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   242篇
  免费   19篇
  2023年   3篇
  2021年   4篇
  2020年   8篇
  2019年   3篇
  2018年   7篇
  2017年   11篇
  2016年   18篇
  2015年   9篇
  2014年   10篇
  2013年   15篇
  2012年   27篇
  2011年   26篇
  2010年   8篇
  2009年   3篇
  2008年   6篇
  2007年   5篇
  2006年   5篇
  2005年   7篇
  2004年   5篇
  2003年   7篇
  2002年   6篇
  2001年   6篇
  2000年   5篇
  1999年   8篇
  1998年   1篇
  1997年   3篇
  1996年   4篇
  1995年   3篇
  1994年   2篇
  1993年   1篇
  1992年   4篇
  1991年   3篇
  1990年   5篇
  1989年   3篇
  1988年   1篇
  1987年   4篇
  1986年   2篇
  1984年   3篇
  1981年   1篇
  1974年   1篇
  1973年   1篇
  1969年   1篇
  1965年   1篇
  1962年   1篇
  1955年   1篇
  1954年   1篇
  1953年   1篇
  1943年   1篇
排序方式: 共有261条查询结果,搜索用时 15 毫秒
51.
The prehistoric lake settlement tradition is spread far beyond the region of the Alps, and it has been known for a long time that lake settlements are not a characteristic of one particular area. The present paper presents the results of the first comprehensive, interdisciplinary investigations of such types of sites in Lithuania, the two lake settlements at Lake Luokesa (Luokesai e?eras). They were excavated with underwater archaeology techniques between 2000 and 2011. They are Late Bronze to early Iron Age transition (LBA–EIA) in date and were probably built and inhabited during a short period between 625 and 535 cal bc. The excavated archaeological material contains a wealth of well-preserved wooden architectural details and other organic materials. Therefore, the importance and unique character of these sites is beyond question. This paper gives an overview of the history of research on lake settlements in northeastern Europe. In addition, the archaeological material of the LBA–EIA settlements at Lake Luokesa is evaluated in the context of the other lake settlements in the southeastern Baltic region. Existing hypotheses and interpretations of the origins, development and use of the lake settlements of this region are discussed. All the investigations which have been done, including archaeobotany, palynology, dendrochronology and geoarchaeology, provide data for a well-grounded interpretation and reconstruction of the Luokesa lake settlements.  相似文献   
52.
Cutaneous fungal infections are common and widespread. Antifungal agents used for the treatment of these infections often have undesirable side effects. Furthermore, increased resistance of the microorganisms to the antifungal drugs becomes the growing problem. Accordingly, the search for natural antifungal compounds continues to receive attention. Apoptosis is highly regulated programmed cell death. During yeast cell apoptosis, amino acids and peptides are released and can stimulate regeneration of human epithelium cells. Thus, detection of chemical compounds inducing apoptosis in yeast and nontoxic for humans is of great medical relevance. The aim of this study was to detect chemical compound inducing apoptosis in pathogenic Candida species with the lowest toxicity to the mammalian cells. Five chemical compounds—acetic acid, sodium bicarbonate, potassium carbonate, lithium acetate, and formic acid—were tested for evaluation of antifungal activity on C. albicans, C. guilliermondii, and C. lusitaniae. The results showed that acetic acid and formic acid at the lowest concentrations induced yeast cells death. Apoptosis analysis revealed that cells death was accompanied by activation of caspase. Minimal inhibitory concentrations of potassium carbonate and sodium bicarbonate induced Candida cells necrosis. Toxicity test with mammalian cell cultures showed that formic acid has the lowest effect on the growth of Jurkat and NIH 3T3 cells. In conclusion, our results show that a low concentration of formic acid induces apoptosis-like programmed cell death in the Candida yeast and has a minimal effect on the survivability of mammalian cells, suggesting potential applications in the treatment of these infections.  相似文献   
53.
In the present study, the 26-residue peptide sequence Ac-KWKSFLKTFKSAVKTVLHTALKAISS-amide (V681) was utilized as the framework to study the effects of peptide hydrophobicity/hydrophilicity, amphipathicity, and helicity (induced by single amino acid substitutions in the center of the polar and nonpolar faces of the amphipathic helix) on biological activities. The peptide analogs were also studied by temperature profiling in reversed-phase high performance liquid chromatography, from 5 to 80 degrees C, to evaluate the self-associating ability of the molecules in solution, another important parameter in understanding peptide antimicrobial and hemolytic activities. A higher ability to self-associate in solution was correlated with weaker antimicrobial activity and stronger hemolytic activity of the peptides. Biological studies showed that strong hemolytic activity of the peptides generally correlated with high hydrophobicity, high amphipathicity, and high helicity. In most cases, the D-amino acid substituted peptides possessed an enhanced average antimicrobial activity compared with L-diastereomers. The therapeutic index of V681 was improved 90- and 23-fold against Gram-negative and Gram-positive bacteria, respectively. By simply replacing the central hydrophobic or hydrophilic amino acid residue on the nonpolar or the polar face of these amphipathic derivatives of V681 with a series of selected D-/L-amino acids, we demonstrated that this method has excellent potential for the rational design of antimicrobial peptides with enhanced activities.  相似文献   
54.
55.
56.
Fatty acids were identified in monofloral beebread (BB) and bee pollen (BP) loads collected from Trifolium pratense L. A gas chromatography method was used to identify and quantify fatty acids: Thirty-five fatty acids were identified in BB and 42 in BP. A high amount of the healthy n-3 fatty acids was found. The ratio of polyunsaturated fatty acids n-3 to n-6 reached a value of 8.42 and 3.35 in the latter products. The proteomic analysis also was performed on the manually collected T. pratense pollen, and the most abundant protein groups were subjected to mass spectrometry analysis. Proteins identified in T. pratense pollen are involved in the main cellular functions (cell membrane formation, organelles traffic, and mainly metabolic processes). Because of the composition of fatty acids in BB and BP and a variety of proteins present in pollen, these products are considered to be favorable for human nutrition and health.  相似文献   
57.

Background

Africa bears 24% of the global burden of disease but has only 3% of the world’s health workers. Substantial variation in health worker performance adds to the negative impact of this significant shortfall. We therefore sought to identify interventions implemented in sub-Saharan African aiming to improve health worker performance and the contextual factors likely to influence local effectiveness.

Methods and Findings

A systematic search for randomised controlled trials of interventions to improve health worker performance undertaken in sub-Saharan Africa identified 41 eligible trials. Data were extracted to define the interventions’ components, calculate the absolute improvement in performance achieved, and document the likelihood of bias. Within-study variability in effect was extracted where reported. Statements about contextual factors likely to have modified effect were subjected to thematic analysis. Interventions to improve health worker performance can be very effective. Two of the three trials assessing mortality impact showed significant reductions in death rates (age<5 case fatality 5% versus 10%, p<0.01; maternal in-hospital mortality 6.8/1000 versus 10.3/1000; p<0.05). Eight of twelve trials focusing on prescribing had a statistically significant positive effect, achieving an absolute improvement varying from 9% to 48%. However, reported range of improvement between centres within trials varied substantially, in many cases exceeding the mean effect. Nine contextual themes were identified as modifiers of intervention effect across studies; most frequently cited were supply-line failures, inadequate supervision or management, and failure to follow-up training interventions with ongoing support, in addition to staff turnover.

Conclusions

Interventions to improve performance of existing staff and service quality have the potential to improve patient care in underserved settings. But in order to implement interventions effectively, policy makers need to understand and address the contextual factors which can contribute to differences in local effect. Researchers therefore must recognise the importance of reporting how context may modify effect size.  相似文献   
58.
OBJECTIVE--To assess the extent of three year follow up of blood pressure, weight, and smoking habit in patients with raised blood pressure identified at health checks. DESIGN--Retrospective audit of medical and nursing records. SETTING--Three general practices in Oxfordshire. PATIENTS--386 of 448 patients with raised blood pressure (diastolic greater than or equal to 90 or systolic greater than or equal to 160 mm Hg) identified from 2935 patients aged 35-64 attending health checks in 1982-4. MEASUREMENTS and MAIN RESULTS--All records of blood pressure, weight, and smoking habit in the medical record were abstracted for three years after the initial health check. All 42 patients with an initial diastolic blood pressure greater than or equal to 105 mm Hg and 316 of 344 patients with an initial pressure of 90-104 mm Hg had at least one further measurement of their blood pressure. Follow up of smoking habit and of weight was less complete with only half of the 100 smokers and 67 of the 87 obese patients (body mass index greater than or equal to 30) having any documented follow up of these risk factors. Annual follow up in the second and third years occurred in 228/297 (76.8%) and 232/320 (72.5%) in patients with blood pressure greater than 95 mm Hg at the beginning of each year. For patients who smoked annual follow up in these years occurred in fewer than a third and for those who were obese in just over half. On the assumption that those not followed up had not changed, at the end of three years the proportion of patients with diastolic blood pressure greater than or equal to 100 mm Hg had fallen from 61 patients (15.8%) to 31 (8.1%); the proportion of smokers had fallen from 103 (26.7%) to 94 (24.4%); and the proportion of obese patients had fallen from 87 (22.5%) to 79 (20.5%). CONCLUSIONS--These changes were modest and in the absence of a control group cannot be attributed necessarily to health checks. Although the standard of follow up was better than in previously reported studies of the management of hypertension, the results emphasise the need to develop formal protocols for dietary and antismoking interventions and to evaluate formally the effectiveness (and cost effectiveness) of health checks.  相似文献   
59.
60.
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