全文获取类型
收费全文 | 6851篇 |
免费 | 700篇 |
国内免费 | 911篇 |
出版年
2024年 | 46篇 |
2023年 | 192篇 |
2022年 | 372篇 |
2021年 | 516篇 |
2020年 | 397篇 |
2019年 | 442篇 |
2018年 | 391篇 |
2017年 | 258篇 |
2016年 | 326篇 |
2015年 | 497篇 |
2014年 | 525篇 |
2013年 | 547篇 |
2012年 | 626篇 |
2011年 | 561篇 |
2010年 | 344篇 |
2009年 | 292篇 |
2008年 | 351篇 |
2007年 | 272篇 |
2006年 | 248篇 |
2005年 | 181篇 |
2004年 | 186篇 |
2003年 | 158篇 |
2002年 | 145篇 |
2001年 | 101篇 |
2000年 | 84篇 |
1999年 | 86篇 |
1998年 | 46篇 |
1997年 | 42篇 |
1996年 | 27篇 |
1995年 | 21篇 |
1994年 | 20篇 |
1993年 | 20篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 10篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1969年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有8462条查询结果,搜索用时 31 毫秒
991.
The key gluconeogenic gene PCK1 is crucial for virulence of Botrytis cinerea via initiating its conidial germination and host penetration 下载免费PDF全文
Jian‐Kang Liu Hao‐Wu Chang Yue Liu Yu Qin Yu‐Han Ding Lan Wang Yue Zhao Ming‐Zhe Zhang Sheng‐Nan Cao Le‐Tao Li Wei Liu Gui‐Hua Li Qing‐Ming Qin 《Environmental microbiology》2018,20(5):1794-1814
The process of initiation of host invasion and survival of some foliar phytopathogenic fungi in the absence of external nutrients on host leaf surfaces remains obscure. Here, we demonstrate that gluconeogenesis plays an important role in the process and nutrient‐starvation adaptation before the pathogen host invasion. Deletion of phosphoenolpyruvate c arboxyk inase gene BcPCK1 in gluconeogenesis in Botrytis cinerea, the causative agent of grey mould, resulted in the failure of the ΔBcpck1 mutant conidia to germinate on hard and hydrophobic surface and penetrate host cells in the absence of glucose, reduction in conidiation and slow conidium germination in a nutrient‐rich medium. The wild‐type and ΔBcpck1 conidia germinate similarly in the presence of glucose (higher concentration) as the sole carbon source. Conidial glucose‐content should reach a threshold level to initiate germination and host penetration. Infection structure formation by the mutants displayed a glucose‐dependent fashion, which corresponded to the mutant virulence reduction. Exogenous glucose or complementation of BcPCK1 completely rescued all the developmental and virulence defects of the mutants. Our findings demonstrate that BcPCK1 plays a crucial role in B. cinerea pathogenic growth and virulence, and provide new insights into gluconeogenesis mediating pathogenesis of plant fungal pathogens via initiation of conidial germination and host penetration. 相似文献
992.
Ya Gong Zheng Zhang Ya Liu Xiu‐Wen Zhou Mian Nabeel Anwar Ze‐Shuo Li Wei Hu Yue‐Zhong Li 《Environmental microbiology》2018,20(7):2552-2567
The use of toxin to attack neighbours and immunity proteins to protect against toxin has been observed in bacterial conflicts, including kin discrimination. Here, we report a novel nuclease‐toxin and its immunity protein function in the colony‐merger incompatibility, a kind of bacterial kin discrimination, in Myxococcus xanthus DK1622. The MXAN_0049 gene was determined to be a genetic determinant for colony‐merger incompatibility, and the incompatibility could be eliminated by deletion of the upstream co‐transcribed MXAN_0050 gene. We demonstrated that the MXAN_0050 protein was a nuclease, and MXAN_0049 protein was able to bind to MXAN_0050 to block nuclease activity in vitro. Expression of MXAN_0050 in Escherichia coli inhibited cellular growth, and the inhibition effect could be recovered by co‐expression of MXAN_0049. We found that deletion of the PAAR‐encoding gene (MXAN_0044) or the type VI secretion system led to the colony‐merger and co‐existence with the ΔMXAN_0049 mutant, suggesting that they were associated with colony‐merger incompatibility. Homologues of the nuclease‐toxin and cognate immunity pair are widely distributed in bacteria. We propose a simplified model to explain the kin discrimination mechanism mediated by the nuclease‐toxin and immunity protein.© 2018 Society for Applied Microbiology and John Wiley & Sons Ltd 相似文献
993.
994.
995.
Hua Gao Mai Yang Haitao Yang Yue Qin Biyun Zhu Gang Xu Chengyuan Xie Dewei Wu Xiaolin Zhang Wanxiang Li Jianbin Yan Susheng Song Tiancong Qi Shou-Wei Ding Daoxin Xie 《遗传学报》2018,45(1):33-40
Viruses can infect host plants to cause severe diseases and substantial agricultural loss, while plants have evolved RNA interference (RNAi) strategy to defend against viral infection. Despite enormous efforts, only a few host proteins in RNAi pathway were shown to mediate antiviral defense, including RNA-dependent RNA polymerase 1 (RDR1), RDR6, DICER-LIKE 2 (DCL2) and DCL4. In this study, we carried out a genetic screen for antiviral factors of RNAi pathway in Arabidopsis rdr6 background via inoculation with a 2b-deficient Cucumber Mosaic Virus (CMV-Δ2b). We identified a mutant susceptible to CMV-Δ2b, referred to as enhancer of rdr6 (enor) 3-1 rdr6, and found that ENOR3 encodes a functionally unknown protein with high homology to the mammalian Non Imprinted in Prader-Willi/Angelman (NIPA) magnesium transporters. ENOR3 inhibits accumulation of CMV-Δ2b and acts additively with RDR1, RDR6, DCL2 and DCL4 in antiviral defense. These results uncover that ENOR3 is a key component in antiviral RNAi pathway, and provide new insights into antiviral immunity. 相似文献
996.
Mounting evidence has indicated that engaging in extrapair copulations (EPCs) might be maladaptive or detrimental to females. It is unclear why such nonadaptive female behavior evolves. In this study, we test two hypotheses about the evolution of female EPC behavior using population genetic models. First, we find that both male preference for allocating extra effort to seek EPCs and female pursuit behavior without costs can be maintained and remain polymorphic in a population via frequency‐dependent selection. However, both behaviors cannot evolve when females with pursuit behavior suffer from a decline in male parental care. Second, we present another novel way in which female pursuit behavior can evolve; indirect selection can act on this behavior through a ratchet‐like mechanism involving oscillating linkage disequilibria between the target EPC pursuit locus and two other loci determining male mate choice and a female sexual signal. Although the overall positive force of such indirect selection is relatively weak, our results suggest that it may still play a role in promoting the evolution of female EPC behavior when this behavior is nonadaptive (i.e., it is neutral) or only somewhat maladaptive (e.g., males only occasionally lower parental care when their mates pursue EPCs). 相似文献
997.
Tiffany M. Heaster Alex J. Walsh Yue Zhao Scott W. Hiebert Melissa C. Skala 《Journal of biophotonics》2018,11(1)
The goal of this study is to validate fluorescence intensity and lifetime imaging of metabolic co‐enzymes NAD(P)H and FAD (optical metabolic imaging, or OMI) as a method to quantify cell‐cycle status of tumor cells. Heterogeneity in tumor cell‐cycle status (e. g. proliferation, quiescence, apoptosis) increases drug resistance and tumor recurrence. Cell‐cycle status is closely linked to cellular metabolism. Thus, this study applies cell‐level metabolic imaging to distinguish proliferating, quiescent, and apoptotic populations. Two‐photon microscopy and time‐correlated single photon counting are used to measure optical redox ratio (NAD(P)H fluorescence intensity divided by FAD intensity), NAD(P)H and FAD fluorescence lifetime parameters. Redox ratio, NAD(P)H and FAD lifetime parameters alone exhibit significant differences (p<0.05) between population means. To improve separation between populations, linear combination models derived from partial least squares ‐ discriminant analysis (PLS‐DA) are used to exploit all measurements together. Leave‐one‐out cross validation of the model yielded high classification accuracies (92.4 and 90.1 % for two and three populations, respectively). OMI and PLS‐DA also identifies each sub‐population within heterogeneous samples. These results establish single‐cell analysis with OMI and PLS‐DA as a label‐free method to distinguish cell‐cycle status within intact samples. This approach could be used to incorporate cell‐level tumor heterogeneity in cancer drug development.
998.
In some clinical development programs, there are potential biomarkers with promising but uncertain predictive effect, while the probability of success in the overall population cannot be readily dismissed. It is risky to focus only on the overall population, or just the biomarker subpopulation. In 2009, Chen and Beckman proposed a Bayesian decision framework to optimize the type I error rate (alpha) allocation in a Phase III clinical study with possible predictive subset effect. The utilization of internal data in this framework is of particular interest because it provides an opportunity to mitigate the potential risk of misspecified study assumptions using an auto-adaptive strategy. In this paper, we examine this auto-adaptive strategy in detail through extensive numerical case studies and provide guidance on the appropriate use of partial current trial (internal) data in this data-driven optimization framework. We show that internal data can be used to inform the alpha allocation to hypothesis testing in the overall population and the subgroup. The resulting adaptive testing strategy is robust with respect to the uncertainty in the predictive subgroup effect and biomarker prevalence. 相似文献
999.
1000.
Aor Pranchai Michael Jenke Juliane Vogt Uwe Grueters Lin Yue Ulf Mehlig Moirah Machado de Menezes Sven Wagner Uta Berger 《Wetlands Ecology and Management》2018,26(2):139-150
The global effort to rehabilitate and restore destroyed mangrove forests is unable to keep up with the high mangrove deforestation rates, which exceed the average pace of global deforestation. Although facilitation theory presents new possibilities for the restoration of heavily degraded mangrove sites, knowledge of tree–tree interactions in stressed mangrove forest ecosystems is too limited to utilize facilitation appropriately. The aim was to determine the mode of local interaction among stressed mangrove trees by investigating the effect of clustering on tree size and crown morphology under contrasting stand densities. The study was conducted in a dwarf Avicennia germinans forest in Northern Brazil, in which tree growth is limited by infrequent inundation and high pore-water salinity. Autoregressive regression, Voronoi tessellation and spatial point pattern statistics were used to address the spatial processes underlying tree interaction. Under low stand density (1.2 trees m?2) dwarf trees which grew in clustered cohorts of A. germinans had a less stunted crown morphology revealing the dominance of a positive neighborhood influence among plants. In contrast, dwarf trees in the denser forest stand (2.7 trees m?2) were interacting competitively as indicated by the more negative effect of neighbors on crown morphology and size. The shift from facilitative to competitive interactions is an important feature of mangrove forest regeneration under harsh environmental conditions. If mangrove trees are unable to regenerate naturally on severely degraded sites, intraspecific facilitation could be used to assist regeneration by planting seedlings in clusters and not evenly spaced. 相似文献