全文获取类型
收费全文 | 49256篇 |
免费 | 3569篇 |
国内免费 | 11篇 |
出版年
2023年 | 284篇 |
2022年 | 338篇 |
2021年 | 729篇 |
2020年 | 671篇 |
2019年 | 688篇 |
2018年 | 1183篇 |
2017年 | 1065篇 |
2016年 | 1678篇 |
2015年 | 2537篇 |
2014年 | 2544篇 |
2013年 | 3290篇 |
2012年 | 4341篇 |
2011年 | 3999篇 |
2010年 | 2295篇 |
2009年 | 1922篇 |
2008年 | 3185篇 |
2007年 | 3037篇 |
2006年 | 2940篇 |
2005年 | 2601篇 |
2004年 | 2547篇 |
2003年 | 2338篇 |
2002年 | 2179篇 |
2001年 | 824篇 |
2000年 | 886篇 |
1999年 | 559篇 |
1998年 | 376篇 |
1997年 | 257篇 |
1996年 | 264篇 |
1995年 | 273篇 |
1994年 | 235篇 |
1993年 | 197篇 |
1992年 | 211篇 |
1991年 | 188篇 |
1990年 | 177篇 |
1989年 | 150篇 |
1988年 | 119篇 |
1987年 | 94篇 |
1986年 | 90篇 |
1985年 | 129篇 |
1984年 | 166篇 |
1983年 | 87篇 |
1982年 | 107篇 |
1981年 | 83篇 |
1980年 | 91篇 |
1979年 | 79篇 |
1978年 | 70篇 |
1977年 | 71篇 |
1976年 | 85篇 |
1975年 | 70篇 |
1974年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Alvaro A. Sandoval-Montiel Martha Zentella-de-Pi?a José L. Ventura-Gallegos Susana Frías-González Ambar López-Macay Alejandro Zentella-Dehesa 《PloS one》2013,8(6)
Background
Among NSAIDs acetyl salicylic acid remains as a valuable tool because of the variety of benefic prophylactic and therapeutic effects. Nevertheless, the molecular bases for these responses have not been complete understood. We explored the effect of acetyl salicylic acid on the heat shock response.Results
Peripheral blood mononuclear cells from rats challenged with acetyl salicylic acid presented a faster kinetics of expression of HSP-72 messenger RNA and protein in response to in vitro heat shock. This effect reaches its maximum 2 h after treatment and disappeared after 5 h. On isolated peripheral blood mononuclear cells from untreated rats, incubation with acetyl salicylic acid was ineffective to produce priming, but this effect was mimicked when the cells were incubated with the combination of H2O2+ ASA.Conclusions
Administration of acetyl salicylic acid to rats alters HSP-72 expression mechanism in a way that it becomes more efficient in response to in vitro heat shock. The fact that in vitro acetyl salicylic acid alone did not induce this priming effect implies that in vivo other signals are required. Priming could be reproduces in vitro with the combination of acetyl salicylic acid+H2O2. 相似文献992.
Alberto Crespo Guardo Carmen álvarez-Fernández Hodei Arberas Javier García-Pérez Felipe García Manuel Enric Bargalló María José Maleno José María Gatell Beatriz Mothe José Alcami Sonsoles Sánchez-Palomino Montserrat Plana 《PloS one》2013,8(3)
Background
Generation of new reagents that can be used to screen or monitor HIV-1-specific responses constituted an interesting field in the development of HIV vaccines to improve their efficacy.Methods
We have evaluated the specific T cell response against different types of NL4-3 virions (including NL4-3 aldrithiol-2 treated, NL4-3/ΔRT and R5 envelopes: NL4-3/ΔRT/ΔEnv[AC10] and NL4-3/ΔRT/ΔEnv[Bal]) and against pools of overlapping peptides (15 mer) encompassing the HIV-1 Gag and Nef regions. Cryopreserved PBMC from a subset of 69 chronic asymptomatic HIV positive individuals have been employed using different techniques including IFN-γ ELISPOT assay, surface activation markers and intracellular cytokine staining (ICS) by flow cytometry.Results
The differential response obtained against NL4-3 aldrithiol-2 treated and NL4-3/ΔRT virions (25% vs 55%, respectively) allow us to divide the population in three groups: “full-responders” (positive response against both viral particles), “partial-responders” (positive response only against NL4-3/ΔRT virions) and “non-responders” (negative responses). There was no difference between X4 and R5 envelopes. The magnitude of the total responses was higher against NL4-3/ΔRT and was positively correlated with gender and inverse correlated with viral load. On the contrary CD4+ T cell count was not associated with this response. In any case responses to the viruses tended to be lower in magnitude than those detected by the overlapping peptides tested. Finally we have found an increased frequency of HLA-B27 allele (23% vs 9%) and a significant reduction in some activation markers (CD69 and CD38) on T cells surface in responders vs non-responders individuals.Conclusions
In summary these virions could be considered as alternative and useful reagents for screening HIV-1-specific T cell responses in HIV exposed uninfected people, HIV infected patients and to assess immunogenicity of new prototypes both in vitro and in vaccine trials, by a feasible, simply, effective and low cost assay. 相似文献993.
Anne Drumond Villela Rodrigo Gay Ducati Leonardo Astolfi Rosado Carlos Junior Bloch Maura Vianna Prates Danieli Cristina Gon?alves Carlos Henrique Inacio Ramos Luiz Augusto Basso Diogenes Santiago Santos 《PloS one》2013,8(2)
Uracil phosphoribosyltransferase (UPRT) catalyzes the conversion of uracil and 5-phosphoribosyl-α-1-pyrophosphate (PRPP) to uridine 5′-monophosphate (UMP) and pyrophosphate (PPi). UPRT plays an important role in the pyrimidine salvage pathway since UMP is a common precursor of all pyrimidine nucleotides. Here we describe cloning, expression and purification to homogeneity of upp-encoded UPRT from Mycobacterium tuberculosis (MtUPRT). Mass spectrometry and N-terminal amino acid sequencing unambiguously identified the homogeneous protein as MtUPRT. Analytical ultracentrifugation showed that native MtUPRT follows a monomer-tetramer association model. MtUPRT is specific for uracil. GTP is not a modulator of MtUPRT ativity. MtUPRT was not significantly activated or inhibited by ATP, UTP, and CTP. Initial velocity and isothermal titration calorimetry studies suggest that catalysis follows a sequential ordered mechanism, in which PRPP binding is followed by uracil, and PPi product is released first followed by UMP. The pH-rate profiles indicated that groups with pK values of 5.7 and 8.1 are important for catalysis, and a group with a pK value of 9.5 is involved in PRPP binding. The results here described provide a solid foundation on which to base upp gene knockout aiming at the development of strategies to prevent tuberculosis. 相似文献
994.
Juan P. de-Torres David Blanco Ana B. Alcaide Luis M. Seijo Gorka Bastarrika María José Pajares Arrate Mu?oz-Barrutia Carlos Ortiz-de-Solorzano Ruben Pio Arantza Campo Usua Montes Victor Segura Jesús Pueyo Luis M. Montuenga Javier J. Zulueta 《PloS one》2013,8(4)
Rationale
Low-grade inflammation and emphysema have been shown to be associated with an increased risk of lung cancer. However, the systemic inflammatory response in patients with emphysema is still unknown.Objective
To compare the plasma cytokine profiles in two groups of current or former smokers without airway obstruction: a control group of individuals without computed tomography (CT) detected emphysema vs. a study group of individuals with CT detected emphysema.Methods
Subjects underwent a chest CT, spirometry, and determination of EGF, IL-15, IL-1ra, IL-8, MCP-1, MIP-1β, TGFα, TNFα, and VEGF levels in plasma. Cytokine levels in each group were compared adjusting for confounding factors.Results
160 current smokers and former smokers without airway obstruction participated in the study: 80 without emphysema and 80 subjects with emphysema. Adjusted group comparisons revealed significant reductions in EGF (−0.317, p = 0.01), IL-15 (−0.21, p = 0.01), IL-8 (−0.180, p = 0.02) and IL-1ra (−0.220, p = 0.03) in subjects with emphysema and normal spirometry.Conclusions
Current or former smokers expressing a well-defined disease characteristic such as emphysema, has a specific plasma cytokine profile. This includes a decrease of cytokines mainly implicated in activation of apoptosis or decrease of immunosurveillance. This information should be taken into account when evaluated patients with tobacco respiratory diseases. 相似文献995.
Rodrigo S. Lacruz José María Bermúdez de Castro María Martinón-Torres Paul O’Higgins Michael L. Paine Eudald Carbonell Juan Luis Arsuaga Timothy G. Bromage 《PloS one》2013,8(6)
The modern human face differs from that of our early ancestors in that the facial profile is relatively retracted (orthognathic). This change in facial profile is associated with a characteristic spatial distribution of bone deposition and resorption: growth remodeling. For humans, surface resorption commonly dominates on anteriorly-facing areas of the subnasal region of the maxilla and mandible during development. We mapped the distribution of facial growth remodeling activities on the 900–800 ky maxilla ATD6-69 assigned to H. antecessor, and on the 1.5 My cranium KNM-WT 15000, part of an associated skeleton assigned to African H. erectus. We show that, as in H. sapiens, H. antecessor shows bone resorption over most of the subnasal region. This pattern contrasts with that seen in KNM-WT 15000 where evidence of bone deposition, not resorption, was identified. KNM-WT 15000 is similar to Australopithecus and the extant African apes in this localized area of bone deposition. These new data point to diversity of patterns of facial growth in fossil Homo. The similarities in facial growth in H. antecessor and H. sapiens suggest that one key developmental change responsible for the characteristic facial morphology of modern humans can be traced back at least to H. antecessor. 相似文献
996.
997.
Fabiana Oliveira Bastos Bonato Marcelo Montebello Lemos José Luiz Cassiolato Maria Eugênia Fernandes Canziani 《PloS one》2013,8(6)
Background and Objectives
Sudden cardiac death is the most common cause of mortality in chronic kidney disease patients, and it occurs mostly due to ventricular arrhythmias. In this study, we aimed at investigating the prevalence of ventricular arrhythmia and the factors associated with its occurrence in nondialyzed chronic kidney disease patients.Design, Setting, Participants and Measurements
This cross-sectional study evaluated 111 chronic kidney disease patients (estimated glomerular filtration rate 34.7±16.1 mL/min/1.73 m2, 57±11.4 years, 60% male, 24% diabetics). Ventricular arrhythmia was assessed by 24-hour electrocardiogram. Left ventricular hypertrophy (echocardiogram), 24-hour ambulatory blood pressure monitoring, and coronary artery calcification (multi-slice computed tomography) and laboratory parameters were also evaluated.Results
Ventricular arrhythmia was found in 35% of the patients. Non-controlled hypertension was observed in 21%, absence of systolic decency in 29%, left ventricular hypertrophy in 27%, systolic dysfunction in 10%, and coronary artery calcification in 49%. Patients with ventricular arrhythmia were older (p<0.001), predominantly men (p = 0.009), had higher estimated glomerular filtration rate (p = 0.03) and hemoglobin (p = 0.005), and lower intact parathyroid hormone (p = 0.024) and triglycerides (p = 0.011) when compared to patients without ventricular arrhythmia. In addition, a higher left ventricular mass index (p = 0.002) and coronary calcium score (p = 0.002), and a lower ejection fraction (p = 0.001) were observed among patients with ventricular arrhythmia. In the multiple logistic regression analysis, aging, increased hemoglobin levels and reduced ejection fraction were independently related to the presence of ventricular arrhythmia.Conclusions
Ventricular arrhythmia is prevalent in nondialyzed chronic kidney disease patients. Age, hemoglobin levels and ejection fraction were the factors associated with ventricular arrhythmia in these patients. 相似文献998.
Chantal Bertrand Angelica Pignalosa Estelle Wanecq Chloé Rancoule Aurélie Batut Simon Deleruyelle Lillà Lionetti Philippe Valet Isabelle Castan-Laurell 《PloS one》2013,8(11)
Various studies have shown that eicosapentaenoic acid (EPA) has beneficial effects on obesity and associated disorders. Apelin, the ligand of APJ receptor also exerts insulin-sensitizing effects especially by improving muscle metabolism. EPA has been shown to increase apelin production in adipose tissue but its effects in muscle have not been addressed. Thus, the effects of EPA supplementation (36 g/kg EPA) in high-fat diet (HFD) (45% fat, 20% protein, 35% carbohydrate) were studied in mice with focus on muscle lipid metabolism and apelin/APJ expression. Compared with HFD mice, HFD+EPA mice had significantly less weight gain, fat mass, lower blood glucose, insulinemia and hepatic steatosis after 10 weeks of diet. In addition, EPA prevented muscle metabolism alterations since intramuscular triglycerides were decreased and β-oxidation increased. In soleus muscles of HFD+EPA mice, apelin and APJ expression were significantly increased compared to HFD mice. However, plasma apelin concentrations in HFD and HFD+EPA mice were similar. EPA-induced apelin expression was confirmed in differentiated C2C12 myocytes but in this model, apelin secretion was also increased in response to EPA treatment. In conclusion, EPA supplementation in HFD prevents obesity and metabolic alterations in mice, especially in skeletal muscle. Since EPA increases apelin/APJ expression in muscle, apelin may act in a paracrine/autocrine manner to contribute to these benefical effects. 相似文献
999.
Phonepasong Arounleut Matthew Bowser Sunil Upadhyay Xing-Ming Shi Sadanand Fulzele Maribeth H. Johnson Alexis M. Stranahan William D. Hill Carlos M. Isales Mark W. Hamrick 《PloS one》2013,8(8)
Objective
Leptin receptors are abundant in human skeletal muscle, but the role of leptin in muscle growth, development and aging is not well understood. Here we utilized a novel mouse model lacking all functional leptin receptor isoforms (POUND mouse, Leprdb/lb) to determine the role of leptin in skeletal muscle.Methods and Findings
Skeletal muscle mass and fiber diameters were examined in POUND mice, and primary myoblast cultures were used to determine the effects of altered leptin signaling on myoblast proliferation and differentiation. ELISA assays, integrated pathway analysis of mRNA microarrays, and reverse phase protein analysis were performed to identify signaling pathways impacted by leptin receptor deficiency. Results show that skeletal muscle mass and fiber diameter are reduced 30–40% in POUND mice relative to wild-type controls. Primary myoblast cultures demonstrate decreased proliferation and decreased expression of both MyoD and myogenin in POUND mice compared to normal mice. Leptin treatment increased proliferation in primary myoblasts from muscles of both adult (12 months) and aged (24 months) wild-type mice, and leptin increased expression of MyoD and myogenin in aged primary myoblasts. ELISA assays and protein arrays revealed altered expression of molecules associated with the IGF-1/Akt and MAPK/MEK signaling pathways in muscle from the hindlimbs of mice lacking functional leptin receptors.Conclusion
These data support the hypothesis that the adipokine leptin is a key factor important for the regulation of skeletal muscle mass, and that leptin can act directly on its receptors in peripheral tissues to regulate cell proliferation and differentiation. 相似文献1000.
Rogelio Perez-Padilla Fernando C. Wehrmeister Bartolome R. Celli Maria Victorina Lopez-Varela Maria Montes de Oca Adriana Mui?o Carlos Talamo Jose R. Jardim Gonzalo Valdivia Carmen Lisboa Ana Maria B. Menezes for the PLATINO Team 《PloS one》2013,8(8)