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   838篇
  免费   66篇
  2023年   4篇
  2022年   5篇
  2021年   19篇
  2020年   12篇
  2019年   13篇
  2018年   28篇
  2017年   12篇
  2016年   27篇
  2015年   43篇
  2014年   55篇
  2013年   86篇
  2012年   65篇
  2011年   57篇
  2010年   40篇
  2009年   16篇
  2008年   30篇
  2007年   42篇
  2006年   34篇
  2005年   32篇
  2004年   40篇
  2003年   27篇
  2002年   31篇
  2001年   16篇
  2000年   14篇
  1999年   12篇
  1998年   13篇
  1997年   3篇
  1996年   5篇
  1995年   3篇
  1994年   4篇
  1993年   6篇
  1992年   8篇
  1991年   14篇
  1990年   6篇
  1989年   6篇
  1988年   6篇
  1987年   6篇
  1986年   8篇
  1985年   7篇
  1984年   9篇
  1983年   4篇
  1979年   6篇
  1977年   2篇
  1976年   3篇
  1972年   2篇
  1970年   2篇
  1967年   5篇
  1930年   1篇
  1925年   1篇
  1921年   1篇
排序方式: 共有904条查询结果,搜索用时 15 毫秒
61.
We previously reported that PLA(2) activity in the gills is higher than that in other tissues in red sea bream and purified PLA(2) from the gills belongs to the group IB PLA(2) as well as other red sea bream PLA(2)s. In this study, we reconfirmed that the level of PLA(2) activity is extremely high in the gills compared with other tissues, and gill PLA(2) was detected only in the gills by immunoblotting and inhibition test using anti-gill PLA(2) monoclonal antibody. The level of PLA(2) activity and protein expression in the gills are well correlated. Fish can be roughly divided into high and low groups based on the level of PLA(2) activity. Gill PLA(2) was detected in the gills of the high group, but not the low group by immunoblotting. In the gills of the high group, gill PLA(2) was detected in the mucous cells and pavement cells located on the surface of gill epithelia by immunohistochemistry. On the other hand, positive signals were observed only in the mucous cells by in situ hybridization. We also isolated inactive proPLA(2), having AR propeptide, preceding the mature enzyme from the gill extract. These results suggest that gill PLA(2) is synthesized as an inactive proPLA(2) in the mucous cells and is secreted to the surface of gill epithelia.  相似文献   
62.
The organic nitrate pentaerythrityl tetranitrate (PETN) is known to exert long-term antioxidant and antiatherogenic effects by as yet unidentified mechanisms. In cultured endothelial cells derived from human umbilical vein, the active PETN metabolite PETriN (0.01-1 mM) increased heme oxygenase (HO)-1 mRNA and protein levels in a concentration-dependent fashion. HO-1 induction was accompanied by a marked increase in catalytic activity of the enzyme as reflected by enhanced formation of carbon monoxide and bilirubin. Pretreatment with PETriN or bilirubin at low micromolar concentrations protected endothelial cells from hydrogen peroxide-mediated toxicity. HO-1 induction and endothelial protection by PETriN were not mimicked by isosorbide dinitrate, another long-acting nitrate. The present study demonstrates that PETriN stimulates mRNA and protein expression as well as enzymatic activity of the antioxidant defense protein HO-1 in endothelial cells. Increased HO-1 expression and ensuing formation of cytoprotective bilirubin may contribute to and explain the specific antioxidant and antiatherogenic actions of PETN.  相似文献   
63.
It has been long postulated that extracellular purines can modulate the function of the male reproductive system by interacting with different purinergic receptors of Sertoli and germinative cells. Many authors have described the biological changes induced by extracellular ATP and/or adenosine in these cells, and some hypothetical models for paracrine communication mediated by purines were proposed; however, the cellular source(s) of these molecules in seminiferous tubules remains unknown. In this study, we demonstrated for the first time that Sertoli cells are able to release ATP (0.3 nmol/mg protein) and adenosine (0.1 nmol/mg protein) in the extracellular medium, while germinative and myoid peritubular cells are able to secrete adenosine (0.02 and 0.37 nmol/mg protein, respectively). Indeed, all the three types of cells were able to release inosine at significant concentrations (about 0.4 nmol/mg protein). This differential secretion depending on the cellular type suggests that these molecules may be involved in the paracrine regulation and/or control of the maturation processes of these cells.  相似文献   
64.
Daily variations in plasma melatonin levels in the rainbow trout Oncorhynchus mykiss were studied under various light and temperature conditions. Plasma melatonin levels were higher at mid-dark than those at mid-light under light-dark (LD) cycles. An acute exposure to darkness (2 hr) during the light phase significantly elevated the plasma melatonin to the level that is comparable with those at mid-dark, while an acute exposure to a light pulse (2 hr) during the dark phase significantly suppressed melatonin to the level that is comparable with those at mid-light. Plasma melatonin kept constantly high and low levels under constant darkness and constant light, respectively. No circadian rhythm was seen under both conditions. When the fish were subjected to simulative seasonal conditions (simulative (S)-spring: under LD 13.1:10.9 at 13 degrees C; S-summer: under LD 14.3:9.7 at 16.5 degrees C; S-autumn: under LD 11.3:12.7 at 13 degrees C; S-winter: under LD 10.1:13.9 at 9 degrees C), melatonin levels during the dark phase were significantly higher than those during the light phase irrespective of simulative seasons. The peak melatonin level in each simulative season significantly correlated with temperature but not with the length of the dark phase employed. In addition, the peak melatonin level in S-autumn was significantly higher than those in S-spring although water temperature was the same under these conditions. These results indicate that the melatonin rhythm in the trout plasma is not regulated by an endogenous circadian clock but by combination of photoperiod and water temperature.  相似文献   
65.
Chronic hypothyroidism is frequently associated with atherosclerosis due to increased cholesterol plasma levels; nevertheless, the contribution of impaired reverse cholesterol transport (RCT) in this process has not been completely elucidated. The aim of this study was to evaluate the effect of thyroidectomy (Htx) upon the main stages of RCT in rats. Plasma lipid alterations induced by thyroidectomy showed a slight, but significant, reduction of total plasma triglycerides, a 300% increase of LDL-cholesterol and a 25% decrease in HDL-cholesterol compared to control rats. We evaluated the first stage of RCT determining 3H-cholesterol efflux in Fu5AH cells. The capacity of HDL obtained from Htx rats to promote cholesterol efflux was similar to that of controls. Lecithin:cholesterol acyltransferase (LCAT) activity, the second stage and the driving force of RCT was 30% lower in Htx animals compared to controls, as determined by reconstituted HDL used as an external substrate. Lipoproteins are remodeled by hepatic lipase; the mean activity of this enzyme in postheparin plasma of Htx animals was reduced by 30% compared to controls, thus suggesting an impaired HDL remodeling by this enzyme in the hypothyroid status. In contrast, lipoprotein lipase activity in the Htx group was unchanged. In summary, this study demonstrates that chronic hypothyroidism in the rat induced an impaired RCT mainly at the cholesterol esterification, and HDL remodeling mediated by hepatic lipase. The latter probably results in an abnormal HDL structure, i.e. phospholipid enrichment, which contributes to decrease HDL-apo AI fractional catabolic rates.  相似文献   
66.
A ubiquitin-like modifier, NEDD8, is covalently attached to cullin-family proteins, but its physiological role is poorly understood. Here we report that the NEDD8-modifying pathway is essential for cell viability and function of Pcu1 (cullin-1 orthologue) in fission yeast. Pcu1 assembled on SCF ubiquitin-ligase was completely modified by NEDD8. Pcu1(K713R) defective for NEDD8 conjugation lost the ability to complement lethality due to pcu1 deletion. Forced expression of Pcu1(K713R) or depletion of NEDD8 in cells resulted in impaired cell proliferation and marked stabilization of the cyclin-dependent kinase inhibitor Rum1, which is a substrate of the SCF complex. Based on these findings, we propose that covalent modification of cullin-1 by the NEDD8 system plays an essential role in the function of SCF in fission yeast.  相似文献   
67.
68.
BackgroundLess than one-third of HIV-infected pregnant women eligible for combination antiretroviral therapy (ART) globally initiate treatment prior to delivery, with lack of access to timely CD4 results being a principal barrier. We evaluated the effectiveness of an SMS-based intervention to improve access to timely antenatal ART.MethodsWe conducted a stepped-wedge cluster randomized trial of a low-cost programmatic intervention in 20 antenatal clinics in Gaborone, Botswana. From July 2011-April 2012, 2 clinics were randomly selected every 4 weeks to receive an ongoing clinic-based educational intervention to improve CD4 collection and to receive CD4 results via an automated SMS platform with active patient tracing. CD4 testing before 26 weeks gestation and ART initiation before 30 weeks gestation were assessed.ResultsThree-hundred-sixty-six ART-naïve women were included, 189 registering for antenatal care under Intervention and 177 under Usual Care periods. Of CD4-eligible women, 100 (59.2%) women under Intervention and 79 (50.6%) women under Usual Care completed CD4 phlebotomy before 26 weeks gestation, adjusted odds ratio (aOR, adjusted for time that a clinic initiated Intervention) 0.87 (95% confidence interval [CI]0.47–1.63, P = 0.67). The SMS-based platform reduced time to clinic receipt of CD4 test result from median of 16 to 6 days (P<0.001), was appreciated by clinic staff, and was associated with reduced operational cost. However, rates of ART initiation remained low, with 56 (36.4%) women registering under Intervention versus 37 (24.2%) women under Usual Care initiating ART prior to 30 weeks gestation, aOR 1.06 (95%CI 0.53–2.13, P = 0.87).ConclusionsThe augmented SMS-based intervention delivered CD4 results more rapidly and efficiently, and this type of SMS-based results delivery platform may be useful for a variety of tests and settings. However, the intervention did not appear to improve access to timely antenatal CD4 testing or ART initiation, as obstacles other than CD4 impeded ART initiation during pregnancy.  相似文献   
69.
70.

Background

Effective coordination between organizations, agencies and bodies providing or financing health services in humanitarian crises is required to ensure efficiency of services, avoid duplication, and improve equity. The objective of this review was to assess how, during and after humanitarian crises, different mechanisms and models of coordination between organizations, agencies and bodies providing or financing health services compare in terms of access to health services and health outcomes.

Methods

We registered a protocol for this review in PROSPERO International prospective register of systematic reviews under number PROSPERO2014:CRD42014009267. Eligible studies included randomized and nonrandomized designs, process evaluations and qualitative methods. We electronically searched Medline, PubMed, EMBASE, Cochrane Central Register of Controlled Trials, CINAHL, PsycINFO, and the WHO Global Health Library and websites of relevant organizations. We followed standard systematic review methodology for the selection, data abstraction, and risk of bias assessment. We assessed the quality of evidence using the GRADE approach.

Results

Of 14,309 identified citations from databases and organizations'' websites, we identified four eligible studies. Two studies used mixed-methods, one used quantitative methods, and one used qualitative methods. The available evidence suggests that information coordination between bodies providing health services in humanitarian crises settings may be effective in improving health systems inputs. There is additional evidence suggesting that management/directive coordination such as the cluster model may improve health system inputs in addition to access to health services. None of the included studies assessed coordination through common representation and framework coordination. The evidence was judged to be of very low quality.

Conclusion

This systematic review provides evidence of possible effectiveness of information coordination and management/directive coordination between organizations, agencies and bodies providing or financing health services in humanitarian crises. Our findings can inform the research agenda and highlight the need for improving conduct and reporting of research in this field.  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