全文获取类型
收费全文 | 8182篇 |
免费 | 91篇 |
国内免费 | 49篇 |
专业分类
安全科学 | 221篇 |
废物处理 | 330篇 |
环保管理 | 987篇 |
综合类 | 1150篇 |
基础理论 | 1766篇 |
环境理论 | 6篇 |
污染及防治 | 1946篇 |
评价与监测 | 662篇 |
社会与环境 | 1213篇 |
灾害及防治 | 41篇 |
出版年
2022年 | 81篇 |
2021年 | 105篇 |
2020年 | 63篇 |
2019年 | 81篇 |
2018年 | 150篇 |
2017年 | 178篇 |
2016年 | 212篇 |
2015年 | 146篇 |
2014年 | 282篇 |
2013年 | 676篇 |
2012年 | 313篇 |
2011年 | 391篇 |
2010年 | 294篇 |
2009年 | 351篇 |
2008年 | 395篇 |
2007年 | 448篇 |
2006年 | 356篇 |
2005年 | 333篇 |
2004年 | 303篇 |
2003年 | 282篇 |
2002年 | 274篇 |
2001年 | 285篇 |
2000年 | 222篇 |
1999年 | 116篇 |
1998年 | 88篇 |
1997年 | 95篇 |
1996年 | 80篇 |
1995年 | 96篇 |
1994年 | 93篇 |
1993年 | 76篇 |
1992年 | 67篇 |
1991年 | 67篇 |
1990年 | 88篇 |
1989年 | 66篇 |
1988年 | 54篇 |
1987年 | 49篇 |
1986年 | 51篇 |
1985年 | 57篇 |
1984年 | 61篇 |
1983年 | 41篇 |
1982年 | 53篇 |
1981年 | 51篇 |
1980年 | 53篇 |
1979年 | 52篇 |
1978年 | 33篇 |
1977年 | 37篇 |
1975年 | 40篇 |
1974年 | 36篇 |
1973年 | 35篇 |
1972年 | 42篇 |
排序方式: 共有8322条查询结果,搜索用时 31 毫秒
971.
Rose M. Shillito Dennis J. Timlin David Fleisher V.R. Reddy Bruno Quebedeaux 《Agriculture, ecosystems & environment》2009,129(1-3):107-116
Although crop response to nitrogen fertilization has long been studied, classical experimental designs have led to inadequate accounting of spatial variability in field properties and yield response. Analytical methods to explicitly account for spatial variability now exist but the complementary modification of experimental design is still developing. There is a need to combine these analytical methods with non-traditional experimental design. A 2-year study was implemented to assess the response of potato (Solanum tuberosum cv. Kennebec) yield to nitrogen fertilizer rate. We used a transect-type plot design where four nitrogen treatments (0, 56, 112, and 280 kg N ha?1) were applied systematically in a continuous sinusoidal pattern along longitudinal transects. Measured field properties included topography, soil texture, pre-application soil nitrate levels, and plant available soil water content. A random field linear model was used to simultaneously account for treatment effects and soil properties. The results showed that treatment effects were significantly different from each other; however, if spatially correlated errors were accounted for, these differences were smaller and significance levels lower. Nitrogen response functions varied widely throughout the field. Of the covariates, only clay content proved important in explaining spatial differences in response to N. The sinusoidal response pattern of N was similar over the 2 years but the amplitudes varied due to differences in weather. Interactions between uncharacteristically high rainfall and a sandy field soil may have minimized discernable effects of the other covariates. The results demonstrated how the statistical analysis of potato response to a patterned application of nitrogen fertilizer can take advantage of spatial correlations to understand the response of potato to nitrogen application over larger areas. 相似文献
972.
Nazario D. Ramírez‐Beltran Joan Manuel Castro Eric Harmsen Ramón Vásquez 《Journal of the American Water Resources Association》2008,44(4):847-865
Abstract: A practical methodology is proposed to estimate the three‐dimensional variability of soil moisture based on a stochastic transfer function model, which is an approximation of the Richard’s equation. Satellite, radar and in situ observations are the major sources of information to develop a model that represents the dynamic water content in the soil. The soil‐moisture observations were collected from 17 stations located in Puerto Rico (PR), and a sequential quadratic programming algorithm was used to estimate the parameters of the transfer function (TF) at each station. Soil texture information, terrain elevation, vegetation index, surface temperature, and accumulated rainfall for every grid cell were input into a self‐organized artificial neural network to identify similarities on terrain spatial variability and to determine the TF that best resembles the properties of a particular grid point. Soil moisture observed at 20 cm depth, soil texture, and cumulative rainfall were also used to train a feedforward artificial neural network to estimate soil moisture at 5, 10, 50, and 100 cm depth. A validation procedure was implemented to measure the horizontal and vertical estimation accuracy of soil moisture. Validation results from spatial and temporal variation of volumetric water content (vwc) showed that the proposed algorithm estimated soil moisture with a root mean squared error (RMSE) of 2.31% vwc, and the vertical profile shows a RMSE of 2.50% vwc. The algorithm estimates soil moisture in an hourly basis at 1 km spatial resolution, and up to 1 m depth, and was successfully applied under PR climate conditions. 相似文献
973.
974.
975.
A Modeling System to Assess Land Cover Land Use Change Effects on SAV Habitat in the Mobile Bay Estuary 下载免费PDF全文
Maurice G. Estes Jr. Mohammad Z. Al‐Hamdan Jean T. Ellis Chaeli Judd Dana Woodruff Ronald M. Thom Dale Quattrochi Brian Watson Hugo Rodriguez Hoyt Johnson III Tom Herder 《Journal of the American Water Resources Association》2015,51(2):513-536
Estuarine ecosystems are largely influenced by watersheds directly connected to them. In the Mobile Bay, Alabama watersheds we examined the effect of land cover and land use (LCLU) changes on discharge rate, water properties, and submerged aquatic vegetation, including freshwater macrophytes and seagrasses, throughout the estuary. LCLU scenarios from 1948, 1992, 2001, and 2030 were used to influence watershed and hydrodynamic models and evaluate the impact of LCLU change on shallow aquatic ecosystems. Overall, our modeling results found that LCLU changes increased freshwater flows into Mobile Bay altering temperature, salinity, and total suspended sediments (TSS). Increased urban land uses coupled with decreased agricultural/pasture lands reduced TSS in the water column. However, increased urbanization or agricultural/pasture land coupled with decreased forest land resulted in higher TSS concentrations. Higher sediment loads were usually strongly correlated with higher TSS levels, except in areas where a large extent of wetlands retained sediment discharged during rainfall events. The modeling results indicated improved water clarity in the shallow aquatic regions of Mississippi Sound and degraded water clarity in the Wolf Bay estuary. This integrated modeling approach will provide new knowledge and tools for coastal resource managers to manage shallow aquatic habitats that provide critical ecosystem services. 相似文献
976.
Modeling Streamflow and Water Quality Sensitivity to Climate Change and Urban Development in 20 U.S. Watersheds 下载免费PDF全文
T. Johnson J. Butcher D. Deb M. Faizullabhoy P. Hummel J. Kittle S. McGinnis L.O. Mearns D. Nover A. Parker S. Sarkar R. Srinivasan P. Tuppad M. Warren C. Weaver J. Witt 《Journal of the American Water Resources Association》2015,51(5):1321-1341
Watershed modeling in 20 large, United States (U.S.) watersheds addresses gaps in our knowledge of streamflow, nutrient (nitrogen and phosphorus), and sediment loading sensitivity to mid‐21st Century climate change and urban/residential development scenarios. Use of a consistent methodology facilitates regional scale comparisons across the study watersheds. Simulations use the Soil and Water Assessment Tool. Climate change scenarios are from the North American Regional Climate Change Assessment Program dynamically downscaled climate model output. Urban and residential development scenarios are from U.S. Environmental Protection Agency's Integrated Climate and Land Use Scenarios project. Simulations provide a plausible set of streamflow and water quality responses to mid‐21st Century climate change across the U.S. Simulated changes show a general pattern of decreasing streamflow volume in the central Rockies and Southwest, and increases on the East Coast and Northern Plains. Changes in pollutant loads follow a similar pattern but with increased variability. Ensemble mean results suggest that by the mid‐21st Century, statistically significant changes in streamflow and total suspended solids loads (relative to baseline conditions) are possible in roughly 30‐40% of study watersheds. These proportions increase to around 60% for total phosphorus and total nitrogen loads. Projected urban/residential development, and watershed responses to development, are small at the large spatial scale of modeling in this study. 相似文献
977.
978.
979.
980.
Md. Abdullah Yousuf Al Harun Joshua Johnson Md. Nazim Uddin Randall W. Robinson 《环境科学学报(英文版)》2015,27(7):1-11
Decomposition of plant litter is a fundamental process in ecosystem function, carbon and nutrient cycling and, by extension, climate change. This study aimed to investigate the role of temperature on the decomposition of water soluble phenolics(WSP), carbon and soil nutrients in conjunction with the phytotoxicity dynamics of Chrysanthemoides monilifera subsp. monilifera(boneseed) litter. Treatments consisted of three factors including decomposition materials(litter alone, litter with soil and soil alone), decomposition periods and temperatures(5–15, 15–25and 25–35°C(night/day)). Leachates were collected on 0, 5, 10, 20, 40 and 60 th days to analyse physico-chemical parameters and phytotoxicity. Water soluble phenolics and dissolved organic carbon(DOC) increased with increasing temperature while nutrients like SO-24 and NO-13 decreased. Speed of germination, hypocotyl and radical length and weight of Lactuca sativa exposed to leachates were decreased with increasing decomposition temperature. All treatment components had significant effects on these parameters. There had a strong correlation between DOC and WSP, and WSP content of the leachates with radical length of test species. This study identified complex interactivity among temperature, WSP, DOC and soil nutrient dynamics of litter occupied soil and that these factors work together to influence phytotoxicity. 相似文献