全文获取类型
收费全文 | 1473篇 |
免费 | 152篇 |
出版年
2023年 | 10篇 |
2022年 | 13篇 |
2021年 | 32篇 |
2020年 | 22篇 |
2019年 | 23篇 |
2018年 | 26篇 |
2017年 | 33篇 |
2016年 | 57篇 |
2015年 | 90篇 |
2014年 | 109篇 |
2013年 | 105篇 |
2012年 | 136篇 |
2011年 | 111篇 |
2010年 | 77篇 |
2009年 | 57篇 |
2008年 | 97篇 |
2007年 | 95篇 |
2006年 | 79篇 |
2005年 | 63篇 |
2004年 | 59篇 |
2003年 | 44篇 |
2002年 | 60篇 |
2001年 | 16篇 |
2000年 | 7篇 |
1999年 | 16篇 |
1998年 | 13篇 |
1997年 | 17篇 |
1996年 | 13篇 |
1995年 | 17篇 |
1994年 | 17篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1969年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有1625条查询结果,搜索用时 15 毫秒
991.
Amy Matser Nancy Luu Ronald Geskus Titia Heijman Marlies Heiligenberg Maaike van Veen Maarten Schim van der Loeff 《PloS one》2013,8(6)
Background
In affluent countries, the prevalence of Chlamydia trachomatis (CT) is often higher in certain ethnic minorities than in the majority population. In the Netherlands, we examined why CT prevalence is higher in Surinamese/Antilleans, the largest minority in the country.Methods
Heterosexuals were recruited for a cross-sectional survey from May through August 2010 at the sexually transmitted infections (STI) clinic in Amsterdam. Participants completed a questionnaire and were tested for STI. A causal directed acyclic graph was assumed to investigate whether the association between ethnicity and CT could be explained by differences in sexual risk behaviour and socio-economic status.Results
Subjects included 1044 with Dutch background and 335 with Surinamese/Antillean background. Median age for the combined population was 25 (IQR 22-30) years, and 55.4% was female. Sexual risk behaviour did not differ significantly between the two groups. CT was diagnosed in 17.9% of Surinamese/Antilleans and in 11.4% of Dutch. Surinamese/Antilleans were significantly more likely to have CT (OR 1.70; 95% CI 1.21-2.38). The association between ethnicity and CT remained statistically significant after adjusting for sexual risk behaviour, age, sex, and ethnic mixing (aOR 1.48; 95% CI 1.00-2.18), but not after adjusting for education and neighbourhood, markers of socio-economic status (aOR 1.08; 95% CI 0.71-1.64).Conclusion
The difference in CT prevalence between the minority and majority groups was not explained by differences in sexual risk behaviour. The higher CT prevalence found among Surinamese/Antilleans appeared to reflect their lower educational level and neighbourhood, two markers of lower socio-economic status. We hypothesise that the effect results from lower health-seeking behaviour. 相似文献992.
Laurens H. Lindenburg Jan L. Vinkenborg Jorn Oortwijn Stijn J. A. Aper Maarten Merkx 《PloS one》2013,8(12)
Magnesium has important structural, catalytic and signaling roles in cells, yet few tools exist to image this metal ion in real time and at subcellular resolution. Here we report the first genetically encoded sensor for Mg2+, MagFRET-1. This sensor is based on the high-affinity Mg2+ binding domain of human centrin 3 (HsCen3), which undergoes a transition from a molten-globular apo form to a compactly-folded Mg2+-bound state. Fusion of Cerulean and Citrine fluorescent domains to the ends of HsCen3, yielded MagFRET-1, which combines a physiologically relevant Mg2+ affinity (K
d = 148 µM) with a 50% increase in emission ratio upon Mg2+ binding due to a change in FRET efficiency between Cerulean and Citrine. Mutations in the metal binding sites yielded MagFRET variants whose Mg2+ affinities were attenuated 2- to 100-fold relative to MagFRET-1, thus covering a broad range of Mg2+ concentrations. In situ experiments in HEK293 cells showed that MagFRET-1 can be targeted to the cytosol and the nucleus. Clear responses to changes in extracellular Mg2+ concentration were observed for MagFRET-1-expressing HEK293 cells when they were permeabilized with digitonin, whereas similar changes were not observed for intact cells. Although MagFRET-1 is also sensitive to Ca2+, this affinity is sufficiently attenuated (K
d of 10 µM) to make the sensor insensitive to known Ca2+ stimuli in HEK293 cells. While the potential and limitations of the MagFRET sensors for intracellular Mg2+ imaging need to be further established, we expect that these genetically encoded and ratiometric fluorescent Mg2+ sensors could prove very useful in understanding intracellular Mg2+ homeostasis and signaling. 相似文献
993.
994.
The causal pie model: an epidemiological method applied to evolutionary biology and ecology 下载免费PDF全文
A general concept for thinking about causality facilitates swift comprehension of results, and the vocabulary that belongs to the concept is instrumental in cross‐disciplinary communication. The causal pie model has fulfilled this role in epidemiology and could be of similar value in evolutionary biology and ecology. In the causal pie model, outcomes result from sufficient causes. Each sufficient cause is made up of a “causal pie” of “component causes”. Several different causal pies may exist for the same outcome. If and only if all component causes of a sufficient cause are present, that is, a causal pie is complete, does the outcome occur. The effect of a component cause hence depends on the presence of the other component causes that constitute some causal pie. Because all component causes are equally and fully causative for the outcome, the sum of causes for some outcome exceeds 100%. The causal pie model provides a way of thinking that maps into a number of recurrent themes in evolutionary biology and ecology: It charts when component causes have an effect and are subject to natural selection, and how component causes affect selection on other component causes; which partitions of outcomes with respect to causes are feasible and useful; and how to view the composition of a(n apparently homogeneous) population. The diversity of specific results that is directly understood from the causal pie model is a test for both the validity and the applicability of the model. The causal pie model provides a common language in which results across disciplines can be communicated and serves as a template along which future causal analyses can be made. 相似文献
995.
996.
Ingvar Bauweraerts Maarten Ameye Timothy M. Wertin Mary Anne McGuire Robert O. Teskey Kathy Steppe 《Plant Ecology》2014,215(7):733-746
Heat wave frequency and intensity are predicted to increase. We investigated whether repeated exposure to heat waves would induce acclimation in Quercus rubra seedlings and considered [CO2] as an interacting factor. We measured gas exchange and chlorophyll fluorescence of seedlings grown in 380 (C A) or 700 (C E) μmol CO2 mol?1, and three temperature treatments (ambient, ambient +3 °C, and an ambient +12 °C heat wave every fourth week). Measurements were performed during the third and fourth +12 °C heat waves (July and August 2010) at Whitehall Forest, GA, USA. Additionally, previously unexposed seedlings were subjected to the August heat wave to serve as a control to determine acclimation of seedlings which were previously exposed. Seedlings with a history of heat wave exposure showed lower net photosynthesis (A net) and stomatal conductance (on average ?47 and ?38 %, respectively) than seedlings with no such history, when both were subjected to the same +12 °C heat wave. During both heat waves, A net significantly declined in the +12 °C treatment compared with the other treatments. Additionally, the A net decline during the August compared with the July heat wave was stronger in C E than in C A, suggesting that elevated [CO2] might have had a negative effect on acclimation capacity. We conclude that seedlings subjected to consecutive heat waves will moderate stomatal conductance outside the heat wave, to reduce water usage at lower temperatures, increasing survival at the expense of carbon assimilation. 相似文献
997.
998.
Guédon E Delorme C Pons N Cruaud C Loux V Couloux A Gautier C Sanchez N Layec S Galleron N Almeida M van de Guchte M Kennedy SP Ehrlich SD Gibrat JF Wincker P Renault P 《Journal of bacteriology》2011,193(18):5024-5025
The commensal bacterium Streptococcus salivarius is a prevalent species of the human oropharyngeal tract with an important role in oral ecology. Here, we report the complete 2.2-Mb genome sequence and annotation of strain JIM8777, which was recently isolated from the oral cavity of a healthy, dentate infant. 相似文献
999.
1000.
Arnold Huurnink Duncan P. Fransz Idsart Kingma Maarten D.W. Hupperets Jaap H. van Dieën 《Journal of biomechanics》2014
In research regarding postural stability, leg preference is often tested and controlled for. However, leg preference may vary between tasks. As athletes are a group of interest for postural stability testing, we evaluated the effect of five leg preference tasks categorization (step up, hop, ball kick, balance, pick up) on single-leg postural stability of 16 field hockey athletes. The ‘center of pressure speed’ was calculated as the primary outcome variable of single-leg postural stability. Secondary variables were ‘mean length of the GRF vector in the horizontal plane’, ‘mean length of the ankle angular velocity vector’, and ‘mean length of the hip angular velocity vector’, as well as the separate outcomes per degree of freedom. Results showed that leg preference was inconsistent between leg preference tasks. Moreover, the primary and secondary variables yielded no significant difference between the preferred and non-preferred legs, regardless of the applied leg preference task categorization (p>0.05). The present findings do not support the usability of leg preference tasks in controlling for bias of postural stability. In conclusion, none of the applied leg preference tasks revealed a significant effect on postural stability in healthy field hockey athletes. 相似文献