全文获取类型
收费全文 | 2201篇 |
免费 | 175篇 |
国内免费 | 1篇 |
出版年
2023年 | 12篇 |
2022年 | 27篇 |
2021年 | 51篇 |
2020年 | 21篇 |
2019年 | 24篇 |
2018年 | 55篇 |
2017年 | 38篇 |
2016年 | 56篇 |
2015年 | 98篇 |
2014年 | 92篇 |
2013年 | 153篇 |
2012年 | 148篇 |
2011年 | 183篇 |
2010年 | 107篇 |
2009年 | 106篇 |
2008年 | 141篇 |
2007年 | 113篇 |
2006年 | 113篇 |
2005年 | 119篇 |
2004年 | 121篇 |
2003年 | 112篇 |
2002年 | 85篇 |
2001年 | 14篇 |
2000年 | 17篇 |
1999年 | 22篇 |
1998年 | 26篇 |
1997年 | 17篇 |
1996年 | 24篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1993年 | 21篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1977年 | 6篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有2377条查询结果,搜索用时 15 毫秒
991.
Growth rate, osmotic potential of the cell, cell wall mechanical properties, sugar composition and molecular weight (MW) distribution of water-soluble hemicellulosic polysaccharides of the second leaf sheath of one tall ( Oryza sativa L. cv. Nihonbare) and two dwarf ( Oryza sativa L. cvs. Tan-ginbozu and Waito C) cultivars of rice were compared. The effect of gibberellic acid (GA3 ) on the above-mentioned parameters was also studied using the tall (Nihonbare) and one of the dwarf (Waito C) cultivar. The minimum stress-relaxation time (T0 ) was higher in the cell wall from the two dwarfs than in the tall cultivar. Furthermore, in the water-soluble hemicellulosic polysaccharides the mass-average MW of β -glucan was higher and that of arabinoxylan was lower in the tall cultivar than in the dwarf ones. Thus, dwarfism of cvs Tan-ginbnozu and Waito C might be correlated with the different MW distributions of β -glucan and arabinoxylan. GA3 induces growth in the dwarf Waito C cultivar, decreases the T0 value of the cell wall, and also decreases the average MW of water-soluble hemicelluloses. Changes in β (1–3)(1–4)glucan or arabinoxylan or in both are proposed as part of the cell wall loosening mechanism induced by gibberellin. 相似文献
992.
Carolina Isaza Carlos Martorell Daniela Cevallos Gloria Galeano Renato Valencia Henrik Balslev 《Population Ecology》2016,58(3):463-476
Oenocarpus bataua is the seventh most abundant tree in the Amazon and one of the most used palms in the region. The main resource obtained from the species is the fruits that are harvested from wild populations for human consumption. Across its distribution area adults are most frequently felled to obtain the racemes, which may affect the palm's populations. In this paper we studied the demography of two populations of Oenocarpus bataua to assess the harvest potential of its fruits and the density variation in different habitats in the western Amazon to estimate fruit yields in different forest types. Non-inundated lands held the greatest densities with an average of 11 adults ha−1 (0–132 adults ha−1). The population finite growth rate (λ) in Amacayacu, Colombia, was 0.9103 because of slow growth and low survival of stemless individuals and low recruitment. On the contrary, in Yasuní, Ecuador, we found a growing population with λ = 1.0368. According to our simulations, adult felling reduced transient population growth (λt) in both populations, especially when harvest was frequent even at low intensities. In Amacayacu a simulated harvest of 60 % year−1 of the fruits by climbing did not modify λt substantially, while in Yasuní, a regime of 80 % of annual harvest did not diminish λt below one and the initial number of adults. The results help to understand the demography of useful palms and to address sustainable management. For instance high yields can be obtained by shifting to non-destructive harvest techniques that can meet the increasing demand and maintain the populations. 相似文献
993.
César Rafael Fanchini Terrasan Caio Casale Aragon Douglas Chodi Masui Benevides Costa Pessela Gloria Fernandez-Lorente Eleonora Cano Carmona 《Biocatalysis and Biotransformation》2016,34(4):161-171
The tetrameric β-xylosidase from Selenomonas ruminantium is very stable in alkaline pH allowing it to easily immobilize by multipoint covalent attachments on highly activated glyoxyl agarose gels. Initial immobilization resulted only in slight stabilization in relation to the free enzyme, since involvement of all subunits was not achieved. Coating the catalyst with aldehyde-dextran or polyethylenimine, fully stabilized the quaternary structure of the enzyme rendering much more stabilization to the biocatalyst. The catalyst coated with polyethylenimine of molecular weight 1300 is the most stable one exhibiting an interesting half-life of more than 10 days at pH 5.0 and 50?°C, being, therefore, 240-fold more stable than free enzyme. Optimum activity was observed in the pH range 4.0–6.0 and at 55?°C. The catalyst retained its side activity against p-nitrophenyl α-l-arabinofuranoside and it was inhibited by xylose and glucose. Kinetic parameters with p-nitrophenyl β-d-xylopyranoside as substrate were Vmax 0.20?μmol.min?1?mg?prot.?1, Km 0.45?mM, Kcat 0.82?s?1, and Kcat/Km 1.82?s?1?mM?1. Xylose release was observed from the hydrolysis of xylooligosaccharides with a decrease in the rate of xylose release by increasing substrate chain-length. Due to the high thermostability and the complete stability after five reuse cycles, the applicability of this biocatalyst in biotechnological processes, such as for the degradation of lignocellulosic biomass, is highly increased. 相似文献
994.
Norma Amador-Licona Teresa A. Díaz-Murillo Genaro Gabriel-Ortiz Fermín P. Pacheco-Moises Texar A. Pereyra-Nobara Juan M. Guízar-Mendoza Gloria Barbosa-Sabanero Gustavo Orozco-Avi?a Sandra C. Moreno-Martínez Rafael Luna-Montalbán Eduardo Vázquez-Valls 《PloS one》2016,11(3)
HIV-seropositive patients show high incidence of coronary heart disease and oxidative stress has been described as relevant key in atherosclerosis development. The aim of this study was to assess the effect of omega 3 fatty acids on different markers of oxidative stress in HIV-seropositive patients. We performed a randomized parallel controlled clinical trial in The Instituto Mexicano del Seguro Social, a public health hospital. 70 HIV-seropositive patients aged 20 to 55 on clinical score A1, A2, B1 or B2 receiving highly active antiretroviral therapy (HAART) were studied. They were randomly assigned to receive omega 3 fatty acids 2.4 g (Zonelabs, Marblehead MA) or placebo for 6 months. At baseline and at the end of the study, anthropometric measurements, lipid profile, glucose and stress oxidative levels [nitric oxide catabolites, lipoperoxides (malondialdehyde plus 4-hydroxialkenals), and glutathione] were evaluated. Principal HAART therapy was EFV/TDF/FTC (55%) and AZT/3TC/EFV (15%) without difference between groups. Treatment with omega 3 fatty acids as compared with placebo decreased triglycerides (-0.32 vs. 0.54 mmol/L; p = 0.04), but oxidative stress markers were not different between groups.
Trial Registration
ClinicalTrials.gov NCT02041520相似文献995.
Gloria Crepaldi Carlo Alberto Scirè Greta Carrara Garifallia Sakellariou Roberto Caporali Ihsane Hmamouchi Maxime Dougados Carlomaurizio Montecucco 《PloS one》2016,11(1)
Objectives
To explore the influence of comorbidities on clinical outcomes and disease activity in rheumatoid arthritis (RA).Methods
In patients included in the cross-sectional observational multicenter international study COMORA, demographics, disease characteristics and comorbidities (hypertension, diabetes, hyperlipidemia, renal failure, ischemic heart disease, stroke, cancer, gastro-intestinal ulcers, hepatitis, depression, chronic pulmonary disease, obesity) were collected. Multivariable linear regression models explored the relationship between each comorbidity and disease activity measures: 28-swollen joint count (SJC), 28-tender joint count (TJC), erythrocyte sedimentation rate (ESR), patient’s and physician’s global assessment (PtGA, PhGA), patient reported fatigue and 28-Disease Activity Score (DAS28). Results are expressed as mean difference (MD) adjusted for the main confounders (age, gender, disease characteristics and treatment).Results
A total of 3,920 patients were included: age (mean ±SD) 56.27 ±13.03 yrs, female 81.65%, disease duration median 7.08 yrs (IQR 2.97–13.27), DAS28 (mean ±SD) 3.74 ± 1.55. Patients with diabetes had more swollen and tender joints and worse PtGA and PhGA (MD +1.06, +0.93, +0.53 and +0.54, respectively). Patients with hyperlipidemia had a lower number of swollen and tender joints, lower ESR and better PtGA and PhGA (MD -0.77, -0.56, -3.56, -0.31 and -0.35, respectively). Patients with history of ischemic heart disease and obese patients had more tender joints (MD +1.27 and +1.07) and higher ESR levels (MD +5.64 and +5.20). DAS28 is influenced exclusively by cardiovascular comorbidities, in particular diabetes, hyperlipidemia, ischemic heart disease and obesity.Conclusions
Cardiovascular comorbidities relate more than others with disease activity in RA. Diabetes and hyperlipidemia in particular seem associated with higher and lower disease activity respectively influencing almost all considered outcomes, suggesting a special importance of this pattern of comorbidities in disease activity assessment and clinical management. 相似文献996.
Elena González Juan J. Díez M. Auxiliadora Bajo Gloria del Peso Cristina Grande Olaia Rodríguez Mariana Díaz-Almirón Pedro Iglesias Rafael Selgas 《PloS one》2016,11(3)
Background
Human fibroblast growth factor 21 (FGF-21) is an endocrine liver hormone that stimulates adipocyte glucose uptake independently of insulin, suppresses hepatic glucose production and is involved in the regulation of body fat. Peritoneal dialysis (PD) patients suffer potential interference with FGF-21 status with as yet unknown repercussions.Objectives
The aim of this study was to define the natural history of FGF-21 in PD patients, to analyze its relationship with glucose homeostasis parameters and to study the influence of residual renal function and peritoneal functional parameters on FGF-21 levels and their variation over time.Methods
We studied 48 patients with uremia undergoing PD. Plasma samples were routinely obtained from each patient at baseline and at 1, 2 and 3 years after starting PD therapy.Results
Plasma FGF-21 levels substantially increased over the first year and were maintained at high levels during the remainder of the study period (253 pg/ml (59; 685) at baseline; 582 pg/ml (60.5–949) at first year and 647 pg/ml (120.5–1116.6) at third year) (p<0.01). We found a positive correlation between time on dialysis and FGF-21 levels (p<0.001), and also, those patients with residual renal function (RRF) had significantly lower levels of FGF-21 than those without RRF (ρ -0.484, p<0.05). Lastly, there was also a significant association between FGF-21 levels and peritoneal protein losses (PPL), independent of the time on dialysis (ρ 0.410, p<0.05).Conclusion
Our study shows that FGF-21 plasma levels in incident PD patients significantly increase during the first 3 years. This increment is dependent on or is associated with RRF and PPL (higher levels in patients with lower RRF and higher PPL). FGF-21 might be an important endocrine agent in PD patients and could act as hormonal signaling to maintain glucose homeostasis and prevent potential insulin resistance. These preliminary results suggest that FGF-21 might play a protective role as against the development of insulin resistance over time in patients undergoing a continuous glucose load. 相似文献997.
Maria Teresa Pagliari Luca A. Lotta Hugoline G. de Haan Carla Valsecchi Gloria Casoli Silvia Pontiggia Ida Martinelli Serena M. Passamonti Frits R. Rosendaal Flora Peyvandi 《PloS one》2016,11(11)
BackgroundDeep vein thrombosis (DVT) genetic predisposition is partially known.ObjectivesThis study aimed at assessing the functional impact of nine ADAMTS13 single nucleotide variants (SNVs) previously reported to be associated as a group with DVT in a burden test and the individual association of selected variants with DVT risk in two replication studies.MethodsWild-type and mutant recombinant ADAMTS13 were transiently expressed in HEK293 cells. Antigen and activity of recombinant ADAMTS13 were measured by ELISA and FRETS-VWF73 assays, respectively. The replication studies were performed in an Italian case-control study (Milan study; 298/298 patients/controls) using a next-generation sequencing approach and in a Dutch case-control study (MEGA study; 4306/4887 patients/controls) by TaqMan assays.ResultsIn vitro results showed reduced ADAMTS13 activity for three SNVs (p.Val154Ile [15%; 95% confidence interval [CI] 14–16], p.Asp187His [19%; 95%[CI] 17–21], p.Arg421Cys [24%; 95%[CI] 22–26]) similar to reduced plasma ADAMTS13 levels of patients carriers for these SNVs. Therefore these three SNVs were interrogated for risk association. The first replication study identified 3 heterozygous carriers (2 cases, 1 control) of p.Arg421Cys (odds ratio [OR] 2, 95%[CI] 0.18–22.25). The second replication study identified 2 heterozygous carriers (1 case, 1 control) of p.Asp187His ([OR] 1.14, 95%[CI] 0.07–18.15) and 10 heterozygous carriers (4 cases, 6 controls) of p.Arg421Cys ([OR] 0.76, 95%[CI] 0.21–2.68).ConclusionsThree SNVs (p.Val154Ile, p.Asp187His and p.Arg421Cys) showed reduced ex vivo and in vitro ADAMTS13 levels. However, the low frequency of these variants makes it difficult to confirm their association with DVT. 相似文献
998.
999.
Andrés S. Liffourrena Mario A. Salvano Gloria I. Lucchesi 《Archives of microbiology》2010,192(6):471-476
The present study examined the aerobic metabolism of trimethylamine in Pseudomonas putida A ATCC 12633 grown on tetradecyltrimethylammonium bromide or trimethylamine. In both conditions, the trimethylamine was used
as a nitrogen source and also accumulated in the cell, slowing the bacterial growth. Decreased bacterial growth was counteracted
by the addition of AlCl3. Cell-free extracts prepared from cells grown aerobically on tetradecyltrimethylammonium bromide exhibited trimethylamine
monooxygenase activity that produced trimethylamine N-oxide and trimethylamine N-oxide demethylase activity that produced dimethylamine. Cell-free extracts from cells grown on trimethylamine exhibited trimethylamine
dehydrogenase activity that produced dimethylamine, which was oxidized to methanal and methylamine by dimethylamine dehydrogenase.
These results show that this bacterial strain uses two enzymes to initiate the oxidation of trimethylamine in aerobic conditions.
The apparent Km for trimethylamine was 0.7 mM for trimethylamine monooxygenase and 4.0 mM for trimethylamine dehydrogenase, but both enzymes
maintain similar catalytic efficiency (0.5 and 0.4, respectively). Trimethylamine dehydrogenase was inhibited by trimethylamine
from 1 mM. Therefore, the accumulation of trimethylamine inside Pseudomonas putida A ATCC 12633 grown on tetradecyltrimethylammonium bromide or trimethylamine may be due to the low catalytic efficiency of
trimethylamine monooxygenase and trimethylamine dehydrogenase. 相似文献
1000.