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   3310篇
  免费   68篇
  国内免费   33篇
安全科学   120篇
废物处理   102篇
环保管理   609篇
综合类   521篇
基础理论   868篇
环境理论   9篇
污染及防治   795篇
评价与监测   192篇
社会与环境   148篇
灾害及防治   47篇
  2023年   13篇
  2022年   17篇
  2021年   39篇
  2020年   20篇
  2019年   32篇
  2018年   79篇
  2017年   76篇
  2016年   83篇
  2015年   86篇
  2014年   95篇
  2013年   243篇
  2012年   156篇
  2011年   202篇
  2010年   149篇
  2009年   163篇
  2008年   174篇
  2007年   205篇
  2006年   205篇
  2005年   150篇
  2004年   107篇
  2003年   102篇
  2002年   116篇
  2001年   65篇
  2000年   59篇
  1999年   49篇
  1998年   50篇
  1997年   60篇
  1996年   46篇
  1995年   54篇
  1994年   49篇
  1993年   29篇
  1992年   31篇
  1991年   23篇
  1990年   23篇
  1989年   11篇
  1988年   14篇
  1987年   14篇
  1986年   19篇
  1985年   17篇
  1984年   19篇
  1983年   21篇
  1982年   17篇
  1981年   16篇
  1980年   18篇
  1979年   20篇
  1978年   13篇
  1977年   10篇
  1965年   11篇
  1963年   8篇
  1957年   10篇
排序方式: 共有3411条查询结果,搜索用时 31 毫秒
471.
Environmental Chemistry Letters - Organic syntheses in aqueous solutions are being developed because water is an environmentally friendly, inexpensive, non-toxic and non-flammable solvent....  相似文献   
472.
Controlling invasive species is critical for conservation but can have unintended consequences for native species and divert resources away from other efforts. This dilemma occurs on a grand scale in the North American Great Lakes, where dams and culverts block tributary access to habitat of desirable fish species and are a lynchpin of long‐standing efforts to limit ecological damage inflicted by the invasive, parasitic sea lamprey (Petromyzon marinus). Habitat restoration and sea‐lamprey control create conflicting goals for managing aging infrastructure. We used optimization to minimize opportunity costs of habitat gains for 37 desirable migratory fishes that arose from restricting sea lamprey access (0–25% increase) when selecting barriers for removal under a limited budget (US$1–105 million). Imposing limits on sea lamprey habitat reduced gains in tributary access for desirable species by 15–50% relative to an unconstrained scenario. Additional investment to offset the effect of limiting sea‐lamprey access resulted in high opportunity costs for 30 of 37 species (e.g., an additional US$20–80 million for lake sturgeon [Acipenser fulvescens]) and often required ≥5% increase in sea‐lamprey access to identify barrier‐removal solutions adhering to the budget and limiting access. Narrowly distributed species exhibited the highest opportunity costs but benefited more at less cost when small increases in sea‐lamprey access were allowed. Our results illustrate the value of optimization in limiting opportunity costs when balancing invasion control against restoration benefits for diverse desirable species. Such trade‐off analyses are essential to the restoration of connectivity within fragmented rivers without unleashing invaders.  相似文献   
473.
Objectives: In this study, we sought to accomplish the following objectives: to (1) calculate the percentage of children considered appropriately restrained across 8 criteria of increasing restrictiveness; (2) examine agreement between age- and size-based appropriateness criteria; (3) assess for changes in the percentage of children considered appropriately restrained by the 8 criteria between 2011 (shortly after updates to U.S. guidelines) and 2015.

Methods: Data from 2 cross-sectional surveys of 928 parents of children younger than 12 years old (n = 591 in 2011, n = 337 in 2015) were analyzed in 2017. Child age, weight, and height were measured at an emergency department visit and used to determine whether the parent-reported child passenger restraint was considered appropriate according to 8 criteria. Age-based criteria were derived from Michigan law and U.S. guidelines. Weight, height, and size-based criteria were derived from typical restraints available in the United States in 2007 and 2011. The percentage appropriate restraint use was calculated for each criterion. The kappa statistic was used to measure agreement between criteria. Change in appropriateness from 2011 to 2015 was assessed with chi-square statistics.

Results: Percentage appropriate restraint use varied from a low of 19% for higher weight limits in 2011 to a high of 91% for Michigan law in 2015. Agreement between criteria was slight to moderate. The lowest kappa was for Michigan law and higher weight limits in 2011 (κ = 0.06) and highest for U.S. guidelines and lower weight limits in 2011 (κ = 0.60). Percentage appropriate restraint use was higher in 2015 than 2011 for the following criteria: U.S. guidelines (74 vs. 58%, P < .001), lower weight (57 vs. 47%, P = .005), higher weight (25 vs. 19%, P = .03), greater height (39 vs. 26%, P < .001), and greater size (42 vs. 30%, P = .001).

Conclusions: The percentage of children considered to be using an appropriate restraint varied substantially across criteria. Aligning the definition of appropriate restraint use with current U.S. guidelines would increase consistency in reporting results from studies of child passenger safety in the United States. Potential explanations for the increased percentage of children considered appropriately restrained between 2011 and 2015 include adoption of the updated U.S. guidelines and the use of child passenger restraints with higher weight and height limits.  相似文献   
474.
Although experiences with ecological restoration continue to accumulate, the effectiveness of restoration for biota remains debated. We complemented a traditional taxonomic analysis approach with information on 56 species traits to uncover the responses of 3 aquatic (fish, macroinvertebrates, macrophytes) and 2 terrestrial (carabid beetles, floodplain vegetation) biotic groups to 43 hydromorphological river restoration projects in Germany. All taxonomic groups responded positively to restoration, as shown by increased taxonomic richness (10–164%) and trait diversity (habitat, dispersal and mobility, size, form, life history, and feeding groups) (15–120%). Responses, however, were stronger for terrestrial than aquatic biota, and, contrary to our expectation, taxonomic responses were stronger than those of traits. Nevertheless, trait analysis provided mechanistic insights into the drivers of community change following restoration. Trait analysis for terrestrial biota indicated restoration success was likely enhanced by lateral connectivity and reestablishment of dynamic processes in the floodplain. The weaker response of aquatic biota suggests recovery was hindered by the persistence of stressors in the aquatic environment, such as degraded water quality, dispersal constraints, and insufficient hydromorphological change. Therefore, river restoration requires combined local- and regional-scale approaches to maximize the response of both aquatic and terrestrial organisms. Due to the contrasting responses of aquatic and terrestrial biota, the planning and assessment of river restoration outcomes should consider effects on both components of riverine landscapes.  相似文献   
475.
476.
Between 1990 and 2007, 15 southern white (Ceratotherium simum simum) and black (Diceros bicornis) rhinoceroses on average were killed illegally every year in South Africa. Since 2007 illegal killing of southern white rhinoceros for their horn has escalated to >950 individuals/year in 2013. We conducted an ecological–economic analysis to determine whether a legal trade in southern white rhinoceros horn could facilitate rhinoceros protection. Generalized linear models were used to examine the socioeconomic drivers of poaching, based on data collected from 1990 to 2013, and to project the total number of rhinoceroses likely to be illegally killed from 2014 to 2023. Rhinoceros population dynamics were then modeled under 8 different policy scenarios that could be implemented to control poaching. We also estimated the economic costs and benefits of each scenario under enhanced enforcement only and a legal trade in rhinoceros horn and used a decision support framework to rank the scenarios with the objective of maintaining the rhinoceros population above its current size while generating profit for local stakeholders. The southern white rhinoceros population was predicted to go extinct in the wild <20 years under present management. The optimal scenario to maintain the rhinoceros population above its current size was to provide a medium increase in antipoaching effort and to increase the monetary fine on conviction. Without legalizing the trade, implementing such a scenario would require covering costs equal to approximately $147,000,000/year. With a legal trade in rhinoceros horn, the conservation enterprise could potentially make a profit of $717,000,000/year. We believe the 35‐year‐old ban on rhinoceros horn products should not be lifted unless the money generated from trade is reinvested in improved protection of the rhinoceros population. Because current protection efforts seem to be failing, it is time to evaluate, discuss, and test alternatives to the present policy.  相似文献   
477.
Changes to runoff due to climate change may influence management of nutrient loading to the sea. Assuming unchanged river nutrient concentrations, we evaluate the effects of changing runoff on commitments to nutrient reductions under the Baltic Sea Action Plan. For several countries, climate projections point to large variability in load changes in relation to reduction targets. These changes either increase loads, making the target more difficult to reach, or decrease them, leading instead to a full achievement of the target. The impact of variability in climate projections varies with the size of the reduction target and is larger for countries with more limited commitments. In the end, a number of focused actions are needed to manage the effects of climate change on nutrient loads: reducing uncertainty in climate projections, deciding on frameworks to identify best performing models with respect to land surface hydrology, and increasing efforts at sustained monitoring of water flow changes.  相似文献   
478.
Fungi are undoubtedly important for ecosystem functioning; however, they have been omitted or given scant attention in most biodiversity policy documents, management plans, and formal conservation schedules throughout the world. This oversight may be due to a general lack of awareness in the scientific community and compounded by a scarcity of mycology‐associated curricula at the tertiary level and a lack of mycologists in research institutions. Although molecular techniques advance the systematic cataloging of fungi and facilitate insights into fungal communities, the scarcity of professional mycologists in the environmental sciences hampers conservation efforts. Conversely, citizen science initiatives are making significant contributions to the mycology discipline by increasing awareness and extending the scope of fungal surveys. Future research by professional and amateur mycologists into the distribution of fungi and their function in ecosystems will help identify wider and more effective conservation goals.  相似文献   
479.
The Ecological Society of America has evaluated current U.S. national policies and practices on biological invasions in light of current scientific knowledge. Invasions by harmful nonnative species are increasing in number and area affected; the damages to ecosystems, economic activity, and human welfare are accumulating. Without improved strategies based on recent scientific advances and increased investments to counter invasions, harm from invasive species is likely to accelerate. Federal leadership, with the cooperation of state and local governments, is required to increase the effectiveness of prevention of invasions, detect and respond quickly to new potentially harmful invasions, control and slow the spread of existing invasions, and provide a national center to ensure that these efforts are coordinated and cost effective. Specifically, the Ecological Society of America recommends that the federal government take the following six actions: (1) Use new information and practices to better manage commercial and other pathways to reduce the transport and release of potentially harmful species; (2) Adopt more quantitative procedures for risk analysis and apply them to every species proposed for importation into the country; (3) Use new cost-effective diagnostic technologies to increase active surveillance and sharing of information about invasive species so that responses to new invasions can be more rapid and effective; (4) Create new legal authority and provide emergency funding to support rapid responses to emerging invasions; (5) Provide funding and incentives for cost-effective programs to slow the spread of existing invasive species in order to protect still uninvaded ecosystems, social and industrial infrastructure, and human welfare; and (6) Establish a National Center for Invasive Species Management (under the existing National Invasive Species Council) to coordinate and lead improvements in federal, state, and international policies on invasive species. Recent scientific and technical advances provide a sound basis for more cost-effective national responses to invasive species. Greater investments in improved technology and management practices would be more than repaid by reduced damages from current and future invasive species. The Ecological Society of America is committed to assist all levels of government and provide scientific advice to improve all aspects of invasive-species management.  相似文献   
480.
Soil samples were taken from residential gardens, grasslands and forests at 22 locations in Marsberg, North Rhine-Westphalia, and analyzed for PCDD/F. Sampling was concentrated on the vicinity of a former copper smelter where copper waste material (calledKieselrot) was deposited and emissions from former stacks contaminated a large land area. Maximum PCDD/F-concentrations were 407 ng TE GBA/kg dm in garden soil (0–30 cm depth), 98 ng TE BGA/kg dm in agricultural grassland (0–10 cm depth), 227 ng TE BGA/kg dm in wasteland, and up to 8073 ng TE BGA/kg dm in forest soils. PCDD/F-levels in soil decreased with increasing distance from the former sources providing a large historic emission problem, apart from the still existing kieselrot waste site. Ash residues from former flue gas duct showed up to 2,4 mg TE BGA/kg dm. PCDD/F-concentrations in vegetable samples from highly contaminated garden soils and grass from agricultural grassland were found to be relatively low in relation to soil values. PCDD/F-levels in salad showed a mean of 2,2 ng TE BGA/kg dm while grass concentrations were <6 ng TE BGA/kg dm. Thus, no correlation was found between soil and vegetation values with the exception for carrot roots where obviously a small transfer of PCDD/F between the two media took place. PCDD/F-content in grass taken over the vegetation period showed a tendency to increase toward the end of the growing season, which is probably related to changes in the dry matter yield over the season. No correlation was found in general between soil, grass and milk PCDD/F contents when all samples were taken from the same grassland. PCDD/F-concentrations in milk ranged between 0,6 and 1,1 pg TE BGA/g milkfat and were thus in the same range as consumer milk in the Federal Republic of Germany. PCDD/F in needles from conifers showed a clear relationship with respect to distance from the former waste site. The relatively high levels in conifer needles [36 ng TE BGA/kg dm] were obviously due to sporting activities (i.e. motocross racing where contaminated material was resuspended and deposited on surrounding trees).  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