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   126篇
  免费   10篇
  2023年   3篇
  2021年   2篇
  2020年   3篇
  2019年   2篇
  2018年   5篇
  2017年   2篇
  2016年   7篇
  2015年   5篇
  2014年   7篇
  2013年   6篇
  2012年   11篇
  2011年   14篇
  2010年   9篇
  2009年   3篇
  2008年   8篇
  2007年   10篇
  2006年   2篇
  2005年   5篇
  2004年   7篇
  2003年   7篇
  2002年   7篇
  2001年   1篇
  2000年   1篇
  1997年   2篇
  1995年   1篇
  1993年   2篇
  1991年   1篇
  1990年   1篇
  1980年   1篇
  1976年   1篇
排序方式: 共有136条查询结果,搜索用时 343 毫秒
31.
ABSTRACT

Due to rapid industrialization and urbanization, social economy develops in an unparalleled speed, while it certainly fosters the consumption of natural resources and the pressure to protect the ecological environment. Hence, there is a two-way relationship between the well-being of humans and the natural environment. In this study, link analysis techniques along with multivariate statistical analysis were employed to discover the effects of environmental risk factors on city life cycle, where suicides, immigration, and emigration were considered as the fundamental indicators of how cities evolve. Association rules, classification trees, MANOVA, and linear discriminant analysis were applied to data on air quality, socioeconomic development, and demographical factors belonging to the cities of Turkey. The results indicate that socioeconomic development levels of cities differ along attraction and life satisfaction dimensions. People tend to choose a city with better development level and better air quality in order to increase their life satisfaction. Additionally, developed cities are less likely to have issues with air quality and citizens who live in a poorly developed city are least satisfied with their lives.  相似文献   
32.
Effective control of the Ca2+ homeostasis in any living cell is paramount to coordinate some of the most essential physiological processes, including cell division, morphological differentiation, and intercellular communication. Therefore, effective homeostatic mechanisms have evolved to maintain the intracellular Ca2+ concentration at physiologically adequate levels, as well as to regulate the spatial and temporal dynamics of Ca2+signaling at subcellular resolution. Members of the superfamily of EF-hand Ca2+-binding proteins are effective to either attenuate intracellular Ca2+ transients as stochiometric buffers or function as Ca2+ sensors whose conformational change upon Ca2+ binding triggers protein-protein interactions, leading to cell state-specific intracellular signaling events. In the central nervous system, some EF-hand Ca2+-binding proteins are restricted to specific subtypes of neurons or glia, with their expression under developmental and/or metabolic control. Therefore, Ca2+-binding proteins are widely used as molecular markers of cell identity whilst also predicting excitability and neurotransmitter release profiles in response to electrical stimuli. Secretagogin is a novel member of the group of EF-hand Ca2+-binding proteins whose expression precedes that of many other Ca2+-binding proteins in postmitotic, migratory neurons in the embryonic nervous system. Secretagogin expression persists during neurogenesis in the adult brain, yet becomes confined to regionalized subsets of differentiated neurons in the adult central and peripheral nervous and neuroendocrine systems. Secretagogin may be implicated in the control of neuronal turnover and differentiation, particularly since it is re-expressed in neoplastic brain and endocrine tumors and modulates cell proliferation in vitro. Alternatively, and since secretagogin can bind to SNARE proteins, it might function as a Ca2+ sensor/coincidence detector modulating vesicular exocytosis of neurotransmitters, neuropeptides or hormones. Thus, secretagogin emerges as a functionally multifaceted Ca2+-binding protein whose molecular characterization can unravel a new and fundamental dimension of Ca2+signaling under physiological and disease conditions in the nervous system and beyond.  相似文献   
33.
DNA sequence comparisons of three mitochondrial DNA genes were used to reveal phylogenetic relationships among four species and a sub-species of Mullidae family. This is the first report using mitochondrial DNA sequence data to infer intraspecific relationship among different populations of Mullus barbatus and Mullus surmuletus; phylogenetic relationships between M. barbatus and its sub-species; M. barbatus ponticus. Cytochrome b, 12S ribosomal RNA, and cytochrome oxidase II regions of 242 individuals belonging to species M. barbatus, M. surmuletus, Upeneus moluccensis, Upeneus pori and sub-species M. barbatus ponticus were sequenced and phylogenetic trees were constructed using four different algorithms. The phylogenetic trees constructed support the existing taxonomical data of two mullid genera (Mullus, Upeneus). Molecular data shows no significant difference between same species of different geographical populations. The results suggest that the molecular difference is not large enough between M. barbatus and M. barbatus ponticus to consider them as sub-species.  相似文献   
34.
A case of otocephaly with anencephaly and meningomyelocele: Otocephaly is a rare lethal syndrome with microstomia, aglossia, agnathia, and synotia as major clinical features due to arrest in development of the first branchial arch. Some associated anomalies may be present as cyclopia, holoprosencephaly, cerebellar hypoplasia, situs inversus, and other visceral anomalies. We describe a case of fetus, spontaneously aborted in the 14th week of gestation with otocephaly complex (agnathia, synotia, microstomia) and associated anencephaly and meningomyelocele.  相似文献   
35.
Gulcin Alp  Belma Aslim 《Anaerobe》2010,16(2):101-105
The purpose of this study was to investigate a possible relation between resistance to bile salts and low pH with exopolysaccharide (EPS) producing of Bifidobacterium spp. In this study, a total of 31 Bifidobacterium spp. were isolated from breast fed infants feces and breast milk samples. As a result of the identification tests, isolates were identified as Bifidobacterium breve (15 strains), B. bifidum (11 strains), B. pseudocatenulatum (3 strains) and B. longum (2 strains). Bifidobacterium spp. were determined exopolysaccharide (EPS) production. EPS productions observed at chance rations (38.00–97.64 mg/l) among of Bifidobacterium spp. Furthermore, Bifidobacterium spp. were determined resistance to bile salts and low pH. Positive correlations between production of exopolysaccharide and resistance to bile salts (p < 0.01) or low pH (p < 0.01) were found Bifidobacterium spp. This investigation showed that high EPS production of Bifidobacteria may be important in the selection of probiotic strains for resistance to bile salts and low pH.  相似文献   
36.
The use of avoparcin as a growth promoter is considered to have selected for vancomycin-resistant enterococci (VRE). In Costa Rica, the use of avoparcin for poultry and swine was intensive until the product was withdrawn from the market in 2000. We evaluated the presence of VRE in poultry, swine, and cattle fecal samples obtained during 1998 and 1999. A total of 185 VRE isolates were recovered from 116 out of 893 samples. Enterococcus faecium was the most frequently isolated species (50.8%), being predominant among poultry (71.6%) and swine (37.7%) isolates, but it was not recovered from the bovine samples. The second-most-frequently-isolated species from poultry and swine, respectively, were E. durans (23.2%) and E. faecalis (21.7%). E. casseliflavus was the only species obtained from bovine samples, but it was not found among the avian isolates. An evident predominance of the vanA determinant among vancomycin-resistant enterococcal species from poultry and swine, but not from cattle, was observed and was similar to the situation in European countries before avoparcin was forbidden. The diversity of the vanA determinant in the isolates was assessed by detection of the IS1251 insertion in the vanSH intergenic region and of the IS1476 insertion in the vanXY intergenic region. However, in none of the 154 vanA+ isolates recovered in this study were those insertions detected.  相似文献   
37.
The complete iron atom vibrational spectrum has been obtained by refinement of normal mode calculations to nuclear inelastic x-ray absorption data from (nitrosyl)iron(II)tetraphenylporphyrin, FeTPP(NO), a useful model for heme dynamics in myoglobin and other heme proteins. Nuclear resonance vibrational spectroscopy (NRVS) provides a direct measurement of the frequency and iron amplitude for all normal modes involving significant displacement of (57)Fe. The NRVS measurements on isotopically enriched single crystals permit determination of heme in-plane and out-of-plane modes. Excellent agreement between the calculated and experimental values of frequency and iron amplitude for each mode is achieved by a force-field refinement. Significantly, we find that the presence of the phenyl groups and the NO ligand leads to substantial mixing of the porphyrin core modes. This first picture of the entire iron vibrational density of states for a porphyrin compound provides an improved model for the role of iron atom dynamics in the biological functioning of heme proteins.  相似文献   
38.
Decreased dietary protein intake and hemodialysis (HD)-associated protein catabolism are among several factors that predispose chronic hemodialysis (CHD) patients to uremic malnutrition and associated muscle wasting. Intradialytic parenteral nutrition (IDPN) acutely reverses the net negative whole body and forearm muscle protein balances observed during the HD procedure. Exercise has been shown to improve muscle protein homeostasis, especially if performed with adequately available intramuscular amino acids. We hypothesized that exercise performance would provide additive anabolic effects to the beneficial effects of IDPN. We studied six CHD patients at two separate HD sessions: 1) IDPN administration only and 2) IDPN + exercise. Patients were studied 2 h before, during, and 2 h after an HD session by use of a primed constant infusion of l-[1-(13)C]leucine and l-[ring-(2)H(5)] phenylalanine. Exercise combined with IDPN promoted additive twofold increases in forearm muscle essential amino acid uptake (455 +/- 105 vs. 229 +/- 38 nmol.100 ml(-1).min(-1), P < 0.05) and net muscle protein accretion (125 +/- 37 vs. 56 +/- 30 microg.100 ml(-1).min(-1), P < 0.05) during HD compared with IDPN alone. Measurements of whole body protein homeostasis and energy expenditure were not altered by exercise treatment. In conclusion, exercise in the presence of adequate nutritional supplementation has potential as a therapeutic intervention to blunt the loss of muscle mass in CHD patients.  相似文献   
39.
40.
Increasing evidence suggests that statins may have pleiotropic effects on vascular wall independent of their cholesterol lowering properties. In the present study, we investigated the acute vascular effects of pravastatin, atorvastatin and cerivastatin on rat isolated aortic rings. Statins effectively and comparably relaxed the aortic rings precontracted submaximally with noradrenaline, in a concentration-dependent manner, in which a high potency was observed with cerivastatin. Endothelium removal or incubation of the aortic rings with nitric oxide synthase inhibitor L-NOARG (10(-4) M) and/or cyclooxygenase inhibitor indomethacin (10(-5) M) significantly attenuated the acute vasorelaxation induced by either of statin. Additionally, different from the other two statins, a significant reduction was observed in response to cerivastatin in the presence of KATP channel inhibitor, glibenclamide (10(-5) M) and Na+- K+ ATPase inhibitor, ouabain (10(-4) M). Furthermore, pretreatment of the rings with the cholesterol precursor mevalonate (10(-3) M) significantly inhibited the endothelium-mediated relaxant effects of the statins. Our findings suggest that statins could acutely modulate vascular tone importantly by endothelium-dependent and mevalonate-related pathways.  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