全文获取类型
收费全文 | 4865篇 |
免费 | 489篇 |
国内免费 | 650篇 |
专业分类
6004篇 |
出版年
2024年 | 41篇 |
2023年 | 203篇 |
2022年 | 221篇 |
2021年 | 377篇 |
2020年 | 294篇 |
2019年 | 366篇 |
2018年 | 257篇 |
2017年 | 233篇 |
2016年 | 211篇 |
2015年 | 236篇 |
2014年 | 336篇 |
2013年 | 398篇 |
2012年 | 227篇 |
2011年 | 278篇 |
2010年 | 232篇 |
2009年 | 297篇 |
2008年 | 317篇 |
2007年 | 260篇 |
2006年 | 207篇 |
2005年 | 161篇 |
2004年 | 155篇 |
2003年 | 107篇 |
2002年 | 92篇 |
2001年 | 76篇 |
2000年 | 39篇 |
1999年 | 46篇 |
1998年 | 63篇 |
1997年 | 40篇 |
1996年 | 29篇 |
1995年 | 33篇 |
1994年 | 33篇 |
1993年 | 24篇 |
1992年 | 22篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 14篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1969年 | 1篇 |
排序方式: 共有6004条查询结果,搜索用时 15 毫秒
61.
Hauck SM Hofmaier F Dietter J Swadzba ME Blindert M Amann B Behler J Kremmer E Ueffing M Deeg CA 《Journal of Proteomics》2012,75(14):4545-4554
Equine recurrent uveitis is a severe and frequent blinding disease in horses which presents with auto-reactive invading T-cells, resulting in the destruction of the inner eye. Infiltration of inflammatory cells into the retina and vitreous is driven by currently unknown guidance cues, however surgical removal of the vitreous (vitrectomy) has proven therapeutically successful. Therefore, proteomic analyses of vitrectomy samples are likely to result in detection of proteins contributing to disease pathogenesis. Vitreous from healthy and ERU diseased horses were directly compared by quantitative mass spectrometry based on label-free quantification of peak intensities across samples. We found a significant upregulation of complement and coagulation cascades and downregulation of negative paracrine regulators of canonical Wnt signalling including the Wnt signalling inhibitors DKK3 and SFRP2. Based on immunohistochemistry, both proteins are expressed in equine retina and suggest localisation to retinal Müller glial cells (RMG), which may be the source cells for these proteins. Furthermore, retinal expression levels and patterns of DKK3 change in response to ERU. Since many other regulated proteins identified here are associated with RMG cells, these cells qualify as the prime responders to autoimmune triggers. 相似文献
62.
George F. Wilhere 《The Journal of wildlife management》2012,76(6):1298-1309
Habitat suitability index (HSI) models rarely characterize the uncertainty associated with their estimates of habitat quality despite the fact that uncertainty can have important management implications. The purpose of this paper was to explore the use of Bayesian belief networks (BBNs) for representing and propagating 3 types of uncertainty in HSI models—uncertainty in the suitability index relationships, the parameters of the HSI equation, and measurement of habitat variables (i.e., model inputs). I constructed a BBN–HSI model, based on an existing HSI model, using Netica™ software. I parameterized the BBN's conditional probability tables via Monte Carlo methods, and developed a discretization scheme that met specifications for numerical error. I applied the model to both real and dummy sites in order to demonstrate the utility of the BBN–HSI model for 1) determining whether sites with different habitat types had statistically significant differences in HSI, and 2) making decisions based on rules that reflect different attitudes toward risk—maximum expected value, maximin, and maximax. I also examined effects of uncertainty in the habitat variables on the model's output. Some sites with different habitat types had different values for E[HSI], the expected value of HSI, but habitat suitability was not significantly different based on the overlap of 90% confidence intervals for E[HSI]. The different decision rules resulted in different rankings of sites, and hence, different decisions based on risk. As measurement uncertainty in habitat variables increased, sites with significantly different (α = 0.1) E[HSI] became statistically more similar. Incorporating uncertainty in HSI models enables explicit consideration of risk and more robust habitat management decisions. © 2012 The Wildlife Society. 相似文献
63.
胃癌(gastric cancer,GC)是我国最常见的恶性肿瘤之一,严重危害人类健康。胃癌发病机制复杂,缺乏特异性预后生物标志物。长链非编码RNA (long non-coding RNA,lncRNA)可作为竞争性内源RNA (competing endogenous RNA,ceRNA),影响microRNA (miRNA)与mRNA的结合,从而影响胃癌的发生、发展。基于TCGA和GEO数据库的转录组数据,筛选GC 中差异表达的 lncRNAs,并构建基于 6 条 lncRNAs(HAGLROS、TMEM92-AS1、LINC01745、HOXC-AS3、SEMA3B-AS1、FEZF1-AS 1)的lncRNA-miRNA-mRNA网络。网络核心基因的KEGG/GO富集和蛋白质互作分析结果显示,lncRNA可能通过miRNA海绵吸附作用,调控胃癌的发生、发展与转移。AC011352.1、AC087636.1、AC093627.1、GAS1RR与胃癌患者的预后相关性具有统计学意义(P<0.05),并可能成为胃癌患者潜在的预后生物标志物。 相似文献
64.
65.
Francesca Spyrakis Fátima Lucas Axel Bidon-Chanal Cristiano Viappiani Victor Guallar F. Javier Luque 《Biochimica et Biophysica Acta - Proteins and Proteomics》2013,1834(9):1957-1967
This study reports a comparative analysis of the topological properties of inner cavities and the intrinsic dynamics of non-symbiotic hemoglobins AHb1 and AHb2 from Arabidopsis thaliana. The two proteins belong to the 3/3 globin fold and have a sequence identity of about 60%. However, it is widely assumed that they have distinct physiological roles. In order to investigate the structure–function relationships in these proteins, we have examined the bis-histidyl and ligand-bound hexacoordinated states by atomistic simulations using in silico structural models. The results allow us to identify two main pathways to the distal cavity in the bis-histidyl hexacoordinated proteins. Nevertheless, a larger accessibility to small gaseous molecules is found in AHb2. This effect can be attributed to three factors: the mutation Leu35(AHb1) → Phe32(AHb2), the enhanced flexibility of helix B, and the more favorable energetic profile for ligand migration to the distal cavity. The net effect of these factors would be to facilitate the access of ligands, thus compensating the preference for the fully hexacoordination of AHb2, in contrast to the equilibrium between hexa- and pentacoordinated species in AHb1. On the other hand, binding of the exogenous ligand introduces distinct structural changes in the two proteins. A well-defined tunnel is formed in AHb1, which might be relevant to accomplish the proposed NO detoxification reaction. In contrast, no similar tunnel is found in AHb2, which can be ascribed to the reduced flexibility of helix E imposed by the larger number of salt bridges compared to AHb1. This feature would thus support the storage and transport functions proposed for AHb2. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins. 相似文献
66.
Functional traits, rather than taxonomic identity, determine the fitness of individuals in their environment: traits of marine organisms are therefore expected to vary across the global ocean as a function of the environment. Here, we quantify such spatial and seasonal variations based on extensive empirical data and present the first global biogeography of key traits (body size, feeding mode, relative offspring size and myelination) for pelagic copepods, the major group of marine zooplankton. We identify strong patterns with latitude, season and between ocean basins that are partially (c. 50%) explained by key environmental drivers. Body size, for example decreases with temperature, confirming the temperature‐size rule, but surprisingly also with productivity, possibly driven by food‐chain length and size‐selective predation. Patterns unrelated to environmental predictors may originate from phylogenetic clustering. Our maps can be used as a test‐bed for trait‐based mechanistic models and to inspire next‐generation biogeochemical models. 相似文献
67.
Limited influence of local and landscape factors on finescale gene flow in two pond‐breeding amphibians 下载免费PDF全文
Stephanie S. Coster Kimberly J. Babbitt Andrew Cooper Adrienne I. Kovach 《Molecular ecology》2015,24(4):742-758
Dispersal and gene flow within animal populations are influenced by the composition and configuration of the landscape. In this study, we evaluated hypotheses about the impact of natural and anthropogenic factors on genetic differentiation in two amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Lithobates sylvaticus) in a commercial forest in central Maine. We conducted this analysis at two scales: a local level, focused on factors measured at each breeding pond, and a landscape level, focused on factors measured between ponds. We investigated the effects of a number of environmental factors in six categories including Productivity, Physical, Land Composition, Land Configuration, Isolation and Location. Embryos were sampled from 56 spotted salamander breeding ponds and 39 wood frog breeding ponds. We used a hierarchical Bayesian approach in the program GESTE at each breeding pond and a random forest algorithm in conjunction with a network analysis between the ponds. We found overall high genetic connectivity across distances up to 17 km for both species and a limited effect of natural and anthropogenic factors on gene flow. We found the null models best explained patterns of genetic differentiation at a local level and found several factors at the landscape level that weakly influenced gene flow. This research indicates multiscale investigations that incorporate local and landscape factors are valuable for understanding patterns of gene flow. Our findings suggest that dispersal rates in this system are high enough to minimize genetic structuring and that current forestry practices do not significantly impede dispersal. 相似文献
68.
Micaela Santos Luciano Cagnolo Tomas Roslin Emmanuel F. Ruperto María Laura Bernaschini Diego P. Vázquez 《Oikos》2021,130(1):133-142
Studying how habitat loss affects the tolerance of ecological networks to species extinction (i.e. their robustness) is key for our understanding of the influence of human activities on natural ecosystems. With networks typically occurring as local interaction networks interconnected in space (a meta-network), we may ask how the loss of specific habitat fragments affects the overall robustness of the meta-network. To address this question, for an empirical meta-network of plants, herbivores and natural enemies we simulated the removal of habitat fragments in increasing and decreasing order of area, age and connectivity for plant extinction and the secondary extinction of herbivores, natural enemies and their interactions. Meta-network robustness was characterized as the area under the curve of remnant species or interactions at the end of a fragment removal sequence. To pinpoint the effects of fragment area, age and connectivity, respectively, we compared the observed robustness for each removal scenario against that of a random sequence. The meta-network was more robust to the loss of old (i.e. long-fragmented), large, connected fragments than of young (i.e. recently fragmented), small, isolated fragments. Thus, young, small, isolated fragments may be particularly important to the conservation of species and interactions, while contrary to our expectations larger, more connected fragments contribute little to meta-network robustness. Our findings highlight the importance of young, small, isolated fragments as sources of species and interactions unique to the regional level. These effects may largely result from an unpaid extinction debt, whereby younger fragments are likely to lose species over time. Yet, there may also be more long-lasting effects from cultivated lands (e.g. water, fertilizers and restricted cattle grazing) and network complexity in small, isolated fragments. Such fragments may sustain important biological diversity in fragmented landscapes, but maintaining their conservation value may depend on adequate restoration strategies. 相似文献
69.
70.
Ozaki TJ Sato N Kitajo K Someya Y Anami K Mizuhara H Ogawa S Yamaguchi Y 《Cognitive neurodynamics》2012,6(2):185-198
An ambiguous figure such as the Necker cube causes spontaneous perceptual switching (SPS). The mechanism of SPS in multistable
perception has not yet been determined. Although early psychological studies suggested that SPS may be caused by fatigue or
satiation of orientation, the neural mechanism of SPS is still unknown. Functional magnetic resonance imaging (fMRI) has shown
that the dorsal attention network (DAN), which mainly controls voluntary attention, is involved in bistable perception of
the Necker cube. To determine whether neural dynamics along the DAN cause SPS, we performed simultaneous electroencephalography
(EEG) and fMRI during an SPS task with the Necker cube, with every SPS reported by pressing a button. This EEG–fMRI integrated
analysis showed that (a) 3–4 Hz spectral EEG power modulation at fronto-central, parietal, and centro-parietal electrode sites
sequentially appeared from 750 to 350 ms prior to the button press; and (b) activations correlating with the EEG modulation
traveled along the DAN from the frontal to the parietal regions. These findings suggest that slow oscillation initiates SPS
through global dynamics along the attentional system such as the DAN. 相似文献