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   41644篇
  免费   434篇
  国内免费   356篇
安全科学   1219篇
废物处理   1582篇
环保管理   5823篇
综合类   6254篇
基础理论   11711篇
环境理论   24篇
污染及防治   11198篇
评价与监测   2537篇
社会与环境   1795篇
灾害及防治   291篇
  2022年   268篇
  2021年   300篇
  2020年   230篇
  2019年   321篇
  2018年   563篇
  2017年   554篇
  2016年   832篇
  2015年   710篇
  2014年   1045篇
  2013年   3288篇
  2012年   1246篇
  2011年   1780篇
  2010年   1450篇
  2009年   1511篇
  2008年   1812篇
  2007年   1919篇
  2006年   1692篇
  2005年   1417篇
  2004年   1416篇
  2003年   1337篇
  2002年   1341篇
  2001年   1677篇
  2000年   1196篇
  1999年   737篇
  1998年   576篇
  1997年   576篇
  1996年   614篇
  1995年   659篇
  1994年   602篇
  1993年   547篇
  1992年   527篇
  1991年   505篇
  1990年   506篇
  1989年   534篇
  1988年   464篇
  1987年   419篇
  1986年   371篇
  1985年   401篇
  1984年   393篇
  1983年   429篇
  1982年   438篇
  1981年   391篇
  1980年   332篇
  1979年   371篇
  1978年   301篇
  1977年   254篇
  1976年   257篇
  1975年   254篇
  1973年   238篇
  1972年   273篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
The purpose of this study was to estimate the total medical care costs of individuals injured in motor vehicle crashes and in crashes where alcohol was involved. Crashes were studied that involved 2,728 vehicle occupants and 191 pedestrians with injuries as reported in 1979 by the National Accident Sampling System, a probability sample of all motor vehicle crashes occurring in the united States. Medical care costs were assigned by using Abbreviated Injury Scale codes in accordance with other published research. Determination of alcohol involvement was based on crash characteristics. Results indicate that 20.2 % of medical care costs for motor vehicle crash injuries may be due to crashes where alcohol was involved. It was estimated that alcohol-related motor vehicle crashes cost between $434 million and $483 million in medical care alone in the United States in 1979.  相似文献   
943.
Hypotheses were developed based on a coping model that views political behaviour (voice) as a fight response and turnover (exit) as a flight response to job stress. Data were collected from a group of professional, public employees and turnover dates were obtained for the group 13 months after completion of questionnaires. Multiple regression analysis was employed to test hypotheses. Stressors of interest were person-environment fit (P-E fit), role conflict (RC), and role ambiguity (RA). Psychological strains (job dissatisfaction and lowered commitment) were hypothesized to mediate the stressor-coping behaviour relationship. Turnover (TO) behaviour was the ultimate organizationally relevant outcome of coping behaviours. Job satisfaction and commitment were significantly related to intentions to leave. Political action was directly related to P-E fit and this relationship was not mediated by satisfaction or commitment. The relationship between RA and politics was moderated by commitment. Less committed employees tended to exhibit political behaviour in response to RA. Both coping responses (intentions to leave and political action) predicted significant portions of retention/turnover variance.  相似文献   
944.
Recent theory regarding the nature of organizational commitment suggests that viewing it as comprised of two dimensions, value commitment and continuance commitment, is of theoretical and practical value. This field study found the differential antecedents of these two commitment dimensions to be consistent with the March and Simon (1958) framework using the two-dimensional organizational commitment questionnaire from Mayer and Schoorman (1992). Organizational tenure, retirement benefits, education, and age were more highly correlated with continuance commitment, while felt participation, perceived prestige, job involvement, and role ambiguity were more highly correlated with value commitment. Analysis using LISREL 7 supported the pattern of relationships between the antecedents and the two commitment dimensions. © 1998 John Wiley & Sons, Ltd.  相似文献   
945.
This study investigates whether departments performing the same functions in different firms incur similar changes in structural configuration in response to industry-wide stimuli. Based on the proposition that the context of functional departments is similar across firms, changes in differentiation, integration, and perspective are hypothesized. Managers' perceptions of the validity of a series of statements to conditions five to 10 years ago and to present conditions are contrasted and show statistically significant shifts in these structural configurations. This change is confirmed by the analysis of responses of other managers in different departments within the same firms. Correlation analysis shows significant agreement among alternative measures of the same aspects of structure, and significant comovement among different structural dimensions. The later result supports the quantum theory of organizations.  相似文献   
946.
This work presents a new process for dechlorinating poly-vinyl chloride (PVC) by the use of oyster-shell waste. The process consists of milling of PVC waste with oyster-shell waste, followed by washing the milled sample with water. The milling of PVC and oyster-shell mixture results in size reduction and rupture in bonds, leading to mechanically induced reactions between the two to form CaCl2 and hydrocarbon with C=C bonds. Washing the milled mixtures with water at room temperature allows complete removal of chlorine from the milled sample. More than 95% of chlorine in PVC was removed when 2h grinding is conducted for the mixture. The present process could offer a potential route to the handling and disposal of oyster-shell and PVC wastes.  相似文献   
947.
There has been increased focus on recycling in Sweden during recent years. This focus can be attributed to external environmental factors such as tougher legislation, but also to the potential gains for raw materials suppliers. Recycling centres are important components in the Swedish total recycling system. Recycling centres are manned facilities for waste collection where visitors can bring, sort and discard worn products as well as large-sized, hazardous, and electrical waste. The aim of this paper was to identify and describe the main flows and layout types at Swedish recycling centres. The aim was also to adapt and apply production theory for designing and managing recycling centre operations. More specifically, this means using lean production principles to help develop guidelines for recycling centre design and efficient control.Empirical data for this research was primarily collected through interviews and questionnaires among both visitors and employees at 16 Swedish recycling centres. Furthermore, adapted observation protocols have been used in order to explore visitor activities. There was also close collaboration with a local recycling centre company, which shared their layout experiences with the researchers in this project.The recycling centres studied had a variety of problems such as queues of visitors, overloading of material and improper sorting. The study shows that in order to decrease the problems, the recycling centres should be designed and managed according to lean production principles, i.e. through choosing more suitable layout choices with visible and linear flows, providing better visitor information, and providing suitable technical equipment. Improvements can be achieved through proper planning of the layout and control of the flow of vehicles, with the result of increased efficiency and capacity, shorter visits, and cleaner waste fractions. The benefits of a lean production mindset include increased visitor capacity, waste flexibility, improved sorting quality, shorter time for visits and improved working conditions.  相似文献   
948.
Treatment of chromium plating process effluents with ion exchange resins.   总被引:7,自引:0,他引:7  
The surface treatment industry deals with various heavy metals, including the elements Cr, Zn, Ni, Cd, and Cu. Conventional treatments of effluents generate class I solid residue. The aim of this investigation was to study the viability of ion exchange as an alternative process for treatment of rinse water and to determine the efficacy of two ion exchange systems, System 1: "strong" cationic resin-"strong" anionic resin and System 2: "strong" cationic resin-"weak" anionic resin. Commercial resins and solutions taken from rinse tanks of chromium plating companies were used in this investigation. A two-column system, one for the cationic resin and another for the anionic resin, both with 150 ml capacity was mounted. The solution was percolated at a rate of 10 ml/min. The following solutions were used for regeneration of the resins: 2% H2SO4 for the cationic and 4% NaOH for the anionic. The percolated solutions revealed chromium contents of less than 0.25 mg/l, independent of the system used. The "strong" cationic resin-"weak" anionic resin gave excellent regeneration results. The "strong" cationic-"strong" anionic resin presented problems during regeneration, and did not release the retained ions after percolation of 2000 ml of 4% NaOH solution. It is concluded that for this type of treatment, the system composed of "strong" cationic resin and "weak" anionic resin is more appropriate.  相似文献   
949.
For both private corporations and military branches, downsizing and consolidation are becoming more commonplace. A range of environmental concerns must be addressed to effectively implement a consolidation program. A facility deactivation program can often become a minefield for an organization. Responsible personnel are typically inexperienced with the process, and this can lead to costly mistakes. This article provides insight into this topic based on experience gained with a multifacility program and related environmental issues. It emphasizes the importance of detailed, up-front, proactive project planning; a solid program management system; and accurate identification of project objectives and deliverables.  相似文献   
950.
In France, the interest in Mechanical Biological Treatment (MBT) prior to landfilling is actually growing. In the absence of acceptance criteria for the waste to be landfilled, an alternative to the intensive, high-technology MBT can only find its place in the French context if it shows substantial benefits from an environmental, economic or operational point of view. This paper presents an experiment of low-cost MBT of size reduced MSW without material splitting. The performance of an experimental, pilot-scale mechanical and biological treatment process has been studied on 37.5 Mg of raw municipal solid waste. The mechanical process has been kept simple with only coarse shredding and no material recovery. The biological treatment, which was a low-cost forced aeration process, was monitored for 25 weeks. The biogas production potential of the waste was reduced by 90% to 19 NL kgDM(-1). The initial AT4 index of 82.9 mg O2 gDM(-1) decreased to 16.0 mg O2 gDM(-1). After 25 weeks of aerobic treatment, the dry mass loss reached 37%, while the mass of waste going to landfill was reduced by 28%. The average performances of the process were explained by the biological process itself, which was not optimal, and also by the characteristics of the input waste. The high particle size of the treated waste and the high content of slowly biodegradable matter (such as paper and cardboard) may both be significant drawbacks for the biological stabilisation of waste.  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