全文获取类型
收费全文 | 1435篇 |
免费 | 141篇 |
出版年
2022年 | 14篇 |
2021年 | 28篇 |
2020年 | 31篇 |
2019年 | 38篇 |
2018年 | 55篇 |
2017年 | 40篇 |
2016年 | 50篇 |
2015年 | 68篇 |
2014年 | 77篇 |
2013年 | 67篇 |
2012年 | 113篇 |
2011年 | 91篇 |
2010年 | 60篇 |
2009年 | 60篇 |
2008年 | 67篇 |
2007年 | 72篇 |
2006年 | 56篇 |
2005年 | 47篇 |
2004年 | 47篇 |
2003年 | 43篇 |
2002年 | 38篇 |
2001年 | 32篇 |
2000年 | 27篇 |
1999年 | 42篇 |
1998年 | 12篇 |
1997年 | 7篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 16篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 10篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1971年 | 5篇 |
1969年 | 5篇 |
1968年 | 7篇 |
排序方式: 共有1576条查询结果,搜索用时 15 毫秒
151.
The C terminus of collagen SQT-3 has complex and essential functions in nematode collagen assembly
下载免费PDF全文
![点击此处可从《Genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The nematode exoskeleton is a multilayered structure secreted by the underlying hypodermal cells and mainly composed of small collagens, which are encoded by a large gene family. In previous work, we reported analysis of the C. elegans dpy-31 locus, encoding a hypodermally expressed zinc-metalloprotease of the BMP-1/TOLLOID family essential for viability and cuticle deposition. We have generated a large set of extragenic suppressors of dpy-31 lethality, most of which we show here to be allelic to the cuticle collagen genes sqt-3 and dpy-17. We analyzed the interaction among dpy-31, sqt-3, and dpy-17 using a SQT-3-specific antiserum, which was employed in immunofluorescence experiments. Our results support a role for DPY-31 in SQT-3 extracellular processing and suggest that the SQT-3 C-terminal nontrimeric region serves multiple roles during SQT-3 assembly. Different missense mutations of this region have diverse phenotypic consequences, including cold-sensitive lethality. Furthermore, the biochemical and genetic data indicate that the extracellular assemblies of DPY-17 and SQT-3 are interdependent, most likely because the collagens are incorporated into the same cuticular substructure. We find that absence of DPY-17 causes extensive intracellular retention of SQT-3, indicating that formation of the SQT-3-DPY-17 polymer could begin in the intracellular environment before secretion. 相似文献
152.
Fredy D.A. Silva Ilka M. Vasconcelos Marina D.P. Lobo Patrícia G. de Castro Vladimir G. Magalhães Cléverson D.T. de Freitas Célia R.R.S. Carlini Paulo M. Pinto Leila M. Beltramini José H.A. Filho Eduardo B. Barros Luciana M.R. Alencar Thalles B. Grangeiro José T.A. Oliveira 《Biochimica et Biophysica Acta (BBA)/General Subjects》2012
Background
Peroxiredoxins have diverse functions in cellular defense-signaling pathways. 2-Cys-peroxiredoxins (2-Cys-Prx) reduce H2O2 and alkyl-hydroperoxide. This study describes the purification and characterization of a genuine 2-Cys-Prx from Vigna unguiculata (Vu-2-Cys-Prx).Methods
Vu-2-Cys-Prx was purified from leaves by ammonium sulfate fractionation, chitin affinity and ion exchange chromatography.Results
Vu-2-Cys-Prx reduces H2O2 using NADPH and DTT. Vu-2-Cys-Prx is a 44 kDa (SDS-PAGE)/46 kDa (exclusion chromatography) protein that appears as a 22 kDa molecule under reducing conditions, indicating that it is a homodimer linked intermolecularly by disulfide bonds and has a pI range of 4.56–4.72; its NH2-terminal sequence was similar to 2-Cys-Prx from Phaseolus vulgaris (96%) and Populus tricocarpa (96%). Analysis by ESI-Q-TOF MS/MS showed a molecular mass/pI of 28.622 kDa/5.18. Vu-2-Cys-Prx has 8% α-helix, 39% β-sheet, 22% of turns and 31% of unordered forms. Vu-2-Cys-Prx was heat stable, has optimal activity at pH 7.0, and prevented plasmid DNA degradation. Atomic force microscopy shows that Vu-2-Cys-Prx oligomerized in decamers which might be associated with its molecular chaperone activity that prevented denaturation of insulin and citrate synthase. Its cDNA analysis showed that the redox-active Cys52 residue and the amino acids Pro45, Thr49 and Arg128 are conserved as in other 2-Cys-Prx.General significance
The biochemical and molecular features of Vu-2-Cys-Prx are similar to other members of 2-Cys-Prx family. To date, only one publication reported on the purification of native 2-Cys-Prx from leaves and the subsequent analysis by N-terminal Edman sequencing, which is crucial for construction of stromal recombinant 2-Cys-Prx proteins. 相似文献153.
João Luiz M. Aranha Filho Leonardo Dias Meireles Peter W. Fritsch Frank Almeda Angela B. Martins 《Brittonia》2012,64(3):252-256
Symplocos minima, a new species of Symplocos section Hopea from the Itatiaia Plateau in the Atlantic Rain Forest biome of southeastern Brazil, is described and illustrated. This species is distinguished by its densely compact shrubby habit, ascending leaves, fasciculate inflorescences with several persistent bracts, corolla with five to six erect lobes, pistillate flowers with the disc not thickened along the margin, fruiting calyx lobes obscuring the disc, and seeds sub-orbicular in cross section. The new species is morphologically related to S. itatiaiae and S. pentandra, but can be differenciated from them mainly due to the tree habit and fruiting calyx lobes not obscuring the disc in S. itatiaiae and the pistillate flowers with a disc that is thickened along the margin in S. pentandra. 相似文献
154.
Diniz Filho JA Rangel TF Santos T Bini LM 《Evolution; international journal of organic evolution》2012,66(4):1079-1090
A number of metrics have been developed for estimating phylogenetic signal in data and to evaluate correlated evolution, inferring broad-scale evolutionary and ecological processes. Here, we proposed an approach called phylogenetic signal-representation (PSR) curve, built upon phylogenetic eigenvector regression (PVR). In PVR, selected eigenvectors extracted from a phylogenetic distance matrix are used to model interspecific variation. In the PSR curve, sequential PVR models are fitted after successively increasing the number of eigenvectors and plotting their R(2) against the accumulated eigenvalues. We used simulations to show that a linear PSR curve is expected under Brownian motion and that its shape changes under alternative evolutionary models. The PSR area, expressing deviations from Brownian motion, is strongly correlated (r= 0.873; P < 0.01) with Blomberg's K-statistics, so nonlinear PSR curves reveal if traits are evolving at a slower or higher rate than expected by Brownian motion. The PSR area is also correlated with phylogenetic half-life under an Ornstein-Uhlenbeck process, suggesting how both methods describe the shape of the relationship between interspecific variation and time since divergence among species. The PSR curve provides an elegant exploratory method to understand deviations from Brownian motion, in terms of acceleration or deceleration of evolutionary rates occurring at large or small phylogenetic distances. 相似文献
155.
Curi NH Brait CH Antoniosi Filho NR Talamoni SA 《Biological trace element research》2012,147(1-3):97-102
In this study, we aimed to assess whether free-ranging wild canids are exposed to heavy metals in one of the most developed and populated regions of Brazil. Hair of 26 wild canids (maned wolves Chrysocyon brachyurus, crab-eating foxes Cerdocyon thous, and hoary foxes Lycalopex vetulus) from the Cerrado biome in Southeast Brazil were analyzed by spectrophotometry to detect cadmium, chromium, and lead, and also the essential copper, iron, manganese, and zinc traces. All samples showed traces of copper, iron, manganese, and zinc. Non-essential lead was detected in 57% (2.35 ± 0.99 mg/kg), and chromium in 88% (2.98 ± 1.56 mg/kg) of samples. Cadmium traces (detection limit 0.8 mg/kg) were not found. Crab-eating foxes had more copper, iron, and manganese in hair than maned wolves. Correlations among element levels differed between maned wolves and crab-eating foxes. Concentrations of chromium and lead were outstandingly higher than in wild canids from other areas. Addressing the causes of such levels and the impacts of the heavy metal pollution in Neotropical ecosystems is urgent for animal health and conservation purposes. We argue that heavy metal pollution should be considered as dangerous threats to wildlife health in Brazil and recommend hair sampling as a biomonitoring tool for heavy metals in Neotropical terrestrial mammals. 相似文献
156.
Leonardo Soriano Francisco de Assis Alves Mour?o Filho Luis Eduardo Aranha Camargo Mariangela Cristofani-Yaly Rodrigo Rocha Latado Camila de Andrade Pacheco Fernando Alves de Azevedo Beatriz Madalena Januzzi Mendes 《Plant Cell, Tissue and Organ Culture》2012,111(3):385-392
Protoplast fusion between sweet orange and mandarin/mandarin hybrids scion cultivars was performed following the model ??diploid embryogenic callus protoplast?+?diploid mesophyll-derived protoplast??. Protoplasts were isolated from embryogenic calli of ??Pera?? and ??Westin?? sweet orange cultivars (Citrus sinensis) and from young leaves of ??Fremont??, Nules??, and ??Thomas?? mandarins (C. reticulata), and ??Nova?? tangelo [C. reticulata?×?(C. paradisi?×?C. reticulata)]. The regenerated plants were characterized based on their leaf morphology (thickness), ploidy level, and simple sequence repeat (SSR) molecular markers. Plants were successfully generated only when ??Pera?? sweet orange was used as the embryogenic parent. Fifteen plants were regenerated being 7 tetraploid and 8 diploid. Based on SSR molecular markers analyses all 7 tetraploid regenerated plants revealed to be allotetraploids (somatic hybrids), including 2 from the combination of ??Pera?? sweet orange?+???Fremont?? mandarin, 3 ??Pera?? sweet orange?+???Nules?? mandarin, and 2 ??Pera?? sweet orange?+???Nova?? tangelo, and all the diploid regenerated plants showed the ??Pera?? sweet orange marker profile. Somatic hybrids were inoculated with Alternaria alternata and no disease symptoms were detected 96?h post-inoculation. This hybrid material has the potential to be used as a tetraploid parent in interploid crosses for citrus scion breeding. 相似文献
157.
GB Menezes FA Pereira CA Duarte TM Carmo HP Silva Filho MA Zarife MA Krieger EA Reis MG Reis 《Memórias do Instituto Oswaldo Cruz》2012,107(5):680-683
The hepatitis C virus (HCV) can be detected in blood and other bodily fluids, such as saliva, semen and gastric juices. The aim of this study was to compare the HCV viral loads in the serum and saliva of infected patients. Twenty-nine patients with detectable HCV RNA in their serum and saliva were included in this study. The HCV viral loads were determined through quantitative real-time polymerase chain reactions. The median viral RNA levels were 5.78 log10 copies in the serum and 3.32 log10 copies in the saliva. We observed that the salivary HCV viral load was significantly lower than the viral load in the serum. Further studies are required to understand the role of saliva in the diagnosis, management and potential transmission of HCV. 相似文献
158.
Jose Alexandre F. Diniz‐Filho Luis Mauricio Bini Thiago Fernando Rangel Ignacio Morales‐Castilla Miguel Á. Olalla‐Tárraga Miguel Á. Rodríguez Bradford A. Hawkins 《Ecography》2012,35(3):239-249
Among the statistical methods available to control for phylogenetic autocorrelation in ecological data, those based on eigenfunction analysis of the phylogenetic distance matrix among the species are becoming increasingly important tools. Here, we evaluate a range of criteria to select eigenvectors extracted from a phylogenetic distance matrix (using phylogenetic eigenvector regression, PVR) that can be used to measure the level of phylogenetic signal in ecological data and to study correlated evolution. We used a principal coordinate analysis to represent the phylogenetic relationships among 209 species of Carnivora by a series of eigenvectors, which were then used to model log‐transformed body size. We first conducted a series of PVRs in which we increased the number of eigenvectors from 1 to 70, following the sequence of their associated eigenvalues. Second, we also investigated three non‐sequential approaches based on the selection of 1) eigenvectors significantly correlated with body size, 2) eigenvectors selected by a standard stepwise algorithm, and 3) the combination of eigenvectors that minimizes the residual phylogenetic autocorrelation. We mapped the mean specific component of body size to evaluate how these selection criteria affect the interpretation of non‐phylogenetic signal in Bergmann's rule. For comparison, the same patterns were analyzed using autoregressive model (ARM) and phylogenetic generalized least‐squares (PGLS). Despite the robustness of PVR to the specific approaches used to select eigenvectors, using a relatively small number of eigenvectors may be insufficient to control phylogenetic autocorrelation, leading to flawed conclusions about patterns and processes. The method that minimizes residual autocorrelation seems to be the best choice according to different criteria. Thus, our analyses show that, when the best criterion is used to control phylogenetic structure, PVR can be a valuable tool for testing hypotheses related to heritability at the species level, phylogenetic niche conservatism and correlated evolution between ecological traits. 相似文献
159.
Brenzan MA Santos AO Nakamura CV Filho BP Ueda-Nakamura T Young MC C?rrea AG Júnior JA Morgado-Díaz JA Cortez DA 《Phytomedicine》2012,19(3-4):223-230
We have previously demonstrated antileishmanial activity on Leishmania amazonensis of the natural (1-2), synthetic (7) and derivatives of coumarin (-) mammea A/BB (3-6) isolated from the dichloromethane extract of Calophyllum brasiliense leaves. The aim of the present study was to evaluate morphological and ultrastructural alterations in Leishmania amazonensis induced by these compounds. In promastigote forms, all seven compounds produced significant morphological and ultrastructural alterations, as revealed by scanning and transmission electron microscopy. The compound 5,7-dihydroxy-8-(2-methylbutanoyl)-6-(3-methylbutyl)-4-phenyl-chroman-2-one (3), the most active antileishmanial with LD?? of 0.9 μM), induced cell shrinkage and a rounded appearance of the cells. Parasites incubated in the presence of compound (3) showed ultrastructural changes, such as the appearance of mitochondrial swelling with a reduction in the density of the mitochondrial matrix and the presence of vesicles inside the mitochondrion, indicating damage and significant change in this organelle; abnormal chromatin condensation, alterations in the nuclear envelope, intense atypical cytoplasmic vacuolization, and the appearance of autophagic vacuoles were also observed. In addition, the compound (3) may be acting to depolarize the mitochondrial membrane potential of the cells, leading to death of the parasite. 相似文献
160.
Dias MO Junqueira TL Cavalett O Cunha MP Jesus CD Rossell CE Maciel Filho R Bonomi A 《Bioresource technology》2012,103(1):152-161
Ethanol production from lignocellulosic materials is often conceived considering independent, stand-alone production plants; in the Brazilian scenario, where part of the potential feedstock (sugarcane bagasse) for second generation ethanol production is already available at conventional first generation production plants, an integrated first and second generation production process seems to be the most obvious option. In this study stand-alone second generation ethanol production from surplus sugarcane bagasse and trash is compared with conventional first generation ethanol production from sugarcane and with integrated first and second generation; simulations were developed to represent the different technological scenarios, which provided data for economic and environmental analysis. Results show that the integrated first and second generation ethanol production process from sugarcane leads to better economic results when compared with the stand-alone plant, especially when advanced hydrolysis technologies and pentoses fermentation are included. 相似文献