全文获取类型
收费全文 | 412篇 |
免费 | 16篇 |
国内免费 | 7篇 |
专业分类
435篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 14篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 8篇 |
2016年 | 12篇 |
2015年 | 23篇 |
2014年 | 37篇 |
2013年 | 35篇 |
2012年 | 26篇 |
2011年 | 34篇 |
2010年 | 23篇 |
2009年 | 17篇 |
2008年 | 20篇 |
2007年 | 18篇 |
2006年 | 15篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 9篇 |
2000年 | 21篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1997年 | 6篇 |
1996年 | 5篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 3篇 |
排序方式: 共有435条查询结果,搜索用时 0 毫秒
411.
412.
Mitochondrial DNA sequence variation in the spruce budworm species complex (Choristoneura: Lepidoptera) 总被引:5,自引:0,他引:5
A combination of polymerase-chain-reaction amplification and automated DNA
sequencing was used to survey variation in a species complex of pest
insects, the spruce budworms (Choristoneura fumiferana species group), and
an outgroup species, C. rosaceana. We sequenced an mtDNA region of 1,573 bp
that extends from the middle of cytochrome oxidase subunit I (COI) through
tRNA leucine (UUR) to the end of cytochrome oxidase subunit II. In
addition, we examined levels of intraspecific variation within a 470-bp
region of the COI gene. Choristoneura fumiferana clearly represented the
oldest lineage within its species group, with 2.7%-2.9% sequence divergence
from the other species. In contrast, the four remaining species (C. pinus,
C. biennis, C. occidentalis, and C. orae) had closely related or identical
mtDNA, with < 1% divergence among most of their haplotypes. Despite its
older lineage and widespread geographic distribution, C. fumiferana showed
significantly lower intraspecific genetic diversity than did C.
occidentalis. Choristoneura orae shared haplotypes with C. occidentalis and
C. biennis, and species-level separation of these three species was not
supported. Two divergent, uncommon haplotypes were also found in C.
occidentalis and C. biennis. The divergent haplotype in C. biennis had an
unusually high number of inferred amino acid replacements, suggesting
selective differences between mitochondrial DNA haplotypes.
Transition:transversion ratios in Choristoneura paralleled those found in
Drosophila; transition:transversion ratios were highest in closely related
sequences but decreased with increasing sequence divergence. Nucleotide
composition showed an A+T bias that was near the high end of the range
known for insects. This work illustrates the potential utility of direct
DNA sequencing in assessing population structures, species limits, and
phylogenetic relationships among organisms that have not previously been
subjected to DNA analysis.
相似文献
413.
During decomposition, petioles and leaf blades of Nymphoides indica (L.) O. Kuntze and stems and leaves of Polygonum ferrugineum Wedd. from the Lobo Reservoir, Sao Paulo, Brazil, showed an initial phase (first seven days) of loss of dry weight, soluble carbohydrates, lipids, polyphenols, phosphorus, potassium and ash content. In both species, the decomposition of leaves and leaf blades was faster than that of stems and petioles. At the end of the experiment (after 149 days) leaf blades of N. indica had lost 98% of the initial dry weight. Except for nitrogen and ash, which increased, all the other components showed two distinct phases during the process with intensive loss during the initial phase and a gradual and reduced loss during the longer second phase.The nutritional value of the detritus and the consequence of nutrient re-cycling in the metabolism of Lobo Reservoir are discussed. 相似文献
414.
415.
Carla S. Francisco Lígia R. Rodrigues Nuno M.F.S.A. Cerqueira Ana M.F. Oliveira-Campos Lígia M. Rodrigues Ana P. Esteves 《Bioorganic & medicinal chemistry》2013,21(17):5047-5053
New tetracyclic benzofurocoumarin (benzopsoralen) analogues were synthesized and their inhibitory effect on the growth of tumor cell lines was evaluated. The human tumor cell lines used were MDA MB231 (breast adenocarcinoma), HeLa (cervix adenocarcinoma) and TCC-SUP (bladder transitional cell carcinoma). The in vitro antitumor activity of the new benzopsoralens was discussed in terms of structure–activity relationship. Molecular docking studies with human-CYP2A6 enzymes were also carried out with the synthesized compounds in order to evaluate the potential of these compounds to interact with the heme group of the enzymes. The results have demonstrated that the linear compounds have the most pronounced activity against tumor cell lines and this might be related to the better accessibility that these compounds have to the active site in relation to the angular ones that have shown in the majority of the cases multiple binding poses in the active site of CYP2A6. 相似文献
416.
The genus Macaca: a review of taxonomy and evolution 总被引:1,自引:0,他引:1
JOHN E. FA 《Mammal Review》1989,19(2):45-81
417.
Katharina Eichbau Esteves 《Environmental Biology of Fishes》1996,46(1):83-101
Synopsis The feeding ecology of three characids (A. fasciatus, A. bimaculatus and A. schubarti) was studied monthly during 1988 in Lake Inferñao, a major floodplain lake of the Mogi-Guaçú River in the State of São Paulo. River flooding directly influenced the diet of the omnivorous A. bimaculatus and A. fasciatus which responded to maximum inundation (March) by consuming predominantly allochthonous insects. In contrast, A. schubarti was less influenced by the river flood cycle on qualitative changes in diet and relied basically on aquatic macrophytes and periphytic algae. The importance of zooplankton in the diet of the three species was low, and may be attributed to its low density in the water column (< 1 ind l–1). Ontogenetic diet changes were evident for the three species. For A. fasciatus and A. bimaculatus the importance of zooplankton was high at the early stages, decreasing with size. A. schubarti at younger stages consumed diversified items which gradually decreased quantitatively up to the size class of 65 mm; from this size onwards, the diet became restricted to the consumption of periphytic algae and macrophytes. 相似文献
418.
R M de Araujo Soares C S Alviano M J Esteves J Angluster F Costa e Silva-Filho W de Souza 《Cell biophysics》1988,13(1):29-41
The surface anionic groups of untreated or dimethyl sulfoxide (DMSO)-treated Herpetomonas samuelpessoai cells were analyzed by cell electrophoresis, ultrastructural cytochemistry, and identification of sialic acids using thin-layer chromatography. Differentiation of H. samuelpessoai induced by DMSO treatment caused a significant increase in the net negative surface charge. In flagellates exposed to DMSO, more cationized ferritin, colloidal iron hydroxide, and sendai virus particles bound to the cell surface. Treatment of both untreated and DMSO-treated flagellates with neuraminidase decreased markedly the EPM of cells to the cathodic pole. These findings suggest that sialic acid residues are the major anionogenic groups exposed on the surface of H. samuelpessoai. Thin-layer chromatography showed that N-acetyl and N,O-diacylneuraminic acids, in equal proportions, were present in H. samuelpessoai. However, N-acetylneuraminic acid predominates in DMSO-treated cells. 相似文献
419.
Gerleni Lopes Esteves 《Brittonia》2000,52(3):256-264
This study was based on the analysis of staminal tube and epicalyx morphology of species ofPavonia (Malvaceae) from northeastern and southeastern Brazil. The importance of characters in the infrageneric taxonomy is discussed.
In general, the variability in staminal tube and epicalyx characters are useful mainly in separating closely related species
and a few sections; these characters, however, cannot be used to separate subgenera. 相似文献
420.