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111.
112.
Evolutionary Comparisons of RecA-Like Proteins Across All Major Kingdoms of Living Organisms 总被引:17,自引:0,他引:17
Volker Brendel Luciano Brocchieri Steven J. Sandler Alvin J. Clark Samuel Karlin 《Journal of molecular evolution》1997,44(5):528-541
Protein sequences with similarities to Escherichia coli RecA were compared across the major kingdoms of eubacteria, archaebacteria, and eukaryotes. The archaeal sequences branch
monophyletically and are most closely related to the eukaryotic paralogous Rad51 and Dmc1 groups. A multiple alignment of
the sequences suggests a modular structure of RecA-like proteins consisting of distinct segments, some of which are conserved
only within subgroups of sequences. The eukaryotic and archaeal sequences share an N-terminal domain which may play a role
in interactions with other factors and nucleic acids. Several positions in the alignment blocks are highly conserved within
the eubacteria as one group and within the eukaryotes and archaebacteria as a second group, but compared between the groups
these positions display nonconservative amino acid substitutions. Conservation within the RecA-like core domain identifies
possible key residues involved in ATP-induced conformational changes. We propose that RecA-like proteins derive evolutionarily
from an assortment of independent domains and that the functional homologs of RecA in noneubacteria comprise an array of RecA-like
proteins acting in series or cooperatively.
Received: 25 October 1996 / Accepted: 31 December 1996 相似文献
113.
Evolution of the WANCY region in amniote mitochondrial DNA 总被引:7,自引:1,他引:6
In most vertebrate mitochondrial genomes, the site for initiation of
light-strand replication, OL, is found within a cluster of five transfer
RNA (tRNA) genes (tRNA(Trp), tRNA(Ala), tRNA(Asn), tRNA(Cys), and
tRNA(Tyr)). This region and part of the adjacent cytochrome c oxydase
subunit I (COI) gene were sequenced for two crocodilian, two turtle, and
one snake species and for Sphenodon punctatus; part of the adjacent
nicotinamide adenine dinucleotide dehydrogenase subunit 2 (ND2) gene was
also sequenced for the crocodilian and turtle species. All had the typical
vertebrate gene order. The turtles and the snake have a lengthy noncoding
sequence between the tRNA(Asn) and tRNA(Cys) genes that we assumed to be
homologous to the mammalian OL. The crocodilians and Sphenodon lack such a
sequence, a condition they share with birds. Most proposed phylogenies for
the amniotes require that OL at this position was lost at least twice
during their diversification or was evolved independently more than once.
Within the five tRNA genes, frequencies of substitutions are much higher in
loops than in stems. Many loops vary dramatically in size among the
species; in the most extreme case, the D-arm of the Sphenodon tRNA(Cys) is
a "D-arm replacement" loop of seven nucleotides. Frequency of transitions
in stems is relatively uniform across tRNAs, but frequency of transversions
varies greatly. Mismatches in stems are infrequent, and their relative
frequency in a specific tRNA is unrelated to the frequency of substitution
in the corresponding gene. Several features of mammalian mitochondrial
tRNAs are conserved in WANCY tRNAs throughout amniotes. The inferred
initiation codon for COI is GTG in crocodilians, turtles, and the snake, a
condition they share with fishes, certain amphibians, and birds. TTG
appears to be the initiation codon for COI in Sphenodon; if correct, this
would be a novel initiation codon for vertebrate mitochondrial DNA.
Phylogenetic analyses of the inferred amino acid sequences of ND2 and COI
support the sister-group relationship of birds and crocodilians and suggest
that mammals are an early derived lineage within the amniotes.
相似文献
114.
The recF, recO, and recR genes form the recFOR epistasis group for DNA repair. recF mutants are sensitive to UV irradiation and fail to properly induce the SOS response. Using plasmid derivatives that overexpress combinations of the recO+ and recR+ genes, we tested the hypothesis that high-level expression of recO+ and recR+ (recOR) in vivo will indirectly suppress the recF mutant phenotypes mentioned above. We found that overexpression of just recR+ from the plasmid will partially suppress both phenotypes. Expression of the chromosomal recO+ gene is essential for the recR+ suppression. Hence we call this RecOR suppression of recF mutant phenotypes. RecOR suppression of SOS induction is more efficient with recO+ expression from a plasmid than with recO+ expression from the chromosome. This is not true for RecOR suppression of UV sensitivity (the two are equal). Comparison of RecOR suppression with the suppression caused by recA801 and recA803 shows that RecOR suppression of UV sensitivity is more effective than recA803 suppression and that RecOR suppression of UV sensitivity, like recA801 suppression, requires recJ+. We present a model that explains the data and proposes a function for the recFOR epistasis group in the induction of the SOS response and recombinational DNA repair. 相似文献
115.
The domiciliary consultation scheme introduced at the start of the NHS enables joint consultation between a consultant and general practitioner in a patient''s home when the patient cannot attend hospital on medical grounds. Consultants claim a fee from the NHS, general practitioners do not. Data from the Department of Health and Social Security on domiciliary consultations in England and Wales during 1981-6 were analysed. The number of domiciliary consultations fell during 1981-6 from 429,759 in 1981 to 387,394 in 1986, a fall of 10%, whereas the numbers of consultants and general practitioners increased by 1404 (12%) and 2400 (10%), respectively. The yearly rate of domiciliary consultation per consultant fell by 19% from 36 in 1981 to 29 in 1986 and that per general practitioner by 18% from 18 to 15. In 1986 geriatric medicine had the highest rate of domiciliary consultation per consultant (187) followed by psychiatry (89), general medicine (52), dermatology (49), rheumatology (42), general surgery (36), gastroenterology (35), thoracic medicine (34), and orthopaedics (30). In 1986 all specialties apart from clinical pharmacology and therapeutics and clinical genetics showed a decrease in the yearly rate of domiciliary consultation when compared with the rate for 1981. Domiciliary consultation seems to have become a domiciliary visit by the consultant alone. At an estimated cost of about 20m pounds for 1988 the scheme needs critical evaluation. 相似文献
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Oxprenolol, a new beta-receptor blocking drug with intrinsic sympathomimetic activity, was used to treat 63 episodes of cardiac arrhythmia occurring in 43 patients with acute myocardial infarction or myocardial ischaemia. The drug was most effective in abolishing ventricular ectopic beats and supraventricular tachycardia. The best method of administration was by continuous intravenous infusion and the most satisfactory bolus does was 6 mg. The main side effect was hypotension, which occurred in 59% of episodes of arrhythmia that had responded previously to intravenous administration. Oxprenolol was often effective in lignocaine-resistant arrhythmia. The two main advantages of oxprenolol over propranolol are the reduced likelihood of adversely affecting myocardial function and the diminished tendency to produce bronchospasm. 相似文献