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排序方式: 共有181条查询结果,搜索用时 15 毫秒
41.
Ashok K Grover Bruce J Forrest Rodger K Buchinski Robert J Cushley 《生物化学与生物物理学报:生物膜》1979,550(2):212-221
The alignment of cholesteryl esters in multilayer phosphatidylcholine membranes was investigated using two spin-labelled cholesteryl esters: 10 : 3 ester () and 1 : 14 ester (). The nitroxide label of is aligned in the membrane with a very large angle of tilt (47° ± 1.5°) with respect to the normal to the membrane surface; does not show such a tilt. gives spectra corresponding to immobilized label while gives nearly isotropic spectra. Ascorbate treatment of the multilayers shows that the labels in and are not present at the phosphatidylcholine-water interphase.The data supports a ‘horseshoe’ configuration for the cholesteryl ester in the bilayer, with both the fatty acid chain and the cholesteryl moiety extending deep into the hydrophobic region of the membrane and with the ester linkage near the surface. 相似文献
42.
43.
Order patterns recurrence plots in the analysis of ERP data 总被引:1,自引:1,他引:0
Recurrence quantification analysis (RQA) is an established tool for data analysis in various behavioural sciences. In this
article we present a refined notion of RQA based on order patterns. The use of order patterns is commonplace in time series
analysis. Exploiting this concept in combination with recurrence plots (RP) and their quantification (RQA) allows for advances
in contemporary EEG research, specifically in the analysis of event related potentials (ERP), as the method is known to be
robust against non-stationary data. The use of order patterns recurrence plots (OPRPs) on EEG data recorded during a language processing experiment exemplifies the potentials of the method. We could show
that the application of RQA to ERP data allows for a considerable reduction of the number of trials required in ERP research
while still maintaining statistical validity. 相似文献
44.
Gary L. Jahns Michael N. Kent Lyle D. Burgoon Nicholas DelRaso Timothy R. Zacharewski Nicholas V. Reo 《Metabolomics : Official journal of the Metabolomic Society》2009,5(2):253-262
Metabolomics offers the potential to assess the effects of toxicants on metabolite levels. To fully realize this potential,
a robust analytical workflow for identifying and quantifying treatment-elicited changes in metabolite levels by nuclear magnetic
resonance (NMR) spectrometry has been developed that isolates and aligns spectral regions across treatment and vehicle groups
to facilitate analytical comparisons. The method excludes noise regions from the resulting reduced spectra, significantly
reducing data size. Principal components analysis (PCA) identifies data clusters associated with experimental parameters.
Cluster-centroid scores, derived from the principal components that separate treatment from vehicle samples, are used to reconstruct
the mean spectral estimates for each treatment and vehicle group. Peak amplitudes are determined by scanning the reconstructed
mean spectral estimates. Confidence levels from Mann–Whitney order statistics and amplitude change ratios are used to identify
treatment-related changes in peak amplitudes. As a demonstration of the method, analysis of 13C NMR data from hepatic lipid extracts of immature, ovariectomized C57BL/6 mice treated with 30 μg/kg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or sesame oil vehicle, sacrificed at 72, 120, or 168 h, identified 152 salient peaks. PCA clustering showed
a prominent treatment effect at all three time points studied, and very little difference between time points of treated animals.
Phenotypic differences between two animal cohorts were also observed. Based on spectral peak identification, hepatic lipid
extracts from treated animals exhibited redistribution of unsaturated fatty acids, cholesterols, and triacylglycerols. This
method identified significant changes in peaks without the loss of information associated with spectral binning, increasing
the likelihood of identifying treatment-elicited metabolite changes. 相似文献
45.
Gene-disease association studies based on case-control designs may often be used to identify candidate polymorphisms (markers) conferring disease risk. If a large number of markers are studied, genotyping all markers on all samples is inefficient in resource utilization. Here, we propose an alternative two-stage method to identify disease-susceptibility markers. In the first stage all markers are evaluated on a fraction of the available subjects. The most promising markers are then evaluated on the remaining individuals in Stage 2. This approach can be cost effective since markers unlikely to be associated with the disease can be eliminated in the first stage. Using simulations we show that, when the markers are independent and when they are correlated, the two-stage approach provides a substantial reduction in the total number of marker evaluations for a minimal loss of power. The power of the two-stage approach is evaluated when a single marker is associated with the disease, and in the presence of multiple disease-susceptibility markers. As a general guideline, the simulations over a wide range of parametric configurations indicate that evaluating all the markers on 50% of the individuals in Stage 1 and evaluating the most promising 10% of the markers on the remaining individuals in Stage 2 provides near-optimal power while resulting in a 45% decrease in the total number of marker evaluations. 相似文献
46.
In many applications, the mean of a response variable can be assumed to be a nondecreasing function of a continuous predictor, controlling for covariates. In such cases, interest often focuses on estimating the regression function, while also assessing evidence of an association. This article proposes a new framework for Bayesian isotonic regression and order-restricted inference. Approximating the regression function with a high-dimensional piecewise linear model, the nondecreasing constraint is incorporated through a prior distribution for the slopes consisting of a product mixture of point masses (accounting for flat regions) and truncated normal densities. To borrow information across the intervals and smooth the curve, the prior is formulated as a latent autoregressive normal process. This structure facilitates efficient posterior computation, since the full conditional distributions of the parameters have simple conjugate forms. Point and interval estimates of the regression function and posterior probabilities of an association for different regions of the predictor can be estimated from a single MCMC run. Generalizations to categorical outcomes and multiple predictors are described, and the approach is applied to an epidemiology application. 相似文献
47.
Evolution of indirect reciprocity by social information: the role of trust and reputation in evolution of altruism 总被引:1,自引:0,他引:1
The complexity of human's cooperative behavior cannot be fully explained by theories of kin selection and group selection. If reciprocal altruism is to provide an explanation for altruistic behavior, it would have to depart from direct reciprocity, which requires dyads of individuals to interact repeatedly. For indirect reciprocity to rationalize cooperation among genetically unrelated or even culturally dissimilar individuals, information about the reputation of individuals must be assessed and propagated in a population. Here, we propose a new framework for the evolution of indirect reciprocity by social information: information selectively retrieved from and propagated through dynamically evolving networks of friends and acquaintances. We show that for indirect reciprocity to be evolutionarily stable, the differential probability of trusting and helping a reputable individual over a disreputable individual, at a point in time, must exceed the cost-to-benefit ratio of the altruistic act. In other words, the benefit received by the trustworthy must out-weigh the cost of helping the untrustworthy. 相似文献
48.
Jürgen Tuchtenhagen Wolfgang Ziegler Alfred Blume 《European biophysics journal : EBJ》1994,23(5):323-335
FT-IR spectroscopy has been used to evaluate the acyl chain conformational ordering of DMPC, DMPE, DMPA (pH 6 and 12), DMPG (pH 1 and 7), and DPPC, DPPE, DPPA (pH 6). The frequencies of the symmetric and antisymmetric methylene stretching vibrations were determined as a function of temperature. In the liquid-crystalline phase the frequencies show a qualitative dependence on the amount of chain disorder. Quantitative data for trans-gauche isomerization were obtained from the integral intensities of the conformation sensitive methylene wagging absorptions at ca. 1368 cm–1 (gtg and gtg sequences), 1356 cm –1 (double gauche) and 1342 cm–1 (end gauche). The integral band intensities were converted to the number of gauche conformers per acyl chain using the calibration factors published by Senak et al. (1991). At 69°C the highest number of gauche conformers excluding contributions from single gauche conformers and jogs (gtttg) are found for PCs (DMPC: 2.6; DPPC: 2.4), followed by DMPG– (2.0), phosphatidylethanolamines (DMPE: 1.4; DPPE: 2.0), protonated DMPG (1.5), and phosphatidic acids (DPPA–: 1.7; DMPA–: 1.4, DMPA2–: 1.7). From 2H-NMR measurements of perdeuterated samples of DMPC, DMPA, DPPC, and DPPA the quadrupolar splittings
Qi
and the order parameter S
CDi
of the CD2-segments close to the chain ends could be determined whereas splittings in the plateau region of the chains could not be resolved. The quadrupolar splittings are affected by trans-gauche isomerization, long axis rotation, and restricted wobbling motions of the acyl chains. In the simplest assumption, the order parameter SCD can be expressed as a product of a segmental order parameter S and a lhain order parameter S
. For comparison of the different lipids we used average order parameters SCD, obtained by averaging over all
values, and S determined from the total number of gauche conformers per chain by FT-IR-spectroscopy, to calculate an empirical average chain order parameter S. The combination of 2H-NMR and FT-IR results allows the estimation of the relative extent of chain wobbling for the different lipid molecules. S is lowest for PCs (S 0.475) while PEs (S 0.51) and PAs (S0.52) show less chain wobbling.Abbreviations FT-IR
Fourier transform infrared
-
2H-NMR
deuterium nuclear magnetic resonance
- DMPC(–d54)
(perdeuterated) dimyristoyl-phosphatidylcholine
- DMPE(–d54)
(perdeuterated) dimyristoyl-phosphatidylethanolamine
- DMPA(–d54)
(perdeuterated) dimyristoyl-phosphatidic acid
- DMPG
dimyristoyl-phosphatidylglycerol
- DPPC(–d62)
(perdeuterated) dipalmitoyl-phosphatidylcholine
- DPPE(–d62)
(perdeuterated) dipalmitoyl-phosphatidylethanolamine
- DPPA(–d62)
(perdeuterated) dipalmitoyl-phosphatidic acid
- gtg
gauche ±-trans-gauche±
- gtg
gauche±-trans-gauche±
- dg
double gauche
- eg
end gauche
Correspondence to: A. Blume 相似文献
49.
In continuation of earlier work, the steady-state fluorescence polarization in a globally oriented system of planar lipid membranes was analyzed experimentally and theoretically for the fluorophores 8-anilino-1-naphthalenesulfonate, 1,6-diphenyl-1,3, 5-hexatriene, dansyllysine-valinomycin and n-(9-anthroyloxy) fatty acids. The theoretical analyses of experiments were mainly done in terms of the mean orientation of transition moments with respect to the membrane normal, an angle describing the region of hindered rotational diffusion and the coefficients of rotational diffusion perpendicular to the membrane and around the membrane normal. The nonvanishing angle between the moments of absorption and emission was taken into account. In the case of n-(9-anthroyloxy) fatty acids it was found that the orientational disorder increases significantly with the depth of the fluorophore within the membrane. In order to compare with recent results from time-dependent fluorescent polarization in globally isotropic membrane suspensions and with 2H-NMR experiments, the second moment ('order parameter') of the steady-state orientational distribution of absorption dipoles was calculated. For all fluorophores the theoretical analysis indicates a preferred orientation of absorption moments within the membrane plane. 相似文献
50.