全文获取类型
收费全文 | 2898篇 |
免费 | 257篇 |
出版年
2023年 | 13篇 |
2022年 | 33篇 |
2021年 | 67篇 |
2020年 | 45篇 |
2019年 | 62篇 |
2018年 | 79篇 |
2017年 | 50篇 |
2016年 | 120篇 |
2015年 | 168篇 |
2014年 | 146篇 |
2013年 | 220篇 |
2012年 | 237篇 |
2011年 | 243篇 |
2010年 | 138篇 |
2009年 | 140篇 |
2008年 | 172篇 |
2007年 | 190篇 |
2006年 | 153篇 |
2005年 | 164篇 |
2004年 | 143篇 |
2003年 | 112篇 |
2002年 | 137篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 21篇 |
1998年 | 32篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 14篇 |
1994年 | 20篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 14篇 |
1984年 | 6篇 |
1983年 | 11篇 |
1982年 | 8篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1973年 | 3篇 |
1969年 | 2篇 |
排序方式: 共有3155条查询结果,搜索用时 15 毫秒
91.
Antonia Barcelo Josep Miquel Bau?a Aina Ya?ez Laura Fueyo Cristina Gomez Monica de la Pe?a Javier Pierola Alberto Rodriguez Manuel Sanchez-de-la-Torre Jorge Abad Olga Mediano Jose Amilibia Maria Jose Masdeu Joaquin Teran Josep Maria Montserrat Mercè Mayos Alicia Sanchez-de-la-Torre Ferran Barbé Spanish Sleep Group 《PloS one》2016,11(3)
Background
Placental growth factor (PlGF) induces angiogenesis and promotes tissue repair, and plasma PlGF levels change markedly during acute myocardial infarction (AMI). Currently, the impact of obstructive sleep apnea (OSA) in patients with AMI is a subject of debate. Our objective was to evaluate the relationships between PlGF levels and both the severity of acute coronary syndrome (ACS) and short-term outcomes after ACS in patients with and without OSA.Methods
A total of 538 consecutive patients (312 OSA patients and 226 controls) admitted for ACS were included in this study. All patients underwent polygraphy in the first 72 hours after hospital admission. The severity of disease and short-term prognoses were evaluated during the hospitalization period. Plasma PlGF levels were measured using an electrochemiluminescence immunoassay.Results
Patients with OSA were significantly older and more frequently hypertensive and had higher BMIs than those without OSA. After adjusting for age, smoking status, BMI and hypertension, PlGF levels were significantly elevated in patients with OSA compared with patients without OSA (19.9 pg/mL, interquartile range: 16.6–24.5 pg/mL; 18.5 pg/mL, interquartile range: 14.7–22.7 pg/mL; p<0.001), and a higher apnea-hypopnea index (AHI) was associated with higher PlGF concentrations (p<0.003). Patients with higher levels of PlGF had also an increased odds ratio for the presence of 3 or more diseased vessels and for a Killip score>1, even after adjustment.Conclusions
The results of this study show that in patients with ACS, elevated plasma levels of PlGF are associated with the presence of OSA and with adverse outcomes during short-term follow-up.Trial Registration
ClinicalTrials.gov NCT01335087相似文献92.
Jeremiah G. Plass-Johnson Marc H. Taylor Aidah A. A. Husain Mirta C. Teichberg Sebastian C. A. Ferse 《PloS one》2016,11(4)
Changes in the coral reef complex can affect predator-prey relationships, resource availability and niche utilisation in the associated fish community, which may be reflected in decreased stability of the functional traits present in a community. This is because particular traits may be favoured by a changing environment, or by habitat degradation. Furthermore, other traits can be selected against because degradation can relax the association between fishes and benthic habitat. We characterised six important ecological traits for fish species occurring at seven sites across a disturbed coral reef archipelago in Indonesia, where reefs have been exposed to eutrophication and destructive fishing practices for decades. Functional diversity was assessed using two complementary indices (FRic and RaoQ) and correlated to important environmental factors (live coral cover and rugosity, representing local reef health, and distance from shore, representing a cross-shelf environmental gradient). Indices were examined for both a change in their mean, as well as temporal (short-term; hours) and spatial (cross-shelf) variability, to assess whether fish-habitat association became relaxed along with habitat degradation. Furthermore, variability in individual traits was examined to identify the traits that are most affected by habitat change. Increases in the general reef health indicators, live coral cover and rugosity (correlated with distance from the mainland), were associated with decreases in the variability of functional diversity and with community-level changes in the abundance of several traits (notably home range size, maximum length, microalgae, detritus and small invertebrate feeding and reproductive turnover). A decrease in coral cover increased variability of RaoQ while rugosity and distance both inversely affected variability of FRic; however, averages for these indices did not reveal patterns associated with the environment. These results suggest that increased degradation of coral reefs is associated with increased variability in fish community functional composition resulting from selective impacts on specific traits, thereby affecting the functional response of these communities to increasing perturbations. 相似文献
93.
Through 17 years and from a sample of 7,790 faecal pellets and 26,346 prey items, we studied the diet of the Balearic lizard Podarcis lilfordi in Aire Island (Menorca, Balearic Islands, Spain). We analysed the diet in terms of prey frequencies, as well as by their volume and biomass contributions. The diet of the Balearic lizard was extremely variable through the years, months and areas under study. The dominance of small clumped prey, particularly ants, was confirmed. However, the main contribution by volume corresponded to beetles, with a relevant role for Diplopoda and terrestrial Isopoda during some months and at particular areas of the island. Several prey items were probably captured at the base of shrubs, under stones or inside rock crevices. Therefore, our estimations of electivity would only be reliable for epigeal and flying prey. The capacity of the Balearic lizard to include marine subsidies in its diet, such as coastal crustaceans, is noteworthy. Also, its consumption of carrion from carcasses of gulls and rabbits and leftovers from human visitors is remarkable. Juvenile conspecifics can also be a sporadic food resource, especially during the second half of summer, whereas the consumption of vegetal matter is constant for each whole year. The shifts of vegetal exploitation among areas of the island and months take place according to availability of different plant species at each area or during a given period. Thus, lizards are able to conduct a thorough monitoring of plant phenology, exploiting a large variety of plant species. Omnivory does not imply the indiscriminate inclusion of any edible food in its diet. Rather, the inclusion of several food items means the adoption of a wide range of foraging behaviours adapted to the exploitation of each food resource. 相似文献
94.
Cassandra L. Pattinson Alicia C. Allan Sally L. Staton Karen J. Thorpe Simon S. Smith 《PloS one》2016,11(1)
The timing, intensity, and duration of exposure to both artificial and natural light have acute metabolic and physiological effects in mammals. Recent research in human adults suggests exposure to moderate intensity light later in the day is concurrently associated with increased body mass; however, no studies have investigated the effect of light exposure on body mass in young children. We examined objectively measured light exposure and body mass of 48 preschool-aged children at baseline, and measured their body mass again 12 months later. At baseline, moderate intensity light exposure earlier in the day was associated with increased body mass index (BMI). Increased duration of light exposure at baseline predicted increased BMI 12-months later, even after controlling for baseline sleep duration, sleep timing, BMI, and activity. The findings identify that light exposure may be a contributor to the obesogenic environment during early childhood. 相似文献
95.
96.
Ocellatin‐PT antimicrobial peptides: High‐resolution microscopy studies in antileishmania models and interactions with mimetic membrane systems 下载免费PDF全文
Mayara Oliveira Ana Georgina Gomes‐Alves Carla Sousa Mariela Mirta Marani Alexandra Plácido Nuno Vale Cristina Delerue‐Matos Paula Gameiro Selma A. S. Kückelhaus Ana M. Tomas José Roberto S. A. Leite Peter Eaton 《Biopolymers》2016,105(12):873-886
Although the mechanism of action of antimicrobial peptides (AMPs) is not clear, they can interact electrostatically with the cell membranes of microorganisms. New ocellatin‐PT peptides were recently isolated from the skin secretion of Leptodactylus pustulatus. The secondary structure of these AMPs and their effect on Leishmania infantum cells, and on different lipid surface models was characterized in this work. The results showed that all ocellatin‐PT peptides have an α‐helix structure and five of them (PT3, PT4, PT6 to PT8) have leishmanicidal activity; PT1 and PT2 affected the cellular morphology of the parasites and showed greater affinity for leishmania and bacteria‐mimicking lipid membranes than for those of mammals. The results show selectivity of ocellatin‐PTs to the membranes of microorganisms and the applicability of biophysical methods to clarify the interaction of AMPs with cell membranes. 相似文献
97.
98.
Rodriguez-Conde Sara Molina Lázaro González Paola García-Puente Alicia Segura Ana 《Applied microbiology and biotechnology》2016,100(24):10627-10636
Applied Microbiology and Biotechnology - At the same time that the European Union (EU) policy recommend to direct efforts towards reductions of heavy metals, polycyclic aromatic hydrocarbons (PAHs)... 相似文献
99.
100.
Alicia Carissimi Alessandra Castro Martins Fabiane Dresch Lilian Corrêa da Silva Cristian Patrick Zeni Maria Paz Hidalgo 《Chronobiology international》2016,33(10):1400-1409
School start time influences sleep parameters. Differences between circadian sleep parameters on weekends and weekdays have been associated with obesity, sleep, and psychiatric disorders. Moreover, circadian rhythm dysregulation affects the secretion of some hormones, such as melatonin and cortisol. In the current study, we investigate the effect of school start time on cortisol and melatonin levels in a community sample of Brazilian children and adolescents. This was a cross-sectional study of 454 students (mean age, 12.81 ± 2.56 years; 58.6% female). From this sample, 80 participants were randomly selected for saliva collection to measure melatonin and cortisol levels. Circadian sleep parameters were assessed by self-reported sleep and wake up schedules and the Morningness–Eveningness Questionnaire. The outcomes, salivary melatonin and cortisol levels, were measured in morning, afternoon and night saliva samples, and behavior problems were assessed using the Child Behavior Checklist (CBCL). The main results revealed that morning school start time decreased the secretion of melatonin. Morning melatonin levels were significantly positively correlated with the sleep midpoint on weekdays and on weekends. Afternoon melatonin levels were positively correlated with the sleep midpoint on weekends in the morning school students. Conversely, in the afternoon school students, night melatonin levels were negatively correlated with the sleep midpoint on weekdays. Cortisol secretion did not correlate with circadian sleep parameters in any of the school time groups. In conclusion, school start time influences melatonin secretion, which correlated with circadian sleep parameters. This correlation depends on the presence of psychiatric symptoms. Our findings emphasize the importance of drawing attention to the influence of school start time on the circadian rhythm of children and adolescents. 相似文献