全文获取类型
收费全文 | 993篇 |
免费 | 55篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 26篇 |
2021年 | 52篇 |
2020年 | 36篇 |
2019年 | 44篇 |
2018年 | 51篇 |
2017年 | 34篇 |
2016年 | 34篇 |
2015年 | 74篇 |
2014年 | 81篇 |
2013年 | 74篇 |
2012年 | 104篇 |
2011年 | 79篇 |
2010年 | 54篇 |
2009年 | 38篇 |
2008年 | 43篇 |
2007年 | 33篇 |
2006年 | 26篇 |
2005年 | 22篇 |
2004年 | 30篇 |
2003年 | 9篇 |
2002年 | 20篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有1048条查询结果,搜索用时 937 毫秒
121.
JL Proenca-Modena FC Pereira Valera MG Jacob GP Buzatto TH Saturno L Lopes JM Souza FE Paula ML Silva LR Carenzi E Tamashiro E Arruda WT Anselmo-Lima 《PloS one》2012,7(8):e42136
Chronic tonsillar diseases are an important health problem, leading to large numbers of surgical procedures worldwide. Little is known about pathogenesis of these diseases. In order to investigate the role of respiratory viruses in chronic adenotonsillar diseases, we developed a cross-sectional study to determine the rates of viral detections of common respiratory viruses detected by TaqMan real time PCR (qPCR) in nasopharyngeal secretions, tonsillar tissues and peripheral blood from 121 children with chronic tonsillar diseases, without symptoms of acute respiratory infections. At least one respiratory virus was detected in 97.5% of patients. The viral co-infection rate was 69.5%. The most frequently detected viruses were human adenovirus in 47.1%, human enterovirus in 40.5%, human rhinovirus in 38%, human bocavirus in 29.8%, human metapneumovirus in 17.4% and human respiratory syncytial virus in 15.7%. Results of qPCR varied widely between sample sites: human adenovirus, human bocavirus and human enterovirus were predominantly detected in tissues, while human rhinovirus was more frequently detected in secretions. Rates of virus detection were remarkably high in tonsil tissues: over 85% in adenoids and close to 70% in palatine tonsils. In addition, overall virus detection rates were higher in more hypertrophic than in smaller adenoids (p = 0.05), and in the particular case of human enteroviruses, they were detected more frequently (p = 0.05) in larger palatine tonsils than in smaller ones. While persistence/latency of DNA viruses in tonsillar tissues has been documented, such is not the case of RNA viruses. Respiratory viruses are highly prevalent in adenoids and palatine tonsils of patients with chronic tonsillar diseases, and persistence of these viruses in tonsils may stimulate chronic inflammation and play a role in the pathogenesis of these diseases. 相似文献
122.
José Alexandre Felizola Diniz-Filho Dayane Borges Melo Guilherme de Oliveira Rosane Garcia Collevatti Thannya Nascimento Soares Jo?o Carlos Nabout Jacqueline de Souza Lima Ricardo Dobrovolski Lázaro José Chaves Ronaldo Veloso Naves Rafael Dias Loyola Mariana Pires de Campos Telles 《Conservation Genetics》2012,13(4):1085-1093
Systematic Conservation Planning (SCP) involves a series of steps that should be accomplished to determine the most cost-effective way to invest in conservation action. Although SCP has been usually applied at the species level (or hierarchically higher), it is possible to use alleles from molecular analyses at the population level as basic units for analyses. Here we demonstrate how SCP procedures can be used to establish optimum strategies for in situ and ex situ conservation of a single species, using Dipteryx alata (a Fabaceae tree species widely distributed and endemics to Brazilian Cerrado) as a case study. Data for the analyses consisted in 52 alleles from eight microsatellite loci coded for a total of 644 individual trees sampled in 25 local populations throughout species’ geographic range. We found optimal solutions in which seven local populations are the smallest set of local populations of D. alata that should be conserved to represent the known genetic diversity. Combining these several solutions allowed estimating the relative importance of the local populations for conserving all known alleles, taking into account the current land-use patterns in the region. A germplasm collection for this species already exists, so we also used SCP approach to identify the smallest number of populations that should be further collected in the field to complement the existing collection, showing that only four local populations should be sampled for optimizing the species ex situ representation. The initial application of the SCP methods to genetic data showed here can be a useful starting point for methodological and conceptual improvements and may be a first important step towards a comprehensive and balanced quantitative definition of conservation goals, shedding light to new possibilities for in situ and ex situ designs within species. 相似文献
123.
Santos-Filho OA Forge D Hoelz LV de Freitas GB Marinho TO Araújo JQ Albuquerque MG de Alencastro RB Boechat N 《Journal of molecular modeling》2012,18(9):4061-4072
Pneumocystis carinii is typically a non-pathogenic fungus found in the respiratory tract of healthy humans. However, it may cause P. carinii pneumonia (PCP) in people with immune deficiency, affecting mainly premature babies, cancer patients and transplant recipients, and people with acquired immunodeficiency syndrome (AIDS). In the latter group, PCP occurs in approximately 80% of patients, a major cause of death. Currently, there are many available therapies to treat PCP patients, including P. carinii dihydrofolate reductase (PcDHFR) inhibitors, such as trimetrexate (TMX), piritrexim (PTX), trimethoprim (TMP), and pyrimethamine (PMT). Nevertheless, the high percentage of adverse side effects and the limited therapeutic success of the current drug therapy justify the search for new drugs rationally planned against PCP. This work focuses on the study of pyrimidine inhibitors of PcDHFR, using both CoMFA and CoMSIA 3D-QSAR methods. 相似文献
124.
Soares JB Pimentel-Nunes P Afonso L Rolanda C Lopes P Roncon-Albuquerque R Gonçalves N Boal-Carvalho I Pardal F Lopes S Macedo G Lara-Santos L Henrique R Moreira-Dias L Gonçalves R Dinis-Ribeiro M Leite-Moreira AF 《Innate immunity》2012,18(5):700-708
We evaluated expression of TLR2, TLR4 and proinflammatory genes [NF-κB, TNF-α, cyclooxygenase-2 (COX-2)] in liver samples of patients in different stages of liver disease. Fifteen patients with unexplained transaminases elevation (reference group), 22 with viral chronic hepatitis (hepatitis group), 14 with virus-induced severe fibrosis/cirrhosis (cirrhosis group) and 10 with hepatocarcinoma (hepatocarcinoma group) were consecutively included in the study. Quantification of TLR2, TLR4, NF-κB, TNF-α and COX-2 mRNA was done by real-time RT-PCR and TLR2 and TLR4 protein expression was evaluated by immunohistochemistry. Compared with reference, TLR2 and TLR4 mRNA was increased in hepatitis (TLR2: 2.66?±?0.69; TLR4: 3.11?±?0.79; P?0.05) and cirrhosis (TLR2: 2.14?±?0.5; TLR4: 1.74?±?0.27; P?0.05) and decreased in hepatocarcinoma (TLR2: 0.48?±?0.15; TLR4: 0.54?±?0.10; P?0.05). This associated with increased TNF-α and COX-2 mRNA in hepatitis (TNF-α: 3.24?±?0.79; COX-2: 2.47?±?0.36; P?0.05) and cirrhosis (TNF-α: 1.73?±?0.28; COX-2: 1.8?±?0.35, P?0.05), whereas NF-κB mRNA was increased in hepatitis (2.42?±?0.31; P?0.05) and unchanged in cirrhosis (1.34?±?0.17; P?=?0.3). Hepatocarcinoma presented increased COX-2 mRNA (1.63?±?0.15; P?0.05) and maintained (at decreased levels) mRNA of NF-κB (0.52?±?0.12) and TNF-α (0.52?±?0.12; P?0.05, all genes). Immunohistochemistry confirmed increased expression of TLR2 and TLR4 in hepatitis and cirrhosis and maintained expression in hepatocarcinoma. Upregulation of TLR2, TLR4 and their proinflammatory mediators is associated with virus-induced hepatic IFC sequence. 相似文献
125.
126.
Vasconcelos AF Monteiro NK Dekker RF Barbosa AM Carbonero ER Silveira JL Sassaki GL da Silva R de Lourdes Corradi da Silva M 《Carbohydrate research》2008,343(14):2481-2485
Four exopolysaccharides (EPS) obtained from Botryosphaeria rhodina strains isolated from rotting tropical fruit (graviola, mango, pinha, and orange) grown on sucrose were purified on Sepharose CL-4B. Total acid hydrolysis of each EPS yielded only glucose. Data from methylation analysis and (13)C NMR spectroscopy indicated that the EPS from the graviola isolate consisted of a main chain of glucopyranosyl (1-->3) linkages substituted at O-6 as shown in the putative structure below: [carbohydrate structure: see text]. The EPS of the other fungal isolates consisted of a linear chain of (1-->6)-linked glucopyranosyl residues of the following structure: [carbohydrate structure: see text]. FTIR spectra showed one band at 891 cm(-1), and (13)C NMR spectroscopy showed that all glucosidic linkages were of the beta-configuration. Dye-inclusion studies with Congo Red indicated that each EPS existed in a triple-helix conformational state. beta-(1-->6)-d-Glucans produced as exocellular polysaccharides by fungi are uncommon. 相似文献
127.
de Lourdes Corradi da Silva M Fukuda EK Vasconcelos AF Dekker RF Matias AC Monteiro NK Cardoso MS Barbosa AM Silveira JL Sassaki GL Carbonero ER 《Carbohydrate research》2008,343(4):793-798
Three D-glucans were isolated from the mycelium of the fungus Botryosphaeria rhodina MAMB-05 by sequential extraction with hot-water and hot aqueous KOH (2% w/v) followed by ethanol precipitation. Following their purification by gel permeation chromatography on Sepharose CL-4B, the structural characteristics of the D-glucans were determined by FT-IR and 13C NMR spectroscopy and, after methylation, by GC-MS. The hot-water extract produced a fraction designated Q1A that was a beta-(1-->6)-D-glucan with the following structure: [Formula: see text] The alkaline extract, when subjected to repeated freeze-thawing, yielded two fractions: K1P (insoluble) that comprised a beta-(1-->3)-D-glucan with beta-D-glucose branches at C-6 with the structure: [Formula: see text] and K1SA (soluble) consisting of a backbone chain of alpha-(1-->4)-linked D-glucopyranosyl residues substituted at O-6 with alpha-D-glucopyranosyl residues: [Formula: see text] 相似文献
128.
José Guilherme Chaui-Berlinck José Alexandre Marzagão Barbuto Luiz Henrique Alves Monteiro 《Theorie in den Biowissenschaften》2004,123(2):195-208
Summary A continuous harvest effort can lead a population to extinction. How an “unconscious” immune system would perpetrate such
an effort in order to eliminate a self-replicating antigen (a pathogen) becomes an intriguing problem if the system responses
are functions of the pathogen population: the responses cannot be a continuous effort as the pathogen vanishes. On theoretical
grounds, we show some qualities an immune response must have to support pathogen elimination. Then, three specific mechanisms
are addressed: a pathogen-independent positive feedback loop among the responding cells of the system (e.g., B-lymphocyte
and T-helper); the persistence of antigen bound to presenting cells; and the programmed expansion/contraction of a pool of
responding cells. The maintenance of responding cells due to these mechanisms is the essential feature to the effective clearance
of self-replicating agents. Thus, evolutionarily, the primary function of a helper lymphocyte would be to amplify a response
and the primary function of memory would be the very elimination of pathogens. 相似文献
129.
Retail Survey of Brazilian Milk and Minas Frescal Cheese and a Contaminated Dairy Plant To Establish Prevalence, Relatedness, and Sources of Listeria monocytogenes Isolates
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J. Renaldi F. Brito Emilia M. P. Santos Edna F. Arcuri Carla C. Lange Maria A. V. P. Brito Guilherme N. Souza Mnica M. P. O. Cerqueira J. Marcela Soto Beltran Jeffrey E. Call Yanhong Liu Anna C. S. Porto-Fett John B. Luchansky 《Applied microbiology》2008,74(15):4954-4961
A study was designed to recover Listeria monocytogenes from pasteurized milk and Minas frescal cheese (MFC) sampled at retail establishments (REs) and to identify the contamination source(s) of these products in the corresponding dairy processing plant. Fifty milk samples (9 brands) and 55 MFC samples (10 brands) were tested from REs located in Juiz de Fora, Minas Gerais, Brazil. All milk samples and 45 samples from 9 of 10 MFC brands tested negative for L. monocytogenes; however, “brand F” of MFC obtained from REs 119 and 159 tested positive. Thus, the farm/plant that produced brand F MFC was sampled; all samples from the milking parlor tested negative for L. monocytogenes, whereas several sites within the processing plant and the MFC samples tested positive. All 344 isolates recovered from retail MFC, plant F MFC, and plant F environmental samples were serotype 1/2a and displayed the same AscI or ApaI fingerprints. Since these results established that the storage coolers served as the contamination source of the MFC, plant F was closed so that corrective renovations could be made. Following renovation, samples from sites that previously tested positive for the pathogen were collected from the processing environment and from MFC on multiple visits; all tested negative for L. monocytogenes. In addition, on subsequent visits to REs 159 and 119, all MFC samples tested negative for the pathogen. Studies are ongoing to quantify the prevalence, levels, and types of L. monocytogenes in MFC and associated processing plants to lessen the likelihood of listeriosis in Brazil. 相似文献
130.
Muricy Guilherme Hajdu Eduardo Minervino José Valter Madeira Ana Verena Peixinho Solange 《Hydrobiologia》2001,443(1-3):103-128
The status, scope and classification of the sublithistid demosponge genus Petromica Topsent are revised through morphological analysis of museum specimens of all seven species (including proposed synonyms and varieties), two of which were collected and observed in situ along the Brazilian coast (P. ciocalyptoides (Van Soest & Zea) and P. citrina sp. n.). The synonymy of Petromica and Monanthus Kirkpatrick with priority to the former is justified due to the consistent presence of monocrepid rhizoclone desmas and oxeas in an halichondroid arrangement, and to the lack of co-variance in other morphological characters among the species studied (presence and shape of papillae, surface texture, ectosomal skeleton and desma shape). The proposed synonymy of P. grimaldii Topsent and P. massalis Dendy is refuted due to differences in habit and spicule shape between the two species. Three forms described as varieties of Monanthus plumosus Kirkpatrick are raised to species level: P. plumosa (Kirkpatrick), P. tubulata (Kirkpatrick) and P. digitata (Burton). Phylogenetic analysis indicates that two possibly monophyletic clades may be recognized within Petromica, although with low bootstrap support (35–59%): (P. ciocalyptoides, P. citrina) and (P. grimaldii, P. massalis) (P. plumosa) (P. tubulata) (P. digitata). The classification of Petromica within the Halichondriidae (order Halichondrida) is supported by the confused reticulation of long oxeote spicules with ascending spicule tracts, present in all species of the genus. 相似文献