全文获取类型
收费全文 | 1522篇 |
免费 | 127篇 |
国内免费 | 2篇 |
专业分类
1651篇 |
出版年
2023年 | 6篇 |
2022年 | 22篇 |
2021年 | 50篇 |
2020年 | 16篇 |
2019年 | 34篇 |
2018年 | 33篇 |
2017年 | 25篇 |
2016年 | 50篇 |
2015年 | 83篇 |
2014年 | 91篇 |
2013年 | 100篇 |
2012年 | 142篇 |
2011年 | 118篇 |
2010年 | 94篇 |
2009年 | 76篇 |
2008年 | 100篇 |
2007年 | 95篇 |
2006年 | 76篇 |
2005年 | 64篇 |
2004年 | 61篇 |
2003年 | 51篇 |
2002年 | 66篇 |
2001年 | 14篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 20篇 |
1997年 | 13篇 |
1996年 | 5篇 |
1995年 | 13篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1984年 | 5篇 |
1981年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1971年 | 4篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1965年 | 2篇 |
1964年 | 4篇 |
1957年 | 2篇 |
排序方式: 共有1651条查询结果,搜索用时 0 毫秒
31.
James E. Polston Carolyn E. Pritchett Jonathan M. Tomasko Ann M. Rogers Lorenzo Leggio Panayotis K. Thanos Nora D. Volkow Andras Hajnal 《PloS one》2013,8(12)
Roux-en-Y gastric bypass surgery (RYGB) is an effective treatment for severe obesity. Clinical studies however have reported susceptibility to increased alcohol use after RYGB, and preclinical studies have shown increased alcohol intake in obese rats after RYGB. This could reflect a direct enhancement of alcohol’s rewarding effects in the brain or an indirect effect due to increased alcohol absorption after RGYB. To rule out the contribution that changes in alcohol absorption have on its rewarding effects, here we assessed the effects of RYGB on intravenously (IV) administered ethanol (1%). For this purpose, high fat (60% kcal from fat) diet-induced obese male Sprague Dawley rats were tested ∼2 months after RYGB or sham surgery (SHAM) using both fixed and progressive ratio schedules of reinforcement to evaluate if RGYB modified the reinforcing effects of IV ethanol. Compared to SHAM, RYGB rats made significantly more active spout responses to earn IV ethanol during the fixed ratio schedule, and achieved higher breakpoints during the progressive ratio schedule. Although additional studies are needed, our results provide preliminary evidence that RYGB increases the rewarding effects of alcohol independent of its effects on alcohol absorption. 相似文献
32.
33.
Richard R. Stein Vanni Bucci Nora C. Toussaint Charlie G. Buffie Gunnar R?tsch Eric G. Pamer Chris Sander Jo?o B. Xavier 《PLoS computational biology》2013,9(12)
The intestinal microbiota is a microbial ecosystem of crucial importance to human health. Understanding how the microbiota confers resistance against enteric pathogens and how antibiotics disrupt that resistance is key to the prevention and cure of intestinal infections. We present a novel method to infer microbial community ecology directly from time-resolved metagenomics. This method extends generalized Lotka–Volterra dynamics to account for external perturbations. Data from recent experiments on antibiotic-mediated Clostridium difficile infection is analyzed to quantify microbial interactions, commensal-pathogen interactions, and the effect of the antibiotic on the community. Stability analysis reveals that the microbiota is intrinsically stable, explaining how antibiotic perturbations and C. difficile inoculation can produce catastrophic shifts that persist even after removal of the perturbations. Importantly, the analysis suggests a subnetwork of bacterial groups implicated in protection against C. difficile. Due to its generality, our method can be applied to any high-resolution ecological time-series data to infer community structure and response to external stimuli. 相似文献
34.
Wendy Blay Puryear Hisashi Akiyama Suzanne D. Geer Nora P. Ramirez Xinwei Yu Bj?rn M. Reinhard Suryaram Gummuluru 《PLoS pathogens》2013,9(4)
Human immunodeficiency virus type 1 (HIV-1) interactions with myeloid dendritic cells (DCs) can result in virus dissemination to CD4+ T cells via a trans infection pathway dependent on virion incorporation of the host cell derived glycosphingolipid (GSL), GM3. The mechanism of DC-mediated trans infection is extremely efficacious and can result in infection of multiple CD4+ T cells as these cells make exploratory contacts on the DC surface. While it has long been appreciated that activation of DCs with ligands that induce type I IFN signaling pathway dramatically enhances DC-mediated T cell trans infection, the mechanism by which this occurs has remained unclear until now. Here, we demonstrate that the type I IFN-inducible Siglec-1, CD169, is the DC receptor that captures HIV in a GM3-dependent manner. Selective downregulation of CD169 expression, neutralizing CD169 function, or depletion of GSLs from virions, abrogated DC-mediated HIV-1 capture and trans infection, while exogenous expression of CD169 in receptor-naïve cells rescued GSL-dependent capture and trans infection. HIV-1 particles co-localized with CD169 on DC surface immediately following capture and subsequently within non-lysosomal compartments that redistributed to the DC – T cell infectious synapses upon initiation of T cell contact. Together, these findings describe a novel mechanism of pathogen parasitization of host encoded cellular recognition machinery (GM3 – CD169 interaction) for DC-dependent HIV dissemination. 相似文献
35.
Mobbing, where birds harass a predator through a combination of vocalizations and stereotyped behaviours, is an effective anti-predator behaviour for many species. Mobbing may be particularly important for juveniles, as these individuals are often more vulnerable than adults. Although the component behaviours of mobbing are often considered to be un-learned, there are few confirmatory data, and the developmental trajectory of mobbing is unknown. In this study, we tested whether conspecific or heterospecific mobbing calls initiated mobbing behaviour in juvenile Blue Tits Cyanistes caeruleus. We located wild adult and recently fledged juvenile Blue Tits and presented them with playback recordings of adult conspecific (Blue Tit) and heterospecific (Great Tit Parus major) mobbing alarm calls. Although adult birds readily mob in response to these types of playbacks, juveniles did not exhibit characteristic mobbing behaviour. Some juveniles did, however, exhibit individual components of mobbing behaviour found in mobbing, despite not producing adult-like mobbing behaviour in response to either conspecific or heterospecific playback. These results suggest that, although birds might be capable of mobbing as juveniles, the associations between the non-vocal stereotyped mobbing behaviours and mobbing calls may be learned. 相似文献
36.
Ziguo Zhang Leifu ChangJing Yang Nora ConinKiran Kulkarni David Barford 《Journal of molecular biology》2013
The anaphase-promoting complex or cyclosome (APC/C) is a large E3 RING-cullin ubiquitin ligase composed of between 14 and 15 individual proteins. A striking feature of the APC/C is that only four proteins are involved in directly recognizing target proteins and catalyzing the assembly of a polyubiquitin chain. All other subunits, which account for > 80% of the mass of the APC/C, provide scaffolding functions. A major proportion of these scaffolding subunits are structurally related. In metazoans, there are four canonical tetratricopeptide repeat (TPR) proteins that form homo-dimers (Apc3/Cdc27, Apc6/Cdc16, Apc7 and Apc8/Cdc23). Here, we describe the crystal structure of the N-terminal homo-dimerization domain of Schizosaccharomyces pombe Cdc23 (Cdc23Nterm). Cdc23Nterm is composed of seven contiguous TPR motifs that self-associate through a related mechanism to those of Cdc16 and Cdc27. Using the Cdc23Nterm structure, we generated a model of full-length Cdc23. The resultant “V”-shaped molecule docks into the Cdc23-assigned density of the human APC/C structure determined using negative stain electron microscopy (EM). Based on sequence conservation, we propose that Apc7 forms a homo-dimeric structure equivalent to those of Cdc16, Cdc23 and Cdc27. The model is consistent with the Apc7-assigned density of the human APC/C EM structure. The four canonical homo-dimeric TPR proteins of human APC/C stack in parallel on one side of the complex. Remarkably, the uniform relative packing of neighboring TPR proteins generates a novel left-handed suprahelical TPR assembly. This finding has implications for understanding the assembly of other TPR-containing multimeric complexes. 相似文献
37.
38.
Nora Hoppe 《Zoology in the Middle East.》2013,59(1):29-32
Summary Weights and standard measurements are given of 568 individuals of 52 bird species ringed in various localities in Turkey in July and August 1973. The Melodious Warbler, Hippolais polyglotta, was recorded in Turkey for the first time. 相似文献
39.
40.
Julie Chaumeil Mariann Micsinai Panagiotis Ntziachristos Ludovic Deriano Joy M.-H. Wang Yanhong Ji Elphege P. Nora Matthew J. Rodesch Jeffrey A. Jeddeloh Iannis Aifantis Yuval Kluger David G. Schatz Jane A. Skok 《Cell reports》2013,3(2):359-370
- Download : Download full-size image