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   217篇
  免费   12篇
  2023年   2篇
  2022年   8篇
  2021年   7篇
  2020年   3篇
  2019年   2篇
  2018年   3篇
  2017年   5篇
  2016年   6篇
  2015年   15篇
  2014年   11篇
  2013年   16篇
  2012年   21篇
  2011年   20篇
  2010年   10篇
  2009年   8篇
  2008年   9篇
  2007年   5篇
  2006年   7篇
  2005年   7篇
  2004年   4篇
  2003年   5篇
  2002年   7篇
  2001年   8篇
  2000年   4篇
  1999年   4篇
  1998年   6篇
  1997年   2篇
  1995年   3篇
  1994年   4篇
  1993年   2篇
  1992年   1篇
  1989年   3篇
  1988年   1篇
  1987年   1篇
  1985年   1篇
  1984年   3篇
  1983年   1篇
  1982年   1篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
排序方式: 共有229条查询结果,搜索用时 15 毫秒
1.
Energy is one of the most important factors in the socioeconomic development of a country. In a developing country like Malaysia, the development of islands is mostly related to the availability of electric power. Power generated by renewable energy sources has recently become one of the most promising solutions for the electrification of islands and remote rural areas. But high dependency on weather conditions and the unpredictable nature of these renewable energy sources are the main drawbacks. To overcome this weakness, different green energy sources and power electronic converters need to be integrated with each other. This study presents a battery storage hybrid standalone photovoltaic-wind energy power supply system. In the proposed standalone hybrid system, a DC-DC buck-boost bidirectional converter controller is used to accumulates the surplus hybrid power in the battery bank and supplies this power to the load during the hybrid power shortage by maintaining the constant dc-link voltage. A three-phase voltage source inverter complex vector control scheme is used to control the load side voltage in terms of the voltage amplitude and frequency. Based on the simulation results obtained from MATLAB/Simulink, it has been found that the overall hybrid framework is capable of working under variable weather and load conditions.  相似文献   
2.
蚕豆植株叶片随茎节自上而下表现出明显的发育与衰老顺序,可作为衰老特征的是叶绿素和蛋白质含量明显下降。蚕豆叶中SOD活性主要定位于12 000× g离心后所得的上清液和叶绿体组分。衰老叶片的SOD总活性和叶绿体组分的相对活性都有所下降,SOD同工酶谱也发生了改变。O_2~ 产生速率随叶龄增大而稍上升;而MDA含量在叶片外观表现枯黄衰老征兆前就急剧上升。可能因为衰老叶片过氧化氢酶活性大幅度下降与SOD之间的不平衡,致使O_2~ 代谢中间产物累积而引起膜的损伤.  相似文献   
3.
Microbial mineralization of organic phosphate in soil   总被引:35,自引:0,他引:35  
Summary Phosphate-dissolving microorganisms were isolated from non-rhizosphere and rhizosphere of plants. These isolates included bacteria, fungi and actinomycetes. In broth cultures, Gram-negative short rod,Bacillus andStreptomyces species were found to be more active in solubilizing phosphate thanAspergillus, Penicillium, Proteus, Serratia, Pseudomonas andMicrococcus spp. The sterile soils mixed with isolated pure culture showed slower mineralization of organic phosphate than that of non-sterile soil samples at all incubation periods. Maximum amount of phosphate mineralization by isolated microorganisms were obtained at the 60th and the 75th day of incubation in sterile and non-sterile soils respectively. The mixed cultures were most effective in mineralizing organic phosphate and individuallyBacillus sp. could be ranked next to mixed cultures. Species ofPseudomonas andMicrococcus were almost the same as that of the control under both sterile and non-sterile conditions.  相似文献   
4.
By in vitro translation of mRNA’s isolated from free and membrane-bound polysomes, direct evidence was obtained for the synthesis of two lysosomal hydrolases, β-glucuronidase of the rat preputial gland and cathespin D of mouse spleen, on polysomes bound to rough endoplasmic reticulum (ER) membranes. When the mRNA’s for these two proteins were translated in the presence of microsomal membranes, the in vitro synthesized polypeptides were cotranslationally glycosylated and transferred into the microsomal lumen. Polypeptides synthesized in the absence of microsomal membranes were approximately 2,000 daltons larger than the respective unglycosylated microsomal polypeptides found after short times of labeling in cultured rat liver cells treated with tunicamycin. This strongly suggests that nascent chains of the lysosomal enzymes bear transient amino terminal signals which determine synthesis on bound polysomes and are removed during the cotranslational insertion of the polypeptides into the ER membranes. In the line of cultured rat liver cells used for this work, newly synthesized lysosomal hydrolases showed a dual destination; approximately 60 percent of the microsomal polypeptides detected after short times of labeling were subsequently processed proteolytically to lower molecular weight forms characteristic of the mature enzymes. The remainder was secreted from the cells without further proteolytic processing. As previously observed by other investigations in cultured fibroblasts (A. Gonzalez-Noriega, J.H. Grubbs, V. Talkad, and W.S. Sly, 1980, J Cell Biol. 85: 839-852; A. Hasilik and E.F. Neufeld, 1980, J. Biol. Chem., 255:4937-4945.) the lysosomotropic amine chloroquine prevented the proteolytic maturation of newly synthesized hydrolases and enhanced their section. In addition, unglycosylated hydrolases synthesized in cells treated with tunicamycin were exclusively exported from the cells without undergoing proteolytic processing. These results support the notions that modified sugar residues serve as sorting out signals which address the hydrolases to their lysosomal destination and that final proteolytic cleavage of hydrolase precursors take place within lysosome itself. Structural differences in the carbohydrate chains of intracellular and secreted precursors of cathespin D were detected from their differential sensitivity to digestion with endoglycosidases H and D. These observations suggest that the hydrolases exported into the medium follow the normal secretory route and that some of their oligosaccharides are subject to modifications known to affect many secretory glycoproteins during their passage through the Golgi apparatus.  相似文献   
5.

Background

Unsafe water supplies continue to raise public health concerns, especially in urban areas in low resource countries. To understand the extent of public health risk attributed to supply water in Dhaka city, Bangladesh, Escherichia coli isolated from tap water samples collected from different locations of the city were characterized for their antibiotic resistance, pathogenic properties and genetic diversity.

Methodology/Principal Findings

A total of 233 E. coli isolates obtained from 175 tap water samples were analysed for susceptibility to 16 different antibiotics and for the presence of genes associated with virulence and antibiotic resistance. Nearly 36% (n = 84) of the isolates were multi-drug(≥3 classes of antibiotics) resistant (MDR) and 26% (n = 22) of these were positive for extended spectrum β-lactamase (ESBL). Of the 22 ESBL-producers, 20 were positive for bla CTX-M-15, 7 for bla OXA-1-group (all had bla OXA-47) and 2 for bla CMY-2. Quinolone resistance genes, qnrS and qnrB were detected in 6 and 2 isolates, respectively. Around 7% (n = 16) of the isolates carried virulence gene(s) characteristic of pathogenic E. coli; 11 of these contained lt and/or st and thus belonged to enterotoxigenic E. coli and 5 contained bfp and eae and thus belonged to enteropathogenic E. coli. All MDR isolates carried multiple plasmids (2 to 8) of varying sizes ranging from 1.2 to >120 MDa. Ampicillin and ceftriaxone resistance were co-transferred in conjugative plasmids of 70 to 100 MDa in size, while ampicillin, trimethoprim-sulfamethoxazole and tetracycline resistance were co-transferred in conjugative plasmids of 50 to 90 MDa. Pulsed-field gel electrophoresis analysis revealed diverse genetic fingerprints of pathogenic isolates.

Significance

Multi-drug resistant E. coli are wide spread in public water supply in Dhaka city, Bangladesh. Transmission of resistant bacteria and plasmids through supply water pose serious threats to public health in urban areas.  相似文献   
6.
7.
8.

Use of probiotics as the biocontrol agent for disease prevention in aquaculture is gaining importance as an alternative to the indiscriminate use of antibiotics and other chemotherapeutics. In view of this trend, the probiotic properties of a potent antagonistic bacterium, Pseudomonas aeruginosa FARP72, was characterized in terms of safety, antagonistic activities, in vitro immunomodulation, and in vivo disease resistance. Immunomodulatory activity was ascertained by measuring the production of intracellular superoxide anion, nitric oxide, total leukocyte peroxidase content, and the leukocyte proliferation in head kidney leukocytes. The bacterium isolated from the skin mucus of freshwater catfish Clarias batrachus was harmless to Labeo rohita. It showed inhibitory activity against Aeromonas caviae, A. hydrophila, Edwardsiella tarda, Pseudomonas putida, and Streptococcus agalactiae as revealed by cross and parallel streaking methods. Significantly higher superoxide anion and nitric oxide production, peroxidase content, and proliferative responses of leucocytes delineated the strains’ ability to interact with immune cells to activate the immune system in vitro. Significant growth inhibition of A. hydrophila from 1.55 × 105 CFU/mL was observed when co-cultured with P. aeruginosa FARP72 in phosphate-buffered saline (PBS) at levels ranging from 2.61 × 107 to 2.61 × 109 CFU/mL in 10 days. P. aeruginosa FARP72 increased the survival rate of rohu fingerlings against pathogenic A. hydrophila challenge in biocontrol study in vivo as determined by cohabitation challenge. These results suggest that P. aeruginosa FARP72 is a potential probiotic strain and can be used in aquaculture to improve the health status and disease resistance of fish.

  相似文献   
9.
Plasmonics - This research illustrates a parametric study based on surface plasmon resonance of a slightly gold-coated photonic crystal fiber (PCF). In verifying sensing accuracy, the proposed...  相似文献   
10.
We tested the hypothesis that cholinergic receptor stimulation recruits actin- and integrin-binding proteins from the cytoplasm to the cytoskeleton-membrane complex in intact airway smooth muscle. We stimulated bovine tracheal smooth muscle with carbachol and fractionated the tissue homogenate into pellet (P) and supernatant (S) by ultracentrifugation. In unstimulated tissues, calponin exhibited the highest basal P-to-S ratio (P/S; 2.74 ± 0.47), whereas vinculin exhibited the lowest P/S (0.52 ± 0.09). Cholinergic receptor stimulation increased P/S of the following proteins in descending order of sensitivity: -actinin > talin metavinculin > -smooth muscle actin > vinculin calponin. Carbachol induced ERK1/2 phosphorylation by 300% of basal value. U0126 (10 µM) completely inhibited carbachol-induced ERK1/2 phosphorylation but did not significantly affect the correlation between -actinin P/S and carbachol concentration. This observation indicates that cytoskeletal/membrane recruitment of -actinin is independent of ERK1/2 mitogen-activated protein kinase activation. Metavinculin and vinculin are splice variants of a single gene, but metavinculin P/S was significantly higher than vinculin P/S. Furthermore, the P/S of metavinculin but not vinculin increased significantly in response to cholinergic receptor stimulation. Calponin and -actinin both belong to the family of calponin homology (CH) domain proteins. However, unlike -actinin, the calponin P/S did not change significantly in response to cholinergic receptor stimulation. These findings indicate differential cytoskeletal/membrane recruitment of actin- and integrin-binding proteins in response to cholinergic receptor stimulation in intact airway smooth muscle. -Actinin, talin, and metavinculin appear to be key cytoskeletal proteins involved in the recruitment process. actinin; mitogen-activated protein kinase; metavinculin; vinculin  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