首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   411篇
  免费   8篇
  国内免费   3篇
安全科学   10篇
废物处理   18篇
环保管理   84篇
综合类   38篇
基础理论   101篇
环境理论   1篇
污染及防治   102篇
评价与监测   31篇
社会与环境   31篇
灾害及防治   6篇
  2023年   3篇
  2021年   5篇
  2019年   4篇
  2018年   9篇
  2017年   11篇
  2016年   10篇
  2015年   11篇
  2014年   9篇
  2013年   41篇
  2012年   14篇
  2011年   28篇
  2010年   13篇
  2009年   17篇
  2008年   27篇
  2007年   16篇
  2006年   24篇
  2005年   13篇
  2004年   16篇
  2003年   11篇
  2002年   13篇
  2001年   13篇
  2000年   6篇
  1999年   6篇
  1998年   9篇
  1996年   6篇
  1995年   4篇
  1994年   8篇
  1993年   3篇
  1992年   7篇
  1991年   3篇
  1990年   4篇
  1989年   3篇
  1988年   5篇
  1987年   1篇
  1986年   4篇
  1985年   6篇
  1984年   6篇
  1983年   5篇
  1982年   1篇
  1981年   2篇
  1980年   2篇
  1979年   5篇
  1977年   3篇
  1976年   1篇
  1974年   2篇
  1972年   3篇
  1970年   2篇
  1969年   1篇
  1967年   3篇
  1965年   1篇
排序方式: 共有422条查询结果,搜索用时 31 毫秒
321.
Patterns of amenity migration and recreational home development in much of the USA since the 1990s are changing the local sociodemographic make-up and the relationships formed among people and place. We use the psychological constructs of place attachment, place identity, and place dependence to assess differences in these relationships among new and long-time residents and absentee and local residents in three rural counties in the Inland Northwest. We measured place bonding using data from a mail survey of local (n = 531) and absentee (n = 239) property owners. We compared structural models suggested in the literature on the psychology of place, and found that a two-dimensional model representing place attachment and place identity was appropriate for both local and absentee property owners. Local owners exhibited stronger place attachment and place identity than absentee owners. Place bonding constructs were also substantially less impacted by the total number of years a property owner had resided on his or her property than by the number of months per year they lived on the property. The findings indicate that sociodemographic changes such as those manifested in second-home development may lead to a population that is less emotionally, behaviorally, and cognitively connected to the places in question, while sociodemographic changes from permanent in-migration may have a substantially smaller effect on place bonding.  相似文献   
322.
Abstract

Broiler chickens and swine fed furazolidone in their diet were sacrificed, and samples of liver, kidney, skin/fat and muscle were harvested and analyzed for furazolidone residue. Chickens fed 200 g of furazolidone/ton of feed were withdrawn from treatment 21, 14, 7, 5, 3, or 0 days before slaughter. Birds withdrawn from medication more than 5 days prior to slaughter had no residues in any of the tissues sampled. One of the 12 birds in each of the 5 day and 3 day withdrawal groups had detectable residues in the skin/fat. Seven of the 12 birds in the 0 day withdrawal group had residues of <2 ppb in skin/fat samples. Chickens fed 400 g furazolidone/ton of feed were withdrawn from treatment 0 days before slaughter. Residues of 0.7 to 3.5 ppb were found in the skin of these birds; residues were not found in other tissues. Swine were fed 300 g furazolidone/ton of feed for 2 weeks or 150 g/ton for 5 weeks. They were withdrawn from treatment 10, 7, 5, 3, or 0 days before slaughter. Tissue samples taken from these swine did not contain detectable furazolidone residues.  相似文献   
323.
Abstract

Field experiments were conducted in corn plots during 1988 that were artificially Infested with stalkborers, Papianema nebris (Guenee'). Two atomizers, a flatfan and a flood nozzle chosen for different droplet size distributions were used to apply two insecticides, chlorpyrifos and cyfluthrin at two application rates. Nozzles, insecticides, rates, and associated interactions were evaluated for control of stalkborer in the field. Laboratory studies involved application of insecticides to soil and glass via a spray track for bioassay at field application rates. Image analysis of percent area travelled on water sensitive paper by stalkborers was compared to droplet percent area covered to obtain percent area contacted per insect. Droplet size distributions for each nozzle were obtained using an Aerometrics particle sizing instrument. Significant differences in stalkborer control were attributed to percent area covered by smaller droplets measured by image analysis.  相似文献   
324.
Climate change is projected to have a strongly negative effect on water supplies in the arid mountains of South America, significantly impacting millions of people. As one of the poorest countries in the region, Bolivia is particularly vulnerable to such changes due to its limited capacity to adapt. Water security is threatened further by glacial recession with Bolivian glaciers losing nearly half their ice mass over the past 50 years raising serious water management concerns. This review examines current trends in water availability and glacier melt in the Bolivian Andes, assesses the driving factors of reduced water availability and identifies key gaps in our knowledge of the Andean cryosphere. The lack of research regarding permafrost water sources in the Bolivian Andes is addressed, with focus on the potential contribution to mountain water supplies provided by rock glaciers.  相似文献   
325.
Exposure to the nonsteroidal anti-inflammatory drug (NSAID) diclofenac resulted in the near extinction of three species of Gyps vultures on the Indian subcontinent. Other NSAIDs present in the environment, including flunixin, may pose a similar risk. In the course of a study to determine the feasibility of detecting NSAIDs in keratinous matrices (i.e., hair, nails and feathers) using GC-MS, wool opportunistically collected from a sheep treated with flunixin was analysed for residues. Flunixin was detected qualitatively in external wool wash and extract samples. While residues of veterinary agents and pesticides have previously been found in sheep’s wool, our preliminary investigation provides the first instance of an NSAID being detected in this matrix. Here we provide the sample preparation methods and GC-MS parameters used to enable further refinement as part of ongoing conservation and consumer quality control measures.  相似文献   
326.
327.
The present study investigates renal inner medullary collecting duct (mIMCD3) cells and human embryonic kidney cells (HEK293) for evaluation of cytotoxicity of nephrotoxic compounds. The 24 h LC(50) values for cisplatin, paraquat and ibuprofen in mIMCD3 cells were 135, 155 and 3600 microM, respectively. The 24 h LC(50) values for paraquat and ibuprofen in HEK293 cells were 180 and 1000 microM, respectively. Effects of hyperosmolality on cytotoxicity of paraquat were additive in mIMCD3 cells. These data demonstrate that renal hyperosmolality has an additive effect on cytoxicity of paraquat.  相似文献   
328.
Storage of large amounts of carbon dioxide (CO2) in deep geologic formations for greenhouse-gas mitigation is gaining momentum and moving from its conceptual and testing stages towards widespread application. In this work we explore various optimization strategies for characterizing surface leakage (seepage) using near-surface measurement approaches such as accumulation chambers and eddy covariance towers. Seepage characterization objectives and limitations need to be defined carefully from the outset especially in light of large natural background variations that can mask seepage. The cost and sensitivity of seepage detection are related to four critical length scales pertaining to the size of the: (1) region that needs to be monitored; (2) footprint of the measurement approach, and (3) main seepage zone; (4) region in which concentrations or fluxes are influenced by seepage. Seepage characterization objectives may include one or all of the tasks of detecting, locating, and quantifying seepage. Each of these tasks has its own optimal strategy. Detecting and locating seepage in a region in which there is no expected or preferred location for seepage nor existing evidence for seepage requires monitoring on a fixed grid, e.g., using eddy covariance towers. The fixed-grid approaches needed to detect seepage are expected to require large numbers of eddy covariance towers for large-scale geologic CO2 storage. Once seepage has been detected and roughly located, seepage zones and features can be optimally pinpointed through a dynamic search strategy, e.g., employing accumulation chambers and/or soil-gas monitoring. Quantification of seepage rates can be done through measurements on a localized fixed grid once the seepage is pinpointed. Background measurements are essential for seepage detection in natural ecosystems. Artificial neural networks are considered as regression models useful for distinguishing natural system behavior from anomalous behavior suggestive of CO2 seepage without need for detailed understanding of natural system processes. Because of the local extrema in CO2 fluxes and concentrations in natural systems, simple steepest-descent algorithms are not effective and evolutionary computation algorithms are proposed as a paradigm for dynamic monitoring networks to pinpoint CO2 seepage areas.  相似文献   
329.
The St. Johns River Water Management District (SJRWMD) has developed a minimum flows and levels (MFLs) method that has been applied to rivers, lakes, wetlands, and springs. The method is primarily focused on ecological protection to ensure systems meet or exceed minimum eco-hydrologic requirements. MFLs are not calculated from past hydrology. Information from elevation transects is typically used to determine MFLs. Multiple MFLs define a minimum hydrologic regime to ensure that high, intermediate, and low hydrologic conditions are protected. MFLs are often expressed as statistics of long-term hydrology incorporating magnitude (flow and/or level), duration (days), and return interval (years). Timing and rates of change, the two other critical hydrologic components, should be sufficiently natural. The method is an event-based, non-equilibrium approach. The method is used in a regulatory water management framework to ensure that surface and groundwater withdrawals do not cause significant harm to the water resources and ecology of the above referenced system types. MFLs are implemented with hydrologic water budget models that simulate long-term system hydrology. The method enables a priori hydrologic assessments that include the cumulative effects of water withdrawals. Additionally, the method can be used to evaluate management options for systems that may be over-allocated or for eco-hydrologic restoration projects. The method can be used outside of the SJRWMD. However, the goals, criteria, and indicators of protection used to establish MFLs are system-dependent. Development of regionally important criteria and indicators of protection may be required prior to use elsewhere.  相似文献   
330.
This work is motivated by the growing interest in injecting carbon dioxide into deep geological formations as a means of avoiding its atmospheric emissions and consequent global warming. Ideally, the injected greenhouse gas stays in the injection zone for a geologic time, eventually dissolves in the formation brine and remains trapped by mineralization. However, one of the potential problems associated with the geologic method of sequestration is that naturally present or inadvertently created conduits in the cap rock may result in a gas leakage from primary storage. Even in supercritical state, the carbon dioxide viscosity and density are lower than those of the formation brine. Buoyancy tends to drive the leaked CO2plume upward. Theoretical and experimental studies of buoyancy-driven supercritical CO2 flow, including estimation of time scales associated with plume evolution and migration, are critical for developing technology, monitoring policy, and regulations for safe carbon dioxide geologic sequestration.In this study, we obtain simple estimates of vertical plume propagation velocity taking into account the density and viscosity contrast between CO2 and brine. We describe buoyancy-driven countercurrent flow of two immiscible phases by a Buckley–Leverett type model. The model predicts that a plume of supercritical carbon dioxide in a homogeneous water-saturated porous medium does not migrate upward like a bubble in bulk water. Rather, it spreads upward until it reaches a seal or until it becomes immobile. A simple formula requiring no complex numerical calculations describes the velocity of plume propagation. This solution is a simplification of a more comprehensive theory of countercurrent plume migration [Silin, D., Patzek, T.W., Benson, S.M., 2007. A Model of Buoyancy-driven Two-phase Countercurrent Fluid Flow. Laboratory Report LBNL-62607. Lawrence Berkeley National Laboratory, Berkeley, CA]. In a layered reservoir, the simplified solution predicts a slower plume front propagation relative to a homogeneous formation with the same harmonic mean permeability. In contrast, the model yields much higher plume propagation estimates in a high-permeability conduit like a vertical fracture.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号