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1.
2.
Levans produced by four Zymomonas mobilis strains showed antitumour activity against sarcoma 180 and Ehrlich carcinoma in Swiss albino mice. Levans from two strains (ZAP and CP4) had the highest effects. NMR analysis showed that the polymers were composed only of fructose units. The results suggested that the antineoplasic effect is associated to the polysaccharide molecular weight and that a particular molecular weight range may be responsible for this effect. 相似文献
3.
The purpose of this study was to determine the cognitive knowledge and clinical skills related to plastic surgery that are essential for inclusion in an undergraduate curriculum. A questionnaire was distributed to surgical clerkship directors, plastic surgeons, and 1980 graduates of four medical schools. Respondents were asked to rate (0-3) the importance of 74 knowledge items and 28 clinical skills in relation to the knowledge/proficiency necessary for students to achieve prior to graduating from medical school (0 = unnecessary, 3 = indepth knowledge/proficiency important). Results of the questionnaire enabled the determination of mean response scores and the hierarchical ranking of questionnaire items. There was a high degree of correlation between the rankings of the three groups of respondents indicating agreement on knowledge and clinical skills in plastic surgery that are essential, as well as those nonessential, for the competent practice of medicine. 相似文献
4.
Variation in the ribosomal internal transcribed spacers (ITS1 and ITS2) among eight taxa of the Mimulus guttatus species complex 总被引:1,自引:0,他引:1
The internal transcribed spacer region (ITS1 and ITS2) of the 18S-25S
nuclear ribosomal DNA sequence and the intervening 5.8S region were
sequenced from three individuals in each of eight taxa of the Mimulus
guttatus species complex. Three discrete variants, or "types," of ITS
sequences were found, among which 30%-40% of sites differed, compared with
1%-2% within types. Dot plots indicate that these types were not related by
conspicuous rearrangements or inversions. More than one ITS type was often
found in the same taxon, and two of three ITS types span species
boundaries, indicating their presence prior to speciation. These ITS
sequences showed essentially no positional homology with the nearest
sequenced relative, tomato. In contrast, the 5.8S region was relatively
unvaried, with 8 of 162 sites varied in the sample among all eight taxa.
The phylogeny inferred by the most common ITS sequence type, rooted by the
two other ITS types, agreed with isozymes in showing the distinctness of M.
nudatus, M. laciniatus, and M. tilingii from the other five taxa.
相似文献
5.
Variation in heat shock proteins within tropical and desert species of poeciliid fishes 总被引:8,自引:0,他引:8
Norris CE; diIorio PJ; Schultz RJ; Hightower LE 《Molecular biology and evolution》1995,12(6):1048-1062
The 70-kilodalton heat shock protein (hsp70) family of molecular
chaperones, which contains both stress-inducible and normally abundant
constitutive members, is highly conserved across distantly related taxa.
Analysis of this protein family in individuals from an outbred population
of tropical topminnows, Poeciliopsis gracilis, showed that while
constitutive hsp70 family members showed no variation in protein isoforms,
inducibly synthesized hsp70 was polymorphic. Several species of
Poeciliopsis adapted to desert environments exhibited lower levels of
inducible hsp70 polymorphism than the tropical species, but constitutive
forms were identical to those in P. gracilis, as they were in the
confamilial species Gambusia affinis. These differences suggest that
inducible and constitutive members of this family are under different
evolutionary constraints and may indicate differences in their function
within the cell. Also, northern desert species of Poeciliopsis synthesize a
subset of the inducible hsp70 isoforms seen in tropical species. This
distribution supports the theory that ancestral tropical fish migrated
northward and colonized desert streams; the subsequent decrease in
variation of inducible hsp70 may have been due to genetic drift or a
consequence of adaptation to the desert environment. Higher levels of
variability were found when the 30- kilodalton heat shock protein (hsp30)
family was analyzed within different strains of two desert species of
Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In
both cases the distribution of hsp30 isoform diversity was similar to that
seen previously with allozyme polymorphisms.
相似文献
6.
Fertilin alpha (also known as ADAM1) is a member of the ADAM (A disintegrin and A metalloprotease domain) family of proteins. In this study, we examine the mechanism of mouse fertilin alpha's in adhesion of sperm to the egg plasma membrane during fertilization. We find that recombinant forms of fertilin alpha corresponding to either the disintegrin-like domain or the cysteine-rich domain and the EGF-like repeat can perturb sperm-egg binding, suggesting that both of these domains can participate in fertilin alpha-mediated adhesion events. In further examination of the fertilin alpha disintegrin-like domain, we find that a subdomain of disintegrin-like domain with the sequence DLEECDCG outside the putative disintegrin loop but with homology to the fertilin beta disintegrin loop can inhibit the binding of both sperm and recombinant fertilin alpha to eggs, suggesting that this is an adhesion-mediating motif of the fertilin alpha disintegrin-like domain. This sequence also inhibits the binding of recombinant fertilin beta to eggs and thus is the first peptide sequence found to block two different sperm ligands. Finally, a monoclonal antibody to the tetraspanin protein CD9, KMC.8, inhibited the binding of recombinant fertilin alpha to eggs in one type of binding assay, suggesting that, under certain conditions, fertilin alpha may interact with a KMC.8-sensitive binding site on the egg plasma membrane. 相似文献
7.
The BPAG1 locus: Alternative splicing produces multiple isoforms with distinct cytoskeletal linker domains, including predominant isoforms in neurons and muscles 下载免费PDF全文
Bullous pemphigoid antigen 1 (BPAG1) is a member of the plakin family with cytoskeletal linker properties. Mutations in BPAG1 cause sensory neuron degeneration and skin fragility in mice. We have analyzed the BPAG1 locus in detail and found that it encodes different interaction domains that are combined in tissue-specific manners. These domains include an actin-binding domain (ABD), a plakin domain, a coiled coil (CC) rod domain, two different potential intermediate filament-binding domains (IFBDs), a spectrin repeat (SR)-containing rod domain, and a microtubule-binding domain (MTBD). There are at least three major forms of BPAG1: BPAG1-e (302 kD), BPAG1-a (615 kD), and BPAG1-b (834 kD). BPAG1-e has been described previously and consists of the plakin domain, the CC rod domain, and the first IFBD. It is the primary epidermal BPAG1 isoform, and its absence that is the likely cause of skin fragility in mutant mice. BPAG1-a is the major isoform in the nervous system and a homologue of the microtubule actin cross-linking factor, MACF. BPAG1-a is composed of the ABD, the plakin domain, the SR-containing rod domain, and the MTBD. The absence of BPAG1-a is the likely cause of sensory neurodegeneration in mutant mice. BPAG1-b is highly expressed in muscles, and has extra exons encoding a second IFBD between the plakin and SR-containing rod domains of BPAG1-a. 相似文献
8.
Tree species effects on ecosystem water-use efficiency in a high-elevation, subalpine forest 总被引:1,自引:0,他引:1
Russell K. Monson Margaret R. Prater Jia Hu Sean P. Burns Jed P. Sparks Kimberlee L. Sparks Laura E. Scott-Denton 《Oecologia》2010,162(2):491-504
Ecosystem water-use efficiency (eWUE; the ratio of net ecosystem productivity to evapotranspiration rate) is a complex landscape-scale
parameter controlled by both physical and biological processes occurring in soil and plants. Leaf WUE (lWUE; the ratio of
leaf CO2 assimilation rate to transpiration rate) is controlled at short time scales principally by leaf stomatal dynamics and this
control varies among plant species. Little is known about how leaf-scale variation in lWUE influences landscape-scale variation
in eWUE. We analyzed approximately seven thousand 30-min averaged eddy covariance observations distributed across 9 years
in order to assess eWUE in two neighboring forest communities. Mean eWUE was 19% lower for the community in which Engelmann
spruce and subalpine fir were dominant, compared to the community in which lodgepole pine was dominant. Of that 19% difference,
8% was attributed to residual bias in the analysis that favored periods with slightly drier winds for the spruce-fir community.
In an effort to explain the remaining 11% difference, we assessed patterns in lWUE using C isotope ratios. When we focused
on bulk tissue from older needles we detected significant differences in lWUE among tree species and between upper and lower
canopy needles. However, when these differences were scaled to reflect vertical and horizontal leaf area distributions within
the two communities, they provided no power to explain differences in eWUE that we observed in the eddy covariance data. When
we focused only on bulk needle tissue of current-year needles for 3 of the 9 years, we also observed differences in lWUE among
species and in needles from upper and lower parts of the canopy. When these differences in lWUE were scaled to reflect leaf
area distributions within the two communities, we were able to explain 6.3% of the differences in eWUE in 1 year (2006), but
there was no power to explain differences in the other 2 years (2003 and 2007). When we examined sugars extracted from needles
at 3 different times during the growing season of 2007, we could explain 3.8–6.0% of the differences in eWUE between the two
communities, but the difference in eWUE obtained from the eddy covariance record, and averaged over the growing season for
this single year, was 32%. Thus, overall, after accounting for species effects on lWUE, we could explain little of the difference
in eWUE between the two forest communities observed in the eddy covariance record. It is likely that water and C fluxes from
soil, understory plants, and non-needle tissues, account for most of the differences observed in the eddy covariance data.
For those cases where we could explain some of the difference in eWUE on the basis of species effects, we partitioned the
scaled patterns in lWUE into two components: a component that is independent of canopy leaf area distribution, and therefore
only dependent on species-specific differences in needle physiology; and a component that is independent of species differences
in needle physiology, and only dependent on species-specific influences on canopy leaf area distribution. Only the component
that is dependent on species influences on canopy leaf area distribution, and independent of inherent species differences
in needle physiology, had potential to explain differences in eWUE between the two communities. Thus, when tree species effects
are important, canopy structure, rather than species-specific needle physiology, has more potential to explain patterns in
eWUE. 相似文献
9.
Hrubec TC Prater MR Toops KA Holladay SD 《Birth defects research. Part B, Developmental and reproductive toxicology》2006,77(1):1-9
BACKGROUND: Maternal diabetes can induce a number of developmental abnormalities in laboratory animals and humans, including facial deformities and defects in neural tube closure. The incidence of birth defects in newborns of diabetic women is approximately 3-5 times higher than among non-diabetics. In mice, non-specific activation of the maternal immune system can reduce fetal abnormalities caused by diverse etiologies, including diabetes induced neural tube defects. This study was conducted to determine whether non-specific maternal immune stimulation could reduce diabetes-induced craniofacial defects as well. METHODS: Maternal immune function was stimulated before streptozocin (STZ) treatment by maternal footpad injection with Freund's complete adjuvant (FCA), maternal intraperitoneal (i.p.) injection with granulocyte-macrophage colony-stimulating factor (GM-CSF), or maternal i.p. injection with interferon-gamma (IFNgamma). Streptozocin (200 mg/kg i.p.) was used to induce hyperglycemia (26-35 mmol blood glucose) in female ICR mice before breeding. Fetuses from 12-18 litters per treatment group, were collected at Day 17 of gestation. RESULTS: Craniofacial defects were observed in fetuses from all hyperglycemic groups. The incidence of defects was significantly decreased in fetuses from dams immune stimulated with IFNgamma or GM-CSF. The most common defects were reduced maxillary and mandibular lengths. Both were prevented by maternal stimulation with GM-CSF. CONCLUSION: Maternal immune stimulation reduced the incidence of diabetic craniofacial embryopathy. The mechanisms for these protective effects are unknown but may involve maternal or fetal production of cytokines or growth factors that protect the fetus from the dysregulatory effects of hyperglycemia. 相似文献
10.
柠檬酸合酶的分子生物学研究进展 总被引:1,自引:0,他引:1
柠檬酸合酶(citrate synthase,CS)是细胞内多种重要代谢途径的关键酶。CS可催化草酰乙酸和乙酰辅酶A之间的缩合反应生成柠檬酸和辅酶A。通常革兰氏阳性细菌、古菌以及真核细胞的CS为同源二聚体,而革兰氏阴性细菌的CS为同源六聚体。根据其在细胞内的定位不同,CS可分为线粒体CS、乙醛酸循环体CS、过氧化物酶体CS。这些同工酶在能量代谢、植物脂肪的代谢、脂肪酸的氧化及细胞解毒过程中起着重要作用。不同来源的CS空间结构、催化机制和动力学性质十分相似。针对其生化特性、空间结构特点、催化机制以及分子进化等研究进展进行综述。 相似文献