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   819篇
  免费   49篇
  国内免费   5篇
电工技术   5篇
综合类   4篇
化学工业   262篇
金属工艺   4篇
机械仪表   18篇
建筑科学   33篇
矿业工程   2篇
能源动力   31篇
轻工业   176篇
水利工程   8篇
石油天然气   9篇
无线电   24篇
一般工业技术   101篇
冶金工业   79篇
原子能技术   3篇
自动化技术   114篇
  2024年   1篇
  2023年   11篇
  2022年   33篇
  2021年   30篇
  2020年   18篇
  2019年   31篇
  2018年   25篇
  2017年   29篇
  2016年   24篇
  2015年   30篇
  2014年   43篇
  2013年   59篇
  2012年   38篇
  2011年   67篇
  2010年   43篇
  2009年   45篇
  2008年   50篇
  2007年   39篇
  2006年   28篇
  2005年   25篇
  2004年   20篇
  2003年   21篇
  2002年   14篇
  2001年   14篇
  2000年   7篇
  1999年   14篇
  1998年   35篇
  1997年   13篇
  1996年   12篇
  1995年   7篇
  1994年   9篇
  1993年   3篇
  1992年   3篇
  1991年   3篇
  1990年   5篇
  1989年   2篇
  1988年   2篇
  1986年   1篇
  1985年   7篇
  1984年   1篇
  1980年   1篇
  1979年   1篇
  1978年   1篇
  1976年   4篇
  1975年   1篇
  1971年   2篇
  1968年   1篇
排序方式: 共有873条查询结果,搜索用时 15 毫秒
21.
This work assessed the risk of protozoa in 10 school restaurants in Armenia (Quindío, Colombia) by analyzing the presence of Cryptosporidium spp, Giardia duodenalis, Blastocystis, and Cyclospora cayetanensis DNA in the food, water, and living and inert surfaces of school restaurants and in stools of children who ate at these restaurants. Of the 213 food, water, and surface samples, 6.6% were positive using PCR to test DNA for Blastocystis; 3.8% for Cryptosporidium spp; 0.9% for G. duodenalis; and 0% for C. cayetanensis. In 187 stool samples analyzed via microscopy from children who attended the restaurants, 40 (21.4%) were positive for Blastocystis and 21 (11.2%) were positive for Giardia spp. Via PCR, 20 (10.7%) were positive for Cryptosporidium and 0 (0%) for C. cayetanensis. A higher positivity in children's stools for Blastocystis spp was correlated with lower compliance in property conditions and for higher positivity of Giardia spp in children's stool was related to lower knowledge by food manipulators. Inspection scores can identify restaurants with higher risk for protozoa infection.  相似文献   
22.
The objective of this study was to characterise the nutritional potential of leaves and identify a diversity centre with low cyanide and high nutrient content among 178 Latin American cassava genotypes. This field-based collection represents the seven diversity centres, held at The International Center for Tropical Agriculture (CIAT Palmira, Colombia) by the Cassava Program. The cyanide, all-trans-β-carotene and lutein concentrations in cassava leaves ranged from 346 to 7484 ppm dry basis (db), from 174–547 μg g−1 db and 15–181 μg g−1 db, respectively. Cassava leaves also showed significant levels of essential amino acids leucine, lysine, phenylalanine, valine and threonine, and average total protein content of 26.24 g 100 g−1 db. Among seven diversity centres, South American rainforest group showed low cyanide and high carotene content in leaves. In addition, VEN77 and PAN51 genotypes stood out for having low cyanide in leaves and roots and high carotene in leaves. This genetic diversity can be used to select high potential progenitors for breeding purposes.  相似文献   
23.
Aqueous and hydroalcoholic extracts from Verbena officinalis L. were obtained and characterised. The analysis by HPLC-DAD and LC-MS allowed the detection and identification of three iridoids, fifteen flavonoids and four phenolic acid derivatives. Four flavonoids, scutellarein 7-diglucuronide (9), scutellarein 7-glucuronide (13), pedalitin 6-galactoside (15) and scutellarein 7-glucoside (19) are reported for the first time from this plant. In addition, three new flavonoids have been isolated: scutellarein 7-O-(2-O-feruloyl)-diglucuronide (5), pedalitin 6-O-diglucuronide (6) and pedalitin 6-O-(2-O-feruloyl)-diglucuronide (13). To our knowledge, these flavonoids have not been reported as natural products. Both extracts showed significant antioxidant activity using three in vitro model systems and the results have been correlated with total phenolic and total flavonoid contents. The results have allowed establishing an important relation structure-activity and significant correlations have also been found between the mineral content and the flavonoids present in both extracts.  相似文献   
24.
25.
26.
The aim of the present research was to study changes in milk composition and fatty acid profile, specifically conjugated linoleic acid (CLA) and its isomers, in goat milk as affected by dietary supplementation of sun-flower oil and whole linseed (0.81 and 1.84% of dry matter on basal diet, respectively) and to assess the persistency of the response. To achieve this objective, bulk milk from a herd and from 6 individual dairy goats fed a diet supplemented with sunflower oil and whole linseed was monitored for a period of 3 mo. Gas chromatography and silver ion HPLC were used to analyze total CLA content and the isomeric profile of these fatty acids, respectively. The contents of α-linolenic acid increased from 0.35% with the reference diet to 0.62% with the supplemented diet. Similarly, CLA milk content increased from 0.46 to 1.18%. The same pattern was also observed for trans-11 C18:1 (1.38 to 4.05%, respectively) in goat milk after 3 mo of lipid supplementation. In contrast, changes in other trans C18:1 isomers were less remarkable. There was a strong linear correlation between cis-9, trans-11 C18:2, the main CLA isomer, and trans-11 C18:1 under the conditions assayed and their concentration remained stable throughout the duration of the study. Levels of the minor CLA isomers were also enhanced as a consequence of lipid supplementation. The most remarkable increases were observed for 11-13 (trans-trans and trans-cis geometric isomers), whereas trans-7, cis-9 (the second most important CLA isomer from a quantitative point of view) and trans-10, cis-12 increased only slightly with lipid supplementation.  相似文献   
27.
BACKGROUND: Plant tannins as rumen modifiers are better than chemicals or antibiotic‐based modifiers since these compounds are natural products which are environmentally friendly and therefore have a better acceptance with regard to feed safety issues. Tropical plants containing phenols such as tannins were found to suppress or eliminate protozoa from the rumen and reduce methane and ammonia production. The screening of these plants is an important step in the identification of new compounds and feed additives which might contribute to mitigate rumen methanogenesis. The present study was carried out to determine the efficacy of tannins from tropical tree leaves for their methane reduction properties. RESULTS: Activity of tannins, as represented by the increase in gas volume with the addition of polyethylene glycol (PEG)‐6000 as a tannin binder (tannin bioassay) was highest in Ficus bengalensis (555%), followed by Azardirachta indica (78.5%). PEG addition did not alter (P > 0.05) methane percentage in Ficus racemosa, Glyricidia maculata, Leucena leucocephala, Morus alba and Semaroba glauca, confirming that tannins in these samples did not affect methanogenesis. The increase (P < 0.05) in protozoa population with PEG was maximal in Ficus religiosa (50), followed by Moringa oleifera (31.2), Azardirachta indica (29.9) and Semaroba glauca (27.5). There was no change (P > 0.05) in the protozoa population in Autocarpus integrifolia, Ficus bengalensis, Jatropha curcus, Morus alba and Sesbania grandiflora, demonstrating that methane reduction observed in these samples per se was not due to defaunation effect of the tannin. The increase in total volatile fatty acid concentration in samples with PEG ranged from 0.6% to > 70%. The highest increase (%) in NH3‐N was recorded in Azardirachta indica (67.4), followed by Ficus mysoriensis (35.7) and Semaroba glauca (32.6) leaves, reflecting strong protein binding properties of tannin. CONCLUSION: The results of our study established that in vitro methanogenesis was not essentially related to the density of protozoa population. Tropical tree leaves containing tannins such as Autocarpus integrifolia, Jatropha curcus and Sesbania grandiflora have the potential to suppress methanogenesis. Therefore tannins contained in these plants could be of interest in the development of new additives in ruminant nutrition. Copyright © 2012 Society of Chemical Industry  相似文献   
28.
Lipopolysaccharide (LPS)-induced endotoxemia induces an acute systemic inflammatory response that mimics some important features of sepsis, the disease with the highest mortality rate worldwide. In this work, we have analyzed a murine model of endotoxemia based on a single intraperitoneal injection of 5 mg/kg of LPS. We took advantage of galectin-3 (Gal3) knockout mice and found that the absence of Gal3 decreased the mortality rate oflethal endotoxemia in the first 80 h after the administration of LPS, along with a reduction in the tissular damage in several organs measured by electron microscopy. Using flow cytometry, we demonstrated that, in control conditions, peripheral immune cells, especially monocytes, exhibited high levels of Gal3, which were early depleted in response to LPS injection, thus suggesting Gal3 release under endotoxemia conditions. However, serum levels of Gal3 early decreased in response to LPS challenge (1 h), an indication that Gal3 may be extravasated to peripheral organs. Indeed, analysis of Gal3 in peripheral organs revealed a robust up-regulation of Gal3 36 h after LPS injection. Taken together, these results demonstrate the important role that Gal3 could play in the development of systemic inflammation, a well-established feature of sepsis, thus opening new and promising therapeutic options for these harmful conditions.  相似文献   
29.
The ability of five strains of different bifidobacterial species (Bifidobacterium animalis, B. bifidum, B. infantis, B. longum, B. pseudolongum) isolated from human and animal gut to degrade myo-inositol hexaphosphate or phytic acid (InsP(6)) has been evaluated. The disappearance of phytate and the generation of lower myo-inositol phosphates were determined in a complex medium in which phytic acid was the only source of phosphorus. Bifidobacterium infantis ATCC 15697 showed the highest level of phytate-degrading activity. This strain displayed optimal activity at slight acid pH (6.0-6.5) and 50 degrees C, but also retained high activity levels at neutral pH and 37 degrees C. B. infantis ATCC 15697 produced maximum activity during the stationary phase of growth and when 1% lactose was used as carbon source. In contrast, the presence of inorganic phosphate in the growth medium inhibited phytase activity. The ability of B. infantis ATCC 15697 to generate lower myo-inositol phosphates and, particularly, accumulate myo-inositol tri-phosphates (InsP(3)) from partial hydrolysis of InsP(6) could contribute to the reduction of the anti-nutritional properties of InsP(6) and the generation of intermediate compounds with beneficial properties during food processing and gastrointestinal transit.  相似文献   
30.
综述了国内外生产 D 泛酸钙的合成方法及工艺路线, 并对其发展前景进行了评述。  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