全文获取类型
收费全文 | 35957篇 |
免费 | 3088篇 |
国内免费 | 22篇 |
专业分类
39067篇 |
出版年
2023年 | 112篇 |
2022年 | 319篇 |
2021年 | 593篇 |
2020年 | 361篇 |
2019年 | 476篇 |
2018年 | 596篇 |
2017年 | 528篇 |
2016年 | 932篇 |
2015年 | 1571篇 |
2014年 | 1708篇 |
2013年 | 2078篇 |
2012年 | 2816篇 |
2011年 | 2882篇 |
2010年 | 1802篇 |
2009年 | 1693篇 |
2008年 | 2377篇 |
2007年 | 2437篇 |
2006年 | 2262篇 |
2005年 | 2112篇 |
2004年 | 2097篇 |
2003年 | 1936篇 |
2002年 | 1883篇 |
2001年 | 415篇 |
2000年 | 286篇 |
1999年 | 411篇 |
1998年 | 483篇 |
1997年 | 348篇 |
1996年 | 312篇 |
1995年 | 276篇 |
1994年 | 239篇 |
1993年 | 260篇 |
1992年 | 238篇 |
1991年 | 183篇 |
1990年 | 162篇 |
1989年 | 177篇 |
1988年 | 143篇 |
1987年 | 128篇 |
1986年 | 104篇 |
1985年 | 141篇 |
1984年 | 162篇 |
1983年 | 113篇 |
1982年 | 129篇 |
1981年 | 118篇 |
1980年 | 96篇 |
1979年 | 59篇 |
1978年 | 77篇 |
1977年 | 67篇 |
1976年 | 42篇 |
1974年 | 40篇 |
1973年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
992.
John W Simmons Kevin K Chung Evan M Renz Christopher E White Casey L Cotant Molly A Tilley Mark O Hardin John A Jones Lorne H Blackbourne Steven E Wolf 《BMC anesthesiology》2010,10(1):1-7
Background
We sought to evaluate agreement between a new and widely implemented method of temperature measurement in critical care, temporal artery thermometry and an established method of core temperature measurement, bladder thermometry as performed in clinical practice.Methods
Temperatures were simultaneously recorded hourly (n = 736 observations) using both devices as part of routine clinical monitoring in 14 critically ill adult patients with temperatures ranging ≥1°C prior to consent.Results
The mean difference between temporal artery and bladder temperatures measured was -0.44°C (95% confidence interval, -0.47°C to -0.41°C), with temporal artery readings lower than bladder temperatures. Agreement between the two devices was greatest for normothermia (36.0°C to < 38.3°C) (mean difference -0.35°C [95% confidence interval, -0.37°C to -0.33°C]). The temporal artery thermometer recorded higher temperatures during hypothermia (< 36°C) (mean difference 0.66°C [95% confidence interval, 0.53°C to 0.79°C]) and lower temperatures during hyperthermia (≥38.3°C) (mean difference -0.90°C [95% confidence interval, -0.99°C to -0.81°C]). The sensitivity for detecting fever (core temperature ≥38.3°C) using the temporal artery thermometer was 0.26 (95% confidence interval, 0.20 to 0.33), and the specificity was 0.99 (95% confidence interval, 0.98 to 0.99). The positive likelihood ratio for fever was 24.6 (95% confidence interval, 10.7 to 56.8); the negative likelihood ratio was 0.75 (95% confidence interval, 0.68 to 0.82).Conclusions
Temporal artery thermometry produces somewhat surprising disagreement with an established method of core temperature measurement and should not to be used in situations where body temperature needs to be measured with accuracy. 相似文献993.
994.
Mark A. Scaife Adam M. Burja Phillip C. Wright 《Biotechnology and bioengineering》2009,103(5):944-955
Carotenoid biosynthesis is highly conserved and well characterized up to the synthesis of β‐carotene. Conversely, the synthesis of astaxanthin from β‐carotene is less well characterized. Regardless, astaxanthin is a highly sought natural product, due to its various industrial applications and elevated antioxidant capacity. In this article, 12 β‐carotene ketolase and 4 β‐carotene hydroxylase genes, isolated from 5 cyanobacterial species, are investigated for their function, and potential for microbial astaxanthin synthesis. Further, this in vivo comparison identifies and applies the most promising genetic elements within a dual expression vector, which is maintained in Escherichia coli. Here, combined overexpression of individual β‐carotene ketolase and β‐carotene hydroxylase genes, within a β‐carotene accumulating host, enables a 23.5‐fold improvement in total carotenoid yield (1.99 mg g?1), over the parental strain, with >90% astaxanthin. Biotechnol. Bioeng. 2009;103: 944–955. © 2009 Wiley Periodicals, Inc. 相似文献
995.
Esperanza Fernández Mark O Collins Rachel T Uren Maksym V Kopanitsa Noboru H Komiyama Mike D R Croning Lysimachos Zografos J Douglas Armstrong Jyoti S Choudhary Seth G N Grant 《Molecular systems biology》2009,5(1)
The molecular complexity of mammalian proteomes demands new methods for mapping the organization of multiprotein complexes. Here, we combine mouse genetics and proteomics to characterize synapse protein complexes and interaction networks. New tandem affinity purification (TAP) tags were fused to the carboxyl terminus of PSD‐95 using gene targeting in mice. Homozygous mice showed no detectable abnormalities in PSD‐95 expression, subcellular localization or synaptic electrophysiological function. Analysis of multiprotein complexes purified under native conditions by mass spectrometry defined known and new interactors: 118 proteins comprising crucial functional components of synapses, including glutamate receptors, K+ channels, scaffolding and signaling proteins, were recovered. Network clustering of protein interactions generated five connected clusters, with two clusters containing all the major ionotropic glutamate receptors and one cluster with voltage‐dependent K+ channels. Annotation of clusters with human disease associations revealed that multiple disorders map to the network, with a significant correlation of schizophrenia within the glutamate receptor clusters. This targeted TAP tagging strategy is generally applicable to mammalian proteomics and systems biology approaches to disease. 相似文献
996.
997.
Madelon Van de Kerk Stephen Arthur Mark Bertram Bridget Borg Jim Herriges James Lawler Buck Mangipane Catherine Lambert Koizumi Brad Wendling Laura Prugh 《The Journal of wildlife management》2020,84(6):1127-1138
Understanding how species respond to environmental conditions can assist with conservation strategies and harvest management, especially in arctic and boreal regions that are experiencing rapid climate change. Although climatic influences on species distributions have been studied, broad-scale effects of climate on survival are less well known. We examined the interactive effects of meteorological and remotely sensed environmental variables on survival of Dall's sheep (Ovis dalli dalli) lambs and adults by synthesizing radio-telemetry data across their range. We used data from 9 studies of adult sheep and 2 studies of lambs that were conducted between 1997 and 2012 at sites spanning the species' range in Alaska, USA, and northwestern Canada. We obtained environmental variables throughout the range of Dall's sheep, including the normalized difference vegetation index (NDVI) from optical remote sensing, freeze-thaw frequency (FTF) from passive microwave remote sensing, and gridded climate variables such as snow water equivalent, temperature, and precipitation. We used Cox proportional hazard regression to investigate the effects of environmental variables recorded during summer, winter, and the previous winter on annual survival rates of Dall's sheep lambs and adults. Summer NDVI was the most influential environmental factor affecting lamb survival, with improved lamb survival occurring in years with a high maximum NDVI. Also, lamb predation by coyotes (Canis latrans) and golden eagles (Aquila chrysaetos) decreased substantially with increasing NDVI. The previous winter FTF had the strongest effect on adult survival, with decreased survival occurring after winters with high FTF. In addition, these remotely sensed environmental factors interacted with meteorological factors to affect survival, such that effects of winter temperature depended on summer NDVI and winter FTF. Warm winters increased lamb survival only when preceded by summers with high NDVI, and warm winters increased adult survival only when winter FTF was low. Thus, potential benefits of climate warming may be counteracted if wintertime freeze-thaw events markedly increase. Correlations among environmental variables across sites were low, and regional climate cycles such as the Pacific Decadal Oscillation (PDO) had weak effects, indicating substantial local variability in climatic conditions experienced by Dall's sheep across their range. These findings can help managers anticipate how Dall's sheep populations will respond to changes in local environmental conditions. Our results also highlight the utility of multiple remotely sensed environmental conditions for ungulate management, especially passive microwave products that provide valuable information on winter icing events. © 2020 The Wildlife Society. 相似文献
998.
Wetherill LF Holmes KK Verow M Müller M Howell G Harris M Fishwick C Stonehouse N Foster R Blair GE Griffin S Macdonald A 《Journal of virology》2012,86(9):5341-5351
High-risk human papillomavirus type 16 (HPV16) is the primary causative agent of cervical cancer and therefore is responsible for significant morbidity and mortality worldwide. Cellular transformation is mediated directly by the expression of viral oncogenes, the least characterized of which, E5, subverts cellular proliferation and immune recognition processes. Despite a growing catalogue of E5-specific host interactions, little is understood regarding the molecular basis of its function. Here we describe a novel function for HPV16 E5 as an oligomeric channel-forming protein, placing it within the virus-encoded "viroporin" family. The development of a novel recombinant E5 expression system showed that E5 formed oligomeric assemblies of a defined luminal diameter and stoichiometry in membranous environments and that such channels mediated fluorescent dye release from liposomes. Hexameric E5 channel stoichiometry was suggested by native PAGE studies. In lieu of high-resolution structural information, established de novo molecular modeling and design methods permitted the development of the first specific small-molecule E5 inhibitor, capable of both abrogating channel activity in vitro and reducing E5-mediated effects on cell signaling pathways. The identification of channel activity should enhance the future understanding of the physiological function of E5 and could represent an important target for antiviral intervention. 相似文献
999.
MrBayes 3.2: efficient Bayesian phylogenetic inference and model choice across a large model space 总被引:7,自引:0,他引:7
Ronquist F Teslenko M van der Mark P Ayres DL Darling A Höhna S Larget B Liu L Suchard MA Huelsenbeck JP 《Systematic biology》2012,61(3):539-542
Since its introduction in 2001, MrBayes has grown in popularity as a software package for Bayesian phylogenetic inference using Markov chain Monte Carlo (MCMC) methods. With this note, we announce the release of version 3.2, a major upgrade to the latest official release presented in 2003. The new version provides convergence diagnostics and allows multiple analyses to be run in parallel with convergence progress monitored on the fly. The introduction of new proposals and automatic optimization of tuning parameters has improved convergence for many problems. The new version also sports significantly faster likelihood calculations through streaming single-instruction-multiple-data extensions (SSE) and support of the BEAGLE library, allowing likelihood calculations to be delegated to graphics processing units (GPUs) on compatible hardware. Speedup factors range from around 2 with SSE code to more than 50 with BEAGLE for codon problems. Checkpointing across all models allows long runs to be completed even when an analysis is prematurely terminated. New models include relaxed clocks, dating, model averaging across time-reversible substitution models, and support for hard, negative, and partial (backbone) tree constraints. Inference of species trees from gene trees is supported by full incorporation of the Bayesian estimation of species trees (BEST) algorithms. Marginal model likelihoods for Bayes factor tests can be estimated accurately across the entire model space using the stepping stone method. The new version provides more output options than previously, including samples of ancestral states, site rates, site d(N)/d(S) rations, branch rates, and node dates. A wide range of statistics on tree parameters can also be output for visualization in FigTree and compatible software. 相似文献
1000.
Schnute ME McReynolds MD Kasten T Yates M Jerome G Rains JW Hall T Chrencik J Kraus M Cronin CN Saabye M Highkin MK Broadus R Ogawa S Cukyne K Zawadzke LE Peterkin V Iyanar K Scholten JA Wendling J Fujiwara H Nemirovskiy O Wittwer AJ Nagiec MM 《The Biochemical journal》2012,444(1):79-88
SphK (sphingosine kinase) is the major source of the bioactive lipid and GPCR (G-protein-coupled receptor) agonist S1P (sphingosine 1-phosphate). S1P promotes cell growth, survival and migration, and is a key regulator of lymphocyte trafficking. Inhibition of S1P signalling has been proposed as a strategy for treatment of inflammatory diseases and cancer. In the present paper we describe the discovery and characterization of PF-543, a novel cell-permeant inhibitor of SphK1. PF-543 inhibits SphK1 with a K(i) of 3.6 nM, is sphingosine-competitive and is more than 100-fold selective for SphK1 over the SphK2 isoform. In 1483 head and neck carcinoma cells, which are characterized by high levels of SphK1 expression and an unusually high rate of S1P production, PF-543 decreased the level of endogenous S1P 10-fold with a proportional increase in the level of sphingosine. In contrast with past reports that show that the growth of many cancer cell lines is SphK1-dependent, specific inhibition of SphK1 had no effect on the proliferation and survival of 1483 cells, despite a dramatic change in the cellular S1P/sphingosine ratio. PF-543 was effective as a potent inhibitor of S1P formation in whole blood, indicating that the SphK1 isoform of sphingosine kinase is the major source of S1P in human blood. PF-543 is the most potent inhibitor of SphK1 described to date and it will be useful for dissecting specific roles of SphK1-driven S1P signalling. 相似文献