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981.
改革开放以来,随着长春市农村城镇化水平的不断提高,农村城镇化快速推进成为该市农村区域的一个重要特征,农村城镇化的动力机制不断地趋于多元化.在这种背景下,从城乡互动、区域非均衡发展的地理学思维,利用城市地理学、区域经济学、城市与区域规划的理论和方法为基础,重点探讨长春市农村城镇化的动力机制问题. 相似文献
982.
Maeve McBride Derek B. Booth 《Journal of the American Water Resources Association》2005,41(3):565-580
ABSTRACT: An assessment of physical conditions in urban streams of the Puget Sound region, coupled with spatially explicit watershed characterizations, demonstrates the importance of spatial scale, drainage network connectivity, and longitudinal downstream trends when considering the effects of urbanization on streams. A rapid stream assessment technique and a multimetric index were used to describe the physical conditions of multiple reaches in four watersheds. Watersheds were characterized using geographic information system (GIS) derived landscape metrics that represent the magnitude of urbanization at three spatial scales and the connectivity of urban land. Physical conditions, as measured by the physical stream conditions index (PSCI), were best explained for the watersheds by two landscape metrics: quantity of intense and grassy urban land in the subwatershed and quantity of intense and grassy urban land within 500 m of the site (R2= 0.52, p > 0.0005). A multiple regression of PSCI with these metrics and an additional connectivity metric (proximity of a road crossing) provided the best model for the three urban watersheds (R2= 0.41, p > 0.0005). Analyses of longitudinal trends in PSCI within the three urban watersheds showed that conditions improved when a stream flowed through an intact riparian buffer with forest or wetland vegetation and without road crossings. Results demonstrate that information on spatial scale and patterns of urbanization is essential to understanding and successfully managing urban streams. 相似文献
983.
W. Harry Doyle 《Journal of the American Water Resources Association》1981,17(2):225-232
ABSTRACT: Urban storm water data from four catchments near Miami, Florida, were collected and compiled by the U.S. Geological Survey and were used for testing the applicability of deterministic modeling for characterizing storm water flows from small land use areas. The four sites were:
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984.
Francis J. Singer 《Environmental management》1981,5(3):263-270
Populations of introduced European wild boar, feral pigs, and combinations of both types (all Susscrola L.) inhabit thirteen areas in the National Park Service system. All parks have relatively stable populations, with the exception of Great Smoky Mountains National Park, which reported a rapidly expanding wild boar population. Suspected and documented impacts were apparently related to pig densities and sensitivity of the ecosystem; the three largest units with dense wild pig populations reported the most damage. Overall, wild pigs are a relatively minor problem for the Park Service; however, problems are severe in at least three parks, and there is potential for invasion of wild boars into several additional parks in the Appalachian Mountains. More specific information is needed on numbers of wild pigs and their impacts in the various parks. 相似文献
985.
Richard H. McCuen Darryl E. Cook Robert L. Powell 《Journal of the American Water Resources Association》1980,16(1):79-85
ABSTRACT: Recent regulations require impact statements for major water development projects, including reservoirs that will be used for water supply, recreation, and pollution control. A water quantity/quality model was developed and used for making water quality projections of a proposed reservoir in Montgomery County, Maryland. The study area is uncommon in that there is an extensive water quality data base. The results indicate that land use changes will have a significant effect on water quality and that the proposed reservoir will improve the quality of the surface waters downstream from the reservoir. A major effect of land use changes is the increase in the variability of water quality. 相似文献
986.
987.
我国城市化过程中应注意土地资源减少的几个问题 总被引:32,自引:0,他引:32
张文忠 《中国人口.资源与环境》1999,9(1):33-37
本文着重论述了在我国城市化过程中应注意的城市建设无度占用土地和耕地,以及城市土地利用结构不合理和利用率低下等土地资源减少的问题。 相似文献
988.
989.
云南地区地震灾害损失的基本特征 总被引:4,自引:0,他引:4
云南是我国地震灾害损失最为严重的地区之一。地震灾害损失评估标准实施以来,云南地区积累了较丰富的地震灾害损失评估资料。以1992~2001年云南地区破坏性地震的灾害损失评估资料为基础,分析了地震灾害损失随时间的变化特征,初步探讨了地震震级与受灾人口、人员伤亡和地震灾害经济损失等方面的关系。结果表明:(1)随着社会经济的不断发展和社会财富的不断积累,等同地震能量所造成的经济损失呈逐渐增大的趋势;(2)在空间上,由于各灾区的经济发展状况不同,等同地震能量所造成的灾害损失存在着地区差异性;(3)地震灾害损失随震级增大而增大,但二者之间并非简单的线性关系,其中生命线工程及其它特殊工程结构、重大工程设施、大型企业等的经济损失随震级的增大而以更大的比例增大。 相似文献
990.
Grazing impact of Daphnia longispina on phytoplankton and bacteria in Lake Paione Superiore (Northern Italy) was evaluated using fluorescently labeled cells in short-term in situ experiments. Structure and size distribution of Daphnia were studied weekly from its appearance in July to its decline in September. Relative importance of algae and bacteria in the diet varied over time, as did consequently the relative impact of Daphnia on the phytoplankton and bacteria populations. Biomass of bacteria in the diet of Daphnia varied from 1 to 42%, and was highest at the beginning of population development when young individuals dominated. The percent biomass of algae in the diet increased with population development, ranging from 58 to 99%. Daphnia population consumed per hour 0.04–1.8% of bacteria and 0.3–17.6% of phytoplankton abundances. 相似文献