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   3097篇
  免费   199篇
  2024年   2篇
  2023年   21篇
  2022年   39篇
  2021年   97篇
  2020年   44篇
  2019年   75篇
  2018年   92篇
  2017年   76篇
  2016年   120篇
  2015年   199篇
  2014年   194篇
  2013年   210篇
  2012年   339篇
  2011年   267篇
  2010年   168篇
  2009年   157篇
  2008年   199篇
  2007年   206篇
  2006年   165篇
  2005年   142篇
  2004年   108篇
  2003年   96篇
  2002年   104篇
  2001年   14篇
  2000年   9篇
  1999年   19篇
  1998年   11篇
  1997年   9篇
  1996年   5篇
  1995年   13篇
  1994年   3篇
  1993年   11篇
  1992年   11篇
  1991年   8篇
  1990年   9篇
  1989年   4篇
  1988年   6篇
  1987年   5篇
  1986年   3篇
  1985年   4篇
  1984年   3篇
  1983年   2篇
  1982年   3篇
  1981年   3篇
  1979年   5篇
  1978年   3篇
  1976年   2篇
  1975年   2篇
  1974年   3篇
  1972年   3篇
排序方式: 共有3296条查询结果,搜索用时 328 毫秒
991.
Mycotoxins are secondary metabolites with potential dangers for animal and human health. In particular, maize (Zea mays L.) infection caused by Fusarium and the consequent fumonisin contamination is widespread in several countries such as Italy. We developed six maize populations differing in their constitution of regulatory genes able to accumulate respectively anthocyanins in the aleurone layer (r1 gene), pericarp (b1 and pl1 genes) and phlobaphene in the pericarp (p1 gene). These coloured populations, with the related control colourless populations were analysed for mycotoxin content in the kernels during three field seasons with the aim of understanding if there were any correlations with their ability to accumulate flavonoids in kernel tissues. Our results indicate that accumulation of flavonoid pigments in the seeds, in particular phlobaphenes, is able to reduce the level of fumonisin B1. This finding could be used to minimize kernel mycotoxin contamination in this crop, in particular, the development of sweet, pop and polenta coloured corn varieties will help the farmer to keep the level of fumonisin under the threshold of contamination established for human corn consumption.  相似文献   
992.
Mediterranean spotted fever (MSF) is a tick-borne acute febrile disease caused by Rickettsia conorii and characterized by fever, a maculo-papular rash and a black eschar at the site of the tick bite. We describe the case of a 3-year-old boy with MSF who developed a transient right coronary artery ectasia. The patient was brought to the hospital after four days of fever and mild myalgia of the legs. The suspicion of MSF arose due to the presence of a maculo-papular skin rash and treatment with oral clarithromycin was started. After four days fever persisted and the differential diagnosis of Kawasaki syndrome was considered. Echocardiography showed a dilated right coronary artery with hyperreflective walls. Treatment with intravenous immunoglobulin was initiated while clarithromycin was continued. After one day the fever disappeared. An immunofluorescent antibody test performed after four weeks confirmed a R. conorii infection. A follow-up echocardiography was normal six weeks and six months later. We suggest that ectasia of the coronary arteries may be a manifestation of rickettsial vasculitis. Prospective studies are needed to understand the frequency and the possible consequences of this phenomenon in the course of MSF.  相似文献   
993.
MOTIVATION: Many models and analysis of signaling pathways have been proposed. However, neither of them takes into account that a biological pathway is not a fixed system, but instead it depends on the organism, tissue and cell type as well as on physiological, pathological and experimental conditions. RESULTS: The Biological Connection Markup Language (BCML) is a format to describe, annotate and visualize pathways. BCML is able to store multiple information, permitting a selective view of the pathway as it exists and/or behave in specific organisms, tissues and cells. Furthermore, BCML can be automatically converted into data formats suitable for analysis and into a fully SBGN-compliant graphical representation, making it an important tool that can be used by both computational biologists and 'wet lab' scientists. Availability and implementation: The XML schema and the BCML software suite are freely available under the LGPL for download at http://bcml.dc-atlas.net. They are implemented in Java and supported on MS Windows, Linux and OS X.  相似文献   
994.
995.
For deeper insights into the function of crustacean haemocytes in immune responses, we studied the morphology and enzyme content of circulating cells of the mantis shrimp Squilla mantis from the North Adriatic Sea, together with their ability to phagocytose foreign cells. We also assayed the enzyme content and the agglutinating and haemolytic activities of cell-free haemolymph. Three haemocyte types, i.e., hyalinocytes, semigranulocytes and granulocytes, can be distinguished, according to cell and nuclear morphology and the presence of cytoplasmic granules. All of them share the same patterns of enzyme activities and are recognised by the same lectins. Spreading cells (hyalinocytes and semigranulocytes) can ingest foreign cells; granules of semigranular and granular cells have similar cytochemical properties. Injection of Micrococcus luteus into the heart sinus results in an increase in the frequency of hyaline cells and a decrease in the frequency of granulocytes. After 24 h from the injection, a decrease in the number of phagocytosing hyalinocytes, and a general decrease in the frequency of acid phosphatase-positive cells was reported. Our data match previous results and suggest the existence of a single differentiation pathway for Squilla haemocytes with the three haemocyte morphs as different stages of cell differentiation. Results also indicate that Squilla haemolymph performs immunosurveillance, through rapid changes in haemocyte distribution, increase of antimicrobial and antioxidant enzymes and secretion of lectins stimulating agglutination, phagocytosis and encapsulation.  相似文献   
996.
997.
Background aimsBone marrow (BM)-derived cells appear to be a promising therapeutic source for the treatment of acute myocardial infarction (AMI). However, the quantity and quality of the cells to be used, along with the appropriate time of administration, still need to be defined. We thus investigated the use of BM CD34+-derived cells as cells suitable for a cell therapy protocol (CTP) in the treatment of experimental AMI.MethodsThe need for a large number of cells was satisfied by the use of a previously established protocol allowing the expansion of human CD34+ cells isolated from neonatal and adult hematopoietic tissues. We evaluated gene expression, endothelial differentiation potential and cytokine release by BM-derived cells during in vitro culture. Basal and expanded CD34+ cells were used as a delivery product in a murine AMI model consisting of a coronary artery ligation (CAL). Cardiac function recovery was evaluated after injecting basal or expanded cells.ResultsGene expression analysis of in vitro-expanded cells revealed that endothelial markers were up-regulated during culture. Moreover, expanded cells generated a CD14+ subpopulation able to differentiate efficiently into VE-cadherin-expressing cells. In vivo, we observed a cardiac function recovery in mice sequentially treated with basal and expanded cells injected 4 h and 7 days after CAL, respectively.ConclusionsOur data suggest that combining basal and expanded BM-derived CD34+ cells in a specific temporal pattern of administration might represent a promising strategy for a successful cell-based therapy.  相似文献   
998.
999.

Introduction  

Interstitial pulmonary fibrosis (IPF) is a frequent manifestation in patients with connective tissue disorders (CTD). Recently the ultrasound (US) criterion validity for its assessment has been proposed; however, the US scoring systems adopted include the study of several lung intercostal spaces (LIS), which could be time-consuming in daily clinical practice. The aim of this study was to investigate the utility of a simplified US B-lines scoring system compared with both the US comprehensive assessment and the high-resolution computed tomography (HRCT) findings of IPF in CTD patients.  相似文献   
1000.
The spectroscopic and ligand-binding properties of a 2/2 globin from the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125 have been studied in the ferrous state. It displays two major conformations characterized by CO-association rates that differ by a factor of 20, with relative fractions that depend on pH. A dynamic equilibrium is found between the two conformations, as indicated by an enhanced slower phase when lower CO levels were used to allow a longer time to facilitate the transition. The deoxy form, in the absence of external ligands, is a mixture of a predominant six-coordinate low spin form and a five-coordinate high-spin state; the proportion of low spin increasing at alkaline pH. In addition, at temperatures above the physiological temperature of 1 °C, an enhanced tendency of the protein to oxidize is observed.  相似文献   
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