全文获取类型
收费全文 | 9038篇 |
免费 | 652篇 |
国内免费 | 3篇 |
出版年
2023年 | 39篇 |
2022年 | 31篇 |
2021年 | 135篇 |
2020年 | 133篇 |
2019年 | 128篇 |
2018年 | 189篇 |
2017年 | 155篇 |
2016年 | 294篇 |
2015年 | 416篇 |
2014年 | 484篇 |
2013年 | 598篇 |
2012年 | 733篇 |
2011年 | 741篇 |
2010年 | 467篇 |
2009年 | 412篇 |
2008年 | 539篇 |
2007年 | 554篇 |
2006年 | 545篇 |
2005年 | 457篇 |
2004年 | 412篇 |
2003年 | 334篇 |
2002年 | 359篇 |
2001年 | 112篇 |
2000年 | 75篇 |
1999年 | 84篇 |
1998年 | 82篇 |
1997年 | 43篇 |
1996年 | 53篇 |
1995年 | 58篇 |
1994年 | 57篇 |
1993年 | 57篇 |
1992年 | 51篇 |
1991年 | 57篇 |
1990年 | 46篇 |
1989年 | 48篇 |
1988年 | 48篇 |
1987年 | 63篇 |
1986年 | 42篇 |
1985年 | 54篇 |
1984年 | 44篇 |
1983年 | 56篇 |
1982年 | 37篇 |
1981年 | 38篇 |
1980年 | 24篇 |
1979年 | 26篇 |
1978年 | 24篇 |
1977年 | 37篇 |
1976年 | 22篇 |
1975年 | 18篇 |
1973年 | 17篇 |
排序方式: 共有9693条查询结果,搜索用时 15 毫秒
1.
Molting phenology of the Pacific harbor seal (Phoca vitulina richardii) on two islands off the Baja California Peninsula,Mexico 下载免费PDF全文
Claudia Tapia‐Harris Gisela Heckel Yolanda Schramm Eva María Fernández‐Martín 《Marine Mammal Science》2017,33(3):817-829
We document and compare the annual molt of the Pacific harbor seal (Phoca vitulina richardii) on two islands off the west coast of the Baja California Peninsula that are the northern and southern extremes of its distribution in Mexico. During 2014, observations were made from March to July on Todos Santos Island (northern extreme) and from January to June on San Roque Island (southern extreme). On Todos Santos, the premolt lasted 15 wk (March–June) and the molt 12 wk (April–July). On San Roque, the premolt lasted 22 wk (January–June) and the molt 17 wk (February–June). The proportion of seals undergoing molt peaked on 26 May on Todos Santos and on 7 June on San Roque. Shedding of old hair most commonly initiated on the torso and progressed to the head and flippers (reverse molting pattern). The period when the highest number of harbor seals haul out in Mexico is in late April on the more southerly islands and in early May on the more northerly islands, when a large proportion of seals are in premolt. 相似文献
2.
3.
4.
Major climatic changes in the Pleistocene had significant effects on marine organisms and the environments in which they lived. The presence of divergent patterns of demographic history even among phylogenetically closely-related species sharing climatic changes raises questions as to the respective influence of species-specific traits on population structure. In this work we tested whether the lifestyle of Antarctic notothenioid benthic and pelagic fish species from the Southern Ocean influenced the concerted population response to Pleistocene climatic fluctuations. This was done by a comparative analysis of sequence variation at the cyt b and S7 loci in nine newly sequenced and four re-analysed species. We found that all species underwent more or less intensive changes in population size but we also found consistent differences between demographic histories of pelagic and benthic species. Contemporary pelagic populations are significantly more genetically diverse and bear traces of older demographic expansions than less diverse benthic species that show evidence of more recent population expansions. Our findings suggest that the lifestyles of different species have strong influences on their responses to the same environmental events. Our data, in conjunction with previous studies showing a constant diversification tempo of these species during the Pleistocene, support the hypothesis that Pleistocene glaciations had a smaller effect on pelagic species than on benthic species whose survival may have relied upon ephemeral refugia in shallow shelf waters. These findings suggest that the interaction between lifestyle and environmental changes should be considered in genetic analyses. 相似文献
5.
Selene Soria Eva GallegoMaite Vidan Javier OrtizJosé Antonio Serra-Rexach 《Revista espa?ola de geriatría y gerontología》2014
Objectives
To identify predictive factors for 6 and 12-months mortality after discharge from a geriatric acute care unit, and from these, derive a mortality-risk index.Methods and analysis
Prospective cohort study will be conducted on patients over 70 years-old admitted to a geriatric acute care unit and survived to hospital discharge. The main outcome measure will be mortality at 6 months and 12 months after discharge. Independent variables include sociodemographics, functional status, comorbidities, and clinical and laboratory characteristics. Risk factors associated with mortality will be constructed using multivariate logistic regression models. To build the mortality index, points will be assigned to each risk factor by dividing each beta coefficient in the logistic model by the lowest beta coefficient. A score will be assigned to each subject by adding up the points for each risk factor present in the model. The predictive accuracy of the model will be determined by comparing the predicted versus observed mortality in the study population and calculating the area under the ROC curves in both populations.Conclusions
The risk-mortality index developed would allow an easy estimate to be made of individual risk of death at 6 months and 12 months after discharge from a geriatric acute care unit, with the purpose of establishing care plans and individualising treatment, according to real objectives. 相似文献6.
Protein exporter function and in vitro ATPase activity are correlated in ABC-domain mutants of HlyB 总被引:6,自引:1,他引:5
Eva Koronakis Colin Hughes Irina Milisav Vassilis Koronakis 《Molecular microbiology》1995,16(1):87-96
The Escherichia coli toxin exporter HlyB comprises an integral membrane domain fused to a cytoplasmic domain of the ATP-binding casette (ABC) super-family, and it directs translocation of the 110kDa haemolysin protein out of the bacterial cell without using an N-terminal secretion signal peptide. We have exploited the ability to purify the soluble HlyB ABC domain as a fusion with glutathione S-transferase to obtain a direct correlation of the in vivo export of protein by HlyB with the degree of ATP binding and hydrolysis measured in vitro. Mutations in residues that are invariant or highly conserved in the ATP-binding fold and glycine-rich linker peptide of prokaryotic and eukaryotic ABC transporters caused a complete less of both HlyB exporter function and ATPase activity in proteins still able to bind ATP effectively and undergo ATP-induced conformational change. Mutation of less-conserved residues caused reduced export and ATP hydrolysis, but not ATP binding, whereas substitutions of poorly conserved residues did not impair activity either in vivo or in vitro. The data show that protein export by HlyB has an absolute requirement for the hydrolysis of ATP bound by its cytoplasmic domain and indicate that comparable mutations that disable other prokaryotic and eukaryotic ABC transporters also cause a specific loss of enzymatic activity. 相似文献
7.
Evidence for Linkage of Bipolar Disorder to Chromosome 18 with a Parent-of-Origin Effect 总被引:16,自引:8,他引:8 下载免费PDF全文
O. Colin Stine Jianfeng Xu Rebecca Koskela Francis J. McMahon Michele Gschwend Carl Friddle Chris D. Clark Melvin G. McInnis Sylvia G. Simpson Theresa S. Breschel Eva Vishio Kelly Riskin Harriet Feilotter Eugene Chen Susan Shen Susan Folstein Deborah A. Meyers David Botstein Thomas G. Marr J. Raymond DePaulo 《American journal of human genetics》1995,57(6):1384-1394
A susceptibility gene on chromosome 18 and a parent-of-origin effect have been suggested for bipolar affective disorder (BPAD). We have studied 28 nuclear families selected for apparent unilineal transmission of the BPAD phenotype, by using 31 polymorphic markers spanning chromosome 18. Evidence for linkage was tested with affected-sib-pair and LOD score methods under two definitions of the affected phenotype. The affected-sib-pair analyses indicated excess allele sharing for markers on 18p within the region reported previously. The greatest sharing was at D18S37: 64% in bipolar and recurrent unipolar (RUP) sib pairs (P = .0006). In addition, excess sharing of the paternally, but not maternally, transmitted alleles was observed at three markers on 18q: at D18S41, 51 bipolar and RUP sib pairs were concordant for paternally transmitted alleles, and 21 pairs were discordant (P = .0004). The evidence for linkage to loci on both 18p and 18q was strongest in the 11 paternal pedigrees, i.e., those in which the father or one of the father's sibs is affected. In these pedigrees, the greatest allele sharing (81%; P = .00002) and the highest LOD score (3.51; θ = 0.0) were observed at D18S41. Our results provide further support for linkage of BPAD to chromosome 18 and the first molecular evidence for a parent-of-origin effect operating in this disorder. The number of loci involved, and their precise location, require further study. 相似文献
8.
Distinct response of Medicago suspension cultures and roots to Nod factors and chitin oligomers in the elicitation of defense-related responses 总被引:2,自引:1,他引:1
Arnould Savouré Christophe Sallaud Joumana El-Turk José Zuanazzi Pascal Ratet Michael Schultze Adam Kondorosi Robert Esnault Eva Kondorosi 《The Plant journal : for cell and molecular biology》1997,11(2):277-287
The induction of plant defense-related responses by chitin oligomers and the Rhizobium meliloti lipo-chito-oligosaccharide nodulation signals (Nod factors) in Medicago cell cultures and roots was investigated by following the expression of genes encoding enzymes of the isoflavonoid biosynthetic pathway, such as chalcone synthase, chalcone reductase, isoflavone reductase, as well as genes encoding a pathogenesis-related protein and a peroxidase. In suspension-cultured cells, all genes except the peroxidase gene were induced by both the R. meliloti Nod factor NodRm-IV(C16:2,S) and chitin oligomers with a minimum of three sugar residues. However, activation of these genes was not elicited by the symbiotically inactive, desulfated NodRm-IV(C16:2). Moreover, the cells were more sensitive to the chitin oligosaccharides than to the Nod factor. Analysis of flavonoids in Medicago microcallus cultures revealed differences between cells treated with N -acetyl-chitotetraose and those treated with Nod factor and demonstrated increased production of the phytoalexin medicarpin in the presence of Nod factor. In Medicago roots, none of the tested genes was activated by the N -acetylchitotetraose, whereas the Nod factor at micro-molar concentration enhanced transient expression of the isoflavonoid biosynthetic genes. The differential responses to Nod factors and chitin oligomers suggest that Medicago cells possess distinct perception systems for these related molecules. 相似文献
9.
The FTD‐like syndrome causing TREM2 T66M mutation impairs microglia function,brain perfusion,and glucose metabolism 下载免费PDF全文
Gernot Kleinberger Matthias Brendel Eva Mracsko Benedikt Wefers Linda Groeneweg Xianyuan Xiang Carola Focke Maximilian Deußing Marc Suárez‐Calvet Fargol Mazaheri Samira Parhizkar Nadine Pettkus Wolfgang Wurst Regina Feederle Peter Bartenstein Thomas Mueggler Thomas Arzberger Irene Knuesel Axel Rominger Christian Haass 《The EMBO journal》2017,36(13):1837-1853
Genetic variants in the triggering receptor expressed on myeloid cells 2 (TREM2) increase the risk for several neurodegenerative diseases including Alzheimer's disease and frontotemporal dementia (FTD). Homozygous TREM2 missense mutations, such as p.T66M, lead to the FTD‐like syndrome, but how they cause pathology is unknown. Using CRISPR/Cas9 genome editing, we generated a knock‐in mouse model for the disease‐associated Trem2 p.T66M mutation. Consistent with a loss‐of‐function mutation, we observe an intracellular accumulation of immature mutant Trem2 and reduced generation of soluble Trem2 similar to patients with the homozygous p.T66M mutation. Trem2 p.T66M knock‐in mice show delayed resolution of inflammation upon in vivo lipopolysaccharide stimulation and cultured macrophages display significantly reduced phagocytic activity. Immunohistochemistry together with in vivo TSPO small animal positron emission tomography (μPET) demonstrates an age‐dependent reduction in microglial activity. Surprisingly, perfusion magnetic resonance imaging and FDG‐μPET imaging reveal a significant reduction in cerebral blood flow and brain glucose metabolism. Thus, we demonstrate that a TREM2 loss‐of‐function mutation causes brain‐wide metabolic alterations pointing toward a possible function of microglia in regulating brain glucose metabolism. 相似文献
10.