全文获取类型
收费全文 | 428篇 |
免费 | 14篇 |
国内免费 | 32篇 |
专业分类
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 |
出版年
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催化剂上苯酚光催化氧化反应研究2-多相光催化氧化与直接光解反应的比较 总被引:14,自引:0,他引:14
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.
104.
张桂华 《湖南环境生物职业技术学院学报》2006,12(3):328-331
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.
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
Melissa Hughes 《Behavioral ecology and sociobiology》1996,38(1):51-57
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