全文获取类型
收费全文 | 3837篇 |
免费 | 376篇 |
国内免费 | 1篇 |
出版年
2023年 | 32篇 |
2022年 | 47篇 |
2021年 | 97篇 |
2020年 | 65篇 |
2019年 | 46篇 |
2018年 | 59篇 |
2017年 | 76篇 |
2016年 | 126篇 |
2015年 | 221篇 |
2014年 | 232篇 |
2013年 | 228篇 |
2012年 | 320篇 |
2011年 | 294篇 |
2010年 | 180篇 |
2009年 | 182篇 |
2008年 | 246篇 |
2007年 | 200篇 |
2006年 | 199篇 |
2005年 | 204篇 |
2004年 | 176篇 |
2003年 | 178篇 |
2002年 | 164篇 |
2001年 | 31篇 |
2000年 | 31篇 |
1999年 | 32篇 |
1998年 | 50篇 |
1997年 | 33篇 |
1996年 | 27篇 |
1995年 | 26篇 |
1994年 | 22篇 |
1993年 | 19篇 |
1992年 | 21篇 |
1991年 | 17篇 |
1990年 | 21篇 |
1989年 | 13篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1984年 | 19篇 |
1983年 | 12篇 |
1981年 | 27篇 |
1980年 | 13篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 19篇 |
1976年 | 10篇 |
1974年 | 8篇 |
1973年 | 13篇 |
1970年 | 10篇 |
1969年 | 8篇 |
1968年 | 10篇 |
排序方式: 共有4214条查询结果,搜索用时 15 毫秒
141.
Short-Term Effects of Traditional and Alternative Community Interventions to Address Food Insecurity
Background
Despite the effects of food insecurity on health are well documented, clear governmental policies to face food insecurity do not exist in western countries. In Canada, interventions to face food insecurity are developed at the community level and can be categorized into two basic strategies: those providing an immediate response to the need for food, defined “traditional” and those targeting the improvement of participants’ social cohesion, capabilities and management of their own nutrition, defined “alternative”.Objective
The objective of this study was to evaluate the effects of food insecurity interventions on food security status and perceived health of participants.Design
This was a longitudinal multilevel study implemented in Montreal, Quebec, Canada. Participants were recruited in a two-stage cluster sampling frame. Clustering units were community organizations working on food insecurity; units of analysis were participants in community food security interventions. A total of 450 participants were interviewed at the beginning and after 9 months of participation in traditional or alternative food security interventions. Food security and perceived health were investigated as dependent variables. Differences overtime were assessed through multilevel regression models.Results
Participants in traditional interventions lowered their food insecurity at follow-up. Decreases among participants in alternative interventions were not statistically significant. Participants in traditional interventions also improved physical (B coefficient 3.00, CI 95% 0.42–5.59) and mental health (B coefficient 6.25, CI 95% 4.15–8.35).Conclusions
Our results challenge the widely held view suggesting the ineffectiveness of traditional interventions in the short term. Although effects may be intervention-dependent, food banks decreased food insecurity and, in so doing, positively affected perceived health. Although study findings demonstrate that food banks offer short term reprise from the effects of food insecurity, the question as to whether food banks are the most appropriate solution to food insecurity still needs to be addressed. 相似文献142.
Background
Dental biomechanics based on finite element (FE) analysis is attracting enormous interest in dentistry, biology, anthropology and palaeontology. Nonetheless, several shortcomings in FE modeling exist, mainly due to unrealistic loading conditions. In this contribution we used kinematics information recorded in a virtual environment derived from occlusal contact detection between high resolution models of an upper and lower human first molar pair (M1 and M1, respectively) to run a non-linear dynamic FE crash colliding test.Methodology
MicroCT image data of a modern human skull were segmented to reconstruct digital models of the antagonistic right M1 and M1 and the dental supporting structures. We used the Occlusal Fingerprint Analyser software to reconstruct the individual occlusal pathway trajectory during the power stroke of the chewing cycle, which was applied in a FE simulation to guide the M1 3D-path for the crash colliding test.Results
FE analysis results showed that the stress pattern changes considerably during the power stroke, demonstrating that knowledge about chewing kinematics in conjunction with a morphologically detailed FE model is crucial for understanding tooth form and function under physiological conditions.Conclusions/Significance
Results from such advanced dynamic approaches will be applicable to evaluate and avoid mechanical failure in prosthodontics/endodontic treatments, and to test material behavior for modern tooth restoration in dentistry. This approach will also allow us to improve our knowledge in chewing-related biomechanics for functional diagnosis and therapy, and it will help paleoanthropologists to illuminate dental adaptive processes and morphological modifications in human evolution. 相似文献143.
Louise Lafortune Steven Martin Sarah Kelly Isla Kuhn Olivia Remes Andy Cowan Carol Brayne 《PloS one》2016,11(2)
Background
Smoking, alcohol consumption, poor diet and low levels of physical activity significantly contribute to the burden of illness in developed countries. Whilst the links between specific and multiple risk behaviours and individual chronic conditions are well documented, the impact of these behaviours in mid-life across a range of later life outcomes has yet to be comprehensively assessed. This review aimed to provide an overview of behavioural risk factors in mid-life that are associated with successful ageing and the primary prevention or delay of disability, dementia, frailty and non-communicable chronic conditions.Methods
A literature search was conducted to identify cohort studies published in English since 2000 up to Dec 2014. Multivariate analyses and a minimum follow-up of five years were required for inclusion. Two reviewers screened titles, abstracts and papers independently. Studies were assessed for quality. Evidence was synthesised by mid-life behavioural risk for a range of late life outcomes.Findings
This search located 10,338 individual references, of which 164 are included in this review. Follow-up data ranged from five years to 36 years. Outcomes include dementia, frailty, disability and cardiovascular disease. There is consistent evidence of beneficial associations between mid-life physical activity, healthy ageing and disease outcomes. Across all populations studied there is consistent evidence that mid-life smoking has a detrimental effect on health. Evidence specific to alcohol consumption was mixed. Limited, but supportive, evidence was available relating specifically to mid-life diet, leisure and social activities or health inequalities.Conclusions
There is consistent evidence of associations between mid-life behaviours and a range of late life outcomes. The promotion of physical activity, healthy diet and smoking cessation in all mid-life populations should be encouraged for successful ageing and the prevention of disability and chronic disease. 相似文献144.
Effects of the Commercial Flame Retardant Mixture DE-71 on Cytokine Production by Human Immune Cells
Thit Mynster Kronborg Juliana Frohnert Hansen Claus Henrik Nielsen Louise Ramh?j Marie Frederiksen Katrin Vorkamp Ulla Feldt-Rasmussen 《PloS one》2016,11(4)
IntroductionAlthough production of polybrominated diphenyl ethers (PBDEs) is now banned, release from existing products will continue for many years. The PBDEs are assumed to be neurotoxic and toxic to endocrine organs at low concentrations. Their effect on the immune system has not been investigated thoroughly. We aimed to investigate the influence of DE-71 on cytokine production by peripheral blood mononuclear cells (PBMCs) stimulated with Escherichia Coli lipopolysaccharide (LPS) or phytohaemagglutinin-L (PHA-L).ResultsAt non-cytotoxic concentrations (0.01–10 μg/mL), DE-71 significantly enhanced secretion of IL-1β, IL-6, CXCL8, IL-10, and TNF-α (p<0.001–0.019; n = 6) from LPS-stimulated PBMCs. IFN-γ, TNF-α, IL-17A, and IL-17F (p = <0.001–0.043; n = 6) secretion were enhanced from PHA-L-stimulated PBMCs as well. Secretion of IL-1β, IL-2, IL-10, IL-8 and IL-6 was not significantly affected by DE-71.ConclusionsWe demonstrate an enhancing effect of DE-71 on cytokine production by normal human PBMCs stimulated with LPS or PHA-L ex vivo. 相似文献
145.
146.
147.
148.
James?A. Poulter Manir Ali David?F. Gilmour Aine Rice Hiroyuki Kondo Kenshi Hayashi David?A. Mackey Lisa?S. Kearns Jonathan?B. Ruddle Jamie?E. Craig Eric?A. Pierce Louise?M. Downey Moin?D. Mohamed Alexander?F. Markham Chris?F. Inglehearn Carmel Toomes 《American journal of human genetics》2016,98(3):592
149.
The human ocular surface, consisting of the cornea and conjunctiva, is colonized by an expansive, diverse microbial community. Molecular-based methods, such as 16S rRNA sequencing, has allowed for more comprehensive and precise identification of the species composition of the ocular surface microbiota compared to traditional culture-based methods. Evidence suggests that the normal microbiota plays a protective immunological role in preventing the proliferation of pathogenic species and thus, alterations in the homeostatic microbiome may be linked to ophthalmic pathologies. Further investigation of the ocular surface microbiome, as well as the microbiome of other areas of the body such as the oral mucosa and gut, and their role in the pathophysiology of diseases is a significant, emerging field of research, and may someday enable the development of novel probiotic approaches for the treatment and prevention of ophthalmic diseases. 相似文献
150.