全文获取类型
收费全文 | 5592篇 |
免费 | 466篇 |
国内免费 | 864篇 |
出版年
2024年 | 17篇 |
2023年 | 122篇 |
2022年 | 117篇 |
2021年 | 192篇 |
2020年 | 255篇 |
2019年 | 276篇 |
2018年 | 264篇 |
2017年 | 295篇 |
2016年 | 326篇 |
2015年 | 309篇 |
2014年 | 285篇 |
2013年 | 376篇 |
2012年 | 229篇 |
2011年 | 268篇 |
2010年 | 198篇 |
2009年 | 243篇 |
2008年 | 296篇 |
2007年 | 291篇 |
2006年 | 299篇 |
2005年 | 248篇 |
2004年 | 239篇 |
2003年 | 215篇 |
2002年 | 256篇 |
2001年 | 177篇 |
2000年 | 139篇 |
1999年 | 130篇 |
1998年 | 122篇 |
1997年 | 107篇 |
1996年 | 77篇 |
1995年 | 80篇 |
1994年 | 65篇 |
1993年 | 46篇 |
1992年 | 51篇 |
1991年 | 33篇 |
1990年 | 30篇 |
1989年 | 23篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 20篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 23篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 26篇 |
1978年 | 9篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1972年 | 4篇 |
排序方式: 共有6922条查询结果,搜索用时 78 毫秒
991.
Hydrogeochemical evolution and risk assessment of human health in a riverbank filtration site,northeastern China 总被引:1,自引:0,他引:1
Intensive agriculture and industrial activities have resulted in contamination in rivers and groundwater quality, which threatens human health. In this study, we used comprehensive physiochemical indicators to assess the quality of groundwater used for drinking and irrigation in addition to the potential risks to local residents in a riverbank filtration site. Human health risks through drinking water intake and dermal contact were also estimated. Moreover, we analyzed the spatial distribution regularities of health risk values in a riverbank filtration site. The assessment results revealed that NH4–N, NO2–N, F?, Mn, and As are main contaminants affecting groundwater quality and that 62% of the total samples is suitable for a variety of purposes. All groundwater in the study area is suitable for irrigation based on the sodium adsorption ratio (SAR), residual sodium carbonate (RSC), Na percentage (%Na), and U.S. Salinity Laboratory (USSL) and Wilcox diagrams. The health risk assessment suggests that residents in the study area are at high health risk, and women and children face higher risk than men in both non-carcinogenic and carcinogenic risks. The spatial distribution regularities of health risk values suggest that the human health risk value of each groundwater sample is different in the study area and has certain regularity. Therefore, effective measurements must be taken to address the groundwater contamination and to reduce the human health risks. 相似文献
992.
To assess natural attenuation and the efficiency of remediation actions after more than two years a large accident with gasoline spill contaminated a wetland in a tropical region, an Ecological Risk Assessment based on the Dutch Triad was applied. In total, eight surface water-sampling points were distributed randomly in the affected area and on reference area upstream the contaminated site, with similar ecological characteristics. Risks based on chemical, ecotoxicological, and ecological lines of evidence (LoE) were calculated to integrate the environmental risk indexes. The chemical risk was derived from toxic pressure coefficients based on the total BTEX and naphthalene concentrations. Ecotoxicological LoE based on acute toxicity with Daphnia similis and Aliivibrio fischeri bioassays and chronic toxicity with Desmodesmus subspicatus bioassay contributed to raise uncertainty due to low sensitivity of acute assays. Genotoxicity and endocrine disruption biomarkers of Oreochromis niloticus were used to calculate the Biomarker Stress Index (BSI) assumed as Ecological Risk Index. The integration of the Chemical Risk Index with BSI to estimate the Biological Vulnerability Index allowed a meaningful analysis of the threats to the aquatic ecosystem, thereby supporting managers and decision-makers. 相似文献
993.
Coastal wetlands are facing an increasingly high risk of degradation and loss due to a wide variety of human activities and natural processes. Human encroachment, including land reclamation, drainage, and introduction of invasive species, has direct negative effects on wetlands, mainly through changes in hydrology and vegetation. Additionally, accelerated sea level rise (SLR) can result in flooding of wetlands in low-lying coastal zones. In this study, we present a rapid risk assessment method for coastal wetland loss and degradation. The main stress factors, i.e., urban sprawl, agriculture, coastal erosion, and SLR, have been examined and quantified through remote sensing and geographic information system spatial analysis. A weighted factor-based linear model has been used to evaluate the spatial risk levels of wetland loss. The proposed methodology is applied to the low-lying coastal wetlands of Hangzhou Bay in Shanghai, China. The results show that the regions closer to the sea have relatively higher risk levels on the landward side of the coastline, but relatively low risk levels on the seaward side of the coastline. This work emphasizes the need to sustainably use and protect wetlands in order to reduce disaster risks and contribute to the improvement of human well-being. 相似文献
994.
This paper investigated the concentrations of Pb in foods and the potential health risk from Pb exposure via surveys and a literature review. It was shown that the mean Pb concentration in different food groups was in the following decreasing order: marine products > meat > egg > vegetable > cereal > bean> dairy > fruit. More precisely, on average the weekly Pb intake (mg kg?1 bw week?1) for men, women, 2–3-year-old children, and 4–17-year-old children was 0.0055, 0.0059, 0.0145, and 0.0091, respectively. We used both deterministic and probabilistic methods to estimate the target hazard quotients (THQs) by comparing the dietary Pb intake estimation with respect to the provisional tolerable weekly intake (PTWI). The result showed that THQ values were lower than 1 in most cases, except the 97.5th percentile THQ values for 2–3-year-old children, and the probability of greater dietary Pb exposure than the tolerant weekly intake (THQ > 1) were 0.2%, 0.6%, 3.7%, and 1.2% for adult men, women, 2–3-year-old children, and 4–17-year-old children, respectively, indicating a low health risk for Chinese consumers. Among all groups, children, especially 2–3-year-old children were the most sensitive sub-population with regard to Pb exposure. Finally, it still appeared necessary to continue undertaking efforts to reduce exposure to Pb. 相似文献
995.
Risk assessment is vital for cost-effective ship management in maritime industry since numerous maritime activities pose potential hazards according to the human causalities. Therefore, safety practitioners attempt to offer proactive approaches to mitigate risk as much as possible. In this context, this article presents a hybrid risk-based approach for maritime industry by adopting Fuzzy Analytic Hierarchy Process (FAHP) with fuzzy VIKOR (FVIKOR) methods under Fine-Kinney approach. To illustrate the hybrid risk-based approach, ballast tank maintenance process is handled since there are various hazards causing fatalities, severe injuries, and illness during ballast tank maintenance procedure than any other type of shipboard work. An extensive risk analysis is performed to enhance environment safety and operational reliability in maritime industry. Besides its theoretical contribution, the outcomes of the paper contribute to improve overall safety level of ship by considering potential hazards in risk management. 相似文献
996.
We present an optimization model for fishing vessel evacuation during typhoon emergencies. Typhoon forecasts often do not accurately predict the typhoon path, so a risk assessment method is developed to evaluate the risk of fishing vessel evacuation processes. Risk assessment is the objective function of the fishing vessel evacuation optimization model. The model used is a many-to-many nonlinear assignment problem. A hybrid closed loop algorithm is used and its efficiency exceeds the traditional algorithm. The model is tested on a typhoon scenario based on harbors' distribution in Zhejiang Province, China. 相似文献
997.
Risk characterization of agricultural soils in the mining areas of Singhbhum copper belt was done by determining the total concentrations of metals using inductively coupled plasma-mass spectrometry and assessing the potential ecological and human health risks. The concentrations were above the average shale values for most of the metals. Principal component analysis showed anthropogenic contributions of Cu, Ni, Co, Mn, Pb, and Cr in the soils. Ecological risk assessment revealed that 50% of the soil samples were at moderate to very high ecological risk. Health risks for adults and children were calculated using hazard quotients (HQs), hazard index (HI), and Cancer risks for the oral, dermal, and inhalation pathways. The HQs for all the metals except As and Co were below 1, which suggested that non-carcinogenic risks due to metal exposure through soils were within the safe limit. However, considering all the metals and pathways, the HI for adults and children was 0.71 and 5.61, respectively, suggesting appreciable risk to local residents. The carcinogenic risks due to As and Cr in the soils were within the acceptable value of 1E–04. For both carcinogenic and non-carcinogenic risks, oral ingestion appeared to be the primary pathway followed by dermal and inhalation pathways. 相似文献
998.
Mujtaba Baqar Muhammad Arslan Yumna Sadef Abdul Qadir Sajid Rashid Ahmad 《人类与生态风险评估》2017,23(6):1249-1271
As a consequence of both increasing population and industrialization in agro-economic sector, Pakistan has inevitably been confronted by multicomplex environmental challenges. Owing in part to poor regulatory framework, pollution due to persistent organic pollutants (POPs) has caused serious problems throughout the country. Resultantly, extensive use of POPs is causing vigorous deterioration of environment and human health. The current study addresses: (1) the general information on associated ecological effects and toxicity assessment by meta-analysis for local fauna and flora (2) their respective occurrence in living organisms; and (3) sources and distribution patterns of various POPs classes in environmental compartments of Pakistan. Based on the study, it can be concluded that the environment of Pakistan is highly contaminated with organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), dechlorane plus (DP), and polychlorinated naphthalenes (PCNs), which is further supported with the meta-analysis. Nevertheless, unavailability of environmental quality standards and food safety for POPs render it a forthcoming challenge of multicompartment toxicity exposure. Therefore, strategies must be planned for risk assessment of biologically active POPs, while the POP waste inventory should be elevated, along with the necessary measures to promote appropriate handling and treatment of POP as a matter of prime importance. 相似文献
999.
Consequential Life Cycle Assessment of Pasture‐based Milk Production: A Case Study in the Waikato Region,New Zealand 下载免费PDF全文
Jeerasak Chobtang Sarah J. McLaren Stewart F. Ledgard Daniel J. Donaghy 《Journal of Industrial Ecology》2017,21(5):1139-1152
Farm intensification options in pasture‐based dairy systems are generally associated with increased stocking rates coupled with the increased use of off‐farm inputs to support the additional feed demand of animals. However, as well as increasing milk production per hectare, intensification can also exacerbate adverse impacts on the environment. The objective of the present study was to investigate environmental trade‐offs associated with potential intensification methods for pasture‐based dairy farming systems in the Waikato region, New Zealand. The intensification scenarios selected were (1) increased pasture utilization efficiency (PUE scenario), (2) increased use of nitrogen (N) fertilizer to boost on‐farm pasture production (N fertilizer scenario), and (3) increased use of brought‐in feed as maize silage (MS) (MS scenario). Twelve impact categories were assessed. The PUE scenario was the environmentally preferred intensification method, and the preferred choice between the N fertilizer and MS scenarios depended upon trade‐offs between different environmental impacts. Sensitivity analysis was carried out to test the effects of choice associated with: (1) the approaches used to account for indirect land‐use change (ILUC) and (2) the competing product systems (conventional beef systems) used to handle the co‐product dairy meat for the climate change (CC) indicator. Results showed that the magnitude of the CC indicator results was influenced by the ILUC accounting approaches and the choice associated with a global marginal beef mix, but the relative CC indicator results for the three intensification scenarios remained unchanged. 相似文献
1000.
Consequences of Future Data Center Deployment in Canada on Electricity Generation and Environmental Impacts: A 2015–2030 Prospective Study 下载免费PDF全文
Thomas Dandres Nathan Vandromme Glasha Obrekht Andy Wong Kim Khoa Nguyen Yves Lemieux Mohamed Cheriet Réjean Samson 《Journal of Industrial Ecology》2017,21(5):1312-1322
The environmental impacts of data centers that provide information and communication technologies (ICTs) services are strongly related to electricity generation. With the increasing use of ICT, many data centers are expected to be built, causing more absolute impacts on the environment. Given that electricity distribution networks are very complex and dynamic systems, an environmental evaluation of future data centers is uncertain. This study proposes a new approach to investigate the consequences of future data center deployment in Canada and optimize this deployment based on the Energy 2020 technoeconomic model in combination with life cycle assessment methodology. The method determines specific electricity sources that will power the future Canadian data centers and computes related environmental impacts based on several indicators. In case‐study scenarios, the largest deployment of data centers leads to the smallest impact per megawatt of data centers for all of the environmental indicators. It is found that an increase in power demand by data centers would lead to a reduction in electricity exports to the United States, driving the United States to generate more electricity to meet its energy demand. Given that electricity generation in the United States is more polluting than in Canada, the deployment of data centers in Canada is indirectly linked to an increase in overall environmental impacts. However, though an optimal solution should be found to mitigate global greenhouse gas emissions, it is not clear whether the environmental burden related to U.S. electricity generation should be attributed to the Canadian data centers. 相似文献