全文获取类型
收费全文 | 452篇 |
免费 | 57篇 |
国内免费 | 1篇 |
专业分类
510篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 13篇 |
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 11篇 |
2017年 | 15篇 |
2016年 | 12篇 |
2015年 | 25篇 |
2014年 | 28篇 |
2013年 | 35篇 |
2012年 | 30篇 |
2011年 | 21篇 |
2010年 | 23篇 |
2009年 | 26篇 |
2008年 | 22篇 |
2007年 | 27篇 |
2006年 | 20篇 |
2005年 | 22篇 |
2004年 | 20篇 |
2003年 | 16篇 |
2002年 | 10篇 |
2001年 | 17篇 |
2000年 | 20篇 |
1999年 | 11篇 |
1998年 | 14篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 4篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1967年 | 2篇 |
排序方式: 共有510条查询结果,搜索用时 15 毫秒
201.
Camilo E López Lina M Quesada-Ocampo Adriana Bohórquez Myriam Cristina Duque Jaime Vargas Joe Tohme Valérie Verdier 《Génome》2007,50(12):1078-1088
Cassava (Manihot esculenta Crantz) is a major root crop widely grown in the tropics. Cassava bacterial blight, caused by Xanthomonas axonopodis pv. manihotis (Xam), is an important disease in Latin America and Africa resulting in significant losses. The preferred control method is the use of resistant genotypes. Mapping expressed sequence tags (ESTs) and determining their co-localization with quantitative trait loci (QTLs) may give additional evidence of the role of the corresponding genes in resistance or defense. Twenty-one EST-derived simple sequence repeats (SSRs) were mapped in 16 linkage groups. ESTs showing similarities with candidate resistance genes or defense genes were also mapped using strategies such as restriction fragment length polymorphisms, cleaved amplified polymorphic sequences, and allele-specific primers. In total, 10 defense-related genes and 2 bacterial artificial chromosomes (BACs) containing resistance gene candidates (RGCs) were mapped in 11 linkage groups. Two new QTLs associated with resistance to Xam strains CIO121 and CIO151 were detected in linkage groups A and U, respectively. The QTL in linkage group U explained 61.6% of the phenotypic variance and was associated with an RGC-containing BAC. No correlation was found between the new EST-derived SSRs or other mapped ESTs and the new or previously reported QTLs. 相似文献
202.
203.
Massimo Mariotti Sara Castiglioni Daniela Bernardini Jeanette AM Maier 《Immunity & ageing : I & A》2006,3(1):4
Background
The functional changes associated with endothelial senescence may be involved in human aging and age-related vascular disorders. Since the inflammatory cytokine interleukin (IL-)1 inhibits endothelial growth, we evaluated the expression of IL-1α, IL-1β and their antagonist, the IL-1 receptor antagonist (IL-1ra), in endothelial in vitro senescence and quiescence. We also examined the expression of IL-1α in human senescent and progeric fibroblasts. 相似文献204.
Bellis M; Jubier-Maurin V; Dod B; Vanlerberghe F; Laurent AM; Senglat C; Bonhomme F; Roizes G 《Molecular biology and evolution》1987,4(4):351-363
The presence of the L1 sequences, L1Md4 next to the pseudogene beta h3 and
I12 found in the twelfth intron of the albumin gene, in certain strains of
laboratory mice but not of others has led to the suggestion that these
sequences were recent insertions into the Mus mus domesticus genome. To be
sure that they are really recent insertions and not relics of an ancestral
chromosome, we investigated the presence or absence of these sequences in
populations of wild mice belonging to the semispecies M. m. domesticus and
M. m. musculus as well as in other species of the genus Mus and in related
murids. The sequence I12 in the albumin gene was found in 34% of the
chromosomes of the wild mice belonging to M. m. domesticus and to a lesser
extent (6%) in M. m. musculus. Of 114 M. m. domesticus chromosomes, L1Md4
was found in only nine, seven of which came from the same locality. Its
presence was associated with the haplotype Hbbp, which is relatively rare
in European populations of M. musculus. Since there was no evidence for the
presence of these two L1 sequences in more distantly related species, we
conclude that they are recent insertions in the M. musculus genome.
相似文献
205.
206.
Rojas A Duque E Mosqueda G Golden G Hurtado A Ramos JL Segura A 《Journal of bacteriology》2001,183(13):3967-3973
In Pseudomonas putida DOT-T1E multidrug efflux pumps of the resistance-nodulation-division family make a major contribution to solvent resistance. Two pumps have been identified: TtgABC, expressed constitutively, and TtgDEF, induced by aromatic hydrocarbons. A double mutant lacking both efflux pumps was able to survive a sudden toluene shock if and only if preinduced with small amounts of toluene supplied via the gas phase. In this article we report the identification and characterization in this strain of a third efflux pump, named TtgGHI. The ttgGHI genes form an operon that is expressed constitutively at high levels from a single promoter. In the presence of toluene the operon is expressed at an even higher level from two promoters, the constitutive one and a previously unreported one that is inducible and that partially overlaps the constitutive promoter. By site-directed mutagenesis we constructed a single ttgH mutant which was shown to be unable to survive sudden 0.3% (vol/vol) toluene shocks regardless of the preculture conditions. The mutation was transferred to single and double mutants to construct mutant strains in which two or all three pumps are knocked out. Survival analysis of induced and noninduced cells revealed that the TtgABC and TtgGHI pumps extruded toluene, styrene, m-xylene, ethylbenzene, and propylbenzene, whereas the TtgDEF pump removed only toluene and styrene. The triple mutant was hypersensitive to toluene, as shown by its inability to grow with toluene supplied via the vapor phase. 相似文献
207.
Segura A Duque E Rojas A Godoy P Delgado A Hurtado A Cronan J Ramos JL 《Environmental microbiology》2004,6(4):416-423
The unusual tolerance of Pseudomonas putida DOT-T1E to toluene is based on the extrusion of this solvent by constitutive and inducible efflux pumps and rigidification of its membranes via phospholipid alterations. Pseudomonas putida DOT-T1E-109 is a solvent-sensitive mutant. Mutant cells were less efficient in solvent extrusion than the wild-type cells, as shown by the limited efflux of 14C-1,2,4-trichlorobenzene from the cell membranes, despite the fact that the efflux pumps are overexpressed as a result of increased expression of the ttgDEF and ttgGHI efflux pump operons. This limitation could be the result of alterations in the outer membrane because the mutant cells released more beta-lactamase to the external medium than the wild-type cells. The mutant P. putida DOT-T1E-109 showed negligible synthesis of fatty acids in the presence of sublethal concentrations of toluene as revealed by analysis of 13CH3-13COOH incorporation into fatty acids. In contrast, the mutant strain in the absence of solvents, and the wild-type strain, both in the presence and in the absence of toluene, incorporated 13CH3-13COOH at a high rate into de novo synthesized lipids. The mutation in P. putida DOT-T1E-109 increases sensitivity to the solvent because of a limited efflux of the solvent from the cell membranes with the concomitant inhibition of fatty acid biosynthesis. 相似文献
208.
Fitness effects of amino acid replacements in the beta-galactosidase of Escherichia coli 总被引:6,自引:1,他引:6
Two genetic procedures were used to obtain amino acid replacements in the
lacZ-encoded beta-galactosidase in Escherichia coli. Amino acid
replacements could be obtained without regard to their effects on lactase
activity by selecting spontaneous mutations that relieved the strong
polarity of six nonsense mutations. When streaked on MacConkey- lactose
indicator plates, approximately 75% of these mutants gave strong red
lactose-fermenting colonies, and 25% gave white nonfermenting colonies.
Mutants from 11 other nonsense codons were isolated directly using
MacConkey-lactose indicator plates, on which positive color indication
requires only 0.5% of the wildtype lactase activity. Among the total of 17
codons, 25 variant beta-galactosidases were identified using
electrophoresis and thermal denaturation studies. The fitness effects of
these variant beta-galactosidases were determined using competition
experiments conducted with lactose as the sole nutrient limiting the growth
rate in chemostat cultures. Three of the replacements were deleterious, one
was selectively advantageous, and the selective effects of the remaining 21
were undetectable under conditions in which the smallest detectable
selection coefficient was approximately 0.4%/generation.
相似文献
209.
In this study, the effect of three different ozone (O3) levels on soluble protein content of Acer negundo, Quercus robur and Platanus spp. pollen was investigated. Pollen was directly collected from each plant and exposed to O3 values below, equal and four times the limit for human health protection in an environmental chamber system. With this chamber, it was possible to control and reproduce the O3 levels between different experiments. Total protein content was determined colorimetrically with Coomassie protein assay reagent (Pierce) by the Bradford method. Results showed that O3 has significant effects on pollen causing a decrease in soluble proteins that seem to be dependent on species and gas concentration. Also, the existence of reproducibility in the effects of O3, within the same concentration, on the protein content of pollen was verified. 相似文献
210.
Bruno Gabriel N Andrade Michel F Abanto Marin Diego Duque Cambuy Erica Louren?o Fonseca Nadjla Ferreira Souza Ana Carolina P Vicente 《Memórias do Instituto Oswaldo Cruz》2014,109(7):972-974
There has been a resurgence in the number of pertussis cases in Brazil and around theworld. Here, the genome of a clinical Bordetella pertussis strain (Bz181) that wasrecently isolated in Brazil is reported. Analysis of the virulence-associated genesdefining the pre- and post-vaccination lineages revealed the presence of theprn2-ptxS1A-fim3B-ptxP3 allelic profile in Bz181, which is characteristic of thecurrent pandemic lineage. A putative metallo-β-lactamase gene presenting all of theconserved zinc-binding motifs that characterise the catalytic site was identified, inaddition to a multidrug efflux pump of the RND family that could confer resistance toerythromycin, which is the antibiotic of choice for treating pertussis disease. 相似文献