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81.
Slipped-strand mispairing: a major mechanism for DNA sequence evolution 总被引:141,自引:13,他引:128
Simple repetitive DNA sequences are a widespread and abundant feature of
genomic DNA. The following several features characterize such sequences:
(1) they typically consist of a variety of repeated motifs of 1-10
bases--but may include much larger repeats as well; (2) larger repeat units
often include shorter ones within them; (3) long polypyrimidine and poly-CA
tracts are often found; and (4) tandem arrangements of closely related
motifs are often found. We propose that slipped-strand mispairing events,
in concert with unequal crossing- over, can readily account for all of
these features. The frequent occurrence of long tandem repeats of
particular motifs (polypyrimidine and poly-CA tracts) appears to result
from nonrandom patterns of nucleotide substitution. We argue that the
intrahelical process of slipped-strand mispairing is much more likely to be
the major factor in the initial expansion of short repeated motifs and
that, after initial expansion, simple tandem repeats may be predisposed to
further expansion by unequal crossing-over or other interhelical events
because of their propensity to mispair. Evidence is presented that
single-base repeats (the shortest possible motifs) are represented by
longer runs in mammalian introns than would be expected on a random basis,
supporting the idea that SSM may be a ubiquitous force in the evolution of
the eukaryotic genome. Simple repetitive sequences may therefore represent
a natural ground state of DNA unselected for coding functions.
相似文献
82.
Complete sequences of the rRNA genes of Drosophila melanogaster 总被引:19,自引:0,他引:19
In this, the first of three papers, we present the sequence of the
ribosomal RNA (rRNA) genes of Drosophila melanogaster. The gene regions of
D. melanogaster rDNA encode four individual rRNAs: 18S (1,995 nt), 5.8S
(123 nt), 2S (30 nt), and 28S (3,945 nt). The ribosomal DNA (rDNA) repeat
of D. melanogaster is AT rich (65.9% overall), with the spacers being
particularly AT rich. Analysis of DNA simplicity reveals that, in contrast
to the intergenic spacer (IGS) and the external transcribed spacer (ETS),
most of the rRNA gene regions have been refractory to the action of
slippage-like events, with the exception of the 28S rRNA gene expansion
segments. It would seem that the 28S rRNA can accommodate the products of
slippage-like events without loss of activity. In the following two papers
we analyze the effects of sequence divergence on the evolution of (1) the
28S gene "expansion segments" and (2) the 28S and 18S rRNA secondary
structures among eukaryotic species, respectively. Our detailed analyses
reveal, in addition to unequal crossing-over, (1) the involvement of
slippage and biased mutation in the evolution of the rDNA multigene family
and (2) the molecular coevolution of both expansion segments and the
nucleotides involved with compensatory changes required to maintain
secondary structures of RNA.
相似文献
83.
84.
Pagotto João Paulo Alves Pessoa Leonardo Antunes Goulart Erivelto Mise Fábio Teruo Ortega Jean Carlo Gonçalves Landgraf Guilherme Okuda 《Hydrobiologia》2022,849(10):2299-2316
Hydrobiologia - Human activities change the environmental conditions of streams and alter their assemblages. However, the environmental factors associated with the change in the ecomorphological... 相似文献
85.
Andrade Elisa Helena Paz Figueiredo Leandra Barcelos Vilela Ana Paula Pessoa Rosa Jlio Csar Cmara Zibaoui Hassan Melo Kroon Erna Geessien 《EcoHealth》2022,19(1):75-84
EcoHealth - Dengue virus (DENV) 1–4 is the etiological agent of dengue, the most important viral infection transmitted by Aedes spp mosquitoes to humans. Our goal was to identify the... 相似文献
86.
87.
88.
H. Faneca Isabel Tomaz Gisela Gonçalves M.C. Pedroso de Lima João Costa Pessoa M. Margarida C.A. Castro 《Journal of inorganic biochemistry》2009,103(4):601-608
The behaviour of three vanadium(V) systems, namely the pyridinone (VV-dmpp), the salicylaldehyde (VV-salDPA) and the pyrimidinone (VV-MHCPE) complexes, is studied in aqueous solutions, under aerobic and physiological conditions using 51V NMR, EPR and UV-Visible (UV-Vis) spectroscopies. The speciations for the VV-dmpp and VV-salDPA have been previously reported. In this work, the system VV-MHCPE is studied by pH-potentiometry and 51V NMR. The results indicate that, at pH ca. 7, the main species present are (VVO2)L2 and (VVO2)LH−1 (L = MHCPE−) and hydrolysis products, similar to those observed in aqueous solutions of VV-dmpp. The latter species is protonated as the pH decreases, originating (VVO2)L and (VVO2)LH. All the VV-species studied are stable in aqueous media with different compositions and at physiological pH, including the cell culture medium. The compounds were screened for their potential cytotoxic activity in two different cell lines. The toxic effects were found to be incubation time and concentration dependent and specific for each compound and type of cells. The HeLa tumor cells seem to be more sensitive to drug effects than the 3T3-L1 fibroblasts. According to the IC50 values and the results on reversibility to drug effects, the VV-species resulting from the VV-MHCPE system show higher toxicity in the tumor cells than in non-tumor cells, which may indicate potential antitumor activity. 相似文献
89.
Julio Benítez Lucía Guggeri Isabel Tomaz João Costa Pessoa Julia Lorenzo Beatriz Garat 《Journal of inorganic biochemistry》2009,103(10):1386-1394
In the search for new metal-based drugs for the treatment of tumoral and parasitic diseases a vanadyl complex, [VIVO(SO4)(H2O)2(dppz)]·2H2O, that includes the bidentate polypyridyl DNA intercalator dipyrido[3,2-a:2′,3′-c]phenazine (dppz), was synthesized, characterized by a combination of techniques, and in vitro evaluated on the human acute promyelocytic leukemia cell line HL-60 and against Dm28c strain epimastigotes of the parasite Trypanosoma cruzi, causative agent of Chagas’ disease. EPR spectroscopy suggests a distorted octahedral geometry for the complex with the dppz ligand acting as bidentate, binding through both nitrogen donor atoms in an axial-equatorial mode. An oxo group, two water molecules and a sulphate donor occupy the remainder coordination positions. The complex, as well as the anti-trypanosomal reference drug Nifurtimox, showed IC50 values in the μM range against T. cruzi Dm28c strain. In addition the complex exhibited excellent in vitro anti-tumor activity against leukemia (HL-60 cell line) comparable to that of cisplatin, inducing cell death by apoptosis with IC50 values in the micromolar range. Data from gel electrophoresis and atomic force microscopy indicate that the complex interacts with DNA, suggesting that its mechanism of action may include DNA as a target. EPR and 51V NMR experiments were also carried out with aged aerated solutions of the complex to get insight into the stability of the complex in solution and the species responsible for the in vitro activities observed. 相似文献
90.
Porto TS Porto CS Cavalcanti MT Filho JL Perego P Porto AL Converti A Pessoa A 《Biotechnology progress》2006,22(6):1637-1642
The kinetic and thermodynamic properties of ascorbate oxidase (AO) activity and stability of a Cucurbita maxima extract were investigated. Activity tests performed at 25 degrees C using initial ascorbic acid concentration in the range 50-750 M allowed estimating the Michaelis constant for this substrate (Km = 126 microM) and the maximum initial rate of ascorbic acid oxidation (A0,max = 1.57 mM min-1). The main thermodynamic parameters of the enzyme reaction (DeltaH* = 10.3 kJ mol-1; DeltaG* = 87.2 kJ mol-1; DeltaS* = -258 J mol-1 K-1) were estimated through activity tests performed at 25-48 C. Within such a temperature range, no decrease in the initial reaction rate was detected. The long-term thermostability of the raw extract was then investigated by means of residual activity tests carried out at 10-70 degrees C, which allowed estimating the thermodynamic parameters of the irreversible enzyme inactivation as well (DeltaH*D = 51.7 kJ mol-1; DeltaG*D = 103 kJ mol-1; S*D = -160 J mol-1 K-1). Taking into account the specific rate of AO inactivation determined at different temperatures, we also estimated the enzyme half-life (1047 min at 10 degrees C and 21.2 min at 70 degrees C) and predicted the integral activity of a continuous system using this enzyme preparation. This work should be considered as a preliminary attempt to characterize the AO activity of a C. maxima extract before its concentration by liquid-liquid extraction techniques. 相似文献