全文获取类型
收费全文 | 4392篇 |
免费 | 287篇 |
出版年
2023年 | 28篇 |
2022年 | 64篇 |
2021年 | 127篇 |
2020年 | 66篇 |
2019年 | 95篇 |
2018年 | 118篇 |
2017年 | 112篇 |
2016年 | 152篇 |
2015年 | 261篇 |
2014年 | 268篇 |
2013年 | 334篇 |
2012年 | 390篇 |
2011年 | 373篇 |
2010年 | 243篇 |
2009年 | 205篇 |
2008年 | 276篇 |
2007年 | 271篇 |
2006年 | 227篇 |
2005年 | 201篇 |
2004年 | 186篇 |
2003年 | 182篇 |
2002年 | 156篇 |
2001年 | 46篇 |
2000年 | 29篇 |
1999年 | 23篇 |
1998年 | 33篇 |
1997年 | 27篇 |
1996年 | 23篇 |
1995年 | 7篇 |
1994年 | 17篇 |
1993年 | 10篇 |
1992年 | 15篇 |
1991年 | 7篇 |
1990年 | 15篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1971年 | 4篇 |
1966年 | 3篇 |
排序方式: 共有4679条查询结果,搜索用时 281 毫秒
941.
Evolution of morphological integration in the skull of Carnivora (Mammalia): Changes in Canidae lead to increased evolutionary potential of facial traits 下载免费PDF全文
Fabio Andrade Machado Thiago Macek Gonçalves Zahn Gabriel Marroig 《Evolution; international journal of organic evolution》2018,72(7):1399-1419
Morphological integration refers to the fact that different phenotypic traits of organisms are not fully independent from each other, and tend to covary to different degrees. The covariation among traits is thought to reflect properties of the species' genetic architecture and thus can have an impact on evolutionary responses. Furthermore, if morphological integration changes along the history of a group, inferences of past selection regimes might be problematic. Here, we evaluated the stability and evolution of the morphological integration of skull traits in Carnivora by using evolutionary simulations and phylogenetic comparative methods. Our results show that carnivoran species are able to respond to natural selection in a very similar way. Our comparative analyses show that the phylogenetic signal for pattern of integration is lower than that observed for morphology (trait averages), and that integration was stable throughout the evolution of the group. That notwithstanding, Canidae differed from other families by having higher integration, evolvability, flexibility, and allometric coefficients on the facial region. These changes might have allowed canids to rapidly adapt to different food sources, helping to explain not only the phenotypic diversification of the family, but also why humans were able to generate such a great diversity of dog breeds through artificial selection. 相似文献
942.
943.
Antonella Tramutola Nidhi Sharma Eugenio Barone Chiara Lanzillotta Andrea Castellani Federica Iavarone Federica Vincenzoni Massimo Castagnola D. Allan Butterfield Silvana Gaetani Tommaso Cassano Marzia Perluigi Fabio Di Domenico 《生物化学与生物物理学报:疾病的分子基础》2018,1864(10):3309-3321
PET scan analysis demonstrated the early reduction of cerebral glucose metabolism in Alzheimer disease (AD) patients that can make neurons vulnerable to damage via the alteration of the hexosamine biosynthetic pathway (HBP). Defective HBP leads to flawed protein O-GlcNAcylation coupled, by a mutual inverse relationship, with increased protein phosphorylation on Ser/Thr residues. Altered O-GlcNAcylation of Tau and APP have been reported in AD and is closely related with pathology onset and progression. In addition, type 2 diabetes patients show an altered O-GlcNAcylation/phosphorylation that might represent a link between metabolic defects and AD progression. Our study aimed to decipher the specific protein targets of altered O-GlcNAcylation in brain of 12-month-old 3×Tg-AD mice compared with age-matched non-Tg mice. Hence, we analysed the global O-GlcNAc levels, the levels and activity of OGT and OGA, the enzymes controlling its cycling and protein specific O-GlcNAc levels using a bi-dimensional electrophoresis (2DE) approach. Our data demonstrate the alteration of OGT and OGA activation coupled with the decrease of total O-GlcNAcylation levels. Data from proteomics analysis led to the identification of several proteins with reduced O-GlcNAcylation levels, which belong to key pathways involved in the progression of AD such as neuronal structure, protein degradation and glucose metabolism. In parallel, we analysed the O-GlcNAcylation/phosphorylation ratio of IRS1 and AKT, whose alterations may contribute to insulin resistance and reduced glucose uptake. Our findings may contribute to better understand the role of altered protein O-GlcNAcylation profile in AD, by possibly identifying novel mechanisms of disease progression related to glucose hypometabolism. 相似文献
944.
Joost Willebrords Michaël Maes Isabel Veloso Alves Pereira Tereza Cristina da Silva Veronica Mollica Govoni Valéria Veras Lopes Sara Crespo Yanguas Valery I. Shestopalov Marina Sayuri Nogueira Inar Alves de Castro Anwar Farhood Inge Mannaerts Leo van Grunsven Jephte Akakpo Margitta Lebofsky Hartmut Jaeschke Bruno Cogliati Mathieu Vinken 《生物化学与生物物理学报:疾病的分子基础》2018,1864(3):819-830
945.
Federica Pierucci Alessia Frati Chiara Battistini Francesca Matteini Maria Chiara Iachini Ambra Vestri Fabio Penna Paola Costelli Elisabetta Meacci 《生物化学与生物物理学报:疾病的分子基础》2018,1864(12):3598-3614
Skeletal muscle (SkM) atrophy is caused by several and heterogeneous conditions, such as cancer, neuromuscular disorders and aging. In most types of SkM atrophy overall rates of protein synthesis are suppressed, protein degradation is consistently elevated and atrogenes, such as the ubiquitin ligase Atrogin-1/MAFbx, are up-regulated. The molecular regulators of SkM waste are multiple and only in part known.Sphingolipids represent a class of bioactive molecules capable of modulating the destiny of many cell types, including SkM cells. In particular, we and others have shown that sphingosine 1phosphate (S1P), formed by sphingosine kinase (SphK), is able to act as trophic and morphogenic factor in myoblasts.Here, we report the first evidence that the atrophic phenotype observed in both muscle obtained from mice bearing the C26 adenocarcinoma and C2C12 myotubes treated with dexamethasone was characterized by reduced levels of active phospho-SphK1. The importance of SphK1 activity is also confirmed by the specific pharmacological inhibition of SphK1 able to increase Atrogin-1/MAFbx expression and reduce myotube size and myonuclei number. Furthermore, we found that SkM atrophy was accomplished by significant increase of S1P transporter Spns2 and in changes in the pattern of S1P receptor (S1PRs) subtype expression paralleled by increased Atrogin-1/MAFbx expression, suggesting a role for the released S1P and of specific S1PR-mediated signaling pathways in the control of the ubiquitin ligase. Altogether, these findings provide the first evidence that SphK1/released S1P/S1PR axis acts as a molecular regulator of SkM atrophy, thereby representing a new possible target for therapy in many patho-physiological conditions. 相似文献
946.
Do cryptic species matter in macroecology? Sequencing European groundwater crustaceans yields smaller ranges but does not challenge biodiversity determinants 下载免费PDF全文
David Eme Maja Zagmajster Teo Delić Cene Fišer Jean‐François Flot Lara Konecny‐Dupré Snæbjörn Pálsson Fabio Stoch Valerija Zakšek Christophe J. Douady Florian Malard 《Ecography》2018,41(2):424-436
Ecologists increasingly rely on molecular delimitation methods (MMs) to identify species boundaries, thereby potentially increasing the number of putative species because of the presence of morphologically cryptic species. It has been argued that cryptic species could challenge our understanding of what determine large‐scale biodiversity patterns which have traditionally been documented from morphology alone. Here, we used morphology and three MMs to derive four different sets of putative species among the European groundwater crustaceans. Then, we used regression models to compare the relative importance of spatial heterogeneity, productivity and historical climates, in shaping species richness and range size patterns across sets of putative species. We tested three predictions. First, MMs would yield many more putative species than morphology because groundwater is a constraining environment allowing little morphological changes. Second, for species richness, MMs would increase the importance of spatial heterogeneity because cryptic species are more likely along physical barriers separating ecologically similar regions than along resource gradients promoting ecologically‐based divergent selection. Third, for range size, MMs would increase the importance of historical climates because of reduced and asymmetrical fragmentation of large morphological species ranges at northern latitudes. MMs yielded twice more putative species than morphology and decreased by 10‐fold the average species range size. Yet, MMs strengthened the mid‐latitude ridge of high species richness and the Rapoport effect of increasing range size at higher latitudes. Species richness predictors did not vary between morphology and MMs but the latter increased the proportion of variance in range size explained by historical climates. These findings demonstrate that our knowledge of groundwater biodiversity determinants is robust to overlooked cryptic species because the latter are homogeneously distributed along environmental gradients. Yet, our findings call for incorporating multiple species delimitation methods into the analysis of large‐scale biodiversity patterns across a range of taxa and ecosystems. 相似文献
947.
Rodrigo R. Domingues Alexandre W. S. Hilsdorf Mahmood M. Shivji Fabio V. H. Hazin Otto B. F. Gadig 《Reviews in Fish Biology and Fisheries》2018,28(1):213-227
The silky shark, Carcharhinus falciformis, is a large-bodied, oceanic-coastal, epipelagic species found worldwide in tropical and subtropical waters. Despite its commercial importance, concerns about overexploitation, and likely ecological significance of this shark as an upper trophic-level predator, understanding of its population dynamics remains unclear for large parts of its distribution. We investigated the genetic diversity, population structure and demographic history of the silky shark along the western Atlantic Ocean based on the use of 707 bp of the mitochondrial DNA control region (mtCR). A total of 211 silky sharks were sampled, originating from five areas along the western Atlantic Ocean. The mitochondrial sequences revealed 40 haplotypes, with overall haplotype and nucleotide diversities of 0.88 (± 0.012) and 0.005 (± 0.003), respectively. The overall population structure was significantly different among the five western Atlantic Ocean regions. Phylogenetic analysis of mtCR sequences from globally sourced silky shark samples revealed two lineages, comprising a western Atlantic lineage and western Atlantic—Indo-Pacific lineage that diverged during the Pleistocene Epoch. In general, tests for the demographic history of silky sharks supported a population expansion for both the global sample set and the two lineages. Although our results showed that silky sharks have high genetic diversity, the current high level of overexploitation of this species requires long-term, scientifically informed management efforts. We recommend that fishery management and conservation plans be done separately for the two western Atlantic matrilineal populations revealed here. 相似文献
948.
949.
Dilva?TerzanoEmail author Ian?Kotzé Christo?Marais Silvio?Cianciullo Alessio?Farcomeni Paolo?Caroli Luca?Malatesta Fabio?AttorreView authors OrcID profile 《Plant Ecology》2018,219(3):277-297
Alien plants invasion has negative impacts on the structure and functionality of ecosystems. Understanding the determinants of this process is fundamental for addressing environmental issues, such as the water availability in South Africa’s catchments. Both environmental and anthropogenic factors determine the invasion of alien species; however, their relative importance has to be quantified. The aim of this paper was to estimate the importance of 32 explanatory variables in predicting the distribution of the major invasive alien plant species (IAPS) of South Africa, through the use of Species Distribution Models. We used data from the National Invasive Alien Plants Survey, delineated at a quaternary catchment level, coupled with climatic, land cover, edaphic, and anthropogenic variables. Using two-part generalized linear models, we compared the accuracy of two different sets of variables in predicting the spatial distribution of IAPS; the first included environmental correlates alone, and the second included both environmental and anthropogenic variables. Using Random Forest, we explored the relative importance of the variables in producing a map of potential distribution of IAPS. Results showed that the inclusion of anthropogenic variables did not significantly improve model predictions. The most important variables influencing the distribution of IAPS appeared to be the climatic ones. The modeled potential distribution was analyzed in relation to provinces, biomes, and species’ minimum residence time. 相似文献
950.
Eleonora Mauri Robertino Dilena Antonio Boccazzi Dario Ronchi Daniela Piga Fabio Triulzi Delia Gagliardi Roberta Brusa Irene Faravelli Nereo Bresolin Francesca Magri Stefania Corti Giacomo P. Comi 《BMC neurology》2018,18(1):220