全文获取类型
收费全文 | 1009篇 |
免费 | 77篇 |
出版年
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 20篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 16篇 |
2017年 | 15篇 |
2016年 | 29篇 |
2015年 | 46篇 |
2014年 | 46篇 |
2013年 | 76篇 |
2012年 | 63篇 |
2011年 | 66篇 |
2010年 | 59篇 |
2009年 | 30篇 |
2008年 | 61篇 |
2007年 | 51篇 |
2006年 | 46篇 |
2005年 | 41篇 |
2004年 | 44篇 |
2003年 | 41篇 |
2002年 | 43篇 |
2001年 | 13篇 |
2000年 | 11篇 |
1999年 | 12篇 |
1998年 | 20篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1973年 | 6篇 |
1971年 | 6篇 |
1970年 | 4篇 |
排序方式: 共有1086条查询结果,搜索用时 203 毫秒
31.
Understanding the ability of species to shift their distribution ranges in response to climate change is crucial for conservation biologists and resources managers. Although freshwater ecosystems include some of the most imperilled fauna worldwide, such range shifts have been poorly documented in streams and rivers and have never been compared to the current velocity of climate change. Based on national monitoring data, we examined the distributional changes of 32 stream fish species in France and quantified potential time lags in species responses, providing a unique opportunity to analyze range shifts over recent decades of warming in freshwater environments. A multi‐facetted approach, based on several range measures along spatial gradients, allowed us to quantify range shifts of numerous species across the whole hydrographic network between an initial period (1980–1992) and a contemporary one (2003–2009), and to contrast them to the rates of isotherm shift in elevation and stream distance. Our results highlight systematic species shifts towards higher elevation and upstream, with mean shifts in range centre of 13.7 m decade?1 and 0.6 km decade?1, respectively. Fish species displayed dispersal‐driven expansions along the altitudinal gradient at their upper range limit (61.5 m decade?1), while substantial range contractions at the lower limit (6.3 km decade?1) were documented for most species along the upstream–downstream gradient. Despite being consistent with the geographic variation in climate change velocities, these patterns reveal that the majority of stream fish have not shifted at a pace sufficient to track changing climate, in particular at their range centre where range shifts lag far behind expectation. Our study provides evidence that stream fish are currently responding to recent climate warming at a greater rate than many terrestrial organisms, although not as much as needed to cope with future climate modifications. 相似文献
32.
The exogenous input of nutrients and energy into island systems fuels a large array of consumers and drives bottom-up trophic cascades in island communities. The input of anthropogenic resources has increased on islands and particularly supplemented non-native consumers with extra resources. We test the hypothesis that the anthropogenic establishments of super-abundant gulls and invasive iceplants Carpobrotus spp. have both altered the dynamics of an introduced black rat Rattus rattus population. On Bagaud Island, two habitats have been substantially modified by the anthropogenic subsidies of gulls and iceplants, in contrast to the native Mediterranean scrubland with no anthropogenic inputs. Rats were trapped in all three habitats over two contrasting years of rainfall patterns to investigate: (1) the effect of anthropogenic subsidies on rat density, age-ratio and growth rates, and (2) the role of rainfall variability in modulating the effects of subsidies between years. We found that the growth rates of rats dwelling in the non-subsidized habitat varied with environmental fluctuation, whereas rats dwelling in the gull colony maintained high growth rates during both dry and rainy years. The presence of anthropogenic subsidies apparently mitigated environmental stress. Age ratio and rat density varied significantly and predictably among years, seasons, and habitats. While rat densities always peaked higher in the gull colony, especially after rat breeding in spring, higher captures of immature rats were recorded during the second year in all habitats, associated with higher rainfall. The potential for non-native rats to benefit from anthropogenic resources has important implications for the management of similar species on islands. 相似文献
33.
Bjarne Brudeli Kjetil Wessel Andressen Lise Román Moltzau Nils Olav Nilsen Finn Olav Levy Jo Klaveness 《Bioorganic & medicinal chemistry》2013,21(22):7134-7145
Serotonin (5-hydroxytryptamine, 5-HT) is an important signaling molecule in the central nervous system (CNS) and in non-neuronal tissues and organs. Serotonin mediates a positive chronotropic and inotropic response through 5-HT4 receptors in the atrium and ventricle of the heart. Recent investigations have revealed increased expression of the 5-HT4(b) isoform in cardiomyocytes of chronic arrhythmic and failing hearts, and that the use of 5-HT4 receptor antagonists may be beneficial for treating these conditions. The 5-HT4 receptor possesses a transmembrane (TM) binding site important for ligand affinity and recognition, as well as a capacity to accommodate bulky ligands. A new series of peripherally-acting 5-HT4 receptor antagonists were prepared by combining the acidic biphenyl group from the class of angiotensin II receptor blockers (ARBs) with the SB207266 (piboserod) scaffold. The new compounds were pharmacologically evaluated and carboxylic acid 21 was identified as a potent and promising 5-HT4 receptor antagonist with moderate affinity for the AT1 receptor. The permeability of carboxylic acid 21 in a Caco-2 assay was low and the corresponding prodrug esters 23a–f were therefore prepared. The pharmacokinetics of methyl ester 20 and n-butyl ester 23c were evaluated in a rat model, revealing incomplete metabolism to carboxylic acid 21. However, methyl ester 20 is a potent 5-HT4 receptor antagonist with binding affinities in the low picomolar range. Methyl ester 20 has promising oral bioavailability and pharmacokinetics and may target 5-HT4 receptors in both CNS and peripheral organs. 相似文献
34.
Charlotte Récapet Lise Dauphin Lisa Jacquin Julien Gasparini Anne‐Caroline Prévot‐Julliard 《Journal of avian biology》2013,44(6):583-590
Urbanisation introduces deep changes in habitats, eventually creating new urban ecosystems where ecological functions are driven by human activities. The higher frequency of some phenotypes in urban vs rural/wild areas has led to the assumption that directional selection in urban habitats occurs, which may thereby favour some behavioural and physiological traits in urban animal populations compared to rural ones. However, empirical evidence of directional selection on phenotypic traits in urban areas remains scarce. In this study we tested whether eumelanin‐based colouration could be linked to survival in two urban populations of the feral pigeon Columba livia. A number of studies in different cities pointed out a higher frequency of darker individuals in more urbanised areas compared to rural ones. To investigate whether directional selection through survival on this highly heritable trait could explain such patterns, we conducted mark–recapture studies on two populations of feral pigeons in highly urbanized areas. We predicted that darker coloured individuals would exhibit higher survival and/or philopatry (integrated into ‘local survival’) than paler coloured ones. No difference in local survival was found between adults of different colouration intensities. However, on one site, we found that darker juveniles had a higher local survival probability than light ones. Juvenile local survival on that site was also negatively correlated with the number of chicks born. This suggests the existence of colour‐ and/or density‐dependent selection processes acting on juvenile feral pigeons in urban environments, acting through differential mortality and/or dispersal. 相似文献
35.
Sumayyah Ebrahim Xolani K. Mndende Ayesha B. M. Kharsany Zizipho Z. A. Mbulawa Vivek Naranbhai Janet Frohlich Lise Werner Natasha Samsunder Quarraisha Abdool Karim Anna-Lise Williamson 《PloS one》2016,11(1)
Objectives
HPV infection causes cervical cancer, yet information on prevalence and risk factors for HPV in Africa remain sparse. This study describes the prevalence of HPV genotypes and risk factors associated with HPV among young women ≤ 30 years of age in KwaZulu-Natal (KZN), South Africa.Methods
Cervicovaginal lavage samples were tested for HPV genotypes in 224 women enrolled in a prospective cohort study. Clinical, behavioural and demographic data were collected. We measured prevalence of HPV genotypes and using logistic regression, examined for factors associated with HPV.Results
Median age of participants was 21 years [interquartile range (IQR):18–23]. The overall prevalence of HPV was 76.3% (171/224) with multiple and single genotypes prevalent in 56.3% and 20.1% of women respectively. Proportion of women with high-risk genotypes (16, 18, 31, 33, 35, 39, 45, 51, 52, 56 and 58) was 54.5%. Women not living with their partner [adjusted odds ratio (aOR)] = 3.42 95% CI1.22–9.60; p = 0.019), was significantly associated with HPV infection and high-risk HPV genotype infection.Conclusion
The high burden of HPV and associated risk behaviours highlight the need to intensify behavioural interventions to prevent HPV acquisition in young women. The large scale delivery of HPV vaccine should be prioritised to prevent HPV acquisition and reduce HPV-related morbidity. 相似文献36.
37.
38.
Lise Pascale Alejandro López González Audrey Di Giorgio Marc Gaysinski Jordi Teixido Closa Roger Estrada Tejedor 《Journal of biomolecular structure & dynamics》2016,34(11):2327-2338
A series of pentameric “Polyamide Amino Acids” (PAAs) compounds derived from the same trimeric precursor have been synthesized and investigated as HIV TAR RNA ligands, in the absence and in the presence of a Tat fragment. All PAAs bind TAR with similar sub-micromolar affinities but their ability to compete efficiently with the Tat fragment strongly differs, IC50 ranging from 35 nM to >2 μM. While NMR and CD studies reveal that all PAA interact with TAR at the same site and induce globally the same RNA conformational change upon binding, a comparative thermodynamic study of PAA/TAR equilibria highlights distinct TAR binding modes for Tat competitor and non-competitor PAAs. This led us to suggest two distinct interaction modes that have been further validated by molecular modeling studies. While the binding of Tat competitor PAAs induces a contraction at the TAR bulge region, the binding of non-competitor ones widens it. This could account for the distinct PAA ability to compete with Tat fragment. Our work illustrates how comparative thermodynamic studies of a series of RNA ligands of same chemical family are of value for understanding their binding modes and for rationalizing structure-activity relationships. 相似文献
39.
Estefania Ugarte‐Berzal Erik Martens Lise Boon Jennifer Vandooren Daniel Blockmans Paul Proost Ghislain Opdenakker 《Journal of cellular and molecular medicine》2019,23(1):576-585
Gelatin zymography analysis is a sensitive method and commonly used to characterize and quantify the presence of the gelatinases (MMP‐2 and MMP‐9) in biological samples. In human plasma samples from healthy controls and systemic lupus erythematosus (SLE) patients, we observed a gelatinolytic molecule at 80 kDa, suggestive for activated human MMP‐9. However, by developing and using the EDTA/gelatin zymography method and after purification of the 80 kDa entity, we proved that this molecule was the C1s subunit of the complement system. The zymolytic capacity of C1s was validated and found to be enhanced, in the absence of calcium and in the presence of EDTA. Our findings indicate that for correct identification of gelatinolytic proteins in complex biological samples the use of EDTA/gelatin zymography for enzyme development is advised. In addition, by quantification of EDTA/gelatin zymography analysis and ELISA, we observed that the levels of C1s were higher in plasma and immune complexes of SLE patients than of healthy individuals. Therefore, our data imply that C1s may become a marker for the diagnosis of SLE. 相似文献
40.
Anne-Marie Lundsgaard Jacob B. Holm Kim A. Sjøberg Kirstine N. Bojsen-Møller Lene S. Myrmel Even Fjære Benjamin A.H. Jensen Trine S. Nicolaisen Janne R. Hingst Sine L. Hansen Sophia Doll Philip E. Geyer Atul S. Deshmukh Jens J. Holst Lise Madsen Karsten Kristiansen Jørgen F.P. Wojtaszewski Erik A. Richter Bente Kiens 《Cell metabolism》2019,29(1):50-63.e4