全文获取类型
收费全文 | 3942篇 |
免费 | 289篇 |
国内免费 | 1篇 |
出版年
2022年 | 36篇 |
2021年 | 74篇 |
2020年 | 69篇 |
2019年 | 66篇 |
2018年 | 55篇 |
2017年 | 64篇 |
2016年 | 104篇 |
2015年 | 163篇 |
2014年 | 196篇 |
2013年 | 240篇 |
2012年 | 310篇 |
2011年 | 298篇 |
2010年 | 172篇 |
2009年 | 134篇 |
2008年 | 252篇 |
2007年 | 197篇 |
2006年 | 199篇 |
2005年 | 188篇 |
2004年 | 178篇 |
2003年 | 152篇 |
2002年 | 124篇 |
2001年 | 62篇 |
2000年 | 61篇 |
1999年 | 61篇 |
1998年 | 43篇 |
1997年 | 30篇 |
1996年 | 25篇 |
1995年 | 36篇 |
1994年 | 36篇 |
1993年 | 33篇 |
1992年 | 27篇 |
1991年 | 38篇 |
1990年 | 40篇 |
1989年 | 23篇 |
1988年 | 37篇 |
1987年 | 21篇 |
1986年 | 26篇 |
1985年 | 19篇 |
1984年 | 19篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1979年 | 19篇 |
1978年 | 19篇 |
1976年 | 20篇 |
1974年 | 14篇 |
1973年 | 23篇 |
1971年 | 17篇 |
1970年 | 18篇 |
1969年 | 12篇 |
1968年 | 22篇 |
排序方式: 共有4232条查询结果,搜索用时 203 毫秒
941.
Erika F. Neave Harvey Seim Scott M. Gifford Olivia Torano Zackary I. Johnson Diego Páez-Rosas Adrian Marchetti 《Environmental microbiology》2022,24(4):1746-1759
The Galápagos Archipelago lies within the Eastern Equatorial Pacific Ocean at the convergence of major ocean currents that are subject to changes in circulation. The nutrient-rich Equatorial Undercurrent upwells from the west onto the Galápagos platform, stimulating primary production, but this source of deep water weakens during El Niño events. Based on measurements from repeat cruises, the 2015/16 El Niño was associated with declines in phytoplankton biomass at most sites throughout the archipelago and reduced utilization of nitrate, particularly in large-sized phytoplankton in the western region. Protistan assemblages were identified by sequencing the V4 region of the 18S rRNA gene. Dinoflagellates, chlorophytes and diatoms dominated most sites. Shifts in dinoflagellate communities were most apparent between the years; parasitic dinoflagellates, Syndiniales, were highly detected during the El Niño (2015) while the dinoflagellate genus, Gyrodinium, increased at many sites during the neutral period (2016). Variations in protistan communities were most strongly correlated with changes in subthermocline water density. These findings indicate that marine protistan communities in this region are regimented by deep water mass sources and thus could be profoundly affected by altered ocean circulation. 相似文献
942.
943.
Erika Friedmann Elizabeth Galik Sue A. Thomas Sue Hall Jooyoung Cheon Narae Han 《Anthrozo?s》2019,32(2):221-238
ABSTRACTIn recent research involving assisted-living residents with mild to moderate cognitive impairment, a structured 12-week Pet Assisted Living (PAL) intervention led to improved physical activity (PA) and mood. Receipt of intervention is important to the efficacy of behavioral interventions. We assessed the behavioral interactions (BIs: looking at, talking to, touching, giving treats to, brushing, and walking the dog) of residents during PAL intervention sessions and evaluated their relationships to changes in PA and mood. Residents with mild to moderate cognitive impairment in seven small assisted-living facilities were randomized by facility to the 12-week PAL or reminiscing interventions. Outcomes included PA and mood. PA was assessed monthly with 24-hour actigraph and Barthel Index, and mood was assessed with the Cornell Scale for Depression in Dementia. Residents of four facilities (n = 22) received the PAL intervention which included bi-weekly activities designed to encourage maintenance or improvement of PA and mood. During each PAL session, participants’ engagement in each BI was noted. Engagement in BIs varied between residents and over sessions. BIs were not correlated with degree of cognitive impairment. In linear mixed models, the more participants walked the dog the more their PA changed, and the more participants looked at the dog the more their moods changed (ps < 0.05). Participants varied in their engagement in BIs. Two specific BIs were related to improvements in PA and mood. Finer assessment of BIs during animal-assisted interventions may enable understanding of their relationships to specific outcomes. 相似文献
944.
945.
946.
Ntale M Mahindi M Ogwal-Okeng JW Gustafsson LL Beck O 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2007,859(1):137-140
A reversed-phase high performance liquid chromatographic method was developed and validated for the quantitative determination of amodiaquine (AQ) and its metabolite desethylamodiaquine (DAQ) in whole blood collected on filter paper. The structure analogue 4-(4-dimethylamino-1-methylbutylamino)-7-chloroquinoline was used as internal standard. Upon collection, blood was added to 10% phosphoric acid in a 1:1 ratio and then spotted onto filter paper. The samples were alkalinized (pH approximately 9.2) with potassium hydroxide at the time of assay and the compounds were extracted together with internal standard into di-isopropyl ether and then re-extracted into an aqueous phase with 0.1M phosphate buffer at pH 4. The chromatographic analysis was performed using an Agilent Technologies ChemStation LC System. The absorbance of the compounds was monitored at 333 nm. Mean extraction recoveries of AQ and DAQ were 49 and 48%, respectively. Intra-day and inter-day coefficients of variation were <10.5%. The limit of quantification was 50 nM for both compounds (sample size 100 microl). Both AQ and DAQ that were previously reported to be unstable have been stored on filter paper for at least 19 weeks. The method was applied on samples from healthy volunteers. 相似文献
947.
Caesar R Palmfeldt J Gustafsson JS Pettersson E Hashemi SH Blomberg A 《Proteomics》2007,7(22):4135-4147
The proteomes of three industrial lager beer strains, CMBS33, OG2252 and A15, were analysed under standardised laboratory growth conditions. Protein spots in the 2-DE pattern of the lager strains were subjected to MS/MS to identify protein variants. We found the protein composition of the three lager strains to be qualitatively rather similar, while being substantially different from the Saccharomyces cerevisiae strain BY4742. Database searches using several fully sequenced genomes from the Saccharomyces genera indicated that the non-cerevisiae proteins in the 2-D pattern of lager strains were most closely related to S. bayanus. For many proteins the regulation of the bayanus-like protein and its cerevisiae counterpart varied in a strain-dependent manner, e.g. the bayanus-like form of Tdh3p was roughly eight-fold more abundant than the cerevisiae form in the OG2252 strain. We also found differential regulation of cerevisiae- and bayanus-like proteins during various stress conditions like low temperature growth, and adaptation to high temperatures or high salinity, e.g. for Arg1p, Sti1p and Pdc1p. Our data on the differential regulation of the two genomes in these hybrid strains may have important industrial implications for strain improvement and strain protection. 相似文献
948.
Tamm E Kivisild T Reidla M Metspalu M Smith DG Mulligan CJ Bravi CM Rickards O Martinez-Labarga C Khusnutdinova EK Fedorova SA Golubenko MV Stepanov VA Gubina MA Zhadanov SI Ossipova LP Damba L Voevoda MI Dipierri JE Villems R Malhi RS 《PloS one》2007,2(9):e829
Native Americans derive from a small number of Asian founders who likely arrived to the Americas via Beringia. However, additional details about the initial colonization of the Americas remain unclear. To investigate the pioneering phase in the Americas we analyzed a total of 623 complete mtDNAs from the Americas and Asia, including 20 new complete mtDNAs from the Americas and seven from Asia. This sequence data was used to direct high-resolution genotyping from 20 American and 26 Asian populations. Here we describe more genetic diversity within the founder population than was previously reported. The newly resolved phylogenetic structure suggests that ancestors of Native Americans paused when they reached Beringia, during which time New World founder lineages differentiated from their Asian sister-clades. This pause in movement was followed by a swift migration southward that distributed the founder types all the way to South America. The data also suggest more recent bi-directional gene flow between Siberia and the North American Arctic. 相似文献
949.
This paper focuses on Confucian formulations of personhood and the implications they may have for bioethics and medical practice.
We discuss how an appreciation of the Confucian concept of personhood can provide insights into the practice of informed consent
and, in particular, the role of family members and physicians in medical decision-making in societies influenced by Confucian
culture. We suggest that Western notions of informed consent appear ethically misguided when viewed from a Confucian perspective. 相似文献
950.
Tauber T Berta B Székely AJ Gyarmati I Kékesi K Márialigeti K Tóth EM 《Acta microbiologica et immunologica Hungarica》2007,54(1):47-55
The aim of the present work was to compare the microbial communities of a mesophilic and a thermophilic pilot scale anaerobe sludge digester. For studying the communities cultivation independent chemotaxonomical methods (RQ and PLFA analyses) and T-RFLP were applied. Microbial communities of the mesophilic and thermophilic pilot digesters showed considerable differences, both concerning the species present, and their abundance. A Methanosarcina sp. dominated the thermophilic, while a Methanosaeta sp. the mesophilic digester among Archaea. Species diversity of Bacteria was reduced in the thermophilic digester. Based on the quinone patterns in both digesters the dominance of sulphate reducing respiratory bacteria could be detected. The PLFA profiles of the digester communities were similar though in minor components characteristic differences were shown. Level of branched chain fatty acids is slightly lower in the thermophilic digester that reports less Gram positive bacteria. The relative ratio of fatty acids characteristic to Enterobacteriaceae, Bacteroidetes and Clostridia shows differences between the two digesters: their importance generally decreased under thermophilic conditions. The sulphate reducer marker (15:1 and 17:1) fatty acids are present in low quantity in both digesters. 相似文献