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921.
Hydrozoan species are renowned for flexible asexual reproduction, which may predispose them to be successful invaders. Polyps of the invasive hydrozoan Moerisia lyonsi (Boulenger, 1908) have very high rates of asexual production of both polyp and medusa buds. In order to determine how environmental factors affect asexual reproduction in M. lyonsi, the quantitative relationships between polyp bud and medusa bud production were studied in a 31-day laboratory experiment during August 2001. The combined effects of prey (4, 8, 12, 16 Acartia tonsa copepods polyp–1 day–1), temperature (20°C, 29°C), and salinity (5, 15, 25) were tested on the development times for polyp buds (DTp) and medusa buds (DTm), the total asexual reproduction rate (ARR, no. buds polyp–1 day–1), and the ratio of medusa bud to total bud production (Rm). Greater food consumption significantly and directly enhanced ARR and Rm and shortened DTp and DTm. A lower temperature (20°C) and higher salinity (25) reduced food consumption, lengthened development times, and decreased ARR and Rm, with opposite effects for the higher temperature (29°C) and lowest salinity (5). The patterns of variation of these reproductive parameters are more complex. DTm was most sensitive and was significantly and directly affected by all three measured factors. In addition to food consumption, direct effects were seen by temperature on DTp and by salinity on Rm. ARR was directly affected only by food consumption. Overall, DTp, DTm, and Rm were more sensitive to environmental differences than was ARR. More favorable conditions enhanced medusa bud production. The adaptive reproductive processes and their significance for the maintenance and dispersal of M. lyonsi are discussed.Communicated by J.P. Grassle, New Brunswick 相似文献
922.
We compared populations of Laminaria hyperborea from different regions along the Norwegian coast (58–71°N). The aim of the study was to examine possible regional differences in population demography and to relate these to latitudinal gradients in ambient temperature and light. A number of population parameters were examined in understory and canopy kelp individuals. We found latitudinal differences in stipe growth rate and growth pattern, mortality, longevity, recruitment and density. Stipe growth rate was higher for young individuals in mid-Norway than in south and north Norway. Mean stipe length was related to temperature and light, and correlated significantly with indices combining temperature during the growth season and daylength in summer. Mortality decreased and longevity increased with increasing latitude, probably because of a temperature decrease with increasing latitude and a general reduction in metabolic rate. Greater longevity may also cause the observed decrease in recruitment rate with increasing latitude, since there are fewer opportunities for understory individuals to replace dead canopy individuals. The development of particularly large kelp in mid-Norway appears to be explained by high growth rates and not a particularly long life span, as earlier assumed. This has consequences for decisions of the optimal harvesting regime for the species in the region, with regard to yield and maintenance of associated biodiversity.Communicated by M. Kühl, Helsingør 相似文献
923.
924.
925.
The study was conducted to assess the potential of Norwegian agricultural ecosystems to sequester carbon (C) based on the data from some long-term agronomic and land use experiments. The total emission of CO2 in Norway in 1998 was 41.4 million metric ton (MMT), of which agriculture contributed only 0.157 MMT, or <0.4% of the total emissions. With regards to methane (CH4) and nitrous oxide (N2O) gases, however, agricultural activities contributed 32.5% and 51.3% of their respective emissions in Norway. The soil organic carbon (SOC) losses associated with accelerated soil erosion in Norway are estimated at 0.475 MMTC yr–1. Land use changes and soil/crop management practices with potential for SOC sequestration include conservation tillage methods, judicious use of fertilizers and manures, use of crop residues, diverse crop rotations, and erosion control measures. The potential for SOC sequestration is 0.146 MMTC yr–1 for adopting conservation tillage, 0.011–0.035 MMTC yr–1 for crop residue management, 0.026 MMTC yr–1 for judicious use of mineral fertilizer, 0.016–0.135 MMTC yr–1 for manure application, and 0.036 MMTC yr–1 for adopting crop rotations. The overall potential of these practices for SOC sequestration ranges from 0.591 to 1.022 MMTC yr–1 with an average value of 0.806 MMTC yr–1. Of the total potential, 59% is due to adoption of erosion control measures, 5.8% to restoration of peat lands, 21% to conversion to conservation tillage and residue management, and 14% to adoption of improved cropping systems. Enhancing SOC sequestration and improving soil quality, through adoption of judicious land use and improved system of soil and crop management, are prudent strategies for sustainable management of soil, water and environment resources.Readers should send their comments on this paper to:
bhaskarn ath@aol.com within 3 months of publication of this issue. 相似文献
926.
Jon?BarnettEmail author Jonathan?Pauling 《Environment, Development and Sustainability》2005,7(2):271-289
This paper explains one way in which New Zealand’s free-market reforms have adversely affected its environment. Liberalisation of New Zealand’s economy has radically changed the determinants of agricultural export success, largely due to the elimination of subsidies to domestic producers, and of tariffs on imports. In this exposed agricultural milieu, the dairy industry has thrived; cow numbers have increased by over 50%, with commensurate increases in herd and farm sizes. With this rapid expansion has come increasing pollution of New Zealand’s waterways. New Zealand’s Resource Management Act 1991 is potentially capable of controlling these adverse effects; however, its implementation was slow and piecemeal throughout the 1990s. So, at the same time as production and pollution from dairy farming expanded, the efficacy of environmental policy was limited. The resulting implementation gap has put at risk the ‘clean and green’ image that is an important component of New Zealand’s agricultural export success.Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue. 相似文献
927.
Ahmed?SaidEmail author David?K.?Stevens Gerald?Sehlke 《Environment, Development and Sustainability》2005,7(4):453-464
A new approach for evaluating water sustainability is introduced by comparing physical and economic sustainability. To achieve
physical sustainability, water should be available in sufficient quantity and of good quality and used efficiently. The economic
sustainability can be achieved by balancing between costs and values of water. The objectives of this study were to estimate
the physical and economic sustainability of surface water in the Big Lost River, south–central Idaho. The study used a Bayesian
network by building a graphical diagram of nodes representing all significant variables related with the sustainability, such
as water demand, water quality, and the different costs and values of water. The study showed that the likelihood of the physical
sustainability is less than that of the economic sustainability, which is attributed to the scarcity of water in the Big Lost
River.
Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue. 相似文献
928.
This paper describes a method of estimating the “true” internal costs of industrial waste, aimed at promoting environmentally
friendly waste management. The study employs contribution margin analysis and a model – The Model for Efficient Use of Resources
for Optimal Production Economy (EUROPE) – introduced by the author for assigning industrial costs to waste. In a business
sense, waste is regarded as having the same basic status as any normal industrial product – the equality principle. Application
of the method is suggested to create incentives for environmental improvement and profitability improvement in companies.
Although the results of two case studies show the generation of waste to have a substantial negative impact on the final operating
income, due to the internal shadow price costs it creates, this is regarded as an unavoidable consequence of the companies'
acting in accordance with the principle of sustainable development.
Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue. 相似文献
929.
Sardar?M.?N.?IslamSmnis@hotmail.com" title="Sardar.Islam@vu.edu.au Smnis@hotmail.com" itemprop="email" data-track="click" data-track-action="Email author" data-track-label="">Email author 《Environment, Development and Sustainability》2005,7(3):377-400
Sustainability science is a new branch of human knowledge. It is necessary to model sustainability science based on a framework
consisting of the interactions of society, ecology, the environment and the economy. This paper develops such a model, the
SEEOSG model, containing the essential structural relationships that incorporate the environmental and economic conditions
required for sustainability. The model is solved as a dynamic optimisation problem. This optimal growth model of ecology and
economic growth enables us also to analyse the issues which are specific to sustainability science such as the ecologically
sustainability and inter-generational equity implications of economic activities and policies. In the model results growth
maximisation goals appear to be fraught with difficulties such as infeasibility and non-sustainability. The results also suggest
also that an equilibrium ecological and economic system does not sustain over a very long period of time unless appropriate
actions are taken.
Readers should send thier comments on this paper to: BhaskarNath@aol.com within 3 months of
publication of this issue. 相似文献
930.
Summary The biomass and productivity of a montane grassland of Garhwal Himalaya were estimated with the objectives to compare these
values of the dominant exotic species, Eupatorium glandulosum HBK. (Asteraceae) with other species, and to compare the sites more dominated by this species with other study sites. The
effect of dominance of this species on other species was undertaken because of its continuous spread in the grasslands of
the Garhwal Himalaya causing replacement of some native grasses and economically important herbaceous plants. Out of six study
sites, SW1, SW2, and NE1 were more dominated by Eupatorium glandulosum. Total net primary productivity (TNP) ranged from 1528.5 to 2163.4 g m−2 yr−1. Eupatorium glandulosum showed individual highest biomass on all the study sites, and the sites more dominated by this species showed higher values
of primary productivity, thereby reducing the biomass and production of other species on these sites. 相似文献