全文获取类型
收费全文 | 2171篇 |
免费 | 246篇 |
专业分类
2417篇 |
出版年
2023年 | 14篇 |
2022年 | 28篇 |
2021年 | 47篇 |
2020年 | 25篇 |
2019年 | 46篇 |
2018年 | 49篇 |
2017年 | 47篇 |
2016年 | 58篇 |
2015年 | 108篇 |
2014年 | 110篇 |
2013年 | 115篇 |
2012年 | 151篇 |
2011年 | 164篇 |
2010年 | 91篇 |
2009年 | 95篇 |
2008年 | 118篇 |
2007年 | 106篇 |
2006年 | 74篇 |
2005年 | 78篇 |
2004年 | 86篇 |
2003年 | 73篇 |
2002年 | 71篇 |
2001年 | 60篇 |
2000年 | 46篇 |
1999年 | 56篇 |
1998年 | 29篇 |
1997年 | 22篇 |
1996年 | 32篇 |
1995年 | 24篇 |
1994年 | 17篇 |
1993年 | 13篇 |
1992年 | 38篇 |
1991年 | 19篇 |
1990年 | 36篇 |
1989年 | 36篇 |
1988年 | 30篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1974年 | 8篇 |
1973年 | 9篇 |
1968年 | 9篇 |
排序方式: 共有2417条查询结果,搜索用时 0 毫秒
41.
42.
Summary It was found that the increase of the hydraulic retention time improved the organic matter removal and the conversion of organic to ammonia nitrogen. Methane concentration in the biogas was not affected by the hydraulic retention time.The reactor in operation during one year was not clogged. 相似文献
43.
44.
Susana Ruiz‐Ruiz Sergio Sanchez‐Carrillo Sergio Ciordia María C. Mena Celia Mndez‐García David Rojo Rafael Bargiela Elisa Zubeldia‐Varela Mnica Martínez‐Martínez Coral Barbas Manuel Ferrer Andrs Moya 《Aging cell》2020,19(1)
Composition of the gut microbiota changes during ageing, but questions remain about whether age is also associated with deficits in microbiome function and whether these changes occur sharply or progressively. The ability to define these deficits in populations of different ages may help determine a chronological age threshold at which deficits occur and subsequently identify innovative dietary strategies for active and healthy ageing. Here, active gut microbiota and associated metabolic functions were evaluated using shotgun proteomics in three well‐defined age groups consisting of 30 healthy volunteers, namely, ten infants, ten adults and ten elderly individuals. Samples from each volunteer at intervals of up to 6 months (n = 83 samples) were used for validation. Ageing gradually increases the diversity of gut bacteria that actively synthesize proteins, that is by 1.4‐fold from infants to elderly individuals. An analysis of functional deficits consistently identifies a relationship between tryptophan and indole metabolism and ageing (p < 2.8e?8). Indeed, the synthesis of proteins involved in tryptophan and indole production and the faecal concentrations of these metabolites are directly correlated (r2 > .987) and progressively decrease with age (r2 > .948). An age threshold for a 50% decrease is observed ca. 11–31 years old, and a greater than 90% reduction is observed from the ages of 34–54 years. Based on recent investigations linking tryptophan with abundance of indole and other “healthy” longevity molecules and on the results from this small cohort study, dietary interventions aimed at manipulating tryptophan deficits since a relatively “young” age of 34 and, particularly, in the elderly are recommended. 相似文献
45.
46.
Multiple myeloma (MM) comprises 1% of all malignancies and 10% of all hematological malignancies. MM is a malignancy of plasma cells in the bone marrow where complex and dynamic interactions with the bone marrow microenvironment lead to tumor progression, skeletal destruction and angiogenesis. Despite the discovery of several novel treatments against MM, including the proteasome inhibitor bortezomib, it is considered to be an incurable disease with an average 4–5 years overall survival. 相似文献
47.
Cristina Besada Gerardo Sanchez Alejandra Salvador Antonio Granell 《Metabolomics : Official journal of the Metabolomic Society》2013,9(1):157-172
High resolution volatile profiling (67 compounds identified) of fruits from 12 persimmon cultivars was established and used to characterize the different astringency types of persimmon fruit before and after deastringency treatment. Analysis of the volatile profile of fruit enables us to differentiate between cultivars that at the moment of harvest produced non-astringent fruit (Pollination Constant Non Astringent—PCNA-type) from astringent ones (non-PCNA-type). Fruit failing to accumulate astringent compounds naturally (PCNA fruit) showed high levels of 3(2H)-benzofuranone, while this compound was not detected in any astringent type fruit (non-PCNA). In addition to this, PCNA cultivars also showed at harvest higher accumulation of benzeneacetaldehyde and lipid-derived aldehydes (hexanal, heptanal, octanal and decanal) than non-PCNA fruit. The application of postharvest deastringency treatment to all non-PCNA cultivars resulted on an important insolubilization of tannins. In general the CO2-treatment enhanced the levels of acetaldehyde, however those cultivars showing high levels of dihydrobenzofuran at harvest did not present an increment of acetaldehyde. In contrast, all non-PCNA cultivars exhibited an important accumulation of lipid-derived aldehydes due to CO2-treatment. Therefore, we propose that lipid-derived aldehydes (mainly decanal, octanal and heptanal) may be playing a role in the astringency loss. Our results suggest that 3(2H)-benzofuranone, benzeneacetaldehyde and lipid-derived aldehydes could be used as markers for both natural and artificial loss of astringency. 相似文献
48.
49.
Sanchez Paulina Espinosa Magali Maldonado Vilma Barquera Rodrigo Belem-Gabiño Nayeli Torres Javier Cravioto Adrian Melendez-Zajgla Jorge 《Molecular biology reports》2020,47(7):5175-5184
Molecular Biology Reports - Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest cancers in humans, with less than 5% 5-year survival rate. PDAC is characterized by a small number of... 相似文献
50.
Alvaro Osorio Esperanza Ortega Jesús M. Torres Pilar Sanchez Estrella Ruiz-Requena 《Molecular and cellular biochemistry》2013,374(1-2):21-27
The increased vascular calcification, cardiovascular morbidity, and mortality in chronic kidney disease (CKD) patients has been associated with disturbances in mineral-bone metabolism. In order to determine markers of the vascular calcification frequently observed in these patients, blood samples of elderly male and female hemodialysis CKD patients were used to measure serum levels of: osteoprotegerin (OPG), total soluble receptor activator of nuclear factor-κB ligand (sRANKL), and fetuin-A by enzyme immunoassay; tartrate-resistant acid phosphatase (TRACP-5b), and bone-specific alkaline phosphatase (BAP) by immunoenzymometric assay; osteocalcin (OC) by ELISA; iPTH by immunoradiometric assay; 25(OH)D3 and 1,25(OH)2D3, by I125 radioimmunoassay; and calcium and phosphorus by photometric assay. Serum OPG, BAP, iPTH, phosphorus, and OC levels were higher and serum 25(OH)D3, 1,25(OH)2D3, and fetuin-A levels lower in both male and female CKD patients than in their respective controls. Our results indicate that the bone formation and resorption parameters are altered in elderly male and female hemodialysis CKD patients. These changes may lead to vascular calcifications and cardiovascular complications, given that elevated OPG and OC levels and reduced fetuin-A levels are associated with cardiovascular events. 相似文献