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   3644篇
  免费   371篇
  国内免费   547篇
安全科学   494篇
废物处理   26篇
环保管理   463篇
综合类   1730篇
基础理论   877篇
环境理论   1篇
污染及防治   123篇
评价与监测   305篇
社会与环境   364篇
灾害及防治   179篇
  2024年   9篇
  2023年   95篇
  2022年   109篇
  2021年   163篇
  2020年   135篇
  2019年   131篇
  2018年   109篇
  2017年   168篇
  2016年   204篇
  2015年   193篇
  2014年   185篇
  2013年   259篇
  2012年   356篇
  2011年   339篇
  2010年   257篇
  2009年   233篇
  2008年   184篇
  2007年   229篇
  2006年   210篇
  2005年   192篇
  2004年   128篇
  2003年   103篇
  2002年   86篇
  2001年   59篇
  2000年   77篇
  1999年   61篇
  1998年   53篇
  1997年   41篇
  1996年   35篇
  1995年   24篇
  1994年   35篇
  1993年   28篇
  1992年   13篇
  1991年   18篇
  1990年   10篇
  1989年   6篇
  1988年   3篇
  1987年   3篇
  1986年   3篇
  1985年   2篇
  1984年   1篇
  1982年   2篇
  1981年   3篇
  1980年   3篇
  1978年   1篇
  1977年   1篇
  1973年   1篇
  1972年   1篇
  1971年   1篇
排序方式: 共有4562条查询结果,搜索用时 375 毫秒
991.
我国东部七省生态系统对酸沉降的相对敏感性   总被引:1,自引:0,他引:1  
讨论了影响亚热带生态系统对酸沉降敏感性的生态因子,提出了敏感性等级划分的指标体系,根据大量资料编制了我国东部7省1市生态系统对酸沉降相对敏感性分区图。结果表明,在研究区域内生态系统的敏感性有相当大的差别,极敏感区和敏感区面积占全区总面积的1/3以上,主要分布在福建、浙江、江西3省。  相似文献   
992.
影响高锰酸盐指数测定准确性的主要因素有样品酸度、蒸馏水水质、高锰酸钾溶液浓度、水浴加热温度和滴定时间。通过环境标准样品的分析试验,考察这5个因素对高锰酸盐指数的影响程度;  相似文献   
993.
修复受污染水体的潜流人工湿地微生物多样性研究   总被引:2,自引:0,他引:2  
进行了潜流人工湿地修复受污染水体试验研究,并比较单一植物与单一填料系统与多种植物系统与多种填料系统的处理效果.运用PCR-DGGE技术研究3种不同类型的潜流人工湿地中微生物种群结构,结合多样性分析和聚类分析方法,分析了人工湿地微生物种群结构特征.  相似文献   
994.
Seres2000型高锰酸盐指数仪器监测数据质量分析   总被引:3,自引:0,他引:3  
水质自动站测定的高锰酸盐指数(CODMn)数据与实验室标准方法测定结果常常产生较大的偏差。作者旨在通过自动仪器与实验室标准方法的比对测试,查找自动监测结果的偏差原因,同时分析和探讨如何保障仪器的正常运行,保持自动仪器监测的数据质量,达到与实验室标准监测结果的统一。  相似文献   
995.
In this study the frequencies of PM10 (as key urban pollutant) in 14 key environmental protection cities in northern China were analyzed. It follows that the PM10 concentration in the high-frequency period is higher with an extent 0.009–0.066 mg m−3 than in the low-frequency period of 2001–2002. Further the impacts of three kinds of dust events on the PM10 concentration in four cities (Beijing, Hohhot, Xi’an and Lanzhou) were explored. The results showed that different kinds of dust events have different influences on variation of PM10 concentration in these four cities. In Lanzhou and Hohhot, which are near the source areas of dust events, the contribution degree of these three dust events to the PM10 is: floating dust>dust storm>blowing dust. Whereas, in Beijing and Xi’an situated in dust event passing areas, the mean value of PM10 concentration is higher in blowing dust than in floating dust (no dust storm). In addition, the influences of dust events on PM10 concentration are different in the cities on different dust event paths. In Beijing and Hohhot (on the northern path), the high PM10 concentration is usually caused by blowing dust. But in both Lanzhou and Xi’an (on the western/northwestern path) the high PM10 pollution concentration is usually caused by floating dust.  相似文献   
996.
Abstract:  We examined six groups of taxa—woody plants, aquatic and terrestrial herpetofauna, small terrestrial birds, orchids, and Orthoptera—to determine their efficiency as biodiversity indicators in the Dadia Reserve in northern Greece. We investigated the indicator value of each group by examining the degree of congruence of its species-richness pattern with that of the other groups and the efficiency of its complementary network in conserving the other groups and biodiversity. The two techniques differed in many respects in their outputs, but they both showed woody plants as the best biodiversity indicator. There was in general low congruence in the species richness patterns across the different groups. Significant relationships were found between woody plants and birds, Orthoptera and terrestrial herpetofauna, and birds and aquatic herpetofauna. None of the optimal complementary networks of the groups we examined protected all species of the other groups. Nevertheless, the complementary network of woody plants adequately conserved all groups except orchids. We conclude that the principle of complementarity must be integrated into the methodology of evaluating an indicator. In an applied context, our results provide a scientific background on which to base a biomonitoring program for the Dadia Reserve. In a wider scope, if the group of woody plants prove an adequate biodiversity indicator for other Mediterranean areas as well, this will be important because it will facilitate conservation-related decisions for the entire Mediterranean region.  相似文献   
997.
Fluoride contamination in soil was studied in the vicinity of a hot spring in Nayagarh district of Orissa. Both bulk soil from 0 to 30 cm depth and profile soils from 0 to 90 cm depth were analyzed for total fluoride (Ft) and 0.01 M CaCl2 extractable fluoride (Fca), major elements, pH, EC and Organic Carbon (OC). High concentrations of both Ft and Fca were observed in the area surrounding the hot spring and the village of Singhpur. Principal factor analysis (PFA) on the parameters of the bulk soils suggests that two major chemical processes due to three factors, control the soil geochemistry of the area. Factor-1 contributes 37.11% of the total variance and is strongly loaded with Al, Si, Fe, Ftand Fca, and explains the fluoride enrichment of the soil, whereas the second and the third factors contribute 16.6 and 12.2%, respectively and explain the controlling process of carbonate precipitation and soil alkalinity. Multiple regression analysis of the scores of the factors was performed to derive a fluoride contamination index in soil. The magnitude of the factor effect on the contamination index follows the order of Factor-1 > Factor-2 > Factor-3. The spatial distribution of the contamination index is used to classify the area into highly contaminated, moderately contaminated and uncontaminated zones.  相似文献   
998.
Effects of New Forestry Practices on Rare Epiphytic Macrolichens   总被引:5,自引:0,他引:5  
Abstract:  The preservation of key habitats is included in modern forest-management practices as one of the main means to preserve biodiversity in northern European production forests. I examined the distribution patterns and persistence of occurrence of rare epiphytic macrolichens in a predominantly unprotected forest landscape with an area of 278 km2 in southern Finland. Occurrence data of macrolichens in two key habitats, rock outcrops and mires, were compared with data from production forests. The density of populations of rare macrolichens was 50-fold higher on rock outcrops and 25-fold higher on mires than in production forests. Most rare species of epiphytic macrolichens were found only in key habitats. In modern, intensively managed forest landscapes, rock outcrops appeared to represent the main habitats for rare macrolichens as a result of the long-term continuity of old trees. Most macrolichen occurrences represented very small populations with a high extinction risk. Of the populations found in 1989–1995 in key habitats, 51% had disappeared, by 2000–2001, mainly as a result of forestry activities. The disappearance of populations significantly exceeded the rate of establishment of new populations. My results emphasize the importance of key habitats for declining forest species. There is also a need to improve and sharpen the guidelines for delimiting and managing key habitats in order to halt the continued decline of epiphytic macrolichens.  相似文献   
999.
外来入侵杂草空心莲子草对植物生物多样性的影响   总被引:2,自引:0,他引:2  
利用样方法调查了南京市空心莲子草(Alternantheraphiloxeroides)生长生境中杂草的种类和分布。结果表明,南京市秋季空心莲子草分布样点有杂草30科101种,其中以禾本科、菊科、蓼科居多。主成分分析表明,影响杂草分布的主要因素是土壤水分条件和人为干扰强度。经Q型分析, 24个样点可划分为3个聚类群:聚类群Ⅰ包括的样点均分布在路边和田边开阔地以及小河、小沟和湖的岸边,以马唐、狗尾草和牛筋草为优势种;聚类群Ⅱ的样点都是农田隔离带如田埂以及农田中的沟壑,以波斯婆婆纳、碎米莎草、野塘蒿和铁苋菜为优势种;聚类群Ⅲ的样点以菜地和果园为主,以马唐、香附子、马齿苋和黄鹌菜为优势种。分析了空心莲子草重要值与物种丰富度之间的关系,当空心莲子草重要值大于1. 5时,样方物种丰富度随重要值的增加而减小。2者之间具有显著相关性,表明空心莲子草的入侵对生物多样性有不利影响。  相似文献   
1000.
A Comparison of Logging Systems and Bat Diversity in the Neotropics   总被引:4,自引:0,他引:4  
Abstract:  Evaluating logging systems to determine which are most compatible with the maintenance of biodiversity is of prime importance if tropical forests are to be managed in a sustainable way. Bats are model taxa for this purpose. Two different logging systems are used in the natural forest of the Victoria-Mayaro Forest Reserve in Trinidad: open range and periodic block. Open range is a continuous harvesting system and, in common with most methods used to log tropical forests worldwide, has few harvest controls other than girth limits for selected species. Periodic block is a polycyclic system, with felling based on ecological criteria assumed to be compatible with the maintenance of biodiversity. To compare the effects of periodic block and open-range systems on biodiversity, we determined bat species richness and abundance in each system and in primary forest. We caught bats in mist nets set at ground level and in the canopy and in harp traps. In total 1959 individuals representing 38 species were captured. Species richness was similar among primary forest and logged forest habitats, although bat diversity was lower in logged forest. The distributions of bat species abundance did not differ significantly between logged forest and primary forest. We found, however, that both logging systems lead to a decrease in gleaning animalivores and an increase in frugivores. The increase in frugivores was likely the result of an increase in the abundance of bat-dispersed pioneer fruiting plants in logged forest. Bats of periodic-block-managed forest were more similar to those of primary forest than those of forest logged using the open-range system, indicating that the periodic-block system is more compatible with the maintenance of bat diversity. Our results support the suggestion that the measured use of tropical forests can largely be compatible with biodiversity conservation.  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