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   260篇
  免费   24篇
  284篇
  2024年   1篇
  2023年   1篇
  2022年   3篇
  2021年   5篇
  2020年   9篇
  2019年   3篇
  2018年   9篇
  2017年   3篇
  2016年   12篇
  2015年   21篇
  2014年   22篇
  2013年   29篇
  2012年   21篇
  2011年   24篇
  2010年   17篇
  2009年   16篇
  2008年   18篇
  2007年   14篇
  2006年   9篇
  2005年   12篇
  2004年   12篇
  2003年   10篇
  2002年   8篇
  2001年   1篇
  1999年   1篇
  1998年   2篇
  1981年   1篇
排序方式: 共有284条查询结果,搜索用时 15 毫秒
281.
Allergic bronchopulmonary aspergillosis (ABPA) is a rare form of asthma that is most common in corticosteroid-dependent asthmatic patients and cystic fibrosis patients. It is caused by an abnormal T-helper class 2 response of the host to Aspergillus antigens. Although signs and symptoms of typical asthma are usually present with ABPA, unusual features such as fever, expectoration of brown plugs, and central bronchiectasis with or without mucoid impaction on chest radiographs may be present. ABPA is important to diagnose because inadequate therapy may lead to permanent lung destruction. Corticosteroids are the drug of choice for ABPA; however, the doses required are often greater than for routine asthma and corticosteroid dependence is not unusual. Azole therapy appears to have an adjunctive role in treatment in terms of improving signs and symptoms of the disease and demonstrating a corticosteroid-sparing effect.  相似文献   
282.
Summary Four monolayer mammalian cell lines were cured ofMycoplasma hyorhinis infections by cloning in microtiter dishes in the presence of tetracycline and kanamycin. During cloning, cultures were refed with fresh antibiotic containing medium every 2 or 3 d for 14 d and were then cultured without effective antibiotics for at least 21 d. From the four lines we recovered 29 clones, none of which were infected after treatment as judged by the lack of extranuclear fluorescence after staining with the fluorochrome Hoechst 33258, and by normal autoradiographic labeling of the cells by tritiated nucleosides. One clone from each line was tested further by attempted culture of mycoplasmas and was also judged to be uninfected. Infection has not reappeared in any of the clones after extensive culture in the absence of the effective antibiotics. This investigation was supported by Public Health Service Research Grant GM26137 from the National Institutes of General Medical Sciences, National Institutes of Health, Bethesda, MD.  相似文献   
283.
Melanin, a black-brown pigment found throughout all kingdoms of life, has diverse biological functions including UV protection, thermoregulation, oxidant scavenging, arthropod immunity, and microbial virulence. Given melanin’s broad roles in the biosphere, particularly in insect immune defenses, it is important to understand how exposure to ubiquitous environmental contaminants affects melanization. Glyphosate—the most widely used herbicide globally—inhibits melanin production, which could have wide-ranging implications in the health of many organisms, including insects. Here, we demonstrate that glyphosate has deleterious effects on insect health in 2 evolutionary distant species, Galleria mellonella (Lepidoptera: Pyralidae) and Anopheles gambiae (Diptera: Culicidae), suggesting a broad effect in insects. Glyphosate reduced survival of G. mellonella caterpillars following infection with the fungus Cryptococcus neoformans and decreased the size of melanized nodules formed in hemolymph, which normally help eliminate infection. Glyphosate also increased the burden of the malaria-causing parasite Plasmodium falciparum in A. gambiae mosquitoes, altered uninfected mosquito survival, and perturbed the microbial composition of adult mosquito midguts. Our results show that glyphosate’s mechanism of melanin inhibition involves antioxidant synergy and disruption of the reaction oxidation–reduction balance. Overall, these findings suggest that glyphosate’s environmental accumulation could render insects more susceptible to microbial pathogens due to melanin inhibition, immune impairment, and perturbations in microbiota composition, potentially contributing to declines in insect populations.

Glyphosate, the most commonly used herbicide in the world, inhibits the production of melanin. Melanin is an important pigment and a key component of the insect immune system; this study shows that glyphosate weakens insects’ melanin-based immune system and makes them more vulnerable to infections, including with the human malaria parasite Plasmodium falciparum.  相似文献   
284.
Fishes in the superorder ostariophysi possess specialized epidermal cells that contain an alarm cue. Fish associate novel odours, such as the odour of a predator, with predation risk after a single, simultaneous exposure to the novel odour and alarm cue. Thereafter, the novel cue is recognized as an indicator of risk and its presence induces antipredator behaviour. Two common antipredator behaviours are reduction in activity and movement to the bottom. This phenomenon has been demonstrated many times in the laboratory setting for a variety of aquatic taxa. In nature however, the detection of novel predator odour may be time-shifted with respect to the detection of alarm cues. Is there a critical period immediately upon the detection of alarm cue in which associative learning can occur? We presented zebra danios, Danio rerio, with the odour of northern pike, Esox lucius, 5?min after presenting them with either alarm cue or water (control). During a predation event, 5?min is a long time. When later retested with pike odour alone, zebra fish conditioned with alarm cue significantly increased antipredator behaviour in terms of decreased activity and movement towards the bottom. Control fish did not recognize pike odour as dangerous when retested. These data show that learned recognition of predation risk is sufficiently robust to accommodate ecologically realistic temporal shifts in stimulus presentation.  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