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   414篇
  免费   15篇
  国内免费   4篇
安全科学   38篇
废物处理   9篇
环保管理   115篇
综合类   36篇
基础理论   110篇
环境理论   1篇
污染及防治   90篇
评价与监测   17篇
社会与环境   9篇
灾害及防治   8篇
  2023年   3篇
  2022年   5篇
  2021年   4篇
  2020年   10篇
  2019年   14篇
  2018年   15篇
  2017年   14篇
  2016年   17篇
  2015年   9篇
  2014年   17篇
  2013年   27篇
  2012年   27篇
  2011年   32篇
  2010年   27篇
  2009年   25篇
  2008年   36篇
  2007年   37篇
  2006年   28篇
  2005年   18篇
  2004年   14篇
  2003年   16篇
  2002年   10篇
  2001年   8篇
  2000年   4篇
  1999年   2篇
  1998年   2篇
  1997年   2篇
  1996年   4篇
  1995年   2篇
  1994年   2篇
  1991年   1篇
  1978年   1篇
排序方式: 共有433条查询结果,搜索用时 31 毫秒
211.
The UV photooxidation with Fe(III) and H2O2 was employed to treat a naval derusting wastewater, which contains the high COD (chemical oxygen demand) and various metal concentrations exceptionally with high concentrations of citric acid and iron. Because of its iron containment, the Fenton-like reaction automatically took place with the added amount of H2O2. The decomposition rate was found in a sequence of: UV/H2O2/Fe(III) > UV/H2O2 > Fe(II)/H2O2. Two H2O2 injection methods, single and multiple points, were evaluated. The multiple-point H2O2 injection was more e cient to decompose the citric acid. The decomposition of the synthetic citric acid and the real derusting citric acid wastewater was also compared. The 93% COD reduction of the derusting wastewater was achieved using the UV/H2O2/Fe(III) treatment.  相似文献   
212.
Harvestmen (Arachnida: Opiliones) are familiar animals in most terrestrial habitats but are rare as fossils, with only a handful of species known from each of the Palaeozoic, Mesozoic, and Cenozoic eras. Fossil harvestmen from Middle Jurassic (ca. 165 Ma) strata of Daohugou, Inner Mongolia, China, are described as Mesobunus martensi gen. et sp. nov. and Daohugopilio sheari gen. et sp. nov.; the two genera differ primarily in the relative length of their legs and details of the pedipalps. Jurassic arachnids are extremely rare and these fossils represent the first Jurassic, and only the fourth Mesozoic, record of Opiliones. These remarkably well-preserved and modern-looking fossils are assigned to the Eupnoi, whereby M. martensi demonstrably belongs in Sclerosomatidae. It thus represents the oldest record of a modern harvestman family and implies a high degree of evolutionary stasis among one of the most widespread and abundant groups of long-legged, round-bodied harvestmen.  相似文献   
213.
Objective: The goal of this study was to evaluate how well an in-laboratory rollover crash test methodology that constrains vehicle motion can reproduce the dynamics of unconstrained full-scale steering-induced rollover crash tests in sand.

Methods: Data from previously-published unconstrained steering-induced rollover crash tests using a full-size pickup and mid-sized sedan were analyzed to determine vehicle-to-ground impact conditions and kinematic response of the vehicles throughout the tests. Then, a pair of replicate vehicles were prepared to match the inertial properties of the steering-induced test vehicles and configured to record dynamic roof structure deformations and kinematic response.

Results: Both vehicles experienced greater increases in roll-axis angular velocities in the unconstrained tests than in the constrained tests; however, the increases that occurred during the trailing side roof interaction were nearly identical between tests for both vehicles. Both vehicles experienced linear accelerations in the constrained tests that were similar to those in the unconstrained tests, but the pickup, in particular, had accelerations that were matched in magnitude, timing, and duration very closely between the two test types. Deformations in the truck test were higher in the constrained than the unconstrained, and deformations in the sedan were greater in the unconstrained than the constrained as a result of constraints of the test fixture, and differences in impact velocity for the trailing side.

Conclusions: The results of the current study suggest that in-laboratory rollover tests can be used to simulate the injury-causing portions of unconstrained rollover crashes. To date, such a demonstration has not yet been published in the open literature. This study did, however, show that road surface can affect vehicle response in a way that may not be able to be mimicked in the laboratory. Lastly, this study showed that configuring the in-laboratory tests to match the leading-side touchdown conditions could result in differences in the trailing side impact conditions.  相似文献   
214.
Headwater streams are the most numerous in terms of both number and length in the conterminous United States and play important roles as spawning and rearing grounds for numerous species of anadromous fish. Stream temperature is a controlling variable for many physical, chemical, and biological processes and plays a critical role in the overall health and integrity of a stream. We investigated the controls on stream temperature in salmon‐bearing headwater streams in two common hydrogeologic settings on the Kenai Peninsula, Alaska: (1) drainage‐ways, which are low‐gradient streams that flow through broad valleys; and (2) discharge‐slopes, which are high gradient streams that flow through narrow valleys. We hypothesize local geomorphology strongly influences surface‐water and groundwater interactions, which control streamflow at the network scale and stream temperatures at the reach scale. The results of this study showed significant differences in stream temperatures between the two hydrogeologic settings. Observed stream temperatures were higher in drainage‐way sites than in discharge‐slope sites, and showed strong correlations as a continuous function with the calculated topographic metric flow‐weighted slope. Additionally, modeling results indicated the potential for groundwater discharge to moderate stream temperature is not equal between the two hydrogeologic settings, with groundwater having a greater moderating effect on stream temperature at the drainage‐way sites.  相似文献   
215.
Local food networks (LFNs) are growing in popularity, in part as a response to broader criticisms of conventional food production. Municipal policy-makers have the opportunity to work with stakeholders to build LFNs to increase access to healthy foods in cities and ultimately improve population health and well-being. Building opportunities for healthy eating is particularly important in our study area. Flint, Michigan, is a post-industrial shrinking city suffering from the economic and health effects of deindustrialisation. Various stakeholders in Flint have responded to a significant issue with access to food by strengthening collaborations through a food policy council (FPC). Growth in the local food system has been supported by administrators and community advocates alike, through supporting community gardens, farmers' markets, and urban agriculture in a manner similar to nearby Detroit. Participant observation was conducted with stakeholders involved in the development of the LFN and the FPC in Flint. Stakeholders were exposed to existing research on the food system to help inform their policy direction. The group expressed several core concerns and prospects for future work, including a strong emphasis on consensus-based decision-making. Based on the synthesis of stakeholder opinions, policy recommendations are made to aid in continued planning of the LFN. Planning for food is an important first step in improving public health and strengthening local economic development in post-industrial cities. This research highlights the issue by making explicit the challenges and opportunities for policy advocacy in LFNs.  相似文献   
216.
One-on-one interviews and focus-group meetings were held at 20 organizations that had implemented a behavior-based safety (BBS) process in order to find reasons for program success/failures. A total of 31 focus groups gave 629 answers to six different questions. A content analysis of these responses uncovered critical information for understanding what employees are looking for in a BBS program. A perception survey administered to individual employees (n = 701) at these organizations measured a variety of variables identified in prior research to influence success in safety efforts. The survey data showed five variables to be significantly predictive of employee involvement in a BBS process: 1) perceptions that BBS training was effective; 2) trust in management abilities; 3) accountability for BBS through performance appraisals; 4) whether or not one had received education in BBS; and 5) tenure with the organization. Also, employees in organizations mandating employee participation in a BBS process (n=8 companies) reported significantly higher levels of: (a) involvement; (b) trust in management; (c) trust in coworkers; and (d) satisfaction with BBS training than did employees whose process was completely voluntary (n = 12 companies). In addition, employees in mandatory processes reported significantly greater frequency of giving and receiving positive behavior-based feedback.  相似文献   
217.
Badri SA  Asgary A  Eftekhari AR  Levy J 《Disasters》2006,30(4):451-468
Planned and involuntary resettlement after natural disasters has been a major policy in post-disaster reconstruction in developing countries over the past few decades. Studies show that resettlement can result in significant adverse impacts on the resettled population. Conversely, a well-planned and managed resettlement process can produce positive long-term development outcomes. This article presents the results of a case study undertaken 11 years after the 1990 Manjil earthquake in Iran. During the reconstruction period, a policy of involuntary planned resettlement was pursued extensively. The socioeconomic changes that occurred as a consequence of this policy of involuntary resettlement are analysed. Data were collected via a questionnaire survey that involved a sample of 194 relocated households (grouped into a settlement that later became a town). The paper shows that relocated families face difficult socioeconomic challenges after relocation and regrouping. This is especially true with respect to employment, income, the empowerment of women and lifestyle issues.  相似文献   
218.
On Behavioral-Environmental Economics   总被引:2,自引:0,他引:2  
  相似文献   
219.
Anthropogenic factors can have simultaneous positive and negative effects on parasite transmission, and thus it is important to quantify their net effects on disease risk. Net effects will be a product of changes in the survival and traits (e.g., susceptibility, infectivity) of both hosts and parasites. In separate laboratory experiments, we exposed cercariae of the trematode Echinostoma trivolvis, and its first and second intermediate hosts, snails (Planorbella trivolvis) and green frog tadpoles (Rana clamitans), respectively, to one of four common pesticides (atrazine, glyphosate, carbaryl, and malathion) at standardized, ecologically relevant concentrations (201.0, 3700.0, 33.5, and 9.6 microg/L, respectively). We measured effects of pesticide exposure on six mechanisms important to this host-parasite interaction: (1) survival of E. trivolvis cercariae over 26 hours, (2) tadpole survival over two weeks, (3) snail survival over four weeks, (4) snail growth and fecundity, (5) cercarial infectivity, and (6) tadpole susceptibility to a fixed number of cercariae. Pesticides, in general, caused significantly greater mortality of E. trivolvis cercariae than did control treatments, but atrazine was the lone chemical to significantly reduce cercarial survival (LC50 value = 267 mg/L) and then only at concentrations greater than commonly found in aquatic ecosystems (> or =200 microg/L). None of the pesticides significantly enhanced E. trivolvis virulence, decreased tadpole survival, or reduced snail survival, growth, or fecundity. Sublethal exposure of the cercariae to the pesticides (4 h) did not significantly affect trematode encystment in R. clamitans. In contrast, sublethal exposure of R. clamitans to each of the four pesticides increased their susceptibility as measured by the percentage of cercariae that encysted. The reduction in exposure to trematodes due to pesticide-induced cercarial mortality (a density-mediated effect) was smaller than the pesticide-induced increase in amphibian susceptibility (a trait-mediated effect), suggesting that the net effect of exposure to environmentally realistic levels of pesticides will be to elevate amphibian trematode infections. These findings highlight the importance of elucidating the lethal and sublethal effects of anthropogenic factors on both hosts and parasites to understand the mechanisms underlying changes in parasite transmission and virulence, an approach that is especially needed for amphibians, a taxon experiencing global disease-related declines.  相似文献   
220.
Hoverman JT  Relyea RA 《Ecology》2007,88(3):693-705
Inducible defenses allow prey to modulate their phenotypic responses to the level of predation risk in the environment and reduce the cost of constitutive defenses. Inherent in this statement is that prey must alter their phenotypes during development in order to form these defenses. This has lead many ecologists and evolutionary biologists to call for studies that examine developmental plasticity to provide insights into the importance of development in controlling the trajectories of trait formation, the integration of phenotypes over ontogeny, and the establishment of developmental windows for trait formation and reversal. By moving away from studies that focus on a single point in development, we can obtain a more complete understanding of the phenotypic decisions and limitations of prey. We exposed freshwater snails (Helisoma trivolvis) to environments in which predatory water bugs (Belostoma flumineum) were always absent, always present, or added and removed at different points in development. We discovered that snails formed morphological defenses against water bugs. Importantly, after the initial induction of defenses, snails showed similar developmental trajectories as snails reared without predators. Further, the snails possessed wide developmental windows for inducible defenses that extended past sexual maturity. However, being induced later in development appeared to have an associated cost (i.e., decreased shell thickness) that was not found when water bugs were always present. This epiphenotype (i.e., new shell formation as an extension of the current shell) suggests that resource limitation plays an important role in responses to temporal variation in predation risk and may have critical ecological costs that limit the benefits of the inducible defense. Lastly, the ability of snails to completely reverse their defenses was limited to early in ontogeny due to the constraints associated with modular growth of shell material. In sum, we demonstrate that taking a developmental perspective is extremely valuable for understanding the ecology of inducible defenses.  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