全文获取类型
收费全文 | 9459篇 |
免费 | 668篇 |
国内免费 | 2篇 |
出版年
2022年 | 38篇 |
2021年 | 104篇 |
2020年 | 67篇 |
2019年 | 86篇 |
2018年 | 106篇 |
2017年 | 97篇 |
2016年 | 197篇 |
2015年 | 307篇 |
2014年 | 373篇 |
2013年 | 515篇 |
2012年 | 541篇 |
2011年 | 560篇 |
2010年 | 402篇 |
2009年 | 338篇 |
2008年 | 484篇 |
2007年 | 541篇 |
2006年 | 502篇 |
2005年 | 535篇 |
2004年 | 502篇 |
2003年 | 477篇 |
2002年 | 483篇 |
2001年 | 127篇 |
2000年 | 94篇 |
1999年 | 118篇 |
1998年 | 162篇 |
1997年 | 104篇 |
1996年 | 113篇 |
1995年 | 125篇 |
1994年 | 121篇 |
1993年 | 122篇 |
1992年 | 89篇 |
1991年 | 84篇 |
1990年 | 102篇 |
1989年 | 93篇 |
1988年 | 71篇 |
1987年 | 79篇 |
1986年 | 72篇 |
1985年 | 75篇 |
1984年 | 77篇 |
1983年 | 79篇 |
1982年 | 65篇 |
1981年 | 78篇 |
1980年 | 62篇 |
1979年 | 57篇 |
1978年 | 50篇 |
1977年 | 51篇 |
1976年 | 47篇 |
1975年 | 43篇 |
1974年 | 41篇 |
1973年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
It is an established fact that allelic variation and post-translational modifications create different variants of proteins, which are observed as isoelectric and size subspecies in two-dimensional gel based proteomics. Here we explore the stromal proteome of spinach and Arabidopsis chloroplast and show that clustering of mass spectra is a useful tool for investigating such variants and detecting modified peptides with amino acid substitutions or post-translational modifications. This study employs data mining by hierarchical clustering of MALDI-MS spectra, using the web version of the SPECLUST program (http://bioinfo.thep.lu.se/speclust.html). The tool can also be used to remove peaks of contaminating proteins and to improve protein identification, especially for species without a fully sequenced genome. Mutually exclusive peptide peaks within a cluster provide a good starting point for MS/MS investigation of modified peptides, here exemplified by the identification of an A to E substitution that accounts for the isoelectric heterogeneity in protein isoforms. 相似文献
992.
Barjaktarovic Z Schmaltz D Shyla A Azimzadeh O Schulz S Haagen J Dörr W Sarioglu H Schäfer A Atkinson MJ Zischka H Tapio S 《PloS one》2011,6(12):e27811
BACKROUND: Radiation therapy treatment of breast cancer, Hodgkin's disease or childhood cancers expose the heart to high local radiation doses, causing an increased risk of cardiovascular disease in the survivors decades after the treatment. The mechanisms that underlie the radiation damage remain poorly understood so far. Previous data show that impairment of mitochondrial oxidative metabolism is directly linked to the development of cardiovascular disease. METHODOLOGY/PRINCIPAL FINDINGS: In this study, the radiation-induced in vivo effects on cardiac mitochondrial proteome and function were investigated. C57BL/6N mice were exposed to local irradiation of the heart with doses of 0.2 Gy or 2 Gy (X-ray, 200 kV) at the age of eight weeks, the control mice were sham-irradiated. After four weeks the cardiac mitochondria were isolated and tested for proteomic and functional alterations. Two complementary proteomics approaches using both peptide and protein quantification strategies showed radiation-induced deregulation of 25 proteins in total. Three main biological categories were affected: the oxidative phophorylation, the pyruvate metabolism, and the cytoskeletal structure. The mitochondria exposed to high-dose irradiation showed functional impairment reflected as partial deactivation of Complex I (32%) and Complex III (11%), decreased succinate-driven respiratory capacity (13%), increased level of reactive oxygen species and enhanced oxidation of mitochondrial proteins. The changes in the pyruvate metabolism and structural proteins were seen with both low and high radiation doses. CONCLUSION/SIGNIFICANCE: This is the first study showing the biological alterations in the murine heart mitochondria several weeks after the exposure to low- and high-dose of ionizing radiation. Our results show that doses, equivalent to a single dose in radiotherapy, cause long-lasting changes in mitochondrial oxidative metabolism and mitochondria-associated cytoskeleton. This prompts us to propose that these first pathological changes lead to an increased risk of cardiovascular disease after radiation exposure. 相似文献
993.
Maarouf CL Daugs ID Kokjohn TA Walker DG Hunter JM Kruchowsky JC Woltjer R Kaye J Castaño EM Sabbagh MN Beach TG Roher AE 《PloS one》2011,6(11):e27291
The amyloid cascade hypothesis provides an economical mechanistic explanation for Alzheimer's disease (AD) dementia and correlated neuropathology. However, some nonagenarian individuals (high pathology controls, HPC) remain cognitively intact while enduring high amyloid plaque loads for decades. If amyloid accumulation is the prime instigator of neurotoxicity and dementia, specific protective mechanisms must enable these HPC to evade cognitive decline. We evaluated the neuropathological and biochemical differences existing between non-demented (ND)-HPC and an age-matched cohort with AD dementia. The ND-HPC selected for our study were clinically assessed as ND and possessed high amyloid plaque burdens. ELISA and Western blot analyses were used to quantify a group of proteins related to APP/Aβ/tau metabolism and other neurotrophic and inflammation-related molecules that have been found to be altered in neurodegenerative disorders and are pivotal to brain homeostasis and mental health. The molecules assumed to be critical in AD dementia, such as soluble or insoluble Aβ40, Aβ42 and tau were quantified by ELISA. Interestingly, only Aβ42 demonstrated a significant increase in ND-HPC when compared to the AD group. The vascular amyloid load which was not used in the selection of cases, was on the average almost 2-fold greater in AD than the ND-HPC, suggesting that a higher degree of microvascular dysfunction and perfusion compromise was present in the demented cohort. Neurofibrillary tangles were less frequent in the frontal cortices of ND-HPC. Biochemical findings included elevated vascular endothelial growth factor, apolipoprotein E and the neuroprotective factor S100B in ND-HPC, while anti-angiogenic pigment epithelium derived factor levels were lower. The lack of clear Aβ-related pathological/biochemical demarcation between AD and ND-HPC suggests that in addition to amyloid plaques other factors, such as neurofibrillary tangle density and vascular integrity, must play important roles in cognitive failure. 相似文献
994.
995.
Vivet-Boudou V Isel C Sleiman M Smyth R Ben Gaied N Barhoum P Laumond G Bec G Götte M Mak J Aubertin AM Burger A Marquet R 《PloS one》2011,6(11):e27456
The occurrence of resistant viruses to any of the anti-HIV-1 compounds used in the current therapies against AIDS underlies the urge for the development of new drug targets and/or new drugs acting through novel mechanisms. While all anti-HIV-1 nucleoside analogues in clinical use and in clinical trials rely on ribose modifications for activity, we designed nucleosides with a natural deoxyribose moiety and modifications of position 8 of the adenine base. Such modifications might induce a steric clash with helix αH in the thumb domain of the p66 subunit of HIV-1 RT at a distance from the catalytic site, causing delayed chain termination. Eleven new 2'-deoxyadenosine analogues modified on position 8 of the purine base were synthesized and tested in vitro and in cell-based assays. In this paper we demonstrate for the first time that chemical modifications on position 8 of 2'-deoxyadenosine induce delayed chain termination in vitro, and also inhibit DNA synthesis when incorporated in a DNA template strand. Furthermore, one of them had moderate anti-HIV-1 activity in cell-culture. Our results constitute a proof of concept indicating that modification on the base moiety of nucleosides can induce delayed polymerization arrest and inhibit HIV-1 replication. 相似文献
996.
The present study evaluated two previously developed methods for amplification of bovine mtDNA segments of 109 and 271 base pairs (bp) by real-time polymerase chain reaction (PCR). Beef samples were sterilised experimentally at different temperatures (126 degrees C, 129 degrees C, 132 degrees C and 135 degrees C). These experimentally sterilised beef samples and nine commercial meat and bone meals (MBM) were mixed to a reference plant concentrate in strengths of 50%, 10%, 5%, and 1%. The results of the following PCR showed that the Bos-109 real-time PCR assay was able to detect all the experimental beef samples with exception of the mixtures of beef heated experimentally to 135 degrees C. In mixtures of industrial MBM bovine DNA were always found. Comparatively, the beef sterilised at 135 degrees C and 132 degrees C (and their respective mixtures) and the mixture containing 1% of beef sterilised at 129 degrees C were not detectable with the PCR assay amplifying a target of 271 bp. Using this PCR mixtures of industrial MBM were only weakly detected. The low concentrated mixtures of the extremely processed MBM-1 and MBM-2 even reported negative. These results indicate that the detectability of bovine DNA is strongly influenced by the degree of the thermal treatment. Only the PCR assay amplifying relatively short fragments of a multi-copy mitochondrial target was reliable for the detection of correctly heated MBM in mixed feed. 相似文献
997.
Maurizio Scarpa Zsuzsanna Almássy Michael Beck Olaf Bodamer Iain A Bruce Linda De Meirleir Nathalie Guffon Encarna Guillén-Navarro Pauline Hensman Simon Jones Wolfgang Kamin Christoph Kampmann Christina Lampe Christine A Lavery Elisa Leão Teles Bianca Link Allan M Lund Gunilla Malm Susanne Pitz Michael Rothera Catherine Stewart Anna Tylki-Szymańska Ans van der Ploeg Robert Walker Jiri Zeman James E Wraith 《Orphanet journal of rare diseases》2011,6(1):1-18
?
Mucopolysaccharidosis type II (MPS II) is a rare, life-limiting, X-linked recessive disease characterised by deficiency of the lysosomal enzyme iduronate-2-sulfatase. Consequent accumulation of glycosaminoglycans leads to pathological changes in multiple body systems. Age at onset, signs and symptoms, and disease progression are heterogeneous, and patients may present with many different manifestations to a wide range of specialists. Expertise in diagnosing and managing MPS II varies widely between countries, and substantial delays between disease onset and diagnosis can occur. In recent years, disease-specific treatments such as enzyme replacement therapy and stem cell transplantation have helped to address the underlying enzyme deficiency in patients with MPS II. However, the multisystem nature of this disorder and the irreversibility of some manifestations mean that most patients require substantial medical support from many different specialists, even if they are receiving treatment. This article presents an overview of how to recognise, diagnose, and care for patients with MPS II. Particular focus is given to the multidisciplinary nature of patient management, which requires input from paediatricians, specialist nurses, otorhinolaryngologists, orthopaedic surgeons, ophthalmologists, cardiologists, pneumologists, anaesthesiologists, neurologists, physiotherapists, occupational therapists, speech therapists, psychologists, social workers, homecare companies and patient societies.Take-home message
Expertise in recognising and treating patients with MPS II varies widely between countries. This article presents pan-European recommendations for the diagnosis and management of this life-limiting disease. 相似文献998.
Dale BM McNerney GP Thompson DL Hubner W de Los Reyes K Chuang FY Huser T Chen BK 《Cell host & microbe》2011,10(6):551-562
HIV-1 can infect T cells by cell-free virus or by direct virion transfer between cells through cell contact-induced structures called virological synapses (VS). During VS-mediated infection, virions accumulate within target cell endosomes. We show that after crossing the VS, the transferred virus undergoes both maturation and viral membrane fusion. Following VS transfer, viral membrane fusion occurs with delayed kinetics and transferred virions display reduced sensitivity to patient antisera compared to mature, cell-free virus. Furthermore, particle fusion requires that the transferred virions undergo proteolytic maturation within acceptor cell endosomes, which occurs over several hours. Rapid, live cell confocal microscopy demonstrated that viral fusion can occur in compartments that have moved away from the VS. Thus, HIV particle maturation activates viral fusion in target CD4+ T cell endosomes following transfer across the VS and may represent a pathway by which HIV evades antibody neutralization. 相似文献
999.
Objectives
Tinnitus is the perception of a sound in the absence of any physical source of it. About 5–15% of the population report hearing such a tinnitus and about 1–2% suffer from their tinnitus leading to anxiety, sleep disorders or depression. It is currently not completely understood why some people feel distressed by their tinnitus, while others don''t. Several studies indicate that the amount of tinnitus distress is associated with many factors including comorbid anxiety, comorbid depression, personality, the psychosocial situation, the amount of the related hearing loss and the loudness of the tinnitus. Furthermore, theoretical considerations suggest an impact of the age at tinnitus onset influencing tinnitus distress.Methods
Based on a sample of 755 normal hearing tinnitus patients we tested this assumption. All participants answered a questionnaire on the amount of tinnitus distress together with a large variety of clinical and demographic data.Results
Patients with an earlier onset of tinnitus suffer significantly less than patients with an onset later in life. Furthermore, patients with a later onset of tinnitus describe their course of tinnitus distress as more abrupt and distressing right from the beginning.Conclusion
We argue that a decline of compensatory brain plasticity in older age accounts for this age-dependent tinnitus decompensation. 相似文献1000.
Frenzel J Gessner C Sandvoss T Hammerschmidt S Schellenberger W Sack U Eschrich K Wirtz H 《PloS one》2011,6(10):e25544