全文获取类型
收费全文 | 433篇 |
免费 | 28篇 |
出版年
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 10篇 |
2017年 | 4篇 |
2016年 | 12篇 |
2015年 | 21篇 |
2014年 | 18篇 |
2013年 | 32篇 |
2012年 | 26篇 |
2011年 | 19篇 |
2010年 | 28篇 |
2009年 | 28篇 |
2008年 | 27篇 |
2007年 | 19篇 |
2006年 | 14篇 |
2005年 | 14篇 |
2004年 | 14篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 16篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有461条查询结果,搜索用时 31 毫秒
1.
Frank Arnal Lucien J. Coté Sara Ginsburg Glen D. Lawrence Ali Naini Mary Sano 《Neurochemical research》1990,15(6):587-591
We have synthesized the tertiary amines of pyridostigmine and neostigmine, 3-pyridinol dimethylcarbamate (norpyridostigmine) and 3-dimethylaminophenol dimethylcarbamate (norneostigmine) respectively, and we have tested their abilities to cross the blood-brain barrier and inhibit mouse brainAChE activity. The in vivo inhibition of AChE activity by norpyridostigmine reaches 72% at 10 minutes which is comparable to that seen with physostigmine (73% at 10 minutes). Inhibition by norneostigmine is less effective (50% at 10 minutes) and approaches that obtained with tetrahydroaminoacridine (57% at 10 minutes). These data show that both norpyridostigmine and norneostigmine cross the blood-brain barrier and that they are effective inhibitors of mouse brain AChE activity. These drugs could be useful in the treatment of memory, impairment associated with Alzheimer's disease, and other memory disorders. 相似文献
2.
3.
4.
5.
6.
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
7.
8.
9.
M Gallego E del Cacho C Arnal C Felices E Lloret J A Bascuas 《European journal of histochemistry : EJH》1992,36(2):205-213
Positivity for S-100 protein in paraffin embedded chicken lymphoid tissue was found by using a polyclonal antibody against whole bovine S-100 protein. The S-100 protein-containing cells were observed in the locations which have been reported to contain avian dendritic cells such as the medulla of the bursal follicles, and the germinal centers and T-dependent areas in the spleen, Peyer's patches, caecal tonsil and Harderian gland. Positive cells were also found in the location where ellipsoid associated cell have been described, and between epithelial cells covering the Peyer's patches and the caecal tonsil, as well as between the cells lining the ducts within the Harderian gland. Macrophages were devoid of immunostaining. Our results confirm the location described elsewhere for chicken dendritic cells and indicate that S-100 protein can be considered as a cell marker for the identification of the chicken dendritic cell. Intraepithelial positive cells may be interdigitating dendritic cells in an unusual location (their function being the transport of the antigen from the epithelium to the diffuse lymphoid tissue), or cytotoxic T-lymphocytes which, in mammals, are immunoreactive for S-100 protein. 相似文献
10.