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   269篇
  免费   10篇
  279篇
  2023年   2篇
  2022年   2篇
  2021年   3篇
  2020年   1篇
  2019年   2篇
  2018年   21篇
  2017年   20篇
  2016年   21篇
  2015年   6篇
  2014年   6篇
  2013年   3篇
  2012年   15篇
  2011年   33篇
  2010年   20篇
  2009年   26篇
  2008年   23篇
  2007年   25篇
  2006年   3篇
  2005年   4篇
  2004年   7篇
  2003年   6篇
  2002年   2篇
  2001年   1篇
  2000年   2篇
  1998年   2篇
  1996年   2篇
  1994年   2篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1990年   2篇
  1989年   8篇
  1988年   2篇
  1985年   1篇
  1969年   1篇
  1929年   1篇
排序方式: 共有279条查询结果,搜索用时 0 毫秒
251.
In search for the substrate of naltrexone and acamprosate action on alcohol craving, we investigated the effects of ethanol alone and combined with naltrexone or acamprosate on expression of nerve growth factor-inducible clone A (NGFI-A; zif268). In Experiments 1 and 3, alcohol (2 g/kg) alone or in combination with naltrexone (15 mg/kg) or acamprosate (300 mg/kg) was injected intraperitoneally into mice. In Experiment 2, treatment was nor-BNI (0.5 mg/kg) to investigate whether the effect of naltrexone involved blockade of κ-opioid receptors. Both ethanol and naltrexone alone induced NGFI-A in the central amygdala, but not in several other areas; these effects were additive. However, acamprosate alone or in combination with ethanol had no effect on NGFI-A mRNA, while nor-BNI induced NGFI-A mRNA in the basolateral amygdala. The central amygdala appears to be an important target of both alcohol and naltrexone. Acamprosate may not share the site of action with naltrexone despite being used for the same therapeutic purpose. Special issue article in honor of Dr.Ji-Sheng Han.  相似文献   
252.
The present study included 223 E. coli strains isolated from homemade white cheeses and was undertaken to determine the prevalence of extended spectrum β-lactamases (ESBL)-producing strains and antibiotic susceptibility. ESBL production was detected using three methods: the NCCLS disk diffusion test, the double disk synergy test and the NCCLS confirmatory test. By the disk diffusion test, 48% isolates were determined as potential ESBL producers. ESBL production by the double disk test and the phenotypic confirmatory test was found to be 16.1 and 9.9%, respectively. Susceptibility of all isolates against 16 antimicrobials was tested by the disk diffusion method. All strains were imipenem- and cefepime-susceptible. Susceptibility of E. coli to ceftazidime, ceftriaxon, cefotaxime and aztreonam was found to be 93.7, 96.4, 81.2, 90.6%, respectively. The least effective antibiotics were ampicillin with a rate of 68.6% and cefuroxime with a rate of 69.1%.  相似文献   
253.
We analysed the influence of contemporary geography on butterfly diversity for islands in the Mediterranean Basin. We found that island size and distance from the mainland has a significant effect on the number of species. We also used butterflies as an indicator group to identify the importance of forest habitats for biodiversity conservation in the island of Cyprus. To understand the relative importance of local vegetation characteristics of butterflies in the Pentadaktylos mountains transect counts were used to assess the abundance and butterfly diversity in two different forest types. A total of 1,602 butterflies and 23 species were recorded during this research. We observed highly significant effects of forest type on abundance and species richness of butterflies. For example, number of butterflies was significantly higher in old forest than young pine forest. Also, the abundance of endemic butterflies was highest in old forest habitats. Therefore, the survival of the majority of endemic butterflies in Cyprus may depend on conservation of old forests and their understorey plants.  相似文献   
254.
Dok adapter proteins have been primarily implicated in negative regulation of tyrosine kinase signaling, but Dok-4 has been reported to exert both inhibitory and stimulatory effects. We have identified a splice variant of Dok-4, Dok-4b, which contains a 39 aa insert within the its C-terminal region. The approximately 45kDa Dok-4b protein was detected in several human epithelial cell lines. Based on genomic sequences, Dok-4b was also predicted to exist in primates and possibly bovines, but not in rodents or other species. Compared to Dok-4, Dok-4b inhibited the tyrosine kinase-induced activation of both Erk and Elk-1 more strongly. Truncation of the C-terminal region of Dok-4 (Dok-4 DeltaCT) also enhanced the inhibitory activity of Dok-4, whereas expression of the isolated C-terminal domain enhanced Elk-1 activation, suggesting that the N-terminus and C-terminus of Dok-4 possess opposing inhibitory and stimulatory properties, respectively, the balance of which is altered by alternative splicing of Dok-4 to Dok-b.  相似文献   
255.
Süzen HS  Duydu Y  Aydin A 《Biochemical genetics》2004,42(11-12):461-467
delta-Aminolevulinic acid dehydratase (ALAD) is a cytosolic enzyme in the heme biosynthetic pathway. ALAD is a polymorphic enzyme showing marked ethnic group differences. In this study, ALAD polymorphism is studied in a Turkish population. Genomic DNA extracted from 230 individuals and polymerase chain reaction (PCR) coupled with the restriction fragment length polymorphism (RFLP) technique were used to identify variants. The frequencies of the alleles ALAD1 and ALAD2 in Turkey were 0.887 and 0.113, respectively. This study provides the first analysis of the allele frequency distribution of the ALAD gene in a Turkish population. The results are compared with other world populations.  相似文献   
256.
CD28 plays crucial costimulatory roles in T cell proliferation, cytokine production, and germinal center response. Mice that are deficient in the inducible costimulator (ICOS) also have defects in cytokine production and germinal center response. Because the full induction of ICOS in activated T cells depends on CD28 signal, the T cell costimulatory capacity of ICOS in the absence of CD28 has remained unclear. We have clarified this issue by comparing humoral immune responses in wild-type, CD28 knockout (CD28 KO), and CD28-ICOS double-knockout (DKO) mice. DKO mice had profound defects in Ab responses against environmental Ags, T-dependent protein Ags, and vesicular stomatitis virus that extended far beyond those observed in CD28 KO mice. However, DKO mice mounted normal Ab responses against a T-independent Ag, indicating that B cell function itself was normal. Restimulated CD4(+) DKO T cells that had been primed in vivo showed decreased proliferation and reduced IL-4 and IL-10 production compared with restimulated CD4(+) T cells from CD28 KO mice. Thus, in the absence of CD28, ICOS assumes the major T cell costimulatory role for humoral immune responses. Importantly, CD28-mediated ICOS up-regulation is not essential for ICOS function in vivo.  相似文献   
257.
258.
Calcium ions (Ca2+) are important second messengers in neurons. Ketamine (KETAM) is an anesthetic and analgesic, with psychotomimetic effects and abuse potential. KETAM modulates the entry of Ca2+ in neurons through glutamate receptors, but its effect on transient receptor potential melastatin 2 (TRPM2) and transient receptor potential vanilloid 1 (TRPV1) channels has not been clarified. This study investigated the short-term effects of KETAM on oxidative stress and TRPM2 and TRPV1 channel gating in hippocampal and dorsal root ganglion (DRG) neurons of rats. Freshly isolated hippocampal and DRG neurons were incubated for 24 h with KETAM (0.3 mM). The TRPM2 channel antagonist, N-(p-amylcinnamoyl)anthranilic acid (ACA), inhibited cumene hydroperoxide and ADP-ribose-induced TRPM2 currents in the neurons, and capsazepine (CPZ) inhibited capsaicin-induced TRPV1 currents. The TRPM2 and TRPV1 channel current densities and intracellular free calcium ion concentration of the neurons were lower in the neurons exposed to ACA and CPZ compared to the control neurons, respectively. However, the values were not further decreased by the KETAM + CPZ and KETAM + ACA treatments. KETAM decreased lipid peroxidation levels in the neurons but increased glutathione peroxidase activity. In conclusion, short-term KETAM treatment decreased oxidative stress levels but did not seem to influence TRPM2- and TRPV1-mediated Ca2+ entry.  相似文献   
259.

Background

Postural stability deficits have been proposed to influence the onset and progression of adolescent idiopathic scoliosis (AIS). This study aimed to systematically identify, critically evaluate and meta-analyse studies assessing postural stability during unperturbed stance with posturography in AIS compared to typically developed adolescents.

Methods

Studies from four electronic databases (PubMed, Scopus, CINAHL, PEDro) were searched and case-control methodological quality assessed using a risk-of-bias assessment tool and a posturography methodological quality checklist. Pooled data regarding centre of pressure (COP) parameters such as sway area, Mediolateral (ML) and Anteroposterior (AP) position and range were compared for AIS and typically developed adolescents using Cohen’s d effect size (ES) and homogeneity estimates.

Results

Eighteen studies for quality analysis and 9 of these for meta-analysis were identified from 971 records. Risk-of-bias assessment identified 6 high, 10 moderate and 2 low risk-of-bias studies. The posturography methodological quality checklist identified 4 low, 7 moderate and 7 high-quality studies. Meta-analysis was performed for sway area whereas ML and AP are presented in three different meta-analyses due to divergent measurement units used in the studies: ML position 1 (MLP1), ML position 2 (MLP2) and ML range (MLR); AP position 1 (APP1), AP position 2 (APP2) and AP range (APR). Cohen’s d showed a medium ES difference in sway area 0.65, 95% CI (0.49–0.63), whereas ML showed no (MLP1, MLP2) and large (MLR) ES differences; MLP1 0.15, 95% CI (0.08–0.22); MLP2 0.14, 95% CI (0.08–0.19); and MLR 0.94, 95% CI (0.83–1.04). Cohen’s d for AP showed small ES (APP1) and large ES difference (APP2 and APR); APP1 0.43, 95% CI (0.31–0.54); APP2 0.85, 95% CI (0.72–0.97); and APR 0.98, 95% CI (0.87–1.09). Cochran’s Q and Higgins I2 showed homogeneity between studies.

Conclusions

There is moderate quality evidence for decreased postural stability in AIS measured as COP parameters sway area, ML and AP range with a positional shift posteriorly in the sagittal plane. The findings support studying postural stability in early stage AIS and also prospectively identify cause and effect of the curvature as well as effectiveness of postural control interventions in the prevention of scoliosis progression.
  相似文献   
260.
Effect of salinity on antioxidant responses of chickpea seedlings   总被引:1,自引:0,他引:1  
The changes in the activity of antioxidant enzymes, like superoxide dismutase, ascorbate peroxidase, catalase and glutathione reductase, and growth parameters such as length, fresh and dry weight, proline and H2O2 contents, chlorophyll fluorescence (Fv/Fm), quantum yield of PSII and the rate of lipid peroxidation in terms of malondialdehyde in leaf and root tissues of a chickpea cultivar (Cicer arietinum L. cv. Gökçe) under salt treatment were investigated. Plants were subjected to 0.1, 0.2 and 0.5 M NaCl treatments for 2 and 4 days. Compared to controls, salinity resulted in the reduction of length and of the fresh and dry weights of shoot and root tissues. Salinity caused significant (< 0.05) changes in proline and MDA levels in leaf tissue. In general, a dose-dependent decrease was observed in H2O2 content, Fv/Fm and quantum yield of photosynthesis under salt stress. Leaf tissue extracts exhibited three activity bands, of which the higher band was identified as MnSOD and the others as FeSOD and Cu/ZnSOD. A significant enhancement was detected in the activities of Cu/ZnSOD and MnSOD isozymes in both tissues. APX and GR activities exhibited significant increases (< 0.05) in leaf tissue under all stress treatments, whereas no significant change was observed in root tissue. The activity of CAT was significantly increased under 0.5 M NaCl stress in root tissue, while its activity was decreased in leaf tissue under 0.5 M NaCl stress for 4 days. These results suggest that CAT and SOD activities play an essential protective role against salt stress in chickpea seedlings.  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