全文获取类型
收费全文 | 79篇 |
免费 | 4篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2017年 | 1篇 |
2015年 | 3篇 |
2014年 | 1篇 |
2013年 | 1篇 |
2012年 | 5篇 |
2011年 | 1篇 |
2010年 | 2篇 |
2009年 | 5篇 |
2008年 | 2篇 |
2007年 | 3篇 |
2006年 | 2篇 |
2005年 | 2篇 |
2003年 | 2篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1969年 | 1篇 |
1968年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有83条查询结果,搜索用时 312 毫秒
21.
R Podstawski DJ Choszcz S Konopka J Klimczak M Starczewski 《Biology of sport / Institute of Sport》2014,31(4):315-321
The aim of the study was to evaluate anthropometric characteristics as determinants of 500 m rowing ergometer performance in physically inactive collegiate females. In this cross-sectional study, which included 196 collegiate females aged 19-23 years not participating in regular physical activities, body mass (BM), body height (BH), length of upper limbs (LA), length of lower limbs (LL), body mass index (BMI), slenderness index (SI), and the Choszcz-Podstawski index (CPI) were measured and a stepwise multiple regression analysis was performed. Participants performed 500 m maximal effort on a Concept II rowing ergometer. BM, BH, LA, LL, and the BMI, SI and CPI indices were found to be statistically significant determinants of 500 m performance. The best results (T) were achieved by females whose BH ranged from 170 to 180 cm, with LA and LL ranging from 75 to 80 cm and 85 to 90 cm, respectively. The best fitting statistical model was identified as: T = 11.6793 LR – 0.1130 LR2 – 0.0589 LN2 + 29.2157 CPI2 + 0.1370 LR·LN - 2.6926 LR·CPI – 211.7796. This study supports a need for additional studies focusing on understanding the importance of anthropometric differences in rowing ergometer performance, which could lead to establishing a better quality reference for evaluation of cardiorespiratory fitness tested using a rowing ergometer in collegiate females. 相似文献
22.
23.
Evolution at the tip and base of the X chromosome in an African population of Drosophila melanogaster 总被引:1,自引:0,他引:1
Hitchhiking effects of advantageous mutations have been invoked to explain
reduced polymorphism in regions of low crossing-over in Drosophila. Besides
reducing DNA heterozygosity, hitchhiking effects should produce strong
linkage disequilibrium and a frequency spectrum skewed toward an excess of
rare polymorphisms (compared to the neutral expectation). We measured DNA
polymorphism in a Zimbabwe population of D. melanogaster at three loci,
yellow, achaete, and suppressor of forked, located in regions of reduced
crossing-over. Similar to previously published surveys of these genomic
regions in other populations, we observed low levels of nucleotide
variability. However, the frequency spectrum was compatible with a neutral
model, and there was abundant evidence for recombination in the history of
the yellow and ac genes. Thus, some aspects of the data cannot be accounted
for by a simple hitchhiking model. An alternative hypothesis, background
selection, might be compatible with the observed patterns of linkage
disequilibrium and the frequency spectrum. However, this model cannot
account for the observed reduction in nucleotide heterozygosity. Thus,
there is currently no satisfactory theoretical model for the data from the
tip and base of the X chromosome in D. melanogaster.
相似文献
24.
Oligogalacturonic acids (OGAs), derived from plant cell wall pectin, have
been implicated in a number of signal transduction pathways involved in
growth, development and defense responses of higher plants. This study
investigates the size range of OGAs capable of inducing ethylene synthesis
in tomato plants, and demonstrates that in contrast with many other
effects, only short chain OGAs are active. Oligomers across a range of DP
from 2-15 were separated and purified to homogeneity by QAE-Sephadex anion
exchange chromatography using a novel elution system. The OGAs were applied
to tomato plants and assayed for their ability to induce ethylene gas
release and changes in steady state levels of mRNA encoding the ethylene
forming enzyme aminocyclopropane-1-carboxylic acid oxidase (ACO). The study
demonstrated that only OGAs in the size range of DP4-6 were active both in
eliciting ACO expression and in the production of ethylene.
相似文献
25.
A change in twist of actin provides the force for the extension of the acrosomal process in limulus sperm: the false-discharge reaction 总被引:6,自引:5,他引:1 下载免费PDF全文
One of the most spectacular motions is the generation of the acrosomal process in the limulus sperm. On contact with the egg, the sperm generates a 60-mum-long process that literally drills its way through the jelly surrounding the egg. This irresversible reaction takes only a few seconds. We suggested earlier that this motion is driven by a change in twist of the actin filaments comprising the acrosomal process. In this paper we analyze the so-called false discharge, a reversible reaction, in which the acrosomal filament bundle extends laterally from the base of the sperm and not anteriorly from the apex. Unlike the true discharge, which is straight, the false discharge is helical. Before extension, the filament bundle is coiled about the base of the sperm. In the coil, the bundle is not smoothly bent but consists of arms (straight segments) and elbows (corners) so that the coil looks like a 14-sided polygon. The extension of the false discharge works as follows: starting at the base of the bundle, the filaments change their twist which concomitantly changes the orientations of the elbows relative to each other; that is, in the coil, the elbows all like in a common plane, but after the change in twist, the plane of each elbow is rotated to be perpendicular to that of its neighbors. This change transforms the bundle from a compact coil into an extended left- handed helix. Because the basal end of the bundle is unconstrained, the extension is lateral. The true discharge works the same way but starts at the apical end of the bundle. The apical end, however, is constrained by its passage through the nuclear canal, which directs the extention anteriorly. Unlike the false discharge, during the true discharge the elbows are melted out, making the reaction irreversible. This study shows that rapid movement can be regenerated by actin without myosin and gives us insight into the molecular mechanism. 相似文献
26.
T.J. McDonald M.A. Ghatei S.R. Bloom N.S. Track J. Radziuk J. Dupre V. Mutt 《Regulatory peptides》1981,2(5):293-304
The effect on plasma gastroenteropancreatic hormone levels on infusing the porcine gastrin-releasing peptide and bombesin into dogs demonstrated no qualitative difference in the spectrum of activity of the two peptides. Sustained elevations in plasma immunoreactive gastrin, pancreatic polypeptide, enteroglucagon, gastric inhibitory polypeptide, pancreatic glucagon and transient elevations in plasma insulin were seen during infusions of both peptides. The similar spectrum of activities and the structural homology between the two peptides suggests that the porcine gastrin releasing peptide is the porcine counterpart of the amphibian peptide bombesin. 相似文献
27.
Osmotic properties of human lymphocyte 总被引:1,自引:0,他引:1
The osmotic properties of human lymphocytes isolated from 15 ml of venous blood were examined. Measurements of the permeability of the membrane to water under an osmotic gradient were also made. The Boyle-Van't Hoff relation held very well for the human lymphocyte when the cells were shrunken in hyperosmotic media to concentrations twice isosmotic. The volume of osmotically inactive material or "b" value averaged 32% of the mean corpuscular volume. These values were independent of temperature. Ponder's R ranged between 0.8 and 0.9. The average value for Lp, the hydralic coefficient was 0.46 mu/min atm +/- 0.02 (S.E.M.) at 25 degrees C. No significant effect of age, sex, or race was noted. The effect of temperature between 10 degrees C and 37 degrees C was measured and heats of activation between 11.1 and 17.4 kcal/mole were calculated with a mean of 14.1 kcal/mole +/- 1.6 (S.E.M.). Concanavalin A at 10 microgram/1.5 X 10(6) lymphocytes produced blastogenesis of 25% or more of the lymphocytes without clumping, agglutination, or toxicity. The mean corpuscular volume increased by 21% after 72 hours due to an increase in the "b" value which increased by 80%. The volume of free water remained constant. Histograms of the distribution of cell volumes showed that volume changes were uniform throughout the population with no evidence of agglutination of clumping. The significance of these results is discussed in the context of membrane fluidity and the state of intracellular water. 相似文献
28.
29.
P K Lauf N C Adragna N Dupre J P Bouchard G A Rouleau 《Biochimie et biologie cellulaire》2006,84(6):1034-1044
Red blood cells (RBCs) possess the K-Cl cotransport (KCC) isoforms 1, 3, and 4. Mutations within a given isoform may affect overall KCC activity. In a double-blind study, we analyzed, with Rb as a K congener, K fluxes (total flux, ouabain-sensitive Na+/K+ pump, and bumetanide-sensitive Na-K-2Cl cotransport, Cl-dependent, and ouabain- and bumetanide-insensitive KCC with or without stimulation by N-ethylmaleimide (NEM) and staurosporine or Mg removal, and basal channel-mediated fluxes, osmotic fragility, and ions and water in the RBCs of 8 controls, and of 8 patients with hereditary motor and sensory neuropathy with agenesis of corpus callosum (HMSN-ACC) with defined KCC3 mutations (813FsX813 and Phe529FsX532) involving the truncations of 338 and 619 C-terminal amino acids, respectively. Water and ion content and, with one exception, mean osmotic fragility, as well as K fluxes without stimulating agents, were similar in controls and HMSN-ACC RBCs. However, the NEM-stimulated KCC was reduced 5-fold (p < 0.0005) in HMSN-ACC vs control RBCs, as a result of a lower Vmax (p < 0.05) rather than a lower Km (p = 0.109), accompanied by corresponding differences in Cl activation. Low intracellular Mg activated KCC in 6 out of 7 controls vs 1 out of 6 HMSN-ACC RBCs, suggesting that regulation is compromised. The lack of differences in staurosporine-activated KCC indicates different action mechanisms. Thus, in HMSN-ACC patients with KCC3 mutants, RBC KCC activity, although indistinguishable from that of the control group, responded differently to biochemical stressors, such as thiol alkylation or Mg removal, thereby indirectly indicating an important contribution of KCC3 to overall KCC function and regulation. 相似文献
30.