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31.
In spite of the shifts in global economic power the scope for increased intervention in commodity markets remains restricted. We have witnessed the beginnings of some changes with the increased willingness of the richer countries to discuss the commodity issue. The interest in individual commodity agreements is likely to be extended as consumers place a higher valuation on security of supplies but commodity agreements can only secure moderate and limited objectives. They represent only one of a number of tools which are available in the attempt to secure a new world economic order and they will need to be used in conjunction with increased flows of foreign aid, trade liberalisation, and schemes of compensatory finance. The integrated approach to commodities seems fraught with difficulties as does any realistic scheme for the indexation of commodity prices.  相似文献   
32.
Lineus ruber and L. viridis are common intertidal heteronemerteans found on the coasts of northern Europe and the east coast of North America. The two species resemble each other morphologically and were synonymised for many years prior to being separated on the basis of larval development. In this study, specimens of L. ruber and L. viridis were collected from sites along the west and southwest coast of Britain, northern France and the east coast of North America. The external morphology and allele frequencies of isozymes of the two species were compared from all sites. The external morphology of L. ruber and L. viridis was similar but they could generally be separated by colour. Allele frequencies for up to 13 enzyme loci between sympatric populations of L. ruber and L. viridis indicated that these two species are genetically very different (Nei's genetic identity=0.090 to 0.083). Allele-frequency data also indicated the presence of a third genetic type occurring sympatrically with populations of both L. ruber and L. viridis on the coasts of Britain and France but not on the coast of North America. Fixed differences in allele frequencies between populations of the third genetic type and sympatric populations of L. ruber and L. viridis were observed across multiple loci. Genetic identity between the third genetic type and sympatric populations of L. ruber and L. viridis were extremely low (Nei's genetic identity =<0.078). Such large genetic differences between populations indicate a barrier to gene flow and reproductive isolation. The aberrant type, which exhibits sufficient morphological variation to prevent individuals being distinguished from those of both L. ruber and L. viridis, therefore represents a separate species. The low genetic identities found in intrageneric comparisons of species found in this study have been found in other studies on nemerteans. They may indicate systematic problems within these groups or other phenomena such as morphological stasis.  相似文献   
33.
We evaluated the genotoxicity of dichloromethane (DCM) extracts of PCB-contaminated soil before and after the soil had been treated by a base-catalyzed dechlorination process. The treatment process involves heating a mixture of the soil, polyethylene glycol (or hydrocarbons with boiling points of 310–387°C), and sodium hydroxide to 250–350°C. Dechlorination reduced by >99% the PCB concentration of the soil, which was initially 2,200 ppm. The DCM extracts of both control and treated soils were not mutagenic in strain TA100 of Salmonella, but they were mutagenic in strain TA98. Based on results in strain TA98, the base-catalyzed dechlorination process reduced the mutagenic potency of the soil by approximately one-half. The DCM extracts of the soils before and after treatment were equally genotoxic in a prophage-induction assay in . , which detects some chlorinated organic carcinogens that are not detected by the Salmonella mutagenicity assay. These results suggest that treatment of PCB-contaminated soil by base-catalyzed dechlorination reduced the mutagenicity of the soil slightly.  相似文献   
34.
The Tampa Bay Ecosystem Services Demonstration Project (TBESDP) is part of the U.S. Environmental Protection Agency’s Ecosystem Services Research Program. The principal objectives of TBESDP are to (1) quantify the ecosystem services of the Tampa Bay watershed, (2) determine the value of ecosystem services to society, (3) predict the supply of ecosystem services under future scenarios of population growth and climate change, and (4) apply this knowledge through models and tools that will support the best informed environmental decisions possible. The scope and complexity of this project required intensive effort to establish which services can be quantified by applying existing models, data, and scientific literature and which services will require supporting research. Research priorities were assessed by: (1) developing and refining conceptual models of major ecosystems in the Tampa Bay region, (2) gathering input from stakeholders about the relative importance and values of various ecosystem services, (3) preparing and reviewing a bibliometric analysis of the volume of scientific literature relevant to the ecosystems and services of interest, and (4) evaluating an integrated analysis of importance, value, and availability of scientific information. This analysis led us to focus on two research priorities, seagrass-habitat functions as support for fishery production, and wetlands as regulators of water quality.  相似文献   
35.
The paper reports the concentrations and patterns of CBs in sediments of the Belgian part of the southern North Sea and the Scheldt estuary for the period 1991-2001. The long-term analytical performance was well within the quality assurance boundaries set at the outset of the study and is consistent with the state of the art for this type of analysis. The CB concentrations (given as the median of the sum of IUPAC Nos 28, 52, 101, 118, 138, 153 and 180) vary between 0.1 microg kg(-1) and 50 microg kg(-1) dry weight in the total sediment and it could be demonstrated that CB patterns in the fine fraction of the sediment were closely similar throughout the investigated area. Isolation of the fine fraction (<63 microm) by sieving can be regarded as a physical normalisation to reduce the differences in sediment granulometric composition. It allows for a better understanding of CB distribution and patterns and improves the trend analysis. A significant downward trend could not be found at any of the stations, which suggests that CB levels have not been changing in the area of interest in the past decade.  相似文献   
36.
The many abandoned base metal mines of the mid-Wales ore field are sources of extensive pollution. Some of the mineralised veins contain large amounts of pyrite and marcasite and oxidative weathering of these produces sulphuric acid resulting in very acidic mine drainage waters. In addition, the spoil tips associated with these mines can contain abundant iron sulphides. Drainage waters from these sources have pH values as low as 2.6 and are heavily contaminated with metals such as Al, Zn, Cd and Ni.Two of the main rivers of the area, the Rheidol and Ystwyth, intercept heavily contaminated acidic drainage which has a marked effect on water quality. The Rheidol contains over 100 g L–1 Zn for 16 km downstream of the acid water influx. This level is over three times the recommended EEC limit for Zn in salmonoid waters of low hardness.  相似文献   
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Since the early 2000’s, invasions and blooms of jellyfish have been increasingly reported in scientific literature as well as in the general media. Despite this increased coverage, the global jellification issue remains unsolved due to the scarcity of extended time series. The aim of this study was to determine to what extent the main messages about jellyfish (increase, causes, threats, solutions, etc.) in the Flemish (Belgian Dutch-language) media correspond with the knowledge and perception of recreational users, tourism-related professionals and local government officials on the Belgian coast. The number of articles in the Flemish media (140) increased from <5 in 2000 to 27 in 2010, with half of them reporting on jellyfish in the Belgian Part of the North Sea. Almost 75 % of these articles reported on the causes (overfishing being mentioned as the main cause) and economic consequences of jellyfish blooms. Articles about the dramatic consequences of stinging, poisonous and non-indigenous species were also common. A questionnaire-based survey carried out on the Belgian coast in summer 2012 indicated that jelly perception is only partly driven by the general media, while personal experience seemed at least equally important as driver. Information on causes, threats, consequences and solutions for problems caused by jellyfish corresponded to a large extent with the answers given by recreational users and tourism-related professionals. Respondents generally agreed that all underlying causes of a potential jellification problem should be addressed and tackled at an international level. With keywords like “pain”, “smell” and “slime” used to describe jellyfish, they have little sympathy from most actors, and most recreational users of beaches and coastal waters are extremely careful with any type of jellyfish, especially when children are involved. Species-specific knowledge (names, ecology, stinging vs. harmless species) presented in the media is not assimilated by most recreational users or local officials, except for divers, who have a very different perception of jellyfish than most recreational users. This lack of knowledge appeared to be a key issue in perception among recreational users. As public perception is a key driver in policy decisions, integrated coastal zone management and measures should provide good and easily understandable information, for example by distributing leaflets and putting up warning signs on the beach. This will result in a better understanding and acceptance of jellyfish as well as generating high-quality data from citizen science programs. Better and more information on jellyfish will thus benefit all the actors and sectors potentially affected by jellification.  相似文献   
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