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41.
Evolution at the tip and base of the X chromosome in an African population of Drosophila melanogaster 总被引:1,自引:0,他引:1
Hitchhiking effects of advantageous mutations have been invoked to explain
reduced polymorphism in regions of low crossing-over in Drosophila. Besides
reducing DNA heterozygosity, hitchhiking effects should produce strong
linkage disequilibrium and a frequency spectrum skewed toward an excess of
rare polymorphisms (compared to the neutral expectation). We measured DNA
polymorphism in a Zimbabwe population of D. melanogaster at three loci,
yellow, achaete, and suppressor of forked, located in regions of reduced
crossing-over. Similar to previously published surveys of these genomic
regions in other populations, we observed low levels of nucleotide
variability. However, the frequency spectrum was compatible with a neutral
model, and there was abundant evidence for recombination in the history of
the yellow and ac genes. Thus, some aspects of the data cannot be accounted
for by a simple hitchhiking model. An alternative hypothesis, background
selection, might be compatible with the observed patterns of linkage
disequilibrium and the frequency spectrum. However, this model cannot
account for the observed reduction in nucleotide heterozygosity. Thus,
there is currently no satisfactory theoretical model for the data from the
tip and base of the X chromosome in D. melanogaster.
相似文献
42.
Stephen B. Sampson David C. Higgins Rosemary W. Elliot Benjamin A. Taylor Kira K. Lueders Robert A. Koza Beverly Paigen 《Mammalian genome》1998,9(9):688-694
We have updated the history of the AXB and BXA recombinant inbred (RI) strains, typed additional loci, and edited the AXB,
BXA RI database. Thirteen of the original 51 AXB and BXA RI strains are either extinct or genetically contaminated, leaving
33 living strains available from The Jackson Laboratory. However, we found a high degree of similarity among three sets of
strains, indicating that these strains are not independent, which leaves 27 independent RI strains in the set. Accordingly,
we modified the database by combining the AXB and BXA RI sets and eliminating strains that were genetically contaminated or
extinct with no available DNA. We added 92 newly typed loci, retyped some questionable genotypings, and removed loci with
excessive double crossovers or an insufficient number of typed strains. The edited strain distribution pattern (SDP) is available
on the World Wide Web (WWW) (http://www.informatics.jax.org/riset.html) and now includes over 700 loci. Each locus is linked
to adjacent loci with a LOD score of at least 3.0 with a few described exceptions. We also carried out a second editing designed
for the analysis of quantitative trait loci by deleting extinct strains and loci with identical SDPs; this edited database
is also available on the WWW.
Received: 20 March 1998 / Accepted: 26 May 1998 相似文献
43.
Oligogalacturonic acids (OGAs), derived from plant cell wall pectin, have
been implicated in a number of signal transduction pathways involved in
growth, development and defense responses of higher plants. This study
investigates the size range of OGAs capable of inducing ethylene synthesis
in tomato plants, and demonstrates that in contrast with many other
effects, only short chain OGAs are active. Oligomers across a range of DP
from 2-15 were separated and purified to homogeneity by QAE-Sephadex anion
exchange chromatography using a novel elution system. The OGAs were applied
to tomato plants and assayed for their ability to induce ethylene gas
release and changes in steady state levels of mRNA encoding the ethylene
forming enzyme aminocyclopropane-1-carboxylic acid oxidase (ACO). The study
demonstrated that only OGAs in the size range of DP4-6 were active both in
eliciting ACO expression and in the production of ethylene.
相似文献
44.
45.
J Koza I Matyásová L Danes V Skovránek M Havelková 《Journal of hygiene, epidemiology, microbiology, and immunology》1984,28(1):25-32
Antibodies against type 1 and 2 poliovirus were tested in 250 infants and against type 3 poliovirus in 341 infants aged 0-13 months to compare the polio antibody outfit of newborns and infants born to three groups of mothers: (a) nonvaccinated, above 35 years of age; (b) vaccinated with attenuated poliovirus but having had chance of contact with wild poliovirus during childhood, age 22-35 years, and (c) vaccinated but not having had contact with wild poliovirus, below 22 years of age. Over 90% of newborns had specific neutralizing antibodies against all three poliovirus types. With increasing infant age the percentage of antibody-positive infants decreased: by age 9-11 months only 46%, 27% and 14% of infants displayed antibodies to polio-virus types 1, 2 and 3, respectively. Geometric mean titres decreased accordingly. Differences between infants born to mothers of the above three groups were nonsignificant: the results obtained suggest that future newborns will also possess satisfactory levels of antibodies acquired from mothers who have only had contact with attenuated vaccine poliovirus. 相似文献
46.
47.
V I Sergevnin N M Koza Z A Kleshcheva N S Gur'ianova N M Gladysheva V I Frizen 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1990,(5):38-42
The dynamics and structure of the epidemic process of Salmonella infections among the population of Perm in 1983-1988 was studied and the results of evaluation of antibiotic resistance of the dominating Salmonella species analyzed. The study revealed that a decrease in salmonellosis morbidity caused by S. typhimurium was associated with a limited circulation of anthroponotic (antibiotic-resistant) variants of Salmonellae and a relative increase in the proportion of zoonotic (antibiotic-sensitive) strains. At the period of elevated morbidity this Salmonella infection affected mainly young children in cold months, whereas in recent years seasonal morbidity rises shifted to spring-summer and summer-autumn months, affecting older age groups of the population. The study also revealed that a rise in salmonellosis morbidity caused by S. enteritidis was due to increased circulation of zoonotic variants of Salmonellae. Changes in the epidemiological situation necessitate correction of the system of epidemiological surveillance on Salmonella infections with the emphasis on sanitation measures in stock-breeding farms with unfavorable epidemiological situation. 相似文献
48.
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50.
A change in twist of actin provides the force for the extension of the acrosomal process in limulus sperm: the false-discharge reaction 总被引:1,自引:5,他引:1 下载免费PDF全文
One of the most spectacular motions is the generation of the acrosomal process in the limulus sperm. On contact with the egg, the sperm generates a 60-mum-long process that literally drills its way through the jelly surrounding the egg. This irresversible reaction takes only a few seconds. We suggested earlier that this motion is driven by a change in twist of the actin filaments comprising the acrosomal process. In this paper we analyze the so-called false discharge, a reversible reaction, in which the acrosomal filament bundle extends laterally from the base of the sperm and not anteriorly from the apex. Unlike the true discharge, which is straight, the false discharge is helical. Before extension, the filament bundle is coiled about the base of the sperm. In the coil, the bundle is not smoothly bent but consists of arms (straight segments) and elbows (corners) so that the coil looks like a 14-sided polygon. The extension of the false discharge works as follows: starting at the base of the bundle, the filaments change their twist which concomitantly changes the orientations of the elbows relative to each other; that is, in the coil, the elbows all like in a common plane, but after the change in twist, the plane of each elbow is rotated to be perpendicular to that of its neighbors. This change transforms the bundle from a compact coil into an extended left- handed helix. Because the basal end of the bundle is unconstrained, the extension is lateral. The true discharge works the same way but starts at the apical end of the bundle. The apical end, however, is constrained by its passage through the nuclear canal, which directs the extention anteriorly. Unlike the false discharge, during the true discharge the elbows are melted out, making the reaction irreversible. This study shows that rapid movement can be regenerated by actin without myosin and gives us insight into the molecular mechanism. 相似文献