全文获取类型
收费全文 | 53篇 |
免费 | 5篇 |
出版年
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 2篇 |
2011年 | 2篇 |
2010年 | 1篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2006年 | 1篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1967年 | 1篇 |
1951年 | 1篇 |
1919年 | 2篇 |
排序方式: 共有58条查询结果,搜索用时 759 毫秒
11.
Replication slippage may cause parallel evolution in the secondary structures of mitochondrial transfer RNAs 总被引:9,自引:4,他引:5
Presence of the dihydrouridine (D) stem in the mitochondrial cysteine tRNA
is unusually variable among lepidosaurian reptiles. Phylogenetic and
comparative analyses of cysteine tRNA gene sequences identify eight
parallel losses of the D-stem, resulting in D-arm replacement loops.
Sampling within the monophyletic Acrodonta provides no evidence for
reversal. Slipped-strand mispairing of noncontiguous repeated sequences
during replication or direct replication slippage can explain repeats
observed within cysteine tRNAs that contain a D-arm replacement loop. These
two mechanisms involving replication slippage can account for the loss of
the cysteine tRNA D-stem in several lepidosaurian lineages, and may
represent general mechanisms by which the secondary structures of
mitochondrial tRNAs are altered.
相似文献
12.
13.
L. J. Henderson Edwin J. Cohn P. H. Cathcart J. D. Wachman W. O. Fenn in Collaboration with the Division of Food Nutrition Medical Department U. S. Army. 《The Journal of general physiology》1919,1(4):459-472
In this paper there are reported studies of the acid-base equilibrium in systems containing gluten suspended in solution of hydrochloric acid and sodium hydroxide. The studies have involved measurements of the hydrogen ion concentration, of the electrical conductivity, and of the solution of the proteins. Further, measurements have been made of the swelling and of the viscosity of the gluten component of such systems. The results seem to show that simple chemical phenomena are most important in such systems, and that the modifications of these, resulting from colloidal and heterogeneous characteristics, are of secondary importance in determining the condition of equilibrium, though somewhat more significant in the progress of the system toward the condition of equilibrium. 相似文献
14.
15.
16.
17.
Bias of some commonly-used time series estimates 总被引:3,自引:0,他引:3
18.
Reini W Bretveld Chris MG Thomas Paul TJ Scheepers Gerhard A Zielhuis Nel Roeleveld 《Reproductive biology and endocrinology : RB&E》2006,4(1):30
Some pesticides may interfere with the female hormonal function, which may lead to negative effects on the reproductive system
through disruption of the hormonal balance necessary for proper functioning. Previous studies primarily focused on interference
with the estrogen and/or androgen receptor, but the hormonal function may be disrupted in many more ways through pesticide
exposure. The aim of this review is to give an overview of the various ways in which pesticides may disrupt the hormonal function
of the female reproductive system and in particular the ovarian cycle. Disruption can occur in all stages of hormonal regulation:
1. hormone synthesis; 2. hormone release and storage; 3. hormone transport and clearance; 4. hormone receptor recognition
and binding; 5. hormone postreceptor activation; 6. the thyroid function; and 7. the central nervous system. These mechanisms
are described for effects of pesticide exposure in vitro and on experimental animals in vivo. For the latter, potential effects of endocrine disrupting pesticides on the female reproductive system, i.e. modulation
of hormone concentrations, ovarian cycle irregularities, and impaired fertility, are also reviewed. In epidemiological studies,
exposure to pesticides has been associated with menstrual cycle disturbances, reduced fertility, prolonged time-to-pregnancy,
spontaneous abortion, stillbirths, and developmental defects, which may or may not be due to disruption of the female hormonal
function. Because pesticides comprise a large number of distinct substances with dissimilar structures and diverse toxicity,
it is most likely that several of the above-mentioned mechanisms are involved in the pathophysiological pathways explaining
the role of pesticide exposure in ovarian cycle disturbances, ultimately leading to fertility problems and other reproductive
effects. In future research, information on the ways in which pesticides may disrupt the hormonal function as described in
this review, can be used to generate specific hypotheses for studies on the effects of pesticides on the ovarian cycle, both
in toxicological and epidemiological settings. 相似文献
19.
R S English J S Lampel TJ Vanden Boom 《Journal of industrial microbiology & biotechnology》1998,21(4-5):219-224
The introduction of plasmid DNA into germinating spores of an industrially improved strain of Saccharopolyspora erythraea was accomplished by electroporation. Various parameters affecting the efficiency of electroporation were examined. The most
critical factor was the extent of spore germination. Electrocompetence was limited to a 4-h period following the initial emergence
of the germ tube. Electroporation efficiencies as high as 2 × 105 CFU μg−1 of plasmid DNA were obtained using electrocompetent germlings. The optimal field strength was 12–14 kV cm−1 with a pulse duration of 15–20 ms. Electrocompetent germlings were stored at −80°C without a significant decrease in transformation
efficiency. The utility of this protocol was demonstrated by isolating a propionyl-CoA carboxylase mutant through targeted
gene disruption and replacement.
Received 3 April 1998/ Accepted in revised form 28 September 1998 相似文献
20.
Sequence variations in small-subunit ribosomal RNAs of Hartmannella vermiformis and their phylogenetic implications 总被引:1,自引:0,他引:1
Evidence of associations between free-living amoebas and human disease has
been increasing in recent years. Knowledge about phylogenetic relationships
that may be important for the understanding of pathogenicity in the genera
involved is very limited at present. Consequently, we have begun to study
these relationships and report here on the phylogeny of Hartmannella
vermiformis, a free-living amoeba that can harbor the etiologic agent of
Legionnaires' disease. Our analysis is based on studies of small-subunit
ribosomal RNA genes (srDNA). Nucleotide sequences were determined for
nuclear srDNA from three strains of H. vermiformis isolated from the United
Kingdom, Germany, and the United States. These sequences then were compared
with a sequence previously obtained for a North American isolate by J. H.
Gunderson and M. L. Sogin. The four genes are 1,840 bp long, with an
average GC content of 49.6%. Sequence differences among the strains range
are 0.38%-0.76%. Variation occurs at 19 positions and includes 2
single-base indels plus 14 monotypic and 3 ditypic single-base
substitutions. Variation is limited to eight helix/loop structures
according to a current model for srRNA secondary structure. Parsimony,
distance, and bootstrap analyses used to examine phylogenetic relationships
between the srDNA sequences of H. vermiformis and other eukaryotes
indicated that Hartmannella sequences were most closely related to those of
Acanthamoeba and the alga Cryptomonas. All ditypic sites were consistent
with a separation between European and North American strains of
Hartmannella, but results of other tests of this relationship were
statistically inconclusive.
相似文献