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   3307篇
  免费   497篇
  国内免费   771篇
  4575篇
  2024年   55篇
  2023年   133篇
  2022年   73篇
  2021年   149篇
  2020年   223篇
  2019年   314篇
  2018年   197篇
  2017年   162篇
  2016年   174篇
  2015年   137篇
  2014年   166篇
  2013年   164篇
  2012年   147篇
  2011年   198篇
  2010年   142篇
  2009年   214篇
  2008年   214篇
  2007年   223篇
  2006年   188篇
  2005年   196篇
  2004年   163篇
  2003年   149篇
  2002年   154篇
  2001年   126篇
  2000年   92篇
  1999年   60篇
  1998年   40篇
  1997年   32篇
  1996年   44篇
  1995年   28篇
  1994年   28篇
  1993年   29篇
  1992年   39篇
  1991年   16篇
  1990年   25篇
  1989年   9篇
  1988年   7篇
  1987年   12篇
  1986年   8篇
  1985年   8篇
  1984年   3篇
  1983年   3篇
  1982年   13篇
  1981年   2篇
  1980年   4篇
  1979年   4篇
  1978年   2篇
  1977年   2篇
  1976年   2篇
  1968年   1篇
排序方式: 共有4575条查询结果,搜索用时 9 毫秒
951.
Restoring degraded lands in rural environments that are heavily managed to meet subsistence needs is a challenge due to high rates of disturbance and resource extraction. This study investigates the efficacy of erosion control structures (ECSs) as restoration tools in the context of a watershed rehabilitation and wet meadow (bofedal) restoration program in the Bolivian Andes. In an effort to enhance water security and increase grazing stability, Aymara indigenous communities built over 15,000 check dams, 9,100 terraces, 5,300 infiltration ditches, and 35 pasture improvement trials. Communities built ECSs at different rates, and we compared vegetation change in the highest restoration management intensity, lowest restoration management intensity, and nonproject control communities. We used line transects to measure changes in vegetation cover and standing water in gullies with check dams and without check dams, and related these ground measurements to a time series (1986–2009) of normalized difference vegetation index derived from Landsat TM5 images. Evidence suggests that check dams increase bofedal vegetation and standing water at a local scale, and lead to increased greenness at a basin scale when combined with other ECSs. Watershed rehabilitation enhances ecosystem services significant to local communities (grazing stability, water security), which creates important synergies when conducting land restoration in rural development settings.  相似文献   
952.
Although the importance of monitoring and evaluation of restoration actions is increasingly acknowledged, availability of accurate, quantitative monitoring data is very rare for most restoration areas, particularly for long‐established restoration projects. We propose using fuzzy rule‐based expert systems to evaluate the degree of success of restoration actions when available information on project results and impacts largely relies on expert‐based qualitative assessments and rough estimates of quantitative values. These systems use fuzzy logic to manage the uncertainty present in the data and to integrate qualitative and quantitative information. To illustrate and demonstrate the potential of fuzzy rule‐based systems for restoration evaluation, we applied this approach to seven forest restoration projects implemented in Spain between 1897 and 1952, using information compiled in the REACTION database on Mediterranean forest restoration projects. The information available includes both quantitative and expert‐based qualitative data, and covers a wide variety of indicators grouped into technical, structural, functional, and socioeconomic criteria. The fuzzy rule‐based system translates expert knowledge of restoration specialists and forest managers into a set of simple logic rules that integrate information on individual indicators into more general evaluation criteria. The rule‐based approach proposed here can be readily applicable to any kind of restoration project, provided that some information, even if vague and uncertain, is available for a variety of assessment indicators. The evaluation of long‐established forest restoration projects implemented in Spain revealed important asymmetries in the degree of restoration success between technical, structural, functional, and socioeconomic criteria.  相似文献   
953.
Patterns of survivorship and growth of rescued boulder corals from two vessel groundings in Biscayne National Park, Homestead, Florida, U.S.A., were evaluated over 5 years and compared to nearby undamaged reference corals. The rescued colonies had been dislodged but reattached in situ 10–12 years later (hereafter termed “restored” corals). Change in live coral tissue area was assessed using novel contoured tissue measurements which proved useful in detecting small changes in tissue area for slow‐growing coral species. At the initial survey, restored boulder corals had a higher level of partial mortality (33.8 ± 3.1%, mean ± SE) relative to reference corals (19.9 ± 2.5%), likely a result of prolonged detachment. During the course of the 5‐year monitoring period, whole‐colony mortality was greater for restored corals (13.1%) compared to reference corals (3.3%). For surviving corals, restored coral growth and recent mortality rates were similar to reference corals even though restored corals, especially those of Dichocoenia stokesii, had greater disease prevalence (19.7%) than reference corals (6.6%). These results suggest that dislodged boulder coral rescue following an acute disturbance can be an effective tool in stemming tissue loss. If dislodged corals were reattached in a more timely manner, we predict that the survival and tissue growth would be greater.  相似文献   
954.
A pluralist and cross‐cultural approach that accommodates differing values while encouraging the collaboration and social cohesion necessary for the complex task of ecological restoration is needed. We used qualitative and quantitative analyses to investigate value assigned to biocultural restoration of coastal forests in northern New Zealand by 26 interviewees from three groups (environmental managers, Māori community members, and community project leaders). Māori community members primarily emphasized the importance of Cultural Stewardship and Use in the restoration process, while placing less emphasis on Ecological Integrity. Otherwise, all participants shared common trends, culminating in three interrelated value sets: (1) Personal Engagement, (2) Connection, and (3) the generation and transfer of Knowledge & Wisdom. These values demonstrate that restoration's benefits to people and community are as significant as its reparations of ecological components. Despite differences, all stakeholders were united in a broadly common goal to restore socio‐ecological systems. Their knowledge and shared passion for conservation signal enormous promise for accelerated and effective restoration of coastal forests, if it is conducted using a pluralistic approach. Because some values expressed were intangible and complex, with cross‐cultural dimensions, current valuation tools used by ecological economists to guide management investment fail to adequately account for, in particular, Māori values of ecological restoration.  相似文献   
955.
Restoration requires techniques similar to those used in agriculture to improve germination and seedling vigor. We treated 6‐year‐old (collected in 2003, S‐2003) and 1‐month‐old (S‐2009) seeds of Dodonaea viscosa with hydropriming (HP). Seeds were made permeable with hot water prior to hydration for 24 or 48 hours (HP‐24 and HP‐48, respectively) followed by dehydration. The resulting seedlings exposed to both HP treatments were sown in a lava field in soil mixed with hydrogel (HG) under the shade projected by five vegetation patches. The effects of these treatments on germination, seedling field survival, and growth were assessed. HP‐24 in S‐2009 and HP‐48 in S‐2003 increased the germination percentage from 22.5 and 31.7% in control seeds (permeable seeds) to 63.3 and 98.3%, respectively. The seedlings‐2009 (from S‐2009) with HG maintained high survival in all vegetation patches. Seedlings‐2003, however, had low survival. The lack of HG was negatively related to the photon flux in each patch. Survival of seedlings‐2009 increased with HG of up to 398.41 µmol m?2 s?1; after which survival decreased. During the rainy season, HP enhanced seedling growth, except the basal diameters and number of leaves in the seedlings‐2003 with HP‐24. During the dry season, the effects of HG and HP were similar for all the seedlings. In the following rainy season, the priming effect was lost while HG continued to promote seedling growth. The combined use of HP and HG and the shade projected by the patches resulted in a successful vegetation recovery strategy.  相似文献   
956.
The loss and degradation of woody vegetation in the agricultural matrix represents a key threat to biodiversity. Strategies for habitat restoration in these landscapes should maximize the biodiversity benefit for each dollar spent in order to achieve the greatest conservation outcomes with scarce funding. To be effective at scale, such strategies also need to account for the opportunity cost of restoration to the farmer. Here, we critique the Whole‐of‐Paddock Rehabilitation program, a novel agri‐environment scheme which seeks to provide a cost‐effective strategy for balancing habitat restoration and livestock grazing. The scheme involves the revegetation of large (minimum 10 ha) fields, designed to maximize biodiversity benefits and minimize costs while allowing for continued agricultural production. The objectives and design of the scheme are outlined, biodiversity and production benefits are discussed, and we contrast its cost‐effectiveness with alternative habitat restoration strategies. Our analysis indicates that this scheme achieves greater restoration outcomes at approximately half the cost of windbreak‐style plantings, the prevailing planting configuration in southeastern Australia, largely due to a focus on larger fields, and the avoidance of fencing costs through the use of existing farm configuration and infrastructure. This emphasis on cost‐effectiveness, the offsetting of opportunity costs through incentive payments, and the use of a planting design that seeks to maximize biodiversity benefits while achieving production benefits to the farmer, has the potential to achieve conservation in productive parts of the agricultural landscape that have traditionally been “off limits” to conservation.  相似文献   
957.
Phylogenetic diversity enhances ecosystem functioning but restoration ecology has not taken advantage of this knowledge. We propose plant facilitation as a mechanism to promote phylogenetic diversity in restoration practices. We planted three functionally different species (Gypsophila struthium, Sedum album, and Limonium sucronicum) in a degraded gypsum ecosystem in Spain and found that after 7 years, the species with nurse traits (G. struthium) survived longer and facilitated the establishment of new species forming phylogenetically diverse neighborhoods. These facilitation‐driven phylodiverse communities may potentially produce a cascade of benefits on ecosystem functioning.  相似文献   
958.
A major challenge in habitat restoration is targeting the key aspects of a species' niche for enhancement, particularly for species that use a diverse set of habitat features. However, restoration that focuses on limited aspects of a species' niche may neglect other resources that are critical to population persistence. We evaluated the ability of native plant hedgerows, planted to increase pollen and nectar resources for wild bees in agricultural landscapes, to provide suitable nesting habitat and enhance nesting rates of ground‐nesting bees. We found that, when compared to unmanaged field edges (controls), hedgerows did not augment most indicators of nest habitat quality (bare ground, soil surface irregularity, and soil hardness), although coarser soils were associated with higher incidence and richness of nesting bees. Hedgerows did not augment nesting rates when compared to control edges. Although all the bee species we detected nesting were also found foraging on floral resources, the foraging versus nesting assemblages found within a site were highly dissimilar. These results may reflect sampling error; or, species found foraging but not nesting in hedgerows could be utilizing hedgerows as “partial habitats,” nesting outside hedgerow plantings but foraging on the floral resources they provide. We conclude that although hedgerows are known to provide critical floral resources to wild bees especially in resource‐poor intensive agricultural landscapes, simply increasing vegetative diversity and structure may not be simultaneously enhancing nesting habitat for ground‐nesting bees.  相似文献   
959.
Restoration can be important in slowing, or reducing, rates of biodiversity loss, but needs to consider the factors influencing fauna recolonization as part of the recovery process. Although many studies of factors influencing faunal recolonization have examined the influence of in situ site factors, fewer have examined the influence of neighborhood landscape factors, especially in landscapes with permeable matrices. To assess the relative influence of landscape and site factors on reptile recolonization in a production landscape with a permeable matrix, we surveyed reptiles at intact reference sites and post‐mining restoration sites (3–20 years post‐mining [YPM]) in a forest ecosystem in southwestern Australia. Reptile assemblages in restoration sites never converged on those in reference habitat. Reptile species composition and individual species abundances (>20 detections) in restoration sites were primarily influenced by site factors such as canopy height, litter cover, and coarse woody debris volume, and not by landscape factors. We suggest that the most common reptile species in our study area are primarily influenced by site factors, not landscape factors, and most reptiles detected in restoration sites were present by 3–4 YPM. Therefore, it is likely that habitat suitability is the main barrier to most species' recolonization of restoration sites in landscapes with permeable matrices. Management should continue to focus on restoring microhabitats and vegetation structure, which is similar to reference habitat to promote recolonization of restoration sites by reptiles.  相似文献   
960.
This article presents an interdisciplinary, on‐campus, student project, titled “The Rain Project” that I designed as an urban ecosystem restoration model as well as a collaborative pedagogical approach between ecological science and art at George Mason University (GMU), Virginia, U.S.A. A group of students from several disciplines (e.g. environmental science, art, civil engineering, biology, communication, and film/media) participated in designing and constructing a floating wetland for a campus stormwater pond as part of sustainable stormwater management. The Rain Project has numerous implications for college education, scholarship, and service while presenting a novel way of building a sense of community among undergraduate students for ecological awareness and literacy. The work of Jackie Brookner, a renowned eco‐artist who worked extensively on stormwater, and its relevance to the project is discussed. I strongly suggest the need for linking art and the science of ecosystem restoration to best obtain improvements in much‐needed communication for the success of community participatory restoration projects. I also believe that this kind of interdisciplinary, campus project can facilitate the changes we need to train higher education students to be able to both think differently and communicate effectively. The Rain Project introduced students to new learning strategies that connected “systems thinking” with art, ecological science, and restoration practices.  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