全文获取类型
收费全文 | 24781篇 |
免费 | 411篇 |
国内免费 | 1923篇 |
专业分类
安全科学 | 888篇 |
废物处理 | 1174篇 |
环保管理 | 3050篇 |
综合类 | 5332篇 |
基础理论 | 6130篇 |
环境理论 | 6篇 |
污染及防治 | 7552篇 |
评价与监测 | 1513篇 |
社会与环境 | 1126篇 |
灾害及防治 | 344篇 |
出版年
2023年 | 154篇 |
2022年 | 401篇 |
2021年 | 364篇 |
2020年 | 245篇 |
2019年 | 315篇 |
2018年 | 479篇 |
2017年 | 513篇 |
2016年 | 684篇 |
2015年 | 645篇 |
2014年 | 890篇 |
2013年 | 2216篇 |
2012年 | 1022篇 |
2011年 | 1310篇 |
2010年 | 973篇 |
2009年 | 1076篇 |
2008年 | 1278篇 |
2007年 | 1276篇 |
2006年 | 1109篇 |
2005年 | 876篇 |
2004年 | 869篇 |
2003年 | 882篇 |
2002年 | 817篇 |
2001年 | 1026篇 |
2000年 | 778篇 |
1999年 | 471篇 |
1998年 | 367篇 |
1997年 | 371篇 |
1996年 | 371篇 |
1995年 | 384篇 |
1994年 | 349篇 |
1993年 | 327篇 |
1992年 | 286篇 |
1991年 | 254篇 |
1990年 | 255篇 |
1989年 | 227篇 |
1988年 | 206篇 |
1987年 | 189篇 |
1986年 | 169篇 |
1985年 | 162篇 |
1984年 | 195篇 |
1983年 | 198篇 |
1982年 | 189篇 |
1981年 | 182篇 |
1980年 | 145篇 |
1979年 | 171篇 |
1978年 | 117篇 |
1977年 | 107篇 |
1975年 | 106篇 |
1973年 | 100篇 |
1972年 | 109篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
981.
Impacts of Changes in Precipitation Amount and Distribution on Water Resources Studied Using a Model Rainwater Harvesting System
下载免费PDF全文
![点击此处可从《Journal of the American Water Resources Association》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Behzad Asadieh Nir Y. Krakauer 《Journal of the American Water Resources Association》2016,52(6):1450-1471
Water supply reliability is expected to be affected by both precipitation amount and distribution changes under recent and future climate change. We compare historical (1951‐2010) changes in annual‐mean and annual‐maximum daily precipitation in the global set of station observations from Global Historical Climatology Network and climate models from the Inter‐Sectoral Impact Model Intercomparison Project (ISI‐MIP), and develop the study to 2011‐2099 for model projections under high radiative forcing scenario (RCP8.5). We develop a simple rainwater harvesting system (RWHS) model and drive it with observational and modeled precipitation. We study the changes in mean and maximum precipitation along with changes in the reliability of the model RWHS as tools to assess the impact of changes in precipitation amount and distribution on reliability of precipitation‐fed water supplies. Results show faster increase in observed maximum precipitation (10.14% per K global warming) than mean precipitation (7.64% per K), and increased reliability of the model RWHS driven by observed precipitation by an average of 0.2% per decade. The ISI‐MIP models show even faster increase in maximum precipitation compared to mean precipitation. However, they imply decreases in mean reliability, for an average 0.15% per decade. Compared to observations, climate models underestimate the increasing trends in mean and maximum precipitation and show the opposite direction of change in reliability of a model water supply system. 相似文献
982.
Augmenting Watershed Model Calibration with Incorporation of Ancillary Data Sources and Qualitative Soft Data Sources
下载免费PDF全文
![点击此处可从《Journal of the American Water Resources Association》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Haw Yen Michael J. White James C. Ascough II Douglas R. Smith Jeffrey G. Arnold 《Journal of the American Water Resources Association》2016,52(3):788-798
Watershed simulation models such as the Soil & Water Assessment Tool (SWAT) can be calibrated using “hard data” such as temporal streamflow observations; however, users may find upon examination of model outputs, that the calibrated models may not reflect actual watershed behavior. Thus, it is often advantageous to use “soft data” (i.e., qualitative knowledge such as expected denitrification rates that observed time series do not typically exist) to ensure that the calibrated model is representative of the real world. The primary objective of this study is to evaluate the efficacy of coupling SWAT‐Check (a post‐evaluation framework for SWAT outputs) and IPEAT‐SD (Integrated Parameter Estimation and Uncertainty Analysis Tool‐Soft & hard Data evaluation) to constrain the bounds of soft data during SWAT auto‐calibration. IPEAT‐SD integrates 59 soft data variables to ensure SWAT does not violate physical processes known to occur in watersheds. IPEAT‐SD was evaluated for two case studies where soft data such as denitrification rate, nitrate attributed from subsurface flow to total discharge ratio, and total sediment loading were used to conduct model calibration. Results indicated that SWAT model outputs may not satisfy reasonable soft data responses without providing pre‐defined bounds. IPEAT‐SD provides an efficient and rigorous framework for users to conduct future studies while considering both soft data and traditional hard information measures in watershed modeling. 相似文献
983.
Irrigation Water Allocation Using an Inexact Two‐Stage Quadratic Programming with Fuzzy Input under Climate Change
下载免费PDF全文
![点击此处可从《Journal of the American Water Resources Association》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mo Li Ping Guo Vijay P. Singh Jie Zhao 《Journal of the American Water Resources Association》2016,52(3):667-684
Agricultural irrigation accounts for nearly 70% of the total water use around the world. Uncertainties and climate change together exacerbate the complexity of optimal allocation of water resources for irrigation. An interval‐fuzzy two‐stage stochastic quadratic programming model is developed for determining the plans for water allocation for irrigation with maximum benefits. The model is shown to be applicable when inputs are expressed as discrete, fuzzy or random. In order to reflect the effect of marginal utility on benefit and cost, the model can also deal with nonlinearities in the objective function. Results from applying the model to a case study in the middle reaches of the Heihe River basin, China, show schemes for water allocation for irrigation of different crops in every month of the crop growth period under various flow levels are effective for achieving high economic benefits. Different climate change scenarios are used to analyze the impact of changing water requirement and water availability on irrigation water allocation. The proposed model can aid the decision maker in formulating desired irrigation water management policies in the wake of uncertainties and changing environment. 相似文献
984.
The degradation of polyacrylamide (PAM) in simulate wastewater was studied in UV/Fenton/C4H4O62? system. The factors such as molecular ratio of H2O2/Fe2+/C4H4O62?, pH, and the dosage of Fenton reagent that could affect the PAM degradation in the UV/Fenton/C4H4O62? system were investigated. The experimental results showed that adding C4H4O62? to UV/Fenton system could form photosensitive ferrous complexes, which led to higher degradation efficiency of PAM. The degradation rate of PAM could be up to 95.2% under the following conditions: the concentration of H2O2, Fe2+, and C4H4O62? were 22.5, 2.25, and 2.25 mmol/L, respectively (i.e., molecular ratio of H2O2/Fe2+/C4H4O62? was 10:1:1), the pH value was 3.0. 相似文献
985.
Zhao Xuxin Ji Jie Sun Hongyuan Ma Rui Wu Qixing 《International Journal of Green Energy》2016,13(3):229-240
The heat-pipe solar water heating (HP-SWH) system and the heat-pipe photovoltaic/thermal (HP-PV/T) system are two practical solar systems, both of which use heat pipes to transfer heat. By selecting appropriate working fluid of the heat-pipes, these systems can be used in the cold region without being frozen. However, performances of these two solar systems are different because the HP-PV/T system can simultaneously provide electricity and heat, whereas the HP-SWH system provides heat only. In order to understand these two systems, this work presents a mathematical model for each system to study their one-day and annual performances. One-day simulation results showed that the HP-SWH system obtained more thermal energy and total energy than the HP-PV/T system while the HP-PV/T system achieved higher exergy efficiency than the HP-SWH system. Annual simulation results indicated that the HP-SWH system can heat the water to the available temperature (45°C) solely by solar energy for more than 121 days per year in typical climate regions of China, Hong Kong, Lhasa, and Beijing, while the HP-PV/T system can only work for not more than 102 days. The HP-PV/T system, however, can provide an additional electricity output of 73.019 kWh/m2, 129.472 kWh/m2, and 90.309 kWh/m2 per unit collector area in the three regions, respectively. 相似文献
986.
Seyfi Polat Ahmet Uyumaz Emre Yilmaz Tolga Topgül H. Serdar Yücesu 《International Journal of Green Energy》2016,13(1):63-70
EGR is one of the most significant strategies for reducing especially nitrogen oxides (NOx) emissions from internal combustion engines. The thermal efficiency of spark ignition engines is lower than compression ignition engines because of its lower compression ratio. If the compression ratio is increased to obtain higher thermal efficiency, there may be a knocking tendency in spark ignition engines. EGR can be used in order to reduce NOx emissions and avoid knocking phenomena at higher compression ratios. In-cylinder temperature at the end of combustion is decreased and heat capacity of fresh charge is increased when EGR applied. Besides EGR, spark timing is another significant parameter for reducing exhaust emissions such as nitrogen oxides, and unburned hydrocarbon (UHC). In this study the effects of EGR and spark timing on spark ignition engine were investigated numerically. KIVA codes were used in order to model combustion process. The combustion process has been modeled for a single cylinder, four stroke and gasoline direct injection (GDI) spark ignition engine. The results showed that in-cylinder pressure and heat release rate decrease as EGR ratio increase. In-cylinder pressure increases with the advancing of spark timing. Advancing spark timing increases the heat release rate and in-cylinder temperature. The simulation results also showed that EGR reduced exhaust gas temperature and NOx emissions. 相似文献
987.
988.
989.
C. M. Shone T. J. S. Jothi 《Environmental science and pollution research international》2016,23(10):9364-9372
Dried leaves are a potential source of energy although these are not commonly used beside to satisfy daily energy demands in rural areas. This paper aims at preparing a leafy biomass feedstock in the form of briquettes which can be directly used for combustion or to extract the combustible gas using a gasifier. Teak (Tectona grandis) and rubber (Hevea brasiliensis) leaves are considered for the present study. A binder-assisted briquetting technique with tapioca starch as binder is adopted. Properties of these leafy biomass briquettes such as moisture content, calorific value, compressive strength, and shatter index are determined. From the study, briquettes with biomass-to-binder ratio of 3:5 are found to be stable. Higher mass percentage of binder is considered for preparation of briquettes due to the fact that leafy biomasses do not adhere well on densification with lower binder content. Ultimate analysis test is conducted to analyze the gasification potential of the briquettes. Results show that the leafy biomass prepared from teak and rubber leaves has calorific values of 17.5 and 17.8 MJ/kg, respectively, which are comparable with those of existing biomass feedstock made of sawdust, rice husk, and rice straw. 相似文献
990.