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   213篇
  免费   16篇
  2022年   4篇
  2021年   6篇
  2020年   3篇
  2019年   6篇
  2018年   11篇
  2017年   9篇
  2016年   10篇
  2015年   11篇
  2014年   19篇
  2013年   20篇
  2012年   12篇
  2011年   15篇
  2010年   13篇
  2009年   9篇
  2008年   13篇
  2007年   8篇
  2006年   13篇
  2005年   7篇
  2004年   4篇
  2003年   3篇
  2002年   7篇
  2001年   3篇
  2000年   2篇
  1999年   1篇
  1998年   1篇
  1997年   1篇
  1995年   3篇
  1993年   2篇
  1991年   1篇
  1990年   1篇
  1989年   2篇
  1987年   1篇
  1979年   2篇
  1978年   1篇
  1975年   2篇
  1970年   2篇
  1960年   1篇
排序方式: 共有229条查询结果,搜索用时 15 毫秒
41.
Lecanosticta acicola is a pine needle pathogen causing brown spot needle blight that results in premature needle shedding with considerable damage described in North America, Europe, and Asia. Microsatellite and mating type markers were used to study the population genetics, migration history, and reproduction mode of the pathogen, based on a collection of 650 isolates from 27 countries and 26 hosts across the range of L. acicola. The presence of L. acicola in Georgia was confirmed in this study. Migration analyses indicate there have been several introduction events from North America into Europe. However, some of the source populations still appear to remain unknown. The populations in Croatia and western Asia appear to originate from genetically similar populations in North America. Intercontinental movement of the pathogen was reflected in an identical haplotype occurring on two continents, in North America (Canada) and Europe (Germany). Several shared haplotypes between European populations further suggests more local pathogen movement between countries. Moreover, migration analyses indicate that the populations in northern Europe originate from more established populations in central Europe. Overall, the highest genetic diversity was observed in south‐eastern USA. In Europe, the highest diversity was observed in France, where the presence of both known pathogen lineages was recorded. Less than half of the observed populations contained mating types in equal proportions. Although there is evidence of some sexual reproduction taking place, the pathogen spreads predominantly asexually and through anthropogenic activity.  相似文献   
42.
43.
Inhibitors of eubacterial and eukaryotic DNA topoisomerases type II exhibited different effects on chloroplasts of the flagellateEuglena gracilis. Antibacterial agents (cinoxacin, nalidixic and oxolinic acids, ciprofloxacin, enoxacin, norfloxacin and ofloxacin) from the group of quinolones and coumarins (coumermycin A1, clorobiocin and novobiocin) — all inhibitors of prokaryotic DNA topoisomerase II — were very potent eliminators of chloroplasts fromE. gracilis. In contrast, antitumor drugs (adriamycin, etoposide, teniposide and mitoxantrone) — antagonists of the eukaryotic counterpart — did not affect these semiautonomous photosynthetic organelles. These findings point out again the close evolutionary relationships between eubacteria and chloroplasts and are in agreement with the hypothesis of an endosymbiotic origin of chloroplasts.  相似文献   
44.
The transplantation of fresh or cryopreserved vascular allografts in patients with a prosthetic graft infection or critical limb ischemia is necessary for their limb salvage and, in many cases, represents a lifesaving procedure. While transplantation of fresh allografts has a long history in the Czech Republic, the standard use of cryopreserved vascular allografts was introduced into the clinical practice in 2011 as a result of the implementation of EU Directive 2004/23/EC into national legislation (Human Cell and Tissue Act No. 296/2008 Coll.). The authors present an organizational model based on cooperation between the majority of Czech Transplant Centers with a tissue establishment licensed by the national competent authority. In various points, we are addressing individual aspects of experimental and clinical studies which affect clinical practice. Based on experimental and clinical work, the first validation of cryopreserved arterial and venous grafts for clinical use was performed between 2011 and 2013. The growing number of centers participating in this programme led to a growing number of patients who underwent transplantation of vascular allografts. In 2015 the numbers of transplanted fresh versus cryopreserved allografts in the Czech Republic were almost equal. Cooperation of the participating centers in the Czech Republic with the licensed Tissue Establishment made it possible to achieve a full compliance with the European Union Directives, and harmonized national legal norms and assured a high quality of cryopreserved vascular allografts.  相似文献   
45.
46.
A successful control or eradication programme using biological control or genetically-mediated methods requires knowledge of the origin and the extent of wasp genetic diversity. Mitochondrial DNA variation in the native and invaded range of the social wasp Vespula germanica was used to examine intra-specific genetic variation and invasive source populations. We also examined wasps for the presence of four viruses found in honey bees: Acute bee paralysis virus, Deformed wing virus, Israeli acute paralysis virus and Kashmir bee virus. German wasps showed reduced genetic diversity in the invaded range compared to that of their native range. Populations in the introduced range are likely to have arrived from different source populations. All four viral honey bee pathogens were found in V. germanica, although they varied in their distribution and strain. Multiple introductions of German wasps have occurred for most invaded regions, though some populations are genetically homogenous. The differing locations of origin will guide researchers searching for biocontrol agents and the reduced genetic diversity may make these wasps a potentially viable target for control via gene drives.  相似文献   
47.

Background

Left atrial (LA) enlargement is a predictor of worse outcome after catheter ablation for atrial fibrillation (AF). Widely used two-dimensional (2D)-echocardiography is inaccurate and underestimates real LA volume (LAV). We hypothesized that baseline clinical characteristics of patients can be used to adjust 2D-ECHO indices of LAV in order to minimize this disagreement.

Methods

The study enrolled 535 patients (59 ± 9 years; 67% males; 43% paroxysmal AF) who underwent catheter ablation for AF in three specialized centers. We investigated multivariately the relationship between 2D-echocardiographic indices of LA size, specifically LA diameter in M-mode in the parasternal long-axis view (LAD), LAV assessed by the prolate-ellipsoid method (LAVEllipsoid), LAV by the planimetric method (LAVPlanimetry), and LAV derived from 3D-electroanatomic mapping (LAVCARTO).

Results

Cubed LAD of 106 ± 45 ml, LAVEllipsoid of 72 ± 24 ml and LAVPlanimetry of 88 ± 30 ml correlated only modestly (r = 0.60, 0.69, and 0.53, respectively) with LAVCARTO of 137 ± 46 ml, which was significantly underestimated with a bias (±1.96 standard deviation) of -31 (-111; +49) ml, -64 (-132; +2) ml, and -49 (-125; +27) ml, respectively; p < 0.0001 for their mutual difference. LA enlargement itself, age, gender, type of AF, and the presence of structural heart disease were independent confounders of measurement error of 2D-echocardiographic LAV.

Conclusion

Accuracy and precision of all 2D-echocardiographic LAV indices are poor. Their agreement with true LAV can be significantly improved by multivariate adjustment to clinical characteristics of patients.  相似文献   
48.
49.
50.
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