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   4080篇
  免费   100篇
  国内免费   53篇
安全科学   263篇
废物处理   156篇
环保管理   840篇
综合类   474篇
基础理论   1008篇
环境理论   3篇
污染及防治   966篇
评价与监测   313篇
社会与环境   169篇
灾害及防治   41篇
  2023年   32篇
  2022年   41篇
  2021年   46篇
  2020年   57篇
  2019年   70篇
  2018年   85篇
  2017年   123篇
  2016年   140篇
  2015年   111篇
  2014年   134篇
  2013年   359篇
  2012年   188篇
  2011年   236篇
  2010年   186篇
  2009年   206篇
  2008年   213篇
  2007年   223篇
  2006年   206篇
  2005年   179篇
  2004年   156篇
  2003年   140篇
  2002年   137篇
  2001年   98篇
  2000年   72篇
  1999年   65篇
  1998年   51篇
  1997年   64篇
  1996年   50篇
  1995年   55篇
  1994年   56篇
  1993年   46篇
  1992年   39篇
  1991年   31篇
  1990年   29篇
  1989年   27篇
  1988年   23篇
  1987年   17篇
  1986年   17篇
  1985年   24篇
  1984年   18篇
  1983年   30篇
  1982年   22篇
  1981年   34篇
  1980年   19篇
  1979年   18篇
  1978年   13篇
  1977年   5篇
  1976年   6篇
  1975年   5篇
  1971年   5篇
排序方式: 共有4233条查询结果,搜索用时 0 毫秒
941.
Safety belt effectiveness in preventing fatalities to drivers is examined versus a number factors (vehicle, accident, and environmental) by applying the double-pair comparison method to appropriate subsets of the Fatal Accident Reporting System (FARS) data. For each of 13 factors studied, safety belt effectiveness (the percent of fatally injured unbelted drivers who would not have been killed if they had been wearing safety belts) is estimated, as is an associated standard error of the estimate. The results, which are presented graphically, provide no evidence that safety belt effectiveness is systematically influenced by most of the factors investigated, including car mass and model year. The absence of any systematic relationship with car mass is in agreement with an earlier finding based on the pedestrian fatality exposure method; this agreement adds plausibility to the assumptions used for both the earlier and the present methods. Safety belt effectiveness is greater for single-car crashes (62 ± 5) % than for crashes involving two cars (30 ± 8) % , this difference being statistically significant at p<.02. The results suggest weakly that safety belt effectiveness is greater for two-door (48 ± 6) % than for four-door (38 ± 10) % cars, and is greater for striking (44 ± 6) % cars than for struck (27 ± 12)% cars. The above differences probably reflect higher effectiveness in frontal (or rollover) crashes than in side impacts.  相似文献   
942.
The European Union’s Green Deal and associated policies, aspiring to long-term environmental sustainability, now require economic activities to ‘do no significant harm’ to EU environmental objectives. The way the European Commission is enacting the do no significant harm principle relies on quantitative tools that try to identify harm and adjudicate its significance. A reliance on established technical approaches to assessing such questions ignores the high levels of imprecision, ambiguity, and uncertainty—levels often in flux—characterizing the social contexts in which harms emerge. Indeed, harm, and its significance, are relational, not absolute. A better approach would thus be to acknowledge the relational nature of harm and develop broad capabilities to engage and ‘stay with’ the harm. We use the case of European research and innovation activities to expose the relational nature of harm, and explore an alternative and potentially more productive approach that departs from attempts to unilaterally or uniformly claim to know or adjudicate what is or is not significantly harmful. In closing, we outline three ways research and innovation policy-makers might experiment with reconfiguring scientific and technological systems and practices to better address the significant harms borne by people, other-than-human beings, and ecosystems.  相似文献   
943.
In the fiddler crab (Uca beebei) males build a small mud pillar next to their burrow which increases their attractiveness to females. Three hypotheses were tested to explain inter-male variation in pillar-building. (1) The benefits of pillar-building are density dependent. The experimental addition of vertical structures did not support this hypothesis as there was no change in the level of pillar-building. (2) There are two classes of males (pillar-builders and non-pillar-builders). This could either be due to an alternative mating strategy, or because pillar building is age or size-dependent. There was also no support for this hypothesis. (3) Pillar-building is an honest signal of male quality dependent on body condition. A food supplementation experiment was performed. Addition of food affected several aspects of male behaviour and resulted in a two fold increase in the number of pillars built between control and food treatments (P < 0.001). However, the percentage of males building pillars did not increase significantly. Pillar building in this species has been attributed to sensory exploitation. Our results indicate that a trait which may well have evolved through sensory exploitation also appears to be condition-dependent. We emphasise that showing that an ornament or behaviour is condition-dependent does not necessarily mean that it evolved through good gene processes. However, in terms of its current selective value, pillar building may be maintained through female choice because it acts as a signal of male condition.  相似文献   
944.
Periodical cicadas emerge from below ground every 13 or 17 years in North American forests, with individual broods representing the synchronous movement of trillions of individuals across geographic regions. Due to predator satiation, most individuals escape predation, die, and become deposited as detritus. Some of this emergent biomass falls into woodland aquatic habitats (small streams and woodland ponds) and serves as a high-quality allochthonous detritus pulse in early summer. We present results of a two-part study in which we (1) quantified deposition of Brood X periodical cicada detritus into woodland ponds and low-order streams in southwestern Ohio, and (2) conducted an outdoor mesocosm experiment in which we examined the effects of deposition of different amounts of cicada detritus on food webs characteristic of forest ponds. In the mesocosm experiment, we manipulated the amount of cicada detritus input to examine if food web dynamics and stability varied with the magnitude of this allochthonous resource subsidy, as predicted by numerous theoretical models. Deposition data indicate that, during years of periodical cicada emergence, cicada carcasses can represent a sizable pulse of allochthonous detritus to forest aquatic ecosystems. In the mesocosm experiment, cicada carcass deposition rapidly affected food webs, leading to substantial increases in nutrients and organism biomass, with the magnitude of increase dependent upon the amount of cicada detritus. Deposition of cicada detritus impacted the stability of organism functional groups and populations by affecting the temporal variability and biomass minima. However, contrary to theory, stability measures were not consistently related to the size of the allochthonous pulse (i.e., the amount of cicada detritus). Our study underscores the need for theory to further explore consequences of pulsed allochthonous subsidies for food web stability.  相似文献   
945.
This study uses a combination of data from U.K. monitoringstations and from modelling undertaken with the U.K.Meteorological Office's NAME Model to investigate therelative influences of primary and secondary particulateson total PM10 levels at sites in the United Kingdom. Co-located PM10 and sulphate aerosol measurementsindicate that sulphate has a disproportionately largeinfluence on the variation of PM10 levels incomparison to its contribution to their total mass.Comparisons of measured PM10 at urban centre, roadsideand rural sites suggest that local primary sources havevery little influence on daily mean levels. NAME has beenused to model both primary particles and sulphate aerosolfrom sources across the whole of Europe. The discrepanciesbetween modelled and observed PM10 suggest that coarseparticles, such as windblown dust and resuspended roaddust,may comprise a very large, if not dominant, proportion ofobserved PM10 levels. The apparently minor role ofprimary particles (especially locally-sourced ones) raisesa number of issues regarding the suitability of current U.K.and European legislation to addressing the particle problem.  相似文献   
946.
Transitioning to renewable energy has become a global phenomenon. Attempts to explain development patterns are often fragmented, focusing on specific rationale for (un)successful deployment or the perspective of specific stakeholders. We recognize the importance for holistic insights for successful and effective environmental policy-making and planning in the context of renewable energy development. Using wind energy as an example, this paper provides methodological toolkits for utilizing content analysis (CA) to gain more holistic insights on renewable energy deployment and policy outcomes. Building on existing literature, past and ongoing research, three variations of CA are presented for understanding stakeholder conflicts surrounding wind energy development as well as public perceptions and responses to the technology across space and over time. Although newspapers are used as an example, these methodological protocols could be applied to diverse forms of data such as interviews, policy documents, reports, public meetings and letters of appeal.  相似文献   
947.
A model which quantifies the relationship between the monthly time series for CO emissions, the monthly time series in ambient CO concentration, and meteorologically driven dispersion was developed. Fifteen cities representing a wide range of geographical and climatic conditions were selected. An eight-year time series (1984–1991 inclusive) of monthly averaged data were examined in each city. A new method of handling missing ambient concentration values which is designed to calculate city-wide average concentrations that follow the trend seen at individual monitor sites is presented. This method is general and can be used in other applications involving missing data. The model uses emissions estimates along with two meteorological variables (wind speed and mixing height) to estimate monthly averages of ambient air pollution concentrations. The model is shown to have a wide range of applicability; it works equally well for a wide range of cities that have very different temporal CO distributions. The model is suited for assessing long-term trends in ambient air pollutants and can also be used for estimating seasonal variations in concentration, estimation of trends in emissions, and for filling in gaps in the ambient concentration record.  相似文献   
948.
While researchers have recently focused their attention on organizational embeddedness, occupational embeddedness has received little theoretical and empirical attention. Using multisource data on 162 employees in multiple jobs and organizations, we found that occupational embeddedness is positively related to both task performance and creativity and is negatively related to counterproductive work behavior, even after controlling for the effects of organizational embeddedness. In addition, we found that trait affect moderated the relationships of occupational embeddedness to job performance. Occupational embeddedness was more strongly related to counterproductive work behavior when trait negative affect was high, while occupational embeddedness was more strongly related to both citizenship behavior and creativity when trait positive affect was high. Results also indicated that the various components of occupational embeddedness had different effects on job outcomes. Fit had a strong positive effect on core task performance, links had a positive effect on creativity, and sacrifice had a small positive effect on citizenship behavior. The article concludes with a discussion of implications for future research and management practice. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
949.
A series of studies was performed to develop an alternative to the U.S. Environmental Protection Agency's gold standard IM240 mass-based emission test. The new IM147 test was based on the second phase of the IM240 that consists of 147 sec of transient vehicle operation. Paired IM240/IM147 tests were conducted on vehicles ranging from 1981 to 1996 to determine IM147 cutpoints and excess emissions were identified. Additionally, an optimized test procedure was developed that combined possible triplicate IM147s with improved drive trace quality control, fast-pass, and retest methods. The optimized procedure was found to provide improved vehicle preconditioning with a relatively minor decrease in excess emissions identification. Resulting identification rates ranged from 96 to 100% for hydrocarbons (HC), 93-100% for CO, and 93-100% for NOx, depending on cutpoint selection, while false failures caused by lack of vehicle preconditioning were reduced to essentially zero. Significant vehicle throughput improvements were achieved through the development of software algorithms involving modal fast-pass and retest procedures. Modal drive trace variation limits also were developed to improve test accuracy. The combination of the algorithms reduced average IM147 test times by nearly 60%.  相似文献   
950.
Although complex pricing schedules are increasingly common among water and electricity providers, it is difficult to determine whether consumers respond to changes in the pricing schedule because price changes are often confounded with simultaneous demand shocks or non-price policies. To overcome this challenge, we exploit a natural experiment - the introduction of a third price block in an increasing block pricing schedule for water - in Santa Cruz, California. Using a regression discontinuity design, we find that consumers do respond to changes in marginal price. Doubling marginal price leads to a 12% decrease in water use (500 cubic feet per bill) among high-use households.  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