全文获取类型
收费全文 | 306篇 |
免费 | 28篇 |
专业分类
334篇 |
出版年
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2015年 | 18篇 |
2014年 | 17篇 |
2013年 | 16篇 |
2012年 | 27篇 |
2011年 | 17篇 |
2010年 | 7篇 |
2009年 | 9篇 |
2008年 | 13篇 |
2007年 | 13篇 |
2006年 | 15篇 |
2005年 | 15篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有334条查询结果,搜索用时 0 毫秒
21.
Rubens Fazan Jr. Carlos Alberto A. Silva José Ant?nio Cortes Oliveira Helio Cesar Salgado Nicola Montano Norberto Garcia-Cairasco 《PloS one》2015,10(6)
Introduction
Risk factors for life-threatening cardiovascular events were evaluated in an experimental model of epilepsy, the Wistar Audiogenic Rat (WAR) strain.Methods
We used long-term ECG recordings in conscious, one year old, WAR and Wistar control counterparts to evaluate spontaneous arrhythmias and heart rate variability, a tool to assess autonomic cardiac control. Ventricular function was also evaluated using the pressure-volume conductance system in anesthetized rats.Results
Basal RR interval (RRi) was similar between WAR and Wistar rats (188±5 vs 199±6 ms). RRi variability strongly suggests that WAR present an autonomic imbalance with sympathetic overactivity, which is an isolated risk factor for cardiovascular events. Anesthetized WAR showed lower arterial pressure (92±3 vs 115±5 mmHg) and exhibited indices of systolic dysfunction, such as higher ventricle end-diastolic pressure (9.2±0.6 vs 5.6±1 mmHg) and volume (137±9 vs 68±9 μL) as well as lower rate of increase in ventricular pressure (5266±602 vs 7320±538 mmHg.s-1). Indices of diastolic cardiac function, such as lower rate of decrease in ventricular pressure (-5014±780 vs -7766±998 mmHg.s-1) and a higher slope of the linear relationship between end-diastolic pressure and volume (0.078±0.011 vs 0.036±0.011 mmHg.μL), were also found in WAR as compared to Wistar control rats. Moreover, Wistar rats had 3 to 6 ventricular ectopic beats, whereas WAR showed 15 to 30 ectopic beats out of the 20,000 beats analyzed in each rat.Conclusions
The autonomic imbalance observed previously at younger age is also present in aged WAR and, additionally, a cardiac dysfunction was also observed in the rats. These findings make this experimental model of epilepsy a valuable tool to study risk factors for cardiovascular events in epilepsy. 相似文献22.
23.
Regarding such an important issue as our origin, as well as the origin of all biological diversity, it is surprising to realize
that evolution still faces drawbacks in keeping its deserved notability as a unifying theory in biology. This does not happen
because evolutionism lacks validity as a scientific theory, but rather because of several misconceptions regarding evolutionary
biology that were and continue to be found in elementary and secondary education. Furthermore, mistaken evolutionary ideas
also affect some philosophical and social issues. The aim of the present study was to evaluate knowledge about evolution among
freshman students from distinct majoring areas at Universidade Estadual do Centro-Oeste do Paraná (UNICENTRO), Brazil. The
research was carried out based on a ten-question questionnaire about evolution with distinct levels of difficulty, comprising
the most observed misconceptions. In this study, 231 students attending classes in biological sciences (morning and evening
schedule), exact sciences (agronomy, physics, chemistry, and math), and human sciences (history, geography, and pedagogy)
were interviewed. The total average of right answers was 48.8%, and the highest average per course obtained was 58.7% from
the students attending biological sciences (evening schedule). Although evolutionary biology and ecology are supposed to represent
teaching guide issues according to the recommendations of the National Curricular Parameters for the Secondary School, the
data obtained suggest that the evidence for evolution, the role of natural selection and random events, as well as the sources
of variation, must be better focused at schools. 相似文献
24.
25.
Clancy A Loar JW Speziali CD Oberg M Heinrichs DE Rubens CE 《Molecular microbiology》2006,59(2):707-721
Mutagenesis of group B streptococcus (GBS) with TnphoZ, a transposon designed to identify secreted protein genes, identified the gene homologues fhuD and fhuG. The encoded proteins participate in siderophore (hydroxamate)-dependent iron(III) transport in other bacterial species. Sequence analysis of the genome determined that fhuD and fhuG are members of a polycistronic operon comprised of four genes, fhuCDBG, that encode a putative ATPase, cell surface receptor and two transmembrane proteins respectively. We hypothesized that FhuD was a siderophore receptor. Western analysis of cell extracts localized FhuD to the bacterial cell membrane. Fluorescence quenching experiments determined that purified FhuD bound hydroxamate-type siderophores. FhuD displayed highest affinity for iron(III)-desferroxamine, with a K(D) (microM) = 0.05, identical to that described for FhuD2 from Staphylococcus aureus. The role of Fhu in siderophore-iron transport was also characterized. A fhu mutant, ACFhu1, was equally sensitive to the iron-dependent antibiotic streptonigrin as the wild-type strain, suggesting that ACFhu1 was not reduced for intracellular iron concentrations in the absence of exogenous siderophore. However, ACFhu1 transported significantly less siderophore-bound iron in (55)Fe accumulation assays. These data provide the first evidence of siderophore-mediated iron acquisition by GBS. 相似文献
26.
27.
Summary We have worked out conditions for the study of competence development and genetic transformation in Streptococcus oralis NCTC 11427 (type strain), a species that contains choline in the cell wall. The peak of competence was found at the early exponential phase of growth and the optimal conditions for transformation were achieved with shuttle plasmids prepared from S. pneumoniae or from Escherichia coli serving as donor DNA. Transformation with dye-bouyant density gradient purified plasmid preparations followed first-order kinetics. The pneumococcal amidase can be expressed in S. oralis harbouring a plasmid carrying the lytA gene. This enzyme lysed the cell wall of the transformed cell in the presence of detergents. 相似文献
28.
Vann WF Daines DA Murkin AS Tanner ME Chaffin DO Rubens CE Vionnet J Silver RP 《Journal of bacteriology》2004,186(3):706-712
The K1 capsule is an essential virulence determinant of Escherichia coli strains that cause meningitis in neonates. Biosynthesis and transport of the capsule, an alpha-2,8-linked polymer of sialic acid, are encoded by the 17-kb kps gene cluster. We deleted neuC, a K1 gene implicated in sialic acid synthesis, from the chromosome of EV36, a K-12-K1 hybrid, by allelic exchange. Exogenously added sialic acid restored capsule expression to the deletion strain (DeltaneuC), confirming that NeuC is necessary for sialic acid synthesis. The deduced amino acid sequence of NeuC showed similarities to those of UDP-N-acetylglucosamine (GlcNAc) 2-epimerases from both prokaryotes and eukaryotes. The NeuC homologue from serotype III Streptococcus agalactiae complements DeltaneuC. We cloned the neuC gene into an intein expression vector to facilitate purification. We demonstrated by paper chromatography that the purified neuC gene product catalyzed the formation of [2-(14)C]acetamidoglucal and [N-(14)C]acetylmannosamine (ManNAc) from UDP-[(14)C]GlcNAc. The formation of reaction intermediate 2-acetamidoglucal with the concomitant release of UDP was confirmed by proton and phosphorus nuclear magnetic resonance spectroscopy. NeuC could not use GlcNAc as a substrate. These data suggest that neuC encodes an epimerase that catalyzes the formation of ManNAc from UDP-GlcNAc via a 2-acetamidoglucal intermediate. The unexpected release of the glucal intermediate and the extremely low rate of ManNAc formation likely were a result of the in vitro assay conditions, in which a key regulatory molecule or protein was absent. 相似文献
29.
Md. Habibur Rahman Tohru Tsuchiya Keita Suwabe Junna Kohori Rubens Norio Tomita Yasuaki Kagaya Issei Kobayashi Katsuyuki Kakeda Yasuo Kowyama 《Sexual plant reproduction》2007,20(2):63-72
Sporophytic self-incompatibility (SSI) in the genus Ipomoea (Convolvulaceae) is controlled by a single polymorphic S locus. We have previously analyzed genomic sequences of an approximately 300 kb region spanning the S locus of the S
1
haplotype and characterized the genomic structure around this locus. Here, we further define the physical size of the S locus region by mapping recombination breakpoints, based on sequence analysis of PCR fragments amplified from the genomic
DNA of recombinants. From the recombination analysis, the S locus of the S
1
haplotype was delimited to a 0.23 cM region of the linkage map, which corresponds to a maximum physical size of 212 kb. To
analyze differences in genomic organization between S haplotypes, fosmid contigs spanning approximately 67 kb of the S
10
haplotype were sequenced. Comparison with the S
1
genomic sequence revealed that the S haplotype-specific divergent regions (SDRs) spanned 50.7 and 34.5 kb in the S
1
and S
10
haplotypes, respectively and that their flanking regions showed a high sequence similarity. In the sequenced region of the
S
10
haplotype, five of the 12 predicted open reading frames (ORFs) were found to be located in the divergent region and showed
co-linear organization of genes between the two S haplotypes. Based on the size of the SDRs, the physical size of the S locus was estimated to fall within the range 34–50 kb in Ipomoea. 相似文献
30.
El Ottra Juliana Hanna Leite de Albuquerque Melo-de-Pinna Gladys Flávia Demarco Diego Pirani José Rubens Ronse De Craene Louis P. 《Journal of plant research》2022,135(2):157-190
Journal of Plant Research - Sapindales is a monophyletic order within the malvid clade of rosids. It represents an interesting group to address questions on floral structure and evolution due to a... 相似文献