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   241篇
  免费   15篇
  国内免费   20篇
安全科学   14篇
废物处理   4篇
环保管理   55篇
综合类   57篇
基础理论   60篇
环境理论   1篇
污染及防治   28篇
评价与监测   26篇
社会与环境   25篇
灾害及防治   6篇
  2023年   6篇
  2022年   7篇
  2021年   14篇
  2020年   4篇
  2019年   5篇
  2018年   4篇
  2017年   9篇
  2016年   13篇
  2015年   9篇
  2014年   10篇
  2013年   13篇
  2012年   17篇
  2011年   11篇
  2010年   12篇
  2009年   18篇
  2008年   15篇
  2007年   16篇
  2006年   7篇
  2005年   18篇
  2004年   12篇
  2003年   7篇
  2002年   8篇
  2001年   3篇
  2000年   6篇
  1999年   4篇
  1998年   4篇
  1997年   2篇
  1996年   5篇
  1995年   2篇
  1994年   3篇
  1993年   3篇
  1992年   1篇
  1988年   4篇
  1986年   1篇
  1985年   2篇
  1971年   1篇
排序方式: 共有276条查询结果,搜索用时 93 毫秒
81.
Evaluation of protected area effectiveness is critical for conservation of biodiversity. Protected areas that prioritize biodiversity conservation are, optimally, located and managed in ways that support relatively large and stable or increasing wildlife populations. Yet evaluating conservation efficacy remains a challenging endeavor. We used an extensive community science data set, eBird, to evaluate the efficacy of protected areas for birds across the Gulf of Mexico and Atlantic coasts of the United States. We modeled trends (2007–2018) for 12 vulnerable waterbirds that use coastal areas during breeding or wintering. We compared two types of protected areas—sites where conservation organizations implemented active stewardship or management or both to reduce human disturbance (hereafter stewardship sites) and local, state, federal, and private protected areas managed to maintain natural land cover (hereafter protected areas)—as well as unprotected areas. We evaluated differences in trends between stewardship, protected, and unprotected areas across the Gulf and Atlantic coasts as a whole. Similar to a background sample, stewardship was known to occur at stewardship sites, but unknown at protected and unprotected areas. Four of 12 target species—Black Skimmer (Rynchops niger), Brown Pelican (Pelecanus occidentalis), Least Tern (Sternula antillarum), and Piping Plover (Charadrius melodus)—had more positive trends (two to 34 times greater) at stewardship sites than protected areas. Furthermore, five target species showed more positive trends at sites with stewardship programs than unprotected sites during at least one season, whereas seven species showed more positive trends at protected than unprotected areas. No species had more negative trends at stewardship sites than unprotected areas, and two species had more negative trends at protected than unprotected areas. Anthropogenic disturbance is a serious threat to coastal birds, and our findings demonstrate that stewardship to reduce its negative impacts helps ensure conservation of vulnerable waterbirds.  相似文献   
82.
长荡湖近61a降水量演化特征   总被引:1,自引:0,他引:1  
基于王母观站和溧阳站1953~2013a系列年降水量资料,采用Spearman和Mann-Kendall非参数统计检验、连续小波变换等技术手段,分析了61a来长荡湖年降水量的演变特征。结果表明,长荡湖多年平均降水量为1 115.1 mm,年内降水量呈明显的季节性变化;年降水量总体呈减少趋势,但仍以正常年份居多,偏多与偏少年份相当;长荡湖湖区年降水量变化周期为9.5a;年降水量变化不存在突变。研究成果可为长荡湖湖区的洪水控制、水资源利用、水调度方案制订、应对气候变化提供科学依据。  相似文献   
83.
Coastal marshes are one of the world's most productive ecosystems. Consequently, they have been heavily used by humans for centuries, resulting in ecosystem loss. Direct human modifications such as road crossings and ditches and climatic stressors such as sea‐level rise and extreme storm events have the potential to further degrade the quantity and quality of marsh along coastlines. We used an 18‐year marsh‐bird database to generate population trends for 5 avian species (Rallus crepitans, Tringa semipalmata semipalmata, Ammodramus nelsonii subvirgatus, Ammodramus caudacutus, and Ammodramus maritimus) that breed almost exclusively in tidal marshes, and are potentially vulnerable to marsh degradation and loss as a result of anthropogenic change. We generated community and species trends across 3 spatial scales and explored possible drivers of the changes we observed, including marsh ditching, tidal restriction through road crossings, local rates of sea‐level rise, and potential for extreme flooding events. The specialist community showed negative trends in tidally restricted marshes (?2.4% annually from 1998 to 2012) but was stable in unrestricted marshes across the same period. At the species level, we found negative population trends in 3 of the 5 specialist species, ranging from ?4.2% to 9.0% annually. We suggest that tidal restriction may accelerate degradation of tidal marsh resilience to sea‐level rise by limiting sediment supply necessary for marsh accretion, resulting in specialist habitat loss in tidally restricted marshes. Based on our findings, we predict a collapse of the global population of Saltmarsh Sparrows (A. caudacutus) within the next 50 years and suggest that immediate conservation action is needed to prevent extinction of this species. We also suggest mitigation actions to restore sediment supply to coastal marshes to help sustain this ecosystem into the future.  相似文献   
84.
岷江乐山段有机污染状况及变化趋势分析   总被引:3,自引:2,他引:1  
何玉 《四川环境》1998,17(2):40-43
“三氧”是衡量水质有机污染的重要指标。本文针对岷江乐山段地面水质污染属有机污染的特点,以“三氧”为依据研究了其有机污染的变化趋势,并对其污染状况进行了分析,提出了防治污染的对策和建议。  相似文献   
85.
The Seine River is a highly artificialised catchment in Europe, comprising both productive agricultural areas and intense industrial and commercial activity. Due to its strategic importance, monitoring programs in the river started as early as the 1970s. The present study compiles and analyses this valuable data set (1970–2014), thoroughly describing the riverine section downstream of Paris and the estuary. We identify long-term trends and shifting patterns in nutrients and oxygen, and pay special attention to the river’s evolution after the year 2000, when the European Water Framework Directive came into force. The study has a manifest management perspective, and the results are discussed on the basis of the environmental quality standards proposed in current environmental regulations. The data show that water quality has improved remarkably over the past two decades, with sharp reductions of ammonium and phosphate and a progressive increase of dissolved oxygen levels. The amelioration is prominent in the estuary, where summer anoxic episodes have nearly disappeared. As a result, these three parameters are nowadays in good or very good condition throughout the year. The successful abatement of point sources contrasts, however, with the low effectiveness of the measures provided for the control of nutrients from diffuse sources. Nitrate concentration has increased by 150% since the early 1980s, and only very recently has the upward trend been reversed. Bold agri-environmental management measures are required if we are to prevent chronic pollution problems and truly restore the good ecological status of rivers.  相似文献   
86.
Recent developments of safer formulations of agrochemicals   总被引:2,自引:0,他引:2  
The primary objectives of formulation technology are to optimise the biological activity of the pesticide, and to give a product which is safe and convenient for use. However, because of the wide variety of pesticide active ingredients which are available, many different types of formulations have been developed depending mainly on the physico-chemical properties of the active ingredients. In the past most formulations were based on simple solutions in water (SL), emulsifiable concentrates in a petroleum-based solvent (EC), or dusts (DP) and wettable powders (WP). The presence of petroleum-based solvents in EC formulations and dusty powders in DP and WP formulations can lead to safety hazards in use and a negative impact on the envirnoment generally. Most government and regulatory authorities are now demanding formulations which are cleaner and safer for the user, have minimal impact on the environment, and can be applied at the lowest dose rate. Developments in formulation technology and novel formulation types, sometimes in special packaging such as water-soluble packs, can also give products a competitive advantage, add value or extend the lif-cycle of active ingredients. There is also a demand from government authorities and consumer groups to use safer formulation additives and adjuvants, and to minimise the residues of pesticides on food crops after spraying. All of these aspects are putting increasing pressure on the development of improved formulation and adjuvant technologies. Pesticide formulations for spray application and for seed treatment are discussed, along with developments in bioenchancement.  相似文献   
87.
88.
Long-term trends (i.e., 1985 through 1999; 14 1/2 yrs) of the phytoplankton community in Chesapeake Bay indicated patterns of increasing phytoplankton abundance and biomass associated with mainly diatoms and chlorophytes, and to a lesser degree dinoflagellates. Decreasing trends in productivity rates above the pycnocline were present over a shorter time period (10 1/2 yrs.), with evidence for increasing nitrogen limitation is indicated. Reduced light availability is inferred due to decreasing trends of Secchi depths and increased suspended solids trends, which were associated with decreasing trends in productivity rates.  相似文献   
89.
抗震性能设计的发展   总被引:1,自引:0,他引:1  
现行建筑抗震设计规范是以保证人的生命安全为基本目标进行抗震设防的,即在小震和中等强度地震作用下控制结构的损伤发展,而在罕遇地震作用下防止结构倒塌.然而,据此设计的建筑由地震所造成的使用功能丧失而震后恢复重建所需费用或所花费的时间可能大大超过社会和业主所能承受的限度.因此,未来建筑在多级水准设防地震下的设计需达到多级性能水准已形成共识.基于性能的抗震设计将发展形成未来抗震设计规范.综述了基于性能的抗震设计的最新发展状况,提出了它存在的问题及进一步发展的趋势.  相似文献   
90.
An understanding of temporal trends in total stream‐flow (TSF), base flow (BF), and storm runoff (RO) can help in the development of water management plans for watersheds and local communities. In this study, 47 streams across Pennsylvania that were unregulated and unaffected by karst environments or coal mining were studied for flow trends and their relationships to selected climate parameters for the period 1971 to 2001. LOWESS curves for annual flow showed that almost all of the selected streams in Pennsylvania had downward trends in total TSF, BF, and RO. Using a seasonal Mann‐Kendall analysis, downward trends were significant at an α= 0.05 level for 68, percent 70 percent, and 62 percent of the streams and at an α= 0.10 level for another 19, 17, and 13 percent of the streams for TSF, BF, and RO, respectively. The ratio of BF to TSF (RBS) had significant upward trends for 34 percent of the streams at an α= 0.05 level and for another 9 percent of the streams at an α= 0.10 level, indicating that TSF decreased relative to BF for more than 40 percent of the streams during the previous 30 years. Downward trends in TSF, BF, and RO were most common for the months of June, July, and December. Trend analyses using monthly and annual total precipitation and mean temperature showed some association between climate and the streamflow trends, but Spearman's correlation and partial Mann‐Kendall analyses revealed that the trends in TSF, BF, and RO could not be explained by trends in precipitation and temperature alone, and thus urbanization and development may have played a role.  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