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   1914篇
  免费   133篇
  2024年   1篇
  2023年   4篇
  2022年   19篇
  2021年   28篇
  2020年   23篇
  2019年   49篇
  2018年   45篇
  2017年   42篇
  2016年   73篇
  2015年   109篇
  2014年   110篇
  2013年   143篇
  2012年   166篇
  2011年   139篇
  2010年   94篇
  2009年   93篇
  2008年   126篇
  2007年   123篇
  2006年   102篇
  2005年   101篇
  2004年   97篇
  2003年   77篇
  2002年   75篇
  2001年   15篇
  2000年   9篇
  1999年   9篇
  1998年   20篇
  1997年   22篇
  1996年   18篇
  1995年   19篇
  1994年   18篇
  1993年   16篇
  1992年   13篇
  1991年   10篇
  1990年   9篇
  1989年   5篇
  1988年   7篇
  1987年   3篇
  1986年   6篇
  1985年   1篇
  1984年   2篇
  1983年   2篇
  1982年   2篇
  1980年   2篇
排序方式: 共有2047条查询结果,搜索用时 15 毫秒
121.
It has been demonstrated that patients showing symptoms of chronic bacterial prostatitis but culture-negative prostate-specific specimens can benefit from administration of antibacterial agents. This suggests that organisms that are not isolated in the routine practice may be responsible for prostate infection in an undefined fraction of subjects. Anaerobic bacteria have been proposed to play a pathogenic role in CBP, on the basis of studies describing clinical remission after eradication of pathogens like Peptostreptococcus spp or Bacterioides spp from prostatic secretions of symptomatic patients, or the significant association between prostatic infection by anaerobes and the presence of inflammation markers in prostatic secretions.In this paper, we report in detail a case of severely symptomatic chronic prostatitis in a patient with evidence of infection by Peptostreptococcus. We also report for the first time that treatment with the 3rd generation fluoroquinolone moxifloxacin was successful in eradicating the pathogen and in causing dramatic resolution of signs and symptoms of chronic bacterial prostatitis.The strict association between eradication of Peptostreptococcus and the rapid disappearance of clinical signs/symptoms points to a causative role of this anaerobe in the chronic bacterial prostatitis case described in this report.  相似文献   
122.
Mutations in the sulfate transporter gene, SCL26A2, lead to cartilage proteoglycan undersulfation resulting in chondrodysplasia in humans; the phenotype is mirrored in the diastrophic dysplasia (dtd) mouse. It remains unclear whether bone shortening and deformities are caused solely by changes in the cartilage matrix, or whether chondroitin sulfate proteoglycan undersulfation affects also signalling pathways involved in cell proliferation and differentiation. Therefore we studied macromolecular sulfation in the different zones of the dtd mouse growth plate and these data were related to growth plate histomorphometry and proliferation analysis.A 2-fold increase of non-sulfated disaccharide in dtd animals compared to wild-type littermates in the resting, proliferative and hypertrophic zones was detected indicating proteoglycan undersulfation; among the three zones the highest level of undersulfation was in the resting zone. The relative height of the hypertrophic zone and the average number of cells per column in the proliferative and hypertrophic zones were significantly reduced compared to wild-types; however the total height of the growth plate was within normal values. The chondrocyte proliferation rate, measured by bromodeoxyuridine labelling, was also significantly reduced in mutant mice. Immunohistochemistry combined with expression data of the dtd growth plate demonstrated that the sulfation defect alters the distribution pattern, but not expression, of Indian hedgehog, a long range morphogen required for chondrocyte proliferation and differentiation.These data suggest that in dtd mice proteoglycan undersulfation causes reduced chondrocyte proliferation in the proliferative zone via the Indian hedgehog pathway, therefore contributing to reduced long bone growth.  相似文献   
123.
Neurotrophins (NTs) represent a family of proteins that play an important role in the survival, development, and function of neurons. Extensive efforts are currently being made to develop small molecules endowed with agonist or antagonist NT activity. The structurally versatile N-termini of these proteins are considered regions of interest for the design of new molecules. By combining experimental and computational approaches, we analyzed the intrinsic conformational preferences of the N-termini of two of the most important NTs: NGF (NGF-Nter) and NT4 (NT4-Nter). Circular dichroism spectra clearly indicate that both peptides show a preference for random coil states. Because this finding does not preclude the possibility that structured forms may occur in solution as minor conformational states, we performed molecular-dynamics simulations to gain insights into the structural features of populated species. In line with the circular dichroism analysis, the simulations show a preference for unstructured states for both peptides. However, the simulations also show that for NT4-Nter, and to a lesser extent for NGF-Nter, helical conformations, which are required for binding to the Trk receptor, are present in the repertoire of structures that are intrinsically accessible to these peptides. Accordingly, molecular recognition of NTs by the Trk receptor is accomplished by the general mechanism known as population shift. These findings provide a structural rationale for the observed activity of synthetic peptides based on these NT regions. They also suggest strategies for the development of biologically active peptide-based compounds.  相似文献   
124.
Bandiera A  Sist P  Urbani R 《Biomacromolecules》2010,11(12):3256-3265
Two synthetic genes that code for artificial proteins have been constructed that were modeled on the most regularly repeated hydrophobic domain of human tropoelastin. We compare the physicochemical properties of the recombinant products that differ in their primary structure; the alanine/lysine-rich cross-linking domains, which are highly conserved in mammalian tropoelastin, were either present or absent in the recombinant products. Both biopolymers showed thermoresponsive properties, and variations were observed that were dependent on solution conditions. Cell compatibility was assayed using the biopolymers as coating agents in culture experiments with a neuroblastoma cell line; cell adhesion and proliferation effects were evaluated. The cells were found to retain their neural differentiation potential. The data presented in our work support the usefulness of these versatile biopolymers for a variety of applications related to biotechnology and biomedicine.  相似文献   
125.
The changes in the expression of glycoconjugates and adhesion molecules were studied by selective lectin binding and immunocytochemical reactions in a human embryonic epithelial cell line (EUE cells), synchronized in the cell cycle phases. The results can be summarized as follows: most of the tested lectins display a more diffuse binding for the cytoplasm in G1 than S and G2 phases; in the S and particularly in G2 phases the cytoplasm glycoconjugates are rearranged around the nucleus; cells in mitosis always show a strong binding towards all tested lectins. Cellular fibronectin and its receptor β1 integrin are well expressed in G1, but the strongest reaction is observed in the S phase. The immunoreactions for laminin and uvomorulin (L-CAM) are poorly positive in all cell cycle phases. The immunocytochemical reaction for heparan sulfate is positive, with a stronger reaction in S and G2 than in G1; on the contrary a diffuse staining with the anti-dermatan sulfate proteoglycan antibody appears unchanged during the cell cycle.  相似文献   
126.
127.
A definitive role for chromogranin A (CGA)-derived fragments in the control of the gastrointestinal smooth muscle contractility has not been yet established. The purpose of the present study was to evaluate, in vitro, the effects of the recombinant vasostatin 1-78 (VS-1), CGA 7-57 and CGA 47-66 on the mouse gastric mechanical activity, recording the changes of intraluminal pressure. VS-1, CGA 7-57 and CGA 47-66 produced concentration-dependent relaxations. Mouse anti-vasostatin-1 monoclonal antibody 5A8, recognising the region 53-57, abolished the relaxation induced by VS-1, indicating the specificity of the effect. The relaxation was significantly reduced by tetrodotoxin (TTX), blocker of neuronal voltage-dependent Na(+) channels, l-NAME, inhibitor of nitric oxide (NO) synthase, or apamin, blocker of small conductance Ca(2+)-dependent K(+) channels. The joint application of TTX and l-NAME did not show any additive effects, whereas TTX plus apamin abolished the VS-1 response. The results suggest that the N-terminal CGA-derived peptides are able to relax mouse gastric muscle and, therefore, they point out an inhibitory role of vasostatin I in the gastrointestinal tract. The relaxation is mediated in part by neural mechanisms through NO production and in part by non-neural mechanisms involving the opening of small conductance Ca(2+)-dependent K(+) channels.  相似文献   
128.
129.
SCN(-) (thiocyanate) is an important physiological anion involved in innate defense of mucosal surfaces. SCN(-) is oxidized by H(2)O(2), a reaction catalyzed by lactoperoxidase, to produce OSCN(-) (hypothiocyanite), a molecule with antimicrobial activity. Given the importance of the availability of SCN(-) in the airway surface fluid, we studied transepithelial SCN(-) transport in the human bronchial epithelium. We found evidence for at least three mechanisms for basolateral to apical SCN(-) flux. cAMP and Ca(2+) regulatory pathways controlled SCN(-) transport through cystic fibrosis transmembrane conductance regulator and Ca(2+)-activated Cl(-) channels, respectively, the latter mechanism being significantly increased by treatment with IL-4. Stimulation with IL-4 also induced the strong up-regulation of an electroneutral SCN(-)/Cl(-) exchange. Global gene expression analysis with microarrays and functional studies indicated pendrin (SLC26A4) as the protein responsible for this SCN(-) transport. Measurements of H(2)O(2) production at the apical surface of bronchial cells indicated that the extent of SCN(-) transport is important to modulate the conversion of this oxidant molecule by the lactoperoxidase system. Our studies indicate that the human bronchial epithelium expresses various SCN(-) transport mechanisms under resting and stimulated conditions. Defects in SCN(-) transport in the airways may be responsible for susceptibility to infections and/or decreased ability to scavenge oxidants.  相似文献   
130.
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