇
  2021年   10篇
  2020年   2篇
  2019年   11篇
  2018年   10篇
  2017年   12篇
  2016年   12篇
  2015年   8篇
  2014年   8篇
  2013年   19篇
  2012年   12篇
  2011年   13篇
  2010年   13篇
  2009年   14篇
  2008年   7篇
  2007年   7篇
  2006年   10篇
  2005年   5篇
  2004年   4篇
  2003年   7篇
  2002年   5篇
  2001年   3篇
  2000年   1篇
  1999年   3篇
  1998年   7篇
  1997年   13篇
  1996年   7篇
  1995年   6篇
  1994年   2篇
  1993年   3篇
  1992年   2篇
  1991年   3篇
  1990年   1篇
  1989年   2篇
  1986年   3篇
  1985年   1篇
  1983年   2篇
  1976年   4篇
  1975年   1篇
  1969年   1篇
排序方式: 共有268条查询结果,搜索用时 15 毫秒
101.
102.
Sixteen Iberian barrows of the same age with an average initial live weight of 100.1kg were randomly distributed in two groups of eight pigs each. One group was fed healthy acorns and the other group received acorns infested of Curculio sp. The subcutaneous backfat from pigs fed healthy acorns had higher C18:1n-9, MUFA and C20:5n-3 and lower C18:0 and SFA proportions than that from the pigs fed acorns infested with Curculio. The consumption of acorns infested with Curculio sp. led to a reduction of C18:1n-9, MUFA, C18:2n-6, C18:3n-3, C22:5n-3 and PUFA proportions in neutral lipids from Longissimus dorsi muscle with respect to consumption of healthy acorns, whereas in polar lipids it produced a reduction in C18:1n-9, MUFA and C18:4n-3 proportions and an increase in C18:2n-6, C20:4n-6, n-6 and C20:5n-3 proportions and of n-6/n-3 ratio with respect to the healthy acorns consumption. The pigs fed healthy acorns had higher intramuscular fat percentage in Longissimus dorsi than pigs fed with acorns infested with Curculio (9.95 vs 7.09% SEM=0.60).  相似文献   
103.
Solar selective surfaces can be constructed in many ways. In particular, low emissivity (ε) is currently sought for by starting with surfaces bearing high infrared reflectance. It is well known that metallic surfaces behave in this way. Then, high solar absorptance (α) can be achieved by adding an appropriate thin layer through a wide variety of possibilities. In this work, a simple direct method to produce such type of coatings on titanium and 304 stainless steel plates is assessed: thermal oxidation. Good selectivities S(=α/ε) 10 or higher in some cases were obtained mainly on steel substrates. An alternative is to expose these metallic surfaces to ionized oxygen species, rather than to neutral oxygen molecules. This was accomplished by oxidizing some plates in a typical glow discharge capacitive system. In this case, acceptable but not so high selectivities, as in the first case, were obtained. Some comments on the metallic surface morphology and the stability of the oxidized surfaces are also presented.  相似文献   
104.
Most food iron in the gut enters into two "common pools" that behave quite differently in terms of absorption. Heme iron present in hemoglobin and myoglobin, is well absorbed and is relatively unaffected by diet composition. Non-heme iron, the form of iron present in vegetables and in man's staples, generally is poorly absorbed and is greatly affected by enhancing or inhibiting substances in the diet. In experiments employing intrinsically-labeled hemoglobin as a tracer, absorption of a dry hemoglobin concentrate added to milk, a rice cereal and wheat cookies, was uniformly good, relatively constant and quite independent from the type of food. In contrast, absorption of iron salts decreases markedly when given with food. The presence or absence of inhibiting or enhancing factors of non-heme iron absorption is determinant in the possibility of obtaining required iron for most people in the world whose diet contains little heme iron. Meat and ascorbic acid are the main enhancers of non-heme food iron absorption. Common inhibitors include carbonates, oxalates, phytate, bran, tea and egg yolk. The enhancing effect of ascorbic acid on the absorption of fortification iron in milk and the effect of tea, eggs or meat on the absorption of bread iron from common Chilean meals are discussed as examples of interactions of food components with non-heme iron.  相似文献   
105.
We have studied the effect of the i.v. administration of 1 g tolbutamide upon glycemia, insulinemia and serotoninemia in normal subjects and obese patients. We have seen an elevation of the last two variables in direct relationship with the previous blood sugar levels. The baseline serotonin level in obese people is higher than in normals, but the tolbutamide induced elevation is of a lesser magnitude. We believe this fact is due to the competitive action of insulin, as our obese patients have shown to have a "hyperinsulinism" with "disinsulinism".  相似文献   
106.
The effect of 2‐(2‐heptadec‐8‐enyl‐4,5‐dihydro‐imidazol‐1‐yl)‐ethylamine on the corrosion behavior of mild steel in aqueous hydrochloric acid was investigated using weight loss measurements, polarization scans, electrochemical impedance, and X‐ray photoelectron spectroscopy (XPS). The inhibition efficiencies and coverage degrees increased with the concentration of inhibitor but decreased proportionally with temperature. It appears that the steric hindrance of the aliphatic chain on the imidazoline ring adsorption may affect inhibitor efficiency. Polarization curves showed that the oleic imidazoline (OI) acted essentially as a mixed type inhibitor, in which the blocking of active sites occurred. As a result of film formation, impedance spectra revealed a considerable increase in the charge transfer resistance as indicated by the second capacitive loop. XPS depth profile analysis observed the presence of nitrogen and carbon species on the inhibitor film, which were associated to the OI.  相似文献   
107.
In this study, the acid resistance and the changes in outer membrane protein (Omps) profiles of Escherichia coli strains isolated from pozol, an acid-fermented maize beverage consumed in Southeastern Mexico, were determined. Results showed that adaptation to acid by these E. coli strains significantly enhances their survival in acid conditions. Changes in Omp profiles were found in non-adapted acid challenged cells compared with non-challenged cells that had not been adapted to acid. Challenged adapted cells showed no significant changes in these profiles when compared with the acid adapted non-challenged strains. N-terminal sequences of some of the Omps were determined. The intensity of the main porins OmpC and OmpA was lower in the acid challenged strains, than in the non-challenged ones. The OmpF porin was identified in non-challenged K12 strain, but did not appear in adapted or non-adapted pozol strains nor in E. coli O157:H7. A protein band with an approximate molecular mass of 22 kDa corresponds to OmpW and its expression decreased in pozol strains challenged with HCl and lactic acid. OmpX was one of the main proteins expressed when strains were acid challenged with organic acids. Seventy out of seventy-three E. coli strains isolated from pozol in a previous work [Sainz, T., Wacher, C., Espinoza, J., Centurion, D., Navarro, A., Molina, J., Cravioto, A., Eslava, C., 2001. Survival and characterization of Escherichia coli strains in a typical Mexican acid-fermented food. International Journal of Food Microbiology 71, 169-176] carry this gene and belong to a reported pathogenic class of E. coli strains, or have virulence factors or survived at pH values less than 4.8. We suggest this protein could be involved in survival to stress conditions.  相似文献   
108.
Pathogenic organisms can be transmitted orally through drinking water or through skin and mucosae by both direct and indirect contact, and their presence in water thus has a negative impact on public health. In wastewater treatment plants (WWTP), water is disinfected to inactivate pathogens. The quantification of several microbial indicators in aquatic systems is required to estimate the biological quality of such systems. So far, coliform bacteria have been used as traditional indicators world-wide. This study has assessed the resistance of total coliforms, Escherichia coli, Pseudomonas aeruginosa and Enterococcus faecalis to three dosages of sodium hypochlorite (NaClO) at two exposure times. The bacteria were isolated from secondary effluents of a WWTP located in Hidalgo, Mexico. The results show that the number of colony-forming units of all studied bacterial types decreased when both the NaClO concentration and exposure times increased. However, they were not eliminated. The inclusion of the species Pseudomonas aeruginosa in regulations for treated wastewater quality as a new indicator is highly recommended due to its importance as an opportunistic pathogen. The detection of this species along with the traditional organisms could be particulary significant for reclaimed water to be used with direct human contact.  相似文献   
109.
We describe chemical separation and mass spectrometric procedures for the measurement of radium isotopes in geologic samples. These methods provide 226Ra/228Ra ratio measurements for 1 g or less of rock sample containing subpicogram amounts of radium with precision better than 1.5% (95% confidence level). Radium-226 concentrations were measured by isotope dilution for smaller sample sizes (100-500 mg) containing as little as 1-10 fg of total 226Ra with similar high precision.  相似文献   
110.
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