全文获取类型
收费全文 | 7137篇 |
免费 | 525篇 |
国内免费 | 1篇 |
出版年
2023年 | 56篇 |
2022年 | 116篇 |
2021年 | 226篇 |
2020年 | 154篇 |
2019年 | 190篇 |
2018年 | 238篇 |
2017年 | 228篇 |
2016年 | 340篇 |
2015年 | 413篇 |
2014年 | 453篇 |
2013年 | 506篇 |
2012年 | 644篇 |
2011年 | 551篇 |
2010年 | 330篇 |
2009年 | 294篇 |
2008年 | 406篇 |
2007年 | 339篇 |
2006年 | 331篇 |
2005年 | 297篇 |
2004年 | 286篇 |
2003年 | 245篇 |
2002年 | 222篇 |
2001年 | 72篇 |
2000年 | 55篇 |
1999年 | 75篇 |
1998年 | 63篇 |
1997年 | 52篇 |
1996年 | 43篇 |
1995年 | 36篇 |
1994年 | 34篇 |
1993年 | 31篇 |
1992年 | 33篇 |
1991年 | 30篇 |
1990年 | 22篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 21篇 |
1985年 | 25篇 |
1984年 | 8篇 |
1983年 | 10篇 |
1982年 | 23篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 12篇 |
1976年 | 6篇 |
1974年 | 6篇 |
1970年 | 5篇 |
1968年 | 14篇 |
排序方式: 共有7663条查询结果,搜索用时 15 毫秒
61.
Sonja K. Glasser Martín Hesajim de Santiago-Hernández Oliverio Delgado-Carrillo Luis Alberto Villanueva Espino Adonaji Cortés Pérez Antonio González-Rodríguez Rafael Lira-Saade Mauricio Quesada 《American journal of botany》2023,110(5):e16170
Premise
Domestication of plant species results in phenotypic modifications and changes in biotic interactions. Most studies have compared antagonistic plant-herbivore interactions of domesticated plants and their wild relatives, but little attention has been given to how domestication influences plant-pollinator interactions. Floral attributes and interactions of floral visitors were compared between sister taxa of the genus Cucurbita (Cucurbitaceae), the domesticated C. moschata, C. argyrosperma ssp. argyrosperma and its wild progenitor C. argyrosperma ssp. sororia in the place of origin.Methods
We conducted univariate and multivariate analyses to compare floral morphological traits and analyzed floral reward (nectar and pollen) quantity and quality between flowers of wild and domesticated Cucurbita taxa. Staminate and pistillate flowers of all three taxa were video recorded, and visitation and behavior of floral visitors were registered and analyzed.Results
Most floral morphological characteristics of flowers of domesticated taxa were larger in both staminate and pistillate flowers. Staminate and pistillate flowers presented distinct correlations between floral traits and integration indices between domesticated and wild species. Additionally, pollen quantity and protein to lipid ratio were greater in domesticated species. Cucurbit pollen specialists, Eucera spp., had the highest probability of visit for all Cucurbita taxa.Conclusions
We provide evidence that floral traits of domesticated and wild Cucurbita species experienced different selection pressures. Domesticated Cucurbita species may have more resources invested towards floral traits, thereby increasing attractiveness to pollinators and potentially plant reproductive success. Wild ancestor plant populations should be conserved in their centers of origin to preserve plant-pollinator interactions. 相似文献62.
Rafael Muñoz-Mas Franz Essl Mark van Kleunen Hanno Seebens Wayne Dawson Christine Marie V. Casal Emili García-Berthou 《Global Ecology and Biogeography》2023,32(9):1632-1644
Aim
Investigating major freshwater fish flows (translocations) between biogeographic regions and their temporal dynamics and also quantifying spatial patterns and temporal changes in the array of introduced species, and the emergence and distance between major donor and recipient regions.Location
Global.Time Period
1800–2020.Major Taxa Studied
Freshwater fishes.Methods
We analysed a global dataset on freshwater fish introductions (4241 events of 688 species). Freshwater fish flows were investigated with flow diagrams and χ2 tests, while PERMANOVA (permutational multivariate analysis of variance) was used to test the association between species and regions and temporal shifts. Cluster analysis revealed major recipient areas and composition of the introduced species. Finally, changes in distances between donor and recipient sites were tested with PERMANOVA.Results
The number of introductions between biogeographic regions mirrored the European and North American dominance before World War II (WWII) and the trends in recreational fishing, biocontrol programmes and food production, especially in the Sino-Oriental region, which has a long tradition of aquaculture and fishkeeping. Over the years, the origins and composition of introduced species changed uniquely in each biogeographic region, although the most introduced species are common to every region. Salmonids and other cold-water species were frequently introduced before the 1950s, whereas tropical ornamental and aquaculture species currently prevail. Distances between donor and recipient sites did not vary over the time. After WWII, the Sino-Oriental region consolidated its dominance and the Ethiopian and Neotropical regions emerged as new global donor and recipient regions.Main Conclusions
Global policy should focus on tropical ornamental and aquaculture species, which could benefit from global warming, especially in the Sino-Oriental region, because it currently dominates freshwater fish species flows, and the Ethiopian and Neotropical regions, because they recently emerged as important global donor and recipient regions of freshwater fish introductions. 相似文献63.
64.
65.
Inhibition of the HIV-1 and HIV-2 proteases by curcumin and curcumin boron complexes 总被引:3,自引:0,他引:3
Zhihua Sui Rafael Salto Jia Li Charles Craik Paul R. Ortiz de Montellano 《Bioorganic & medicinal chemistry》1993,1(6):415-422
Curcumin, a relatively non-toxic natural product isolated from Curcuma longa, is a modest inhibitor of the HIV-1 (1050 = 100 μM) and HIV-2 (IC50 = 250 μM) proteases. Simple modifications of the curcumin structure raise the IC50 value but complexes of the central dihydroxy groups of curcumin with boron lower the IC50 to a value as low as 6 μM. The boron complexes are also time-dependent inactivators of the HIV proteases. The increased affinity of the boron complexes may reflect binding of the orthogonal domains of the inhibitor in intersecting sites within the substrate-binding cavity of the enzyme, while activation of the ,β-unsaturated carbonyl group of curcumin by chelation to boron probably accounts for time-dependent inhibition of the enzyme. 相似文献
66.
Jennifer L. Wright Heather A. Stewart Ivette Candanedo Evan D'Alessandro Maria Estevanez Rafael J. Araújo 《Biotropica》2023,55(2):299-305
We conducted visual fish surveys in coexisting mangrove-coral (CMC) habitats in Panama to analyze the effect of coral presence in mangrove habitats on the fish assemblage. Our study revealed that CMC habitats harbor distinct fish assemblages compared to mangrove habitats without coral, with greater species richness and increased herbivore abundance. Abstract in Spanish is available with online material. 相似文献
67.
Rafael Radi Stephen Sims Adriana Cassina Julio F. Turrens 《Free radical biology & medicine》1993,15(6)
A recent report (Radi et al., J. Biol. Chem. 266:22028–22034, 1991) showed that rat heart mitochondria contain catalase. The protective role of mitochondrial catalase was tested by exposing heart or kidney mitochondria and mitoplasts to two oxidants (H2O2) or tert-butyl hydroperoxide, t-BOOH), estimating lipid peroxidation (as thiobarbituric acid-reactive substances, TBARS) and overall oxidative stress (as chemiluminescence). Additional controls included heart and kidney preparations from aminotriazole-treated (catalase-depleted) rats. Both oxidants increased TBARS in catalase-free preparations to similar extents over their respective controls (between 200 to 350%). In catalase-containing preparations, H2O2 lipid peroxidation increased by only 40 to 96% over controls. Similar qualitative results were obtained when measuring chemiluminescence. The catalytic role of cytochrome c in mitochondrial lipid peroxidation was investigated by exposing either control or cytochrome-c-depleted kidney mitoplasts (catalase free) to either H2O2 or t-BOOH. Hydrogen-peroxide-dependent mitochondrial lipid peroxidation varied with cytochrome c concentrations, remaining close to controls when cytochrome c concentration decreased by 66%, even though there was no catalase present. Tert-butyl hydroperoxide-dependent lipid peroxidation was less affected by cytochrome c remaining 2.3-fold above controls under the same conditions, suggesting that organic peroxides are more likely to remain in the less polar membrane environment being decomposed by heme or nonheme iron imbedded in the inner mitochondrial membrane. Chemiluminescence was less affected by cytochrome c depletion. Comparing control and cytochrome-c-deficient mitochondria, chemiluminescence was 1.7-fold and 2.8-fold higher when control preparations were challenged with t-BOOH or H2O2, respectively. 相似文献
68.
Molecular cloning of a gene involved in glucose sensing in the yeast Saccharomyces cerevisiae 总被引:6,自引:1,他引:5
Linda Van Aelst Stefan Hohmann Botchaka Bulaya Wim de Koning Laurens Sierkstra Maria José Neves Kattie Luyten Rafael Alijo José Ramos Paola Coccetti Enzo Martegani Neuza Maria de Magalhães-Rocha Rogelio Lopes Brandão Patrick Van Dijck Mieke Vanhalewyn Peter Durnez Arnold W. H. Jans Johan M. Thevelein 《Molecular microbiology》1993,8(5):927-943
69.
Coelho-Rocha Nina Dias de Jesus Luís Cláudio Lima Barroso Fernanda Alvarenga Lima da Silva Tales Fernando Ferreira Enio Gonçalves José Eduardo dos Santos Martins Flaviano de Oliveira Carvalho Rodrigo Dias Barh Debmalya Azevedo Vasco Ariston de Carvalho 《Probiotics and antimicrobial proteins》2023,15(1):160-174
Probiotics and Antimicrobial Proteins - Beneficial effects of Lactiplantibacillus plantarum strains have been widely reported. Knowing that the effects of probiotic bacteria are strain-dependent,... 相似文献
70.
Roberto de la Herrán Miguel Hermida Juan Andres Rubiolo Jèssica Gómez-Garrido Fernando Cruz Francisca Robles Rafael Navajas-Pérez Andres Blanco Paula Rodriguez Villamayor Dorinda Torres Pablo Sánchez-Quinteiro Daniel Ramirez Maria Esther Rodríguez Alberto Arias-Pérez Ismael Cross Neil Duncan Teresa Martínez-Peña Ana Riaza Adrian Millán M. Cristina De Rosa Davide Pirolli Marta Gut Carmen Bouza Diego Robledo Laureana Rebordinos Tyler Alioto Carmelo Ruíz-Rejón Paulino Martínez 《Molecular ecology resources》2023,23(4):886-904
Sex determination (SD) shows huge variation among fish and a high evolutionary rate, as illustrated by the Pleuronectiformes (flatfishes). This order is characterized by its adaptation to demersal life, compact genomes and diversity of SD mechanisms. Here, we assembled the Solea senegalensis genome, a flatfish of great commercial value, into 82 contigs (614 Mb) combining long- and short-read sequencing, which were next scaffolded using a highly dense genetic map (28,838 markers, 21 linkage groups), representing 98.9% of the assembly. Further, we established the correspondence between the assembly and the 21 chromosomes by using BAC-FISH. Whole genome resequencing of six males and six females enabled the identification of 41 single nucleotide polymorphism variants in the follicle stimulating hormone receptor (fshr) consistent with an XX/XY SD system. The observed sex association was validated in a broader independent sample, providing a novel molecular sexing tool. The fshr gene displayed differential expression between male and female gonads from 86 days post-fertilization, when the gonad is still an undifferentiated primordium, concomitant with the activation of amh and cyp19a1a, testis and ovary marker genes, respectively, in males and females. The Y-linked fshr allele, which included 24 nonsynonymous variants and showed a highly divergent 3D protein structure, was overexpressed in males compared to the X-linked allele at all stages of gonadal differentiation. We hypothesize a mechanism hampering the action of the follicle stimulating hormone driving the undifferentiated gonad toward testis. 相似文献