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排序方式: 共有61条查询结果,搜索用时 15 毫秒
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Connexin 26 (GJB2) mutations in the Turkish population: implications for the origin and high frequency of the 35delG mutation in Caucasians 总被引:3,自引:0,他引:3
Mustafa Tekin Nejat Akar Şükrü Cin Susan Blanton Xia Xia Xue Liu Walter Nance Arti Pandya 《Human genetics》2001,108(5):385-389
Mutations in the Connexin 26 (GJB2/Cx26) gene are responsible for more than half of all cases of prelingual non-syndromic recessive deafness in many Caucasian populations. To determine the importance of Cx26 mutations as a cause of deafness in Turks we screened 11 families with prelingual non-syndromic deafness, seven (64%) of which were found to carry the 35delG mutation. We subsequently screened 674 Turkish subjects with no known hearing loss and found twelve 35delG heterozygotes (1.78%; 95% confidence interval: 0.9%-3%) but no examples of the 167delT mutation. To search for possible founder effects, we typed chromosomes carrying the 35delG mutation for closely linked polymorphic markers in samples from Turkey and United States and compared the allele frequencies with those of hearing subjects. The data showed a modest degree of disequilibrium in both populations. Analyses of two pedigrees from Turkey demonstrated both conserved and different haplotypes, suggesting possible founder effects and multiple origins of the 35delG mutation. 相似文献
4.
Positive selection is a general phenomenon in the evolution of abalone sperm lysin 总被引:15,自引:21,他引:15
Lysin is a 16kDa acrosomal protein used by abalone sperm to create a hole
in the egg vitelline envelope (VE). The interaction of lysin with the VE is
species-selective and is one step in the multistep fertilization process
that restricts heterospecific (cross-species) fertilization. For this
reason, the evolution of lysin could play a role in establishing prezygotic
reproductive isolation between species. Previously, we sequenced sperm
lysin cDNAs from seven California abalone species and showed that positive
Darwinian selection promotes their divergence. In this paper an additional
13 lysin sequences are presented representing species from Japan, Taiwan,
Australia, New Zealand, South Africa, and Europe. The total of 20 sequences
represents the most extensive analysis of a fertilization protein to date.
The phylogenetic analysis divides the sequences into two major clades, one
composed of species from the northern Pacific (California and Japan) and
the other composed of species from other parts of the world. Analysis of
nucleotide substitution demonstrates that positive selection is a general
process in the evolution of this fertilization protein. Analysis of
nucleotide and codon usage bias shows that neither parameter can account
for the robust data supporting positive selection. The selection pressure
responsible for the positive selection on lysin remains unknown.
相似文献
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D. Gisselsson Mattias Höglund Fredrik Mertens Bertil Johansson Paola Dal Cin Herman Van den Berghe William C. Earnshaw Felix Mitelman Nils Mandahl 《Human genetics》1999,104(4):315-325
Acquired ring chromosomes have been found in most types of human neoplasia, with a frequency approaching 10% in malignant
mesenchymal tumours. In this study, the composition and dynamics of ring chromosomes were analysed in eight cases of acute
myelogenous leukaemia, 17 solid tumours, and five cases with constitutional rings. Chromosomal banding and fluorescence in
situ hybridisation were performed to determine the content and the structural heterogeneity of the rings. Telomeric repeats
were detected using peptide nucleic acid probes or primed in situ labelling, whereas centromeric activity was evaluated by
detection of kinetochore proteins. Mitotic instability was assessed by the frequency of anaphase bridges. The results suggest
that human ring chromosomes can be structurally and functionally divided into two categories. In the first of these, size
variation is minimal and rearrangement at cell division is uncommon. The majority of such rings contain subtelomeric sequences.
Constitutional ring chromosomes and most rings in leukaemias belong to this group, whereas only a few mesenchymal tumours
exhibit rings of this type. The second category consists of rings with amplified sequences, primarily from chromosome 12,
characteristically occurring in atypical lipomatous tumours and other subtypes of low or borderline malignant mesenchymal
neoplasms. Variation in size and number is extensive, and breakage-fusion-bridge events occur at a high frequency. Abnormalities
in pericentromeric sequences are common and, in some cases, kinetochores assemble in the absence of alphoid DNA. We conclude
that it is not only the ring structure per se or the neoplastic nature of the host cell that determines ring instability,
but probably also the functional role of the genes carried in the ring.
Received: 24 November 1998 / Accepted: 18 January 1999 相似文献
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Farioli-Vecchioli S Saraulli D Costanzi M Pacioni S Cinà I Aceti M Micheli L Bacci A Cestari V Tirone F 《PLoS biology》2008,6(10):e246
Adult neurogenesis in the dentate gyrus plays a critical role in hippocampus-dependent spatial learning. It remains unknown, however, how new neurons become functionally integrated into spatial circuits and contribute to hippocampus-mediated forms of learning and memory. To investigate these issues, we used a mouse model in which the differentiation of adult-generated dentate gyrus neurons can be anticipated by conditionally expressing the pro-differentiative gene PC3 (Tis21/BTG2) in nestin-positive progenitor cells. In contrast to previous studies that affected the number of newly generated neurons, this strategy selectively changes their timing of differentiation. New, adult-generated dentate gyrus progenitors, in which the PC3 transgene was expressed, showed accelerated differentiation and significantly reduced dendritic arborization and spine density. Functionally, this genetic manipulation specifically affected different hippocampus-dependent learning and memory tasks, including contextual fear conditioning, and selectively reduced synaptic plasticity in the dentate gyrus. Morphological and functional analyses of hippocampal neurons at different stages of differentiation, following transgene activation within defined time-windows, revealed that the new, adult-generated neurons up to 3–4 weeks of age are required not only to acquire new spatial information but also to use previously consolidated memories. Thus, the correct unwinding of these key memory functions, which can be an expression of the ability of adult-generated neurons to link subsequent events in memory circuits, is critically dependent on the correct timing of the initial stages of neuron maturation and connection to existing circuits. 相似文献
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Summary In this paper genetic, clinical, and epidemiological studies on a muscular dystrophy which originated and is concentrated in the village of Çullar, Nevehir of inland Turkey, are reported. A pedigree chart has been constructed by careful and repeated inquiries, and both clinical and laboratory examinations have generally been carried out in the field. The consideration, facioscapulohumeral muscular dystrophy of Landouzy-Déjérine, has been found to have affected at least 53 individuals, 9 of whom are deceased. Both sexes in six generations are involved as would be expected from a dominant mendelian gene freshly mutated at least 100 years ago. Additionally, some 19 individuals have been described as having the disease or some of its stigmata, but have not been examined by us. Initial signs and symptoms seem to appear early in infancy, though variable, and because of complete dominance, some 75 individuals are at risk. The disease progresses slowly without interfering significantly with survival and reproduction. For prevention the so-called Çullar example measures have been taken to improve the area culturally and socioeconomically. 相似文献