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   729篇
  免费   8篇
  国内免费   46篇
安全科学   57篇
废物处理   11篇
环保管理   173篇
综合类   159篇
基础理论   67篇
环境理论   1篇
污染及防治   107篇
评价与监测   17篇
社会与环境   52篇
灾害及防治   139篇
  2023年   10篇
  2022年   9篇
  2021年   13篇
  2020年   22篇
  2019年   10篇
  2018年   14篇
  2017年   21篇
  2016年   16篇
  2015年   18篇
  2014年   10篇
  2013年   37篇
  2012年   15篇
  2011年   47篇
  2010年   29篇
  2009年   38篇
  2008年   49篇
  2007年   35篇
  2006年   32篇
  2005年   19篇
  2004年   19篇
  2003年   37篇
  2002年   24篇
  2001年   21篇
  2000年   17篇
  1999年   12篇
  1998年   19篇
  1997年   25篇
  1996年   34篇
  1995年   31篇
  1994年   16篇
  1993年   22篇
  1992年   16篇
  1991年   8篇
  1990年   9篇
  1989年   1篇
  1988年   2篇
  1987年   4篇
  1986年   5篇
  1985年   4篇
  1984年   2篇
  1983年   3篇
  1982年   5篇
  1981年   1篇
  1980年   1篇
  1978年   1篇
排序方式: 共有783条查询结果,搜索用时 343 毫秒
371.
Community-based natural resource management (CBNRM) institutions are challenged with finding common ground as a basis for action among diverse resource users and stakeholders. Establishing and maintaining institutional credibility within their regions, catchments, communities and among their membership is fundamental to overcoming the challenge. So too is applying appropriate institutional and governance structures and appointing appropriate leaders. Drawing on triangulated case study data collected over a 12-month period using multiple methods, this paper examines the influence of institutional credibility and leadership on the functioning, decision-making and governance of two CBNRM institutions in Queensland, Australia. The paper shows that stakeholders have very different expectations of what makes a CBNRM institution credible. Satisfying the multiple expectations requires CBNRM institutions to incorporate diverse stakeholder representation, assert their legitimacy and demonstrate accountability, transparency, fairness and justice. The paper also draws attention to the value and importance of appointing inspirational leaders who focus on encouraging followers to pursue collective goals. Comparing the merits and constraints of appointing average Joes versus community elites to the Boards of CBNRM institutions, the paper highlights the urgent need for community-based natural resource governance and inspirational leadership education and training programs to improve the availability and quality of CBNRM leadership in rural Australia. Since combining credible CBNRM institutions with inspirational leaders does not necessarily equate to sustainable on-ground NRM outcomes, it is critical that the education and training programs emphasise the importance of monitoring and evaluating the improvements in decision-making processes and in decision outcomes.  相似文献   
372.
A 2D physical model of the human head was used to investigate how the irregular skull base structure affects brain kinematics during sagittal plane head dynamics. The model consisted of a rigid skull vessel with interchangeable skull base structures. One version of the model used a skull base mimicking the irregular geometry of the human. A second version used a skull base structure approximating the anterior and middle fossae as a flat surface. Silicone gel simulated the brain and was separated from the vessel by a paraffin layer which provided a slip condition at the interface between the gel and vessel. The model was exposed to 7600 rad/s2 peak rotational acceleration with 6 ms pulse duration and 5° forced rotation. After 90° free rotation, the model was decelerated during 30 ms. Five repeated tests were conducted with each version. Rigid body displacement, shear strain and principal strains were determined from high-speed video recorded trajectories of grid markers located at different positions in the surrogate brain. The humanlike skull base reduced peak displacements of the inferior surfaces of the temporal and frontal lobes up to 87% and 48%, respectively. Up to 48% and 36% higher peak strains were obtained in the frontal and superior regions of the surrogate brain in the version containing the humanlike skull base. In contrast, the humanlike skull base decreased peak strain up to 28% in the central region of the surrogate brain. The results indicate that the irregular skull base offers natural protection of nerves and vessels passing through fissures and foramina in the cranial floor but also that it affects kinematics in different regions throughout the cerebrum. Implications of these results are discussed with respect to brain injury and modeling of head impact.  相似文献   
373.
Burns PE  Hyun S  Lee LS  Murarka I 《Chemosphere》2006,63(11):1879-1891
Leachate derived from unlined coal ash disposal facilities is a potential anthropogenic source of arsenic to the environment. To establish a theoretical framework for predicting attenuation of arsenic by soils subject to ash landfill leachate, which is typically enriched in calcium and sulfate, the adsorption of As(V) and As(III) was characterized from 1 mM CaSO4 for 18 soils obtained down-gradient from three ash landfill sites and representing a wide range in soil properties. As(V) consistently exhibited an order of magnitude greater adsorption than As(III). As(V) adsorption was best described by coupling pH with 15 s DCB-Fe (R2 = 0.851,  = 0.001), although pH coupled to clay, DCB-Fe, or DCB-Al also generated strong correlations. For As(III), pH coupled to Ox–Fe (R2 = 0.725,  = 0.001) or Ox–Fe/Al (R2 = 0.771,  = 0.001) provided the best predictive relationships. Ca2+ induced increases in As(V) adsorption whereas sulfate suppressed both As(V) and As(III) adsorption. Attenuation of arsenic from ash leachate agreed well with adsorption measured from 1 mM CaSO4 suggesting that the use of 1 mM CaSO4 in laboratory adsorption tests is a reasonable approach for estimating arsenic behavior in soils surrounding ash landfills. We also showed that the impact of leachate-induced changes in soil pH over time may not be significant for As(V) adsorption at pH < 7; however, As(III) adsorption may be impacted over a wider pH range especially if phyllosilicate clays contribute significantly to adsorption. The benefits and limitations of predicting arsenic mobility using linearized adsorption coefficients estimated from nonlinear adsorption isotherms or from the relationships generated in this study are also discussed.  相似文献   
374.
Adsorption isotherms of Direct Red 80 (DR80) and Acid Blue 25 (AB25) on the egg shell membrane (ESM) were performed at 20 ± 1 °C. Physical characteristics of ESM such as surface area and presence of functional groups were verified. The Fourier transform infra-red (FTIR) spectra proved the presence of fuctional groups such as hydroxyl, amine and carbonyl groups in ESM. The surface area of ESM was found to be 2.2098 m2/g. The effects of operational parameters such as initial dye concentration, pH0, contact time, particle size and ESM doses were studied. The Langmuir, Freundlich, BET, Redlich-Peterson and Temkin adsorption models were applied to describe the equilibrium isotherms. The pseudo-first-order and pseudo-second-order kinetics models were examined to evaluate the kinetics data at different pH0 values (2–12) and the rate constants were calculated. Maximum desorption of 81.8% was achieved for both dyes in aqueous solution at pH0 12. Also scanning electron micrographs (SEM) of the treated and untreated adsorbent were performed. Results indicate that ESM could be employed as a natural and Eco-Friendly adsorbent material for the removal of trace organics in solutions.  相似文献   
375.
Natural organic matter (NOM) is one of the main sources of environmental pollution to drinking water supplies in much of the UK and the US. Whilst traditional treatment with trivalent coagulants has proven a successful strategy in the past, operational problems are now being reported during periods of elevated organic levels in the water. Characterisation of the pollutants in terms of polarity, molecular weight and charge, provides a method to understand the impact of the observed temporal and spatial variations in terms of a mechanistic parameter relevant to the treatment processes. Results from this study demonstrate that it is not simply the increased organic concentration, but also the change in NOM composition and character, which influences the impact on the treatment processes. Consequently, monitoring of these parameters provides an insight into how to manage the impact caused by environmental changes to the catchments.  相似文献   
376.
Given progress in policies for pursuing sustainable development, promoting commitment to thinking and acting more far-sightedly has become the primary strategic challenge. In the face of impatience, selfishness, uncertainty, analytical limitations, and vulnerability, strategies for promoting far-sightedness can be identified by assessing how these obstacles can be overcome. Strategies for creating or rescheduling tangible and deference rewards, realigning performance evaluations, implementing cognitive exercises, framing communications, altering decision-making processes, using self-restraint devices both to resist temptation and to enhance credibility, altering institutions to empower the patient, and stabilizing living conditions are the major categories for identifying and assessing the many strategies which arise out of both ordinary and constitutive policy initiatives.
William AscherEmail: Phone: +1-909-6073071Fax: +1-909-6218419
  相似文献   
377.
Regulated rivers in the United States are required to support human water uses while preserving aquatic ecosystems. However, the effectiveness of hydropower license requirements nationwide has not been demonstrated. One requirement that has become more common is “run-of-river” (ROR) operation, which restores a natural flow regime. It is widely believed that ROR requirements (1) are mandated to protect aquatic biota, (2) decrease hydropower generation per unit flow, and (3) decrease energy revenue. We tested these three assumptions by reviewing hydropower projects with license-mandated changes from peaking to ROR operation. We found that ROR operation was often prescribed in states with strong water-quality certification requirements and migratory fish species. Although benefits to aquatic resources were frequently cited, changes were often motivated by other considerations. After controlling for climate, the overall change in annual generation efficiency across projects because of the change in operation was not significant. However, significant decreases were detected at one quarter of individual hydropower projects. As expected, we observed a decrease in flow during peak demand at 7 of 10 projects. At the remaining projects, diurnal fluctuations actually increased because of operation of upstream storage projects. The economic implications of these results, including both producer costs and ecologic benefits, are discussed. We conclude that regional-scale studies of hydropower regulation, such as this one, are long overdue. Public dissemination of flow data, license provisions, and monitoring data by way of on-line access would facilitate regional policy analysis while increasing regulatory transparency and providing feedback to decision makers.  相似文献   
378.
Aging in water of a TiO2-based nanocomposite used in sunscreen cosmetics has been studied as a function of light and time. It consisted initially in a TiO2 core, coated with Al(OH)3 and polydimethylsiloxane (PDMS) layers. Size measurement, coating alteration, and surface charge were followed by laser diffraction, TEM/EDS, ICP-AES and electrophoretic mobility measurement.The nanocomposite rapidly underwent progressive dispersion in the aqueous phase, enabled by the dissolution of the PDMS layer. A stable suspension of colloidal byproducts from 50 to 700 nm in size was formed. Their positively charged Al(OH)3 surface was evidenced with an isoelectric point around 7-8, controlling the dispersion stability. The critical coagulation concentrations measured with NaCl and CaCl2 was 2 × 10−2 and 8 × 10−3 M respectively. The presence of natural organic matter affected the colloidal stability according to the NOM/byproduct ratio. A 2 wt% ratio favored bridging flocculation, whereas a 20 wt% ratio induced sterical stabilization.  相似文献   
379.
Co‐management involves the shared administration of natural resources by two or more parties. This study examines the role of social capital in the process of developing co‐management in three river corridors in Canada. Qualitative analysis reveals that social capital acts as a catalyst helping groups to progress through the stages of the co‐management process. Forms of social capital (bridging and bonding) are identified that advance and/or inhibit the development of co‐management. The article reaffirms the need to expand the institutional basis for natural resource management and provides empirical evidence that social capital plays a fundamental role in developing co‐management. In conclusion, the article suggests that resource agencies need to recognize the value of social capital and the necessity for government representatives to be informed of and practiced in these skills, if they are to engage meaningfully with the civilian population.  相似文献   
380.
本文选取内蒙古锡林郭勒盟太仆寺旗温带半干旱典型草原及其邻近不同开垦年限的农田(5年,10年,50年)为研究对象,利用静态暗箱法对土壤CH4的吸收通量进行了野外观测试验。结果表明:天然草地转化为农田后,土壤吸收CH4的能力增强,随农垦年限的增加,土壤对CH4的吸收能力呈现逐渐降低趋势,依次为F5〉FIO〉F50〉G。  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