全文获取类型
收费全文 | 2459篇 |
免费 | 264篇 |
国内免费 | 18篇 |
出版年
2023年 | 9篇 |
2022年 | 26篇 |
2021年 | 47篇 |
2020年 | 55篇 |
2019年 | 58篇 |
2018年 | 73篇 |
2017年 | 60篇 |
2016年 | 94篇 |
2015年 | 115篇 |
2014年 | 105篇 |
2013年 | 159篇 |
2012年 | 153篇 |
2011年 | 163篇 |
2010年 | 99篇 |
2009年 | 91篇 |
2008年 | 106篇 |
2007年 | 113篇 |
2006年 | 95篇 |
2005年 | 94篇 |
2004年 | 103篇 |
2003年 | 93篇 |
2002年 | 78篇 |
2001年 | 93篇 |
2000年 | 79篇 |
1999年 | 62篇 |
1998年 | 33篇 |
1997年 | 25篇 |
1996年 | 20篇 |
1995年 | 16篇 |
1994年 | 21篇 |
1993年 | 20篇 |
1992年 | 42篇 |
1991年 | 37篇 |
1990年 | 35篇 |
1989年 | 26篇 |
1988年 | 33篇 |
1987年 | 23篇 |
1986年 | 30篇 |
1985年 | 24篇 |
1984年 | 14篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 12篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 9篇 |
1976年 | 10篇 |
1974年 | 7篇 |
1969年 | 4篇 |
排序方式: 共有2741条查询结果,搜索用时 15 毫秒
101.
Cesar D. Bordenave Francisco J. Escaray Ana B. Menendez Eva Serna Pedro Carrasco Oscar A. Ruiz Andrés Gárriz 《PloS one》2013,8(12)
Lotus japonicus is a model legume broadly used to study many important processes as nitrogen fixing nodule formation and adaptation to salt stress. However, no studies on the defense responses occurring in this species against invading microorganisms have been carried out at the present. Understanding how this model plant protects itself against pathogens will certainly help to develop more tolerant cultivars in economically important Lotus species as well as in other legumes. In order to uncover the most important defense mechanisms activated upon bacterial attack, we explored in this work the main responses occurring in the phenotypically contrasting ecotypes MG-20 and Gifu B-129 of L. japonicus after inoculation with Pseudomonas syringae DC3000 pv. tomato. Our analysis demonstrated that this bacterial strain is unable to cause disease in these accessions, even though the defense mechanisms triggered in these ecotypes might differ. Thus, disease tolerance in MG-20 was characterized by bacterial multiplication, chlorosis and desiccation at the infiltrated tissues. In turn, Gifu B-129 plants did not show any symptom at all and were completely successful in restricting bacterial growth. We performed a microarray based analysis of these responses and determined the regulation of several genes that could play important roles in plant defense. Interestingly, we were also able to identify a set of defense genes with a relative high expression in Gifu B-129 plants under non-stress conditions, what could explain its higher tolerance. The participation of these genes in plant defense is discussed. Our results position the L. japonicus-P. syringae interaction as a interesting model to study defense mechanisms in legume species. 相似文献
102.
Emilio García García María-Ángeles Vázquez López Rafael Galera Martínez Irene Alias Manuel Martín González Antonio Bonillo Perales José Eugenio Cabrera Sevilla Icíar García Escobar Sara Gómez Bueno Encarnación López Ruzafa Francisco-Javier Muñoz Vico Patricia Oliva Pérez María Ortiz Pérez Juan Poveda González Marisa Rodríguez Lucenilla Firma-Isabel Rodríguez Sánchez Ana Ruiz Sánchez Lucía Ruiz Tudela Sara Torrico 《Endocrinología y nutrición》2013,60(3):121-126
ObjectivesTo estimate the prevalence of obesity and overweight in children and adolescents in our city and to investigate the associated factors.Subjects and methodsA cross-sectional study of 1317 children and adolescents aged 2-16 years. Multistage probability sampling was used to select three groups of subjects: 411 aged 12 to 16 years, 504 aged 6 to 12 years, and 402 aged 2 to 6 years. Body mass index was calculated, and obesity and overweight were diagnosed using the threshold levels of the International Obesity Task Force for children and adolescents. Parents were asked about eating habits, health, social, and demographic aspects. Results are given as percentages (95% confidence interval). The relationship between obesity and overweight and the different variables was studied using multiple logistic regression. The adjusted odds ratio (OR) was calculated.ResultsAmong children and adolescentes aged 2-16 years, 9.5% (8.0%-11.0%) were obese and 22.4% (23.3%-24.6%) were overweight. Of subjects aged 12-16 years, 8.5% (5.9%-11.2%) were obese and 20.5% (16.7%-24.3%) were overweight. In the groups aged 6-12 years and 2-6 years, rates of obesity and overweight were 11.6% (8.9% -14.3%) and 31.0% (27.0-35.0) and 8.0% (5.4%-10.6%) and 13.6% (10.3%-16.9%) respectively. Obesity or overweight was associated to age (OR 1.21; P< 0.001), maternal obesity (OR 10.99; P= 0.008), a birthweight higher than 4 kg (OR 2.91; p 0.002), and formula feeding (OR 1.82; P= 0.005).ConclusionObesity and overweight in children and adolescents are highly prevalent problems in our city. 相似文献
103.
Francisco B. Ortega Jonatan R. Ruiz Manuel J. Castillo 《Endocrinología y nutrición》2013,60(8):458-469
Physical activity and fitness play a significant role in prevention of overweight and obesity in children and adolescentes. Current understanding and evidence from epidemiologic studies provide useful insights to better understand how they relate to each other and how to develop future intervention strategies. This paper summarizes the most relevant information from cross-sectional and longitudinal studies on the relationships between physical activity, physical fitness, and overweight in early life. According to current scientific evidence: (i) High levels of physical activity during childhood and adolescence, particularly vigorous physical activity, are associated to lower total and central adiposity at this age and later in life; (ii) the level of physical fitness, especially aerobic fitness, is inversely related to current and future adiposity levels; (iii) overweight children and adolescents with a high fitness level have a healthier cardiovascular profile than their overweight, low fit peers and a similar profile to their normal weight, low fit peers. This suggests that high fitness levels may counteract the negative consequences attributed to body fat. These findings suggest that increasing physical fitness in overweight children and adolescentes may have many positive effects on health, including lower body fat levels. 相似文献
104.
Enrique Palomo Atance M. José Ballester Herrera Patricio Giralt Muiña Rafael Ruiz Cano Alberto León Martín Juan Giralt Muiña 《Endocrinología y nutrición》2013,60(7):379-385
ObjectiveTo assess the estimated glucose disposal rate (eGDR), insulin dose, and lipoprotein profile in children with type 1 diabetes mellitus (T1DM) and overweight or obesity as compared to children with T1DM and normal weight.MethodsA total of 115 patients (aged 5-16 years) with T1DM on intensive insulin therapy were recruited. The following parameters were measured: weight, height, body mass index, waist and hip circumference, insulin dose, eGDR, glycosylated hemoglobin, blood pressure, and lipoprotein profile. Results were stratified by sex and age.ResultsNo significant differences were found in eGDR between children with normal weight, overweight, and obesity. However, obese children older than 11 years had lower eGDR values (9.3 ± 1.3 vs 10.1 ± 0.8 mg kg-1min-1; p < 0.01). Insulin dose was higher in overweight and obese children, especially in IU/m2/day (37.7 vs 36.1 vs 29.4 respectively; p < 0.01). Obese children had higher low-density lipoprotein cholesterol levels than children with overweight and normal weight (106.5 vs 91.7 vs 91.5 mg/dL respectively; p < 0.01). No correlation was found between waist circumference and the different markers of insulin resistance.ConclusionsValues of eGDR values were lower in obese children with T1DM older than 11 years, and this may therefore be considered a marker of insulin resistance. Insulin dose was higher in diabetic patients with overweight or obesity, specially in IU/m2/day. Obese children with T1DM had a lipoprotein profile of cardiovascular risk. 相似文献
105.
Journal of Ichthyology - Allometric power equations are generated using otolith length and width in order to estimate the total length of five demersal species inhabiting the San Matias Gulf, the... 相似文献
106.
In a three-hour bioassay, we tested the palatability and feeding preferences of Uresiphita maorialis (kōwhai moth) for Sophora tetraptera, Sophora microphylla and Sophora prostrata. Palatability tests showed no differences among the Sophora species. Feeding preferences, on the other hand, showed that S. tetraptera and S. microphylla leaves are preferred over S. prostrata leaves. Our results support our field observations in Wellington city parks and gardens showing that S. tetraptera and S. microphylla plants frequently have higher densities of larvae than S. prostrata. 相似文献
107.
Luciana da Silva Ruiz Sonia Khouri Rosane Christine Hahn Eriques Gonçalves da Silva Vanessa Krummer Perinazzo de Oliveira Rinaldo Ferreira Gandra Claudete Rodrigues Paula 《Mycopathologia》2013,175(3-4):231-239
Opportunistic infections are an increasingly common problem in hospitals, and the yeast Candida parapsilosis has emerged as an important nosocomial pathogen. The aims of this study were to determine and compare (i) the prevalence rate among C. parapsilosis complex organisms isolated from blood in a public children’s hospital in São Paulo state, (ii) the ability of the complex C. parapsilosis species identified to produce biofilm and (iii) the antifungal susceptibility profiles. Forty-nine (49) specimens of isolated blood yeast were analyzed, previously identified as C. parapsilosis by conventional methods. After the molecular analysis, the isolates were characterized as C. parapsilosis sensu stricto (83.7 %), C. orthopsilosis (10.2 %) and C. metapsilosis (6.1 %). All species were able to form biofilm. The species with the highest biofilm production was C. parapsilosis sensu stricto, followed by C. orthopsilosis and further by C. metapsilosis. All of the strains have demonstrated similar susceptibility to fluconazole, caspofungin, voriconazole, cetoconazole and 5-flucytosine. Only one strain of C. parapsilosis was resistant to amphotericin B. Regarding itraconazole, 66.6 and 43.9 % isolates of C. metapsilosis and C. parapsilosis, respectively, have demonstrated to be susceptible dose-dependent, with one isolate of the latter species resistant to the drug. Candida parapsilosis sensu stricto has demonstrated to be the less susceptible, mainly to amphotericin B, caspofungin and “azoles” such as fluconazole. Therefore, C. metapsilosis and C. orthopsilosis are still involved in a restricted number of infections, but these data have become essential for there are very few studies of these species in Latin America. 相似文献
108.
Galileo is a DNA transposon responsible for the generation of several chromosomal inversions in Drosophila. In contrast to other members of the P-element superfamily, it has unusually long terminal inverted-repeats (TIRs) that resemble those of Foldback elements. To investigate the function of the long TIRs we derived consensus and ancestral sequences for the Galileo transposase in three species of Drosophilids. Following gene synthesis, we expressed and purified their constituent THAP domains and tested their binding activity towards the respective Galileo TIRs. DNase I footprinting located the most proximal DNA binding site about 70 bp from the transposon end. Using this sequence we identified further binding sites in the tandem repeats that are found within the long TIRs. This suggests that the synaptic complex between Galileo ends may be a complicated structure containing higher-order multimers of the transposase. We also attempted to reconstitute Galileo transposition in Drosophila embryos but no events were detected. Thus, although the limited numbers of Galileo copies in each genome were sufficient to provide functional consensus sequences for the THAP domains, they do not specify a fully active transposase. Since the THAP recognition sequence is short, and will occur many times in a large genome, it seems likely that the multiple binding sites within the long, internally repetitive, TIRs of Galileo and other Foldback-like elements may provide the transposase with its binding specificity. 相似文献
109.
Uxmal and Tulum are two important Mayan sites in the Yucatan peninsula. The buildings are mainly composed of limestone and grey/black discoloration is seen on exposed walls and copious greenish biofilms on inner walls. The principal microorganisms detected on interior walls at both Uxmal and Tulum were cyanobacteria; heterotrophic bacteria and filamentous fungi were also present. A dark‐pigmented mitosporic fungus and Bacillus cereus, both isolated from Uxmal, were shown to be acidogenic in laboratory cultures. Cyanobacteria belonging to rock‐degrading genera Synechocystis and Gloeocapsa were identified at both sites. Surface analysis previously showed that calcium ions were present in the biofilms on buildings at Uxmal and Tulum, suggesting the deposition of biosolubilized stone. Apart from their potential to degrade the substrate, the coccoid cyanobacteria supply organic nutrients for bacteria and fungi, which can produce organic acids, further increasing stone degradation. 相似文献
110.