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   261篇
  免费   8篇
  国内免费   3篇
  2023年   4篇
  2022年   4篇
  2021年   7篇
  2020年   3篇
  2019年   7篇
  2018年   9篇
  2017年   7篇
  2016年   4篇
  2015年   7篇
  2014年   12篇
  2013年   15篇
  2012年   6篇
  2011年   6篇
  2010年   10篇
  2009年   16篇
  2008年   21篇
  2007年   21篇
  2006年   15篇
  2005年   7篇
  2004年   7篇
  2003年   4篇
  2000年   5篇
  1999年   2篇
  1998年   3篇
  1997年   4篇
  1996年   8篇
  1995年   3篇
  1994年   4篇
  1993年   2篇
  1992年   4篇
  1991年   4篇
  1990年   5篇
  1989年   3篇
  1988年   3篇
  1987年   4篇
  1986年   3篇
  1984年   1篇
  1982年   1篇
  1980年   2篇
  1979年   3篇
  1978年   2篇
  1977年   2篇
  1976年   1篇
  1973年   1篇
  1972年   1篇
  1970年   1篇
  1969年   1篇
  1967年   2篇
  1966年   1篇
  1965年   1篇
排序方式: 共有272条查询结果,搜索用时 46 毫秒
241.
Feranec RS  Hadly EA  Paytan A 《Oecologia》2007,153(4):943-950
The use of the landscape by animals is predicted to be a function of their body size. However, empirical data relating these two variables from an array of body sizes within a single mammalian community are scarce. We tested this prediction by assessing landscape use of mammals by analyzing strontium (Sr) isotope signatures found in mammalian hard tissues representing a 3,000-year record. We examined: (1) the Sr-determined landscape area of small (∼100 g), medium (∼1,500 g) and large (∼100,000 g) mammals, and; (2) whether the area used by these mammals varied during periods of environmental change. Strontium isotope values were obtained from 46 specimens from the Holocene paleontological deposits of Lamar Cave and Waterfall Locality in Wyoming, USA, as well as from 13 modern ungulate specimens from the same area. Our data indicate that medium- and large-sized species use larger percentages of the landscape than do species of small body size. The isotope values for specimens from each of the paleontological sites are similar across all stratigraphic levels, suggesting no change in home range over the last 3,000 years, even though climate is known to have fluctuated at these sites over this time period. Further, our study verifies that the fossil localities represent the local community. Where bedrock geology is appropriate, the use of strontium isotope analyses provides a valuable tool for discerning landscape use by vertebrate communities, an important though generally difficult aspect of an ancient species niche to identify. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   
242.
Recently, considerable intraspecific variation in the diets and ranging behavior of colobine monkeys has been described, although in most cases this has involved documenting variation between, not within, sites. Some African colobines, such as guerezas (Colobus guereza), are relatively abundant in disturbed habitats that are very heterogeneous, raising the intriguing possibility that even groups with overlapping home ranges may exhibit large behavioral differences. If such differences occur, it will be important to understand what temporal and spatial scales adequately portray a species’ or population’s diet and ranging behavior. This study documents within-site variation in the diet and ranging behavior of guerezas in the habitat types in which they are described to be most successful—forest edge and regenerating forest. We collected data on eight groups of guerezas with overlapping home ranges for 3–5 months each in Kibale National Park, Uganda. The guerezas were highly folivorous, with leaves constituting 78.5–94.0% of the groups’ diets. The percentage of mature leaves and fruit in the diet varied widely among and within groups. We show that differences among groups in the intensity with which they fed on specific tree species were not just related to phenology, but also to differences in the forest compositions of groups’ core areas. Range size estimates varied more than fivefold among groups and the minimum distance from groups’ core areas to eucalyptus forest (which all groups regularly fed in) was a better predictor of range size than was group size. These results reveal considerable variation in the diet and ranging behavior among groups with overlapping ranges and have implications for comparative studies, investigations of within- and between-group feeding competition, and the potential for populations to adapt to anthropogenic or natural environmental change.  相似文献   
243.
It has become increasingly evident that the spatial distribution and the motion of membrane components like lipids and proteins are key factors in the regulation of many cellular functions. However, due to the fast dynamics and the tiny structures involved, a very high spatio-temporal resolution is required to catch the real behavior of molecules. Here we present the experimental protocol for studying the dynamics of fluorescently-labeled plasma-membrane proteins and lipids in live cells with high spatiotemporal resolution. Notably, this approach doesn’t need to track each molecule, but it calculates population behavior using all molecules in a given region of the membrane. The starting point is a fast imaging of a given region on the membrane. Afterwards, a complete spatio-temporal autocorrelation function is calculated correlating acquired images at increasing time delays, for example each 2, 3, n repetitions. It is possible to demonstrate that the width of the peak of the spatial autocorrelation function increases at increasing time delay as a function of particle movement due to diffusion. Therefore, fitting of the series of autocorrelation functions enables to extract the actual protein mean square displacement from imaging (iMSD), here presented in the form of apparent diffusivity vs average displacement. This yields a quantitative view of the average dynamics of single molecules with nanometer accuracy. By using a GFP-tagged variant of the Transferrin Receptor (TfR) and an ATTO488 labeled 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphoethanolamine (PPE) it is possible to observe the spatiotemporal regulation of protein and lipid diffusion on µm-sized membrane regions in the micro-to-milli-second time range.  相似文献   
244.
本文采用无线电遥测技术对栖息在自然环境中香鼬(Mustealaltaica)的活动节律及其巢区进行了较为系统的研究。结果表明,香鼬多营独居生活.除繁殖期外,无论雌雄个体均无长期稳定的巢穴,经常更换活动的位置。香鼬的每日活动主要为玩耍、自身的修饰、光浴、探视和取食,在繁殖期还有育幼及对幼鼬的保护。在不同时期香鼬日活动高峰和巢区大小均有不同。幼鼬出洞活动前,其亲体雌性成鼬活动呈现两个明显的高峰,11:00~13:00和16:00~17:00,雄性成鼬则只有一个活动高峰在11:00左右;在这一时期,成体香鼬的地面活动高峰与其食物──高原鼠兔的地面活动高峰不相吻合,雌性成鼬的巢区面积为7.21ha,雄性成鼬的巢区面积为11.7ha。幼鼬出洞活动后,雌性成鼬的活动高峰为8:00~9:00和17:00~19:00,巢区面积平均为82.72ha。幼鼬扩散期间;雌性成鼬的活动高峰期分别为8:00~9:00和15:00~20:00。在这两个时期。成体香鼬的地面活动高峰与高原鼠兔的地面活动高峰趋于一致。影响香鼬活动和巢区大小的主要因素是食物的丰富度、猎物的活动性和繁殖行为,同时种群密度也是主要因素之一。  相似文献   
245.
Fencing conservation areas is ubiquitous in South Africa, however, the impact of these on predator ecology has not been tested. We used relationships between prey abundance and predator space use to create equations to predict the home range size of lions Panthera leo and leopards Panthera pardus. We then successfully tested these predictions using published data (Phinda, Makalali) and home range estimates from radio collared individuals reintroduced to Addo Elephant National Park. Spotted hyaena Crocuta crocuta ranges also seem food dependent. Lion home ranges in Addo (114 ± 5 km2) required 180 fixes to be accurately estimated, spotted hyaena ranges (91 ± 10 km2) required 200 fixes, and the solitary leopard had 295 fixes for a range of 38 km2. There were no sexual differences in home range sizes of lions or hyaenas. The daily food intake rate of lions, measured during continuous follows, was 9.8 kg per female equivalent unit. Dominant male lions (14.3 km for 8.3 kg) traveled furthest but obtained the least amount of food per day compared to subordinate males (8.9 km for 16.0 kg) and females (5.8 km for 17.9 kg). Subordinate males traveled the fastest and during the day, to avoid competition and harassment from the dominant males. From an evolutionary viewpoint, the use of fences for conservation has not affected the natural behaviour of the predators as they still conform to predictions derived from unfenced reserves; that is, prey abundance is the key factor in determining space use of large predators.  相似文献   
246.
247.
We used a 3-arm randomized control trial to investigate whether abdominal hollowing (AH) home exercise using pocket-sized ultrasonography (US)—miruco (AH with miruco group)—was more effective than conventional AH home exercise using abdominal palpation and or also a wait-and-see approach (control group) to improve isolated control of the transversus abdominis (TrA) muscle during AH. We randomized 60 participants with low back pain into the three groups equally. Primary outcome measures for the US group were percentage of change in TrA thickness and excursion of the edge of the TrA fascia during AH when the thickness of the internal or external oblique muscles increased. Score on the Oswestry Disability Index (ODI) was a secondary outcome measure. The intervention period was 1 week, followed by 1 week without intervention. As a result, we found no statistically significant interaction effect (P > .05) in changes of the primary outcome measures from baseline for each follow-up period. The AH with miruco group had a statistically lower ODI (P = .036) than did the control group after the intervention. Results indicate a limited benefit for use of the miruco in AH home exercise to improve isolated control of the TrA muscle during AH.  相似文献   
248.
249.
Understanding how large felids use space is essential for the design of conservation plans that are required for their survival. Jaguars (Panthera onca) and pumas (Puma concolor) are the largest felids in the Neotropics, and they are sympatric throughout the entire range of the jaguar. However, there is very little information about the spatial requirements of these two species in the tropical rainforests of Central America. Using satellite GPS collars, we compared the spatial ecology of jaguars and pumas in a tropical rainforest in southern Mexico. We found that jaguars had home ranges that were 2–6 times larger than those of pumas. The mean annual home range was 181.4 ± 4.0 km2 for female jaguars and 431.6 ± 152.6 km2 for males. Annual home range for the only female puma tracked was 34.3 km2, and 72.0 ± 85.2 km2 for males. Jaguars and pumas with overlapping home ranges showed little overlap of core areas and avoided using the same sites at the same time, which suggested that territoriality and avoidance were in play. Further evidence of avoidance was derived from our observation that pumas exhibited greater movement during the lightest periods of the day and jaguars moved most during the darkest. This temporal separation probably facilitates coexistence. Our data suggest that habitat destruction and fragmentation has more severe effects on jaguars than on pumas. According to our estimates, patches of at least 180 km2 of primary forest are required to meet the annual spatial requirements of female jaguars. Thus, to conserve jaguars in this region, large tracts of primary forest should be preserved. Importantly, this population of jaguars depends on the adequate preservation of connectivity between natural reserves in Mexico and Guatemala.  相似文献   
250.
The lack of long-term studies remains a limiting factor in understanding the home range, spatial ecology and movement of giraffes. We equipped eight giraffes with GPS satellite units and VHF capacity, which were built in to the collars for the remote collection of data on their movements and home ranges over two years on Khamab Kalahari Nature Reserve (KKNR) within the Kalahari region of South Africa. Giraffe numbers in KKNR dropped from 135 individuals to 111 in just five years, revealing the lack of knowledge about their required habitat needs, space use and diet. With over 1000 km2 available for roaming within the reserve, habitat selection, principle and preferred food species played a significant role in home range size and overlap between individuals. These giraffes used an average annual home range of 206 km2 (20 602 ha) as calculated by a 95% minimum convex polygon (MCP) with a standard deviation core home range calculated by a 50% MCP of 10.1 km2 to satisfy their annual needs for survival and reproduction in their preferred vegetation. In the wet, hot season (summer: December–February) when food was abundant, giraffes frequented smaller areas (average 177 km2), while in the dry, cool season (winter: June to August) the mean home range size increased to approximately 245 km2. Rainfall influenced spatial distribution since it determined vegetation productivity and leaf phenology. The different seasons influenced giraffe movements, while different vegetation types and season influenced their home range size. Season and food availability also influenced home range overlap between different giraffe herds. Home range overlap occurred when giraffes were forced to roam in overlapping areas during the dryer months when the winter deciduous nature of the majority of the tree species resulted in lower food availability. In winter, the overlap was approximately 31% and in autumn approximately 23%. During the wet and warmer months, overlapping was 15% in summer and 19% in spring, respectively. The percentage of time spent in different vegetation type areas was influenced by the abundance of the principal food species of that plant community. It is thus concluded that the movements of giraffes were primarily influenced by a combination of environmental factors such as season, rainfall and vegetation density.  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