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   10124篇
  免费   121篇
  国内免费   95篇
安全科学   293篇
废物处理   471篇
环保管理   1301篇
综合类   1211篇
基础理论   2740篇
环境理论   2篇
污染及防治   2845篇
评价与监测   731篇
社会与环境   693篇
灾害及防治   53篇
  2022年   103篇
  2021年   79篇
  2020年   68篇
  2019年   76篇
  2018年   154篇
  2017年   144篇
  2016年   244篇
  2015年   176篇
  2014年   243篇
  2013年   760篇
  2012年   306篇
  2011年   460篇
  2010年   374篇
  2009年   411篇
  2008年   488篇
  2007年   491篇
  2006年   434篇
  2005年   385篇
  2004年   337篇
  2003年   391篇
  2002年   336篇
  2001年   505篇
  2000年   332篇
  1999年   197篇
  1998年   139篇
  1997年   135篇
  1996年   144篇
  1995年   164篇
  1994年   129篇
  1993年   104篇
  1992年   124篇
  1991年   119篇
  1990年   132篇
  1989年   130篇
  1988年   98篇
  1987年   87篇
  1986年   66篇
  1985年   91篇
  1984年   92篇
  1983年   86篇
  1982年   86篇
  1981年   74篇
  1980年   62篇
  1979年   70篇
  1978年   47篇
  1977年   53篇
  1976年   48篇
  1975年   55篇
  1974年   53篇
  1973年   53篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
791.
During the 1976–77 drought, three principal mechanisms were used to reduce water use in Utah communities: price increases, maximum monthly use restrictions, and restrictions on outdoor watering times. A regression model was developed to explain observed changes in water use, with price, type of restriction, household size, and summer rainfall as independent variables. For an average system, a 1 percent increase in price would reduce water use by 0.07 to 0.09 percent. A 1 percent increase in outdoor watering time restriction reduces use by 0.064 to 0.075 percent. A 1 percent increase in quantity restrictions leads to a reduction in water use of 0.014 to 0.054 percent. The effectiveness of rationing policies is influenced by system characteristics. For example, outdoor watering time restrictions were less effective in systems with above average household size and below average monthly use.  相似文献   
792.
A multivariate statistical method for analyzing spatial patterns of water quality in Georgia and Kansas was tested using data in the US Environmental Protection Agency's STORET data system. Water quality data for Georgia and Kansas were organized by watersheds. We evaluated three questions: (a) can distinctive regional water quality patterns be detected and predicted using only a few water quality variables, (b) are regional water quality patterns correlated with terrestrial biotic regions, and (c) are regional water quality patterns correlated with fish distributions? Using existing data, this method can distinguish regions with water quality very different from the average conditions (as in Georgia), but it does not discriminate well between regions that do not have diverse water quality conditions (as in Kansas). Data that are spatially and temporally adequate for representing large regions and for multivariate statistical analysis are available for only a few common water quality parameters. Regional climate, lithology, and biotic regimes all have the potential to affect water quality, and terrestrial biotic regions and fish distributions do compare with regional water quality patterns, especially in a state like Georgia, where watershed characteristics are diverse. Thus, identifiable relationships between watershed characteristics and water quality should allow the development of an integrated landaquatic classification system that would be a valuable tool for resource management. Because geographical distributions of species may be limited by Zoogeographic and environmental factors, the recognition of patterns in fish distributions that correlate with regional water quality patterns could influence management strategies and aid regional assessments.  相似文献   
793.
ABSTRACT: Texas is one of the states in which limitations in water supplies could severely constrain economic growth in certain areas. The traditional planning approach for addressing this problem has involved devising schemes for large water development projects, which for many years included the importation of water from other states. Now the attitude towards water resource management is changing, and it is generally agreed that better management of existing supplies is the preferred approach. In this paper we review some of the changes that have recently occurred in Texas, including attempts to streamline the water institutions in such a way that they might be more responsive to the need for more comprehensive management of water resources statewide, with greater emphasis on social and environmental concerns.  相似文献   
794.
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   
795.
Using structural equations, we estimated the relationship between employees' experiences of seven job conditions, that have been identified as potential job stressors, and psychological distress in a random sample of 504 full-time employed men and women in dual-earner couples. The seven job conditions were: skill discretion, decision authority, schedule control, job demands, pay adequacy, job security, and relations with supervisor. We found that two job conditions — skill discretion and job demands — were related to psychological distress, whereas five other conditions were not. These findings lend partial support to Karasek's job demand — job control model. In our analysis, skill discretion, one of the two components of job control (referred to jointly as decision latitude) was related to distress, however, decision authority, the second component, was not. A third aspect of control, schedule control, was also unrelated to distress. For full-time employed women and men in dual-earner couples, the additive effects of feeling concerned about having to do dull, monotonous work and having to work under pressure of time and conflicting demands were associated with psychological distress. Finally, the magnitude of the relationships between these job experiences and psychological distress did not differ between men and women.  相似文献   
796.
Five extracellular PHB depolymerases of bacteria isolated from various sources were purified to electrophoretic homogeneity and compared with known extracellular PHB depolymerase fromAlcaligenes faecalis T1. The molecular mass of these enzymes were all around 40–50 kDa. Nonionic detergent, diisopropylfluorophosphate and dithiothreitol inhibited the PHB depolymerase activity of all these enzymes. Trypsin abolished PHB depolymerase activity, but not theD-3-hydroxybutyric acid dimer hydrolase activity of all the enzymes. These results showed that the basic properties of these PHB depolymerases resemble those of theA. faecalis T1 enzyme. Analysis ofN-terminal amino acid sequence of the purified enzymes revealed that these enzymes includingA. faecalis T1 enzyme fall into three groups.  相似文献   
797.
Production methods for food from U.K. livestock industries (milk, dairy products, meat, eggs, fibre) are undergoing substantial change as a result of the need to respond to environmental and animal welfare awareness of purchasing customers, and to espouse the principles of environmental protection. There appears to be a strong will on the part of livestock farmers to satisfy the environmental imperative, led by the need to maintain market share and by existing and impending legislation. There has been support forthcoming in the form of Government-sponsored scientific research and technological development to provide the necessary framework for new environmentally sensitive practices. The agricultural community has itself made substantial responses to market demand through the inception of Farm Assured Quality Assurance Schemes. These appear to have a more sustainable future than the extremes of organic farming and free-range practices. Pollution of agricultural land with nitrate and phosphate by intensive livestock industries is a greater problem in some parts of continental Europe than it is in the U.K. The distribution of livestock out of intensive units and into mixed farming systems, would require substantial restructuring of the industry. Many of the animal welfare requirements which have been forwarded as a part of the environmental agenda for agriculture have been voluntarily accepted by livestock producers. However, some major aspects, such as alternative housing systems for pigs and poultry, remain unresolved. Analysis of the science and technology support for the environmental imperative, especially from Government sources, would suggest that, although dramatically increased in recent years, environmentally orientated research remains a relatively small proportion of the whole. Whilst a movement away from governmental funding of volume production appears to be justifiable, there has not been an equivalent balancing of effort toward funding for product quality, sustainability, environmental protection and animal welfare. Nevertheless, the university education system is producing a generation of more environmentally aware agricultural science graduates who are opting to pursue Government-sponsored environmentally orientated postgraduate research programs.  相似文献   
798.
Summary Rivers are the main source of water in India, and are particularly used for agricultural irrigation and drinking water supply. As most of the rivers pass through agricultural fields, they are subject to contamination with the different insecticides used for crop protection. Residues of persistent organochlorines, which are still used in large quantities in India, are found in water from many Indian rivers. In certain rivers, the concentrations of DDT, aldrin and heptachlor are often present in excess of their guideline limits. Although the concentration level of gamma-HCH is well below the guideline limit, the accumulation of the carcinogenic beta isomer is a matter of great concern. A few organophosphorus insecticides have also been detected in river water. Recently, some organochlorine insecticides have been banned from use in India. The use of new, readily biodegradable insecticides and biocides in agriculture and public health programmes offers some optimism.Drs Satya P. Mohapatia, Vijay T. Gajbhiye and Narendra R. Agnihotri all work within the Division of Agricultural Chemicals at the above address. Dr Manju Raina is employed by the Ganga Project Directorate of the Ministry of Environment and Forests, New Delhi 11003, India.  相似文献   
799.
800.
Summary The author was a consultant, assigned from the United Nations Development Programme (UNDP), to provide technical assistance to China's environmental pollution research and control. His assignment in China from September 1 through October 8, 1983 was filled with visits and meetings at key research institutes, universities, and regulatory agencies in the cities of Beijing (Peiking), Shanghai, Hangchow, Zhuji and Zhiaxing (Fig. 1). Trips to famous historical sites and scenic points in and around those cities were squeezed in between the heavily scheduled meetings. Dr Shen was born and educated in China through college. This is a report of his first trip back to his homeland since he left 35 years ago. His ability to communicate with the Chinese professionals and social strata in their native tongue provided him with a greater advantage in understanding the current status of China's environmental sciences and technology in preventing air, water, and land pollution. His contribution lies not only in the technical transfer of environmental sciences and engineering, but also in strengthening the ties of cooperation and communication between American and Chinese professionals. Dr Shen is a senior research scientist with the New York State Department of Environmental Conservation and an adjunct faculty member of the Division of Environmental Sciences, Columbia University.  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