全文获取类型
收费全文 | 1051篇 |
免费 | 102篇 |
专业分类
1153篇 |
出版年
2023年 | 3篇 |
2022年 | 12篇 |
2021年 | 25篇 |
2020年 | 27篇 |
2019年 | 33篇 |
2018年 | 47篇 |
2017年 | 34篇 |
2016年 | 41篇 |
2015年 | 58篇 |
2014年 | 62篇 |
2013年 | 57篇 |
2012年 | 91篇 |
2011年 | 77篇 |
2010年 | 52篇 |
2009年 | 49篇 |
2008年 | 54篇 |
2007年 | 52篇 |
2006年 | 43篇 |
2005年 | 41篇 |
2004年 | 37篇 |
2003年 | 36篇 |
2002年 | 27篇 |
2001年 | 19篇 |
2000年 | 21篇 |
1999年 | 18篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 12篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 3篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1970年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有1153条查询结果,搜索用时 0 毫秒
61.
C. R. C. Moreno F. M. Louzada L. R. Teixeira F. Borges G. Lorenzi‐Filho 《Chronobiology international》2013,30(6):1295-1303
Recent studies suggest that short‐sleep duration is independently associated with obesity in the general population. The population of truck drivers is of particular interest, because they frequently work irregular shifts that in turn are associated with short‐sleep duration. In addition, truck drivers have a high prevalence of sedentary habits, poor diet, and obesity. The present study aimed at verifying the association between sleep patterns and factors associated with obesity in this population. The study sample consisted in 4,878 truck drivers who participated in a campaign promoted by a highway company in the State of São Paulo, Brazil. This campaign offered highway truck drivers a medical and laboratorial evaluation. The truck drivers completed a questionnaire concerning demographic data, sleep duration, consumption of medications, and medical problems, such as diabetes, cardiopathy, and hypertension; as well as the Berlin questionnaire, which is able to discriminate low and high risk for obstructive sleep apnea. Blood samples were collected to measure glucose and cholesterol levels. Also, body weight and height were registered to calculate the body mass index (BMI). The mean age (±SD) of the truck drivers studied was 40±10 years. Out of the truck drivers analyzed, 28.3% (n=1,379) had a BMI ≥30.0 Kg/m2 (obesity). Among the 4,878 drivers included in the study, 1,199 (24.6%) were on medications and 334 (6.8%) were diabetic. Drivers (26.9%) with the greater BMI had a short sleep length. The independent factors associated with obesity were sleep duration <8 h/day (OR=1.24), age >40 years (OR=1.20), glucose levels >200 (OR=2.02), cholesterol levels >240 (OR=1.57), snoring (OR=1.74), and hypertension (OR=2.14). Smoking was not associated with obesity (OR=0.69), and diabetes was considered a control variable. In conclusion, this study supports the hypothesis that short sleep duration as well as age >40 years are independently associated with obesity. This particular combination (short‐sleep duration and obesity) is independently associated with several healthcare problems, including high levels of cholesterol, glucose, snoring, and hypertension. However, due to the cross‐sectional nature of this study, no cause–effect relationship can be drawn from these results. 相似文献
62.
Roberto Gargione Junqueira Filho Andréa Beatriz Mendes-Bonato Maria Suely Pagliarini Nilton Cesar Pires Bione Cacilda Borges do Valle Maria Isabel de Oliveira Penteado 《Génome》2003,46(1):83-88
Meiotic division and male gametophyte development were analyzed in one tetraploid (2n = 4x = 36) accession of Brachiaria decumbens cv. Basilisk that showed some pollen sterility. Meiotic process was typical of polyploids in that it consisted of multiple chromosome associations. Precocious chromosome migration to the poles, laggards, and micronucleus formation were abundant in both meiosis I and II and resulted in tetrads with micronuclei. After callose dissolution, microspores were released into the anther locule and had the semblance of being normal. Although each microspore initiated its differentiation by pollen mitosis, in 43.24% of the microspores, nuclear polarization was not observed and the typical hemispherical cell plate was not detected. Division was symmetric and microspores lacked differentiation between the vegetative and the generative cell. Both nuclei were of equal size, presented equal chromatin condensation, and had a spherical shape. After the first pollen mitosis and cytokinesis, each cell underwent a new symmetric mitosis without nuclear polarization. At the end of the second pollen mitosis, four equal nuclei were observed in each pollen grain. After the second cytokinesis, the cells gave rise to four equal-sized pollen grains with a similar tetrad configuration that initially remained together. Sterile pollen grains resulted from abnormal pollen mitosis. This anomaly may be explained by a mutation, probably affecting microtubule cytoskeleton formation. The importance of this male-sterile mutation for Brachiaria breeding programs is discussed. 相似文献
63.
Luciano?Almeida?LealEmail author Leonardo?Evaristo?de?Sousa Patrick?Pascoal?de?Brito Bernhard?Georg?Enders?Neto Artemis?Marti?Ceschin Wiliam?Ferreira?da?Cunha Luiz?Antonio?RibeiroJr. Demétrio?Antonio?da?Silva Filho 《Journal of molecular modeling》2018,24(1):32
The optical properties of systems composed of the polymers PolyeraActivInk? N2200 and P3HT are experimentally and theoretically investigated using UV-Vis spectroscopy and time-dependent density functional theory calculations, respectively. From a theoretical point of view, we carried out an analysis considering several functionals and model oligomers of different sizes to mimic the polymers. As our studies were performed with and without solvents, a first important result regards the fact that, by considering solvent effects, a better agreement between theoretical and experimental results could be achieved. Our findings also show that an optimally tuned functional is better suited to describe the experimental absorption profile than a hybrid one for the flexible polymer (P3HT). For the almost rigid polymer considered here (N2200), on the other hand, hybrid functionals may perform better than tuned functionals. 相似文献
64.
Granja Nde M Ricardo SA Longatto Filho A Alves VA Bedrossian CW Wiley EL Schmitt FC 《Analytical and quantitative cytology and histology / the International Academy of Cytology [and] American Society of Cytology》2005,27(2):61-66
OBJECTIVE: To evaluate the presence of allelic loss in 16q22.1, including the locus of E-cadherin, in pleural effusions in breast cancer patients. STUDY DESIGN: Molecular analysis of DNA was performed using a DNA extraction kit (NucleoSpin, Macherey-Nagel, Germany). Loss of heterozygosity (LOH) in primary tumors and pleural effusions was analyzed using a microsatellite marker of the CDH1 gene, D16S265, described in previous studies. LOH was evaluated by radioactive polymerase chain reaction assay in 17 samples of pleural effusions and breast tissues (primary tumors and nonneoplastic adjacent tissue) from breast cancer patients: 7 positive for neoplastic cells, 6 suspected and 4 cases without evidence of neoplastic cells in the effusions. RESULTS: Thirteen cases (76%) were informative. LOH was detected in 5 cases (38.5%). In 3 of them LOH was detected only in the cytologic sample, and in 2 of them LOH was detected in the primary tumor and cytologic sample. CONCLUSION: Results show that LOH in the CDH1 gene can identify tumor cells in pleural effusions when morphologic analysis is difficult. 相似文献
65.
RJ Pereira RS Verneque PS Lopes ML Santana MR Lagrotta RA Torres AE Vercesi Filho MA Machado 《Genetics and molecular research : GMR》2012,11(2):1599-1609
With the objective of evaluating measures of milk yield persistency, 27,000 test-day milk yield records from 3362 first lactations of Brazilian Gyr cows that calved between 1990 and 2007 were analyzed with a random regression model. Random, additive genetic and permanent environmental effects were modeled using Legendre polynomials of order 4 and 5, respectively. Residual variance was modeled using five classes. The average lactation curve was modeled using a fourth-order Legendre polynomial. Heritability estimates for measures of persistency ranged from 0.10 to 0.25. Genetic correlations between measures of persistency and 305-day milk yield (Y305) ranged from -0.52 to 0.03. At high selection intensities for persistency measures and Y305, few animals were selected in common. As the selection intensity for the two traits decreased, a higher percentage of animals were selected in common. The average predicted breeding values for Y305 according to year of birth of the cows had a substantial annual genetic gain. In contrast, no improvement in the average persistency breeding value was observed. We conclude that selection for total milk yield during lactation does not identify bulls or cows that are genetically superior in terms of milk yield persistency. A measure of persistency represented by the sum of deviations of estimated breeding value for days 31 to 280 in relation to estimated breeding value for day 30 should be preferred in genetic evaluations of this trait in the Gyr breed, since this measure showed a medium heritability and a genetic correlation with 305-day milk yield close to zero. In addition, this measure is more adequate at the time of peak lactation, which occurs between days 25 and 30 after calving in this breed. 相似文献
66.
The Noronha wrasse Thalassoma noronhanum was recorded cleaning 19 client fish species at Fernando de Noronha Archipelago, o. north–eastern Brazil. The preferred clients were non–dangerous, mostly planktivorous species, whereas the potentially dangerous, predatory species were rarely cleaned. T. noronhanum acts as a cleaner in two distinct ecological situations, at and outside the cleaning stations, and attends different client species in each of them. Potentially dangerous clients were mostly attended outside the cleaning stations. Many attacks and two instances of predation on the cleaner wrasse by the grouper client Cephalopholis fulva were recorded. The attacks occurred on individual wrasses foraging near the bottom outside the cleaning stations. 相似文献
67.
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
68.
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69.
AIMS: The objective of the study was to determine the microbiological quality of samples of water and dialysate in a haemodialysis unit. METHODS AND RESULTS: Seventy-two samples each of water and dialysate were collected during November 2003 to April 2004. The following microbiological analyses were performed: test for total and faecal coliforms, which produced negative results for all the samples; counts of total heterotrophic bacteria, where three samples of water and two of dialysate showed levels higher than those permitted by national standards; and endotoxin assay, which revealed high quantities only in samples of water that preceded reverse osmosis. Nonfermenting Gram-negative bacteria were identified in 54 samples of dialysate and in 26 samples of water. The test for adhesion to an inert surface showed that various bacteria were capable of forming biofilms. Twenty-seven per cent of the bacteria were resistant to sodium hypochlorite at 500 ppm for 10-min contact time. Sixty per cent of the isolates were resistant to three or more antibiotics. CONCLUSIONS: Water and dialysate can be a source of infection for patients who need haemodialysis. SIGNIFICANCE AND IMPACT OF THE STUDY: An adequate system for water treatment, disinfection of the haemodialysis system and microbiological monitoring of the water and dialysate are necessary to reduce bacteraemia and pyrogenia outbreaks. 相似文献
70.
Despite the importance of Leucoptera coffeella (Guérin-Mèneville) in coffee production worldwide, there is a lack of information on its reproductive biology. This knowledge will help in mass rearing, as well as support the development of behavioral control techniques for this insect. The purpose of the study was to determine the periodicity of mating and male capture and describe the mating behavior L. coffeella. In laboratory, we observed the periodicity of mating with virgin couples of different ages, zero to five days after emergence. Male activity was studied in a 0.7 ha coffee plantation, cv. Catuaí, where Delta traps were installed at 0.5 m above ground, using either virgin females or rubber septa lured with the synthetic sex pheromone. The sequence of mating behavior was studied by making visual observations and recorded of pairs placed on individual plastic tubes. Mating occurred between 4h and 6h of photophase, when the highest frequencies involved pairs with ages of one and three days after emergence, with peak of mating occurring in 5th hour of photophase. The young or old pairs showed significantly copulation frequency and the peak of matings advance in 1h. The highest male capture occurred at 12p.m. and 13 p.m. by traps with virgin females or traps with synthetic sex pheromone lures, respectively. L. coffeella is one insect with diurnal mating and the mating behavior was not different from what is know for other Lepidoptera species. 相似文献