全文获取类型
收费全文 | 384篇 |
免费 | 25篇 |
学科分类
生物科学 | 409篇 |
出版年
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 7篇 |
2015年 | 14篇 |
2014年 | 18篇 |
2013年 | 23篇 |
2012年 | 15篇 |
2011年 | 17篇 |
2010年 | 25篇 |
2009年 | 26篇 |
2008年 | 15篇 |
2007年 | 13篇 |
2006年 | 14篇 |
2005年 | 13篇 |
2004年 | 14篇 |
2003年 | 4篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 10篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 16篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1971年 | 2篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1958年 | 1篇 |
1933年 | 1篇 |
1931年 | 2篇 |
1930年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有409条查询结果,搜索用时 390 毫秒
1.
Nucleotide sequence analysis of alpha-amylase and thiol protease genes that are hormonally regulated in barley aleurone cells. 总被引:13,自引:3,他引:10 下载免费PDF全文
We have determined the nucleotide sequences of Amy32b, a type A alpha-amylase gene, and of the gene for aleurain, a thiol protease closely related to mammalian cathepsin H. Both are expressed in barley aleurone cells under control of the plant hormones gibberellic acid and abscisic acid, but only aleurain is expressed at high levels in other barley tissues. Sequence analysis indicates that the 5' end of the aleurain gene, comprising 3 exons and 2 introns, may have become associated with the remainder of the gene, encoding the protease domain of the protein, by some sort of recombination event. This 5' domain of the gene is very G + C-rich and is flanked by inverted repetitive sequences. We found two different groups of homologous sequence elements. The first group consists of four blocks of sequences conserved in the same spatial arrangement in both genes; these are arranged at similar intervals upstream from the Amy32b TATA box and from a TATA box present in intron 3 of aleurain, outside of the 5' domain and upstream from the protease domain. A part of two of these conserved sequences is similar to the core sequence of certain enhancer elements characterized from mammalian cells. The second group of homologous elements is present in the upstream region of both genes. We speculate that these conserved sets of sequences may have some role in either the tissue specificity of expression of the genes or in some part of the hormonal regulation imposed on them. 相似文献
2.
Junzou Hiratsuka Hiroaki Shimada Robert Whittier Takashi Ishibashi Masahiro Sakamoto Masao Mori Chihiro Kondo Yasuko Honji Chong-Rong Sun Bing-Yuan Meng Yu-Qing Li Akira Kanno Yoko Nishizawa Atsushi Hirai Kazuo Shinozaki Masahiro Sugiura 《Molecular & general genetics : MGG》1989,217(2-3):185-194
Summary The entire chloroplast genome of the monocot rice (Oryza sativa) has been sequenced and comprises 134525 bp. Predicted genes have been identified along with open reading frames (ORFs) conserved
between rice and the previously sequenced chloroplast genomes, a dicot, tobacco (Nicotiana tabacum), and a liverwort (Marchantia polymorpha). The same complement of 30 tRNA and 4 rRNA genes has been conserved between rice and tobacco. Most ORFs extensively conserved
betweenN. tabacum andM. polymorpha are also conserved intact in rice. However, several such ORFs are entirely absent in rice, or present only in severely truncated
form. Structural changes are also apparent in the genome relative to tobacco. The inverted repeats, characteristic of chloroplast
genome structure, have expanded outward to include several genes present only once per genome in tobacco and liverwort and
the large single copy region has undergone a series of inversions which predate the divergence of the cereals. A chimeric
tRNA pseudogene overlaps an apparent endpoint of the largest inversion, and a model invoking illegitimate recombination between
tRNA genes is proposed which accounts simultaneously for the origin of this pseudogene, the large inversion and the creation
of repeated sequences near the inversion endpoints. 相似文献
3.
A quantitative analysis of the relationship between pseudocopulatory behaviour and the ovarian cycle in the parthenogenetic lizard Cnemidophorus uniparens indicates (1) that this behaviour is frequently and regularly expressed by captive individuals, and (2) that the sexual role, either male-like or female-like, exhibited by an animal is correlated with its ovarian state. The expression of female-like behaviour patterns was associated with and primarily limited to the vitellogenic stage of the cycle. Male-like behaviour patterns occurred most frequently during post-ovulatory stages but was not limited to these stages. Neither behavioural role was ever expressed by non-reproductive individuals. Reproductive individuals often alternated in assuming the female-like and male-like roles during the progress of the ovarian cycle. These observations suggest that pseudosexual behaviour is hormonally activated in this species. However, it also appears that the prevailing social situation is an important factor determining which behavioural role is taken. This work strengthens the hypothesis that pseudosexual behaviour in all-female lizards occurs as the result of natural selection. 相似文献
4.
5.
6.
Plasma levels of prostaglandin F2α (PGF2α) in female red-sided garter snakes (
) were measured at intervals after mating or exposure to males. PGF2α levels increased significantly within 15 minutes of mating and peaked 6–24 hr after mating. Females that did not mate, but received similar amounts of male courtship, had levels of PGF2α significantly lower than those of females that mated. These results extend previous findings that unmated female garter snakes injected with PGF2α exhibit sexual behavior characteristics of females that have mated. Together these data indicate that female garter snakes elaborate PGF2α in response to stimuli associated with mating and that PGF2α has a functional role in inducing post-mating declines in sexual behavior of this species. 相似文献
Full-size image (<1K)
7.
8.
9.
The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
相似文献
10.
D. Smith Y. Yanai Y.-G. Liu S. Ishiguro K. Okada D. Shibata R.F. Whittier N.V. Fedoroff 《The Plant journal : for cell and molecular biology》1996,10(4):721-732
The transposition patterns of the Ds —GUS transposon T-DNA in 23 independent single-copy lines have been characterized and the map positions of 10 of them on three of the five Arabidopsis chromosomes are reported. Using overexpressed Activator ( Ac ) elements as a transposase source, it was found that the primary determinant of transposition frequency is the insertion site of the Ac -T-DNA. Neither the structure of the transposon T-DNA nor, in most cases, its insertion site have a significant effect on transposition frequency. Both the frequency and timing of transposition are influenced by the parent through which the transposon and transposase T-DNAs are transmitted. Overall, nearly 75% of plants in which excision has occurred bear a reinserted element and very short-range transpositions predominate, underlining the advantage of using mapped transposons for insertional mutagenesis. 相似文献