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   771篇
  免费   60篇
  2024年   3篇
  2023年   3篇
  2022年   5篇
  2021年   12篇
  2020年   9篇
  2019年   6篇
  2018年   8篇
  2017年   8篇
  2016年   19篇
  2015年   50篇
  2014年   39篇
  2013年   43篇
  2012年   64篇
  2011年   55篇
  2010年   40篇
  2009年   43篇
  2008年   65篇
  2007年   59篇
  2006年   44篇
  2005年   42篇
  2004年   40篇
  2003年   43篇
  2002年   32篇
  2001年   14篇
  2000年   10篇
  1999年   12篇
  1998年   9篇
  1997年   8篇
  1996年   4篇
  1995年   7篇
  1994年   4篇
  1993年   5篇
  1992年   4篇
  1991年   1篇
  1990年   2篇
  1988年   4篇
  1987年   2篇
  1986年   1篇
  1984年   3篇
  1983年   2篇
  1982年   1篇
  1978年   1篇
  1976年   2篇
  1972年   1篇
  1970年   1篇
  1969年   1篇
排序方式: 共有831条查询结果,搜索用时 31 毫秒
101.
102.
Two hypotheses, based on previous work on Neandertal anterior and premolar teeth, are investigated here: (1) that estimated molar lateral enamel formation times in Neandertals are likely to fall within the range of modern human population variation, and (2) that perikymata (lateral enamel growth increments) are distributed across cervical and occlusal halves of the crown differently in Neandertals than they are in modern humans. To investigate these hypotheses, total perikymata numbers and the distribution of perikymata across deciles of crown height were compared for Neandertal, northern European, and southern African upper molar mesiobuccal (mb) cusps, lower molar mesiobuccal cusps, and the lower first molar distobuccal (db) cusp. Sample sizes range from five (Neandertal M(1)db) to 29 (southern African M(1)mb). Neandertal mean perikymata numbers were found to differ significantly from those of both modern human samples (with the Neandertal mean higher) only for the M(2)mb. Regression analysis suggests that, with the exception of the M(2)mb, the hypothesis of equivalence between Neandertal and modern human lateral enamel formation time cannot be rejected. For the M(2)mb, regression analysis strongly suggests that this cusp took longer to form in the Neandertal sample than it did in the southern African sample. Plots of perikymata numbers across deciles of crown height demonstrate that Neandertal perikymata are distributed more evenly across the cervical and occlusal halves of molar crowns than they are in the modern human samples. These results are integrated into a discussion of Neandertal and modern human lateral enamel formation across the dentition, with reference to issues of life history and enamel growth processes.  相似文献   
103.
Obliterative bronchiolitis (OB), the major cause of chronic lung allograft dysfunction, is characterized by airway neutrophilia, inflammation, and remodeling, with progressive fibroproliferation and obliteration of small airways that ultimately leads to patient death. Statins have potential anti-inflammatory effects and have been demonstrated to confer a survival advantage in lung transplant patients. We postulated that the beneficial effects of simvastatin in lung transplantation are in part due to inhibition of the epithelial production of key mediators of neutrophil chemotaxis, inflammation, and airway remodeling. Our objective was to assess the effect of simvastatin on a unique population of primary bronchial epithelial cells (PBECs) derived from stable lung allografts, with specific reference to airway neutrophilia and remodeling. PBEC cultures were stimulated with IL-17 or transforming growth factor (TGF)-beta, with and without simvastatin. Supernatant levels of factors critical to driving airway neutrophilia and remodeling were measured. IL-17 upregulated IL-8, IL-6, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor (GM-CSF), and VEGF, whereas TGF-beta increased IL-6, GM-CSF, matrix metalloproteinase (MMP)-2, and MMP-9. Simvastatin attenuated effects of both IL-17 and TGF-beta. We have demonstrated the ability of simvastatin to attenuate release of airway neutrophilic and remodeling mediators and to inhibit their upregulation by TGF-beta and IL-17. These data illustrate the potential of simvastatin to alleviate neutrophilic airway inflammation and remodeling in the transplanted lung and may have additional relevance to other neutrophilic airway conditions, such as chronic obstructive pulmonary disease.  相似文献   
104.
There is increasing evidence for the involvement of plasma membrane microdomains in insulin receptor function. Moreover, disruption of these structures, which are typically enriched in sphingomyelin and cholesterol, results in insulin resistance. Treatment strategies for insulin resistance include the use of vanadium (V) compounds which have been shown in animal models to enhance insulin responsiveness. One possible mechanism for insulin-enhancing effects might involve direct effects of V compounds on membrane lipid organization. These changes in lipid organization promote the partitioning of insulin receptors and other receptors into membrane microdomains where receptors are optimally functional. To explore this possibility, we have used several strategies involving V complexes such as [VO(2)(dipic)](-) (pyridin-2,6-dicarboxylatodioxovanadium(V)), decavanadate (V(10)O(28)(6-), V(10)), BMOV (bis(maltolato)oxovanadium(IV)), and [VO(saltris)](2) (2-salicylideniminato-2-(hydroxymethyl)-1,3-dihydroxypropane-oxovanadium(V)). Our strategies include an evaluation of interactions between V-containing compounds and model lipid systems, an evaluation of the effects of V compounds on lipid fluidity in erythrocyte membranes, and studies of the effects of V-containing compounds on signaling events initiated by receptors known to use membrane microdomains as signaling platforms.  相似文献   
105.
The study has been designed to investigate the anti-diabetic effects of cesium aqua (N,N′-ethylene (salicylideneiminato)-5-sulfonato) oxovanadium (IV) dihydrate (VO(salen-SO3)), an organic vanadium compound, in streptozotocin-induced diabetic rats. VO(salen-SO3) was orally administrated to diabetic rats at the dose of 0.3 mg/ml through drinking water for 24 days. Blood glucose level was significantly declined, and oral glucose tolerance was improved after VO(salen-SO3) treatment. Moreover, liver and muscle glycogen concentrations were markedly increased in VO(salen-SO3)-treated diabetic rats. On the other hand, aspartate amino transferase and blood urea nitrogen in serum were significantly decreased after treatment with VO(salen-SO3). Take together, these results suggested that VO(salen-SO3) may be of potential value in the therapy of diabetic symptom and hyperglycemia-induced hepatic and renal dysfunction.  相似文献   
106.
In order to assess the role of osteopontin (OPN) in leukocyte accumulation in inflammatory conditions, native OPN and its thrombin cleaved form (OPN + Thr) were studied in vivo using a rodent subcutaneous air pouch model (AP). Both forms of OPN-induced macrophage infiltration into the AP in wild-type mice. In animals lacking CD44, macrophage numbers were significantly reduced within the cavity, but cells still accumulated along the subcutaneous lining. In animals lacking endogenous OPN, no differences were found in exogenous OPN-induced macrophage accumulation, although macrophage exhibited increased α4 integrin expression. These studies reveal that both OPN and OPN + Thr attract macrophages in vivo through CD44.  相似文献   
107.
Given that signal sequences between secreted proteins of different species can be interchanged, it is reasonable to expect that both mammalian and yeast signal sequence trapping (SST) systems would secrete Haemonchus contortus proteins with similar efficiency and quality. To determine if H. contortus cDNAs that contain a signal sequence could re-establish secretion of a reporter protein, mammalian and yeast SST vectors were designed, 10 H. contortus genes selected, and their respective cDNAs cloned into these two SST vectors. The selected molecules included genes known to code for excretory/secretory or membrane-bound proteins as potential test 'positives', and genes known to code for non-secreted proteins as test 'negatives'. While differentiation between secretion and non-secretion was evident in both systems, the results indicated greater efficiency was achieved when the mammalian system was used. Therefore, mammalian SST using COS cells would be a more useful tool to screen H. contortus cDNA libraries for potential secreted and type-1 integral membrane proteins than yeast SST.  相似文献   
108.
Metal complexation reactions can be used effectively as sensors to measure concentrations of phosphate and phosphate analogs. Recently, a method was described for the detection of phosphate or ATP in aqueous solution based on the displacement by these ligands of pyrocatechol violet (PV) from a putative 2:1 (Yb3+)2PV complex. We have not been able to reproduce this stoichiometry and report this work in order to correct the coordination chemistry upon which sensor applications are based. In our work, colorimetric and spectrophotometric detection of phosphate was confirmed qualitatively (blue PV + Yb3+; yellow + Pi); however, the sequence of visual changes on the titration of PV with 2 equiv. of Yb3+ and back titration with ATP as described previously could not be reproduced. In contrast to the linear response to Pi that was reported previously, the absorbance response at 443 or 623 nm was found to be sigmoidal using the recommended 2:1 Yb3+:PV solution (100 μM:50 μM, pH 7, HEPES). Furthermore, both continuous variation titration and molar ratio analysis (Job plot) experiments are consistent with 1:1, not 2:1, YbPV complex stoichiometry at pH 7 in HEPES buffer, indicating that the deviation from linearity is produced by excess Yb3+. Indeed, using a 1:1 Yb3+:PV ratio produces a linear response in ΔAbs at 443 or 623 nm on back titration with analyte (phosphate or ATP). In addition, speciation analysis of the Yb–ATP system demonstrates that a 1:1 complex containing Yb3+ and ATP predominates in solution at μM metal ion and ATP concentrations. Paramagnetic 1H NMR spectroscopy directly establishes the formation of Yb3+–solute complexes in dilute aqueous solution. The 1:1 YbPV complex can be used for the colorimetric measurement of phosphate and ATP concentrations from ~2 μM. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Charles E. McKenna (Corresponding author)Email:
  相似文献   
109.
Objective To assess whether a nurse led, flow monitored protocol for optimising circulatory status in patients after cardiac surgery reduces complications and shortens stay in intensive care and hospital.Design Randomised controlled trial.Setting Intensive care unit and cardiothoracic unit of a university teaching hospital.Participants 174 patients who underwent cardiac surgery between April 2000 and January 2003.Interventions Patients were allocated to conventional haemodynamic management or to an algorithm guided by oesophageal Doppler flowmetry to maintain a stroke index above 35 ml/m2.Results 26 control patients had postoperative complications (two deaths) compared with 17 (four deaths) protocol patients (P = 0.08). Duration of hospital stay in the protocol group was significantly reduced from a median of nine (interquartile range 7-12) days to seven (7-10) days (P = 0.02). The mean duration of hospital stay was reduced from 13.9 to 11.4 days, a saving in hospital bed days of 18% (95% confidence interval -12% to 47%). Usage of intensive care beds was reduced by 23% (-8% to 59%).Conclusion A nurse delivered protocol for optimising circulatory status in the early postoperative period after cardiac surgery may significantly shorten hospital stay.  相似文献   
110.
Microarrays allow monitoring of gene expression for tens of thousands of genes in parallel and are being used routinely to generate huge amounts of valuable data. Handling and analysis of such data are becoming major bottlenecks in the utilization of the technology. To enable the researcher to interpret the results postanalysis, we have developed a laboratory information management system for microarrays (LIMaS) with an n-tier Java front-end and relational database to record and manage large-scale expression data preanalysis. This system enables the laboratory to replace the paper trail with an efficient and fully customizable interface giving it the ability to adapt to any working practice, e.g., handling many resources used to form many products (chaining of resources). The ability to define sets of activities, resources, and workflows makes LIMaS MIAME-supportive.LIMaS is available for download at (http://www.mgu.har.mrc.ac.uk/microarray.)  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