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41.
Whitehouse DB; Tomkins J; Lovegrove JU; Hopkinson DA; McMillan WO 《Molecular biology and evolution》1998,15(4):456-462
The expanding molecular database provides unparalleled opportunities for
characterizing genes and for studying groups of related genes. We use
sequences drawn from the database to construct an evolutionary framework
for examining the important glycolytic enzyme phosphoglucomutase (PGM).
Phosphoglucomutase plays a pivotal role in the synthesis and utilization of
glycogen and is present in all organisms. In humans, there are three
well-described isozymes, PGMI, PGM2, and PGM3. PGM1 was cloned 5 years ago;
however, repeated attempts using both immunological approaches and
molecular probes designed from PGM1 have failed to isolate either PGM2 or
PGM3. Using a phylogenetic strategy, we first identified 47 highly
divergent prokaryotic and eukaryotic PGM-like sequences from the database.
Although overall amino acid identity often fell below 20%, the relative
order, position, and sequence of three structural motifs, the active site
and the magnesium-- and sugar-binding sites, were conserved in all 47
sequences. The phylogenetic history of these sequences was complex and
marked by duplications and translocations; two instances of transkingdom
horizontal gene transfer were identified. Nonetheless, the sequences fell
within six well-defined evolutionary lineages, three of which contained
only prokaryotes. Of the two prokaryotic/eukaryotic lineages, one contained
bacterial, yeast, slimemold, invertebrate, and vertebrate homologs to human
PGM1 and the second contained likely homologs to human PGM2. Indeed, an
amino acid sequence, derived from a partial human cDNA, that fell within
the second cross-kingdom lineage bears several characteristics expected for
PGM2. A third lineage may contain homologs to human PGM3. On a general
level, our phylogenetic-based approach shows promise for the further
utilization of the extensive molecular database.
相似文献
42.
Initiation of DNA Synthesis in HeLa Cell-free System 总被引:6,自引:0,他引:6
THE molecular mechanism for initiating DNA replication can be studied using a subcellular system. Rao and Johnson1 found that HeLa cells in the pre-DNA-synthetic (G-1) period of the cell cycle initiate DNA synthesis after fusion with cells that are in the DNA synthetic (S) period. A previous subcellular system of DNA replication from HeLa cells2–4 consisted of intact nuclei, supplemented with the four deoxy-nucleoside triphosphates, salt, ATP and a cytosol factor. The nuclei in this system appeared to be permeable to proteins and DNA synthesis was very similar to that within intact cells. We report here the initiation of DNA synthesis in nuclei isolated from HeLa cells. Our results suggest that, with the synchronization method used, a small percentage of dormant G-1 nuclei can be stimulated by S-phase cytoplasm; this would be the case if the cells were receptive to stimulation for only 30–60 min during the cell cycle. illustration
相似文献
43.
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45.
Abstract: Occurrences of fossil lungfishes (Dipnoi: Sarcopterygii) in the Famennian Catskill Formation of Pennsylvania are reviewed. A nearly complete dermal skull roof is assigned to a new genus and species, Apatorhynchus opistheretmus . Other recently discovered lungfish specimens include an incomplete postcranium similar to that of the Frasnian genus Fleurantia , a small parasphenoid of uncertain affinities, and isolated toothplates. Previously described dipnoan remains from the Catskill Formation include a partial skull roof of Soederberghia groenlandica , toothplates assigned to several species of Dipterus , a putative rostral or symphysial region placed in the problematic form taxon Ganorhynchus , and sedimentary structures interpreted as burrows. The toothplates attributed to Dipterus are indeterminate and are placed in open nomenclature, while the specimen identified as Ganorhynchus is not convincingly dipnoan. The status of the burrows remains uncertain pending the discovery of lungfish remains within these or similar structures in Catskill deposits. The distinct ichthyofaunas within the Catskill Formation and their lungfish components are briefly reviewed. Lungfishes are found in the Holoptychius - and Bothriolepis -dominated faunas common in the Catskill succession, as well as in the compositionally distinctive Red Hill assemblage. Many of the Devonian continental faunas that contain tetrapods also include long-snouted, denticle-bearing lungfishes ('rhynchodipterids', fleurantiids, or both). The composition of Late Devonian ichthyofaunas may have predictive qualities that will allow researchers to identify localities likely to produce the remains of early tetrapods. 相似文献
46.
47.
Goldstein DB; Zhivotovsky LA; Nayar K; Linares AR; Cavalli-Sforza LL; Feldman MW 《Molecular biology and evolution》1996,13(9):1213-1218
It has recently been suggested that observed levels of variation at
microsatellite loci can be used to infer patterns of selection in genomes
and to assess demographic history. In order to evaluate the feasibility of
these suggestions it is necessary to know something about how levels of
variation at microsatellite loci are expected to fluctuate due simply to
stochasticity in the processes of mutation and inheritance (genetic
sampling). Here we use recently derived properties of the stepwise mutation
model to place confidence intervals around the variance in repeat score
that is expected at mutation-drift equilibrium and outline a statistical
test for whether an observed value differs significantly from expectation.
We also develop confidence intervals for the time course of the buildup of
variation following a complete elimination of variation, such as might be
caused by a selective sweep or an extreme population bottleneck. We apply
these methods to the variation observed at human Y-specific
microsatellites. Although a number of authors have suggested the
possibility of a very recent sweep, our analyses suggest that a sweep or
extreme bottleneck is unlikely to have occurred anytime during the last
approximately 74,000 years. To generate this result we use a recently
estimated mutation rate for microsatellite loci of 5.6 x 10(-4) along with
the variation observed at autosomal microsatellite loci to estimate the
human effective population size. This estimate is 18,000, implying an
effective number of 4,500 Y chromosomes. One important general conclusion
to emerge from this study is that in order to reject mutation-drift
equilibrium at a set of linked microsatellite loci it is necessary to have
an unreasonably large number of loci unless the observed variance is far
below that expected at mutation-drift equilibrium.
相似文献
48.
49.
MILTON J. FRIEDMAN 《The Journal of eukaryotic microbiology》1979,26(2):195-199
The process by which malaria parasites are killed in sickled erythrocytes was studied by electron microscopy. In vitro cultures of Plasmodium falciparum in sickle cell hemoglobin (HbS) homozygous (SS) and heterozygous (SA) red cells were deoxygenated for up to 6 h and fixed under anaerobic conditions. Parasites in SS cells appeared to be disrupted by intrusions of needle-like deoxyHbS aggregates; disintegration of cytoplasm and membranes followed. In SA red cells, the parasites were generally not disrupted. Instead, extensive vacuolization occurred, a sign of metabolic inhibition. The resistance of HbS gene carriers to malaria results partly from these causes of intracellular parasite death. 相似文献
50.
A 28s ribosomal RNA phylogeny of certain cyclorrhaphous Diptera based upon a hypervariable region 总被引:2,自引:0,他引:2
Abstract The method of primer extension dideoxy ribosomal RNA sequencing coupled with maximum parsimony analysis was used to obtain partial 28s rRNA sequences of a variety of calyptrate and acalyptrate Diptera with which to establish a possible genealogy of these organisms. Analysis of the data shows the calyptrates to be more closely related to the drosophiloids than to the tephritoids. Thus, the acalyptrates are a paraphyletic group. The analyses also establish the oestroid character of the gasterophilids and the status of the fanniids as a family or higher taxon. 相似文献