全文获取类型
收费全文 | 2695篇 |
免费 | 162篇 |
专业分类
2857篇 |
出版年
2023年 | 21篇 |
2022年 | 50篇 |
2021年 | 93篇 |
2020年 | 63篇 |
2019年 | 67篇 |
2018年 | 99篇 |
2017年 | 71篇 |
2016年 | 121篇 |
2015年 | 148篇 |
2014年 | 161篇 |
2013年 | 196篇 |
2012年 | 210篇 |
2011年 | 209篇 |
2010年 | 159篇 |
2009年 | 115篇 |
2008年 | 137篇 |
2007年 | 137篇 |
2006年 | 122篇 |
2005年 | 100篇 |
2004年 | 90篇 |
2003年 | 59篇 |
2002年 | 74篇 |
2001年 | 46篇 |
2000年 | 30篇 |
1999年 | 47篇 |
1998年 | 25篇 |
1997年 | 15篇 |
1996年 | 9篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1969年 | 4篇 |
排序方式: 共有2857条查询结果,搜索用时 15 毫秒
71.
Mylenne Calciolari Pinheiro Silva Aline Fernandes Figueiredo Fernando Dini Andreote Elke Jurandy Bran Nogueira Cardoso 《World journal of microbiology & biotechnology》2013,29(1):163-171
Brachiaria brizantha is considered one of the preferred fodders among farmers for having high forage yield and large production of root mass. The association of beneficial bacteria with these grasses can be very valuable in the recovery of the pasture areas with nutritional deficiency. With the aim of studying this possibility, we carried out the sampling of soil and roots of B. brizantha in three areas (Nova Odessa-SP, S?o Carlos-SP and Campo Verde-MT, Brazil). Seventy-two bacterial strains were isolated and used in tests to evaluate their biotechnological potential. Almost all isolates presented at least one positive feature. Sixty-eight isolates produced analogues of indole-3-acetic acid, ten showed nitrogenase activity when subjected to the method of increasing the concentration of total nitrogen (total N) in the culture medium and sixty-five isolates showed nitrogenase activity when subjected to acetylene reduction technique. The partial sequencing of 16S rRNA of these isolates allowed the identification of seven main groups, with the prevalence of those affiliated to the genus Stenotrophomonas (69?%). At the end, this work elected the strains C4 (Pseudomonadaceae) and C7 (Rhodospirillaceae) as promising organisms for the development of inoculants due to their higher nitrogenase activity. 相似文献
72.
73.
74.
Israel de Souza Pinto Bruna Dias das Chagas Andressa Alencastre Fuzari Rodrigues Adelson Luiz Ferreira Helder Ricas Rezende Rafaela Vieira Bruno Aloisio Falqueto José Dilermando Andrade-Filho Eunice Aparecida Bianchi Galati Paloma Helena Fernandes Shimabukuro Reginaldo Pe?anha Brazil Alexandre Afranio Peixoto 《PloS one》2015,10(10)
DNA barcoding has been an effective tool for species identification in several animal groups. Here, we used DNA barcoding to discriminate between 47 morphologically distinct species of Brazilian sand flies. DNA barcodes correctly identified approximately 90% of the sampled taxa (42 morphologically distinct species) using clustering based on neighbor-joining distance, of which four species showed comparatively higher maximum values of divergence (range 4.23–19.04%), indicating cryptic diversity. The DNA barcodes also corroborated the resurrection of two species within the shannoni complex and provided an efficient tool to differentiate between morphologically indistinguishable females of closely related species. Taken together, our results validate the effectiveness of DNA barcoding for species identification and the discovery of cryptic diversity in sand flies from Brazil. 相似文献
75.
Aurigena Antunes de Araújo Hugo Varela Caroline Addison Carvalho Xavier de Medeiros Gerly Anne de Castro Brito Kênio Costa de Lima Ligia Moreno de Moura Raimundo Fernandes de Araújo Júnior 《PloS one》2015,10(2)
Oral mucositis (OM) is a common complication of treatments for head and neck cancer, particularly radiotherapy with or without chemotherapy. OM is characterised by oral erythema, ulceration, and pain. The aim of this study was to evaluate the effect of azilsartan (AZT), an angiotensin II receptor antagonist, on 5-fluorouracil (5-FU)-induced oral mucositis (OM) in Syrian hamsters. OM was induced by the intraperitoneal administration of 5-FU on experimental days 1 (60mg/Kg) and 2 (40mg/Kg). Animals were pretreated with oral AZT (1, 5, or 10 mg/kg) or vehicle 30 min before 5-FU injection and daily until day 10. Experimental treatment protocols were approved by the Animal Ethics Committee Use/CEUA (Number 28/2012) of the UFRN. Macroscopic analysis and cheek pouch samples were removed for histopathologic analysis. Myeloperoxidase (MPO), Malonyldialdehyde (MDA), interleukin-1 beta (IL-1β), interleukin-10 (IL-10), and tumour necrosis factor-alpha (TNF-α) were analysed by Enzyme Linked Immuno Sorbent Assay (ELISA). Vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF), keratinocyte growth factor (KGF), and transforming growth factor (TGF)-α were measured by immunohistochemistry. Analysis of variance followed by Bonferroni’s test was used to calculate the means of intergroup differences (p ≤ 0.05). Treatment with 1 mg/kg AZT reduced levels MPO (p<0.01), MDA (p<0.5) and histological inflammatory cell infiltration, and increased the presence of granulation tissue. AZT treatment at 1 mg/kg reduced the TNF-α (p<0.05) and IL-1β (p<0.05) levels, increased the cheek pouch levels of IL-10 (p<0.01), and upregulated VEGF, FGF, KGF, and TGF-α. Administration of AZT at higher doses (5 and 10 mg/kg) did not significantly reverse the OM. AZT at a dose of 1 mg/kg prevented the mucosal damage and inflammation associated with 5-FU-induced OM, increasing granulation and tissue repair. 相似文献
76.
Márcio S. Araújo Eduardo G. Martins Leonardo D. Cruz Fernanda R. Fernandes Arício X. Linhares Sérgio F. Dos Reis Paulo R. Guimarães Jr 《Oikos》2010,119(1):81-88
Many generalist populations may actually be composed of relatively specialist individuals. This 'individual specialization' may have important ecological and evolutionary implications. Although this phenomenon has been documented in more than one hundred taxa, it is still unclear how individuals within a population actually partition resources. Here we applied several methods based on network theory to investigate the intrapopulation patterns of resource use in the gracile mouse opossum Gracilinanus microtarsus . We found evidence of significant individual specialization in this species and that the diets of specialists are nested within the diets of generalists. This novel pattern is consistent with a recently proposed model of optimal foraging and implies strong asymmetry in the interactions among individuals of a population. 相似文献
77.
Sheryl?Oliveira?Fernandes K.?P.?Krishnan V.?D.?Khedekar P.?A.?Loka BharathiEmail author 《Biometals》2005,18(5):483-492
The abundance and activity of culturable manganese-oxidizing bacteria were assessed from near-bottom water samples of the
tectonically active Carlsberg Ridge. Retrievable counts as colony forming units (CFU) on dilute nutrient agar medium (dilNA
= 2 gm l−1 nutrient broth+2% agar) and on dilNA supplemented with 1, 2 and 3 mM MnCl2·4H2O were in the order of 106 CFU l−1. Retrievability of heterotrophs ranged from non-detectable levels (ND) to 2.82 × 106 CFU l−1. The retrievable counts on Mn amended dilNA ranged from ND to 3.21× 106, 1.47 × 106 and 1.45 × 106 CFU l−1 on 1, 2 and 3 mM, respectively. About 87% of the Mn tolerant isolates (n = 39) showed taxonomic affinities to Pseudomonas I and II sp. Two representative strains CR35 and CR48 (CR–Carlsberg Ridge) isolated on manganese-supplemented media were
tested for their ability to tolerate a range of Mn amendments from 1 nM to 100 mM in terms of growth and respiration. CR35
represents 66% of the total CFU (3.04 × 106 CFU l−1), while CR48 represented only 6% of the total CFU (1.05 × 106 CFU l−1). The colonies of these two isolates were dark brown in color suggesting precipitation of Mn as oxide. Tests for the effect
on growth and respiration were conducted in media simulating heterotrophic (amended with 0.01% glucose) and lithotrophic (unamended)
conditions. Maximum stimulation in growth and respiration of CR35 occurred at 100 μM Mn both in unamended and amended media. At levels of Mn greater than 100 μM the counts decreased steadily. Total respiring cells of CR48 were stimulated to a maximum at 1 μM Mn in unamended medium and 1 nM in amended medium. Total cells counts for the same decreased beyond 100 μM Mn in unamended and 1 nM in amended medium. The isolates were tested for their ability to oxidize Mn ammendments from 1 μM to 10 mM Mn. At the end of a 76-day incubation period, there was evidence of manganese oxide precipitation at high Mn concentrations
(≥1 mM) as a dark brown coloration on the sides of culture tubes. Highest Mn oxidation rates were observed at 10 mM Mn(II)
concentration with CR35 oxidizing 27 and 25 μM Mn day−1 in unamended and amended condition, respectively. CR48 oxidized Mn at the rate of 26 μM Mn day−1 in unamended medium and 35 μM Mn day−1 in amended medium. Scanning electron microscope (SEM) observations of both isolates revealed free-living cells in clustered
matrices ≈2 μm diameter. Energy dispersive spectrum of the cell matrix of CR35 cultured in 1 mM Mn detected 30% Mn, while
the cell aggregates of CR48 harbored 7–10% Mn. The relatively high specific activity of these mixotrophic bacteria under relatively
oligotrophic conditions suggests that they may be responsible for scavenging dissolved Mn from the Carlsberg Ridge waters
and could potentially participate in oxidation. 相似文献
78.
Raimundo Fernandes de Araújo Júnior Tatiana Oliveira Souza Caroline Addison Xavier de Medeiros Lélia Batista de Souza Maria de Lourdes Freitas Hévio Freitas de Lucena Maria do Socorro Costa Feitosa Alves Aurigena Antunes de Araújo 《PloS one》2013,8(7)
Periodontal diseases are initiated primarily by Gram-negative, tooth-associated microbial biofilms that elicit a host response that causes osseous and soft tissue destruction. Carvedilol is a β-blocker used as a multifunctional neurohormonal antagonist that has been shown to act not only as an anti-oxidant but also as an anti-inflammatory drug. This study evaluated whether Carvedilol exerted a protective role against ligature-induced periodontitis in a rat model and defined how Carvedilol affected metalloproteinases and RANKL/RANK/OPG expression in the context of bone remodeling. Rats were randomly divided into 5 groups (n = 10/group): (1) non-ligated (NL), (2) ligature-only (LO), and (3) ligature plus Carvedilol (1, 5 or 10 mg/kg daily for 10 days). Periodontal tissue was analyzed for histopathlogy and using immunohistochemical analysis characterized the expression profiles of MMP-2, MMP-9, COX-2, and RANKL/RANK/OPG and determined the presence of IL-1β, IL-10 and TNF-α, myeloperoxidase (MPO), malonaldehyde (MDA) and, glutathione (GSH). MPO activity in the group with periodontal disease was significantly increased compared to the control group (p<0.05). Rats treated with 10 mg/kg Carvedilol presented with significantly reduced MPO and MDA concentrations (p<0.05) in addition to presenting with reduced levels of the pro-inflammatory cytokines IL-1 β and TNF-α (p<0.05). IL-10 levels in Carvedilol-treated rats remained unaltered. Immunohistochemical analysis demonstrated reduced expression of MMP-2, MMP-9, RANK, RANKL, COX-2, and OPG in rats treated with 10 mg/kg Carvedilol. This study demonstrated that Carvedilol affected bone formation/destruction and anti-inflammatory activity in a rat model of periodontitis. 相似文献
79.
Vania Castriani Fernandes da Silva Fabiano Jares Contesini Patrícia de Oliveira Carvalho 《Journal of industrial microbiology & biotechnology》2009,36(7):949-954
Considering the extraordinary microbial diversity and importance of fungi as enzyme producers, the search for new biocatalysts
with special characteristics and possible applications in biocatalysis is of great interest. Here, we report the performance
in the resolution of racemic ibuprofen of a native enantioselective lipase from Aspergillus niger, free and immobilized in five types of support (Accurel EP-100, Amberlite MB-1, Celite, Montmorillonite K10 and Silica gel).
Amberlite MB-1 was found to be the best support, with a conversion of 38.2%, enantiomeric excess of 50.7% and enantiomeric
ratio (E value) of 19 in 72 h of reaction. After a thorough optimization of several parameters, the E value of the immobilized Aspergillus niger lipase was increased (E = 23) in a shorter reaction period (48 h) at 35°C. Moreover, the immobilized Aspergillus niger lipase maintained an esterification activity of at least 80% after 8 months of storage at 4°C and could be reused at least
six times. 相似文献
80.
In order to invade mammalian cells, Trypanosoma cruzi infective forms cause distinct rearrangements of membrane and host cell cytoskeletal components. Rho GTPases have been shown to regulate three separate signal transduction pathways, linking plasma membrane receptors to the assembly of distinct actin filament structures. Here, we examined the role of Rho GTPases on the interaction between different T. cruzi infective forms of strains from the two major phylogenetic lineages with nonpolarized MDCK cells transfected with different Rho GTPase constructs. We compared the infectivity of amastigotes isolated from infected cells (intracellular amastigotes) with forms generated from the axenic differentiation of trypomastigotes (extracellular amastigotes), and also with metacyclic trypomastigotes. No detectable effect of GTPase expression was observed on metacyclic trypomastigote invasion and parasites of Y and CL (T. cruzi II) strains invaded to similar degrees all MDCK transfectants, and were more infective than either G or Tulahuen (T. cruzi I) strains. Intracellular amastigotes were complement sensitive and showed very low infectivity towards the different transfectants regardless of the parasite strain. Complement-resistant T. cruzi I extracellular amastigotes, especially of the G strain, were more infective than T. cruzi II parasites, particularly for the Rac1V12 constitutively active GTPase transfectant. The fact that in Rac1N17 dominant-negative cells, the invasion of G strain extracellular amastigotes was specifically inhibited suggested an important role for Rac1 in this process. 相似文献