全文获取类型
收费全文 | 324篇 |
免费 | 29篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 13篇 |
2016年 | 21篇 |
2015年 | 30篇 |
2014年 | 19篇 |
2013年 | 28篇 |
2012年 | 36篇 |
2011年 | 32篇 |
2010年 | 17篇 |
2009年 | 12篇 |
2008年 | 18篇 |
2007年 | 20篇 |
2006年 | 17篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 11篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有353条查询结果,搜索用时 687 毫秒
101.
Dore MP Negrini R Tadeu V Marras L Maragkoudakis E Nieddu S Simula L Cherchi GB Massarelli G Realdi G 《Helicobacter》2004,9(3):228-232
BACKGROUND: A number of noninvasive tests have been developed to establish the presence of Helicobacter pylori infection. Although polyclonal antibody-based stool antigen testing has a good sensitivity and specificity, it is less accurate than urea breath testing. Recently, a monoclonal antibody-based stool antigen test demonstrated an excellent performance in diagnosing H. pylori infection in adults and in pediatric populations. AIM: To evaluate the diagnostic accuracy of a novel stool test based on monoclonal antibodies to detect H. pylori antigens in frozen human stool in the pretreatment setting. PATIENTS AND METHODS: Stool specimens were prospectively collected from 78 patients undergoing gastroscopy and stored at -20 degrees C until tested. Helicobacter pylori infection was evaluated by histology, rapid urease testing and urea breath tests ((13)C-UBT). Positivity of the three tests was considered the gold standard for H. pylori active infection. Patients with no positive test were considered negative. The gold standard was compare to the results of the monoclonal antibody stool antigen test. Frozen stool specimens were tested using a novel monoclonal-antibody-based enzyme immunoassay (HePy-Stool, Biolife-Italiana, Milan, Italy). RESULTS: The sensitivity and specificity of the monoclonal stool antigen test were 97%[95% confidence interval, (CI) 86-100] and 94% (95% CI: 81-99), respectively. Negative and positive predictive values were 97% (95% CI: 85-99), and 95% (95% CI: 83-99), respectively. The diagnostic accuracy was 96% (95% CI: 88-99). The likelihood ratio for a positive test was 17 and for a negative test was 0. CONCLUSIONS: Although the (13)C-UBT is the most accurate among the available noninvasive tests, our results show that an H. pylori stool test using monoclonal antibody might be an excellent alternative. 相似文献
102.
Riccio EK Neves I Banic DM Corte-Real S Alecrim Md Morgado M Daniel-Ribeiro CT Ferreira-da-Cruz Mde F 《Cryobiology》2002,45(2):127-134
Studies performed with malaria patients living in endemic areas are frequently conducted in laboratories located hundreds of kilometer away from research centers, due to the difficulties in performing the assays in field conditions. Thus, we considered the potential indication of cryopreservation of peripheral blood mononuclear cells (PBMC), in most fieldwork, and decided to evaluate the effect of cryopreservation of PBMC on spontaneous apoptosis. The membrane integrity of PBMC was tested using three previously described protocols of cryopreservation. Cell samples were obtained from 19 healthy volunteers. Percentage of apoptotic nuclei in short-term PBMC cultures was determined by a sensitive method using 7-aminoactinomycin D followed by flow cytometry. Our results indicate that although cryopreservation can to some extent affect lymphocyte membrane integrity rates, flow cytometry analysis showed that frequencies of spontaneous apoptosis in cryopreserved cells were not significantly modified after 24-h culture. It is concluded that cryopreserved PBMC could be used for measuring spontaneous apoptosis and therefore, could be employed for the study of populations living in areas distant from research centers, allowing the comparative evaluation of samples obtained at different time. 相似文献
103.
Saúl A. Villafañe-Barajas João Paulo T. Baú María Colín-García Alicia Negrón-Mendoza Alejandro Heredia-Barbero Teresa Pi-Puig Dimas A. M. Zaia 《Origins of life and evolution of the biosphere》2018,48(2):181-200
Any proposed model of Earth’s primitive environments requires a combination of geochemical variables. Many experiments are prepared in aqueous solutions and in the presence of minerals. However, most sorption experiments are performed in distilled water, and just a few in seawater analogues, mostly inconsistent with a representative primitive ocean model. Therefore, it is necessary to perform experiments that consider the composition and concentration of dissolved salts in the early ocean to understand how these variables could have affected the absorption of organic molecules into minerals. In this work, the adsorption of adenine, adenosine, and 5’AMP onto Na+montmorillonite was studied using a primitive ocean analog (4.0 Ga) from experimental and computational approaches. The order of sorption of the molecules was: 5’AMP?>?adenine > adenosine. Infrared spectra showed that the interaction between these molecules and montmorillonite occurs through the NH2 group. In addition, electrostatic interaction between negatively charged montmorillonite and positively charge N1 of these molecules could occur. Results indicate that dissolved salts affect the sorption in all cases; the size and structure of each organic molecule influence the amount sorbed. Specifically, the X-ray diffraction patterns show that dissolved salts occupy the interlayer space in Na-montmorillonite and compete with organic molecules for available sites. The adsorption capacity is clearly affected by dissolved salts in thermodynamic terms as deduced by isotherm models. Indeed, molecular dynamic models suggest that salts are absorbed in the interlamellar space and can interact with oxygen atoms exposed in the edges of clay or in its surface, reducing the sorption of the organic molecules. This research shows that the sorption process could be affected by high concentration of salts, since ions and organic molecules may compete for available sites on inorganic surfaces. Salt concentration in primitive oceans may have strongly affected the sorption, and hence the concentration processes of organic molecules on minerals. 相似文献
104.
Christiano Robles Rodrigues Alves Marcello Tadeu Caetano Borelli Vitor de Salles Paineli Rafael de Almeida Azevedo Claudia Cristine Gomes Borelli Ant?nio Herbert Lancha Junior Bruno Gualano Guilherme Giannini Artioli 《PloS one》2015,10(4)
The current investigation aimed to develop a valid specific field test to evaluate anaerobic physical performance in Aerobic Gymnastics athletes. We first designed the Specific Aerobic Gymnast Anaerobic Test (SAGAT), which included gymnastics-specific elements performed in maximal repeated sprint fashion, with a total duration of 80-90 s. In order to validate the SAGAT, three independent sub-studies were performed to evaluate the concurrent validity (Study I, n=8), the reliability (Study II, n=10) and the sensitivity (Study III, n=30) of the test in elite female athletes. In Study I, a positive correlation was shown between lower-body Wingate test and SAGAT performance (Mean power: p = 0.03, r = -0.69, CI: -0.94 to 0.03 and Peak power: p = 0.02, r = -0.72, CI: -0.95 to -0.04) and between upper-body Wingate test and SAGAT performance (Mean power: p = 0.03, r = -0.67, CI: -0.94 to 0.02 and Peak power: p = 0.03, r = -0.69, CI: -0.94 to 0.03). Additionally, plasma lactate was similarly increased in response to SAGAT (p = 0.002), lower-body Wingate Test (p = 0.021) and a simulated competition (p = 0.007). In Study II, no differences were found between the time to complete the SAGAT in repeated trials (p = 0.84; Cohen’s d effect size = 0.09; ICC = 0.97, CI: 0.89 to 0.99; MDC95 = 0.12 s). Finally, in Study III the time to complete the SAGAT was significantly lower during the competition cycle when compared to the period before the preparatory cycle (p < 0.001), showing an improvement in SAGAT performance after a specific Aerobic Gymnastics training period. Taken together, these data have demonstrated that SAGAT is a specific, reliable and sensitive measurement of specific anaerobic performance in elite female Aerobic Gymnastics, presenting great potential to be largely applied in training settings. 相似文献
105.
106.
Camilo Guzmán Salim Mattar Silvana Levis Noemí Pini Tadeu Figueiredo James Mills Jorge Salazar-Bravo 《Memórias do Instituto Oswaldo Cruz》2013,108(2):167-171
We tested sera from 286 agricultural workers and 322 rodents in the department of Córdoba, northeastern Colombia, for antibodies against two hantaviruses. The sera were analysed by indirect ELISA using the lysate of Vero E6 cells infected with Maciel virus (MACV) or the N protein of Araraquara virus (ARAV) as antigens for the detection of antibodies against hantaviruses. Twenty-four human sera were IgG positive using one or both antigens. We detected anti-MACV IgG antibodies in 10 sera (3.5%) and anti-ARAV antibodies in 21 sera (7.34%). Of the 10 samples that were positive for MACV, seven (70%) were cross-reactive with ARAV; seven of the 21 ARAV-positive samples were cross-reactive with MACV. Using an ARAV IgM ELISA, two of the 24 human sera (8.4%) were positive. We captured 322 rodents, including 210 Cricetidae (181 Zygodontomys brevicauda, 28 Oligoryzomys fulvescens and 1 Oecomys trinitatis), six Heteromys anomalus (Heteromyidae), one Proechimys sp. (Echimyidae) and 105 Muridae (34 Rattus rattus and 71 Mus musculus). All rodent sera were negative for both antigens. The 8.4% detection rate of hantavirus antibodies in humans is much higher than previously found in serosurveys in North America, suggesting that rural agricultural workers in northeastern Colombia are frequently exposed to hantaviruses. Our results also indicate that tests conducted with South American hantavirus antigens could have predictive value and could represent a useful alternative for the diagnosis of hantavirus infection in Colombia. 相似文献
107.
Paulo Silva de Almeida Alan Sciamarelli Paulo Mira Batista Ademar Dimas Ferreira Jo?o Nascimento Josué Raizer José Dilermando Andrade Filho Rodrigo Gurgel-Gon?alves 《Memórias do Instituto Oswaldo Cruz》2013,108(8):992-996
To understand the geographic distribution of visceral leishmaniasis (VL) in the state
of Mato Grosso do Sul (MS), Brazil, both the climatic niches of Lutzomyia
longipalpis and VL cases were analysed. Distributional data were obtained
from 55 of the 79 counties of MS between 2003-2012. Ecological niche models (ENM) of
Lu. longipalpis and VL cases were produced using the maximum
entropy algorithm based on eight climatic variables. Lu. longipalpis
showed a wide distribution in MS. The highest climatic suitability for Lu.
longipalpis was observed in southern MS. Temperature seasonality and
annual mean precipitation were the variables that most influenced these models. Two
areas of high climatic suitability for the occurrence of VL cases were predicted: one
near Aquidauana and another encompassing several municipalities in the southeast
region of MS. As expected, a large overlap between the models for Lu.
longipalpis and VL cases was detected. Northern and northwestern areas of
MS were suitable for the occurrence of cases, but did not show high climatic
suitability for Lu. longipalpis . ENM of vectors and human cases
provided a greater understanding of the geographic distribution of VL in MS, which
can be applied to the development of future surveillance strategies. 相似文献
108.
109.
Islands are simplified, isolated ecosystems, providing an ideal set‐up to study evolution. Among several traits that are expected to change on islands, an interesting but poorly understood example concerns signals used in animal communication. Islands are typified by reduced species diversity, increased population density, and reduced mate competition, all of which could affect communication signals. We used birdsong to investigate whether there are systematic changes in communication signals on islands, by undertaking a broad comparison based on pairs of closely related island‐mainland species across the globe. We studied song traits related to complexity (number of different syllables, frequency bandwidth), to vocal performance (syllable delivery rate, song duration), and also three particular song elements (rattles, buzzes, and trills) generally implicated in aggressive communication. We also investigated whether song complexity was related to the number of similar sympatric species. We found that island species were less likely to produce broadband and likely aggressive song elements (rattles and buzzes). By contrast, various aspects of song complexity and performance did not differ between island and mainland species. Species with fewer same‐family sympatric species used wider frequency bandwidths, as predicted by the character release hypothesis, both on continents and on islands. Our study supports the hypothesis of a reduction in aggressive behavior on islands and suggests that discrimination against closely related species is an important factor influencing birdsong evolution. 相似文献
110.
Amanda Mizukami Maristela D. Orellana Sâmia R. Caruso Karen de Lima Prata Dimas T. Covas Kamilla Swiech 《Biotechnology progress》2013,29(2):568-572
The need for efficient and reliable technologies for clinical‐scale expansion of mesenchymal stromal cells (MSC) has led to the use of disposable bioreactors and culture systems. Here, we evaluate the expansion of cord blood‐derived MSC in a disposable fixed bed culture system. Starting from an initial cell density of 6.0 × 107 cells, after 7 days of culture, it was possible to produce of 4.2(±0.8) × 108 cells, which represents a fold increase of 7.0 (±1.4). After enzymatic retrieval from Fibra‐Cell disks, the cells were able to maintain their potential for differentiation into adipocytes and osteocytes and were positive for many markers common to MSC (CD73, CD90, and CD105). The results obtained in this study demonstrate that MSC can be efficiently expanded in the culture system. This novel approach presents several advantages over the current expansion systems, based on culture flasks or microcarrier‐based spinner flasks and represents a key element for MSC cellular therapy according to GMP compliant clinical‐scale production system. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29: 568–572, 2013 相似文献