全文获取类型
收费全文 | 404篇 |
免费 | 38篇 |
专业分类
442篇 |
出版年
2023年 | 11篇 |
2022年 | 6篇 |
2021年 | 17篇 |
2020年 | 5篇 |
2019年 | 10篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 20篇 |
2015年 | 19篇 |
2014年 | 22篇 |
2013年 | 38篇 |
2012年 | 40篇 |
2011年 | 32篇 |
2010年 | 16篇 |
2009年 | 16篇 |
2008年 | 31篇 |
2007年 | 17篇 |
2006年 | 18篇 |
2005年 | 20篇 |
2004年 | 15篇 |
2003年 | 21篇 |
2002年 | 12篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1977年 | 3篇 |
1954年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有442条查询结果,搜索用时 0 毫秒
1.
Calluses induced fromPterocladia capillacea have been kept in culture for more than three years. They exhibit a fast growth rate, owing to the release of single cells, which in turn develop into new callus. The effect of various media and culture conditions upon growth was investigated. In order to confirm the identity of the callus cells, a 0,45 mg incoculum was grown that yielded 15 g dried callus within six weeks. Polysaccharides from this material (5.5 g) were analysed by13C NMR spectroscopy. This produced a spectrum typical of agar and very similar to the one obtained for agar extracted fromP. capillacea plants. However, the callus agar displayed no gel-forming properties, even after alkali modification.author for correspondence 相似文献
2.
3.
Lucie Mahaut Philippe Choler Pierre Denelle Eric Garnier Wilfried Thuiller Jens Kattge Servane Lemauviel-Lavenant Sandra Lavorel François Munoz Delphine Renard Josep M. Serra-Diaz Nicolas Viovy Cyrille Violle 《Global Ecology and Biogeography》2023,32(4):561-572
Aim
It is crucial to monitor how the productivity of grasslands varies with its temporal stability for management of these ecosystems. However, identifying the direction of the productivity–stability relationship remains challenging because ecological stability has multiple components that can display neutral, positive or negative covariations. Furthermore, evidence suggests that the direction of the productivity–stability relationship depends on the biotic interactions and abiotic conditions that underlie ecosystem productivity and stability. We decipher the relationships between grassland productivity and two components of its stability in four habitat types with contrasting environments and flora.Location
France.Time period
2000–2020.Major taxa
Grassland plant species.Methods
We used c. 20,000 vegetation plots spread across French permanent grasslands and remotely sensed vegetation indices to quantify grassland productivity and temporal stability. We decomposed stability into constancy (i.e., temporal invariability) and resistance (i.e., maximum deviation from average) and deciphered the direct and indirect effects of abiotic (namely growing season length and nitrogen input) and biotic (namely plant taxonomic diversity, trait diversity and community-weighted mean traits) factors on productivity–stability relationships using structural equation models.Results
We found a positive relationship between productivity and constancy and a negative relationship between productivity and resistance in all habitats. Abiotic factors had stronger effects on productivity and stability compared with biotic factors. A longer growing season enhanced grassland productivity and constancy. Nitrogen input had positive and negative effects on grassland productivity and resistance, respectively. Trait values affected the constancy and resistance of grassland more than taxonomic and trait diversity, with effects varying from one habitat to another. Productivity was not related to any biotic factor.Main conclusions
Our findings reveal how vital it is to consider both the multiple components of stability and the interaction between environment and biodiversity to gain an understanding of the relationships between productivity and stability in real-world ecosystems, which is a crucial step for sustainable grassland management. 相似文献4.
From November 1977 to March 1978 we recorded the scent-marking behaviour of free-ranging coyotes in southern Québec. Fourteen animals were marked by foot-pad ablation, which made it possible to recognize individuals' tracks in the snow and therefore to relate scent-marking with social organization. We observed 949 scent-marks. The identity of the animals was known for 50% of the tracking distances. Animals living in territorial groups (pairs and pairs with juveniles) marked more than twice as much as solitary non-territorial individuals. In addition the former used stronger forms of marking significantly more often than the latter. 相似文献
5.
Stefanie Wagner Frédéric Lagane Andaine Seguin‐Orlando Mikkel Schubert Thibault Leroy Erwan Guichoux Emilie Chancerel Inger Bech‐Hebelstrup Vincent Bernard Cyrille Billard Yves Billaud Matthias Bolliger Christophe Croutsch Katarina Čufar Frédérique Eynaud Karl Uwe Heussner Joachim Köninger Fabien Langenegger Frédéric Leroy Christine Lima Nicoletta Martinelli Garry Momber André Billamboz Oliver Nelle Antoni Palomo Raquel Piqué Marianne Ramstein Roswitha Schweichel Harald Stäuble Willy Tegel Xavier Terradas Florence Verdin Christophe Plomion Antoine Kremer Ludovic Orlando 《Molecular ecology》2018,27(5):1138-1154
Reconstructing the colonization and demographic dynamics that gave rise to extant forests is essential to forecasts of forest responses to environmental changes. Classical approaches to map how population of trees changed through space and time largely rely on pollen distribution patterns, with only a limited number of studies exploiting DNA molecules preserved in wooden tree archaeological and subfossil remains. Here, we advance such analyses by applying high‐throughput (HTS) DNA sequencing to wood archaeological and subfossil material for the first time, using a comprehensive sample of 167 European white oak waterlogged remains spanning a large temporal (from 550 to 9,800 years) and geographical range across Europe. The successful characterization of the endogenous DNA and exogenous microbial DNA of 140 (~83%) samples helped the identification of environmental conditions favouring long‐term DNA preservation in wood remains, and started to unveil the first trends in the DNA decay process in wood material. Additionally, the maternally inherited chloroplast haplotypes of 21 samples from three periods of forest human‐induced use (Neolithic, Bronze Age and Middle Ages) were found to be consistent with those of modern populations growing in the same geographic areas. Our work paves the way for further studies aiming at using ancient DNA preserved in wood to reconstruct the micro‐evolutionary response of trees to climate change and human forest management. 相似文献
6.
Prasanna Maruthi Podsiadla-Bialoskorska Malgorzata Mielecki Damian Ruffier Nicolas Fateh Amina Lambert Annie Fanuel Mathieu Camberlein Emilie Szolajska Ewa Grandjean Cyrille 《Glycoconjugate journal》2021,38(4):437-446
Glycoconjugate Journal - Virus-Like Particles (VLPs) have been used as immunogenic molecules in numerous recombinant vaccines. VLPs can also serve as vaccine platform to exogenous antigens, usually... 相似文献
7.
Jonathan Woodward Holly J. Marquess Cyrille S. Picker 《Preparative biochemistry & biotechnology》2013,43(4):337-352
Affinity chromatography of a commercial preparation of 3-glu-cosidase from Aspergillus niger using concanavalin A-Sepharose (CAS) was employed as a means of purifying this glycoprotein. However, mannose (up to 1.08 M) was ineffective as an eluent of this enzyme from CAS, as were several other sugars and their derivatives, including 0.5 M glucose. Also, washing the CAS:8-glucosidase complex with buffer at pH 3.5 in the absence of MnCl2 and CaCl2 (required to preserve the binding activity of concanavalin A below pH 5.0) did not result in elution of this enzyme. On the contrary, endo-glucanase activity present in a crude cellulase complex (A. niger) which bound to CAS could be eluted by mannose (0.5–0.7 M) and was fractionated Into at least two components. The CAS:β-glucosidase complex hydrolyzed cellobiose to glucose and possessed an activity of 2, 158 units/g dry CAS. It could be used, therefore, for continuous cellobiose hydrolysis without leakage of enzyme from the support. 相似文献
8.
Erwan Quéméré Fabrice Hibert Christian Miquel Emeline Lhuillier Emmanuel Rasolondraibe Julie Champeau Clément Rabarivola Louis Nusbaumer Cyrille Chatelain Laurent Gautier Patrick Ranirison Brigitte Crouau-Roy Pierre Taberlet Lounès Chikhi 《PloS one》2013,8(3)
In tropical regions, most primary ecosystems have been replaced by mosaic landscapes in which species must cope with a large shift in the distribution of their habitat and associated food resources. Primates are particularly vulnerable to habitat modifications. Most species persist in small fragments surrounded by complex human-mediated matrices whose structure and connectivity may strongly influence their dispersal and feeding behavior. Behavioral plasticity appears to be a crucial parameter governing the ability of organisms to exploit the resources offered by new matrix habitats and thus to persist in fragmented habitats. In this study, we were interested in the dietary plasticity of the golden-crowned sifaka (Propithecus tattersalli), an endangered species of lemur, found only in the Daraina region in north-eastern Madagascar. We used a DNA-based approach combining the barcoding concept and Illumina next-generation sequencing to (i) describe the species diet across its entire range and (ii) evaluate the influence of landscape heterogeneity on diet diversity and composition. Faeces from 96 individuals were sampled across the entire species range and their contents were analyzed using the trnL metabarcoding approach. In parallel, we built a large DNA reference database based on a checklist of the plant species of the Daraina region. Our results suggest that golden-crowned sifakas exhibit remarkable dietary diversity with at least 130 plant species belonging to 80 genera and 49 different families. We highlighted an influence of both habitat type and openness on diet composition suggesting a high flexibility of foraging strategies. Moreover, we observed the presence of numerous cultivated and naturalized plants in the faeces of groups living in forest edge areas. Overall, our findings support our initial expectation that P. tattersalli is able to cope with the current level of alteration of the landscape and confirm our previous results on the distribution and the dispersal ability of this species. 相似文献
9.
Kokou-Kpolou Cyrille Kossigan Moukouta Charlemagne S. Sani Livia McIntee Sara-Emilie Cénat Jude Mary Awesso Atiyihwè Bacqué Marie-Frédérique 《Culture, medicine and psychiatry》2020,44(4):501-523
Culture, Medicine, and Psychiatry - The current article focused on examining the potential benefits of the End-of-Life (EoL) informal caregiving, communication, and ritualistic behaviors in... 相似文献
10.
Cyrille Gavazzi Catherine Isel Emilie Fournier Vincent Moules Annie Cavalier Daniel Thomas Bruno Lina Roland Marquet 《Nucleic acids research》2013,41(2):1241-1254
The genome of influenza A viruses (IAV) is split into eight viral RNAs (vRNAs) that are encapsidated as viral ribonucleoproteins. The existence of a segment-specific packaging mechanism is well established, but the molecular basis of this mechanism remains to be deciphered. Selective packaging could be mediated by direct interaction between the vRNA packaging regions, but such interactions have never been demonstrated in virions. Recently, we showed that the eight vRNAs of a human H3N2 IAV form a single interaction network in vitro that involves regions of the vRNAs known to contain packaging signals in the case of H1N1 IAV strains. Here, we show that the eight vRNAs of an avian H5N2 IAV also form a single network of interactions in vitro, but, interestingly, the interactions and the regions of the vRNAs they involve differ from those described for the human H3N2 virus. We identified the vRNA sequences involved in five of these interactions at the nucleotide level, and in two cases, we validated the existence of the interaction using compensatory mutations in the interacting sequences. Electron tomography also revealed significant differences in the interactions taking place between viral ribonucleoproteins in H5N2 and H3N2 virions, despite their canonical ‘7 + 1’ arrangement. 相似文献