首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   280篇
  免费   12篇
  2022年   3篇
  2021年   8篇
  2020年   5篇
  2019年   6篇
  2018年   6篇
  2017年   5篇
  2016年   13篇
  2015年   9篇
  2014年   17篇
  2013年   24篇
  2012年   29篇
  2011年   17篇
  2010年   24篇
  2009年   10篇
  2008年   15篇
  2007年   21篇
  2006年   12篇
  2005年   21篇
  2004年   12篇
  2003年   9篇
  2002年   9篇
  2001年   2篇
  2000年   1篇
  1999年   5篇
  1998年   3篇
  1997年   1篇
  1991年   1篇
  1990年   1篇
  1988年   1篇
  1986年   1篇
  1984年   1篇
排序方式: 共有292条查询结果,搜索用时 421 毫秒
281.
The structural, vibrational and electronic properties of nitrotyrosine and 8-nitroguanine have been investigated theoretically by performing the molecular mechanics (MM+ force field), the semi-empirical self-consistent-field molecular-orbital (PM3), and density functional theory calculations. The geometry of the nitrotyrosine and 8-nitroguanine molecules have been optimized, the vibrational dynamics and the electronic properties calculated in their ground states in the gas phase.  相似文献   
282.
BackgroundThe aim of this study was to determine levels of Mid-regional Pro-adrenomedullin (MR-proADM) and Mid-regional Pro-atrial Natriuretic Peptide (MR-proANP) in patients with acute pulmonary embolism (PE), the relationship between these parameters and the risk classification in addition to determining the relationship between 1and 3month mortality.Methods82 PE patients and 50 healthy control subjects were included in the study. Blood samples for Mr-proANP and Mr-proADM were obtained from the subjects prior to the treatment. Risk stratification was determined according to sPESI (Simplified Pulmonary Embolism Severity Index). Following these initial measurements, cases with PE were assessed in terms of all causative and PE related mortalities.ResultsThe mean serum Mr-proANP and Mr-proADM levels in acute PE patients were found to be statistically higher compared to the control group (p < 0.001, p < 0.01; respectively) and statistically significantly higher in high-risk patients than low-risk patients (p < 0.01, p < 0.05; respectively). No statistical difference was determined in high-risk patients in case of sPESI compared to low-risk patients while hospital mortality rates were higher. It was determined that the hospital mortality rate in cases with Mr-proANP ≥ 123.30 pmol/L and the total 3-month mortality rate in cases with Mr-proADM ≥ 152.2 pg/mL showed a statistically significant increase.ConclusionsThis study showed that Mr-proANP and MRproADM may be an important biochemical marker for determining high-risk cases and predicting the mortality in PE patients and we believe that these results should be supported by further and extensive studies.  相似文献   
283.
Is the alpha rhythm a control parameter for brain responses?   总被引:4,自引:0,他引:4  
 The main goal of the present study is to develop a conceptual analysis of alpha response in the brain based on single sweep evaluation. A new method was employed to estimate a set of single-sweep parameters and quantify the oscillatory behaviour of single, electroencephalograph (EEG) sweeps. It was aimed to demonstrate that brain alpha responses are governed by spontaneous alpha activity and to validate the principle of brain response excitability. Because the spontaneous alpha activity depends on both the topology of recording and the subject’s age, topology and age models were used. Spontaneous and evoked alpha activity were recorded at frontal and occipital sites in three groups of subjects: 3-year-old children, young adults and middle-aged subjects. Amplitude, enhancement and phase-locking of single alpha responses to visual stimuli were analysed. Major results showed that: (1) visual alpha responses could be recorded only if the alpha rhythm was developed in the spontaneous EEG independent of electrode location; (2) middle-aged adults showed more expressed frontal spontaneous alpha activity in comparison with young adults; (3) accordingly, alpha responses with higher amplitude and stronger phase-locking were produced over the frontal brain area in middleaged than young adults. These results validate the principle of brain response excitability and demonstrate that a shift towards frontal brain areas for both the spontaneous and evoked alpha activity occurs with increasing age in adults. The results are discussed in the context of the diffuse and distributed alpha system of the brain. Age-dependent changes in frontal alpha activity are suggested to be related to frontal brain functioning during aging. Received: 6 November 1995 / Accepted in revised form: 13 March 1997  相似文献   
284.
In this study, the morphological and anatomical features of Lamium lycium Boiss. (Lamiaceae) are described in detail. L. lycium has a perennial tap-root, and the stem is ascending and clearly quadrangular. The leaves are simple and broadly ovate to narrowly ovate in shape. The inflorescense is a verticillate cyme. The corolla is purple and the upper lip is hooded. For anatomy, the cross-sections of root, stem, leaf, petiole, calyx, corolla and generative organs were examined and the anatomical features of the taxon are discussed. The morphological features were in most respects congruent with previous reports. However, the anatomy of L. lycium has not been studied before and the results are here compared with trose of previous studies on other members of Lamiaceae. Furthermore, glandular trichomes are illustrated. The results are presented with photographs and tables.  相似文献   
285.
Circularly permuted green fluorescent protein (cGFP) was inserted into the hyperthermophilic maltose binding protein at two different locations. cGFP was inserted between amino acid residues 206 and 207, or fused to the N-terminal of maltose binding protein from Thermotoga maritima. The cloned DNA constructs were expressed in Escherichia coli cells, and purified by metal chelate affinity chromatography. Conformational change upon ligand binding was monitored by the increase in fluorescence intensity. Both of the fusion proteins developed significant fluorescence change at 0.5 mM maltose concentration, whereas their maltose binding affinities and optimum incubation times were different. Fluorescent biosensors based on mesophilic maltose binding proteins have been described in the literature, but there is a growing interest in biosensors based on thermostable proteins. Therefore, the developed protein constructs could be models for thermophilic protein-based fluorescent biosensors.  相似文献   
286.
287.
ABSTRACT: BACKGROUND: In this study, the clinical and morphological features of vesiculobullous lesions observed in Kaposi sarcoma are analyzed, and the features of bullous Kaposi sarcoma cases are emphasized. METHODS: A total of 178 biopsy materials of 75 cases diagnosed as classic-type cutaneous Kaposi sarcoma were reviewed. Twenty-five cases showing vesiculobullous features were included in the study. Tumor, epidermis, dermis, and clinical data regarding these cases was evaluated. RESULTS: Vesicular changes were observed in 21 (12%) out of 178 lesions of the 75 cases, while bullous changes were present in only 4 (2%). In all cases where vesicular and bullous changes were detected, tumor, epidermis, and dermis changes were similar. All cases were nodular stage KS lesions, whereas hyperkeratosis and serum exudation in the epidermis, marked edema in the dermis, and enlarged lymphatic vessels and chronic inflammatory response were observed. CONCLUSIONS: Our findings suggest that changes in vascular resistance occurring during tumor progression are the most important factors comprising vesiculobullous morphology. Virtual slides The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1646397188748474.  相似文献   
288.
289.
290.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号