全文获取类型
收费全文 | 66篇 |
免费 | 19篇 |
出版年
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 4篇 |
2012年 | 2篇 |
2011年 | 1篇 |
2010年 | 3篇 |
2009年 | 3篇 |
2008年 | 1篇 |
2007年 | 3篇 |
2006年 | 2篇 |
2004年 | 1篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 7篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1993年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1937年 | 1篇 |
1934年 | 1篇 |
1933年 | 1篇 |
1931年 | 1篇 |
1910年 | 1篇 |
1879年 | 3篇 |
排序方式: 共有85条查询结果,搜索用时 359 毫秒
41.
Julian Parfitt Mark Barthel Sarah Macnaughton 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2010,365(1554):3065-3081
Food waste in the global food supply chain is reviewed in relation to the prospects for feeding a population of nine billion by 2050. Different definitions of food waste with respect to the complexities of food supply chains (FSCs)are discussed. An international literature review found a dearth of data on food waste and estimates varied widely; those for post-harvest losses of grain in developing countries might be overestimated. As much of the post-harvest loss data for developing countries was collected over 30 years ago, current global losses cannot be quantified. A significant gap exists in the understanding of the food waste implications of the rapid development of ‘BRIC’ economies. The limited data suggest that losses are much higher at the immediate post-harvest stages in developing countries and higher for perishable foods across industrialized and developing economies alike. For affluent economies, post-consumer food waste accounts for the greatest overall losses. To supplement the fragmentary picture and to gain a forward view, interviews were conducted with international FSC experts. The analyses highlighted the scale of the problem, the scope for improved system efficiencies and the challenges of affecting behavioural change to reduce post-consumer waste in affluent populations. 相似文献
42.
43.
44.
45.
Genomic but not antigenomic hepatitis delta virus RNA is preferentially exported from the nucleus immediately after synthesis and processing 总被引:4,自引:0,他引:4 下载免费PDF全文
Hepatitis delta virus (HDV) contains a viroid-like circular RNA that replicates via a double rolling circle replication mechanism. It is generally assumed that HDV RNA is synthesized and remains exclusively in the nucleus until being exported to the cytoplasm for virion assembly. Using a [32P]orthophosphate metabolic labeling procedure to study HDV RNA replication (T. B. Macnaughton, S. T. Shi, L. E. Modahl, and M. M. C. Lai. J. Virol. 76:3920-3927, 2002), we unexpectedly found that a significant amount of newly synthesized HDV RNA was detected in the cytoplasm. Surprisingly, Northern blot analysis revealed that the genomic-sense HDV RNA is present almost equally in both the nucleus and cytoplasm, whereas antigenomic HDV RNA was mostly retained in the nucleus, suggesting the specific and highly selective export of genomic HDV RNA. Kinetic studies showed that genomic HDV RNA was exported soon after synthesis. However, only the monomer and, to a lesser extent, the dimer HDV RNAs were exported to the cytoplasm; very little higher-molecular-weight HDV RNA species were detected in the cytoplasm. These results suggest that the cleavage and processing of HDV RNA may facilitate RNA export. The export of genomic HDV RNA was resistant to leptomycin B, indicating that a cell region maintenance 1 (Crm1)-independent pathway was involved. The large form of hepatitis delta antigen (L-HDAg), which is responsible for virus packaging, was not required for RNA export, as a mutant HDV RNA genome unable to synthesize L-HDAg was still exported. The proportions of genomic HDV RNA in the nucleus and cytoplasm remained relatively constant throughout replication, indicating that export of genomic HDV RNA occurred continuously. In contrast, while antigenomic HDV RNA was predominantly in the nucleus, there was a proportionally large fraction of antigenomic HDV RNA in the cytoplasm at early time points of RNA replication. These findings uncover a previously unrecognized presence of HDV RNA in the cytoplasm, which may have implications for viral RNA synthesis and packaging. 相似文献
46.
Large hepatitis delta antigen is not a suppressor of hepatitis delta virus RNA synthesis once RNA replication is established 下载免费PDF全文
Moderation of hepatitis delta virus (HDV) replication is a likely prerequisite in the establishment of chronic infections and is thought to be mediated by the intracellular accumulation of large hepatitis delta antigen (L-HDAg). The regulatory role of this protein was suggested from several studies showing that cotransfection of plasmid cDNAs expressing both L-HDAg and HDV RNA results in a potent inhibition of HDV RNA replication. However, since this approach differs significantly from natural HDV infections, where HDV RNA replication is initiated from an RNA template, and L-HDAg appears only late in the replication cycle, it remains unclear whether L-HDAg can modulate HDV RNA replication in the natural HDV replication cycle. In this study, we investigated the effect of L-HDAg, produced as a result of the natural HDV RNA editing event, on HDV RNA replication. The results showed that following cDNA-free HDV RNA transfection, a steady-state level of RNA was established at 3 to 4 days posttransfection. The same level of HDV RNA was reached when a mutant HDV genome unable to make L-HDAg was used, suggesting that L-HDAg did not play a role. The rates of HDV RNA synthesis, as measured by metabolic labeling experiments, were identical at 4 and 8 days posttransfection and in the wild type and the L-HDAg-deficient mutant. We further examined the effect of overexpression of L-HDAg at various stages of the HDV replication cycle, showing that HDV RNA synthesis was resistant to L-HDAg when it was overexpressed 3 days after HDV RNA replication had initiated. Finally, we showed that, contrary to conventional thinking, L-HDAg alone, at a certain molar ratio with HDV RNA, can initiate HDV RNA replication. Thus, L-HDAg does not inherently inhibit HDV RNA synthesis. Taken together, these results indicated that L-HDAg affects neither the rate of HDV RNA synthesis nor the final steady-state level of HDV RNA and that L-HDAg is unlikely to act as an inhibitor of HDV RNA replication in the natural HDV replication cycle. 相似文献
47.
Competitive PCR-DGGE analysis of bacterial mixtures: an internal standard and an appraisal of template enumeration accuracy 总被引:11,自引:0,他引:11
Brüggemann J Stephen JR Chang YJ Macnaughton SJ Kowalchuk GA Kline E White DC 《Journal of microbiological methods》2000,40(2):111-123
Analysis of polymerase chain reaction (PCR) amplified 16S rDNA fragments from environmental samples by denaturing gradients of chemicals or heat [denaturing gradient gel electrophoresis (DGGE) and thermal gradient gel electrophoresis (TGGE)] within polyacrylamide gels is a popular tool in microbial ecology. Difficulties in acceptance of the technique and interpretation of the results remain, due to its qualitative nature. In this study we have addressed this problem by the construction and evaluation of a quantitative standard for incorporation into test DNA samples. The standard was based on a naturally occurring 16S rRNA gene carried by the X-endosymbiont of the psyllid Anomoneura mori, a gamma-proteobacterium. This sequence is the most AT-rich 16S rDNA gene recovered from any cultured organism or environmental sample described to date, and a specifically amplified rDNA fragment denatured under exceptionally low stringency denaturing conditions. The native sequence was modified to incorporate perfect matches to the PCR primers used. The efficiency of amplification of this standard in comparison to a range of 16S rDNA sequences and the errors involved in enumerating template molecules under a range of PCR conditions are demonstrated and quantified. Tests indicated that highly accurate counts of released target molecules from a range of bacterial cells could be achieved in both laboratory mixtures and compost. 相似文献
48.
Physiological Status and Community Composition of Microbial Mats of the Ebro Delta, Spain, by Signature Lipid Biomarkers 总被引:3,自引:0,他引:3
Navarrete A Peacock A Macnaughton SJ Urmeneta J Mas-Castellà J White DC Guerrero R 《Microbial ecology》2000,39(1):92-99
Abstract
Physiological status of microbial mats of the Ebro Delta (Tarragona, Spain) based on the extraction of lipids considered ``signature
lipid biomarkers' (SLB) from the cell membranes and walls of microorganisms has been analyzed. Data from a day–night cycle
show significant differences in viable cells countings (PLFA cells counts) ranging from 1.5 × 1010 to 5.0 × 1010 cells g−1 of sediment. Minimum values were observed at 18:00 and 6:00, when physicochemical conditions change drastically. The diversity
of the microbial community was assessed by GC/MS analysis of phospholipid fatty acids (PLFA). The ratio of PLFA, representative
of Gram-negative bacteria, comprises 47.8% of the total PLFA of the microbial mat community. The remaining PLFA was representative
of Gram-positive (10.0%), anaerobic (5.7%), and eukaryotic microorganisms (5.7%), and other common lipids. Two different approaches
were used as a comparative study to assess the physiological status of the microbial mats. Two parameters (cyclopropane fatty
acids/ω7c monoenoic fatty acids, and measurement of the trans/cis monoenoic PLFA ratio) showed a minimum at midnight, suggesting the highest microbial activity. Higher values were observed
at 18:00 and 6:00, coinciding with lower PLFA cell counts.
Received: 14 May 1999; Accepted: 6 September 1999; Online Publication: 24 March 2000 相似文献
49.
During an expedition into the Arctic Ocean, in September 2004, six different species of amphipods were collected in the ice
above 82°N. All six species (Apherusa glacialis, Gammarus wilkitzkii, Onisimus nanseni, O. glacialis, Pleusymtes karstensi and Eusirus holmii) were observed to be living adjacent to the sea ice or partly within its brine channels. The nature of the association with
the ice for the last two species is uncertain, but the finding raises important questions regarding our knowledge of the sympagic
fauna. Based on the obtained material, the two species E. holmii and P. karstensi are redescribed, and their association with the sea ice is discussed. 相似文献
50.
J Oloya R Kazwala A Lund J Opuda-Asibo B Demelash E Skjerve TB Johansen B Djønne 《BMC microbiology》2007,7(1):95