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   271篇
  免费   10篇
  国内免费   2篇
  283篇
  2023年   3篇
  2022年   5篇
  2021年   8篇
  2020年   4篇
  2019年   5篇
  2018年   8篇
  2017年   3篇
  2016年   10篇
  2015年   14篇
  2014年   15篇
  2013年   18篇
  2012年   23篇
  2011年   21篇
  2010年   19篇
  2009年   8篇
  2008年   15篇
  2007年   10篇
  2006年   13篇
  2005年   10篇
  2004年   4篇
  2003年   6篇
  2002年   11篇
  2001年   4篇
  2000年   1篇
  1999年   5篇
  1998年   5篇
  1997年   4篇
  1996年   4篇
  1995年   4篇
  1994年   5篇
  1993年   5篇
  1992年   2篇
  1991年   2篇
  1987年   2篇
  1984年   1篇
  1982年   2篇
  1981年   2篇
  1980年   1篇
  1979年   1篇
排序方式: 共有283条查询结果,搜索用时 15 毫秒
141.
142.
Cyclooxygenases are responsible for the production of prostaglandin H2 (PGH2) from arachidonic acid. PGH2 can be converted into some bioactive prostaglandins, including prostaglandin F (PGF), a potent chemical messenger used as a biological regulator in the fields of obstetrics and gynecology. The chemical messenger PGF has been industrially produced by chemical synthesis. To develop a biotechnological process, in which PGF can be produced by a microorganism, we transformed an oleaginous fungus, Mortierella alpina 1S-4, rich in triacylglycerol consisting of arachidonic acid using a cyclooxygenase gene from a red alga, Gracilaria vermiculophylla. PGF was accumulated not only in the mycelia of the transformants but also in the extracellular medium. After 12 days of cultivation approximately 860 ng/g and 6421 µg/L of PGF were accumulated in mycelia and the extracellular medium, respectively. The results could facilitate the development of novel fermentative methods for the production of prostanoids using an oleaginous fungus.  相似文献   
143.
Forty microbial strains isolated from raw milk samples and black and green olives were grown in MP5 (mineral pectin 5) medium containing 0.5% lemon pectin. All strains synthesized an extracellular polygalacturonase. Rhodotorula sp. ONRh9 (0.44 U x mL(-1)) and Leuconostoc sp. LLn1 (0.16 U x mL(-1)), which had a more active polygalacturonase in MP5 medium, were studied in MAPG5 medium containing polygalacturonic acid. Highest biomass and polygalacturonase production by these two strains were observed for polygalacturonic acid concentrations of 10 g x L(-1) (Rhodotorula sp. ONRh9) and 5 g x L(-1) (Leuconostoc sp. LLn1) and for initial pH values of 6 (Rhodotorula sp. ONRh9) and 5.5 (Leuconostoc sp. LLn1). The two strains grown in fermenters in MAPG5 medium generated the following results: with controlled initial pH, Rhodotorula sp. produced maximum biomass (DO) and polygalacturonase (PG) after 20 h (DO, 3.86; PG, 0.24 U x mL(-1)) of growth, and this level was sustained until the end of the culture; Leuconostoc sp. LLn1 synthesized more cells and polygalacturonase between 4 h (DO, 1.80; PG, 0.17 U x mL(-1)) and 24 h (DO, 3.90; PG, 0.27 U x mL(-1)) of culture. With uncontrolled initial pH, the cultures produced maximum biomass and polygalacturonase after 20 h (DO, 3.30; PG, 0.26 U x mL(-1)) for Rhodotorula sp. ONRh9 and 10 h (DO, 2.84; PG, 0.17 U x mL(-1)) for Leuconostoc sp. LLn1.  相似文献   
144.
We studied the influence of xenobiotics of various chemical natures, including N,N’-dicyclohexylcarbodiimide, diethylstilbestrol, and chlorpromazine, on the activity of peroxidase, a redox-enzyme that participates in defense reactions of plants. It was shown that the influence of the studied xenobiotics on excised roots of wheat seedlings caused an increase in the permeability of plasmalemma for K+ and H+ and stimulated the activity of the extracellular peroxidase that forms the superoxide radical anion. It is assumed that the extracellular peroxidase can initiate the transformation of alien compounds on the cell surface, before their entrance into the cells.  相似文献   
145.
Several new highly functionalized imidazolium derivatives were synthesized, via appropriate synthetic routes, using imidazole, 1-methylimidazole and 2-phenyl-1-methylimidazole as key intermediates. The antibacterial activity of the prepared compounds was evaluated against: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Salmonella thipymurium using disk-diffusion and MIC methods. Crystal X-ray structures are reported for six compounds.  相似文献   
146.
Mitochondria are dynamic organelles, capable of fusion and fission as a part of cellular responses to various signals, such as the shifts in the redox status of a cell. The mitochondrial electron transport chain (ETC.) is involved in the generation of reactive oxygen species (ROS), with complexes I and III contributing the most to this process. Disruptions of ETC. can lead to increased ROS generation. Here, we demonstrate the appearance of giant mitochondria in wheat roots in response to simultaneous application of the respiratory inhibitors rotenone (complex I of mitochondrial ETC.) and antimycin A (complex III of mitochondrial ETC.). The existence of such megamitochondria was temporary, and following longer treatment with inhibitors mitochondria resumed their conventional size and oval shape. Changes in mitochondrial morphology were accompanied with a decrease in mitochondrial potential and an unexpected increase in oxygen consumption. Changes in mitochondrial morphology and activity may result from the fusion and fission of mitochondria induced by the disruption of mitochondrial ETC. Results from experiments with the inhibitor of mitochondrial fission Mdivi-1 suggest that the retarded fission may facilitate plant mitochondria to appear in a fused shape. The processes of mitochondrial fusion and fission are involved in the regulation of the efficacy of the functions of the respiratory chain complexes and ROS metabolism during stresses. The changes in morphology of mitochondria, along with the changes in their functional activity, can be a part of the strategy of the plant adaptation to stresses.  相似文献   
147.

Introduction

Streptococcus pneumoniae is a worldwide occurring pathogen Nasopharyngeal carriage of Streptococcus pneumoniae precedes pneumonia and other pneumococcal diseases in the community. Little is known about S. pneumoniae carriage in Indonesia, complicating strategies to control pneumococcal diseases. We investigated nasopharyngeal carriage of S. pneumoniae in Semarang, Indonesia.

Methods

A population-based survey was performed in Semarang, Indonesia. Nasopharyngeal swabs and questionnaires were taken from 496 healthy young (6–60 month-old) children and 45–70 year-old adults.

Results

Forty-three percent of children aged 6–60 months and 11% of adults aged 45–75 years carried S. pneumoniae. Determinants of carriage were being a child (OR 7.7; 95% CI = 4.5–13.0), passive smoking (OR 2.1; 95% CI = 1.3–3.4), and contact with toddler(s) at home (OR 3.0; 95% CI = 1.9–4.7). The most frequent serotypes found were 6A/B and 15B/C. The current commercially available vaccines cover <50% serotypes found in children. Twenty-four percent of S. pneumoniae strains were penicillin non-susceptible, and 45% were resistant to cotrimoxazol.

Conclusions

The limited coverage of commercially available vaccines against the serotypes found in this population, and the high proportion of non-susceptibility to penicillin and cotrimoxazol suggest the need for region-specific information and strategies to control S. pneumoniae.  相似文献   
148.
During the breeding season, a major androgen-dependent protein with an apparent molecular weight of 21 kDa was isolated and purified from the seminal vesicles of three Saharan rodents (MLVSP21 from Meriones libycus, MSVSP21 from Meriones shawi, and MCVSP21 from Meriones crassus). The 21-kDa protein was isolated and purified from soluble seminal vesicle proteins of homogenate by one-dimensional polyacrylamide gel electrophoresis (SDS-PAGE). Using polyclonal antibodies directed against POSVP21 (Psammomys obesus seminal vesicles protein of 21 kDa), a major androgen-dependent secretory protein from sand rat seminal vesicles, identified previously as transgelin, we showed an immunological homology with POSVP21 by immunoblotting. These three major androgen-dependent proteins with a same apparent molecular weight of 21 kDa designated as MLVSP21 (Meriones libycus seminal vesicles protein of 21 kDa), MSVSP21 (Meriones shawi seminal vesicles protein of 21 kDa), and MCVSP21 (Meriones crassus seminal vesicles protein of 21 kDa) were localized by immunohistochemistry and identified by applying a proteomic approach. Our results indicated that the isolated proteins MLSVP21, MSSVP21, and MCSVP21 seem to correspond to the same protein: the transgelin. So that transgelin can be used as a specific marker of these rodent physiological reproduction mechanisms.  相似文献   
149.
The identification of genes and understanding of genes'' expression and regulation in common bean (Phaseolus vulgaris L.) is necessary in order to strategize its improvement using genetic engineering techniques. Generation of expressed sequence tags (ESTs) is useful in rapid isolation, identification and characterization of the genes. To study the gene expression in P. vulgaris pods tissue, ESTs generation work was initiated. Early stage and late stage bean-pod-tissues cDNA libraries were constructed using CloneMiner cDNA library construction kit. In total, 5972 EST clones were isolated using random method of gene isolation. While processing ESTs, we found lycopene β-cyclase (PvLCY-β) and β-carotene hydroxylase (PvCHY-β) gene''s cDNA. In carotenoid biosynthesis pathway, PvLCY-β catalyzes the production of carotene; and PvCHY-β is known to function as a catalyst in the production of lutein and zeaxanthin. To understand more about PvLCY-β and PvCHY-β, both strands of both cDNA clones were sequenced using M13 forward and reverse primers. Nucleotide and deduced protein sequences were analyzed and annotated using online bioinformatics tools. Results showed that PvLCY-β and PvCHY-β cDNAs are 1639 and 1107 bp in length, respectively. Analysis results showed that PvLCY-β and PvCHY-β gene''s cDNA contains an open reading frame (ORF) that encodes for 502 and 305 amino acid residues, respectively. The deduced protein sequence analysis results also showed the presence of conserved domains needed for PvLCY-β and PvCHY-β functions. The phylogenetic analysis of both PvLCY-β and PvCHY-β proteins showed it''s closeness with the LCY-β and CHY-β proteins from Glycine max, respectively. The nucleotide sequence of PvLCY-β and PvCHY-β gene''s cDNA and it''s annotation is reported in this paper.  相似文献   
150.
Diphtheria toxin (DT) is a potent toxin produced by the so-called diphtheria group which includes Corynebacterium diphtheriae (C. diphtheriae), Corynebacterium ulcerans (C. ulcerans), and Corynebacterium pseudotuberculosis (C. pseudotuberculosis). The present investigation is aimed to study in detail the production of DT by C. pseudotuberculosis. Twenty isolates were obtained from sheep diseased with caseous lymphadenitis (CLA) and twenty-six isolates were obtained from 26 buffaloes diseased with oedematous skin disease (OSD). All isolates were identified by standard microbiological and DT production was assayed serologically by modified Elek test and immunoblotting. All sheep isolates were nitrate negative, failed to hydrolyze starch and could not produce DT, while all buffalo isolates (biotype II) revealed positive results and a specific band of 62 kDa, specific to DT, was resulted in all concentrated cell fractions (CF), but was absent from non-toxigenic biotype I isolates. At the same time, another band of 31 kDa specific to the PLD gene was obtained with all isolates of biotype I and II. Moreover, all isolates showed positive synergistic hemolytic activity and antagonistic hemolysis with β-hemolytic Staphylococci. The obtained results also indicated that C. pseudotuberculosis could be classified into two strains; non-toxigenic biotype I strain, which failed to produce DT as well as being negative to nitrate and starch hydrolysis, and toxigenic biotype II strain, which can reduce nitrate, hydrolyze starch as well as produce DT.  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