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   1408篇
  免费   187篇
  国内免费   134篇
安全科学   545篇
废物处理   12篇
环保管理   237篇
综合类   370篇
基础理论   299篇
环境理论   2篇
污染及防治   38篇
评价与监测   9篇
社会与环境   134篇
灾害及防治   83篇
  2024年   3篇
  2023年   38篇
  2022年   57篇
  2021年   74篇
  2020年   77篇
  2019年   92篇
  2018年   61篇
  2017年   85篇
  2016年   105篇
  2015年   63篇
  2014年   55篇
  2013年   109篇
  2012年   107篇
  2011年   83篇
  2010年   71篇
  2009年   72篇
  2008年   70篇
  2007年   78篇
  2006年   64篇
  2005年   50篇
  2004年   50篇
  2003年   44篇
  2002年   27篇
  2001年   23篇
  2000年   26篇
  1999年   21篇
  1998年   19篇
  1997年   18篇
  1996年   15篇
  1995年   11篇
  1994年   9篇
  1993年   6篇
  1992年   2篇
  1990年   4篇
  1989年   2篇
  1987年   3篇
  1986年   1篇
  1985年   2篇
  1984年   2篇
  1983年   1篇
  1982年   6篇
  1981年   3篇
  1980年   2篇
  1979年   3篇
  1978年   2篇
  1977年   1篇
  1973年   4篇
  1972年   2篇
  1971年   2篇
  1970年   2篇
排序方式: 共有1729条查询结果,搜索用时 187 毫秒
101.
In many salmonid species, males exhibit morphological dimorphism associated with alternative mating behaviors. ”Precocious males” have a small body size with little or no development of sexual characters and adopt sneaking to gain access to females, while ”migratory males” of large body size and well-developed secondary sexual characters fight. We quantified selection on precocious male parr of masu salmon (Oncorhynchus masou) under simulated natural conditions to examine the contribution of morphology to sneaking success. In contrast to the prediction that sneaking behavior favors small body size, we detected selection favoring relatively large body size for sneaking success. This selection pressure was caused by the dominance hierarchy within parr and may have been facilitated by indifference of dominant migratory males to parr. Unlike the secondary sexual characters exhibited by migratory male salmon, such as the hooked snout and humped back, no morphological characters other than body size contributed to the reproductive success of masu salmon parr. This non-contribution may have been responsible for the lack of development of sexual characters in precocious males. Received: 15 November 1999 / Accepted: 20 May 2000  相似文献   
102.
Natural hazards affect development and can cause significant and long-term suffering for those affected. Research has shown that sustained long-term disaster preparedness combined with appropriate response and recovery are needed to deliver effective risk reductions. However, as the newly agreed Sendai framework recognises, this knowledge has not been translated into action. This research aims to contribute to our understanding of how to deliver longer term and sustained risk reduction by evaluating the role of political decentralisation in disaster outcomes. Specifically, we investigate whether countries which devolve power to the local level experience reduced numbers of people affected by storms and earthquakes, and have lower economic damage. Using regression analysis and cross-country data from 1950 to 2006, we find that, in relation to both storms and earthquakes, greater transfers of political power to subnational tiers of government reduce hazard impacts on the population. The downside is that more politically decentralised countries, which are usually wealthier countries, can increase the direct economic losses associated with a natural hazard impact after the storm or earthquake than those which are more centralised. However, overall, it seems advantageous to give subnational governments more authority and autonomy in storm and earthquake risk planning.  相似文献   
103.
人群疏散行为仿真技术研究   总被引:3,自引:1,他引:2  
提出并建立了一种人群疏散仿真模型。针对疏散空间中障碍物的动态布局,采用网格法获得各障碍物包围盒坐标,依据最短路径原则采用几何法确定每个个体起始疏散路径,解决了人群疏散的空间连续性问题。针对人群疏散时个体之间的差异性,依据个体与个体之间的作用力、摩擦力动态改变个体的行进方向,以及依据人群密度采用人群疏散速度模型实时确定每个个体的运动速度,解决了个体之间的动态避碰、绕行和超越等问题。针对人群疏散时多个出口的选择问题,提出了把出口拥挤状态与个体心理慌乱状态相结合的出口选择方法。最后采用粒子系统实现了上述人群疏散行为的二维仿真并取得了较好的效果。  相似文献   
104.
汪毅  何淼 《资源开发与市场》2012,(12):1105-1108,1117,F0004
创意产业集聚区在促进创意产业发展、优化城市空间结构等方面具有重要意义,而以满足创意阶层特征和需求的创意产业集聚区内部公共空间规划的研究相对较少。从创意阶层交往的“心理-行为-空间”这一互动视角出发,选取南京具有代表性的“创意东8区”为研究对象,通过调查问卷、深入访谈和实地观察对创意阶层的“交往心理-交往行为-交往空间”进行了研究。在此基础上,从人口交往空间、中心交往空间、节点交往空间、道路交往空间等方面提出符合创意阶层心理和行为特征,并能促进交往产生的外部交往空间规划设计建议。  相似文献   
105.
We examined the behavior of individual mature female Mediterranean fruit flies (medflies), Ceratitis capitata (Wiedemann), transferred from a holding cage without fruit to a clean host kumquat fruit already occupied by another medfly female engaged in ovipositional behavior. A significantly greater proportion of transferred (=test) ovipositionally naive females initiated ovipositor boring into a fruit in the presence than in the absence of an occupying medfly. Moreover, test females commenced boring significantly sooner in the presence than in the absence of another medfly. Interestingly, similar results occurred when a test medfly was transferred to a kumquat occupied by an ovipositing female oriental fruit fly, Bactrocera dorsalis Hendel. In contrast, there was no enhancement of propensity to bore when a test medfly was transferred to a kumquat occupied by a female Biosteres arisanus (Sonan), a parasitoid attacking medfly eggs. The principal proximate stimulus giving rise to the higher tendency to oviposit of a test medfly in the presence of an occupying medfly or oriental fruit fly appeared to be wing-waving by the occupant during an encounter. We consider our findings to be good evidence of socially facilitated ovipositional behavior in ovipositionally naive medflies, and suggest that such females may benefit from acquisition of a cue demonstrating the acceptability of a host for oviposition. Received: 7 July 1997 / Accepted after revision: 30 August 1997  相似文献   
106.
Although it is clear that coworker absenteeism, tardiness, and turnover can influence an employee's actions, scholars have yet to consider the impact of relational demography on the adoption of these behavioral norms. Inspired by social identity, situational strength, and attraction‐selection‐attrition theories, we proposed that individuals who differ from their coworkers in age, sex, or racioethnicity would feel threatened by their outnumbered status and subsequently motivated to be absent, tardy, or more likely to turnover. However, we expected coworker withdrawal behavior to moderate whether or not dissimilar personnel act on these desires. Results from hierarchical multilevel modeling analyses of data from 470 U.S. call center workers nested in 51 work groups revealed that racioethnic dissimilarity was positively related to time‐lagged changes in absenteeism and tardiness as well as heightened turnover likelihood. These effects emerged only among employees whose coworkers engaged in greater withdrawal behavior. Importantly, racioethnically dissimilar employees working in more permissive climates (i.e., those with high levels of coworker absenteeism, tardiness, or turnover) exhibited the greatest increases in absenteeism and tardiness over three months and had the highest supervisor‐rated turnover likelihood. Implications for diversity management are discussed. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
107.
This paper examines the role of affect as a linking mechanism between experiences at work (perceived prosocial impact and situational constraints) and two distinct components of proactive work behavior (issue identification and implementation). Based on a dual‐tuning perspective, we argue that both positive affect and negative affect can be beneficial for proactive work behavior. Multi‐level path analysis using daily‐survey data from 153 employees showed that perceived prosocial impact predicted positive affect and that situational constraints as a typical hindrance stressor predicted negative affect. Negative affect, in turn, predicted issue identification, and positive affect predicted implementation. Overall, our study suggests that both positive and negative affects can be valuable in the organizational context by contributing to distinct components of proactive behavior. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
108.
Management of fresh water resources meets a range of often conflicting interests. Waterways usually run across political and administrative borders and hence make management difficult and collective action politically challenging. In order to meet these challenges, multi-level bioregional approaches to water management have been called for. Such an approach is institutionalised in the EU's Water Framework Directive (WFD). This paper presents the experiences of the Morsa water sub-district in southern Norway, a pilot for implementing the WFD. The paper discusses Morsa in the light of four principles for multi-level water governance: management on a bioregional scale; polycentric governance; public participation; and an experimental approach to water governance. Contrary to widely held assumptions that collective action in polycentric networks will be difficult because actors will follow their own narrow interests, the findings demonstrate how this is not an absolute truth, and how social action cannot be fully explained by rational action theories. The analysis concludes that the relative success of Morsa relates to a complex of factors, including openness of practices and active involvement of key actors, strong but including leadership, and a knowledge based ‘hybrid’ type of multi-level network combining horizontal and vertical network governance.  相似文献   
109.
绿灯倒计时信号对驾驶行为的影响   总被引:1,自引:0,他引:1  
为揭示绿灯倒计时信号对交叉口交通安全的影响,针对不同交通负荷与信号控制方式下的驾驶行为开展研究。选择大连市内的倒计时信号交叉口与非倒计时信号交叉口各2处,开展车辆行驶速度及不良驾驶行为调查。用数理统计方法,对比分析2类交叉口在平峰与高峰时段的车辆行驶速度特性,同时对比分析上述不同条件下闯黄灯及违规变道行为的发生数量。研究表明,绿灯倒计时信号在绿灯时间末期,会诱发一部分驾驶员加速行驶通过交叉口;绿灯倒计时信号在平峰时段对闯黄灯行为数量的影响较小,而对违规变道行为的数量有显著影响。  相似文献   
110.
National authorities in many countries aim at having climate change adaptation mainstreamed into existing policy domains in order to achieve coherence and synergies, and to avoid mal-adaptation. Because of local variations in climate change impacts, the lion's share of climate adaptation work will have to take place at the local level. This means also that the mainstreaming process needs to occur locally. This article examines the mainstreaming of climate change adaptation into existing sectors in five Norwegian municipalities. Applying theories of mainstreaming and policy integration we find that policy development is slower, but perhaps more robust in the municipalities that have chosen a horizontal, cross-sectoral approach to mainstreaming than in the municipalities that have chosen a vertical sector approach to mainstreaming.  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