全文获取类型
收费全文 | 1952篇 |
免费 | 150篇 |
出版年
2023年 | 7篇 |
2022年 | 9篇 |
2021年 | 34篇 |
2020年 | 17篇 |
2019年 | 23篇 |
2018年 | 40篇 |
2017年 | 27篇 |
2016年 | 63篇 |
2015年 | 82篇 |
2014年 | 99篇 |
2013年 | 114篇 |
2012年 | 154篇 |
2011年 | 128篇 |
2010年 | 85篇 |
2009年 | 81篇 |
2008年 | 119篇 |
2007年 | 118篇 |
2006年 | 126篇 |
2005年 | 98篇 |
2004年 | 98篇 |
2003年 | 109篇 |
2002年 | 88篇 |
2001年 | 10篇 |
2000年 | 16篇 |
1999年 | 28篇 |
1998年 | 25篇 |
1997年 | 25篇 |
1996年 | 20篇 |
1995年 | 13篇 |
1994年 | 17篇 |
1993年 | 10篇 |
1992年 | 9篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 12篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 15篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 10篇 |
1974年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有2102条查询结果,搜索用时 15 毫秒
121.
Takahashi N Yamada W Masuda K Araki H Tsukamoto Y Galinha A Sautès C Kato K Shimada I 《Glycoconjugate journal》1998,15(9):905-914
N-glycans of a recombinant mouse soluble Fc receptor II (sFcRII) expressed in baby hamster kidney cells were released from glycopeptides by digestion with glycoamidase A (from sweet almond), and the reducing ends of the oligosaccharides were reductively aminated with 2-aminopyridine. The derivatized N-glycans were separated and structurally identified by a three-dimensional high-performance liquid chromatography (HPLC) mapping technique on three kinds of HPLC columns [Takahashi, et al. (1995) Anal. Biochem. 226: 139–46]. Eighteen different major N-glycan structures were identified, of which six were neutral (45%), five mono-sialyl (49%), one di-sialyl (4.6%), five tri-sialyl (1.1%), and one tetra-sialyl (0.3%). All N-glycan structures determined were complex type with fucosylation at the N-acetylglucosamine residue of the reducing end, and N-acetylneuraminic acid, when present, was -(2,3)-linked. The existence of a unique structure containing both N-acetylgalactosamine and -(2,3)-N-acetylneuraminic acid residues at the reducing ends, as below, was confirmed by MALDI-TOF mass spectrometry. 相似文献
122.
The impact of length-variable data and alignment criterion on the phylogeny of Decapodiformes (Mollusca: Cephalopoda) 总被引:1,自引:0,他引:1
Annie R. Lindgren Marymegan Daly 《Cladistics : the international journal of the Willi Hennig Society》2007,23(5):464-476
In molecular phylogenetics, mode of analysis is typically the primary reason cited for obtaining different topologies. However, sequence alignment is as important in determining topology as analytical method or optimality criterion, particularly for length-variable sequences. We investigate the effect of alignment strategy and parameters in an analysis of length-variable 18S rDNA sequences from 41 oceanic squids (Decapodiformes), focusing particularly on the impact of including variable regions on the resulting topology. Decapodiformes are an enigmatic group of molluscs whose evolutionary relationships remain unclear because standard molecular analyses have continued to produce poorly supported or poorly resolved trees, possibly due to elevated levels of molecular evolution. We find that alignment strategy (Clustal X versus POY) has a greater affect on topology than does parameter choice. Some groups were robust to shifts in methodology, including cuttlefishes (Sepiidae), bobtail squids (Sepiolidae) and pygmy squids (Idiosepiidae). No alignment strategy supported the monophyly of Oegopsida, although Myopsida did consistently form a monophyletic group. The variable regions consistently provided more well-supported and well-resolved trees than the conserved regions alone, indicating the phylogenetic importance of including length-variable data. © The Willi Hennig Society 2007. 相似文献
123.
Rajmohan Rajamuthiah Beth Burgwyn Fuchs Annie L. Conery Wooseong Kim Elamparithi Jayamani Bumsup Kwon Frederick M. Ausubel Eleftherios Mylonakis 《PloS one》2015,10(4)
Staphylococcus aureus is a Gram-positive bacterium that has become the leading cause of hospital acquired infections in the US. Repurposing Food and Drug Administration (FDA) approved drugs for antimicrobial therapy involves lower risks and costs compared to de novo development of novel antimicrobial agents. In this study, we examined the antimicrobial properties of two commercially available anthelmintic drugs. The FDA approved drug niclosamide and the veterinary drug oxyclozanide displayed strong in vivo and in vitro activity against methicillin resistant S. aureus (minimum inhibitory concentration (MIC): 0.125 and 0.5 μg/ml respectively; minimum effective concentration: ≤ 0.78 μg/ml for both drugs). The two drugs were also effective against another Gram-positive bacteria Enterococcus faecium (MIC 0.25 and 2 μg/ml respectively), but not against the Gram-negative species Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter aerogenes. The in vitro antimicrobial activity of niclosamide and oxyclozanide were determined against methicillin, vancomycin, linezolid or daptomycin resistant S. aureus clinical isolates, with MICs at 0.0625-0.5 and 0.125-2 μg/ml for niclosamide and oxyclozanide respectively. A time-kill study demonstrated that niclosamide is bacteriostatic, whereas oxyclozanide is bactericidal. Interestingly, oxyclozanide permeabilized the bacterial membrane but neither of the anthelmintic drugs exhibited demonstrable toxicity to sheep erythrocytes. Oxyclozanide was non-toxic to HepG2 human liver carcinoma cells within the range of its in vitro MICs but niclosamide displayed toxicity even at low concentrations. These data show that the salicylanilide anthelmintic drugs niclosamide and oxyclozanide are suitable candidates for mechanism of action studies and further clinical evaluation for treatment of staphylococcal infections. 相似文献
124.
Planting Sentinel European Trees in Eastern Asia as a Novel Method to Identify Potential Insect Pest Invaders 总被引:2,自引:0,他引:2
Alain Roques Jian-ting Fan Béatrice Courtial Yan-zhuo Zhang Annie Yart Marie-Anne Auger-Rozenberg Olivier Denux Marc Kenis Richard Baker Jiang-hua Sun 《PloS one》2015,10(5)
Quarantine measures to prevent insect invasions tend to focus on well-known pests but a large proportion of the recent invaders were not known to cause significant damage in their native range, or were not even known to science before their introduction. A novel method is proposed to detect new potential pests of woody plants in their region of origin before they are introduced to a new continent. Since Asia is currently considered to be the main supplier of insect invaders to Europe, sentinel trees were planted in China during 2007-2011 as an early warning tool to identify the potential for additional Asian insect species to colonize European trees. Seedlings (1-1.5 m tall) of five broadleaved (Quercus petraea, Q. suber, Q. ilex, Fagus sylvatica, and Carpinus betulus) and two conifer species (Abies alba and Cupressus sempervirens) were planted in blocks of 100 seedlings at two widely separated sites (one in a nursery near Beijing and the other in a forest environment near Fuyang in eastern China), and then regularly surveyed for colonization by insects. A total of 104 insect species, mostly defoliators, were observed on these new hosts, and at least six species were capable of larval development. Although a number of the insects observed were probably incidental feeders, 38 species had more than five colonization events, mostly infesting Q. petraea, and could be considered as being capable of switching to European trees if introduced to Europe. Three years was shown to be an appropriate duration for the experiment, since the rate of colonization then tended to plateau. A majority of the identified species appeared to have switched from agricultural crops and fruit trees rather than from forest trees. Although these results are promising, the method is not appropriate for xylophagous pests and other groups developing on larger trees. Apart from the logistical problems, the identification to species level of the specimens collected was a major difficulty. This situation could be improved by the development of molecular databases. 相似文献
125.
Jia-Yee S. Yap Thore Rohner Abigail Greenfield Marlien Van Der Merwe Hannah McPherson Wendy Glenn Geoff Kornfeld Elessa Marendy Annie Y. H. Pan Alan Wilton Marc R. Wilkins Maurizio Rossetto Sven K. Delaney 《PloS one》2015,10(6)
The Wollemi pine (Wollemia nobilis) is a rare Southern conifer with striking morphological similarity to fossil pines. A small population of W. nobilis was discovered in 1994 in a remote canyon system in the Wollemi National Park (near Sydney, Australia). This population contains fewer than 100 individuals and is critically endangered. Previous genetic studies of the Wollemi pine have investigated its evolutionary relationship with other pines in the family Araucariaceae, and have suggested that the Wollemi pine genome contains little or no variation. However, these studies were performed prior to the widespread use of genome sequencing, and their conclusions were based on a limited fraction of the Wollemi pine genome. In this study, we address this problem by determining the entire sequence of the W. nobilis chloroplast genome. A detailed analysis of the structure of the genome is presented, and the evolution of the genome is inferred by comparison with the chloroplast sequences of other members of the Araucariaceae and the related family Podocarpaceae. Pairwise alignments of whole genome sequences, and the presence of unique pseudogenes, gene duplications and insertions in W. nobilis and Araucariaceae, indicate that the W. nobilis chloroplast genome is most similar to that of its sister taxon Agathis. However, the W. nobilis genome contains an unusually high number of repetitive sequences, and these could be used in future studies to investigate and conserve any remnant genetic diversity in the Wollemi pine. 相似文献
126.
Victoria I. Siarkou Fabien Vorimore Nadia Vicari Simone Magnino Annie Rodolakis Yvonne Pannekoek Konrad Sachse David Longbottom Karine Laroucau 《PloS one》2015,10(5)
Chlamydia abortus, an obligate intracellular bacterium, is the most common infectious cause of abortion in small ruminants worldwide and has zoonotic potential. We applied multilocus sequence typing (MLST) together with multiple-locus variable-number tandem repeat analysis (MLVA) to genotype 94 ruminant C. abortus strains, field isolates and samples collected from 1950 to 2011 in diverse geographic locations, with the aim of delineating C. abortus lineages and clones. MLST revealed the previously identified sequence types (STs) ST19, ST25, ST29 and ST30, plus ST86, a recently-assigned type on the Chlamydiales MLST website and ST87, a novel type harbouring the hemN_21 allele, whereas MLVA recognized seven types (MT1 to MT7). Minimum-spanning-tree analysis suggested that all STs but one (ST30) belonged to a single clonal complex, possibly reflecting the short evolutionary timescale over which the predicted ancestor (ST19) has diversified into three single-locus variants (ST86, ST87 and ST29) and further, through ST86 diversification, into one double-locus variant (ST25). ST descendants have probably arisen through a point mutation evolution mode. Interestingly, MLVA showed that in the ST19 population there was a greater genetic diversity than in other STs, most of which exhibited the same MT over time and geographical distribution. However, the evolutionary pathways of C. abortus STs seem to be diverse across geographic distances with individual STs restricted to particular geographic locations. The ST30 singleton clone displaying geographic specificity and represented by the Greek strains LLG and POS was effectively distinguished from the clonal complex lineage, supporting the notion that possibly two separate host adaptations and hence independent bottlenecks of C. abortus have occurred through time. The combination of MLST and MLVA assays provides an additional level of C. abortus discrimination and may prove useful for the investigation and surveillance of emergent C. abortus clonal populations. 相似文献
127.
The lack of a reliable and innocuous mark-recapture method has limited studies that would provide essential information for the management of commercial sea cucumbers. Tagging sea cucumbers is notoriously difficult because of their plastic nature and autolysis capacities. The markers that have so far been tested, mainly on or through the body wall, were either lost rapidly or had major drawbacks (e.g. suitable only for batch identification, requiring complex analysis, causing infections, necrosis, behavioural changes and mortality). The present study explored the efficacy of passive integrated transponder (PIT) tags for individually marking sea cucumbers by assessing retention rates and long-term side effects of tags inserted in previously unstudied tissues/organs. Individuals of the species Cucumaria frondosa were tagged in the body wall, aquapharyngeal bulb and at the base of the oral tentacles. They were monitored closely for evidence of stress, infection, change in feeding and spawning behaviour and tag retention rate. Implanting the tag in an oral tentacle to reach the hydrovascular system of the aquapharyngeal bulb achieved the best retention rates in full-size individuals: from a maximum of 92% after 30 days to 68% at the end of the experimental period (300 days). Efficacy was lower in smaller individuals (84% after 30 d and 42% after 300 d). Following a slight increase in cloacal movements for 15 h post tagging, no side effect was noted in sea cucumbers tagged in the aquapharyngeal bulb via the tentacles. Feeding and spawning behaviours were not affected and no signs of infections or abnormal cell development in the vicinity of the tags were observed. This study indicates that marking sea cucumbers with 8.2 mm long PIT tags implanted via the oral tentacle is an effective technique, yielding relatively high retention rates over long periods without any detectable physiological or behavioural effects. 相似文献
128.
Zhao Sun Jean‐François Hamel Christopher C. Parrish Annie Mercier 《Ecology and evolution》2015,5(5):1117-1129
Classical optimality models of offspring size and number assume a monotonically increasing relationship between offspring size and performance. In aquatic organisms with complex life cycles, the size–performance function is particularly hard to grasp because measures of performance are varied and their relationships with size may not be consistent throughout early ontogeny. Here, we examine size effects in premetamorphic (larval) and postmetamorphic (juvenile) stages of brooding marine animals and show that they vary contextually in strength and direction during ontogeny and among species. Larger offspring of the sea anemone Urticina felina generally outperformed small siblings at the larval stage (i.e., greater settlement and survival rates under suboptimal conditions). However, results differed when analyses were conducted at the intrabrood versus across‐brood levels, suggesting that the relationship between larval size and performance is mediated by parentage. At the juvenile stage (15 months), small offspring were less susceptible than large ones to predation by subadult nudibranchs and both sizes performed similarly when facing adult nudibranchs. In a sympatric species with a different life history (Aulactinia stella), all juveniles suffered similar predation rates by subadult nudibranchs, but smaller juveniles performed better (lower mortalities) when facing adult nudibranchs. Size differences in premetamorphic performance of U. felina were linked to total lipid contents of larvae, whereas size‐specific predation of juvenile stages followed the general predictions of the optimal foraging strategy. These findings emphasize the challenge in gathering empirical support for a positive monotonic size–performance function in taxa that exhibit complex life cycles, which are dominant in the sea. 相似文献
129.
Etienne Karita Matt A Price Shabir Lakhi William Kilembe Anatoli Kamali Eugene Ruzagira Eric Hunter Paul Farmer Susan Allen Gwynn Stevens Paramesh Chetty Sabrina Welsh Annie Yang Jill Gilmour Pat Fast The IAVI Africa HIV Prevention Partnership 《PloS one》2015,10(8)
Background
2013 WHO guidelines recommend starting ART at CD4+ T-cell counts ≤500 cells/μL. We present the T-cell counts from adult Africans with HIV shortly following transmission to their sexual partners.Methods
HIV-discordant couples in Zambia, Uganda and Rwanda were followed prospectively and received couples counseling and condoms. HIV uninfected partners were tested for HIV at least quarterly and HIV-infected partners received HIV care and referral for ART per national guidelines. Upon diagnosis of incident HIV infection in the previously HIV-uninfected partner, a blood sample was collected from both partners to measure CD4+ T-cells and perform viral linkage. The estimated date of infection (EDI) of the incident case was calculated based on testing history. EDI was unknown for suspected transmitting partners.Results
From 2006–2011, 4,705 HIV-discordant couples were enrolled in this cohort, and 443 cases of incident HIV infection were documented. Virus linkage analysis was performed in 374 transmission pairs, and 273 (73%) transmissions were linked genetically. CD4 counts in the transmitting partner were measured a median of 56 days after EDI (mean:90.5, min:10, max:396). The median CD4 count was 339 cells/μl (mean:386.4, min:15, max:1,434), and the proportion of partners with a CD4+ T-cell count above 500/μl was 25% (95% CI:21, 31).Conclusions
In our cohort of discordant couples, 73% of HIV transmissions occurred within the relationship, and the transmitter CD4+ T cell count shortly after the transmission event was frequently higher than the WHO 2013 ART-initiation guidelines. 相似文献130.
Brady W. Bennett Brandon D. L. Marshall Annie Gjelsvik Stephen T. McGarvey Mark N. Lurie 《PloS one》2015,10(11)