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   642篇
  免费   49篇
  2022年   5篇
  2021年   21篇
  2020年   10篇
  2019年   13篇
  2018年   14篇
  2017年   4篇
  2016年   17篇
  2015年   25篇
  2014年   33篇
  2013年   30篇
  2012年   37篇
  2011年   36篇
  2010年   24篇
  2009年   17篇
  2008年   35篇
  2007年   42篇
  2006年   25篇
  2005年   36篇
  2004年   32篇
  2003年   21篇
  2002年   30篇
  2001年   5篇
  2000年   7篇
  1999年   5篇
  1998年   8篇
  1997年   6篇
  1996年   9篇
  1995年   8篇
  1994年   4篇
  1993年   14篇
  1992年   13篇
  1991年   9篇
  1990年   8篇
  1989年   11篇
  1988年   4篇
  1987年   6篇
  1986年   4篇
  1985年   8篇
  1984年   15篇
  1982年   4篇
  1981年   2篇
  1980年   4篇
  1977年   2篇
  1976年   3篇
  1975年   2篇
  1973年   2篇
  1970年   2篇
  1954年   3篇
  1953年   2篇
  1929年   1篇
排序方式: 共有691条查询结果,搜索用时 15 毫秒
681.
682.
  1. Growing developmental activities, such as hydropower construction, farm roads, and other human activities, are affecting the critically endangered white-bellied heron (WBH). Out of a known global population of 60, 28 individuals inhabit the river basin area and freshwater lakes and ponds of Bhutan. Several constraints impede continuous monitoring of endangered species, such as the isolated and cryptic nature of the species and the remoteness of its habitat; to date, there are no long-term reference data or techniques implemented for continuous monitoring of this species.
  2. In this study, we designed acoustic detection and habitat characterisation methods using long-duration recordings from three habitat areas in Bhutan. Acoustic indices were extracted and used to implement a species-specific call detector and to generate habitat soundscape representations. Using WBH calls annotated in month-long recordings from a known site, a novel indices-based detector was implemented and tested. A total of 960 hr of continuous audio recordings from three habitats in Bhutan were analysed.
  3. We found that a species call detector implemented using a combination of acoustic indices (that includes measures of spectral and temporal entropy and different angles of spectral ridges) has a correct detection rate of 81%. Additionally, visual inspection of the species’ acoustic habitat using long-duration false-colour spectrograms enabled qualitative assessment of acoustic habitat structure and other dominant acoustic events.
  4. This study proposes a combined approach of species acoustic detection and habitat soundscape analysis for holistic acoustic monitoring of endangered species. As a direct outcome of this work, we documented acoustic reference data on the critically endangered WBH from multiple habitat areas and have analysed its temporal vocalisation patterns across sites.
  相似文献   
683.
Females and males differ significantly in gross anatomy and physiology of the lower urinary tract, and these differences are commonly discussed in the medical and scientific literature. However, less attention is dedicated to investigating the varied development, function, and biology between females and males on a cellular level. Recognizing that cell biology is not uniform, especially in the lower urinary tract of females and males, is crucial for providing context and relevance for diverse fields of biomedical investigation. This review serves to characterize the current understanding of biological sex differences between female and male lower urinary tracts, while identifying areas for future research. First, the differences in overall cell populations are discussed in the detrusor smooth muscle, urothelium, and trigone. Second, the urethra is discussed, including anatomic discussions of the female and male urethra followed by discussions of cellular differences in the urothelial and muscular layers. The pelvic floor is then reviewed, followed by an examination of the sex differences in hormonal regulation, the urinary tract microbiome, and the reticuloendothelial system. Understanding the complex and dynamic development, anatomy, and physiology of the lower urinary tract should be contextualized by the sex differences described in this review.  相似文献   
684.
Analysis of natural killer (NK) activity in different organs from mice or rats fractionated using discontinuous density gradients have revealed typical distinct density profiles according to the organ from which the NK cells were derived. High NK level organs thus tended to have significant lytic activity extending into 1.090 density fractions whereas the low NK population had its peak activity more strictly confined to the 1.067 fraction. The reason for this skewedness we find to be dependent upon the presence of an inhibitor cell for NK cells to be found in the higher-density fractions. The significance of this inhibitor cell was more apparent when NK activity was low, thus skewing peak levels to lower fractions. The activity of this inhibitory cell was not found to vary with age, thus failing to explain the age-dependent rise and fall of NK activity in rodents. Presence of such an inhibitory cell also explains why sizeable NK activity can be disclosed in a fraction of cells obtained from a population which before fractionation failed to disclose NK function.  相似文献   
685.
686.
Weaving Identities: Construction of Dress and Self in. Highland Guatemala Town. Carol Hendrickson. Austin: University of Texas Press, 1995. 245 pp.  相似文献   
687.
Pacific Island countries have a high burden of scabies and impetigo. Understanding of the epidemiology of these diseases is needed to target public health interventions such as mass drug administration (MDA). The aim of this study is to determine the prevalence of scabies and impetigo in Solomon Islands as well as the relationship between them and their distribution. We conducted a prevalence study in 20 villages in Western Province in Solomon Islands. All residents of the village were eligible to participate. Nurses conducted clinical assessments including history features and skin examination. Diagnosis of scabies was made using the 2020 International Alliance for the Control of Scabies diagnostic criteria. Assessments were completed on 5239 participants across 20 villages. Overall scabies prevalence was 15.0% (95%CI 11.8–19.1). There was considerable variation by village with a range of 3.3% to 42.6%. There was a higher prevalence of scabies in males (16.7%) than females (13.5%, adjusted relative risk 1.2, 95%CI 1.1–1.4). Children aged under two years had the highest prevalence (27%). Overall impetigo prevalence was 5.6% (95%CI 4.2–7.3), ranging from 1.4% to 19% by village. The population attributable risk of impetigo associated with scabies was 16.1% (95% CI 9.8–22.4). The prevalence of scabies in our study is comparable to previous studies in Solomon Islands, highlighting a persistent high burden of disease in the country, and the need for public health strategies for disease control.  相似文献   
688.
689.
690.
Background and AimsMammals and molluscs (MaM) are abundant herbivores of tree seeds and seedlings, but how the trees and their environment affect MaM herbivory has been little studied. MaM tend to move much larger distances during the feeding stage than the more frequently studied insect herbivores. We hypothesize that MaM (1) select and stay within the patches that promise to be relatively the richest in seeds and seedlings, i.e. patches around adult trees that are old and within a distantly related, less productive neighborhood; and (2) try to remain sheltered from predators while foraging, i.e. mammals remain close to adult trees or to cover by herbs while foraging, and might force their mollusc prey to show the opposite distribution.MethodsWe exposed oak acorns and seedlings in a temperate forest along transects from adult conspecifics in different neighbourhoods. We followed acorn removal and leaf herbivory. We used exclusion experiments to separate acorn removal by ungulates vs. rodents and leaf herbivory by insects vs. molluscs. We measured the size of the closest conspecific adult tree, its phylogenetic isolation from the neighbourhood and the herbaceous ground cover.Key ResultsConsistent with our hypothesis, rodents removed seeds around adult trees surrounded by phylogenetically distant trees and by a dense herb cover. Molluscs grazed seedlings surrounding large conspecific adults and where herb cover is scarce. Contrary to our hypothesis, the impact of MaM did not change from 1 to 5 m distance from adult trees.ConclusionsWe suggest that foraging decisions of MaM repulse seedlings from old adults, and mediate the negative effects of herbaceous vegetation on tree recruitment. Also, an increase in mammalian seed predation might prevent trees from establishing in the niches of phylogenetically distantly related species, contrary to what is known from insect enemies.  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