全文获取类型
收费全文 | 3532篇 |
免费 | 249篇 |
国内免费 | 1篇 |
出版年
2024年 | 3篇 |
2023年 | 40篇 |
2022年 | 87篇 |
2021年 | 146篇 |
2020年 | 99篇 |
2019年 | 95篇 |
2018年 | 158篇 |
2017年 | 111篇 |
2016年 | 191篇 |
2015年 | 256篇 |
2014年 | 248篇 |
2013年 | 340篇 |
2012年 | 365篇 |
2011年 | 292篇 |
2010年 | 187篇 |
2009年 | 143篇 |
2008年 | 197篇 |
2007年 | 191篇 |
2006年 | 153篇 |
2005年 | 122篇 |
2004年 | 111篇 |
2003年 | 83篇 |
2002年 | 72篇 |
2001年 | 15篇 |
2000年 | 8篇 |
1999年 | 10篇 |
1998年 | 14篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1973年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有3782条查询结果,搜索用时 406 毫秒
871.
Alice Rogers Alastair R. Harborne Christopher J. Brown Yves‐Marie Bozec Carolina Castro Iliana Chollett Karlo Hock Cheryl A. Knowland Alyssa Marshell Juan C. Ortiz Tries Razak George Roff Jimena Samper‐Villarreal Megan I. Saunders Nicholas H. Wolff Peter J. Mumby 《Global Change Biology》2015,21(2):504-514
Under projections of global climate change and other stressors, significant changes in the ecology, structure and function of coral reefs are predicted. Current management strategies tend to look to the past to set goals, focusing on halting declines and restoring baseline conditions. Here, we explore a complementary approach to decision making that is based on the anticipation of future changes in ecosystem state, function and services. Reviewing the existing literature and utilizing a scenario planning approach, we explore how the structure of coral reef communities might change in the future in response to global climate change and overfishing. We incorporate uncertainties in our predictions by considering heterogeneity in reef types in relation to structural complexity and primary productivity. We examine 14 ecosystem services provided by reefs, and rate their sensitivity to a range of future scenarios and management options. Our predictions suggest that the efficacy of management is highly dependent on biophysical characteristics and reef state. Reserves are currently widely used and are predicted to remain effective for reefs with high structural complexity. However, when complexity is lost, maximizing service provision requires a broader portfolio of management approaches, including the provision of artificial complexity, coral restoration, fish aggregation devices and herbivore management. Increased use of such management tools will require capacity building and technique refinement and we therefore conclude that diversification of our management toolbox should be considered urgently to prepare for the challenges of managing reefs into the 21st century. 相似文献
872.
Cheril?Tapia-Rojas Carolina?B.?Lindsay Carla?Montecinos-Oliva Macarena?S.?Arrazola Rocio?M.?Retamales Daniel?Bunout Sandra?Hirsch Nibaldo?C.?Inestrosa
Background
L-methionine, the principal sulfur-containing amino acid in proteins, plays critical roles in cell physiology as an antioxidant and in the breakdown of fats and heavy metals. Previous studies suggesting the use of L-methionine as a treatment for depression and other diseases indicate that it might also improve memory and propose a role in brain function. However, some evidence indicates that an excess of methionine can be harmful and can increase the risk of developing Type-2 diabetes, heart diseases, certain types of cancer, brain alterations such as schizophrenia, and memory impairment.Results
Here, we report the effects of an L-methionine-enriched diet in wild-type mice and emphasize changes in brain structure and function. The animals in our studypresented 1) higher levels of phosphorylated tau protein, 2) increased levels of amyloid-β (Aβ)-peptides, including the formation of Aβ oligomers, 3) increased levels of inflammatory response,4) increased oxidative stress, 5) decreased level of synaptic proteins, and 6) memory impairment and loss. We also observed dysfunction of the Wnt signaling pathway.Conclusion
Taken together, the results of our study indicate that an L-methionine-enriched diet causes neurotoxic effects in vivo and might contribute to the appearance of Alzheimer’s-like neurodegeneration.873.
Irradiation is a postharvest quarantine treatment option to control ants and other hitchhiker pests on fresh horticultural products exported from Hawaii. The radiotolerance of the invasive little fire ant, Wasmannia auropunctata (Roger) (Hymenoptera: Formicidae: Myrmicinae), was studied to determine a dose sufficient for its control. Queens from each of five laboratory microcolonies started from five geographic locations in Argentina were irradiated at 20, 50, 70, or 100 Gy or left untreated as controls and then followed for 13 wk to observe colony growth. In general, queen survivorship, and the number of eggs, larvae, and pupae observed in the microcolonies decreased with increasing irradiation dose. In the 50-, 70-, and 100-Gy treatments, the number of eggs observed was reduced by 68, 66, and 76%, respectively, compared with untreated control microcolonies. The number of larvae in the 50-, 70-, and, 100-Gy treatments was reduced by 99.6%, and only one pupa was observed in the 50-Gy treatment and none in the 70- and 100-Gy treatments during the 13-wk experiment. Queens in the 100-Gy treatment had significantly reduced longevity compared with queens in the other treatments. Radiation doses > or = 70 Gy stopped reproduction in W. auropunctata queens and should be sufficient as a phytosanitary treatment. Information from additional invasive ants in Myrmicinae and other subfamilies is needed before recommending a generic irradiation treatment for ants. 相似文献
874.
875.
Silveira RX Chagas AC Botura MB Batatinha MJ Katiki LM Carvalho CO Bevilaqua CM Branco A Machado EA Borges SL Almeida MA 《Experimental parasitology》2012,131(2):162-168
Active compounds from Agave sisalana with antiparasitic action against gastrointestinal nematodes (GINs) could be an alternative to diversify the range of parasite management methods in the livestock sector. The objective of this study was to evaluate the in vitro action of A. sisalana extract on the development of sheep and goat GINs. The extract, obtained from shredded sisal leaves, was utilized at various concentrations in the egg hatch test (EHT), larval development test (LDT), larval feeding inhibition test (LFIT) and adult motility test (AMT). The LC(50) and LC(95) in the EHT were 6.90 and 24.79 mg/mL, in the LDT were 0.041 and 0.067 mg/mL and in the LFIT were 0.053 and 0.24 mg/mL, respectively, showing a dose-dependent relationship. The development and feeding inhibition on L(1) were both 100% at a dose of 0.12 mg/mL. In the AMT there was 100% inhibition at 75 mg/mL after 24h of exposure. The extract of A. sisalana therefore demonstrated significant action on L(1) at 0.12 mg/mL. So, if part of the A. sisalana extract passes through the animal's gastrointestinal system, this material can have a significant effect on the parasites in the feces. This is an interesting approach because it can drastically reduce the pasture contamination as well as the infection of herds. 相似文献
876.
de Sá Morais LL Garza DR Loureiro EC Nunes KN Vellasco RS da Silva CP Nunes MR Thompson CC Vicente AC Santos EC 《Journal of bacteriology》2012,194(10):2772
We report the genome sequence of Vibrio cholerae strain IEC224, which fails to ferment sucrose. It was isolated from a cholera outbreak in the Amazon. The defective sucrose phenotype was determined to be due to a frameshift mutation, and a molecular marker of the Latin American main epidemic lineage was identified. 相似文献
877.
878.
Prados-Rosales RC Roldán-Rodríguez R Serena C López-Berges MS Guarro J Martínez-del-Pozo Á Di Pietro A 《The Journal of biological chemistry》2012,287(26):21970-21979
The pathogenesis-related PR-1-like protein family comprises secreted proteins from the animal, plant, and fungal kingdoms whose biological function remains poorly understood. Here we have characterized a PR-1-like protein, Fpr1, from Fusarium oxysporum, an ubiquitous fungal pathogen that causes vascular wilt disease on a wide range of plant species and can produce life-threatening infections in immunocompromised humans. Fpr1 is secreted and proteolytically processed by the fungus. The fpr1 gene is required for virulence in a disseminated immunodepressed mouse model, and its function depends on the integrity of the proposed active site of PR-1-like proteins. Fpr1 belongs to a gene family that has expanded in plant pathogenic Sordariomycetes. These results suggest that secreted PR-1-like proteins play important roles in fungal pathogenicity. 相似文献
879.
880.
Carolina Madeira Maria Judite Alves Natacha Mesquita Sara Ema Silva José Paula 《Biological journal of the Linnean Society. Linnean Society of London》2012,107(3):647-663
In the present study, we assessed the inter‐ and intrapopulation genetic and morphological variation of Cerithidea decollata along the eastern coast of Africa. The population structure of C. decollata along the latitudinal gradient was examined by sequencing 420 bp of the mitochondrial cytochrome c oxidase I (COI) gene in 172 snails from 29 sites, in a combined analysis with geometric morphometrics in 1799 snails from 32 sites. Analysis of molecular variance and spatial analysis of molecular variance showed a moderate spatial population differentiation from Kenya to the Republic of South Africa, suggesting genetic divergence between the northern, central, and southern regions. This structure appears to be the result of life‐history traits combined with oceanographic features. Haplotype network and mismatch analysis suggest a recent population expansion during the Holsteinian interglacial period in the northern region and several colonization events in the central and southern regions. The morphometric approach suggests that morphological variation in shell shape is somewhat independent of the genetic divergence, revealing an overlap of shape across the latitudinal gradient but significant differences among‐population at a local level. This may indicate that similar ecological pressures are acting along the coast, leading to the occurrence of similar morphological characters. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107 , 647–663. 相似文献