全文获取类型
收费全文 | 1192篇 |
免费 | 170篇 |
国内免费 | 119篇 |
出版年
2023年 | 39篇 |
2022年 | 15篇 |
2021年 | 41篇 |
2020年 | 71篇 |
2019年 | 70篇 |
2018年 | 64篇 |
2017年 | 63篇 |
2016年 | 75篇 |
2015年 | 63篇 |
2014年 | 48篇 |
2013年 | 68篇 |
2012年 | 38篇 |
2011年 | 49篇 |
2010年 | 32篇 |
2009年 | 56篇 |
2008年 | 77篇 |
2007年 | 73篇 |
2006年 | 66篇 |
2005年 | 58篇 |
2004年 | 49篇 |
2003年 | 45篇 |
2002年 | 44篇 |
2001年 | 40篇 |
2000年 | 28篇 |
1999年 | 22篇 |
1998年 | 28篇 |
1997年 | 17篇 |
1996年 | 21篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 17篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 11篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有1481条查询结果,搜索用时 15 毫秒
21.
Marina Mazn Nikolay Aguirre Cristian Echeverría James Aronson 《Restoration Ecology》2019,27(5):992-999
Ecological restoration is becoming mainstreamed worldwide but target ecosystems' responses to restorative interventions are not sufficiently monitored, in terms of the wide range of ecological, social, and economic attributes available. In order to highlight and better understand this problem, we conducted a literature review of the ecological, social, and economic attributes cited in the scientific literature used for monitoring the success of ecological restoration projects in Latin America and the Caribbean region, where no regional study of this kind has previously been conducted. In 84 of the 91 articles retained for the study, ecological indicators were evaluated, while only seven articles included measurements of socioeconomic indicators. Regarding the Society for Ecological Restoration Primer attributes of restored ecosystems, we only found indicators measuring attributes 1–6, with attribute 1 (species assemblages) predominating (73%), followed by physical conditions (54%) and ecological functions (51%). Brazil was the country in the region where most monitoring was being carried out (51% of the articles), and tropical rainforest (33%) and tropical dry forest (25%) were the ecosystem types where ecological restoration was most frequently monitored. Highly vulnerable ecosystems such as mangroves and paramos were underrepresented. Attributes related to ecosystem stability or to governance and education of communities were not monitored at all. More real long‐term monitoring, instead of chronosequences, is needed, especially where understanding socioeconomic implications of, and barriers to, effective ecological restoration is a top priority. 相似文献
22.
Urban green spaces provide manifold environmental benefits and promote human well‐being. Unfortunately, these services are largely undervalued, and the potential of urban areas themselves to mitigate future climate change has received little attention. In this study, we quantified and mapped city‐wide aboveground carbon storage of urban green spaces in China's capital, Beijing, using field survey data of diameter at breast height (DBH) and tree height from 326 field survey plots, combined with satellite‐derived vegetation index at a fine resolution of 6 m. We estimated the total amount of carbon stored in the urban green spaces to be 956.3 Gg (1 Gg = 109 g) in 2014. There existed great spatial heterogeneity in vegetation carbon density varying from 0 to 68.1 Mg C ha‐1, with an average density of 7.8 Mg C ha?1. As expected, carbon density tended to decrease with urban development intensity (UDI). Likely being affected by vegetation cover proportion and configuration of green space patches, large differences were presented between the 95th and 5th quantile carbon density for each UDI bin, showing great potential for carbon sequestration. However, the interquartile range of carbon density narrowed drastically when UDI reached 60%, signifying a threshold for greatly reduced carbon sequestration potentials for higher UDI. These findings suggested that urban green spaces have great potential to make contribution to mitigating against future climate change if we plan and design urban green spaces following the trajectory of high carbon density, but we should be aware that such potential will be very limited when the urban development reaches certain intensity threshold. 相似文献
23.
24.
《Systematic and applied microbiology》2022,45(2):126304
A novel anaerobic, mesophilic, alkaliphilic, chemoorganotrophic bacterium (strain M08fumT) was isolated from a salsa lake of a terrestrial mud volcano (Taman Peninsula, Russia). Cell of strain M08fumT were Gram-stain-negative, rod-shaped, non-spore forming motile rods. The temperature range for growth was 10–45 °C (optimum at 30 °C). The pH range for growth was 7.0–11.0, with an optimum at pH 8.5–9.0. The isolate was capable of organic acids fermentation and anaerobic respiration with elemental sulfur, Fe(III) and arsenate. The end products of fumarate fermentation were succinate, acetate and CO2. The closest phylogenetic relatives of strain M08fumT were members of the family Geopsychrobacteraceae, class Desulfuromonadia. The genome of strain M08fumT had a size of 3.10 Mb with a DNA G + C content of 53.1% (WGS). Genome analysis revealed the presence of genes involved in fumarate fermentation, arsenate reduction and resistance, sulfur respiration and Fe (III) reduction. Based on the phenotypic, genotypic and phylogenetic characteristics we propose to assign strain M08fumT to a new species of a novel genus Pelovirga terrestris gen. nov., sp. nov. within the family Geopsychrobacteraceae. The type strain of Pelovirga terrestris is M08fumT (=KCTC 15919T = VKM B-3407T). This is the first representative of the class Desulfuromonadia, isolated in pure culture from a mud volcano and the first alkaliphile in the family Geopsychrobacteraceae. 相似文献
25.
Terrestrial origin of bacterial communities in complex boreal freshwater networks 总被引:1,自引:0,他引:1 下载免费PDF全文
Clara Ruiz‐González Juan Pablo Niño‐García Paul A. del Giorgio 《Ecology letters》2015,18(11):1198-1206
Bacteria inhabiting boreal freshwaters are part of metacommunities where local assemblages are often linked by the flow of water in the landscape, yet the resulting spatial structure and the boundaries of the network metacommunity have never been explored. Here, we reconstruct the spatial structure of the bacterial metacommunity in a complex boreal aquatic network by determining the taxonomic composition of bacterial communities along the entire terrestrial/aquatic continuum, including soil and soilwaters, headwater streams, large rivers and lakes. We show that the network metacommunity has a directional spatial structure driven by a common terrestrial origin of aquatic communities, which are numerically dominated by taxa recruited from soils. Local community assembly is driven by variations along the hydrological continuum in the balance between mass effects and species sorting of terrestrial taxa, and seems further influenced by priority effects related to the spatial sequence of entry of soil bacteria into the network. 相似文献
26.
Jian Yang Robert A. Spicer Teresa E. V. Spicer Nan Crystal Arens Frédéric M. B. Jacques Tao Su Elizabeth M. Kennedy Alexei B. Herman David C. Steart Gaurav Srivastava Rakesh C. Mehrotra Paul J. Valdes Naresh C. Mehrotra Zhe‐Kun Zhou Jiang‐Shan Lai 《Global Ecology and Biogeography》2015,24(10):1113-1125
27.
28.
We introduce a measure of Environmental Consistency (ECo), which assesses the probability of reducing homogeneity in the environmental factors within a species’ distribution by randomly displacing its occurrences. ECo is computed by applying null model analysis to a species incidence matrix where each locality is associated with a set of environmental values. Environmental homogeneity is measured, for each species, as the average multiparametric distance between any pair of localities where the species occurs. ECo can account for the effect of species interactions and resource availability by using different null models that permit or forbid occurrence displacements altering species local abundance or species prevalence. ECo provides researchers with a flexible statistical framework to address a wide range of ecological and biogeographical issues. We investigated in depth the properties and the potentialities of ECo, showing how it integrates the concepts of Eltonian and Grinnelian niches. We demonstrate that a close relationship exists between niche breadth at species level and environmental consistency of species assemblages. In addition, we provide evidence that ecological consistency is closely related to species range. A software to compute ECo is freely available at http://forest.jrc.ec.europa.eu/download/software/eco. 相似文献
29.
The effects of deer exclusion on the development of a Mediterranean plant community affected by a wildfire 下载免费PDF全文
Joaquim S. Silva Filipe X. Catry Francisco Moreira Miguel N. Bugalho 《Restoration Ecology》2015,23(6):760-767
Despite the resilience of Mediterranean ecosystems to fire, the ecological restoration of burned plant communities can be hindered by ungulate herbivores, particularly in areas with high population densities. This study compares the postfire development of a shrub community with and without deer, after a wildfire occurred in 2003 in a protected area in Central Portugal. We monitored 12 fenced and 12 unfenced plots 2, 3, 4, and 8 years after fire. Within each plot, we established a linear transect and measured the monospecific canopy projections (plant patches). Five plant community indicators (patch number, average patch length, average patch height, patch cover, and patch phytovolume per square meter) were obtained. The diameter and height of individuals of the most abundant shrub species (Cistus salvifolius, Erica scoparia, Myrtus communis, Pistacia lentiscus, Rubus ulmifolius, and Ulex jussiaei) were also measured. These measurements were used as response variables in generalized linear mixed models in order to assess the effects of time‐after‐fire and fencing, on the development of the plant community. Patch height and phytovolume had a significantly higher growth in fenced plots. At the species level, C. salvifolius, M. communis, R. ulmifolius, and U. jussiaei showed a higher growth across time both in height and in diameter, in the absence of herbivory. This work shows that deer exclusion needs to be considered when aiming at the postfire restoration of Mediterranean shrub communities. 相似文献
30.
Jussi Jyväsjärvi Hannu Marttila Pekka M. Rossi Pertti Ala‐Aho Bo Olofsson Jakob Nisell Birgitta Backman Jari Ilmonen Risto Virtanen Lauri Paasivirta Ritva Britschgi Bjørn Kløve Timo Muotka 《Global Change Biology》2015,21(12):4561-4569
Interest in climate change effects on groundwater has increased dramatically during the last decade. The mechanisms of climate‐related groundwater depletion have been thoroughly reviewed, but the influence of global warming on groundwater‐dependent ecosystems (GDEs) remains poorly known. Here we report long‐term water temperature trends in 66 northern European cold‐water springs. A vast majority of the springs (82%) exhibited a significant increase in water temperature during 1968–2012. Mean spring water temperatures were closely related to regional air temperature and global radiative forcing of the corresponding year. Based on three alternative climate scenarios representing low (RCP2.6), intermediate (RCP6) and high‐emission scenarios (RCP8.5), we estimate that increase in mean spring water temperature in the region is likely to range from 0.67 °C (RCP2.6) to 5.94 °C (RCP8.5) by 2086. According to the worst‐case scenario, water temperature of these originally cold‐water ecosystems (regional mean in the late 1970s: 4.7 °C) may exceed 12 °C by the end of this century. We used bryophyte and macroinvertebrate species data from Finnish springs and spring‐fed streams to assess ecological impacts of the predicted warming. An increase in spring water temperature by several degrees will likely have substantial biodiversity impacts, causing regional extinction of native, cold‐stenothermal spring specialists, whereas species diversity of headwater generalists is likely to increase. Even a slight (by 1 °C) increase in water temperature may eliminate endemic spring species, thus altering bryophyte and macroinvertebrate assemblages of spring‐fed streams. Climate change‐induced warming of northern regions may thus alter species composition of the spring biota and cause regional homogenization of biodiversity in headwater ecosystems. 相似文献