首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   117篇
  免费   10篇
  2021年   2篇
  2020年   1篇
  2017年   3篇
  2016年   2篇
  2015年   5篇
  2014年   8篇
  2013年   4篇
  2012年   4篇
  2011年   4篇
  2010年   10篇
  2009年   7篇
  2008年   5篇
  2007年   2篇
  2006年   6篇
  2005年   3篇
  2004年   6篇
  2003年   8篇
  2002年   2篇
  2001年   2篇
  2000年   6篇
  1999年   7篇
  1998年   6篇
  1997年   4篇
  1996年   1篇
  1994年   3篇
  1993年   1篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1982年   1篇
  1978年   3篇
  1977年   2篇
  1975年   1篇
  1962年   1篇
  1955年   1篇
  1952年   1篇
  1948年   1篇
  1947年   1篇
排序方式: 共有127条查询结果,搜索用时 15 毫秒
1.
2.
Transposition in plants: a molecular model   总被引:47,自引:14,他引:33       下载免费PDF全文
A molecular model for transposition of plant transposable elements is described. This process may occur via excision and re-integration of the element. Excision generates DNA sequence diversity which suggests the participation of DNA repair enzymes in the healing of the donor molecule.  相似文献   
3.
4.
Root colonization was studied in ten species of the Epacridaceaeat three sites in Victoria by morphological and cross-inoculationexperiments. The sites and genera chosen were Cranbourne [Epacrisimpressa Labill. andLeucopogon ericoides(Smith) R. Br.] andRye [L. parviflorus(Andrews) Lindley] on the Mornington Peninsula,and the Grampians[Astroloma conostephioides(Sond.) Benth.,A.humifusum(Cav.) R. Br.,A pinifolium(R. Br.) Benth,Brachylomadaphnoides(Smith) Benth.,E. impressa, E. impressavar.grandifloraBenth.andStyphelia adscendensR. Br.] in western Victoria. For morphologicalstudies, samples of roots from each species at each site werecleared and stained and examined microscopically. For cross-inoculationstudies, cuttings from each site were struck in potting mediuminoculated with soil from the same and other sites. The ericoidmycorrhizae in the roots of plants found at or grown in Cranbourneand Rye soils were similar. Both were significantly differentfrom the internal hyphae found in the roots of plants foundat or grown in Grampians soils, which were three times largerin diameter and formed dense coils which filled the host celland invaded adjacent epidermal cells. This suggests that morethan one fungus is involved in the relationships, that the MorningtonPeninsula sites had a different fungus from the Grampians siteand that host specificity is low. Vesicular structures werealso found commonly on plants at the Grampians site, in contrastwith other sites. Epacridaceae; root; fungus; mycorrhiza; morphology; inoculation  相似文献   
5.
Studies on solar inactivation of Escherichia coli in freshwater and in situ have been limited. At 63rd St. Beach, Chicago, Ill., factors influencing the daily periodicity of culturable E. coli, particularly insolation, were examined. Water samples for E. coli analysis were collected twice daily between April and September 2000 three times a week along five transects in two depths of water. Hydrometeorological conditions were continuously logged: UV radiation, total insolation, wind speed and direction, wave height, and relative lake level. On 10 days, transects were sampled hourly from 0700 to 1500 h. The effect of sunlight on E. coli inactivation was evaluated with dark and transparent in situ mesocosms and ambient lake water. For the study, the number of E. coli samples collected (n) was 2,676. During sunny days, E. coli counts decreased exponentially with day length and exposure to insolation, but on cloudy days, E. coli inactivation was diminished; the E. coli decay rate was strongly influenced by initial concentration. In situ experiments confirmed that insolation primarily inactivated E. coli; UV radiation only marginally affected E. coli concentration. The relationship between insolation and E. coli density is complicated by relative lake level, wave height, and turbidity, all of which are often products of wind vector. Continuous importation and nighttime replenishment of E. coli were evident. These findings (i) suggest that solar inactivation is an important mechanism for natural reduction of indicator bacteria in large freshwater bodies and (ii) have implications for management strategies of nontidal waters and the use of E. coli as an indicator organism.  相似文献   
6.

Background

Atypical scrapie was first identified in Norwegian sheep in 1998 and has subsequently been identified in many countries. Retrospective studies have identified cases predating the initial identification of this form of scrapie, and epidemiological studies have indicated that it does not conform to the behaviour of an infectious disease, giving rise to the hypothesis that it represents spontaneous disease. However, atypical scrapie isolates have been shown to be infectious experimentally, through intracerebral inoculation in transgenic mice and sheep. The first successful challenge of a sheep with 'field' atypical scrapie from an homologous donor sheep was reported in 2007.

Results

This study demonstrates that atypical scrapie has distinct clinical, pathological and biochemical characteristics which are maintained on transmission and sub-passage, and which are distinct from other strains of transmissible spongiform encephalopathies in the same host genotype.

Conclusions

Atypical scrapie is consistently transmissible within AHQ homozygous sheep, and the disease phenotype is preserved on sub-passage.  相似文献   
7.

Introduction  

Rheumatoid arthritis (RA) frequently involves the loss of tolerance to citrullinated antigens, which may play a role in pathogenicity. Citrullinated fibrinogen is commonly found in inflamed synovial tissue and is a frequent target of autoantibodies in RA patients. To obtain insight into the B-cell response to citrullinated fibrinogen in RA, its autoepitopes were systematically mapped using a new methodology.  相似文献   
8.
9.
We describe an analysis, applicable to any spotted microarray dataset produced using genomic DNA as a reference, that quantifies prokaryotic levels of mRNA on a genome-wide scale. Applying this to Mycobacterium tuberculosis, we validate the technique, show a correlation between level of expression and biological importance, define the complement of invariant genes and analyze absolute levels of expression by functional class to develop ways of understanding an organism's biology without comparison to another growth condition.  相似文献   
10.

Background

The number of completely sequenced plastid genomes available is growing rapidly. This array of sequences presents new opportunities to perform comParative analyses. In comParative studies, it is often useful to compare across wide phylogenetic spans and, within angiosperms, to include representatives from basally diverging lineages such as the genomes reported here: Nuphar advena (from a basal-most lineage) and Ranunculus macranthus (a basal eudicot). We report these two new plastid genome sequences and make comparisons (within angiosperms, seed plants, or all photosynthetic lineages) to evaluate features such as the status of ycf15 and ycf68 as protein coding genes, the distribution of simple sequence repeats (SSRs) and longer dispersed repeats (SDR), and patterns of nucleotide composition.

Results

The Nuphar [GenBank:NC_008788] and Ranunculus [GenBank:NC_008796] plastid genomes share characteristics of gene content and organization with many other chloroplast genomes. Like other plastid genomes, these genomes are A+T-rich, except for rRNA and tRNA genes. Detailed comparisons of Nuphar with Nymphaea, another Nymphaeaceae, show that more than two-thirds of these genomes exhibit at least 95% sequence identity and that most SSRs are shared. In broader comparisons, SSRs vary among genomes in s of abundance and length and most contain repeat motifs based on A and T nucleotides.

Conclusion

SSR and SDR abundance varies by genome and, for SSRs, is proportional to genome size. Long SDRs are rare in the genomes assessed. SSRs occur less frequently than predicted and, although the majority of the repeat motifs do include A and T nucleotides, the A+T bias in SSRs is less than that predicted from the underlying genomic nucleotide composition. In codon usage third positions show an A+T bias, however variation in codon usage does not correlate with differences in A+T-richness. Thus, although plastome nucleotide composition shows "A+T richness", an A+T bias is not apparent upon more in-depth analysis, at least in these aspects. The pattern of evolution in the sequences identified as ycf15 and ycf68 is not consistent with them being protein-coding genes. In fact, these regions show no evidence of sequence conservation beyond what is normal for non-coding regions of the IR.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号