全文获取类型
收费全文 | 6882篇 |
免费 | 663篇 |
国内免费 | 3篇 |
专业分类
7548篇 |
出版年
2023年 | 44篇 |
2022年 | 122篇 |
2021年 | 234篇 |
2020年 | 97篇 |
2019年 | 136篇 |
2018年 | 152篇 |
2017年 | 112篇 |
2016年 | 227篇 |
2015年 | 395篇 |
2014年 | 360篇 |
2013年 | 436篇 |
2012年 | 611篇 |
2011年 | 542篇 |
2010年 | 350篇 |
2009年 | 261篇 |
2008年 | 390篇 |
2007年 | 396篇 |
2006年 | 345篇 |
2005年 | 313篇 |
2004年 | 324篇 |
2003年 | 269篇 |
2002年 | 251篇 |
2001年 | 79篇 |
2000年 | 60篇 |
1999年 | 71篇 |
1998年 | 73篇 |
1997年 | 41篇 |
1996年 | 43篇 |
1995年 | 35篇 |
1994年 | 43篇 |
1993年 | 41篇 |
1992年 | 32篇 |
1991年 | 36篇 |
1990年 | 34篇 |
1989年 | 30篇 |
1988年 | 24篇 |
1987年 | 27篇 |
1986年 | 23篇 |
1985年 | 30篇 |
1984年 | 38篇 |
1983年 | 23篇 |
1982年 | 29篇 |
1980年 | 21篇 |
1979年 | 25篇 |
1978年 | 29篇 |
1977年 | 32篇 |
1976年 | 25篇 |
1975年 | 22篇 |
1974年 | 23篇 |
1973年 | 20篇 |
排序方式: 共有7548条查询结果,搜索用时 15 毫秒
41.
An obligately anaerobic bacterium, Eubacterium lentum, was shown to contain cytochromes a, b, and c and a carbon monoxide-binding pigment. Extracts of cells grown with hemin gave a typical absorption spectrum for cytochrome c with maxima at 424, 525, and 553 nm. Extracts from cells grown in the absence of hemin also had an absorption peak corresponding to cytochrome b (562 nm) in their reduced versus oxidized spectrum. Extraction of hemes and formation of pyridine hemochromes allowed quantitation of protoheme IX and heme c. Large amounts of cytochrome c masked the presence of cytochrome b in cells grown in medium containing hemin. When cells were grown in the presence of 50 mM nitrate, cytochrome A (606 nm) was detected. In anaerobic extracts of cells grown either with or without nitrate, cytochromes b and c were reduced by formate and oxidized by NO3. Cytochrome a appeared to be partially oxidized by NO3 and completely oxidized by air. 相似文献
42.
Quercetin 3-O-(6″-O-galloyl)-β-d-glucoside has been identified as a constituent of Tellima grandiflora (Saxifragaceae). In all, twelve gallates were encountered: two isomeric gallates of quercetin 3-O-glucoside and two of quercetin 3-O-galactoside, a similar set involving kaempferol, and a similar set involving myricetin. 相似文献
43.
Nicola Pirastu Ciara McDonnell Eryk J. Grzeszkowiak Ninon Mounier Fumiaki Imamura Jordi Merino Felix R. Day Jie Zheng Nele Taba Maria Pina Concas Linda Repetto Katherine A. Kentistou Antonietta Robino Tnu Esko Peter K. Joshi Krista Fischer Ken K. Ong Tom R. Gaunt Zoltn Kutalik John R. B. Perry James F. Wilson 《PLoS genetics》2022,18(6)
Diet is considered as one of the most important modifiable factors influencing human health, but efforts to identify foods or dietary patterns associated with health outcomes often suffer from biases, confounding, and reverse causation. Applying Mendelian randomization in this context may provide evidence to strengthen causality in nutrition research. To this end, we first identified 283 genetic markers associated with dietary intake in 445,779 UK Biobank participants. We then converted these associations into direct genetic effects on food exposures by adjusting them for effects mediated via other traits. The SNPs which did not show evidence of mediation were then used for MR, assessing the association between genetically predicted food choices and other risk factors, health outcomes. We show that using all associated SNPs without omitting those which show evidence of mediation, leads to biases in downstream analyses (genetic correlations, causal inference), similar to those present in observational studies. However, MR analyses using SNPs which have only a direct effect on the exposure on food exposures provided unequivocal evidence of causal associations between specific eating patterns and obesity, blood lipid status, and several other risk factors and health outcomes. 相似文献
44.
Minh Son Phan Katherine Matho Emmanuel Beaurepaire Jean Livet Anatole Chessel 《PLoS computational biology》2022,18(7)
Tridimensional microscopy and algorithms for automated segmentation and tracing are revolutionizing neuroscience through the generation of growing libraries of neuron reconstructions. Innovative computational methods are needed to analyze these neuronal traces. In particular, means to characterize the geometric properties of traced neurites along their trajectory have been lacking. Here, we propose a local tridimensional (3D) scale metric derived from differential geometry, measuring for each point of a curve the characteristic length where it is fully 3D as opposed to being embedded in a 2D plane or 1D line. The larger this metric is and the more complex the local 3D loops and turns of the curve are. Available through the GeNePy3D open-source Python quantitative geometry library (https://genepy3d.gitlab.io), this approach termed nAdder offers new means of describing and comparing axonal and dendritic arbors. We validate this metric on simulated and real traces. By reanalysing a published zebrafish larva whole brain dataset, we show its ability to characterize different population of commissural axons, distinguish afferent connections to a target region and differentiate portions of axons and dendrites according to their behavior, shedding new light on the stereotypical nature of neurites’ local geometry. 相似文献
45.
Katherine M. Littlefield Rene O. Watson Jennifer M. Schneider Charles P. Neff Eiko Yamada Min Zhang Thomas B. Campbell Michael T. Falta Sarah E. Jolley Andrew P. Fontenot Brent E. Palmer 《PLoS pathogens》2022,18(5)
As of January 2022, at least 60 million individuals are estimated to develop post-acute sequelae of SARS-CoV-2 (PASC) after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While elevated levels of SARS-CoV-2-specific T cells have been observed in non-specific PASC, little is known about their impact on pulmonary function which is compromised in the majority of these individuals. This study compares frequencies of SARS-CoV-2-specific T cells and inflammatory markers with lung function in participants with pulmonary PASC and resolved COVID-19 (RC). Compared to RC, participants with respiratory PASC had between 6- and 105-fold higher frequencies of IFN-γ- and TNF-α-producing SARS-CoV-2-specific CD4+ and CD8+ T cells in peripheral blood, and elevated levels of plasma CRP and IL-6. Importantly, in PASC participants the frequency of TNF-α-producing SARS-CoV-2-specific CD4+ and CD8+ T cells, which exhibited the highest levels of Ki67 indicating they were activity dividing, correlated positively with plasma IL-6 and negatively with measures of lung function, including forced expiratory volume in one second (FEV1), while increased frequencies of IFN-γ-producing SARS-CoV-2-specific T cells associated with prolonged dyspnea. Statistical analyses stratified by age, number of comorbidities and hospitalization status demonstrated that none of these factors affect differences in the frequency of SARS-CoV-2 T cells and plasma IL-6 levels measured between PASC and RC cohorts. Taken together, these findings demonstrate elevated frequencies of SARS-CoV-2-specific T cells in individuals with pulmonary PASC are associated with increased systemic inflammation and decreased lung function, suggesting that SARS-CoV-2-specific T cells contribute to lingering pulmonary symptoms. These findings also provide mechanistic insight on the pathophysiology of PASC that can inform development of potential treatments to reduce symptom burden. 相似文献
46.
Alexander J McIntyre Charlotte Z Angel James S Smith Amy Templeman Katherine Beattie Shannon Beattie Alice Ormrod Eadaoin Devlin Charles McGreevy Chloe Bothwell Sharon
L Eddie Niamh
E Buckley Rich Williams Paul
B Mullan 《Nucleic acids research》2022,50(11):6154
Chromosome 17q23 amplification occurs in 20% of primary breast tumours and is associated with poor outcome. The TBX2 gene is located on 17q23 and is often over-expressed in this breast tumour subset. TBX2 is an anti-senescence gene, promoting cell growth and survival through repression of Tumour Suppressor Genes (TSGs), such as NDRG1 and CST6. Previously we found that TBX2 cooperates with the PRC2 complex to repress several TSGs, and that PRC2 inhibition restored NDRG1 expression to impede cellular proliferation. Here, we now identify CoREST proteins, LSD1 and ZNF217, as novel interactors of TBX2. Genetic or pharmacological targeting of CoREST emulated TBX2 loss, inducing NDRG1 expression and abolishing breast cancer growth in vitro and in vivo. Furthermore, we uncover that TBX2/CoREST targeting of NDRG1 is achieved by recruitment of TBX2 to the NDRG1 promoter by Sp1, the abolishment of which resulted in NDRG1 upregulation and diminished cancer cell proliferation. Through ChIP-seq we reveal that 30% of TBX2-bound promoters are shared with ZNF217 and identify novel targets repressed by TBX2/CoREST; of these targets a lncRNA, LINC00111, behaves as a negative regulator of cell proliferation. Overall, these data indicate that inhibition of CoREST proteins represents a promising therapeutic intervention for TBX2-addicted breast tumours. 相似文献
47.
Ruofan Wang Camille R. Simoneau Jessie Kulsuptrakul Mehdi Bouhaddou Katherine A. Travisano Jennifer M. Hayashi Jared Carlson-Stevermer James R. Zengel Christopher M. Richards Parinaz Fozouni Jennifer Oki Lauren Rodriguez Bastian Joehnk Keith Walcott Kevin Holden Anita Sil Jan E. Carette Nevan J. Krogan Andreas S. Puschnik 《Cell》2021,184(1):106-119.e14
48.
Istem Fer Anthony K. Gardella Alexey N. Shiklomanov Eleanor E. Campbell Elizabeth M. Cowdery Martin G. De Kauwe Ankur Desai Matthew J. Duveneck Joshua B. Fisher Katherine D. Haynes Forrest M. Hoffman Miriam R. Johnston Rob Kooper David S. LeBauer Joshua Mantooth William J. Parton Benjamin Poulter Tristan Quaife Ann Raiho Kevin Schaefer Shawn P. Serbin James Simkins Kevin R. Wilcox Toni Viskari Michael C. Dietze 《Global Change Biology》2021,27(1):13-26
In an era of rapid global change, our ability to understand and predict Earth's natural systems is lagging behind our ability to monitor and measure changes in the biosphere. Bottlenecks to informing models with observations have reduced our capacity to fully exploit the growing volume and variety of available data. Here, we take a critical look at the information infrastructure that connects ecosystem modeling and measurement efforts, and propose a roadmap to community cyberinfrastructure development that can reduce the divisions between empirical research and modeling and accelerate the pace of discovery. A new era of data‐model integration requires investment in accessible, scalable, and transparent tools that integrate the expertise of the whole community, including both modelers and empiricists. This roadmap focuses on five key opportunities for community tools: the underlying foundations of community cyberinfrastructure; data ingest; calibration of models to data; model‐data benchmarking; and data assimilation and ecological forecasting. This community‐driven approach is a key to meeting the pressing needs of science and society in the 21st century. 相似文献
49.
Pessani NK Atiyeh HK Wilkins MR Bellmer DD Banat IM 《Bioresource technology》2011,102(22):10618-10624
Switchgrass (Panicum virgatum) was subjected to hydrothermolysis pretreatment and then used to study the effect of enzyme loading and temperature in a simultaneous saccharification and fermentation (SSF) with the thermotolerant yeast strain Kluyveromyces marxianus IMB3 at 8% solid loading. Various loadings of Accellerase 1500 between 0.1 and 1.1 mL g(-1) glucan were tested in SSF at 45 °C (activity of enzyme was 82.2 FPU mL(-1)). The optimum enzyme loading was 0.7 mL g(-1) glucan based on the six different enzyme loadings tested. SSFs were performed at 37, 41 and 45 °C with an enzyme loading of 0.7 mL g(-1) glucan. The highest ethanol concentration of 22.5 g L(-1) was obtained after 168 h with SSF at 45 °C, which was equivalent to 86% yield. Four different batch and fed-batch strategies were evaluated using a total solid loading of 12% (dry basis). About 32 g L(-1) ethanol was produced with the four strategies, which was equivalent to 82% yield. 相似文献
50.
SNP frequency, haplotype structure and linkage disequilibrium in elite maize inbred lines 总被引:3,自引:0,他引:3
Ada Ching Katherine S Caldwell Mark Jung Maurine Dolan Oscar S Smith Scott Tingey Michele Morgante Antoni J Rafalski 《BMC genetics》2002,3(1):19-14