全文获取类型
收费全文 | 350篇 |
免费 | 14篇 |
国内免费 | 6篇 |
出版年
2022年 | 6篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 9篇 |
2014年 | 7篇 |
2013年 | 9篇 |
2012年 | 7篇 |
2011年 | 9篇 |
2010年 | 8篇 |
2009年 | 17篇 |
2008年 | 14篇 |
2007年 | 16篇 |
2006年 | 12篇 |
2005年 | 14篇 |
2004年 | 9篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 7篇 |
1998年 | 9篇 |
1997年 | 4篇 |
1996年 | 10篇 |
1995年 | 17篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1953年 | 1篇 |
排序方式: 共有370条查询结果,搜索用时 15 毫秒
1.
On blocking rules for the bootstrap with dependent data 总被引:9,自引:0,他引:9
We address the issue of optimal block choice in applicationsof the block bootstrap to dependent data. It is shown that optimalblock size depends significantly on context, being equal ton1/3, n1/4 and n1/5 in the cases of variance or bias estimation,estimation of a onesided distribution function, and estimationof a two-sided distribution function, respectively. A clearintuitive explanation of this phenomenon is given, togetherwith outlines of theoretical arguments in specific cases. Itis shown that these orders of magnitude of block sizes can beused to produce a simple, practical rule for selecting blocksize empirically. That technique is explored numerically. 相似文献
2.
Moment-based criteria for determining bioequivalence 总被引:1,自引:0,他引:1
3.
W. C. Louv Ph. D. 《Biometrical journal. Biometrische Zeitschrift》1987,29(1):81-92
The simultaneous estimation of individual growth curves and a mean growth curve is accomplished by weighted least squares. A polynomial curve is fitted for each individual and the polynomial parameters are linear functions of parameters corresponding to covariates. A simple, computationally efficient variance-covariance estimator is derived. The resultant estimate is used in the weighted least squares estimation. The results are compared to empirical Bayes estimation. 相似文献
4.
5.
J. Crossa C. O. Gardner 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,77(1):33-38
Summary The maize (Zea mays L.) improvement program of the International Maize and Wheat Improvement Center (CIMMYT) develops broad-based maize populations and, until recently, improved all of them through full-sib family selection with international testing. The purpose of this study was to estimate the genetic and genetic × environment variance components for ten of those populations and to measure expected yield improvement from full-sib selection. Mean yield ranged from 3.35–6.81 t ha–1. For five populations the average yield in the last cycle was higher than in the initial cycles. Several populations showed no improvement or yielded less in the final cycle of selection, either because selection intensity was low or because strong selection pressure was applied simultaneously for several traits. Variation resulting from differences among family means within cycles and from interaction between families and locations within cycles were significant in all populations and cycles. Results indicate that variability among full-sib families was maintained throughout the cycles for all populations. The large
ge
2
/
g
2
ratio shown by most populations suggests that yield response per cycle could be maximized if the environments in which progenies are tested were subdivided and classified into similar subsets. The proportion of the predicted response realized in improved yield varied for each population.Journal Paper No. 8640, Nebraska Agric. Res. Div. Project No. 12-159. Research was supported in part by USAID/USDA/ CSRS Research Grant No. 86-CRSR-2-2789 相似文献
6.
J. B. T. M. Roerdink 《Journal of mathematical biology》1989,27(3):309-319
In a previous paper (J. Math. Biol. 26, 199–215 (1988)) we calculated the mean and variance of the long-run geometric growth rate of a discrete-time population model with two age classes in a random environment. The formula which was used in that paper as the starting point for the computation of the variance represents only the contribution of the one-period variances. Here we supplement these results by a calculation of the exact variance. All qualitative conclusions reached before are unaffected. 相似文献
7.
R. Chakraborty 《International Journal of Anthropology》1990,5(1):33-42
Simple heritability estimators of continuous as well as discrete traits from twin data are known to overestimate the degree
of genetic determination of the measured traits for several reasons. Errors of zygosity determination will, however, underestimate
the true heritability. The bias due to wrong assignment of dizygous twin pairs into monozygous type is evaluated here, and
the results indicate that this negative bias has a compensatory effect on the estimate of the degree of genetic determination
when other factors of similarity between twin pairs are taken into account. It is shown that when an estimate of zygosity
error is available, the bias due to this factor can be evaluated quantitatively, and hence the adjustment for zygosity error
can be incorporated in the estimation of the degree of genetic determination of a trait.
Although this theory is explicitly developed here for twin studies, the general principle also applies for other types of
errors of determining the degree of biological relationships for estimation of heritability, in which case this type of error
may be more important than the simple zygosity error. 相似文献
8.
Bhabesh Sen Franklin A. Graybill Naitee Ting 《Biometrical journal. Biometrische Zeitschrift》1992,34(3):259-274
The model considered in this article is the two-factor nested unbalanced variance component model: for p = 1, 2, …, P; q = 1, 2, …, Qp; and r = 1, 2, …, Rpq. The random variables Ypqr are observable. The constant μ is an unknown parameter, and Ap, Bpq and Cpqr are (unobservable) normal and independently distributed random variables with zero means and finite variances σ2A, σ2B, and σ2C, respectively. Approximate confidence intervals on ?A and ?B using unweighted means are derived, where The performance of these approximate confidence intervals are evaluated using computer simulation. The simulated results indicate that these proposed confidence intervals perform satisfactorily and can be used in applied problems. 相似文献
9.
10.
Fifteen common native British plants were each sampled at a range of sites in Great Britain and green tissues analysed for several inorganic nutrients. Sampling criteria are discussed. The inter-site variation of each element within a species is assessed as a frequency distribution of raw data. Sample values of parameters including arithmetic mean, variance (coefficient of variation), skewness and kurtosis are presented. Their stability is assessed from nitrogen in sub-samples of Pteridium. This suggested sample sizes were adequate but some distributions had sufficient kurtosis to affect the variance. These parameters showed distinctions between macro- and micro-elements and between species. Some mean values sharply distinguished between species and may help to assess current theories of strategy and adaptation but a wider range of species is needed to clarify trends. Coefficients of variation are discussed and were relatively low for a nation-wide survey after allowing for sampling constraints. Coefficients of skewness and kurtosis showed two-thirds of the sample distributions were non-normal. Ecological aspects of the distributions are discussed and are relevant to studies along environmental gradients. Published hypotheses linking positive skewness to stress in the field are considered and two other postulates discussed. Distribution bounds such as those confining 95% of the values are discussed in relation to possible critical levels of nutrients.Nomenclature follows Clapham et al. (1981), Excursion flora of the British Isles. 3rd ed. University Press, Cambridge, except Chamaenerion. 相似文献