全文获取类型
收费全文 | 7046篇 |
免费 | 820篇 |
国内免费 | 3篇 |
专业分类
7869篇 |
出版年
2023年 | 20篇 |
2022年 | 47篇 |
2021年 | 113篇 |
2020年 | 55篇 |
2019年 | 82篇 |
2018年 | 64篇 |
2017年 | 74篇 |
2016年 | 150篇 |
2015年 | 260篇 |
2014年 | 291篇 |
2013年 | 328篇 |
2012年 | 477篇 |
2011年 | 495篇 |
2010年 | 266篇 |
2009年 | 271篇 |
2008年 | 419篇 |
2007年 | 450篇 |
2006年 | 401篇 |
2005年 | 436篇 |
2004年 | 412篇 |
2003年 | 424篇 |
2002年 | 384篇 |
2001年 | 81篇 |
2000年 | 56篇 |
1999年 | 102篇 |
1998年 | 122篇 |
1997年 | 88篇 |
1996年 | 88篇 |
1995年 | 74篇 |
1994年 | 88篇 |
1993年 | 72篇 |
1992年 | 66篇 |
1991年 | 62篇 |
1990年 | 48篇 |
1989年 | 52篇 |
1988年 | 51篇 |
1987年 | 70篇 |
1986年 | 46篇 |
1985年 | 48篇 |
1984年 | 79篇 |
1983年 | 57篇 |
1982年 | 87篇 |
1981年 | 61篇 |
1980年 | 56篇 |
1979年 | 46篇 |
1978年 | 31篇 |
1977年 | 40篇 |
1976年 | 31篇 |
1975年 | 25篇 |
1974年 | 21篇 |
排序方式: 共有7869条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
995.
996.
Nancy S. Jecker 《Developing world bioethics》2018,18(2):144-155
How should healthcare systems prepare to care for growing numbers and proportions of older people? Older people generally suffer worse health than younger people do. Should societies take steps to reduce age‐related health inequalities? Some express concern that doing so would increase age‐related inequalities in healthcare. This paper addresses this debate by (1) presenting an argument in support of three principles for distributing scarce resources between age groups; (2) framing these principles of age group justice in terms of life stages; and (3) indicating policy implications that merit further attention in light of rapidly aging societies. 相似文献
997.
Evolutionary processes have been described not only in biology but also for a wide range of human cultural activities including languages and law. In contrast to the evolution of DNA or protein sequences, the detailed mechanisms giving rise to the observed evolution-like processes are not or only partially known. The absence of a mechanistic model of evolution implies that it remains unknown how the distances between different taxa have to be quantified. Considering distortions of metric distances, we first show that poor choices of the distance measure can lead to incorrect phylogenetic trees. Based on the well-known fact that phylogenetic inference requires additive metrics, we then show that the correct phylogeny can be computed from a distance matrix \({\mathbf {D}}\) if there is a monotonic, subadditive function \(\zeta\) such that \(\zeta ^{-1}({\mathbf {D}})\) is additive. The required metric-preserving transformation \(\zeta\) can be computed as the solution of an optimization problem. This result shows that the problem of phylogeny reconstruction is well defined even if a detailed mechanistic model of the evolutionary process remains elusive. 相似文献
998.
Obesity in Adolescence Predicts Lower Educational Attainment and Income in Adulthood: The Project EAT Longitudinal Study 下载免费PDF全文
Simone A. French Melanie Wall Thomas Corbeil Nancy E. Sherwood Jerica M. Berge Dianne Neumark‐Sztainer 《Obesity (Silver Spring, Md.)》2018,26(9):1467-1473
Objective
Prospective associations between obesity in adolescence and adult socioeconomic outcomes, and potential mediators, were examined in a contemporary cohort.Methods
Longitudinal data collected in 1998 to 1999 (Project EAT‐I) and 2015 to 2016 (EAT‐IV) were analyzed for 1,796 participants who provided data at both time points. Adolescents (mean age = 14.8 years) self‐reported demographic and psychosocial variables (EAT‐I) and follow‐up outcomes (EAT‐IV). Body weight and height were directly measured. Bachelor's degree or more education, income ≥ US $50,000, and partnered status at follow‐up were examined by baseline obesity (>95th BMI percentile) using logistic regression. Self‐esteem, depression, and weight‐related teasing were examined as mediators using multivariate probit regressions. All analyses were adjusted for race, baseline age, and parent socioeconomic status.Results
Girls with obesity were significantly less likely to have achieved a bachelor’s degree (OR 0.32, 95% CI [0.18, 0.58]; P < 0.001), earn ≥ $50,000 annually (OR 0.57, 95% CI [0.33, 0.99]; P < 0.04), or be partnered (OR 0.45, 95% CI [0.27, 0.75]; P < 0.002) in adulthood. No associations were observed among boys. Among girls, depression mediated 8.5% and 23.6% of the association between adolescent obesity and adult education and income, respectively.Conclusions
Adolescent girls with obesity have lower educational attainment and income and are less likely to be partnered in later adulthood. Depression may partly mediate the associations.999.
1000.