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1.
T. Fatima Mitterboeck Sarah J. Adamowicz 《Proceedings. Biological sciences / The Royal Society》2013,280(1767)
The loss of flight ability has occurred thousands of times independently during insect evolution. Flight loss may be linked to higher molecular evolutionary rates because of reductions in effective population sizes (Ne) and relaxed selective constraints. Reduced dispersal ability increases population subdivision, may decrease geographical range size and increases (sub)population extinction risk, thus leading to an expected reduction in Ne. Additionally, flight loss in birds has been linked to higher molecular rates of energy-related genes, probably owing to relaxed selective constraints on energy metabolism. We tested for an association between insect flight loss and molecular rates through comparative analysis in 49 phylogenetically independent transitions spanning multiple taxa, including moths, flies, beetles, mayflies, stick insects, stoneflies, scorpionflies and caddisflies, using available nuclear and mitochondrial protein-coding DNA sequences. We estimated the rate of molecular evolution of flightless (FL) and related flight-capable lineages by ratios of non-synonymous-to-synonymous substitutions (dN/dS) and overall substitution rates (OSRs). Across multiple instances of flight loss, we show a significant pattern of higher dN/dS ratios and OSRs in FL lineages in mitochondrial but not nuclear genes. These patterns may be explained by relaxed selective constraints in FL ectotherms relating to energy metabolism, possibly in combination with reduced Ne. 相似文献
2.
In a variety of tumour systems, individuals carrying progressively growing neoplasms have lymphoid cells with a specific cytotoxic effect on cultured tumour cells from the same individual1–4. Since the sera of tumour-bearing individuals have been shown to prevent tumour cell destruction by immune lymphocytes in vitro2,5–8 and since this serum blocking activity appears early in primary and transplant tumour development5,7, it has been suggested that the appearance of this serum blocking activity might be responsible for the progressive growth of tumours in individuals having cytotoxic lymphocytes. Counteraction of this blocking activity would thus be of primary importance in facilitating the function of an already existing or bolstered cell-mediated immunity. The serum blocking activity might be inhibited in various ways, by preventing the formation of blocking antibody or by interfering with its action (“unblocking”), as demonstrated in Moloney sarcoma regressor sera9. This type of serum also has a therapeutic effect on Moloney sarcomas in vivo10,11, which has been tentatively attributed to its unblocking activity8,9 or, possibly, to a complement-dependent cytotoxicity10. Tumour growth in the Moloney sarcoma system, however, might be due in part to continuous recruitment of neoplastic cells by virus-induced transformation and so the therapeutic effect could be due to a virus-neutralizing serum activity9,10. 相似文献
3.
On the mechanism of ATP-induced shape changes in the human erythrocyte membranes: the role of ATP 下载免费PDF全文
In the preceding paper (Sheetz, M. and S.J. Singer. 1977. J Cell Biol. 73:638-646) it was shown that erythrocyte ghosts undergo pronounced shape changes in the presence of mg-ATP. The biochemical effects of the action of ATP are herein examined. The biochemical effects of the action of ATP are herein examined. Phosphorylation by ATP of spectrin component 2 of the erythrocyte membrane is known to occur. We have shown that it is only membrane protein that is significantly phosphorylated under the conditions where the shape changes are produced. The extent of this phosphorylation rises with increasing ATP concentration, reaching nearly 1 mol phosphoryle group per mole of component 2 at 8mM ATP. Most of this phosphorylation appears to occur at a single site on the protein molecule, according to cyanogen bromide peptide cleavage experiments. The degree of phosphorylation of component 2 is apparently also regulated by a membrane-bound protein phosphatase. This activity can be demonstrated in erythrocyte ghosts prepared from intact cells prelabeled with [(32)P]phosphate. In addition to the phosphorylation of component 2, some phosphorylation of lipids, mainly of phosphatidylinositol, is also known to occur. The ghost shape changes are, however, shown to be correlated with the degree of phosphorylation of component 2. In such experiment, the incorporation of exogenous phosphatases into ghosts reversed the shape changes produced by ATP, or by the membrane-intercalating drug chlorpromazine. The results obtained in this and the preceding paper are consistent with the proposal that the erythrocyte membrane possesses kinase and phosphates activities which produce phosphorylation and dephosphorylation of a specific site on spectrin component 2 molecules; the steady-state level of this phosphorylation regulates the structural state of the spectrin complex on the cytoplasmic surface of the membrane, which in turn exerts an important control on the shape of the cell. 相似文献
4.
5.
Gold salts and phenylbutazone selectively inhibit the synthesis of PGF2α and PGE2 respectively. Lowered production of one prostaglandin species is accompanied by an increased production of the other. Selective inhibition by these drugs was observed in the presence of adrenaline, reduced glutathione and copper sulphate under conditions when most anti-inflammatory compounds inhibited PGE2 and PGF2α syntheses equally. It is postulated that selective inhibitors may have a different mode of action
and beneficial effects may be related to the endogenous ratio of PGE to PGF required for normal function. 相似文献
6.
7.
Cardenas-Navarro R; Adamowicz S; Gojon A; Robin P 《Journal of experimental botany》1999,50(334):625-635
The effects of light and NO3- nutrition on
15NO3- influx in roots were
investigated in young, 19-d-old, induced tomato plants grown at a constant
air and solution temperature of 20C. Nitrate
influx was measured by 15N accumulation for 5 min,
on plants exposed to a wide range of exogenous concentrations, from 10 x
10-3 to 30 mol m-3. Influx
kinetics, fitted to the data following a non-linear procedure, showed
multiphasic patterns. The best fits were obtained when three pure and
non-additive Michaelis-Menten kinetics were applied, with phase transitions
at approximately 0.8 and 4 mol m-3. In plants grown
at 3.0 mol m-3 NO3-, the
asymptotic maximum influx rate (Imax) of each phase
declined during the night until 24 h darkness. At the end of the day
period, about a 2-fold enhancement of Imax was
observed when plants were pretreated for 3 d with 0.2 instead of 3.0 mol
m-3 NO3-. The influx rates
measured at any given NO3- concentration and the
Imax for any phase showed a negative non-linear
correlation with plant nitrate concentration. Furthermore, the results
suggest the existence of a set point, approximately 66 mol
m-3 plant nitrate, for which influx is null at any
given solution nitrate concentration. A model using modified
Michaelis-Menten kinetics is proposed to predict the influx rate as a
function of both solution and plant NO3-
concentrations. 相似文献
8.
This study provides C-value (haploid nuclear DNA content) estimates for 31 species of ladybird beetles (representing 6 subfamilies and 8 tribes), the first such data for the family Coccinellidae. Despite their unparalleled diversity, the Coleoptera have been very poorly studied in terms of genome size variation, such that even this relatively modest sample of species makes the Coccinellidae the third best studied family of beetles, behind the Tenebrionidae and Chrysomelidae. The present study provides a comparison of patterns of genome size variation with these two relatively well-studied families. No correlation was found between genome size and body size in the ladybirds, in contrast to some other invertebrate groups but in keeping with findings for other beetle families. However, there is some indication that developmental time and/or feeding ecology is related to genome size in this group. Some phylogenetic patterns and possible associations with subgenomic features are also discussed. 相似文献
9.
It has long been known that polyploid organisms are more prevalent in arctic than in temperate environments. Past explanations for this geographical trend have focused on the role of glacial cycles in generating polyploids and the influence of abiotic factors in favouring polyploidy in the north. In combination, these mechanisms probably suffice to explain the observed geographical cline in ploidy levels in members of the Daphnia pulex complex in the Holarctic. While only diploid members of the D. pulex complex are found in the temperate regions of North America and Europe, allozyme and DNA quantification analyses indicate that the southern Argentine pulex-complex fauna is dominated by polyploids. Indeed, the present study is the first to document the presence of polyploid members of the D. pulex complex in any temperate climate. The results of phylogeographic analyses suggest that this difference in polyploid distribution between the northern and southern hemispheres is based more on ecological and historical contingencies than direct selection for polyploidy. Specifically, competition with diploid relatives probably limits the lower latitudinal range of polyploids in the north, but appears not to have occurred in Argentina. Because of these differences, the present study provides important insights into the diverse factors that determine the distributions and evolutionary fates of polyploid organisms. 相似文献
10.
Diurnal nitrate uptake in young tomato (Lycopersicon esculentum Mill.) plants: test of a feedback-based model 总被引:3,自引:0,他引:3
A simple model is proposed to describe diurnal net nitrate uptake rate
patterns observed experimentally on young plants grown under constant
non-limiting nutrition. It rests on two hypotheses: net uptake rate is
under negative feedback control by internal plant nitrate content, and
nitrogen metabolism occurs only during the light period. The model
parameters were determined from the results of three independent
experiments performed under non-disturbing conditions in a growth room at
constant air and solution temperatures. Net hourly nitrate uptake rate was
measured through a diurnal cycle and after an extended 28 h period of
darkness. It increased continuously during the light period and decreased
during the dark period. Under prolonged darkness, net uptake declined to an
asymptotic positive uptake rate of about 10-5 mol
h-1 g-1 total plant dry
weight. The measured hourly nitrate uptake rate values were consistent with
independent determinations of long-term nitrate and total N accumulations
in the plant. Realistic simulations of experimental data are achieved with
the proposed model. Furthermore, the maintenance of a positive net uptake
rate, measured in non-growing plants subjected to prolonged darkness, is
explained in the model by the continuous increase of plant water content.
The importance of the diurnal variations of plant water content for nitrate
uptake rate is emphasized and gives consistency to the homeostasis
hypothesis of the model. The diurnal changes in nitrate uptake predicted by
the model are strongly dependent on the assumption made for diurnal changes
in nitrate assimilation. While the purely photosynthetic assumption is
convenient, a more realistic metabolism sub-model is
needed. 相似文献