全文获取类型
收费全文 | 1189篇 |
免费 | 60篇 |
国内免费 | 191篇 |
专业分类
安全科学 | 36篇 |
废物处理 | 10篇 |
环保管理 | 298篇 |
综合类 | 585篇 |
基础理论 | 190篇 |
污染及防治 | 36篇 |
评价与监测 | 25篇 |
社会与环境 | 191篇 |
灾害及防治 | 69篇 |
出版年
2024年 | 4篇 |
2023年 | 19篇 |
2022年 | 31篇 |
2021年 | 37篇 |
2020年 | 38篇 |
2019年 | 30篇 |
2018年 | 26篇 |
2017年 | 46篇 |
2016年 | 47篇 |
2015年 | 44篇 |
2014年 | 53篇 |
2013年 | 83篇 |
2012年 | 73篇 |
2011年 | 80篇 |
2010年 | 60篇 |
2009年 | 53篇 |
2008年 | 44篇 |
2007年 | 60篇 |
2006年 | 60篇 |
2005年 | 68篇 |
2004年 | 52篇 |
2003年 | 54篇 |
2002年 | 47篇 |
2001年 | 44篇 |
2000年 | 43篇 |
1999年 | 41篇 |
1998年 | 24篇 |
1997年 | 17篇 |
1996年 | 30篇 |
1995年 | 22篇 |
1994年 | 13篇 |
1993年 | 23篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有1440条查询结果,搜索用时 703 毫秒
951.
农产品物流组织形式及其发展趋势 总被引:1,自引:0,他引:1
阐述了农产品物流组织的内涵和组织形式,提出了农产品物流组织发展的主流方向是第三方物流企业,发展的切入重点是农产品配送中心组织,发展的新趋势是农产品虚拟物流组织,并对不同农产品物流组织形式的发展等方面进行了分析。 相似文献
952.
市场经济条件下江西农业资源的综合开发 总被引:2,自引:0,他引:2
本文简述了市场经济的基本特征及其对农业资源综合开发提出的新要求,分析了目前江西农业资源开发利用中存在的问题,提出了在社会主义市场经济体制条件下,综合开发江西农业资源,发展高产优质高效农业应遵循的原则及应采取的对策和措施。 相似文献
953.
论市场经济条件下农业资源的综合开发 总被引:3,自引:0,他引:3
本文论述了农业资源综合开发的含义与特点,社会主义市场经济对农业资源综合开发提出的新要求及对策,并以江苏省南通市为例具体探讨了如何开展与社会主义市场经济相适应的农业资源综合开发。 相似文献
954.
955.
The premise of this article is that technologies are not neutral in terms of their design objectives, their scale, and the fact that they reflect the physical and social environments in which they have developed. Specific agricultural technologies, the midwestern plow, the California tomato harvester, and various biotechnologies, are evaluated in these terms and shown to have generally predictable impacts upon rural regions and farmers. Finally, the article examines a series of major threats such as climate change that require the rethinking and restructuring of agriculture along more sustainable lines, something the can be accomplished only with a conscious recognition of the non-neutrality of technologies.This article was prepared for the conference Ethical Choice in an Age of Pervasive Technology, University of Guelph, October 25–29, 1989. 相似文献
956.
本文总结了近年来农业开发的经验,从提高开发意识、增加开发投资力度、强化开发管理机制、优化开发资金投向等方面,对农业综合开发长期发展问题进行了探讨。 相似文献
957.
D. G. Boyer G. C. Pasquarell 《Journal of the American Water Resources Association》1995,31(4):729-736
ABSTRACT: The impact on water quality by agricultural activity in karst terrain is an important consideration for resource management within the Appalachian Region. Karst areas comprise about 18 percent of the Region's land area. An estimated one-third of the Region's farms, cattle, and agricultural market value are located on karst terrain. Nitrate concentrations were measured in several karst springs in Southeastern West Virginia in order to determine the impact of animal agriculture on nitrate pollution of the karst ground water system. Karst basins with 79, 51, 16, and 0 percent agriculture had mean nitrate concentrations of 15.8, 12.2, 2.7, and 0.4 mg/l, respectively. A strong linear relationship between nitrate concentration and percent agricultural land was shown. Median nitrate concentration increased about 0.19 mg l-1 per percent increase in agricultural land. Weather patterns were also found to significantly affect the median nitrate concentrations and the temporal variability of those concentrations. Lower nitrate concentrations and lower temporal variability were observed during a severe drought period. It was concluded that agriculture was significantly affecting nitrate concentrations in the karst aquifer. Best management practices may be one way to protect the ground water resource. 相似文献
958.
959.
Michael Martin Linda Cox Stuart Nakamoto John Halloran 《Journal of the American Water Resources Association》1990,26(1):35-39
ABSTRACT: Accurately estimating the price elasticity of demand for irrigation electricity is important to major electricity suppliers such as the Bonneville Power Administration (BPA) of the Pacific Northwest. The BPA has a revenue maximization objective, and the elasticity of demand is central to its rate setting process. Several studies have attempted to estimate demand for irrigation electricity, but none has explicitly included federal agricultural policy and program variables. Tins paper discusses how agricultural programs may influence farmers irrigation decisions and thus their demand for irrigation electricity. It suggests that existing programs serve to make farmers more responsive to electricity rate increases than would otherwise be the case. Thus, studies that fail to include them may underestimate the responsiveness of farmers to electricity rate increases. 相似文献
960.
B. P. Mohanty U. S. Tim C. E. Anderson T. Woestman 《Journal of the American Water Resources Association》1994,30(4):687-703
ABSTRACT: Much of north-central Iowa is characterized by flat topography, shallow depressions, and poor natural surface drainage. Land drainage systems comprising of tile drains and agricultural drainage wells (ADWs) are used as outlets for subsurface drainage of cropland under corn and soybean production. Studies have shown that these drainage systems, mainly the ADWs, are potential routes for agricultural chemicals to underground aquifers. To protect the region's vital groundwater resource, researchers are evaluating alternative outlets ranging from complete closure of existing ADWs (and creation of wetlands) to continued use of ADWs and chemical management in a comprehensive policy framework. This paper presents the results of a study designed to provide government jurisdictions, farmers, and land managers information for assessing the impact of closing ADWs on crop production. The study couples a geographic information systems database for a 471-hectare watershed in Humboldt County, Iowa, with a groundwater flow model (MODFLOW) and an empirical crop yield loss model to predict long-term effects of complete closure of ADWs on crop production. The cropland areas inundated and the relative crop yield loss due to ADW closure are determined as a function of long-term climatic data. The results indicate that elimination of drainage outlets in the watershed could result in ponding of low-lying areas and poorly drained soils, making them unsuitable for crop production. Such wetness also decreases the efficiency of production in the no-ponding areas by isolating fields, and the crop yield loss can be reduced by an annual average of about 18 percent. 相似文献