全文获取类型
收费全文 | 1374篇 |
免费 | 176篇 |
国内免费 | 42篇 |
出版年
2024年 | 3篇 |
2023年 | 54篇 |
2022年 | 34篇 |
2021年 | 68篇 |
2020年 | 56篇 |
2019年 | 72篇 |
2018年 | 52篇 |
2017年 | 65篇 |
2016年 | 62篇 |
2015年 | 70篇 |
2014年 | 78篇 |
2013年 | 78篇 |
2012年 | 69篇 |
2011年 | 65篇 |
2010年 | 53篇 |
2009年 | 58篇 |
2008年 | 84篇 |
2007年 | 79篇 |
2006年 | 68篇 |
2005年 | 58篇 |
2004年 | 49篇 |
2003年 | 48篇 |
2002年 | 25篇 |
2001年 | 32篇 |
2000年 | 24篇 |
1999年 | 35篇 |
1998年 | 19篇 |
1997年 | 15篇 |
1996年 | 15篇 |
1995年 | 13篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有1592条查询结果,搜索用时 15 毫秒
1.
Parvinder Kaur 《Biometrical journal. Biometrische Zeitschrift》1985,27(1):107-110
For the estimation of population mean in simple random sampling, an efficient regression-type estimator is proposed which is more efficient than the conventional regression estimator and hence than mean per unit estimator, ratio and product estimators and many other estimators proposed by various authors. Some numerical examples are included for illustration. 相似文献
2.
D. BERNER 《Journal of evolutionary biology》2009,22(12):2563-2565
Testing for an association between the leading vectors of multivariate trait (co)variation within populations (the ‘line of least resistance’) and among populations is an important tool for exploring variational bias in evolution. In a recent study of stickleback fish populations, a bootstrap‐based test was introduced that takes into account estimation error in both vectors and hence improves the previously available bootstrap method. Because this test was implemented incorrectly, however, I here describe the correct test protocol and provide a reanalysis of the original data set. The application of this new test protocol should improve future investigations of evolution along lines of least resistance and other vector comparisons. 相似文献
3.
4.
Aiyi Liu James F. Troendle Kai F. Yu Vivian W. Yuan 《Biometrical journal. Biometrische Zeitschrift》2004,46(6):760-768
We consider estimation after a group sequential test. An estimator that is unbiased or has small bias may have substantial conditional bias (Troendle and Yu, 1999, Coburger and Wassmer, 2001). In this paper we derive the conditional maximum likelihood estimators of both the primary parameter and a secondary parameter, and investigate their properties within a conditional inference framework. The method applies to both the usual and adaptive group sequential test designs. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
Summary We examined the codon usages in wellconserved and less-well-conserved regions of vertebrate protein genes and found them to be similar. Despite this similarity, there is a statistically significant decrease in codon bias in the less-well-conserved regions. Our analysis suggests that although those codon changes initially fixed under amino acid replacements tend to follow the overall codon usage pattern, they also reduce the bias in codon usage. This decrease in codon bias leads one to predict that the rate of change of synonymous codons should be greater in those regions that are less well conserved at the amino acid level than in the better-conserved regions. Our analysis supports this prediction. Furthermore, we demonstrate a significantly elevated rate of change of synonymous codons among the adjacent codons 5 to amino acid replacement positions. This provides further support for the idea that there are contextual constraints on the choice of synonymous codons in eukaryotes. 相似文献
6.
L. P. Jones W. A. Compton 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1985,70(3):318-321
Summary The use of several S1 individuals to represent an S0 individual permits the use of a Design II mating scheme for plants with only one pistillate flower per plant. Estimates of additive (V
A
) and dominance (V
D
) variance from this mating scheme will be biased upwards, when a small number (10) of individuals of each S1 line are used. This bias can be computed, and the additive and dominance estimates can be corrected. Of particular interest is the observation that the additive genetic variance contributes to bias in estimates of V
D
. When S0 plants are non inbred and their selfedprogeny (S1 lines) are used to represent them in developing families for use in the Design II,
where m1 is the number of individuals used to represent an S1 line in developing half sib-families and m2 is the number of individuals used to represent the S1 line in making up full sib-families. For example, in a 3×3 Design II, with about 10 individuals used to represent each S1 line in each cross, m2 = 10 and m1 = 30. When m1 = m2 = 1,
and
Joint contribution from Department of Agronomy, University of Nebraska 68583, and the S. S. Cameron Laboratory, Werribee, Victoria 3030, Australia. Published as paper No. 7395, Journal Series 相似文献
7.
8.
Christian Tessier Gian-Paolo Rossini Jean-François Pageaux Hélène Cohen Michel Lagarde Christian Laugier Jean-Michel Fayard 《FEBS letters》1996,390(3):311-314
Rat uterine stromal cells (UIII) express pancreatic type PLA2 (PLA2-I) receptor and internalize the enzyme bound to receptors. Here, we investigate the proliferating effect and alterations in binding of PLA2-I. There is a dramatic decline in PLA2-I binding in UIII cells as they progress from a nonconfluent proliferating state (40,000 sites/cell) to a confluent state (1300 sites/cell). Intracellular concentration of PLA2-I changed with the alteration in binding, suggesting that regulation in the PLA2 binding capacity may have important implications in growth control mechanisms. 相似文献
9.
小鼠胚胎与子宫单层上皮细胞共培养的研究 总被引:11,自引:0,他引:11
本文报道建立了小鼠胚胎与小鼠子宫单层上皮细胞体外共培养系统。结果揭示;小鼠胚胎与 子宫单层上皮细胞共培养可以促进胚胎的发育、粘附和扩展;如果培养液中加入 3、67 × 10-6mol/L 17β-雌二醇,可以显著提高胚胎在共培养系统中的发育率、粘附率和扩展率。以上结果表明:小鼠 胚胎与小鼠子宫单层上皮细胞共培养系统是研究胚泡着床机理较理想的研究手段。 相似文献
10.
Phylogenetic relationships of the garter snakes based on DNA sequence and allozyme variation 总被引:1,自引:0,他引:1
ALAN DE QUEIROZ ROBIN LAWSON 《Biological journal of the Linnean Society. Linnean Society of London》1994,53(3):209-229
We estimated phylogenetic relationships among 26 species of garter snakes (genus Thamnophis ) using allozyme and mitochondrial cytochrome b gene nucleotide sequence variation. Parsimony analyses of the two data sets give substantially different estimates of phylogeny. Several lines of evidence indicate that much of this conflict is due to error associated with the restricted number of characters in each data set. Such sampling error may be reduced by combining all the characters; we therefore present an estimate of phylogeny based on parsimony analysis of all the data combined. All our analyses support several conclusions in conflict with previous views: a very distant relationship between T.errans and T. elegans , non-monophyly of the elegans group (even excluding T: errans ), and nesting of the form validus (previously considered a member of the genus Nerodia ) within Thamnophis.
The combined analysis gives an almost fully resolved tree. However, bootstrapping indicates only weak support for many clades in this tree. Furthermore, paraphyly of the assemblages of cytochrome b gene lineages within T. elegans and T. radix indicate the potential for discordance between the mitochondrial DNA (mtDNA) and species phylogenies through the sorting of ancestral mtDNA polymorphisms. These problems suggest the need for assaying additional characters, especially ones likely to be independent of those used in the present study. 相似文献
The combined analysis gives an almost fully resolved tree. However, bootstrapping indicates only weak support for many clades in this tree. Furthermore, paraphyly of the assemblages of cytochrome b gene lineages within T. elegans and T. radix indicate the potential for discordance between the mitochondrial DNA (mtDNA) and species phylogenies through the sorting of ancestral mtDNA polymorphisms. These problems suggest the need for assaying additional characters, especially ones likely to be independent of those used in the present study. 相似文献