全文获取类型
收费全文 | 630篇 |
免费 | 40篇 |
专业分类
670篇 |
出版年
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 12篇 |
2020年 | 6篇 |
2019年 | 13篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 21篇 |
2015年 | 32篇 |
2014年 | 25篇 |
2013年 | 45篇 |
2012年 | 56篇 |
2011年 | 54篇 |
2010年 | 20篇 |
2009年 | 33篇 |
2008年 | 57篇 |
2007年 | 44篇 |
2006年 | 32篇 |
2005年 | 32篇 |
2004年 | 56篇 |
2003年 | 23篇 |
2002年 | 27篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1978年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有670条查询结果,搜索用时 0 毫秒
651.
The microbial degradation of dibenzothiophene (DBT) and other organosulphur compounds such as thiophene-2-carboxylate (T2C) is of interest for the potential desulphurization of coal. The feasibility of degradation of DBT and T2C by Pseudomonas putida and other bacteria was analysed. Pseudomonas putida oxidized sulphur from DBT in the presence of yeast extract, but it did not when DBT was the sole source of carbon. 相似文献
652.
DNA barcodes,cryptic diversity and phylogeography of a W Mediterranean assemblage of thermosbaenacean crustaceans 下载免费PDF全文
Fernando Cánovas José A. Jurado‐Rivera Elena Cerro‐Gálvez Carlos Juan Damià Jaume Joan Pons 《Zoologica scripta》2016,45(6):659-670
We assess the occurrence of crypticism and analyse the phylogeography of a thermosbaenacean crustacean, the monodellid Tethysbaena scabra, endemic to the Balearic Islands (W Mediterranean). This species occurs only in mixohaline waters of coastal wells and caves adjacent to the seashore. We have used the mitochondrial DNA barcode region to assess its genetic population structure throughout the anchialine environment of the islands. Maximum likelihood phylogenetic analyses showed that the Balearic Tethysbaena and those from the NW Italian Peninsula form a monophyletic assemblage subdivided into several lineages. Cytochrome c oxidase subunit 1 (cox1) p‐distances among the more divergent Mallorcan lineages are remarkably high and on par with those established between the formally described species T. scabra from Menorca and T. argentarii from Italy. This result and the application of the generalised mixed Yule coalescence model (GMYC) suggest that at least some of the Mallorcan lineages represent cryptic species. A clear‐cut phylogeographic pattern is displayed by this anchialine assemblage: six of its seven lineages appear in allopatry, with the exception of a Mallorcan lineage limited to a single cave nested within the geographic range of another lineage. All lineages show a distribution reduced to a single cave or to short portions of coast not exceeding 60 km in length. Our coalescence estimations suggest an early Tortonian (10.7 Ma) origin for the Balearic + Italy Tethysbaena clade, an age that is largely prior to the onset of the eustatic oscillations associated with the Quaternary glaciations. Only the diversification that took place within some of the Mallorcan lineages could be coeval with the broad glacio‐eustatic oscillations of the Quaternary. 相似文献
653.
We propose a model for membrane-cortex adhesion that couples membrane deformations, hydrodynamics, and kinetics of membrane-cortex ligands. In its simplest form, the model gives explicit predictions for the critical pressure for membrane detachment and for the value of adhesion energy. We show that these quantities exhibit a significant dependence on the active acto-myosin stresses. The model provides a simple framework to access quantitative information on cortical activity by means of micropipette experiments. We also extend the model to incorporate fluctuations and show that detailed information on the stability of membrane-cortex coupling can be obtained by a combination of micropipette aspiration and fluctuation spectroscopy measurements. 相似文献
654.
Leaf photosynthesis, stomatal conductance, internal CO2 concentrationand leaf composition (photosynthetic pigments, total solubleprotein and Rubisco content) during leaf ontogeny of field grownNicotiana tabacum L. lines selected for survival at low atmosphericCO2 concentrations are described. Selection at low CO2 concentrations resutted in lines with highertotal dry matter production than their parent cultivar, butthis could not be related to improved photosynthesis which theselection method was designed to achieve (shown in previouswork). In the present work we report higher rates of photosynthesisin the selected lines in mature and old leaves, not found inyoung leaves when the capacity for photosynthesis was maximum.Differences in the regulation of the photosynthetic carbon reductioncycle as well as differences in the diffusive characteristicsof the mesophyll, due to changes in the size of the cells, maybe the cause for the higher rates of photosynthesis during leafsenescence in the selected lines. Key words: Photosynthesis, leaf ontogeny, tobacco, lines 相似文献
655.
Francesco Fabbrini Riccardo Ludovisi Omar Alasia Jaume Flexas Cyril Douthe Miquel Ribas Carb Paul Robson Gail Taylor Giuseppe Scarascia‐Mugnozza Joost J. B. Keurentjes Antoine Harfouche 《Global Change Biology Bioenergy》2019,11(1):152-170
Giant reed (Arundo donax L.) is a perennial rhizomatous grass, which has attracted great attention as a potential lignocellulosic feedstock for bioethanol production due to high biomass yield in marginal land areas, high polysaccharide content and low inhibitor levels in microbial fermentations. However, little is known about the trait variation that is available across a broad ecotypic panel of A. donax nor the traits that contribute most significantly to yield and growth in drought prone environments. A collection of 82 ecotypes of A. donax sampled across the Mediterranean basin was planted in a common garden experimental field in Savigliano, Italy. We analysed the collection using 367 clumps representing replicate plantings of 82 ecotypes for variation in 21 traits important for biomass accumulation and to identify the particular set of ecotypes with the most promising potential for biomass production. We measured morpho‐physiological, phenological and biomass traits and analysed causal relationships between traits and productivity characteristics assessed at leaf and canopy levels. The results identified differences among the 82 ecotypes for all studied traits: those showing the highest level of variability included stomatal resistance, stem density (StN), stem dry mass (StDM) and total biomass production (TotDM). Multiple regression analysis revealed that leaf area index, StDM, StN, number of nodes per stem, stem height and diameter were the most significant predictors of TotDM and the most important early selection criteria for bioenergy production from A. donax. These traits were used in a hierarchical cluster analysis to identify groups of similar ecotypes, and a selection was made of promising ecotypes for multiyear and multisite testing for biomass production. Heritability estimates were significant for all traits. The potential of this ecotype collection as a resource for studies of germplasm diversity and for the analysis of traits underpinning high productivity of A. donax is highlighted. 相似文献
656.
Rafael Romero Joan Fibla David Bueno Lauro Sumoy Marc Aureli Soriano Jaume Baguñà 《Hydrobiologia》1991,227(1):73-79
We have produced monoclonal antibodies (mAb's) against antigens of the fresh-water planarian Dugesia (G.) tigrina (Girard) using standard protocols. Labeling these mAb's with PAP (peroxidase-antiperoxidase) and indirect-immunofluorescence methods, we then determined the distribution of their antigens in the planarian. Out of 112 mAb's that showed some specificity for restricted parts of the planarian, 71 were found to be cell- or tissue-specific — among them 36 for parenchymal cells, 7 for muscle cells, 11 for epidermal cells, 8 for gastrodermis, and 7 to basement membrane. Another 41 showed different, but overlapping, regional specificities, namely to pharynx and parenchyma. So far, we have been unable to isolate specific mAb's against undifferentiated cells (neoblasts). These mAb's should be important tools in study of tissue and cell morphology, regeneration, and growth and degrowth. 相似文献
657.
Jordina Belmonte Mercè Vendrell Joan M. Roure Josep Vidal Jaume Botey Àlvar Cadahía 《Aerobiologia》2000,16(1):93-99
Ambrosia pollen is known as an importantallergen in North America, and more recently in someEuropean countries. From 1989 to 1995, the Ambrosia pollen levels detected at the stationsmonitored by the Aerobiological Network of Catalonia(Xarxa Aerobiològica de Catalunya, XAC) wereinsignificant. In 1996, a considerable althoughtemporary increase in the concentration of this pollenwas detected in the atmosphere over Girona, Barcelona,Bellaterra, Manresa, and Tarragona. Most of the Ambrosia pollen collected in 1996 was concentrated ina single day. Its appearance on that day wasattributed to long range transportation, caused byunusual conditions of atmospheric circulation, fromthe Lyon region in France where the species isabundant. This is the only day where concentrations ofAmbrosia pollen that may be dangerous to humanhealth have been reached.
Ambrosia coronopifolia is the most abundantspecies of the genus in Catalonia, and although rare,its expansion is favoured by the fact that it growsthrough rhizomes and sprouts easily. It is, therefore,important to monitor the growth of its population andthe release of its pollen in order to predict theappearance of pollen levels that may precipitateallergic symptoms. 相似文献
658.
Jaume Cambra 《Biologia》2010,65(4):577-586
The results of a phycological study on the chrysophyte flora in the eastern Pyrenees (Catalonia, Spain) are presented. The
studied area is located between 1600 and 2600 m above sea level, on primarily acid substrate. A total of 34 taxa have been
identified, 25 of which are new or very rarely known in Spain. Information about the cell morphology and ecological data of
the studied aquatic systems are presented. 相似文献
659.
660.
Giorgio Bertorelle Francesc Calafell Paolo Francalacci Jaume Bertranpetit G. Barbujani 《Human genetics》1996,98(2):145-150
The geographical distribution of 49 mtDNA sequences from 22 localities in Southern Tuscany, Italy, was studied by molecular
analysis of variance, by a new spatial autocorrelation statistic specifically designed for sequence data and by reconstructing
genealogies of haplotypes. All these methods indicated a high homogeneity of populations. Nevertheless, genetic variability
showed significant departure from equilibrium expectations, in agreement with the predicted effects of a population expansion.
We suggest that a past population expansion that was probably associated with a migrational wave and with local gene flow
between localities prevented spatial structuring in Southern Tuscany.
Received: 30 November 1995 / Revised: 5 March 1996 相似文献