全文获取类型
收费全文 | 319篇 |
免费 | 11篇 |
国内免费 | 4篇 |
出版年
2018年 | 2篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 13篇 |
2012年 | 9篇 |
2011年 | 9篇 |
2010年 | 14篇 |
2009年 | 17篇 |
2008年 | 5篇 |
2007年 | 6篇 |
2006年 | 8篇 |
2005年 | 2篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 15篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1972年 | 6篇 |
1971年 | 4篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1960年 | 2篇 |
1959年 | 6篇 |
1958年 | 16篇 |
1957年 | 14篇 |
1956年 | 10篇 |
1955年 | 16篇 |
1954年 | 12篇 |
1953年 | 8篇 |
1952年 | 15篇 |
1951年 | 8篇 |
1950年 | 5篇 |
1949年 | 6篇 |
1948年 | 8篇 |
1946年 | 3篇 |
排序方式: 共有334条查询结果,搜索用时 670 毫秒
271.
Comparison of the effects of concentration, pH and anion species on astringency and sourness of organic acids 总被引:4,自引:1,他引:3
The separate effects of concentration, pH and anion species on intensity of
sourness and astringency of organic acids were evaluated. Judges rated
sourness and astringency intensity of lactic, malic, tartaric and citric
acid solutions at three levels of constant pH varying in normality and at
three levels of constant concentration varying in pH. To assess the
comparative sourness and astringency of the organic acid anions of study,
binary acid solutions matched in pH and titratable acidity were also rated.
As pH was decreased in equinormal solutions, both sourness and astringency
increased significantly (P < 0.001). By contrast, as the normality of
the equi-pH solutions was increased, only sourness demonstrated significant
increases (P < 0.001) while astringency remained constant or decreased
slightly. At the lowest normality tested, all solutions were more
astringent than sour (P < 0.05). Although lactic acid was found to be
significantly more sour than citric acid (P < 0.05), no other sourness
or astringency differences among the organic acid anions were noted. This
study demonstrates for the first time that astringency elicited by acids is
a function of pH and not concentration or anion species, and confirms that
sourness is independently influenced by concentration, pH and anion species
of the acid.
相似文献
272.
273.
Deuterostome phylogeny and the sister group of the chordates: evidence from molecules and morphology 总被引:13,自引:3,他引:10
Complete coding regions of the 18S rRNA gene of an enteropneust
hemichordate and an echinoid and ophiuroid echinoderm were obtained and
aligned with 18S rRNA gene sequences of all major chordate clades and four
outgroups. Gene sequences were analyzed to test morphological character
phylogenies and to assess the strength of the signal. Maximum- parsimony
analysis of the sequences fails to support a monophyletic Chordata; the
urochordates form the sister taxon to the hemichordates, and together this
clade plus the echinoderms forms the sister taxon to the cephalochordates
plus craniates. Decay, bootstrap, and tree-length distribution analyses
suggest that the signal for inference of dueterostome phylogeny is weak in
this molecule. Parsimony analysis of morphological plus molecular
characters supports both monophyly of echinoderms plus enteropneust
hemichordates and a sister group relationship of this clade to chordates.
Evolutionary parsimony does not support chordate monophyly.
Neighbor-joining, Fitch-Margoliash, and maximum-likelihood analyses support
a chordate lineage that is the sister group to an
echinoderm-plus-hemichordate lineage. The results illustrate both the
limitations of the 18S rRNA molecule alone for high- level phylogeny
inference and the importance of considering both molecular and
morphological data in phylogeny reconstruction.
相似文献
274.
ERVIN ÁRNYAS JUDIT BERECZKI ANDREA TÓTH KATALIN VARGA KATALIN PECSENYE ANDRÁS TARTALLY GYÖRGY KÖVICS DÓRA KARSA ZOLTÁN VARGA 《Ecological Entomology》2009,34(1):90-97
Abstract 1. The influence of infestation of the larval host plant Gentiana cruciata on the egg‐laying preferences of the xerophilous ecotype of Alcon Blue butterfly (Maculinea alcon) was studied in a semi‐dry grassland area (Aggtelek Karst Region, Northern Hungary). 2. We examined whether oviposition patterns of females differed when G. cruciata stems were uninfested compared with when they were infested by an aphid (Aphis gentianae) or a rust (Puccinia gentianae) species. 3. Females laid more than 90% of their eggs on fertile, uninfested G. cruciata stems, although these stems comprised only ~ 50% of the total stems available. Stems infested by aphids were similar to uninfested ones in properties that had a strong correlation with egg numbers, and yet there were significantly fewer eggs on infested stems than on intact ones. 4. Females never laid eggs on parts of Gentiana stems infested by aphids, and the presence of Lasius paralienus ants, which have a mutualistic interaction with Aphis gentianae, did not increase the repulsive effect of aphids. Infection of Gentiana by Puccinia did not influence the egg‐laying behaviour of females, even though the flowers and buds of infested stems exhibited a delayed development. 5. Aphid infestation can influence butterfly oviposition patterns through both direct and indirect effects. The presence of aphids directly excluded oviposition, but our data also indicated the possibility of an indirect effect of aphid infestation. Stems that had no aphids at the last egg counting, but were infested prior to it, had significantly fewer eggs than those that were never infested. 相似文献
275.
CHRISTOPHE PAMPOULIE MAGNÚS ÖRN STEFÁNSSON THÓRA DÖGG JÖRUNDSDÓTTIR BRET S. DANILOWICZ ANNA KRISTÍN DANÍELSDÓTTIR 《Biological journal of the Linnean Society. Linnean Society of London》2008,94(2):315-329
Most studies of the genetic structure of Atlantic cod have focused on small geographical scales. In the present study, the genetic structure of cod sampled on spawning grounds in the North Atlantic was examined using eight microsatellite loci and the Pan I locus. A total of 954 cod was collected from nine different regions: the Baltic Sea, the North Sea, the Celtic Sea, the Irish Sea and Icelandic waters during spring 2002 and spring 2003, from Norwegian waters and the Faroe Islands (North and West spawning grounds) in spring 2003, and from Canadian waters in 1998. Temporal stability among spawning grounds was observed in Icelandic waters and the Celtic Sea, and no significant difference was observed between the samples from the Baltic Sea and between the samples from Faroese waters. F -statistics showed significant differences between most populations and a pattern of isolation-by-distance was described with microsatellite loci. The Pan I locus revealed the presence of two genetically distinguishable basins, the North-west Atlantic composed of the Icelandic and Canadian samples and the North-east Atlantic composed of all other samples. Permutation of allele sizes at each microsatellite locus among allelic states supported a mutational component to the genetic differentiation, indicating a historical origin of the observed variation. Estimation of the time of divergence was approximately 3000 generations, which places the origin of current genetic pattern of cod in the North Atlantic in the late Weichselian (Wisconsinian period), at last glacial maximum. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 315–329. 相似文献
276.
277.
278.
279.
280.