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   2124篇
  免费   87篇
  国内免费   194篇
  2024年   1篇
  2023年   35篇
  2022年   64篇
  2021年   38篇
  2020年   34篇
  2019年   56篇
  2018年   56篇
  2017年   76篇
  2016年   105篇
  2015年   81篇
  2014年   121篇
  2013年   118篇
  2012年   65篇
  2011年   82篇
  2010年   71篇
  2009年   202篇
  2008年   224篇
  2007年   204篇
  2006年   151篇
  2005年   126篇
  2004年   82篇
  2003年   79篇
  2002年   52篇
  2001年   31篇
  2000年   32篇
  1999年   25篇
  1998年   26篇
  1997年   23篇
  1996年   17篇
  1995年   30篇
  1994年   16篇
  1993年   14篇
  1992年   10篇
  1991年   14篇
  1990年   11篇
  1989年   8篇
  1988年   7篇
  1987年   6篇
  1986年   7篇
  1985年   1篇
  1984年   3篇
  1982年   1篇
排序方式: 共有2405条查询结果,搜索用时 296 毫秒
151.
云南省小黑山自然保护区兰科植物多样性及保护评价   总被引:7,自引:0,他引:7  
云南省小黑山自然保护区孕育了丰富的兰科植物。据调查,保护区有兰科植物43属、134种,约占云南省135属、780种的31.9%和17.2%,是保护区种子植物种类最多的科。兰科植物在保护区的各个生态类型中均有出现。保护区134种兰科植物以附生兰占优势,占67.16%(90种);其次,地生兰占31.34%(42种),腐生兰为1.50%(2种)。保护区兰科植物起源于新、旧世界的热带和温带,热带属占70.0%(28),温带属占27.5%(11)。鉴于兰科植物重要的保护价值,应加强保护区兰科植物的保护。首先应加强保护区的建设和管理,还应加强社区经济发展,加强科学研究,实施社区共管以及加大保护宣传力度。  相似文献   
152.
海南鹦哥岭自然保护区的珍稀濒危植物与保育   总被引:1,自引:0,他引:1  
对鹦哥岭的珍稀濒危植物进行野外调查表明,本区共有野生分布的珍稀濒危植物79种,隶属于47科71属。其中属于1999年国家重点一级保护4种,如海南苏铁(Cycas hainansis)、坡垒(Hopea hainansis)、台湾苏铁(Cy-cas taiwaniana)和伯乐树(Bretschneidera sinensis),国家二级保护14种。建议将18种列入国家保护名录中,20种列入省级保护名录,其中有30种为海南特有种。鹦哥岭珍稀濒危植物面临的威胁主要有原始森林面积的减少、人为毁林开荒和分布区限制。针对珍稀濒危植物的现状和受到的威胁,提出了应重点加强保护的6个地点及相应的保护对策和建议。  相似文献   
153.
The Neotropical region is renowned for its high biodiversity, and the Amazon River basin contains the highest number of fish species of any river system in the world. In recent years, habitat fragmentation and exploitation of biotic resources have threatened biological integrity and provoked to need for sustainable management and conservation of the Amazon River system. We studied 36 floodplain lakes along 2000 km of the Amazon River. The fish assemblages associated with flood forests are moderately diverse, with low species dominance and reduced populations. To detect nestedness of fish assemblage composition in floodplain lakes, a nested subset analysis was performed on species presence–absence. The incidence matrix (species × lakes) was maximally packed using the Nestedness Temperature Calculator software. The results of ranking lakes and species allow us to establish targets for conservation. Such strategy for sustainable management should be focused on maintaining the Amazonian biodiversity.  相似文献   
154.
Conflicts involving wildlife are, in essence, often conflicts between human parties with differing wildlife management objectives. However, the study and management of wildlife conflicts often focuses on the ecological context without addressing disagreements between people over these objectives. This research uses quantitative approaches to examine actors’ views on a complex wildlife-related conflict: a raptor of conservation concern that impacts on game-bird management. Four dominant elements of the debate emerged from initial semi-structured interviews: perceptions of conflict related issues; perceptions of each other; perceived barriers to consensus within the debate; and assessment of proposed practical management solutions. A quantitative survey that built on these elements demonstrates the degree to which perceptions differ between groups and how local variation in these elements may be obscured in a regional or national level debate. The findings emphasise the importance of understanding the social issues involved in wildlife related conflicts if management aims are to be agreed and achieved.  相似文献   
155.
The success of the hotspot approach for biodiversity conservation depends on the spatial scale and the indicator species used. In this study, we investigated grasshopper species richness in Switzerland at a 1 ha resolution including a total of 111 species. We compared the representativeness of common and of endangered grasshopper species for the overall grasshopper species richness and we assessed the efficiency of the hotspot approach for grasshopper conservation. The pattern of overall grasshopper species richness was well represented by both the number of common and the number of endangered grasshopper species. For evaluating the efficiency of different hotspot approaches for conservation, we compared hotspots of common species, hotspots of endangered species (rarity hotspots), and hotspots of all grasshopper species (richness hotspots). Among these hotspot types, richness hotspots not only featured most common grasshopper species, but they even contained more endangered species than the rarity hotspots. The combination of rarity hotspots and hotspots of common species featured more species than the other combinations of hotspot types. However, the gain of combining two hotspot types compared to the single-hotspot approach was low (max. 3 species). About 24% of the species were not contained in any of the hotspots. These grasshopper species require species-specific action plans. As rarity hotspots were located in areas that are rather strongly affected by landscape change, species richness in rarity hotspots may decrease in the future. We conclude that, for grasshoppers, the hotspot approach on the 1 ha scale can be an effective way to conserve a high proportion of species richness.  相似文献   
156.
An analysis of the distribution patterns of 124 Mexican gymnosperm species was undertaken, in order to detect the Mexican areas with high species richness and endemism, and with this information to propose areas for conservation. Our study includes an analysis of species richness, endemism and distributional patterns of Mexican species of gymnosperms based on three different area units (states, biogeographic provinces and grid-cells of 1° × 1° latitude/longitude). The richest areas in species and endemism do not coincide; in this way, the Sierra Madre Oriental province, the state of Veracruz and a grid-cell located in the state of Oaxaca were the areas with the highest number of species, whereas the Golfo de México province, the state of Chiapas and a grid-cell located in this state were the richest areas in endemic species. A weighted endemism and corrected weighted endemism indices were calculated, and those grid-cells with high values in both indices and with high species richness were considered as hotspots; these grid-cells are mainly located in Southern and Central Mexico.  相似文献   
157.
The conservation of Himalayan forests is big concern in view of global agenda. Many studies in this endeavor reported that the rate of forests degradation is posing a severe threat to the landscape and existing biodiversity in the Himalayas. Currently there many conservation approaches exists and of them four are widely recognized (1) Conservation through traditional religious beliefs “traditional conserved forests” (TCF); (2) Conservation through governmental planning and schemes “government conserved forests” (GCF); (3) Conservation through creation of protected areas (PAF); and (4) Conservation through community efforts “community conserved forests” (CCF). Our hypothesis in this direction says that all the conservation approaches lead to same results concerning to forest conservation. To testify our hypothesis we have studied the forests of each conservation regimes and evaluated them based on the identified indicators. We have done empirical studies and following the cloud-free satellite data were used for last three decades (such as Multi-Spectral Scanner, Linear Imaging and Self Scanning, and Enhanced Thematic Mapper ) to study a change in vegetation dynamics of the mountain forests in multi-temporal dimension. Our research concluded that community conservation approach have greater significance for biodiversity conservation and management in the Himalayan region. Here we support the model of CCF for forest ecosystem conservation, alongside the sustainable livelihood of the mountain societies. But every conservation regimes has its own importance in viewpoint of the particular objectives. Therefore, we suggests advancement and revision of PAF and GCF however, some elements of CCF can be introduced in TCF for making up it more sound in view of rapid socio-economic and cultural changes taking place in the communities. An erratum to this article can be found at  相似文献   
158.
The UK Government has set targets for biodiversity conservation in England based on several indicators, including the status of protected areas [e.g. Sites of Special Scientific Interest (SSSIs)]. Specifically, the Government aims to achieve favourable condition [defined by Common Standards Monitoring (CSM)] on 95% by area of SSSIs by 2010. SSSIs are important for threatened butterflies and management to achieve favourable condition will play a key role in determining future population levels of these high-profile insects. Because only notified features of SSSIs are considered within CSM, we investigated the level of notification for three threatened butterflies. We found that these species were notified at only 15–33% of SSSIs where they occurred; though most site managers did manage for them under broader site conservation objectives. We investigated the relationship between SSSI condition status and population trend for eight butterfly species of conservation concern to assess the benefit to butterflies of sites attaining favourable condition status. The majority (80%) of population trends on SSSIs in favourable condition were positive, suggesting an overall beneficial impact of SSSI management. However, four of the eight species maintained lower populations at favourable condition SSSIs than at sites in one of the unfavourable condition categories. We suggest that current condition assessment based chiefly on notified vegetation communities lacks the sensitivity to identify the complex habitat conditions for these (mosaic) species. As butterflies are good indictors for a wide range of invertebrates, many species requiring fine-scale habitat heterogeneity may be at risk from the Government’s target.  相似文献   
159.
Perspectives of diverse constituencies need to be incorporated when developing conservation strategies. In Menri (Medicine Mountains) of the Eastern Himalayas, Tibetan doctors and professional botanists were interviewed about conservation of useful plants. We compare these two perspectives and find they differ significantly in conservation priorities (Wilcoxon Signed Ranks P < 0.05), both in how they prioritized, as well as the priorities themselves. Tibetan doctors first consider which plants are most important to their medical practice and, then secondarily, the conservation status of these plants. Additionally, perceptions of threatened medicinal plants differ among Tibetan doctors who received medical training in Lhasa, who were local trained, and who were self-taught. In contrast, professional botanists came to a consensus among themselves by first considering the conservation status of plants and then considering use. We conclude that, in order to effect community based conservation, opinions from both Tibetan doctors and professional botanists should be considered in establishing conservation priorities and sustainable conservation programs. Furthermore, we set our own research agenda based on combined perspectives.  相似文献   
160.
Attitudinal studies are increasingly being adopted as tools for evaluating public understanding, acceptance and the impact of conservation interventions. The findings of these studies have been useful in guiding the policy interventions. Many factors affect conservation attitudes positively or negatively. The factors inspiring positive attitudes are likely to enhance the conservation objectives while those inducing negative attitudes may detrimentally undermine these objectives. The magnitude of the resultant effects of each particular factor is determined by the historical, political, ecological, socio-cultural and economic conditions and this may call for different management interventions. In this study we examined how conservation attitudes in western Serengeti are shaped by the following factors: level of conflicts with protected areas; wildlife imposed constraints (inadequate pasture, water, diseases, loss of livestock during migration, theft and depredation); participation in the community based project; and socio-demographic factors (age, education level, wealth, immigration, gender and household size). The results indicated that the level of conflicts, participation in the community based project, inadequate pasture, lack of water, diseases, wealth and education were important in shaping peoples’ attitudes. However, in a stepwise linear regression analysis, 59% of the variation in peoples’ attitudes was explained by three variables i.e., conflict level with protected areas, lack of water and participation in the community based project. In addition to these variables, level of education also contributed in explaining 51% of the variation in people’s attitude regarding the status of the game reserves. Five variables (lack of water, level of education, inadequate pasture, participation in the community based project and diseases) explained 12% of the variation in people’s attitude towards Serengeti National Park. The paper discusses the implications for conservation of these results and recommends some measures to realise effective conservation of wildlife resources.  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