全文获取类型
收费全文 | 2359篇 |
免费 | 120篇 |
国内免费 | 297篇 |
专业分类
安全科学 | 326篇 |
废物处理 | 131篇 |
环保管理 | 413篇 |
综合类 | 1291篇 |
基础理论 | 233篇 |
环境理论 | 2篇 |
污染及防治 | 179篇 |
评价与监测 | 39篇 |
社会与环境 | 135篇 |
灾害及防治 | 27篇 |
出版年
2024年 | 4篇 |
2023年 | 22篇 |
2022年 | 31篇 |
2021年 | 64篇 |
2020年 | 51篇 |
2019年 | 40篇 |
2018年 | 52篇 |
2017年 | 67篇 |
2016年 | 68篇 |
2015年 | 69篇 |
2014年 | 105篇 |
2013年 | 143篇 |
2012年 | 134篇 |
2011年 | 200篇 |
2010年 | 135篇 |
2009年 | 164篇 |
2008年 | 100篇 |
2007年 | 189篇 |
2006年 | 178篇 |
2005年 | 120篇 |
2004年 | 121篇 |
2003年 | 118篇 |
2002年 | 97篇 |
2001年 | 97篇 |
2000年 | 92篇 |
1999年 | 65篇 |
1998年 | 46篇 |
1997年 | 40篇 |
1996年 | 27篇 |
1995年 | 34篇 |
1994年 | 25篇 |
1993年 | 17篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有2776条查询结果,搜索用时 46 毫秒
241.
长江流域冬季农业主要作物的耕地竞争机制及案例研究 总被引:2,自引:0,他引:2
长江流域是世界最大的油菜籽生产带,增加油菜籽种植面积和产量是提高我国油料供给能力的重要方面。在该区域,油菜籽和小麦是最主要的冬季农作物,也是具备耕地竞争关系的2种主要作物。在对长江流域这两种作物的耕地竞争机制进行理论分析的基础上,系统阐述了耕地竞争力各影响因素之间的内在联系;根据实地调查的数据与结果,对油菜籽和冬小麦的耕地竞争关系进行深入分析。研究结果显示:油菜籽耕地竞争力的影响因素主要有单产、收购价格、机械化水平、劳动力价格及国家政策;稳定油菜籽收购价格是提高油菜籽耕地竞争力的关键;随着农村劳动力成本的提高,油菜籽生产的机械化水平成为影响种植效益的重要因素;国家补贴的影响作用不大。另外,结论也表明长江流域存在很大的油菜籽生产潜力。 相似文献
242.
Brian Furze 《Journal of Agricultural and Environmental Ethics》1989,2(1):59-67
Food is a basic human need and therefore a basic human right. While food output has increased to a level where there is enough food produced to feed the world, still millions starve. Using the concept of capitalist world economy as a framework, this paper provides a structural analysis of the food production and distribution system within monopoly capitalism and its implications for countries of the underdeveloped world. Focusing on the impact of a dominant world food supply system on indigenous systems (particularly through the rise of science, technology, and monopoly capital), considerations relating to environmental use and food production and distribution are raised. Finally a call is made for a new agricultural ethic. 相似文献
243.
Environmental degradation, competition for resources, increasing food demands, and the integration of agriculture into the
international economy threaten the sustainability of many food production systems. Despite these concerns, the concept of
sustainable food production systems remains unclear, and recent attempts to appraise sustainability have been hampered by
conceptual inconsistencies and the absence of workable definitions. Six perspectives are shown to underpin the concept. Environmental
accounting identifies biophysical limits for agriculture. Sustained yield refers to output levels that can be maintained continuously.
Carrying capacity defines maximum population levels that can be supported in perpetuity. Production unit viability refers
to the capacity of primary producers to remain in agriculture. Product supply and security focuses on the adequacy of food
supplies. Equity is concerned with the spatial and temporal distribution of products dervied from resource use. Many studies
into sustainable agriculture cover more than one of these perspectives, indicating the concept is complex and embraces issues
relating to the biophysical, social, and economic environments. Clarification of the concept would facilitate the development
of frameworks and analytical systems for appraising the sustainability of food production systems.
LRRC Contribution No. 90–46. 相似文献
244.
王文杰 《中国安全科学学报》1991,(2)
本文试用系统论、控制论和信息论的观点探索我国安全生产宏管理模式。文中主要分析了生产安全系统的内涵;行业生产安全系统的内涵;以及生产安全系统的宏观控制的内涵。并指出了行业生产安全系统是生产安全系统的主体控制系统,劳动安全监察系统是生产安全系统的强化控制系统。 相似文献
245.
本文提出安全科学技术也是第一生产力的观点。文中简析了科学、技术和科学技术的内涵及其相互关系;研究了科学技术与生产力的关系;阐述安全科学技术也是第一生产力:探讨了发展高科技与安全科学技术的关系;安全科学技术发展中应注意的问题。 相似文献
246.
Roger B. Long 《Journal of the American Water Resources Association》1987,23(6):1117-1124
ABSTRACT: Pressure is increasing in the western United States to reallocate water from irrigated agriculture to other competitive uses. Since water is normally allocated through water rights and not necessarily by the price system, the question of economic efficiency is a continual concern. Study results show that returns per acre-foot of water used in western irrigation are quite high and are closely tied to the livestock industry. Returns per acre-foot of water used for crops ranged from $60 to $1,500. When water was used to support livestock, returns per acre-foot ranged from $100 to $600. Clearly, losses of water supply that reduced irrigation production could also lower farm income significantly. Estimated returns also show what alternative uses would have to pay for water under competitive market conditions. Production elasticities are also shown for various states. 相似文献
247.
Paul N. Wilson Teddy J. Goldammer James C. Wade 《Journal of the American Water Resources Association》1988,24(1):1-9
ABSTRACT: Urban wastewater can be a valuable source of water and plant nutrients for agricultural producers, particularly in arid regions. The scientific literature reveals cautious optimism concerning the biological, institutional, and economic viability of irrigating crops with secondary-treated effluent. A derived effluent demand function for agricultural producers near Tucson, Arizona, reveals a potential annual demand of 11,000 acre-feet under present price and proposed delivery system conditions. In this case, wastewater could be exchanged for ground water and both the urban and rural areas would gain. 相似文献
248.
249.
本文分析了江苏省近几十年来、特别是80年代以来冬季气温的变化特征,根据农业灾害发生的条件,讨论了“暖冬”对农业生产及农业灾害的影响,为农业生产部门和防灾抗灾部门决策提供科学依据. 相似文献
250.
A. L. Jensen 《Environmental management》1984,8(2):135-140
Conventional surplus production models indicate that destruction of fish populations by overfishing is difficult, if not impossible, but catastrophic declines in abundance of exploited populations are common. Surplus production models also do not predict large continuing fluctuations in yield, but large fluctuations in yield are common. Conventional surplus production models assume that fisheries do not impact the population's capacity to increase, but changes in age structure or a decrease in age-specific fecundity resulting from fishing can decrease the coefficient of increase. A surplus production model is developed in which fishing reduces the capacity of a population to increase; the model is applied to describe the fluctuations observed in yield of lake herring (Coregonus artedii) from the upper Great Lakes. The fisheries of the Great Lakes were decimated by the combined effects of heavy fishing and a changing environment. For some species, yield increased to high levels and then the fisheries collapsed; for other species, yield and effort fluctuated greatly. 相似文献