全文获取类型
收费全文 | 1318篇 |
免费 | 74篇 |
国内免费 | 197篇 |
专业分类
安全科学 | 141篇 |
废物处理 | 18篇 |
环保管理 | 344篇 |
综合类 | 359篇 |
基础理论 | 431篇 |
环境理论 | 1篇 |
污染及防治 | 106篇 |
评价与监测 | 53篇 |
社会与环境 | 77篇 |
灾害及防治 | 59篇 |
出版年
2024年 | 7篇 |
2023年 | 26篇 |
2022年 | 26篇 |
2021年 | 54篇 |
2020年 | 50篇 |
2019年 | 31篇 |
2018年 | 25篇 |
2017年 | 38篇 |
2016年 | 55篇 |
2015年 | 51篇 |
2014年 | 40篇 |
2013年 | 105篇 |
2012年 | 47篇 |
2011年 | 95篇 |
2010年 | 67篇 |
2009年 | 105篇 |
2008年 | 79篇 |
2007年 | 71篇 |
2006年 | 84篇 |
2005年 | 63篇 |
2004年 | 52篇 |
2003年 | 52篇 |
2002年 | 43篇 |
2001年 | 30篇 |
2000年 | 33篇 |
1999年 | 16篇 |
1998年 | 29篇 |
1997年 | 18篇 |
1996年 | 17篇 |
1995年 | 16篇 |
1994年 | 13篇 |
1993年 | 13篇 |
1992年 | 7篇 |
1991年 | 4篇 |
1990年 | 8篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1973年 | 6篇 |
1972年 | 7篇 |
1971年 | 5篇 |
排序方式: 共有1589条查询结果,搜索用时 21 毫秒
91.
Numerous analyses of the possible impacts of future climatic changes on tree species composition have been published for
both lowland and high-elevation forests. Most of these studies were based on the application of forest "gap" models, and the
vast majority of them considered only changes in the average of climatic parameters over time. In this study, we use a unique
data set on reconstructed past climatic variations to analyse forest dynamics simulated by the forest gap model ForClim. This
analysis forms the basis for a systematic exploration of the ecological effects of changing means vs. changing variability
of climate on central European forests. A reconstruction of historical climate covering the last 470 years in the Swiss lowlands
(ClimIndex) is extrapolated to a transect across the alpine (cold) treeline and used to simulate the influence of climate
variations on the time scale of decades on forest biomass and tree species composition at both sites. While the simulation
at the low-elevation site shows little sensitivity to climate variations, the results from upper subalpine forests suggest
that two major dieback events would have occurred at elevations above the current but below the climatic tree line, induced
by clusters of exceptionally cold summers. The results are in agreement with available dendrochronological data and with documentary
evidence on massive negative impacts on flora and fauna at high elevations during these periods. We conclude that ForClim
is capable of capturing the effects on tree population dynamics of climate variability at these sites as reconstructed from
the ClimIndex record. A factorial design is used to address the sensitivity of ForClim to changes of the long-term averages
vs. changes of the variability of monthly temperature and precipitation data. To this end, the simulated tree species composition
of near-natural forests is examined along a climate gradient in Europe. The results indicate that there are three types of
forest response: (1) little sensitivity to both kinds of change, (2) strong sensitivity to changes in the means, but little
sensitivity to changing variability, and (3) strong sensitivity to changing variability at least in parts of the examined
climate space. Half of the cases investigated fall under the third category, suggesting that emphasis should be placed on
also assessing the sensitivity of ecosystems to future changes in climate variability rather than on changes of average values
alone.
Electronic Publication 相似文献
92.
膨胀土地基中大比例模型桩浸水试验研究 总被引:2,自引:0,他引:2
通过对埋设在膨胀土地基中的一试桩的长时间浸水试验观测,模拟了自然降雨气候条件下单桩位移、沿桩身轴力、侧摩阻力分布、地基胀缩及其时间变化等基桩一系列工作性状和桩-土共同作用规律。试验结果显示:桩顶位移呈现出先下沉后回升并最后趋于稳定的3阶段特征;桩身全长受拉,轴力沿桩身分布呈“波峰”形态。基桩的最大轴力位于桩的中下部,轴力峰值历经由小到大的过程;中性点在浸水过程中,其位置有从桩下部上移的现象;桩侧摩阻力与桩端阻力荷载分担比随时间呈现出先减小后增大并渐趋稳定的3阶段特征。研究结果对膨胀土地基中的桩基设计和施工提供了理论依据。 相似文献
93.
Annika Porsborg Nielsen Jesper Lassen Peter Sandøe 《Journal of Agricultural and Environmental Ethics》2007,20(1):13-35
Over recent decades, public participation in technology assessment has spread internationally as an attempt to overcome or
prevent societal conflicts over controversial technologies. One outcome of this new surge in public consultation initiatives
has been the increased use of participatory consensus conferences in a number of countries. Existing evaluations of consensus
conferences tend to focus on the modes of organization, as well as the outcomes, both procedural and substantial, of the conferences
they examine. Such evaluations seem to rest on the assumption that this type of procedure has universally agreed goals and
meanings, and that therefore consensus conferences can readily be interpreted and applied across national boundaries. This
article challenges this approach to consensus conferences. The core of the article is a study of national differences in ideas
about what constitutes legitimate goals for participatory arrangements. The study looks at three consensus conferences on
GMOs, which took place in France, Norway, and Denmark. Drawing on this study, the article discusses the ways in which interpretations
of the concept of participation; the value attributed to lay knowledge vs. technical expertise; as well as ideas about the
role of the layperson, are all questions that prompt entirely different answers from country to country. Further, the article
analyses these national differences within a theoretical framework of notions of democratic legitimacy. 相似文献
94.
95.
J. Marsalek T. M. Dick P. E. Wisner W. G. Clarke 《Journal of the American Water Resources Association》1975,11(2):306-328
ABSTRACT: Three urban runoff models, namely, the Road Research Laboratory Model (RRLM), the Storm Water Management Model (SWMM) and the University of Cincinnati Urban Runoff Model (UCURM), were examined by comparing the model simulated hydrographs with the hydrographs measured on several instrumented urban watersheds. This comparison was done for the hydrograph peak points as well as for the entire hydrographs using such statistical measures as the correlation coefficient, the special correlation coefficient and the integral square error. The results of the study indicated that, when applying the three selected non-calibrated models on small urban catchments, the SWM model performed marginally better than the RRL model and both these models were more accurate than the UCUR model. On larger watersheds, the comparisons between the SWM model and the other two models would be likely even more favourable for the SWM model, because it has the most advanced flow routing scheme among the studied models. 相似文献
96.
Jerry F. Franklin 《Environmental management》1979,3(1):2-5
Simulation models are becoming increasingly important as tools for synthesizing and applying information in almost all aspects of land management. They are particulary valuable for predicting and comparing outcomes of alternative decisions and assumptions. Models also permit managers to consider and integrate the potential influences of a large number of variables. 相似文献
97.
Thomas J. Jackson Richard H. McCuen 《Journal of the American Water Resources Association》1979,15(2):436-446
ABSTRACT: Remote sensing offers an attractive alternative to conventional data collection employed in the estimation of certain hydrologic model parameters. In this investigation, the standard error of parameters estimated from Landsat data are examined. Relationships between the standard error and the size of the spatial-modeling units are developed that allow extending results to larger areas. Based upon the investigations conducted, a generalized model of the error relationships could not be developed. 相似文献
98.
Stuart G. Walesh Daniel F. Snyder 《Journal of the American Water Resources Association》1979,15(3):644-659
ABSTRACT: The use of continuous hydrologic-hydraulic-water quality models is inhibited by their large computer run costs relative to cost incurred with discrete event models. The fixed recurrence interval transfer (FRIT) technique is a means of achieving substantial reductions in computer costs associated with continuous models while retaining their technical advantages. The FRIT technique is applicable where it is reasonable to assume that the recurrence interval of the response of a watershed to a causative meteorologic event is the same for both “before” and “after” conditions. Example applications of the FRIT technique to the hydrologic-hydraulic modeling of floodwater storage, land use changes, and channel modifications are presented to demonstrate the procedure, to suggest the expected accuracy, and to illustrate how computer run costs might be reduced by 99% or more. The FRIT technique is intended for preliminary assessment of the impact of alternative land use conditions and structural water control measures. 相似文献
99.
Michael L. Shrader Richard H. McCuen Walter J. Rawls 《Journal of the American Water Resources Association》1980,16(1):49-55
ABSTRACT: With the increased use of models in hydrologic design, there is an immediate need for a comprehensive comparison of hydrologic models, especially those intended for use at ungaged locations (i.e., where measured data are either not available or inadequate for model calibration). But some past comparisons of hydrologic models have used the same data base for both calibration and testing of the different models or implied that the results of model calibration are indicative of the accuracy at ungaged locations. This practice was examined using both the regression equation approach to peak discharge estimation and a unit hydrograph model that was intended for use in urban areas. The results suggested that the lack of data independence in the calibration and testing of regression equations may lead to both biased results and misleading statements about prediction accuracy. Additionally, although split-sample testing is recognized as desirable, the split-samples should be selected using a systematic-random sampling scheme, rather than random sampling, because random sampling with small samples may lead to a testing sample that is not representative of the population. A systematic-random sampling technique should lead to more valid conclusions about model reliability. For models like a unit hydrograph model, which are more complex and for which calibration is a more involved process, data independence is not as critical because the data fitting error variation is not as dominant as the error variation due to the calibration process and the inability of the model structure to conform with data variability. 相似文献
100.
Peter G. Ashton James B. Pickens Coryell Ohlander Bruce Benninghoff 《Journal of the American Water Resources Association》1980,16(4):738-744
ABSTRACT: Decisionmaking associated with the Nation's 1.7 billion acres of forest and range land has become increasingly complicated because of the rise in competition for resource use and in the awareness of environmental and social effects. This system analysis approach uses four models to synthesize pertinent masses of information into measures of economic, environmental, and social impacts. The system results can be used to help evaluate alternative national programs. The models are: