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   6952篇
  免费   742篇
  国内免费   1925篇
安全科学   685篇
废物处理   87篇
环保管理   1201篇
综合类   4399篇
基础理论   1222篇
环境理论   4篇
污染及防治   253篇
评价与监测   314篇
社会与环境   1041篇
灾害及防治   413篇
  2024年   39篇
  2023年   174篇
  2022年   390篇
  2021年   437篇
  2020年   404篇
  2019年   365篇
  2018年   362篇
  2017年   444篇
  2016年   457篇
  2015年   428篇
  2014年   360篇
  2013年   482篇
  2012年   567篇
  2011年   583篇
  2010年   449篇
  2009年   393篇
  2008年   326篇
  2007年   439篇
  2006年   417篇
  2005年   369篇
  2004年   256篇
  2003年   261篇
  2002年   206篇
  2001年   176篇
  2000年   170篇
  1999年   115篇
  1998年   93篇
  1997年   80篇
  1996年   56篇
  1995年   47篇
  1994年   52篇
  1993年   26篇
  1992年   19篇
  1991年   15篇
  1990年   22篇
  1989年   9篇
  1988年   13篇
  1987年   13篇
  1986年   12篇
  1985年   5篇
  1982年   10篇
  1981年   6篇
  1980年   16篇
  1979年   5篇
  1978年   9篇
  1977年   8篇
  1975年   6篇
  1973年   6篇
  1972年   5篇
  1971年   5篇
排序方式: 共有9619条查询结果,搜索用时 390 毫秒
991.
Trends in the anthropogenic transformation of flora in the city of Astrakhan and its environs over the past 100 years are discussed. In general, the process of flora synanthropization is observed, with natural aboriginal plant communities being replaced by anthropogenically altered communities.  相似文献   
992.
The research related here focuses on municipal situations where problems of sustainability may be defined and tackled on the basis of bottom-up management procedures with the participation of organized society. The aim is to build management models that may be implemented with reasonable administrative effort and cost. Implementation pursues the target of approaching a sustainable situation in the municipality. Environmental parameters for an ideal municipality with undefined geographical location are presented. For each parameter, a set of indicators is developed that can measure the prospect of sustainability. The indicators are defined in terms of numbers or literal concepts according to the possibility of measurement. Examples of management models are presented, which are able to approach the situation defined as sustainable by the indicators. The basic management tool is the learning curve of targeted communities, which is experimentally developed and applied. The indicators are grouped according to their range of applicability.  相似文献   
993.
利用1996~2007年苏锡常地区土地利用变更数据,从土地利用变化幅度、动态度、变化强度、相对变化率及景观生态学角度,对区域土地利用结构的动态变化及区域差异进行分析。研究结果表明:近十多年来,由于区域经济快速发展,工业用地扩展迅猛,城镇加速蔓延,从而导致区内耕地面积锐减,居民点及工矿用地、交通用地所占比例则逐年上升,交通用地的变化幅度及动态度最大;各用地类型的变化强度在此期间呈一定波动,除牧草地外,交通用地历年的变化强度之和最大,其次为园地、居民点及工矿用地、水利设施用地、耕地、其他农用地、林地、未利用地;区域土地利用结构逐渐向均衡状态发展,用地结构的均质性逐渐增强,地区土地利用结构渐趋稳定;各市耕地、居民点及工矿用地、其他农用地的变化幅度及相对变化率差别不大,而园地、林地、牧草地、交通用地、水利设施用地及未利用地的变化幅度及相对变化率区域差异较大,且三市园地、牧草地及未利用地的变化方向不一致。  相似文献   
994.
快速设置装配式防洪子堤的设计及应用   总被引:2,自引:0,他引:2  
针对防洪工程要求和目前防洪子堤技术存在的问题,提出了可折叠的装配式防洪子堤的设计思想,进行了子堤的材料性能试验和结构设计,研制了一种装配式玻璃钢桐木夹层防洪子堤.通过对子堤在土堤和混凝土堤表面挡水试验和快速设置技术的应用研究,表明该防洪子堤具有重量轻、可重复使用和快速设置等特点,特别适合在需要临时加高的水库大坝、江防大堤和城市河岸堤防工程中使用.  相似文献   
995.
Monitoring data from ozone(O3) automatic stations in three typical cities with different climatic areas in the southern and northern parts of eastern China are used to analyze temporal and spatial characteristics of ozone pollution at ground level. The results show that ozone pollution level has distinct regional differences and the concentration in the suburbs is higher than that in the urban areas. The seasonal variation of ozone concentration in different climatic areas is greatly affected by the variation of precipitation. Ozone concentration in Shenyang and Beijing , in the temperate zone, has one perennial peak concentration, occurring in early summer, May or June. Ozone concentration in Guangzhou, in sub-tropical zone, has two peak values year round. The highest values occur in October and the secondary high value in June. The ozone season in the south is longer than that in the north. The annual average daily peak value of ozone concentrations in different climates usually occur around 3 pm. The diurnal variation range of ozone concentration declines with the increase of latitude. Ozone concentration does not elevate with the increase of traffic flow. Ozone concentration in Guangzhou has a distinct reverse relation to CO and NOx. This complicated non-linearity indicates that the equilibrium of ozone photochemical reaction has regional differences. Exceeding the rate of Beijing's lh ozone concentration is higher than that of Guangzhou, whereas the average 8h ozone level is lower than that of Guangzhou, indicating that areas in low latitude are more easily affected by moderate ozone concentrations and longer exposure. Thus, China should work out standards for 8h ozone concentration.  相似文献   
996.
城市可持续发展的关键自然资本研究   总被引:2,自引:0,他引:2  
城市是社会、经济与环境相互作用最为集中与深刻的区域,随着城市环境问题的日益严重,城市可持续发展成为共同关注的焦点。自然资本在可持续发展体系中起到关键的作用,因此,识别城市系统的关键自然资本是实现城市可持续发展的前提。通过分析城市绿色空间的生态服务功能,结果表明绿色空间是影响城市可持续发展的重要的自然资本。在此基础上,提出了通过保护与投资于绿色空间两种途径实现城市可持续发展的措施与建议。  相似文献   
997.
In this study, the relationship between inhalable particulate (PM10), fine particulate (PM2.5), coarse particles (PM2.5 – 10) and meteorological parameters such as temperature, relative humidity, solar radiation, wind speed were statistically analyzed and modelled for urban area of Kolkata during winter months of 2003–2004. Ambient air quality was monitored with a sampling frequency of twenty-four hours at three monitoring sites located near traffic intersections and in an industrial area. The monitoring sites were located 3–5 m above ground near highly trafficked and congested areas. The 24 h average PM10 and PM2.5 samples were collected using Thermo-Andersen high volume samplers and exposed filter papers were extracted and analysed for benzene soluble organic fraction. The ratios between PM2.5 and PM10 were found to be in the range of 0.6 to 0.92 and the highest ratio was found in the most polluted urban site. Statistical analysis has shown a strong positive correlation between PM10 and PM2.5 and inverse correlation was observed between particulate matter (PM10 and PM2.5) and wind speed. Statistical analysis of air quality data shows that PM10 and PM2.5 are showing poor correlation with temperature, relative humidity and solar radiation. Regression equations for PM10 and PM2.5 and meteorological parameters were developed. The organic fraction of particulate matter soluble in benzene is an indication of poly aromatic hydrocarbon (PAH) concentration present in particulate matter. The relationship between the benzene soluble organic fraction (BSOF) of inhalable particulate (PM10) and fine particulate (PM2.5) were analysed for urban area of Kolkata. Significant positive correlation was observed between benzene soluble organic fraction of PM10 (BSM10) and benzene soluble organic fraction of PM2.5 (BSM2.5). Regression equations for BSM10 and BSM2.5 were developed.  相似文献   
998.
The dominant use of coal in power sectors has been associated with adverse environmental impacts. Ambient air monitoring for the two size fractions of particulate matter, respirable suspended particulate matter (RSPM) and non-respirable suspended particulate matter (NRSPM) in the downwind and upwind directions of a large coal-fired power station in central India, was carried out. Collected samples of ambient particulate matter were analysed atomic absorption spectrophotometrically for 15 elements. Spatial variability in elemental composition of RSPM and NRSPM and the degree of enrichment of these toxic metals in RSPM were investigated. A significant spatial variability for the elements in RSPM and NRSPM and higher degrees of enrichment of the elements were observed.  相似文献   
999.
The spatial structure of populations has been studied in two rodent species inhabiting the subzone of meadow steppes of the steppe zone of Omsk oblast: the narrow-sculled vole (Microtus gregalis Pall.) and steppe lemming (Lagurus lagurus Pall.). Their populations are represented by combinations of territorial family groups whose structure and spatial distribution vary by season depending on population density, the phase of the population cycle, and the status of their members in the population. In the areas cohabited by M. gregalis and L. lagurus, the pattern of territory use and the rhythm of animal activity during the day depend primarily on their total density: under conditions of low density, the population groups of both species are spatially separated; at increased density, they are distributed with respect to the pattern of daily activity. Both species jointly use part of the territory but at different times of day: M. gregalis, mainly at night and in the morning; L. lagurus, in the daytime.  相似文献   
1000.
The spatiotemporal structure of the muskrat population has been studied by means of the prenatal radioactive marking of juveniles with 45 Ca and their subsequent recapture in the test area. The muskrat population is characterized by a cyclic type of spatial structure, with seasonal transition from a mosaic type of settling to a diffuse type and, after the breeding season, vice versa.  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