全文获取类型
收费全文 | 4630篇 |
免费 | 320篇 |
国内免费 | 2篇 |
出版年
2023年 | 26篇 |
2022年 | 42篇 |
2021年 | 109篇 |
2020年 | 70篇 |
2019年 | 97篇 |
2018年 | 134篇 |
2017年 | 104篇 |
2016年 | 158篇 |
2015年 | 239篇 |
2014年 | 224篇 |
2013年 | 303篇 |
2012年 | 316篇 |
2011年 | 301篇 |
2010年 | 203篇 |
2009年 | 190篇 |
2008年 | 228篇 |
2007年 | 214篇 |
2006年 | 215篇 |
2005年 | 189篇 |
2004年 | 178篇 |
2003年 | 148篇 |
2002年 | 162篇 |
2001年 | 89篇 |
2000年 | 83篇 |
1999年 | 77篇 |
1998年 | 34篇 |
1997年 | 32篇 |
1996年 | 42篇 |
1995年 | 42篇 |
1994年 | 28篇 |
1993年 | 30篇 |
1992年 | 47篇 |
1991年 | 44篇 |
1990年 | 36篇 |
1989年 | 44篇 |
1988年 | 34篇 |
1987年 | 40篇 |
1986年 | 43篇 |
1985年 | 36篇 |
1984年 | 22篇 |
1981年 | 23篇 |
1979年 | 18篇 |
1978年 | 21篇 |
1977年 | 17篇 |
1976年 | 18篇 |
1975年 | 17篇 |
1974年 | 27篇 |
1973年 | 23篇 |
1969年 | 17篇 |
1968年 | 19篇 |
排序方式: 共有4952条查询结果,搜索用时 15 毫秒
991.
Background
Reducing health care costs requires the ability to identify patients most likely to incur high costs. Our objective was to evaluate the ability of the Charlson comorbidity score to predict the individuals who would incur high costs in the subsequent year and to contrast its predictive ability with other commonly used predictors.Methods
We contrasted the prior year Charlson comorbidity index, costs, Diagnostic Cost Group (DCG) and hospitalization as predictors of subsequent year costs from claims data of fund that provides comprehensive health benefits to a large union of health care workers. Total costs in the subsequent year was the principal outcome.Results
Of the 181,764 predominantly Black and Latino beneficiaries, 70% were adults (mean age 45.7 years; 62% women). As the comorbidity index increased, total yearly costs increased significantly (P<.001). At lower comorbidity, the costs were similar across different chronic diseases. Using regression to predict total costs, top 5th and 10th percentile of costs, the comorbidity index, prior costs and DCG achieved almost identical explained variance in both adults and children.Conclusions and Relevance
The comorbidity index predicted health costs in the subsequent year, performing as well as prior cost and DCG in identifying those in the top 5% or 10%. The comorbidity index can be used prospectively to identify patients who are likely to incur high costs.Trial Registration
ClinicalTrials.gov NCT01761253相似文献992.
Speranza Rubattu Simona Marchitti Franca Bianchi Sara Di Castro Rosita Stanzione Maria Cotugno Cristina Bozzao Sebastiano Sciarretta Massimo Volpe 《PloS one》2014,9(11)
Background
Abnormalities of vascular smooth muscle cells (VSMCs) contribute to development of vascular disease. Atrial natriuretic peptide (ANP) exerts important effects on VSMCs. A common ANP molecular variant (T2238C/αANP) has recently emerged as a novel vascular risk factor.Objectives
We aimed at identifying effects of CC2238/αANP on viability, migration and motility in coronary artery SMCs, and the underlying signaling pathways.Methods and Results
Cells were exposed to either TT2238/αANP or CC2238/αANP. At the end of treatment, cell viability, migration and motility were evaluated, along with changes in oxidative stress pathway (ROS levels, NADPH and eNOS expression), on Akt phosphorylation and miR21 expression levels. CC2238/αANP reduced cell vitality, increased apoptosis and necrosis, increased oxidative stress levels, suppressed miR21 expression along with consistent changes of its molecular targets (PDCD4, PTEN, Bcl2) and of phosphorylated Akt levels. As a result of increased oxidative stress, CC2238/αANP markedly stimulated cell migration and increased cell contraction. NPR-C gene silencing with specific siRNAs restored cell viability, miR21 expression, and reduced oxidative stress induced by CC2238/αANP. The cAMP/PKA/CREB pathway, driven by NPR-C activation, significantly contributed to both miR21 and phosphoAkt reduction upon CC2238/αANP. miR21 overexpression by mimic-hsa-miR21 rescued the cellular damage dependent on CC2238/αANP.Conclusions
CC2238/αANP negatively modulates viability through NPR-C/cAMP/PKA/CREB/miR21 signaling pathway, and it augments oxidative stress leading to increased migratory and vasoconstrictor effects in coronary artery SMCs. These novel findings further support a damaging role of this common αANP variant on vessel wall and its potential contribution to acute coronary events. 相似文献993.
994.
Floristic relationship between scrubland and grassland patches in the Mediterranean landscape of the Iberian Peninsula 总被引:3,自引:0,他引:3
Ramírez-Sanz L. Casado M.A. de Miguel J.M. Castro I. Costa M. Pineda F.D. 《Plant Ecology》2000,149(1):63-70
In the rural Mediterranean landscape, mosaics of patches of sclerophyllous scrubland and semi-natural grasslands are frequent. The plant communities of these patches, which are physiognomically easy to recognise, are very heterogeneous. The objective of this paper is to determine whether the patches of scrub-grassland represent an integrated response unit of the vegetation with regard to the physical environment (climatic, geographical and edaphic factors) and human use, or whether, on the contrary, this is an independent response. In order to do this a total of 50 sampling sites where scrubland and grassland patches were in contact were studied along a 370 km E-W mesoclimatic gradient from central Spain to Portugal (Iberian Peninsula). Two distinct zones, the east and the west halves of the study area, were identified according to the plant communities. Within each of these zones, each type of patch responded to the previously mentioned factors, differentially and independently. This determined a general lack of inter-community association or floristic correlation between scrub and grassland plant communities in contact. The spatial association is a random process probably related to the particular human management realised on every scrubland and grassland patch. The scrub–grassland pattern, which is characteristic of the Mediterranean landscape, does not represent an integrated response unit of the vegetation to a given environment, but rather the sum of the independent responses to the environment of the two patches in contact.Nomenclature for taxa: T. G. Tutin et al. 1694–1980. Flora Europaea Cambridge University Press, Cambridge. 相似文献
995.
996.
Cozzolino Salvatore Caputo Paolo De Castro Olga Moretti Aldo Pinto Gabriele 《Hydrobiologia》2000,433(1-3):145-151
Cyanidium caldarium, Cyanidioschyzon merolae and Galdieria sulphuraria are three unicellular algae characteristic, of acid thermal environments. Recently, on the basis of morphological characters, three new species of Galdieria (G. partita, G. daedala, G. maxima ) isolated from acid-thermal springs in Russia have been instituted. A selected region of rbcL and the sequence of the intergenic spacer between the rbcL and rbcS have been amplified and sequenced from different Galdieria species and strains, in order to define molecular relationship among these interesting algae. The obtained cladogram shows that Cyanidium caldarium and Cyanidioschyzon merolae form a sister group which, in turn, is in a sister group relationship with Galdieria. This last genus is divided in two clades, one of which includes G. sulphuraria accessions from Naples (Italy), California, and Yellowstone and the other one includes G. sulphuraria accessions from Java (Indonesia) and from the Russian species. These results support the status of the genus Galdieria and suggest that G. daedala, G. maxima and G. partita are three very similar strains of G. sulphuraria; the rbcL variation within Galdieria accessions has a pattern which is broadly connected to the geographial distribution. The data obtained from the intergenic rbcL-rbcS spacer partly confirm those from the rbcL analysis. 相似文献
997.
Murilo L. Bello Aridio M. Junior Bárbara A. Vieira Luiza R. S. Dias Valéria P. de Sousa Helena C. Castro Carlos R. Rodrigues Lucio M. Cabral 《PloS one》2015,10(3)
Layered drug delivery carriers are current targets of nanotechnology studies since they are able to accommodate pharmacologically active substances and are effective at modulating drug release. Sodium montmorillonite (Na-MMT) is a clay that has suitable properties for developing new pharmaceutical materials due to its high degree of surface area and high capacity for cation exchange. Therefore Na-MMT is a versatile material for the preparation of new drug delivery systems, especially for slow release of protonable drugs. Herein, we describe the intercalation of several amine-containing drugs with Na-MMT so we can derive a better understanding of how these drugs molecules interact with and distribute throughout the Na-MMT interlayer space. Therefore, for this purpose nine sodium montmorillonite/amine-containing drugs complexes (Na-MMT/drug) were prepared and characterized. In addition, the physicochemical properties of the drugs molecules in combination with different experimental conditions were assessed to determine how these factors influenced experimental outcomes (e.g. increase of the interlayer spacing versus drugs arrangement and orientation). We also performed a molecular modeling study of these amine-containing drugs associated with different Na-MMT/drug complex models to analyze the orientation and arrangement of the drugs molecules in the complexes studied. Six amine-containing drugs (rivastigmine, doxazosin, 5-fluorouracil, chlorhexidine, dapsone, nystatin) were found to successfully intercalate Na-MMT. These findings provide important insights on the interlayer aspect of the molecular systems formed and may contribute to produce more efficient drug delivery nanosystems. 相似文献
998.
999.
Michelle S. Libério Graziella A. Joanitti Ricardo B. Azevedo Eduardo M. Cilli Lanuse C. Zanotta Anna C. Nascimento Marcelo V. Sousa Osmindo R. Pires Júnior Wagner Fontes Mariana S. Castro 《Amino acids》2011,40(1):51-59
Nowadays, the emergence of resistance to the current available chemotherapeutic drugs by cancer cells makes the development
of new agents imperative. The skin secretion of amphibians is a natural rich source of antimicrobial peptides (AMP), and researchers
have shown that some of these wide spectrum molecules are also toxic to cancer cells. The aim of this study was to verify
a putative anticancer activity of the AMP pentadactylin isolated for the first time from the skin secretion of the frog Leptodactylus labyrinthicus and also to study its cytotoxic mechanism to the murine melanoma cell line B16F10. The results have shown that pentadactylin
reduces the cell viability of B16F10 cells in a dose-dependent manner. It was also cytotoxic to normal human fibroblast cells;
nevertheless, pentadactylin was more potent in the first case. The studies of action mechanism revealed that pentadactylin
causes cell morphology alterations (e.g., round shape and shrinkage morphology), membrane disruption, DNA fragmentation, cell
cycle arrest at the S phase, and alteration of mitochondrial membrane potential, suggesting that B16F10 cells die by apoptosis.
The exact mechanism that causes reduction of cell viability and cytotoxicity after treatment with pentadactylin is still unknown.
In conclusion, as cancer cells become resilient to death, it is worthwhile the discovery of new drugs such as pentadactylin
that induces apoptosis. 相似文献
1000.