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   428篇
  免费   14篇
  国内免费   32篇
安全科学   51篇
环保管理   147篇
综合类   113篇
基础理论   63篇
污染及防治   22篇
评价与监测   26篇
社会与环境   37篇
灾害及防治   15篇
  2024年   1篇
  2023年   8篇
  2022年   11篇
  2021年   12篇
  2020年   14篇
  2019年   3篇
  2018年   9篇
  2017年   12篇
  2016年   11篇
  2015年   9篇
  2014年   8篇
  2013年   23篇
  2012年   15篇
  2011年   31篇
  2010年   19篇
  2009年   30篇
  2008年   36篇
  2007年   24篇
  2006年   27篇
  2005年   18篇
  2004年   24篇
  2003年   8篇
  2002年   17篇
  2001年   12篇
  2000年   14篇
  1999年   8篇
  1998年   15篇
  1997年   8篇
  1996年   7篇
  1995年   2篇
  1994年   5篇
  1993年   3篇
  1992年   3篇
  1991年   12篇
  1990年   3篇
  1989年   1篇
  1988年   2篇
  1987年   4篇
  1984年   1篇
  1983年   1篇
  1980年   1篇
  1976年   1篇
  1973年   1篇
排序方式: 共有474条查询结果,搜索用时 31 毫秒
101.
无人机遥感调查黄河源玛多县岩羊数量及分布   总被引:1,自引:0,他引:1  
本研究于2017年利用无人机航拍调查对黄河源玛多县县域内的岩羊种群数量进行了估算,并对其分布规律进行了研究。无人机航拍共获取影像23784张,有效面积326.6 km~2,通过目视解译,获取样带内的岩羊种群数量为203只,种群密度为0.6215只/km~2。通过推算,得到玛多县岩羊种群数量为8968只。对玛多县岩羊分布位置与环境因子的分析结果显示:岩羊偏好于选择海拔为4100~4200 m、距公路大于3 km、距悬崖峭壁200 m以内的区域活动。本研究利用无人机航拍样带调查估算黄河源玛多县岩羊种群数量与密度,并结合ArcGIS软件对其生境进行分析,将3S技术与野生动物调查相结合,为青藏高原地区大型野生动物相关研究提供了新思路。  相似文献   
102.
在TiO2悬浆体系,中压汞灯作用下,通过苯酚降解过程中总碳浓度变化及二氧化碳生成速度的变化规律,研究了光催化氧化与直接光解反应的不同,并着得比较了当反应条件如催化剂量,气相氧浓度以及光强度变化对两种反应的影响。实验结果证明了两种反应的历程和产物各不相同,多相光催化氧化更有利于有机物分子的降解,而光解作用会引起聚合反应,同时也说明充分利用太阳能不仅是开发光催化水处理技术的重要途径,也是抑制直接光解加  相似文献   
103.
城市级环境信息系统总体方案的研究与开发   总被引:8,自引:0,他引:8       下载免费PDF全文
在分析我国城市级环境信息现状和需求的基础上,提出了我国城市级环境信息系统的总体方案,系统依靠现有的环境数据和管理软件建立城市环境信息基础数据库,依照数据仓库的组织方式对环境数据重新进行整合,并在此基础上开发出数据查询分析应用和地理信息系统,同时结合城市环保局的办公自动化系统,建立了一个统一的环境信息发布平台,提高了环境信息的共享水平。  相似文献   
104.
围绕文化差异与跨文化营销的主要研究成果,分析文化差异与跨文化营销研究的兴起情况以及国内外学者对文化差异和跨文化营销的研究的现状.  相似文献   
105.
GIS在环境保护中的应用现状与发展   总被引:7,自引:2,他引:7  
结合国内外地理信息系统(GIS)在环境保护研究工作中的介入情况,阐述了GIS在环境保护领域的应用现状,并探讨了GIS在此领域应用的未来发展趋势。  相似文献   
106.
The extent of diversity within closely related taxa may be a function of their shared evolutionary history or of selective forces causing adaptive changes. Examining variation among taxa within a single genus may help to identify flexibility in trait variation because recently diverged populations are more likely living in the environment of adaptation. This study examines correlates of diversity in Eulemur, a genus that has a wide distribution in a variety of habitat types throughout Madagascar. Previously published data were gathered from 11 long-term studies of Eulemur populations. Variables were categorized into multiple datasets: (1) environmental characteristics, (2) social organization, and (3) ecology, which included subsets for ranging behavior, diet, and activity budget. Molecular phylogenies from the literature were used to create the fourth and final dataset, a dissimilarity matrix of evolutionary distance among the 12 species and subspecies. Principal components and cluster analyses were implemented to examine the overall ecological similarity among Eulemur populations and to determine which variables contribute most to the variation among taxa. Partial Mantel tests were conducted to test for correlations among the dataset matrices. The results suggest ecological flexibility for the genus, in particular, populations in similar environments displayed similar activity patterns. In contrast, social organization showed no relationship with environment but was correlated with phylogenetic distance among populations. While Eulemur seems to demonstrate some flexibility for ecological adaptations, characteristics related to group size and sex ratio more closely track phylogeny and thus may be less flexible.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible to authorized users.  相似文献   
107.
In recent decades numerous diversity indices have been introduced. Among them the quadratic entropy index Q expresses the mean difference between two individuals chosen from the community at random. Differing from diversity indices habitually employed, Q does not satisfy a property postulated earlier for those measures. Namely, the uniform distribution of species does not necessarily yield the maximal index value. Q is based on the difference matrix of species. For a given matrix one can seek for the vector yielding the maximum quadratic entropy. This task leads to a quadratic programming problem. Using the appropriate program of a program package, we determined the maximum vector for a genetic difference matrix of crane species, as published in the literature. We discovered that some components (frequencies) in the maximum vector are equal to zero. That is, by maximizing the quadratic diversity some species can be eliminated. We discuss briefly the possible implications of this observation. Moreover, even if all elements in the maximum vector are positive, the elements can differ.  相似文献   
108.
Size assessment via a visual signal in snapping shrimp   总被引:2,自引:0,他引:2  
Snapping shrimp are highly aggressive decapod crustaceans, with large, asymmetric chelae. Body size determines the outcome of both inter- and intrasexual interactions. Both the body and chela sizes of mated pairs are correlated, but the body size correlation is significantly stronger. In competitive interactions between individuals of the same sex, larger individuals usually win. Because the size of the major chela is a function of body size in both males and females, chela size could be used to assess body size early in interactions, before engaging in more high risk behaviors. To determine whether the major chela is used in size assessment, I presented shrimp with isolated chelae. Male snapping shrimp responded aggressively to isolated chelae when they were fixed open in a display posture, and the degree of aggressive response depended on the relative size of the chela. These data provide direct experimental evidence for the use of a visual signal in size assessment. Females, in contrast, responded aggressively to both the open and closed chela, and their responses did not depend on relative size. This sex difference in response may be due to differences in the value of certain resources, such as shelters, to males and females: females may be more willing to respond aggressively regardless of the apparent size of their opponent, in order to acquire more reliable information regarding size, motivation or fighting ability. Received: 30 December 1994/Accepted after revision: 14 August 1995  相似文献   
109.
以滇池流域为例,介绍一种利用概化网络进行水资源调控仿真与预测的思路与方法,为流域水资源的宏观调控与管理规划提供决策支持。  相似文献   
110.
"三S"技术应用与环境科技发展   总被引:3,自引:0,他引:3  
叙述了遥感,全球定位系统和地理信息系统和环境科技发展的关系,以及在环境科技中的实际应用,提出了在大力开展集RS,GPS,GIS于一体,适合环境科学应用的,综合多功能的“三S”技术,以适应可持续发展的需要。  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