全文获取类型
收费全文 | 1126篇 |
免费 | 43篇 |
国内免费 | 24篇 |
专业分类
安全科学 | 56篇 |
废物处理 | 63篇 |
环保管理 | 310篇 |
综合类 | 105篇 |
基础理论 | 298篇 |
环境理论 | 4篇 |
污染及防治 | 222篇 |
评价与监测 | 77篇 |
社会与环境 | 49篇 |
灾害及防治 | 9篇 |
出版年
2023年 | 14篇 |
2022年 | 14篇 |
2021年 | 17篇 |
2020年 | 24篇 |
2019年 | 16篇 |
2018年 | 43篇 |
2017年 | 45篇 |
2016年 | 64篇 |
2015年 | 49篇 |
2014年 | 45篇 |
2013年 | 86篇 |
2012年 | 66篇 |
2011年 | 88篇 |
2010年 | 53篇 |
2009年 | 57篇 |
2008年 | 60篇 |
2007年 | 63篇 |
2006年 | 49篇 |
2005年 | 31篇 |
2004年 | 45篇 |
2003年 | 34篇 |
2002年 | 33篇 |
2001年 | 15篇 |
2000年 | 18篇 |
1999年 | 17篇 |
1998年 | 19篇 |
1997年 | 19篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1968年 | 1篇 |
排序方式: 共有1193条查询结果,搜索用时 15 毫秒
201.
Using Paleo Reconstructions to Improve Streamflow Forecast Lead Time in the Western United States 总被引:2,自引:0,他引:2
Christopher Carrier Ajay Kalra Sajjad Ahmad 《Journal of the American Water Resources Association》2013,49(6):1351-1366
In water stressed regions, water managers are exploring new horizons that would help in long‐range streamflow forecasts. Oceanic‐atmospheric oscillations have been shown to influence streamflow variability. In this study, long‐lead time streamflow forecasts are made using a multiclass kernel‐based data‐driven support vector machine (SVM) model. The extended streamflow records based on tree ring reconstructions were used to provide a longer time series data. Reconstructed data were used from 1658 to 1952 and the instrumental record was used from 1953 to 2007. Reconstructions for oceanic‐atmospheric oscillations included the El Niño‐Southern Oscillation, Pacific Decadal Oscillation, Atlantic Multidecadal Oscillation, and North Atlantic Oscillation. Streamflow forecasts using all four oscillations were made with one‐year to five‐year lead times for 21 gages in the western United States. This is the first study that uses both instrumental and reconstructed data of oscillations in SVM model to improve streamflow forecast lead time. SVM model was able to provide “satisfactory” to “very good” forecasts with one‐ to five‐year lead time for the selected gages. The use of all the oscillation indices helped in achieving better predictability compared to using individual oscillations. The SVM modeling results are better when compared with multiple linear regression model forecasts. The findings are statistical in nature and are expected to be useful for long‐term water resources planning and management. 相似文献
202.
A new assemblage of basal dichobunoid artiodactyls from the middle-Eocene Shanghuang fissure fillings includes the diacodexeid
Jiangsudon shanghuangensis gen. and sp. nov., a new species of the lantianine dichobunoid Elaschitotherium, Elaschitotherium crepaturus sp. nov., and an indeterminate suoid which is presently the earliest record of this clade. Diacodexeids are also represented
by two forms provisionally referred to cf. Diacodexis sp. and to an indeterminate Diacodexeidae, respectively. The occurrence of diacodexeids in Shanghuang contrasts with the
early and earliest middle-Eocene chronological range of the family in Europe and North America and suggests that the stratigraphic
range of the family in Asia extends up to the middle Eocene. This may reflect particular habitats in coastal China that may
have been relatively stable during the early and middle Eocene, thus preserving forest-dwelling artiodactyls that became extinct
in the other Holarctic regions. Compared to other supposedly coeval North American, European, and Asian faunas, the Shanghuang
mammalian assemblage is most similar to early Uintan faunas of North America but is also remarkable in recording forms close
to taxa that are characteristic of the Wasatchian and Bridgerian North American Land Mammal Ages. The Irdinmanhan age of the
Shanghuang fauna is supported by the mammalian assemblage recovered from the fissure D, but an Arshantan age cannot be completely
ruled out at this point. Although the Shanghuang assemblage is biased towards preservation of small components of the mammalian
fauna, the Shanghuang fauna provide an important and unique window into the Eocene diversity and early evolution of cetartiodactyls
in eastern Asia. 相似文献
203.
This study presents a method for assessing conservation opportunity on private land based on landholders' socio-economic, behavioral, and farm characteristics. These characteristics include age, gender, education, level of off-farm income, farm size, proportion of remnant native vegetation on-farm, and ecological value of native vegetation on-farm. A sample of landholders who own greater than 2 ha of land in the South Australian Murray-Darling Basin region were sent a mail-based survey about their values and preferences for environmental management (N = 659, 52% response). Cross-tabulations and ANOVA statistical analysis techniques were used to compare the socio-economic attributes across three landholder classes: disengaged, moderately engaged, and highly engaged in native vegetation planting. Results indicate that highly engaged landholders were more likely to be female, formally educated, hobby farmers who managed small parcels of land and have high off-farm incomes, whereas disengaged landholders held significantly stronger farming connections (more farming experience, family have lived on the farm for more generations). Spatial analysis revealed area-specific differences in conservation opportunity and conservation priority. In some areas, properties of high ecological value were managed by highly engaged landholders, but nearby properties of high value were managed by moderately engaged or disengaged landholders. Environmental managers therefore cannot assume areas of high conservation priority will be areas of high conservation opportunity. At the regional scale, the potential for revegetation seems most promising within the moderately engaged landholder group considering the vast amount of land managed by this group in areas of high ecological value, particularly within the less represented Mallee and Coorong and Rangelands sub-regions. We suggest that incentive schemes which purchase conservation need to be targeted at disengaged landholders; mentoring schemes led by commercial farmers highly engaged in native vegetation planting should be directed at moderately engaged landholders, and; awards programs which acknowledge conservation successes should be targeted at highly engaged landholders. 相似文献
204.
Many alpine ski areas have recently adopted voluntary environmental programs (VEPs) such as using recycling, renewable energy,
and biofuels to help reduce their environmental impacts. Studies have addressed the performance of these VEPs in mitigating
environmental impacts of this industry, but little is known about visitor awareness and perceptions of these programs. This
article addresses this knowledge gap by exploring skier and snowboarder knowledge of VEPs at a ski area and the influence
of these programs on their motivations to visit this area currently and behavioral intentions to visit again in the future.
Data were obtained from an onsite survey at the Mt. Bachelor ski area in Oregon, USA (n = 429, 89.7% response rate). Few skiers and snowboarders were knowledgeable of VEPs at this area and fewer than 20% were
motivated to visit on their current trip because of these programs. Other attributes such as scenery, snow conditions, and
access were more important for influencing visitation. Up to 38% of skiers and snowboarders, however, intend to visit this
ski area more often if it adopts and promotes more VEPs. Managers can use these results to inform communication and marketing
of their environmental programs and performance to visitors. Additional implications for management and future research are
discussed. 相似文献
205.
The even-aged northern hardwood forests of the Upper Great Lakes Region are undergoing an ecological transition during which structural and biotic complexity is increasing. Early-successional aspen (Populus spp.) and birch (Betula papyrifera) are senescing at an accelerating rate and are being replaced by middle-successional species including northern red oak (Quercus rubra), red maple (Acer rubrum), and white pine (Pinus strobus). Canopy structural complexity may increase due to forest age, canopy disturbances, and changing species diversity. More structurally complex canopies may enhance carbon (C) sequestration in old forests. We hypothesize that these biotic and structural alterations will result in increased structural complexity of the maturing canopy with implications for forest C uptake. At the University of Michigan Biological Station (UMBS), we combined a decade of observations of net primary productivity (NPP), leaf area index (LAI), site index, canopy tree-species diversity, and stand age with canopy structure measurements made with portable canopy lidar (PCL) in 30 forested plots. We then evaluated the relative impact of stand characteristics on productivity through succession using data collected over a nine-year period. We found that effects of canopy structural complexity on wood NPP (NPPw) were similar in magnitude to the effects of total leaf area and site quality. Furthermore, our results suggest that the effect of stand age on NPPw is mediated primarily through its effect on canopy structural complexity. Stand-level diversity of canopy-tree species was not significantly related to either canopy structure or NPPw. We conclude that increasing canopy structural complexity provides a mechanism for the potential maintenance of productivity in aging forests. 相似文献
206.
Species interactions can induce morphological changes in organisms that affect their subsequent growth and survival. In Moorea,
French Polynesia, epibiotic gammaridean amphipods induce the formation of long, branch-like coral “fingers” on otherwise flat,
encrusting, or plating Montipora coral colonies. The fingers form as corals encrust tubes built by the amphipods and lead to significant changes in colony
morphology. This study examines the costs and benefits of this association to the amphipods and corals and demonstrates that
the interaction is a mutualism. Amphipods gain protection from predators by living within corals, and corals benefit by enhanced
growth and survival. Benefits to the coral arise through direct effects due to the amphipods’ presence as well as through
benefits derived from the altered colony morphology. This study demonstrates that induced morphological plasticity can be
a mechanism for facilitation, adding to our knowledge of the roles mutualism, and phenotypic plasticity play in ecology. 相似文献
207.
Benjamin M. Sleeter Tamara S. Wilson Christopher E. Soulard Jinxun Liu 《Environmental monitoring and assessment》2011,173(1-4):251-266
We present the first comprehensive multi-temporal analysis of land-cover change for California across its major ecological regions and primary land-cover types. Recently completed satellite-based estimates of land-cover and land-use change information for large portions of the United States allow for consistent measurement and comparison across heterogeneous landscapes. Landsat data were employed within a pure-panel stratified one-stage cluster sample to estimate and characterize land-cover change for 1973?C2000. Results indicate anthropogenic and natural disturbances, such as forest cutting and fire, were the dominant changes, followed by large fluctuations between agriculture and rangelands. Contrary to common perception, agriculture remained relatively stable over the 27-year period with an estimated loss of 1.0% of agricultural land. The largest net declines occurred in the grasslands/shrubs class at 5,131 km2 and forest class at 4,722 km2. Developed lands increased by 37.6%, composing an estimated 4.2% of the state??s land cover by 2000. 相似文献
208.
Impellitteri CA Saxe JP Schmitt EC Young KR 《Journal of environmental monitoring : JEM》2011,13(8):2277-2283
Samples of river water and treated drinking water were obtained from eight sites along the Potomac River between western Maryland and Washington DC. Samples were collected each month from October 2007 to September 2008 and analyzed for perchlorate by ion chromatography/mass spectrometry. Data on anions were also collected for seven of the twelve months. Data were analyzed to identify spatial and temporal patterns for the occurrence of perchlorate in the Potomac. Over the year of sampling, the largest monthly increase occurred from June to July, with levels then decreasing from July to September. Samples from the period between December and May had lower perchlorate concentrations, relative to the remainder of the study year. Spatially, higher levels of perchlorate were found at sites located in west-central Maryland, the eastern panhandle of West Virginia, and central northern Virginia, with levels decreasing slightly as the Potomac approaches Washington DC. Within the sampling boundaries, river (untreated) water perchlorate concentrations ranged from 0.03 μg L(-1) to 7.63 μg L(-1), averaged 0.67 ± 0.97 μg L(-1) over the year-long period and had a median value of 0.37 μg L(-1). There was no evidence that any of the existing drinking water treatment technologies at the sampling sites were effective in removing perchlorate. There were no correlations found between the presence of perchlorate and any of the anions or water quality parameters examined in the source water with the exception of a weak positive correlation with water temperature. Results from the summer (June-August) and fall (September-November) months sampled in this study were generally higher than from the winter and spring months (December-May). All but one of the locations had annual average perchlorate levels below 1 μg L(-1); however, 7 of the 8 sites sampled had river water perchlorate detections over 1 μg L(-1) and 5 of the 8 sites had treated water detections over this level. 相似文献
209.
Eleni Costa Christopher Thrasivoulou David L. Becker Jan A. Deprest Anna L. David Tina T. Chowdhury 《黑龙江环境通报》2023,43(10):1284-1295
Objective
The effects of mechanical stimulation in preterm amniotic membrane (AM) defects were explored.Methods
Preterm AM was collected from women undergoing planned preterm caesarean section (CS) due to fetal growth restriction or emergency CS after spontaneous preterm prelabour rupture of the membranes (sPPROM). AM explants near the cervix or placenta were subjected to trauma and/or mechanical stimulation with the Cx43 antisense. Markers for nuclear morphology (DAPI), myofibroblasts (αSMA), migration (Cx43), inflammation (PGE2) and repair (collagen, elastin and transforming growth factor β [TGFβ1]) were examined by confocal microscopy, second harmonic generation, qPCR and biochemical assays.Results
In preterm AM defects, myofibroblast nuclei were highly deformed and contractile and expressed αSMA and Cx43. Mechanical stimulation increased collagen fibre polarisation and the effects on matrix markers were dependent on tissue region, disease state, gestational age and the number of fetuses. PGE2 levels were broadly similar but reduced after co-treatment with Cx43 antisense in late sPPROM AM defects. TGFβ1 and Cx43 gene expression were significantly increased after trauma and mechanical stimulation but this response dependent on gestational age.Conclusion
Mechanical stimulation affects Cx43 signalling and cell/collagen mechanics in preterm AM defects. Establishing how Cx43 regulates mechanosignalling could be an approach to repair tissue integrity after trauma. 相似文献210.
Christopher James Lemieux Jessica Thompson D. Scott Slocombe Rudy Schuster 《Journal of Environmental Planning and Management》2015,58(4):654-677
It has been argued that regional collaboration can facilitate adaptation to climate change impacts through integrated planning and management. In an attempt to understand the underlying institutional factors that either support or contest this assumption, this paper explores the institutional factors influencing adaptation to climate change at the regional scale, where multiple public land and natural resource management jurisdictions are involved. Insights from two mid-western US case studies reveal that several challenges to collaboration persist and prevent fully integrative multi-jurisdictional adaptation planning at a regional scale. We propose that some of these challenges, such as lack of adequate time, funding and communication channels, be reframed as opportunities to build interdependence, identify issue-linkages and collaboratively explore the nature and extent of organisational trade-offs with respect to regional climate change adaptation efforts. Such a reframing can better facilitate multi-jurisdictional adaptation planning and management of shared biophysical resources generally while simultaneously enhancing organisational capacity to mitigate negative effects and take advantage of potentially favourable future conditions in an era characterised by rapid climate change. 相似文献