全文获取类型
收费全文 | 3218篇 |
免费 | 310篇 |
国内免费 | 1篇 |
专业分类
3529篇 |
出版年
2023年 | 9篇 |
2022年 | 19篇 |
2021年 | 56篇 |
2020年 | 30篇 |
2019年 | 43篇 |
2018年 | 66篇 |
2017年 | 52篇 |
2016年 | 96篇 |
2015年 | 137篇 |
2014年 | 151篇 |
2013年 | 168篇 |
2012年 | 229篇 |
2011年 | 229篇 |
2010年 | 167篇 |
2009年 | 149篇 |
2008年 | 200篇 |
2007年 | 193篇 |
2006年 | 150篇 |
2005年 | 160篇 |
2004年 | 153篇 |
2003年 | 158篇 |
2002年 | 149篇 |
2001年 | 44篇 |
2000年 | 35篇 |
1999年 | 44篇 |
1998年 | 40篇 |
1997年 | 38篇 |
1996年 | 30篇 |
1995年 | 42篇 |
1994年 | 32篇 |
1993年 | 40篇 |
1992年 | 50篇 |
1991年 | 29篇 |
1990年 | 31篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1975年 | 9篇 |
1970年 | 15篇 |
1913年 | 8篇 |
排序方式: 共有3529条查询结果,搜索用时 10 毫秒
111.
One major characteristic of invasive alien species is their occurrence at high abundances in their new habitat. Flowering
invasive plant species that are visited by native insects and overlap with native plant species in their pollinators may facilitate
or disrupt native flower visitation and fertilisation by forming large, dense populations with high numbers of flowers and
copious rewards. We investigated the direction of such a proposed effect for the alien invasive Rhododendron ponticum in Irish habitats. Flower visitation, conspecific and alien pollen deposition, fruit and seed set were measured in a self-compatible
native focal plant, Digitalis purpurea, and compared between field sites that contained different relative abundances of R. ponticum. Flower visitation was significantly lower at higher alien relative plant abundances than at lower abundances or in the absence
of the alien. Native flowers experienced a significant decrease in conspecific pollen deposition with increasing alien abundance.
Heterospecific pollen transfer was very low in all field sites but increased significantly with increasing relative R. ponticum abundance. However, lower flower visitation and lower conspecific pollen transfer did not alter reproductive success of D. purpurea. Our study shows that indirect interactions between alien and native plants for pollination can be modified by population
characteristics (such as relative abundance) in a similar way as interactions among native plant species. In D. purpurea, only certain aspects of pollination and reproduction were affected by high alien abundances which is probably a result of
high resilience due to a self-compatible breeding system. Native species that are more susceptible to pollen limitation are
more likely to experience fitness disadvantages in habitats with high relative alien plant abundances. 相似文献
112.
Determination of stereochemistry in the fatty acid hydroperoxide products of lipoxygenase catalysis 总被引:1,自引:0,他引:1
High-performance liquid chromatography has been found to be an effective method for the determination of absolute configuration in the products of the lipoxygenase-catalyzed oxygenation of polyunsaturated fatty acids. Methyl esters of fatty acid hydroperoxides that had been reduced to the corresponding alcohols were converted into (+)-alpha-methoxy-alpha-trifluoromethylphenylacetic acid esters. Enantiomeric alcohols were converted into diastereomeric esters that were readily resolved by normal-phase HPLC. The instrumental requirements for the technique are an isocratic HPLC and a uv absorbance monitor. The method was found to be effective in the determination of stereochemistry in the products derived from the action of plant lipoxygenases on linoleic acid. In addition, the chromatography of the derivatives obtained from lipoxygenase catalysis on arachidonic acid was found to be effective for the assignment of stereochemistry in those products. A comparison of the chromatography of these derivatives with that for the corresponding menthyloxycarbonyl derivatives demonstrated the superiority of this approach for the resolution of the diastereomeric pairs. The technique was applied to the determination of stereochemistry in the products derived from soybean lipoxygenase isoenzymes under a variety of experimental conditions. 相似文献
113.
Wiedemann N Urzica E Guiard B Müller H Lohaus C Meyer HE Ryan MT Meisinger C Mühlenhoff U Lill R Pfanner N 《The EMBO journal》2006,25(1):184-195
Mitochondria are indispensable for cell viability; however, major mitochondrial functions including citric acid cycle and oxidative phosphorylation are dispensable. Most known essential mitochondrial proteins are involved in preprotein import and assembly, while the only known essential biosynthetic process performed by mitochondria is the biogenesis of iron-sulfur clusters (ISC). The components of the mitochondrial ISC-assembly machinery are derived from the prokaryotic ISC-assembly machinery. We have identified an essential mitochondrial matrix protein, Isd11 (YER048w-a), that is found in eukaryotes only. Isd11 is required for biogenesis of cellular Fe/S proteins and thus is a novel subunit of the mitochondrial ISC-assembly machinery. It forms a complex with the cysteine desulfurase Nfs1 and is required for formation of an Fe/S cluster on the Isu scaffold proteins. We conclude that Isd11 is an indispensable eukaryotic component of the mitochondrial machinery for biogenesis of Fe/S proteins. 相似文献
114.
High competitiveness of a resource demanding invasive acacia under low resource supply 总被引:1,自引:0,他引:1
Mechanisms controlling the successful invasion of resource demanding species into low-resource environments are still poorly
understood. Well-adapted native species are often considered superior competitors under stressful conditions. Here we investigate
the competitive ability of the resource demanding alien Acacia longifolia, which invades nutrient-poor Mediterranean sand dunes such as in coastal areas of Portugal. We explore the hypothesis that
drought may limit invasion in a factorial competition experiment of the alien invasive versus two native species of different
functional groups (Halimium halimifolium, Pinus pinea), under well-watered and drought conditions. Changes in biomass, allocation pattern, and N-uptake-efficiency (via 15N-labeling) indicated a marked drought sensitivity of the invader. However, highly efficient drought adaptations of the native
species did not provide a competitive advantage under water limiting conditions. The competitive strength of H.
halimifolium towards the alien invader under well-watered conditions turned into a positive interaction between both species under drought.
Further, low resource utilization by native species benefited A. longifolia by permitting continued high nitrogen uptake under drought. Hence, the N-fixing invader expresses low plasticity by continuous
high resource utilization, even under low resource conditions. The introduction of novel traits into a community like N-fixation
and high resource use may promote A. longifolia invasiveness through changes in the physical environment, i.e., the water and nutrient cycle of the invaded sand dune system,
thereby potentially disrupting the co-evolved interactions within the native plant community. 相似文献
115.
Tatarkiewicz K Smith PA Sablan EJ Polizzi CJ Aumann DE Villescaz C Hargrove DM Gedulin BR Lu MG Adams L Whisenant T Roy D Parkes DG 《American journal of physiology. Endocrinology and metabolism》2010,299(6):E1076-E1086
The risk of developing pancreatitis is elevated in type 2 diabetes and obesity. Cases of pancreatitis have been reported in type 2 diabetes patients treated with GLP-1 (GLP-1R) receptor agonists. To examine whether the GLP-1R agonist exenatide potentially induces or modulates pancreatitis, the effect of exenatide was evaluated in normal or diabetic rodents. Normal and diabetic rats received a single exenatide dose (0.072, 0.24, and 0.72 nmol/kg) or vehicle. Diabetic ob/ob or HF-STZ mice were infused with exenatide (1.2 and 7.2 nmol·kg(-1)·day(-1)) or vehicle for 4 wk. Post-exenatide treatment, pancreatitis was induced with caerulein (CRN) or sodium taurocholate (ST), and changes in plasma amylase and lipase were measured. In ob/ob mice, plasma cytokines (IL-1β, IL-2, IL-6, MCP-1, IFNγ, and TNFα) and pancreatitis-associated genes were assessed. Pancreata were weighed and examined histologically. Exenatide treatment alone did not modify plasma amylase or lipase in any models tested. Exenatide attenuated CRN-induced release of amylase and lipase in normal rats and ob/ob mice but did not modify the response to ST infusion. Plasma cytokines and pancreatic weight were unaffected by exenatide. Exenatide upregulated Reg3b but not Il6, Ccl2, Nfkb1, or Vamp8 expression. Histological analysis revealed that the highest doses of exenatide decreased CRN- or ST-induced acute inflammation, vacuolation, and acinar single cell necrosis in mice and rats, respectively. Ductal cell proliferation rates were low and similar across all groups of ob/ob mice. In conclusion, exenatide did not modify plasma amylase and lipase concentrations in rodents without pancreatitis and improved chemically induced pancreatitis in normal and diabetic rodents. 相似文献
116.
N. F. A. Zimmermann Christiane M. Ritz F. H. Hellwig 《Plant Systematics and Evolution》2010,286(1-2):39-58
The cosmopolitan genus Euphorbia is one of the largest plant genera with an extreme phenotypic plasticity ranging from globose succulents to large shrubs and trees adapted to very divergent habitats like forests or deserts. We compiled the current knowledge about the evolution of Euphorbia by reconstructing a molecular phylogeny based on nearly all available internal transcribed spacer (nrITS) sequence data from previous investigations and sequences of newly sampled species. We compared the results with phylogenetic analyses based on a combined data set of nrITS and trnL–trnF intergenic spacer sequences of a subset of taxa. Apart from a few exceptions, the results correspond well to recently published studies based on different molecular markers. The genus Euphorbia is divided into four major clades, of which the clade comprising subgen. Rhizanthium is restricted to Africa and Madagascar, whereas the remaining three clades are distributed over several continents. Our results support the hypothesis that Euphorbia evolved in Africa from progenitors of subgen. Esula. 相似文献
117.
Neele Wendler Martin Mascher Christiane Nöh Axel Himmelbach Uwe Scholz Brigitte Ruge‐Wehling Nils Stein 《Plant biotechnology journal》2014,12(8):1122-1131
Crop wild relatives (CWR) provide an important source of allelic diversity for any given crop plant species for counteracting the erosion of genetic diversity caused by domestication and elite breeding bottlenecks. Hordeum bulbosum L. is representing the secondary gene pool of the genus Hordeum. It has been used as a source of genetic introgressions for improving elite barley germplasm (Hordeum vulgare L.). However, genetic introgressions from H. bulbosum have yet not been broadly applied, due to a lack of suitable molecular tools for locating, characterizing, and decreasing by recombination and marker‐assisted backcrossing the size of introgressed segments. We applied next‐generation sequencing (NGS) based strategies for unlocking genetic diversity of three diploid introgression lines of cultivated barley containing chromosomal segments of its close relative H. bulbosum. Firstly, exome capture‐based (re)‐sequencing revealed large numbers of single nucleotide polymorphisms (SNPs) enabling the precise allocation of H. bulbosum introgressions. This SNP resource was further exploited by designing a custom multiplex SNP genotyping assay. Secondly, two‐enzyme‐based genotyping‐by‐sequencing (GBS) was employed to allocate the introgressed H. bulbosum segments and to genotype a mapping population. Both methods provided fast and reliable detection and mapping of the introgressed segments and enabled the identification of recombinant plants. Thus, the utilization of H. bulbosum as a resource of natural genetic diversity in barley crop improvement will be greatly facilitated by these tools in the future. 相似文献
118.
Niklas M?hler Otilia Cheregi Christiane Funk Sergiu Netotea Torgeir R. Hvidsten 《PloS one》2014,9(11)
Despite being a highly studied model organism, most genes of the cyanobacterium Synechocystis sp. PCC 6803 encode proteins with completely unknown function. To facilitate studies of gene regulation in Synechocystis, we have developed Synergy (http://synergy.plantgenie.org), a web application integrating co-expression networks and regulatory motif analysis. Co-expression networks were inferred from publicly available microarray experiments, while regulatory motifs were identified using a phylogenetic footprinting approach. Automatically discovered motifs were shown to be enriched in the network neighborhoods of regulatory proteins much more often than in the neighborhoods of non-regulatory genes, showing that the data provide a sound starting point for studying gene regulation in Synechocystis. Concordantly, we provide several case studies demonstrating that Synergy can be used to find biologically relevant regulatory mechanisms in Synechocystis. Synergy can be used to interactively perform analyses such as gene/motif search, network visualization and motif/function enrichment. Considering the importance of Synechocystis for photosynthesis and biofuel research, we believe that Synergy will become a valuable resource to the research community. 相似文献
119.
Global variation in the beta diversity of lake macrophytes is driven by environmental heterogeneity rather than latitude 下载免费PDF全文
Janne Alahuhta Sarian Kosten Munemitsu Akasaka Dominique Auderset Mattia M. Azzella Rossano Bolpagni Claudia P. Bove Patricia A. Chambers Eglantine Chappuis John Clayton Mary de Winton Frauke Ecke Esperança Gacia Gana Gecheva Patrick Grillas Jennifer Hauxwell Seppo Hellsten Jan Hjort Mark V. Hoyer Christiane Ilg Agnieszka Kolada Minna Kuoppala Torben Lauridsen En Hua Li Balázs A. Lukács Marit Mjelde Alison Mikulyuk Roger P. Mormul Jun Nishihiro Beat Oertli Laila Rhazi Mouhssine Rhazi Laura Sass Christine Schranz Martin Søndergaard Takashi Yamanouchi Qing Yu Haijun Wang Nigel Willby Xiao Ke Zhang Jani Heino 《Journal of Biogeography》2017,44(8):1758-1769
120.
Hervé Chneiweiss François Hirsch Lluis Montoliu Albrecht M. Müller Solveig Fenet Marion Abecassis Jennifer Merchant Bernard Baertschi Mylène Botbol-Baum James A. Houghton Mihalis Kritikos Janet Mifsud Ewa Bartnik Johannes Rath Christiane Druml Bärbel Friedrich Ana Sofia Carvalho Dirk Lanzerath Agnès Saint-Raymond 《Transgenic research》2017,26(5):709-713
In this consensus paper resulting from a meeting that involved representatives from more than 20 European partners, we recommend the foundation of an expert group (European Steering Committee) to assess the potential benefits and draw-backs of genome editing (off-targets, mosaicisms, etc.), and to design risk matrices and scenarios for a responsible use of this promising technology. In addition, this European steering committee will contribute in promoting an open debate on societal aspects prior to a translation into national and international legislation. 相似文献