全文获取类型
收费全文 | 705篇 |
免费 | 123篇 |
国内免费 | 143篇 |
出版年
2024年 | 2篇 |
2023年 | 18篇 |
2022年 | 19篇 |
2021年 | 40篇 |
2020年 | 37篇 |
2019年 | 51篇 |
2018年 | 40篇 |
2017年 | 38篇 |
2016年 | 34篇 |
2015年 | 37篇 |
2014年 | 33篇 |
2013年 | 49篇 |
2012年 | 29篇 |
2011年 | 41篇 |
2010年 | 27篇 |
2009年 | 39篇 |
2008年 | 32篇 |
2007年 | 41篇 |
2006年 | 36篇 |
2005年 | 30篇 |
2004年 | 28篇 |
2003年 | 28篇 |
2002年 | 18篇 |
2001年 | 27篇 |
2000年 | 21篇 |
1999年 | 20篇 |
1998年 | 19篇 |
1997年 | 15篇 |
1996年 | 12篇 |
1995年 | 13篇 |
1994年 | 25篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1976年 | 3篇 |
1974年 | 1篇 |
排序方式: 共有971条查询结果,搜索用时 15 毫秒
101.
贡嘎山峨眉冷杉林原生扰动土壤溶质运移的持续降雨模拟研究 总被引:5,自引:0,他引:5
以人工持续(5d)降雨模拟方式研究了贡嘎山物眉冷杉林原生土壤地表覆被层破坏后土壤中矿质元素与营养盐的迁移输出动态与规律。模拟降雨采用当地最为常见的小到中雨雨型(5.7-26mm/h),壤中流以垂直入渗为主,并滞后于降雨0.2-4.2h,通过0模拟实验发现,降雨总量和降雨事件的持续时间对壤中流产生量的影响比单位时间降雨强度的影响更为明显,在持续降雨影响下,主要离子(Mg^2 ,Ca^2 ,Cl^-,SO4^2-和Na^ K^ )和营养盐(NH4^ -N,NO3^--N和活性磷酸盐)在短期内急剧流失,模拟降雨的第1天,壤中流结束时离子浓度仅为初始时浓度的29%,营养盐浓度为初始浓度的21%-55%。至第3天,上述离子和营养盐输出浓度趋于恒定,约为首日降雨壤中流初始浓度的1%-15%,在主要矿质元素流失后,原生土壤内过程转为有机质控制的HCO3^-输出过程,伴随着土壤矿质养分的输出,土壤缓冲能力下降,壤中流pH值由6.1降为5.2,研究结果表明,贡嘎山区峨眉冷杉林原生土壤系统十分脆弱,养分易于流失,对人类活动的敏感性很高。 相似文献
102.
103.
Mountain, western, and Grauer's gorillas exhibit broad differences in ecological patterns with western gorillas eating more fruit and having larger home ranges than their largely folivorous counterparts in the Virunga Volcanoes. We studied the home range and frugivory patterns of one group of Gorilla beringei beringei in the little-studied population of Bwindi Impenetrable National Park, Uganda, to compare with other populations and to investigate whether there was any relationship between patterns of frugivory and home range size. During the 3-year study, the gorillas ate 16 species of fruit on 27% of observation days. There was high variability in frugivory among the 3 years and no consistent seasonal pattern. Annual home range size was ca. 21 km2 for Years 1 and 2, and it increased dramatically to 40 km2 in Year 3. Home range size varied considerable between months and seasons, but there is no clear relationship between occurrence of fruit-eating and home range size. The group exhibited more fruit-eating and a larger home range size those ofthe gorillas in the Virunga Volcanoes. Their home range size is comparable to that of western gorillas, though Bwindi gorillas consumed less fruit. Home range size and utilization by all gorillas probably depends on a complex relationship between the distribution and abundance of both fruit and herbaceous vegetation and social factors such as male mating tactics. 相似文献
104.
Guerrera William Sleeman Jonathan M. Jasper Ssebide B. Pace Lonny B. Ichinose Travers Y. Reif John S. 《International journal of primatology》2003,24(1):197-207
There has been increasing contact between mountain gorillas (Gorilla gorilla beringei) and the human population surrounding Bwindi Impenetrable Forest National Park (BIFNP) in Uganda. Due to the close taxonomic relationship between humans and gorillas there is potential for disease transmission between them. Preventing the introduction or spread of transmissible diseases to the gorillas is essential to protect them. We interviewed 301 villagers living in close proximity to BIFNP with a medical questionnaire in July, 2000. We collected information on demographics, vaccination and health history, and human/gorilla interaction. Our objectives were to estimate the prevalence of several diseases in the human population and to evaluate the risk of anthropozoonotic transmission from humans to gorillas. We found a high prevalence of disease symptoms such as coughing (72.1%) and fever (56.1%) compatible with acute infectious diseases; over half of the respondents (59.1%) had a specific disease diagnosis within the 6 mo preceding the study. We compared villagers who had visual contact with gorillas in the 6 mo preceding the study (53.5%) to villagers who had no visual contact (46.5%). Men were 2.3 times more likely than women to have visual contact with gorillas. In general, the frequency of disease history and symptoms was similar for people with and without contact. The high prevalence of acute infectious diseases in the population surrounding BIFNP and the high rate of contact with gorillas creates the potential for anthropozoonotic disease transmission. 相似文献
105.
Charudutt Mishra Herbert H. T. Prins Sipke E. Van Wieren 《Human ecology: an interdisciplinary journal》2003,31(4):595-609
We describe the diversity and dynamism of social, agricultural, and livestock husbandry practices in a traditional mountain production system in the Indian Trans-Himalaya. These are interpreted in the context of their role in mediating environmental risk. The production system is a little known Buddhist agropastoral system in the high altitude Spiti Valley (agriculture up to 4450 m, livestock grazing 4900 m, total area ca. 12,000 km2) in the Himalayan state of Himachal Pradesh. The local population (ca. 10,000) belongs to one of the three Buddhist sects Gelukpa, Shakyapa, or Ningmapa, is related by blood, and shares a common Tibetan dialect. Family is the basic unit of production, though families are highly dependent upon the community to meet production goals. A village council appointed on rotation and functioning democratically is responsible for village administration, and is the arbiter of all decision-making pertaining to collective work and settling disputes. The council ensures equal access of families to common resources, as well as equitable distribution of responsibilities among them. Systems of primogeniture, celibacy, and polygamy seem to have prevented the fragmentation of land holdings and limited population growth. The diversity of practices in the agropastoral system seems adapted to the risk-prone mountainous environment, the risks being climatic, geological, and those posed by wildlife. The system seems to aim at maximizing production while mediating environmental risk. The production system comes forth as highly dynamic, characterized by continuous innovation and experimentation. Recent changes in the production system are in response to both changes in local conditions as well as increasing integration of the local economy with regional markets, though many aspects of the traditional lifestyle continue to be maintained. 相似文献
106.
107.
Antje Burke 《植被学杂志》2002,13(4):483-492
Abstract. Three granite inselbergs and six dolerite dykes and their surroundings were investigated in the Central Namib, at the interface between the Namib Desert and Nama Karoo biomes. The main objectives of this study included a phytoso‐ciological interpretation of the described plant communities, explanation of the correlation of the communities with environmental variables and quantification of the relative contribution of different types of variables to structuring plant communities. Nine grassland and shrubland plant communities were recognized, largely organized according to general habitat, elevation, size of inselberg and geology. Soil properties, often thought to play an important role in arid environments, showed no clear patterns in the level of analyses used in this study. Other environmental parameters of importance in arid mountain habitats, such as slope aspect and angle, also played a minor role. The main implications of the study are: 1. Central Namib inselbergs, particularly granite domes, harbour diverse plant communities, often with species from neighbouring higher rainfall areas, and are thus of high conservation value. 2. The poor contribution of environmental variables in this study, which are conventionally used in field studies of plant community – environment relationships, may demand a critical review of additional parameters to be included when analysing plant community – environment relations in arid environments. In particular between‐season variation, phytogeographic aspects and the heterogeneity of microhabitats, often contained within a plant community, need to be taken into account. 相似文献
108.
Romina E. Principe Maricel F. Boccolini Maria C. Corigliano 《International Review of Hydrobiology》2008,93(3):342-357
Structure of benthic Chironomidae assemblages and their spatial‐temporal dynamic were analyzed in upland and lowland habitats from the Chocancharava River basin (Córdoba, Argentina). Sampling was performed in three tributary streams and in three lowland reaches of the river during high and low rainfall periods. Characteristic taxa of upland and lowland reaches and of the different habitats in these reaches were identified using the IndVal method. Chironomidae assemblages were different between upland and lowland reaches and among habitats in each reach, as assessed by Multiresponse Permutation Procedure and Canonical Correspondence Analyses. Substrate type and current velocity were the major explanatory variables structuring the assemblages in upland reaches whereas in lowland reaches current velocity and aquatic vegetation were the most important variables. The highest richness was found in the most complex habitat units in both upland and lowland stretches as assessed by Analyses of Variance. Chironomidae larvae responded to longitudinal changes of hydraulic variables and to local variations of fluvial habitats at different reaches. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
109.
110.
Antje Burke 《植被学杂志》2001,12(1):53-60
Abstract. To determine the relationship between vegetation and environmental parameters in a desert‐savanna ecotone, vegetation in the Naukluft Mountains of Namibia (southern Africa) was described and analysed in terms of environmental parameters determining the observed patterns. 12 plant communities, largely characterized by low shrubs, were described on the basis of a classification. Through ordination altitude, clay, potassium content of the substrate and, to a lesser extent, habitats were identified as underlying environmental factors determining the composition of these plant communities. The edaphic parameters showed some correlation with subsurface geology, but microclimatic conditions, water availability and level of disturbance appeared to override the effect of nutrient composition provided by different substrate. Communities of conservation importance, such as plant communities composed of Karoo shrubs, are prevalent on the mountain plateau, presenting an isolated outpost of Nama Karoo vegetation. The transitional status between desert and savanna, remnant patches of Nama Karoo and the high habitat diversity mark the importance of this high altitude area for biodiversity conservation. 相似文献