全文获取类型
收费全文 | 1217篇 |
免费 | 74篇 |
国内免费 | 70篇 |
专业分类
安全科学 | 60篇 |
废物处理 | 5篇 |
环保管理 | 355篇 |
综合类 | 372篇 |
基础理论 | 331篇 |
污染及防治 | 59篇 |
评价与监测 | 44篇 |
社会与环境 | 120篇 |
灾害及防治 | 15篇 |
出版年
2024年 | 4篇 |
2023年 | 8篇 |
2022年 | 16篇 |
2021年 | 25篇 |
2020年 | 26篇 |
2019年 | 20篇 |
2018年 | 16篇 |
2017年 | 24篇 |
2016年 | 28篇 |
2015年 | 32篇 |
2014年 | 35篇 |
2013年 | 54篇 |
2012年 | 46篇 |
2011年 | 71篇 |
2010年 | 78篇 |
2009年 | 88篇 |
2008年 | 79篇 |
2007年 | 85篇 |
2006年 | 91篇 |
2005年 | 76篇 |
2004年 | 63篇 |
2003年 | 65篇 |
2002年 | 52篇 |
2001年 | 53篇 |
2000年 | 54篇 |
1999年 | 21篇 |
1998年 | 21篇 |
1997年 | 22篇 |
1996年 | 10篇 |
1995年 | 22篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有1361条查询结果,搜索用时 0 毫秒
981.
Mark B. Green Christian H. Fritsen 《Journal of the American Water Resources Association》2006,42(3):659-674
ABSTRACT: Because the Truckee River connects two lakes along the Eastern Sierra Nevada Mountains with different limiting nutrients, this research addresses whether the nitrogen:phosphorus (N:P) balance of the river ecosystem changes longitudinally. Historical (1990 to 2000) total nitro‐gen:total phosphorus (TN:TP) ratios in river water exhibited the expected gradient from high N:P ratios upstream to low N:P ratios downstream, with the major gradient of the N:P balance occurring within the transition between montane and high desert terrain. During 2001, the river contained anomalously low total nitrogen concentrations in the far upper reaches and dissolved inorganic nitrogen concentrations in the lower reaches, resulting in a less apparent longitudinal gradient of N:P ratios. Measurements of periphyton growth and physiology (nutrient bioassays and ectoenzyme activities) and stoichiometry during the summer of 2001 also exhibited a complex picture of the spatial variation of N:P balance that was not entirely consistent with a strong N:P gradient. However, the compendium of the indicators did support the overall picture of an overarching longitudinal gradient from high to low N:P ratios. The results suggest that periphyton management efforts in the Truckee River should consider the overall spatial gradient as well as the small‐scale dynamics of the stream ecosystem structure. 相似文献
982.
Eric W. Larsen Alexander K. Fremier Evan H. Girvetz 《Journal of the American Water Resources Association》2006,42(4):1063-1075
ABSTRACT: Flow regulation impacts the ecology of major rivers in various ways, including altering river channel migration patterns. Many current meander migration models employ a constant annual flow or dominant discharge value. To assess how flow regulation alters river function, variable annual flows ‐ based on an empirical relationship between bank erosion rates and cumulative effective stream power ‐ were added into an existing migration model. This enhanced model was used to evaluate the potential geomorphic and ecological consequences of four regulated flow scenarios (i.e., different hydrographs) currently being proposed on the Sacramento River in California. The observed rate of land reworked correlated significantly with observed cumulative effective stream power during seven time increments from 1956 to 1975 (r2= 0.74, p = 0.02). The river was observed to rework 3.0 ha/yr of land (a mean channel migration rate of 7.7 m/yr) with rates ranging from 0.8 ha/yr to 5.1 ha/yr (2.0 to 13.3 m/yr), during the analyzed time periods. Modeled rates of land reworked correlated significantly with observed rates of land reworked for the variable flow model (r2= 0.78, p = 0.009). The meander migration scenario modeling predicted a difference of 1 to 8 percent between the four flow management scenarios and the base scenario. 相似文献
983.
984.
Remotely sensed data have been used extensively for environmental monitoring and modeling at a number of spatial scales; however,
a limited range of satellite imaging systems often constrained the scales of these analyses. A wider variety of data sets
is now available, allowing image data to be selected to match the scale of environmental structure(s) or process(es) being
examined. A framework is presented for use by environmental scientists and managers, enabling their spatial data collection
needs to be linked to a suitable form of remotely sensed data. A six-step approach is used, combining image spatial analysis
and scaling tools, within the context of hierarchy theory. The main steps involved are: (1) identification of information
requirements for the monitoring or management problem; (2) development of ideal image dimensions (scene model), (3) exploratory
analysis of existing remotely sensed data using scaling techniques, (4) selection and evaluation of suitable remotely sensed
data based on the scene model, (5) selection of suitable spatial analytic techniques to meet information requirements, and
(6) cost–benefit analysis. Results from a case study show that the framework provided an objective mechanism to identify relevant
aspects of the monitoring problem and environmental characteristics for selecting remotely sensed data and analysis techniques. 相似文献
985.
986.
Peter?M.?KappelerEmail author Hans?G.?Erkert 《Behavioral ecology and sociobiology》2003,54(4):359-369
Whether animals are active at night or during the day has profound consequences for many aspects of their behavioral ecology. Because of ecological and physiological trade-offs, most animals, including primates, are either strictly nocturnal or diurnal. However, a few primate species exhibit cathemeral activity, i.e., their activity is irregularly distributed throughout the 24-h cycle. Details and determinants of this unusual activity pattern are poorly understood because long-term 24-h observations are not feasible in the field. We therefore used small data loggers to record the activity of cathemeral redfronted lemurs (Eulemur fulvus rufus) from several neighboring groups quantitatively and continuously over a complete annual cycle in order to evaluate various proposed proximate and ultimate determinants of cathemeral activity. Activity data were examined for variation as a function of ambient temperature, time of day, lunar phase, and season. We found that cathemeral activity occurred year-round and that, on average, 3.5 times more activity occurred during the day. Total and diurnal activity increased during the long days of the austral summer. Nocturnal activity increased during the longer nights of the cool dry season. Irrespective of season, lunar phase had a significant effect on the distribution of activity across the 24-h cycle, with most nocturnal activity recorded during parts of the night with greatest brightness. These data indicate that light availability is the primary proximate determinant for the patterning of cathemeral activity. Several lines of evidence suggest that cathemerality in lemurs has evolved from nocturnal ancestors and that it represents a transitory state on the way to the diurnal niche.Communicated by F. Trillmich 相似文献
987.
988.
生态工业园区概念的理论渊源 总被引:5,自引:0,他引:5
生态工业园区概念来自于可持续发展理论,生产布局学和工业生态学三大理论体系,本对此进行了梳理。 相似文献
989.
张学书 《中国人口.资源与环境》2002,(5)
人类在长期与自然的斗争中滋生起来的对自然的征服感和优越感以及在私有制条件下滋生起来的自我中心主义和实用利己主义 ,是产生生态问题的根本原因。生态问题启示我们应当正确认识和评价人的实践活动的正负效应 ,应当不断完善和发展人自身的本质力量 ,应当建立起一种双向的、新型的主客体实践关系 ,才能最终避免生态问题的产生。 相似文献
990.
A broad and objective perspective of ecological and socioenomic knowledge is required to underlie a scientific approach to
the problems of terrestrial restoration ecology. Uncertainty associated with limited scientific knowledge highlights the crucial
importance of the interaction between science and policy in weighing ecological restoration alternatives in relation to other
management options. In this paper, we provide a pragmatic definition for restoration ecology that is suitable for extensive
terrestrial applications and present a decision framework to help organize and clarify different phases of the decision process
as it is related to ecological restoration. We argue that restoration planning should include a wider spectrum of participants
and decisions than have traditionally been employed. 相似文献