全文获取类型
收费全文 | 3757篇 |
免费 | 347篇 |
国内免费 | 1篇 |
专业分类
4105篇 |
出版年
2022年 | 43篇 |
2021年 | 68篇 |
2020年 | 43篇 |
2019年 | 64篇 |
2018年 | 53篇 |
2017年 | 57篇 |
2016年 | 95篇 |
2015年 | 158篇 |
2014年 | 165篇 |
2013年 | 211篇 |
2012年 | 229篇 |
2011年 | 216篇 |
2010年 | 134篇 |
2009年 | 119篇 |
2008年 | 176篇 |
2007年 | 156篇 |
2006年 | 134篇 |
2005年 | 145篇 |
2004年 | 139篇 |
2003年 | 120篇 |
2002年 | 119篇 |
2001年 | 80篇 |
2000年 | 102篇 |
1999年 | 84篇 |
1998年 | 39篇 |
1997年 | 39篇 |
1996年 | 36篇 |
1995年 | 34篇 |
1994年 | 34篇 |
1993年 | 36篇 |
1992年 | 65篇 |
1991年 | 60篇 |
1990年 | 52篇 |
1989年 | 46篇 |
1988年 | 56篇 |
1987年 | 46篇 |
1986年 | 45篇 |
1985年 | 46篇 |
1984年 | 40篇 |
1983年 | 37篇 |
1982年 | 36篇 |
1981年 | 20篇 |
1979年 | 25篇 |
1978年 | 33篇 |
1977年 | 30篇 |
1976年 | 24篇 |
1975年 | 26篇 |
1974年 | 18篇 |
1973年 | 18篇 |
1971年 | 19篇 |
排序方式: 共有4105条查询结果,搜索用时 15 毫秒
991.
Denise Campbell-Scherer Yvonne Chiu Nicole Naadu Ofosu Thea Luig Karen Heather Hunter Badi Jabbour Sauleha Farooq Ali Mahdi Aline Gayawira Fransiska Awasis Funke Olokude Hannah Goa Hina Syed Judy Sillito Lydia Yip Lyn Belle Mawien Akot Monique Nutter Nadia Farhat Yan Wang Niga Jalal Saida Khalif Shiva Chapagain Stephanie Fernandez Susan Azarcon Zhewar Hama 《CMAJ》2021,193(31):E1203
BACKGROUND:The COVID-19 pandemic has exacerbated disparities in poverty and illness for people in vulnerable circumstances in ethnocultural communities. We sought to understand the evolving impacts of COVID-19 on ethnocultural communities to inform intersectoral advocacy and community action.METHODS:The Illuminate Project used participatory action research, with cultural health brokers as peer researchers, from Sept. 21 to Dec. 31, 2020, in Edmonton, Alberta. Twenty-one peer researchers collected narratives from members of ethnocultural communities and self-interpreted them as they entered the narratives into the SenseMaker platform, a mixed-method data collection tool. The entire research team analyzed real-time, aggregate, quantitative and qualitative data to identify emerging thematic domains, then visualized these domains with social network analysis.RESULTS:Brokers serving diverse communities collected 773 narratives. Identified domains illuminate the evolving and entangled impacts of COVID-19 including the following: COVID-19 prevention and management; care of acute, chronic and serious illnesses other than COVID-19; maternal care; mental health and triggers of past trauma; financial insecurity; impact on children and youth and seniors; and legal concerns. We identified that community social capital and cultural brokering are key assets that facilitate access to formal health and social system supports.INTERPRETATION:The Illuminate Project has illustrated the entangled, systemic issues that result in poor health among vulnerable members of ethnocultural communities, and the exacerbating effects of COVID-19, which also increased barriers to mitigation. Cultural brokering and community social capital are key supports for people during the COVID-19 pandemic. These findings can inform policy to reduce harm and support community resiliency.Mahatma Gandhi observed that “the true measure of any society can be found in how it treats its most vulnerable members.” Ethnocultural communities, defined by their unique shared characteristics (e.g., cultural traditions, language, country of origin),1 face greater challenges and have higher rates of poverty and illness than the general Canadian population. Migration results in conditions that affect all social determinants of health and disproportionally affect health outcomes, herein referred to as vulnerable circumstances.2,3 The emergence of major outbreaks of SARS-CoV-2 infections in ethnocultural communities highlights both the vulnerable circumstances of these communities and the disparities they face in accessing high-quality, culturally appropriate information and support.4–7 Studies have shown substantial variation in deaths attributed to COVID-19 based on factors such as age, sex, ethnicity, length of time in Canada, income and education.8–11 However, given the well-known gap in reporting comprehensive COVID-19 data in relation to race and ethnicity, efforts to measure its impact are hampered.8–12 There is an urgent need to understand the evolving challenges of COVID-19 to inform action and public policy that can mitigate these challenges.To understand evolving situations of complexity and crisis, sensemaking, defined as “a continuous process to establish situational awareness,”13 is a crucial undertaking.14 Using participatory action research,15–18 we sought to understand the evolving impacts of COVID-19 on ethnocultural communities to inform broader national efforts to migitate the impacts of COVID-19. Particularly, we sought to understand how the challenges of COVID-19 are entangled with contextual factors at multiple levels, how families and communities are leveraging strengths and social capital to adapt, and the role of cultural brokers in managing the crisis. 相似文献
992.
Lydia M. Hopper 《Biological reviews of the Cambridge Philosophical Society》2010,85(4):685-701
The focus of this review is the experimental techniques used to identify forms of social learning shown by humans and nonhuman animals. Specifically, the ‘ghost display’ and ‘end‐state’ conditions, which have been used to tease apart imitative and emulative learning are evaluated. In a ghost display, the movements of an apparatus are demonstrated, often through the discrete use of fishing‐line or hidden mechanisms, without a live model acting directly upon the apparatus so that the apparatus appears to be operated as if by a ‘ghostly’ agent. In an end‐state condition, an observing individual is shown the initial state of the test apparatus, the apparatus is then manipulated out‐of‐sight and then represented to the individual in its final state. The aim of the ghost display condition is to determine whether individuals are able to emulate by replicating the movements of an apparatus, or perform a task, without requiring information about the bodily movements required to do so (imitation). The end‐state condition is used to identify goal‐emulation by assessing whether the observer can replicate the steps required to solve the task without having been shown the required body actions or task movements. The responses of individuals tested with either the ghost display and/or end‐state conditions are compared to those of further individuals who have observed a full demonstration by either a human experimenter or a conspecific. The responses of a control group, to whom no information has been provided about the test apparatus or required actions, are also compared and evaluated. The efficacy of these experimental techniques employed with humans, nonhuman primates, dogs, rats and birds are discussed and evaluated. The experiments reviewed herein emphasise the need to provide ghost displays and end‐state conditions in combination, along with full live demonstrations and a no‐information control. Future research directions are proposed. 相似文献
993.
T. J. Kornecook A. P. McKinney M. T. Ferguson J.‐C. Dodart 《Genes, Brain & Behavior》2010,9(2):182-192
The ε4 allele of apolipoprotein E (apoE4) is the predominant genetic risk factor for late‐onset Alzheimer's disease (AD) and is also implicated in cognitive deficits associated with normal aging. The biological mechanisms by which APOE genotype affects cognitive processes or AD pathogenesis remain unclear, but interactions of apoE with amyloid β peptide (Aβ) are thought to play an important role in mediating apoE's isoform‐specific effects on brain function. Here, we investigated the potential isoform‐dependent effects of apoE on behavioral and cognitive performance in human apoE3 and apoE4 targeted‐replacement (TR) mice that also overexpress the human amyloid precursor protein (APP). Beginning at 6–7 months of age, female APP‐Yac/apoE3‐TR (‘poE3’) and APP‐Yac/apoE4‐TR (‘poE4’) mice were tested on a battery of tests to evaluate basic sensorimotor functioning, spatial working memory, spatial recognition, episodic‐like memory and attentional processing. Compared with apoE3 mice, a generalized reduction in locomotor activity was observed in apoE4 mice. Moderate, but significant, cognitive impairments were also detected in apoE4 mice in the novel object‐location preference task, the contextual fear conditioning test, and a two‐choice visual discrimination/detection test, however spontaneous alternation performance in the Y‐maze was spared. These results offer additional support for the negative impact of apoE4 on both memory and attention and further suggest that APP‐Yac/apoE‐TR mice provide a novel and useful model for investigating the role of apoE in mediating susceptibility to cognitive decline. 相似文献
994.
SUMMARY Natural selection requires genetically based phenotypic variation to facilitate its action and cause adaptive evolution. It has become increasingly recognized that morphological development can become canalized likely as a result of selection. However, it is largely unknown how selection may influence canalization over ontogeny and differing environments. Changes in environments or colonization of a novel one is expected to result in adaptive divergence from the ancestral population when selection favors a new phenotypic optimum. In turn, a novel environment may also expose variation previously hidden from natural selection. We tested for changes in phenotypic variation over ontogeny and environments among ecomorphs of Arctic charr (Salvelinus alpinus) from two Icelandic lakes. Populations represented varying degrees of ecological specialization, with one lake population possessing highly specialized ecomorphs exhibiting a large degree of phenotypic divergence, whereas the other displayed more subtle divergence with more ecological overlap. Here we show that ecomorphs hypothesized to be the most specialized in each lake possess significant reductions in shape variation over ontogeny regardless of environmental treatment suggesting canalized development. However, environments did change the amount of shape variation expressed in these ecomorphs, with novel environments slowing the rate at which variation was reduced over ontogeny. Thus, environmental conditions may play an important role in determining the type and amount of genetically based phenotypic variation exposed to natural selection. 相似文献
995.
996.
Jean O'Connell Lydia Lynch Tom J. Cawood Anna Kwasnik Niamh Nolan Justin Geoghegan Aiden McCormick Cliona O'Farrelly Donal O'Shea 《PloS one》2010,5(4)
Objective
Several studies have reported the existence of a subgroup of obese individuals with normal metabolic profiles. It remains unclear what factors are responsible for this phenomenon. We proposed that adipocyte size might be a key factor in the protection of metabolically healthy obese (MHO) individuals from the adverse effects of obesity.Subjects
Thirty-five patients undergoing bariatric surgery were classified as MHO (n = 15) or metabolically unhealthy obese (MUO, n = 20) according to cut-off points adapted from the International Diabetes Federation definition of the metabolic syndrome. Median body mass index (BMI) was 48 (range 40–71).Results
There was a moderate correlation between omental adipocyte size and subcutaneous adipocyte size (r = 0.59, p<0.05). The MHO group had significantly lower mean omental adipocyte size (80.9±10.9 µm) when compared with metabolically unhealthy patients (100.0±7.6 µm, p<0.0001). Mean subcutaneous adipocyte size was similar between the two groups (104.1±8.5 µm versus 107.9±7.1 µm). Omental, but not subcutaneous adipocyte size, correlated with the degree of insulin resistance as measured by HOMA-IR (r = 0.73, p<0.0005), as well as other metabolic parameters including triglyceride/HDL-cholesterol ratio and HbA1c. Twenty-eight patients consented to liver biopsy. Of these, 46% had steatohepatitis and fibrosis. Fifty percent (including all the MHO patients) had steatosis only. Both omental and subcutaneous adipocyte size were significantly associated with the degree of steatosis (r = 0.66, p<0.0001 and r = 0.63, p<0.005 respectively). However, only omental adipocyte size was an independent predictor of the presence or absence of fibrosis.Conclusion
Metabolically healthy individuals are a distinct subgroup of the severely obese. Both subcutaneous and omental adipocyte size correlated positively with the degree of fatty liver, but only omental adipocyte size was related to metabolic health, and possibly progression from hepatic steatosis to fibrosis. 相似文献997.
Lydia Foucan Nabila Ezourhi Suliya Maimaitiming Segho Hedreville Jocelyn Inamo Andre Atallah Jacqueline Bangou‐Bredent Roberte Aubert Roger Chout Frederic Fumeron Jean‐Paul Donnet Michel Marre 《Obesity (Silver Spring, Md.)》2010,18(7):1466-1468
Ethnic differences may affect the association of adiponectin (Ad) multimers with coronary artery disease (CAD). We analyzed the associations of total Ad, Ad multimers, and T45G polymorphism of ADIPOQ gene with pre‐existing CAD. We carried out a cross‐sectional study of 216 Afro‐Caribbean type 2 diabetic (T2D) subjects. Levels of total Ad, high molecular weight (HMW), middle molecular weight (MMW), and low molecular weight (LMW) isoforms were measured. Subjects were genotyped. Of the subjects studied, 57 had pre‐existing CAD, 77% of whom have had myocardial infarction. Subjects with CAD had lower Ad levels (total and multimers) and a higher frequency carried the minor allele 45G, GG/TG, (18% vs. 8%, P = 0.03) than subjects without CAD. In logistic regression analysis, the models used evaluate Ad in the context of adjustment for metabolic syndrome characteristics. The adjusted odds ratio (OR) of CAD was increased significantly (by factors of 1.05–3.27) for males, older subjects, low high‐density lipoprotein cholesterol (HDL‐C), high triglycerides (TGs), and carriers of the 45 G allele. For Ad, in model 1 (including only total Ad) the adjusted OR was 2.30; P = 0.03 and, in model 2 (including the three multimers, but not total Ad), the adjusted ORs were 0.73; P = 0.52 (HMW), 2.90; P = 0.01 (MMW), and 2.08; P = 0.09 (LMW). The T45G polymorphism in the ADIPOQ gene and hypoadiponectinemia were associated with CAD in our T2D subjects of predominantly African background. This effect of Ad level was mainly related to the MMW Ad form. 相似文献
998.
999.
Murakami M Ferguson CE Perez O Boediono A Paccamonti D Bondioli KR Godke RA 《Cloning and stem cells》2006,8(1):51-60
Presence of placental tissues from more normal noncloned embryos could reduce the pregnancy failure of somatic cloning in cattle. In this study, inner cell mass (ICM) cells of in vitro-produced (IVP) embryos was replaced with those of nuclear transfer (NT) embryos to reconstruct bovine blastocysts with ICM and trophoblast cells from NT and IVP embryos, respectively. A total of 65 of these reconstructed embryos were nonsurgically transferred to 20 recipient beef females. Of those, two females were diagnosed pregnant by ultrasonography on day 30 of gestation. One pregnancy was lost at 60-90 days of gestation, and the other recipient cow remained pregnant at day 240 of gestation; however, this female died on day 252 of gestation. Gross pathology of the internal organs of the recipient female, a large fetus, and a large placental tissue mass suggested the massive size of the fetus and placental tissue were likely involved in terminating the life of the recipient female. Biopsy samples were harvested from the skin of the dead recipient cow, the fetus and from cotyledonary tissue. Microsatellite DNA analysis of these samples revealed that the genotype of the fetus was the same as that of the NT donor cells and different from that of the recipient cow. Correspondingly, neither the fetus nor recipient cow had the same genotype with that of the fetal cotyledonary tissue. These results present the first known documented case of a bovine somatic NT pregnancy with nonclone placental tissues after transfer of a blastocyst reconstructed by a microsurgical method to exchange of ICM cells and trophoblast tissue between NT and IVP blastocysts. 相似文献
1000.