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   497篇
  免费   51篇
  2023年   6篇
  2022年   6篇
  2021年   11篇
  2020年   4篇
  2019年   20篇
  2018年   17篇
  2017年   14篇
  2016年   15篇
  2015年   36篇
  2014年   31篇
  2013年   33篇
  2012年   43篇
  2011年   29篇
  2010年   30篇
  2009年   17篇
  2008年   22篇
  2007年   31篇
  2006年   21篇
  2005年   21篇
  2004年   25篇
  2003年   27篇
  2002年   19篇
  2001年   7篇
  2000年   4篇
  1999年   5篇
  1998年   5篇
  1997年   3篇
  1996年   5篇
  1995年   4篇
  1993年   2篇
  1992年   6篇
  1991年   6篇
  1990年   5篇
  1989年   1篇
  1988年   2篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1978年   1篇
  1972年   2篇
  1971年   2篇
  1968年   1篇
  1955年   1篇
  1943年   1篇
  1942年   1篇
排序方式: 共有548条查询结果,搜索用时 15 毫秒
511.
M. A. Line 《Plant and Soil》1990,125(1):149-152
Nitrogen-fixing enterobacteria (Enterobacter agglomerans and Citrobacter freundii) were commonly found associated with the microflora of stained Sassafras (Atherosperma moschatum Labill.) in forests of SE Tasmania. However, their populations never exceeded 3× 104 cells g−1 dry wood and comprised at most 3% of the total bacterial flora. Bacterial colonization of the wood appeared to coincide with that by non-hymenocetous fungi: bacteria were never isolated in significant numbers from wood not infected with fungi. The contribution of the N2-fixing flora to the N economy of the habitat is considered to be negligible.  相似文献   
512.
Negative regulation of immune pathways is essential to achieve resolution of immune responses and to avoid excess inflammation. DNA stimulates type I IFN expression through the DNA sensor cGAS, the second messenger cGAMP, and the adaptor molecule STING. Here, we report that STING degradation following activation of the pathway occurs through autophagy and is mediated by p62/SQSTM1, which is phosphorylated by TBK1 to direct ubiquitinated STING to autophagosomes. Degradation of STING was impaired in p62‐deficient cells, which responded with elevated IFN production to foreign DNA and DNA pathogens. In the absence of p62, STING failed to traffic to autophagy‐associated vesicles. Thus, DNA sensing induces the cGAS‐STING pathway to activate TBK1, which phosphorylates IRF3 to induce IFN expression, but also phosphorylates p62 to stimulate STING degradation and attenuation of the response.  相似文献   
513.
  1. It is often suggested to release oaks (Quercus robur) from competition, to ensure their survival and boost their conservational value. However, few studies have explored how long-lasting this effect is and how it affects saproxylic beetles.
  2. Ten years after cutting, we investigated effects of different release cutting levels (high, medium, and no release) around 140-year-old retained oaks in a commercial forest with Norway spruce (Picea abies).
  3. We evaluated oak vitality using crown and dead wood measurements. Saproxylic beetles were caught in window traps, identified to species level, and grouped according to their association with oak and/or Norway spruce.
  4. Released oaks had more light, higher temperatures, greater crown growth, and less dead wood in the crown compared to the no-release control.
  5. After 10 years we still found a higher abundance of oak-associated beetles and higher overall species richness of saproxylic beetles in the released oaks. Beetle species composition significantly differed between released oaks and control.
  6. We suggest avoiding planting trees beneath retained oaks when regenerating conifer forests and to proceed with conservation management during subsequent thinning by removing regeneration under the oak crowns. We emphasize the benefits of monitoring the retained oaks to maintain tree vitality, habitat quality, and insolation.
  相似文献   
514.

Background  

Salmonella enterica serotype Gallinarum (S. Gallinarum) remains an important pathogen of poultry, especially in developing countries. There is a need to develop effective and safe vaccines. In the current study, the effect of crp deletion was investigated with respect to virulence and biochemical properties and the possible use of a deletion mutant as vaccine candidate was preliminarily tested.  相似文献   
515.
516.
Wetlands Ecology and Management - The study central goal was to analyze secondary succession in a degraded peatland: (1) Sphagnum distribution trends and (2) successional patterns. Main study sites...  相似文献   
517.
Environmental enrichment devices are a potential way to enhance psychological well-being in laboratory animals. The effects of such devices need to be systematically evaluated before they are recommended for widespread use. The purpose of this research was to monitor the behavioural and physiological responses of adult female rhesus macaques to a simple enrichment device. The apparatus consisted of a box attached to the monkey's home cage that contained a radio and a food dispenser, which could be controlled by the monkeys via contact detectors. Radio and food dispenser use were automatically recorded. Whole blood serotonin (WBS), plasma cortisol and abnormal behaviour were measured in 5 monkeys before, during and after a 20-week period in which the monkey's cages were equipped with the device. All monkeys used the device (3 of the 5 subjects earned an average of more than 200 food pellets per day). Mean plasma cortisol and whole blood serotonin did not differ across sampling times, suggesting that the apparatus had no effect on basal stress levels. There was an inverse relationship between apparatus use and cortisol levels in 76% of the samples, but only 3 of 17 coefficients were significant. There was a significant but small negative correlation between apparatus use and self-abusive behaviour. This enrichment device was readily used by adult rhesus monkeys and could be adapted for use in a wide variety of laboratory settings.  相似文献   
518.
Newly proposed federal regulations will mandate that singly caged non-human primates be kept in cages larger than the current minimum standard, or be given 4 hours in an exercise cage per week. In order to evaluate the effectiveness of increasing cage size in improving well-being, the behavioral and heart rate responses of 10 female rhesus monkeys (Macaca mulatta) to three different cage sizes were measured. With the exception of vocalizations, no significant differences in behavior were obtained. Grunts increased in the largest cage, following the birth of an infant in a cage within view of the test cages. No differences with respect to cage size were found in heart rate or activity level, although there were significant variations at different times of day. We conclude that modest increases in cage size are less likely to enrich the environment of singly caged laboratory primates than are changes in social opportunities or increases in environmental complexity.  相似文献   
519.
520.
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