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排序方式: 共有206条查询结果,搜索用时 15 毫秒
1.
Marion Laig Michael Pape Joachim Hundrieser Gebhard Flatz Torpong Sanguansermsri B. M. Das Ranjan Deka Puangrat Yongvanit Naret Mularlee 《Human genetics》1990,84(2):188-190
Summary The distribution of the hemoglobin Constant Spring (Hb CS) gene in eight populations in Southeast Asia (including Assam) was determined using oligonucleotide hybridization. Hb CS was absent in two Assamese populations with a high prevalence of Hb E. The Hb CS gene frequency was 0.033 in northern Thailand and near 0.01 in central Thailand and Cambodia. High frequencies, between 0.05 and 0.06, were observed in northeastern Thailand. The present data and a similar study in Laotians suggest that the Lao-speaking populations of the Mekong River basin in northeastern Thailand and Laos have the highest frequencies of the Hb CS gene in Southeast Asia. 相似文献
2.
Five tandem repeat loci were studied in humans and chimpanzees using VNTR probes derived from human DNA. Shared alleles were found at three loci and were often the modal allele in one species but never in both. There was no difference in the mean number of alleles per locus. However, these species exhibited substantially different levels of gene diversity, with chimpanzees monomorphic at two loci. Evidence of reduced variability in chimpanzees corroborates earlier comparisons using isozymes and plasma proteins. Molecular mechanisms, population dynamics, or both may be responsible for these differences. Equal numbers of alleles per locus may reflect high mutation rates. By one test, chimpanzees were out of equilibrium at one locus, which may reflect a typing error or population substructure. The long divergence time, and the high probability of backward mutations, precludes accurate estimation of genetic distance between these species. 相似文献
3.
DNA haplotypes and frameworks associated with the beta-globin gene in the Kachari population of Assam (India) 总被引:1,自引:0,他引:1
DNA haplotypes and frameworks associated with the beta-globin gene were determined in a Tibeto-Burman group, the Kachari, from Upper Assam, India, using restriction analysis at eight restriction sites. Of the total of 59 subjects, 26 were homozygous for HBB*A and 33 homozygous for HBB*E. Complete haplotype determination in 33 subjects revealed a conspicuous difference in haplotype distribution between HBB*A- and HBB*E-bearing chromosomes. The Southeast Asian HBB*E-associated haplotype -+- +- (27-2 in the present terminology) predominated on HBB*E chromosomes. The previously established beta-globin-associated frameworks 1, 2 and 3 were evenly distributed among the HBB*A chromosomes, whereas all HBB*E chromosomes had framework 2. These findings favor a common origin of the HBB*E gene in Southeast Asia and Assam. 相似文献
4.
R Deka A P Reddy B N Mukherjee B M Das S Banerjee M Roy B Dey K C Malhotra H Walter 《Human heredity》1988,38(5):261-266
Previous studies have reported a high incidence of hemoglobin E (HbE) in Northeast Indian populations. In the present study 10 endogamous populations of Assam belonging to two racial groups, Caucasoid and Mongoloid, were examined. The frequency of HbE gene (Hb beta E) in the Caucasoid caste populations is around 0.1, whereas the gene is highly prevalent in the Mongoloid populations, frequencies ranging between 0.2 and 0.6. Predominance of Hb beta E in the Tibeto-Burman speakers is contrary to observations made in Southeast Asia, where an association between Austro-Asiatic speakers and high prevalence of HbE exist. The highest occurrence of the gene in this area, which is on the far end of the proposed centre of distribution in Northern Kampuchea and Northeast Thailand, is also a deviation from the expected pattern of gene distribution. It is speculated that Hb beta E in the Tibeto-Burman populations of Assam arose by an independent mutation which contributed to the high frequencies of Hb beta E in the Northeast Indian populations. 相似文献
5.
The effects of mispair and nonpair correction in hybrid DNA on base ratios (G + C content) and total amounts of DNA 总被引:1,自引:0,他引:1
Base ratios and total DNA amounts can vary substantially between and within
higher taxa and genera, and even within species. Gene conversion is one of
several mechanisms that could cause such changes. For base substitutions,
disparity in conversion direction is accompanied by an equivalent disparity
in base ratio at the heterozygous site. Disparity in the direction of gene
conversion at meiosis is common and can be extreme. For transitions (which
give purine [R]/pyrimidine [Y] mispairs) and for transversions giving
unlike R/R and Y/Y mispairs in hybrid DNA, this disparity could give slow
but systematic changes in G + C percentage. For transversions giving like
R/R and Y/Y mispairs, it could change AT/TA and CG/GC ratios. From the
extent of correction direction disparity, one can deduce properties of
repair enzymes, such as the ability (1) to excise preferentially the purine
from one mispair and the pyrimidine from the other for two different R/Y
mispairs from a single heterozygous site and (2) to excise one base
preferentially from unlike R/R or Y/Y mispairs. Frame-shifts usually show
strong disparity in conversion direction, with preferential cutting of the
nonlooped or the looped-out strand of the nonpair in heterozygous h-DNA.
The opposite directions of disparity for frame-shifts and their intragenic
suppressors as Ascobolus suggest that repair enzymes have a strong,
systematic bias as to which strand is cut. The conversion spectra of
mutations induced with different mutagens suggest that the nonlooped strand
is preferentially cut, so that base additions generally convert to mutant
and deletions generally convert to wild-type forms. Especially in
nonfunctional or noncoding DNA, this could cause a general increase in DNA
amounts. Conversion disparity, selection, mutation, and other processes
interact, affecting rates of change in base ratios and total DNA.
相似文献
6.
Segregation distortion of the CTG repeats at the myotonic dystrophy locus. 总被引:3,自引:0,他引:3 下载免费PDF全文
R. Chakraborty D. N. Stivers R. Deka L. M. Yu M. D. Shriver R. E. Ferrell 《American journal of human genetics》1996,59(1):109-118
Myotonic dystrophy (DM), an autosomal dominant neuromuscular disease, is caused by a CTG-repeat expansion, with affected individuals having > or = 50 repeats of this trinucleotide, at the DMPK locus of human chromosome 19q13.3. Severely affected individuals die early in life; the milder form of this disease reduces reproductive ability. Alleles in the normal range of CTG repeats are not as unstable as the (CTG)(> or = 50) alleles. In the DM families, anticipation and parental bias of allelic expansions have been noted. However, data on mechanism of maintenance of DM in populations are conflicting. We present a maximum-likelihood model for examining segregation distortion of CTG-repeat alleles in normal families. Analyzing 726 meiotic events in 95 nuclear families from the CEPH panel pedigrees, we find evidence of preferential transmission of larger alleles (of size < or = 29 repeats) from females (the probability of transmission of larger alleles is .565 +/- 0.03, different from .5 at P approximately equal .028). There is no evidence of segregation distortion during male meiosis. We propose a hypothesis that preferential transmission of larger CTG-repeat alleles during female meiosis can compensate for mutational contraction of repeats within the normal allelic size range, and reduced viability and fertility of affected individuals. Thus, the pool of premutant alleles at the DM locus can be maintained in populations, which can subsequently mutate to the full mutation status to give rise to DM. 相似文献
7.
A PstI polymorphism in the 3 flanking region of the p21CiP1/Waf1 cyclin-dependent kinase inhibitor gene is described. DNA sequencing analysis identified a CT base substitution in the 3 flanking region of the gene. This substitution leads to the destruction of a PstI site and results in a biallelic DNA polymorphism. This restriction fragment length polymorphism (RFLP) provides the first known genetic marker for this cell cycle regulatory gene. 相似文献
8.
Ranjan Deka 《Human genetics》1981,59(2):172-174
Summary The Kachari in upper Assam, a Bodo tribe whose language belongs to the Tibeto-Burman family, have a 0.5 frequency of the haemoglobin E gene (HbE), the highest prevalence of an abnormal haemoglobin gene so far reported. In view of this high prevalence, the reproductive performance of 200 Kachari couples with different Hb genotypes and the prereproductive mortality of their offspring were examined. The differences of relative fertility observed were very small and there was no differential mortality of children. These findings indicate that at present there is no selection at the haemoglobin -chain locus in the Kachari population. 相似文献
9.
Summary Protoplasts from mesophyll cells and callus cells of rice (Oryza sativa L.) have been isolated by enzyme treatment involving 2% pectinase followed by 3% cellulase at pH 5.4 in 0.45 M mannitol (viable protoplasts from mesophyll cells in 50–60% yield, 60–70% yield of viable protoplasts from callus cells through treatment with the mixture of the above mentioned enzymes at the same concentration). Our completely defined medium is the combination of three established media (Table 1). Culture conditions are: soft agar in petri dishes at 26° C, where they regenerated cell walls after 24 h. The first cell division was observed after 4 days in culture for callus protoplasts and after 5 days in culture for mesophyll protoplasts. Cell division continues thereafter, and after 4 weeks of culture small white calli were visible in the petri dishes. The type of plant material (whitish leaf sheaths) and cell density are important factors for the efficiency of colony formation (30% plating efficiency). Healthy root formation through transfer to suitable medium is up to now the morphogenetic reaction of the calli.Work carried out at Molecular Cytogenetics Research Unit, Deptt, of Genetics and Plant Breeding, Banaras Hindu University, Varanasi, India 相似文献
10.
Deka RK Brautigam CA Goldberg M Schuck P Tomchick DR Norgard MV 《Journal of molecular biology》2012,416(5):678-696
Treponema pallidum, the bacterial agent of syphilis, is predicted to encode one tripartite ATP-independent periplasmic transporter (TRAP-T). TRAP-Ts typically employ a periplasmic substrate-binding protein (SBP) to deliver the cognate ligand to the transmembrane symporter. Herein, we demonstrate that the genes encoding the putative TRAP-T components from T. pallidum, tp0957 (the SBP), and tp0958 (the symporter), are in an operon with an uncharacterized third gene, tp0956. We determined the crystal structure of recombinant Tp0956; the protein is trimeric and perforated by a pore. Part of Tp0956 forms an assembly similar to those of "tetratricopeptide repeat" (TPR) motifs. The crystal structure of recombinant Tp0957 was also determined; like the SBPs of other TRAP-Ts, there are two lobes separated by a cleft. In these other SBPs, the cleft binds a negatively charged ligand. However, the cleft of Tp0957 has a strikingly hydrophobic chemical composition, indicating that its ligand may be substantially different and likely hydrophobic. Analytical ultracentrifugation of the recombinant versions of Tp0956 and Tp0957 established that these proteins associate avidly. This unprecedented interaction was confirmed for the native molecules using in vivo cross-linking experiments. Finally, bioinformatic analyses suggested that this transporter exemplifies a new subfamily of TPATs (TPR-protein-associated TRAP-Ts) that require the action of a TPR-containing accessory protein for the periplasmic transport of a potentially hydrophobic ligand(s). 相似文献