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   706篇
  免费   43篇
  国内免费   1篇
电工技术   6篇
化学工业   165篇
金属工艺   10篇
机械仪表   8篇
建筑科学   32篇
能源动力   13篇
轻工业   125篇
水利工程   13篇
无线电   51篇
一般工业技术   79篇
冶金工业   192篇
原子能技术   7篇
自动化技术   49篇
  2023年   10篇
  2022年   24篇
  2021年   18篇
  2020年   19篇
  2019年   18篇
  2018年   23篇
  2017年   17篇
  2016年   14篇
  2015年   13篇
  2014年   18篇
  2013年   50篇
  2012年   39篇
  2011年   58篇
  2010年   34篇
  2009年   41篇
  2008年   43篇
  2007年   38篇
  2006年   20篇
  2005年   25篇
  2004年   12篇
  2003年   13篇
  2002年   13篇
  2001年   12篇
  2000年   13篇
  1999年   13篇
  1998年   29篇
  1997年   12篇
  1996年   14篇
  1995年   4篇
  1994年   10篇
  1993年   5篇
  1992年   8篇
  1990年   3篇
  1989年   4篇
  1988年   8篇
  1986年   4篇
  1985年   2篇
  1984年   6篇
  1983年   6篇
  1982年   6篇
  1981年   2篇
  1980年   3篇
  1978年   4篇
  1977年   5篇
  1976年   4篇
  1973年   2篇
  1968年   1篇
  1967年   1篇
  1965年   2篇
  1963年   1篇
排序方式: 共有750条查询结果,搜索用时 15 毫秒
91.
92.
This work was aimed at isolating and identifying the microbiota present during the semi-dry method of coffee processing using polyphasic methods and to evaluate microbial diversity with PCR-DGGE. Samples of Coffea arabica L. were collected during different processing stages in southern Minas Gerais, Brazil. The bacterial and fungal isolates were phenotypically characterised and grouped according to the ARDRA technique, in which the 16–23S and ITS1-5.8S regions of the rDNA were sequenced for species identification. The bacterial counts varied from 3.7 to 7 log CFU g−1. The yeast counts ranged from 3.4 to 6.9 log CFU g−1, and the filamentous fungal population varied from 2 to 3.7 log CFU g−1. Bacillus subtilis, Escherichia coli, Enterobacter agglomerans, Bacillus cereus and Klebsiella pneumoniae were the predominant bacteria detected during the processing of the coffee, and Pichia anomala, Torulaspora delbrueckii and Rhodotorula mucilaginosa were the dominant yeasts. All of the yeast and bacterial species detected by PCR-DGGE were isolated using culture-dependent methods, with the exception of one uncultivable bacterial species. Aspergillus was the most common genus among the filamentous fungal isolates. The use of polyphasic methods allowed a better characterization of the microbiota that is naturally present in semi-dry processed coffee.  相似文献   
93.
In Quebec, Canada, industrial bark wastelands cover several hundred hectares of land. Bark residue that has piled up for decades tends to remain free of vegetation for years. To assess the revegetation potential of such sites, we sought to determine those factors responsible for poor plant growth. Phenolic compounds from fresh to 20-year-old bark residues were extracted with four solvents and quantified by high-performance liquid chromatography (HPLC). We simulated solutions (mixtures of standard phenolic compounds) to evaluate the potential toxic effects of phenolic compounds on the rhizobial growth, germination index, plant growth, nodule number, and nitrogen fixation activity of two legume species under laboratory conditions. The concentration of individual phenolic compounds varied from none detected to 350 μg/g bark residue. The extracted phenolic compounds differed among solvents and bark residues. The highest concentration of total phenolic compounds was from fresh bark; most of these were soluble in water or 0.1 M NaOH. For older bark residues, the total phenolic content depended on solvent strength, generally in the order of 2.0 M NaOH > 0.1 M NaOH = hot water > cold water. The biological activity of the simulated bark extracts was not established with the rhizobial growth inhibition test but with the germination index and rhizobium–legume symbiosis tests. With these, the toxicity of the simulated phenolic extracts decreased from fresh to the older bark residues. Plant dry weight, nodule number, and nitrogen fixation activity of vetch (Vicia sativa L.) were less negatively affected by high concentrations of phenolics than birdsfoot trefoil (Lotus corniculatus L.), although birdsfoot trefoil grew at lower concentrations. The rhizobium–legume symbiosis has potential for revegetating bark wastelands with less than 1 year old and older bark residues.  相似文献   
94.
Chiral pyridines with a fluorine atom in the benzylic position are easily accessible from optically active propargylic fluorides by using the Bohlmann–Rahtz reaction. Such pyridines, possessing four points of molecular diversity, are useful scaffolds for the preparation of chemical libraries.  相似文献   
95.
Analysis of arsenic concentrations in New Jersey well water from the Newark Basin showed up to 15% of the wells exceed 10 microg L(-1), with a maximum of 215 microg L(-1). In some geologic settings in the basin, this mobile arsenic could be from the weathering of pyrite (FeS2) found in black shale that contains up to 4% arsenic by weight. We hypothesized that under oxic conditions at circumneutral pH, the microbially mediated oxidation of sulfide in the pyrite lattice would lead to the release of pyrite-bound arsenic. Moreover, the oxidation of aqueous As(III) to As(V) by aerobic microorganisms could further enhance arsenic mobilization from the solid phase. Enrichment cultures under aerobic, As(III)-oxidizing conditions were established under circumneutral pH with weathered black shale from the Newark Basin as the inoculum source. Strain WAO, an autotrophic inorganic-sulfur and As(III)-oxidizer, was isolated and phylogenetically and physiologically characterized. Arsenic mobilization studies from arsenopyrite (FeAsS) mineral, conducted with strain WAO at circumneutral pH, showed microbially enhanced mobilization of arsenic and complete oxidation of released arsenic and sulfur to stoichiometric amounts of arsenate and sulfate. In addition, WAO preferentially colonized pyrite on the surface of arsenic-bearing, black shale thick sections. These findings support the hypothesis that microorganisms can directly mobilize and transform arsenic bound in mineral form at circumneutral pH and suggest that the microbial mobilization of arsenic into groundwater may be important in other arsenic-impacted aquifers.  相似文献   
96.
Customer perception of switch-feel in luxury sports utility vehicles   总被引:1,自引:0,他引:1  
Successful new product introduction requires that product characteristics relate to the customer on functional, emotional, aesthetic and cultural levels. As a part of research into automotive human machine interfaces (HMI), this paper describes holistic customer research carried out to investigate how the haptics of switches in luxury sports utility vehicles (SUVs) are perceived by customers. The application of these techniques, including an initial proposal for objective specifications, is addressed within the broader new product introduction context, and benefits described.One-hundred and one customers of SUVs assessed the feel of automotive push switches, completing the tasks both in, and out of vehicles to investigate the effect of context. Using the semantic differential technique, hedonic testing, and content analysis of customers’ verbatim comments, a holistic picture has been built up of what influences the haptic experience. It was found that customers were able to partially discriminate differences in switch-feel, alongside considerations of visual appearance, image, and usability. Three factors named ‘Affective’, ‘Robustness and Precision’, and ‘Silkiness’ explained 61% of the variance in a principle components analysis. Correlations of the factors with acceptance scores were 0.505, 0.371, and 0.168, respectively.  相似文献   
97.
Canary seed is a true cereal with unique composition. The current study employed light and fluorescence microscopy to visualise starch, protein, phenolics and phytate in hairless canary seed (CDC Maria), a cultivar developed potentially for food use. Macronutrients, minerals and vitamins were evaluated in the developed cultivar and compared with a commercial hairy canary seed, cv. Keet. A control common wheat, cv. Katepwa, was grown adjacent to the canary seed varieties. The compositions of the two canary seed varieties were found to be similar with an average of 55.8 g/100 g of starch, 23.7% g/100 g of protein, 7.9% of crude fat, 7.3 g/100 g of total dietary fibre, 1.8 g/100 g of soluble sugar and 2.3 g/100 g of total ash in the whole grain. Regardless of the milling fraction (whole grain flour, white flour or bran), canary seed had more protein and crude fat and less starch, total dietary fibre and soluble sugar than had wheat. It also had higher concentrations of several minerals and vitamins than did wheat. The structure of the canary seed grain exhibited compound starch granules and protein bodies embedded in a protein matrix similar to that of the oat kernel. Baking tests showed that bread made with 100% hairless canary seed flour was significantly lower in loaf volume and crust and crumb colour than was wheat bread. However, bread with loaf volume, specific volume and crust colour comparable to those of the bread control was achieved by using up to 25% of hairless canary seed or 15% of roasted canary seed flour, thus demonstrating its potential for food applications.  相似文献   
98.
As the Maillard reaction is known to occur in heat-treated foods, unheated and heated honey samples were subjected to the activity-guided fractionation and size-exclusion chromatography to compare the degree of browning, radical scavenging activity (ORAC) and molecular size of the fractions obtained. Heat-treatment increased browning in the fractions of light- and medium-coloured honeys (p < 0.002), accelerated the formation of high molecular weight melanoidins (85–232 kDa) and significantly increased ORAC values (p < 0.0001). In contrast, melanoidin content and ORAC decreased in the fractions of heat-treated dark buckwheat honey (p < 0.001). Unheated dark honey contained a significantly higher amount of melanoidins than other honeys (p < 0.007). Together, results showed that at low initial concentration of melanoidins, heat-treatment accelerated formation of new melanoidins and increased ORAC, while at high concentration it caused decrease and a reduction of radical scavenging activity. This study emphasises the importance of non-enzymatic browning in the prediction of the antioxidant pool in thermally processed honeys.  相似文献   
99.
Fenretinide (4-HPR) is a synthetic derivative of all-trans-retinoic acid (ATRA) characterised by improved therapeutic properties and toxicological profile relative to ATRA. 4-HPR has been mostly investigated as an anti-cancer agent, but recent studies showed its promising therapeutic potential for preventing metabolic syndrome. Several biological targets are involved in 4-HPR's activity, leading to the potential use of this molecule for treating different pathologies. However, although 4-HPR displays quite well-understood multitarget promiscuity with regards to pharmacology, interpreting its precise physiological role remains challenging. In addition, despite promising results in vitro, the clinical efficacy of 4-HPR as a chemotherapeutic agent has not been satisfactory so far. Herein, we describe the preparation of a library of 4-HPR analogues, followed by the biological evaluation of their anti-cancer and anti-obesity/diabetic properties. The click-type analogue 3 b showed good capacity to reduce the amount of lipid accumulation in 3T3-L1 adipocytes during differentiation. Furthermore, it showed an IC50 of 0.53±0.8 μM in cell viability tests on breast cancer cell line MCF-7, together with a good selectivity (SI=121) over noncancerous HEK293 cells. Thus, 3 b was selected as a potential PET tracer to study retinoids in vivo, and the radiosynthesis of [18F] 3b was successfully developed. Unfortunately, the stability of [18F] 3b turned out to be insufficient to pursue imaging studies.  相似文献   
100.
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