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71.
72.
Early origin of foraminifera suggested by SSU rRNA gene sequences 总被引:11,自引:3,他引:8
Pawlowski J; Bolivar I; Fahrni JF; Cavalier-Smith T; Gouy M 《Molecular biology and evolution》1996,13(3):445-450
Foraminifera are one of the largest groups of unicellular eukaryotes with
probably the best known fossil record. However, the origin of foraminifera
and their phylogenetic relationships with other eukaryotes are not well
established. In particular, two recent reports, based on ribosomal RNA gene
sequences, have reached strikingly different conclusions about
foraminifera's evolutionary position within eukaryotes. Here, we present
the complete small subunit (SSU) rRNA gene sequences of three species of
foraminifera. Phylogenetic analysis of these sequences indicates that they
branch very deeply in the eukaryotic evolutionary tree: later than those of
the amitochondrial Archezoa, but earlier than those of the Euglenozoa and
other mitochondria-bearing phyla. Foraminifera are clearly among the
earliest eukaryotes with mitochondria, but because of the peculiar nature
of their SSU genes we cannot be certain that they diverged first, as our
data suggest.
相似文献
73.
74.
Expression of N-linked sialyl Le(x) determinants and O-glycans in the carbohydrate moiety of human amniotic fluid transferrin during pregnancy 总被引:3,自引:0,他引:3
Transferrin, a glycoprotein involved in iron transport in body fluids, was
isolated from amniotic fluid of a hydramniospatient by sequential
anion-exchange chromatography and gel filtration. The N-glycans of human
amniotic fluid transferrin (hAFT) were enzymatically liberated by PNGase-F
digestion, isolated by gel filtration and fractionated by (high-pH)
anion-exchange chromatography. After alkaline borohydride treatment of
native hAFT, the released O-glycans were isolated by gel filtration and
fractionated by anion-exchange chroma-tography. Structure elucidation of 14
N- and 2 O-glycans was performed by 500 or 600 MHz1H-NMR spectroscopy.
Besides conventional N-glycans established earlier for human serum
transferrin (hST), new (alpha1-3)-fucosylated N- glycans were found,
representing sialyl Le(x) elements. Furthermore, as compared to hST, a
higher degree of (alpha1-6)-fucosylation and an increase in branching from
di- to triantennary compounds has been detected. The presence of O-glycans
is demonstrated for the first time in transferrin.
相似文献
75.
A male cause is responsible in near 50% of infertilities. The radiologist takes place in a multidisciplinary management, after clinical and biological screening, which distinguishes: - excretory infertilities, of which some causes are curable. Transrectal sonography (TRUS) and scrotal sonography are the first tests. In case of epididymal obstacle, scrotal abnormalities may correspond to constitutional or acquired causes; TRUS is normal. TRUS usually identifies congenital bilateral absence of vas deferens; without renal agenesia, a genital form of cystic fibrosis must be evocated. In case of distal obstacles, TRUS may be completed with MRI, especially in case of voluminous cystic tumors. Vasography, which directly shows was deferens patency, is required to accurately diagnose obstruction when ultrasound is not conclusive; vasography must be integrated in a surgical strategy. - secretory azoospermies, from gonadic or hypothalamo-hypophyseal causes. Scrotal sonography may complete clinical examination. When hypothalamo-hypophyseal axis must be explored, MRI is the reference test. - oligo-astheno-teratospermies, where infertilities are often mixed, with various male factors. Three groups must be explored: hyperprolactinemies (MRI); chronic genital infection (ultrasound); varicoceles; Doppler color ultrasound may help to the detection; spermatic phlebography produce a pretherapeutic cartography, and may be the first step of a percutaneous sclerotherapy. 相似文献
76.
Kevin?WhittingstallEmail author Gerhard?Stroink Larry?Gates JF?Connolly Allen?Finley 《Biomedical engineering online》2003,2(1):14
Background
The electroencephalogram (EEG) reflects the electrical activity in the brain on the surface of scalp. A major challenge in this field is the localization of sources in the brain responsible for eliciting the EEG signal measured at the scalp. In order to estimate the location of these sources, one must correctly model the sources, i.e., dipoles, as well as the volume conductor in which the resulting currents flow. In this study, we investigate the effects of dipole depth and orientation on source localization with varying sets of simulated random noise in 4 realistic head models. 相似文献77.
Oliver Beckstein Ekaterina Ivanova Tian Geng Simone Weyand David Drew Joseph Lanigan David J Sharples Mark SP Sansom So Iwata Colin WG Fishwick A Peter Johnson Alexander D Cameron Peter JF Henderson 《The EMBO journal》2014,33(16):1831-1844
The hydantoin transporter Mhp1 is a sodium‐coupled secondary active transport protein of the nucleobase‐cation‐symport family and a member of the widespread 5‐helix inverted repeat superfamily of transporters. The structure of Mhp1 was previously solved in three different conformations providing insight into the molecular basis of the alternating access mechanism. Here, we elucidate detailed events of substrate binding, through a combination of crystallography, molecular dynamics, site‐directed mutagenesis, biochemical/biophysical assays, and the design and synthesis of novel ligands. We show precisely where 5‐substituted hydantoin substrates bind in an extended configuration at the interface of the bundle and hash domains. They are recognised through hydrogen bonds to the hydantoin moiety and the complementarity of the 5‐substituent for a hydrophobic pocket in the protein. Furthermore, we describe a novel structure of an intermediate state of the protein with the external thin gate locked open by an inhibitor, 5‐(2‐naphthylmethyl)‐L‐hydantoin, which becomes a substrate when leucine 363 is changed to an alanine. We deduce the molecular events that underlie acquisition and transport of a ligand by Mhp1. 相似文献
78.
Helen A Arcuri Geraldo FD Zafalon Evandro A Marucci Carlos E Bonalumi Nelson JF da Silveira José M Machado Walter F de AzevedoJr Mário S Palma 《BMC bioinformatics》2010,11(1):12
Background
The functional and structural characterisation of enzymes that belong to microbial metabolic pathways is very important for structure-based drug design. The main interest in studying shikimate pathway enzymes involves the fact that they are essential for bacteria but do not occur in humans, making them selective targets for design of drugs that do not directly impact humans. 相似文献79.
80.
Avise JC; Shapira JF; Daniel SW; Aquadro CF; Lansman RA 《Molecular biology and evolution》1983,1(1):38-56
We address the problem of the possible significance of biological
speciation to the magnitude and pattern of divergence of asexually
transmitted characters in bisexual species. The empirical data for this
report consist of restriction endonuclease site variability in maternally
transmitted mitochondrial DNA (mtDNA) isolated from 82 samples of
Peromyscus polionotus and P. leucopus collected from major portions of the
respective species' ranges. Data are analyzed together with previously
published information on P. maniculatus, a sibling species to polionotus.
Maps of restriction sites indicate that all of the variation observed can
be reasonably attributed to base substitutions leading to loss or gain of
particular recognition sites. Magnitude of mtDNA sequence divergence within
polionotus (maximum approximately equal to 2%) is roughly comparable to
that observed within any of five previously identified mtDNA assemblages in
maniculatus. Sequence divergence within leucopus (maximum approximately
equal to 4%) is somewhat greater than that within polionotus. Consideration
of probable evolutionary links among mtDNA restriction site maps allowed
estimation of matriarchal phylogenies within polionotus and leucopus.
Clustering algorithms and qualitative Wagner procedures were used to
generate phenograms and parsimony networks, respectively, for the
between-species comparisons. Three simple graphical models are presented to
illustrate some conceivable relationships of mtDNA differentiation to
speciation. In theoretical case I, each of two reproductively defined
species (A and B) is monophyletic in matriarchal genealogy; the common
female ancestor of either species can either predate or postdate the
speciation. In case II, neither species is monophyletic in matriarchal
genotype. In case III, species B is monophyletic but forms a subclade
within A which is thus paraphyletic with respect to B. The empirical
results for mtDNA in maniculatus and polionotus appear to conform closely
to case III. These theoretical and empirical considerations raise a number
of questions about the general relationship of the speciation process to
the evolution of uniparentally transmitted traits. Some of these
considerations are presented, and it is suggested that the distribution
patterns of mtDNA sequence variation within and among extant species should
be of considerable relevance to the particular demographies of speciation.
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