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141.
High levels of genetic diversity are generated in Haemophilus influenzae populations through DNA repeat-mediated phase variation and recombination with DNA fragments acquired by uptake from the external milieu. Conversely, multiple pathways for maintenance of the genome sequence are encoded in H. influenzae genomes. In Escherichia coli, mutations in single-stranded-DNA exonucleases destabilise tandem DNA repeats whilst inactivation of recG can stabilise repeat tracts. These enzymes also have varying effects on recombination. Deletion mutations were constructed in H. influenzae genes encoding homologs of ExoI, RecJ and RecG whilst ExoVII was refractory to mutation. Inactivation of RecJ and RecG, but not ExoI, increased sensitivity to irradiation with ultraviolet light. An increase in spontaneous mutation rate was not observed in single mutants but only when both RecJ and ExoI were mutated. None of the single- or double-mutations increased or decreased the rates of slippage in tetranucleotide repeat tracts. Furthermore, the exonuclease mutants did not exhibit significant defects in horizontal gene transfer. We conclude that RecJ, ExoI and RecG are required for maintenance of the H. influenzae genome but none of these enzymes influence the generation of genetic diversity through mutations in the tetranucleotide repeat tracts of this species. 相似文献
142.
Although microsatellite mutation rates generally increase with increasing length of the repeat tract, interruptions in a microsatellite may stabilize it. We have performed a direct analysis of the effect of microsatellite interruptions on mutation rate and spectrum in cultured mammalian cells. Two mononucleotide sequences (G17 and A17) and a dinucleotide [(CA)17] were compared with interrupted repeats of the same size and with sequences of 8 repeat units. MMR-deficient (MMR−) cells were used for these studies to eliminate effects of this repair process. Mutation rates were determined by fluctuation analysis on cells containing a microsatellite sequence at the 5′ end of an antibiotic-resistance gene; the vector carrying this sequence was integrated in the genome of the cells. In general, interrupted sequences had lower mutation rates than perfect ones of the same size, but the magnitude of the difference was dependent upon the sequence of the interrupting base(s). Some interrupted repeats had mutation rates that were lower than those of perfect sequences of the same length but similar to those of half the length. This suggests that interrupting bases effectively divide microsatellites into smaller repeat runs with mutational characteristics different from those of the corresponding full-length microsatellite. We conclude that interruptions decrease microsatellite mutation rate and influence the spectrum of frameshift mutations. The sequence of the interrupting base(s) determines the magnitude of the effect on mutation rate. 相似文献
143.
Catalina Monzón-Argüello Joaquín Muñoz Adolfo Marco Luis Felipe López-Jurado Ciro Rico 《Conservation Genetics》2008,9(4):1045-1049
We describe 12 new polymorphic dinucleotide microsatellite loci and multiplex Polymerase Chain Reaction conditions from the
loggerhead sea turtle Caretta caretta. Levels of polymorphism were assessed in 50 individuals from the nesting population of the Cape Verde Islands. Number of
alleles ranged from 3 to 13 (average of 7.33) and the values of observed heterozygosities from 0.32 to 0.80 (average of 0.61).
Cross-species amplification on three other marine turtles, Chelonia mydas, Eretmochelys imbricata and Dermochelys coriacea, revealed polymorphism and variability at eight, eleven and three loci, respectively. 相似文献
144.
X. Wang R. Trigiano M. Windham B. Scheffler T. Rinehart J. Spiers 《Tree Genetics & Genomes》2008,4(3):461-468
Abundant, codominant simple sequence repeats (SSRs) markers can be used for constructing genetic linkage maps and in marker-assisted
breeding programs. Enrichment methods for SSR motifs were optimized with the ultimate aim of developing numerous loci in flowering
dogwood (C. florida L.) genome. Small insert libraries using four motifs (GT, CT, TGG, and AAC) were constructed with C. florida ‘Cherokee Brave’ deoxyribonucleic acid (DNA). Colony polymerase chain reaction (PCR) of 2,208 selected clones with three
primers we reported previously indicated that 47% or 1,034 of the clones harbored one of the four targeted SSR motifs. Sequencing
the putative positive clones confirmed that nearly 99% (1,021 of 1,034) of them contained the desired motifs. Of the 871 unique
SSR loci, 617 were dinucleotide repeats (70.8%), and 254 were trinucleotide or longer repeats (29.2%). In total, 379 SSR loci
had perfect structure, 237 had interrupted, and 255 had compound structure. Primer pairs were designed from 351 unique sequences.
The ability of the 351 SSR primer pairs to amplify specific loci was evaluated with genomic DNA of ‘Appalachian Spring’ and
‘Cherokee Brave’. Of these primers, 311 successfully amplified product(s) with ‘Cherokee Brave’ DNA, 21 produced weak or faint
products, and 19 did not amplify any products. Additionally, 218 of the 311 primers pairs revealed polymorphisms between the
two cultivars, and 20 out of 218 primers detected an average of 13.7 alleles from 38 selected Cornus species and hybrids. These SSR loci constitute a valuable resource of ideal markers for both genetic linkage mapping and
gene tagging of flowering dogwood.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
145.
Muraguchi H Abe K Nakagawa M Nakamura K Yanagi SO 《Molecular genetics and genomics : MGG》2008,280(3):223-232
A Coprinopsis cinerea homokaryotic fruiting strain was mutagenised, identifying a mutant that exhibited a hyphal growth temperature sensitive defect and hyphal knot development defect at an early fruiting stage, even at the hyphal growth permissive temperature. Microscopic observation suggested that the mutant nuclei exhibited defects in the metaphase to anaphase transition at the restrictive temperature. The gene in which the mutation occurred was cloned, sequenced and determined to be homologous to smc1. Sequence analyses of the mutant revealed deletion of 28 base pairs in the 19th intron of the Cc.smc1 gene, resulting in complete failure of splicing of that intron and in insertion of 14 amino acids in the C-terminal region of the Cc.Smc1 protein. We isolated eight hyphal growth revertants and identified four intragenic suppressors. All were the result of amino acid substitutions in the C-terminal region. Three of the suppressors caused reversion of the arrest in an early fruiting stage. One of the suppressors exhibited cold sensitivity and failed to suppress the fruiting defect, suggesting that flexibility of a lobe in the C-terminal region is important for proper function of Cc.Smc1. 相似文献
146.
Short tandem repeats (STRs) are subjected to two kinds of mutational modifications: point mutations and replication slippages.
The latter is found to be the more frequent cause of STR modifications, but a satisfactory quantitative measure of the ratio
of the two processes has yet to be determined. The comparison of entire genome sequences of closely enough related species
enables one to obtain sufficient statistics by counting the differences in the STR regions. We analyzed human–chimpanzee DNA
sequence alignments to obtain the counts of point mutations and replication slippage modifications. The results were compared
with the results of a computer simulation, and the parameters quantifying the replication slippage probability as well as
the probabilities of point mutations within the repeats were determined. It was found that within the STRs with repeated units
consisting of one, two or three nucleotides, point mutations occur approximately twice as frequently as one would expect on
the basis of the 1.2% difference between the human and chimpanzee genomes. As expected, the replication slippage probability
is negligible below a 10-bp threshold and grows above this level. The replication slippage events outnumber the point mutations
by one or two orders of magnitude, but are still lower by one order of magnitude relative to the mutability of the markers
that are used for genotyping purposes. 相似文献
147.
Promoter fragments of deoxyribonuclease II (DNAse II) and calcium-modulating cyclophilin ligand (CAML) associated with Alu family repeats have been inserted into luciferase reporter vectors. The constructs were introduced into A549 and HEK293 cell lines by transient transfection. Transfected cells were lysed to analyze luciferase activities. It has been shown that Alu repeats inserted into constructs influence the luciferase expression. Therefore, Alu copies associated with cis-regulatory modules in protein-coding genes have biological activity. 相似文献
148.
Polypteridae (Cladistia) is a family of archaic fishes, confined to African freshwaters. On account of their primitiveness
in anatomical and morphological characters and mosaic relationships among lower Osteichthyans fishes, they constitute an important
subject for the study of evolution in vertebrates. Very little is known about the karyological structure of these species.
In this article, a cytogenetic analysis on twenty specimens of Polypterus senegalus (Cuvier, 1829) was performed using both classical and molecular techniques. Karyotype (2n = 36; FN = 72), chromosome location of telomeric sequences (TTAGGG)
n
, (GATA)7 repeats and ribosomal 5S and 18S rRNA genes were examined by using Ag-NOR, classical C-banding, CMA3 staining and FISH. Staining with Ag-NOR showed the presence of two GC rich NORs on the p arm of the chromosome pair no. 1.
CMA3 marked all centromerical and some (no. 1 and no. 14) telomeric regions. FISH with 5S rDNA marked the subtelomeric region
of the q arm of the chromosome pair no. 14. FISH with 18S rDNA marked the telomeric region of the p arm of the chromosome
pair no. 1, previously marked by Ag-NOR. (GATA)7 repeats marked the subtelomeric regions of all chromosome pairs, with the exclusion of the no. 1, 3 and 14. Hybridization
with telomeric probes (TTAGGG)
n
showed bright signals at the end of all chromosomes. After cloning, the 5SrDNA alignment revealed an organization of sequences
made up of two different classes of tandem arrays (5S type I and 5S type II) of different lengths. 相似文献
149.
DXS6804/DXS9896/GATA144D04基因座在中国汉族群体中的遗传多态性及其法医学应用 总被引:4,自引:0,他引:4
为了调查X染色体上DXS6804、DXS9896和GATA144D04等3个STR基因座在中国汉族群体的遗传多态性及其法医学应用价值,来用PCR和聚丙烯酰胺凝胶电泳对X染色体3个STR基因座进行分型,并检验女性基因型频率分布是否符合Hardy Weinberg平衡,计算法医学常用各种概率。DXS6804、DXS9896和GATA144D04的非父排除率分别为0 5990、0 6220、0 4280,表明3个STR基因座在中国汉族群体均具有遗传多态性,χ2检验表明女性的基因型频率分布符合Hardy Weinberg平衡。X染色体上的基因座DXS6804、DXS9896和GATA144D04在中国汉族群体中具有较高的遗传多态性,可应用于法医学检验和群体遗传学分析。 相似文献
150.
We describe specific primers and conditions to amplify two dinucleotide and five trinucleotide microsatellite DNA loci isolated from the oomycete Phytophthora ramorum, the causal agent of sudden oak death. The primer sets were tested on 14–30 isolates from North America and Europe. Seven of 14 loci differentiated between A1 and A2 mating types. All seven loci successfully amplified DNA isolated from infected plant tissue. Four loci may be useful for the diagnosis of P. ramorum because they do not amplify closely related Phytophthora species. 相似文献