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621.
蒋端生 《湖南环境生物职业技术学院学报》1995,(1)
本文介绍了南岳的自然条件以及森林土壤的基本特点如酸碱度、土壤含水量、比重、浸水容重、质地、有机质、有效氮、速效磷、速效钾等情况。作者首次应用定量方法即回归分析研究了土壤紧实度与土壤层次、结构及其有机质含量的关系,还讨论了土壤侵蚀和人畜践踏对土壤紧实度的影响。 相似文献
622.
We investigated quantitatively the sensitivity of plant species response curves to sampling characteristics (number of plots, occurrence and frequency of species), along a simulated pH gradient. We defined 54 theoretical unimodal response curves, issued from combinations of six values for optimum (opt = 3, 4, …, 8), three values for tolerance (tol = 0.5, 1.0, and 1.5, sensu ter Braak and Looman [ter Braak, C.J.F., Looman, C.W.N., 1986. Weighted averaging, logistic regression and the Gaussian response model. Vegetatio 65, 3–11]), and three values for maximum probability of presence (pmax = 0.05, 0.20, and 0.50). For each of these 54 theoretical response curves, we built artificial binary data sets (presence/absence) to test the influence of species occurrence, frequency, or number of available plots. With real data extracted from EcoPlant, a phytoecological database for French forests [Gégout, J.-C., Coudun, Ch., Bailly, G., Jabiol, B., 2005. EcoPlant: a forest sites database linking floristic data with soil characteristics and climatic conditions. J. Veg. Sci. 16, 257–260], we compared the ecological response of 50 plant species to soil pH, based first on a small data set (100 randomly sampled plots), and then based on the whole data set available (3810 plots). 相似文献
623.
624.
保护和恢复阿拉善梭梭生态林的探讨 总被引:2,自引:0,他引:2
本文分析了近 40年来阿拉善盟梭梭生态林退化的原因 ,并提出了今后保护与恢复这片梭梭生态林的对策和建议。 相似文献
625.
An ecological data base for the San Jacinto Mountains, California, USA, was used to construct a probability model of wildland
fire occurrence. The model incorporates both environmental and human factors, including vegetation, temperature, precipitation,
human structures, and transportation. Spatial autocorrelation was examined for both fire activity and vegetation to determine
the specification of neighborhood effects in the model. Parameters were estimated using stepwise logistic regressions. Among
the explanatory variables, the variable that represents the neighborhood effects of spatial processes is shown to be of great
importance in the distribution of wildland fires. An important implication of this result is that the management of wildland
fires must take into consideration neighborhood effects in addition to environmental and human factors. The distribution of
fire occurrence probability is more accurately mapped when the model incorporates the spatial term of neighborhood effects.
The map of fire occurrence probability is useful for designing large-scale management strategies of wildfire prevention. 相似文献
626.
Sociological edge effects: Spatial distribution of human impact in suburban forest fragments 总被引:4,自引:0,他引:4
Glenn R. Matlack 《Environmental management》1993,17(6):829-835
Suburban forest fragments often experience heavy recreational and waste disposal use, with considerable damage to the vegetation.
To suggest strategies for conservation of the forest flora, spatial distributions of human impact were described in 40 fragmentary
stands in northern New Castle County, Delaware. The distribution of human impact showed a significant bias to the forest edge,
with 95% of localized damage occurring in the first 82 m. Forms of impact related to lawn maintenance fell significantly closer
to the edge than impacts related to recreation and showed the strongest edge orientation. Edge distances of campsites, vandalized
trees, and firewood gathering were negatively correlated with distance to the nearest graded road, indicating the importance
of road access. Several forms of impact were also clustered near footpaths, although distance to paths was independent of
edge distance in all cases. In terms of penetration of the forest and severity of damage, human impact greatly exceeds natural
edge effects reported for this community. These findings suggest that damage may be minimized by limiting road access and
avoiding the creation of small forest fragments. 相似文献
627.
628.
火灾烟气伤害机理和伤害模型 总被引:2,自引:0,他引:2
建筑物发生火灾时,燃烧产生的烟气对人构成主要威胁。本文分析火灾烟气的伤害机理,提出烟气伤害指数概念及其计算方法,探讨它在材料防火性能评价和建筑物火灾安全评价方面的应用可能性。 相似文献
629.
烃类流体火灾伤害破坏作用定量分析 总被引:6,自引:2,他引:4
对烃类流体火灾的伤害破坏作用进行正确的定量分析是开展重大消防目标火灾风险评估工作的基础。针对烃类流体火灾伤害破坏作用定量分析中存在的问题,系统论述烃类流体火灾伤害破坏作用的定量分析方法,分析并讨论火球、池火、喷射火和蒸气云火灾等不同火灾形式的热辐射通量计算模型及其前提条件,对不同热辐射伤害破坏作用准则及伤害概率模型的适用条件和模型基础进行了论述。 相似文献
630.
Forest fire is regarded as one of the most significant factors leading to land degradation. While evaluating fire hazard or producing fire risk zone maps, quantitative analyses using historic fire data is often required, and during all these modeling and multi-criteria analysis processes, the fire event itself is taken as the dependent variable. However, there are two main problematic issues in analyzing historic fire data. The first difficulty arises from the fact that it is in point format, whereas a continuous surface is frequently needed for statistically analyzing the relationship of fire events with other factors, such as anthropogenic, topographic and climatic conditions. Another, and probably the most bothersome challenge is to overcome inaccuracy inherent in historic fire data in point format, since the exact coordinates of ignition points are mostly unknown. In this study, kernel density mapping, a widely used method for converting discrete point data into a continuous raster surface, was used to map the historic fire data in Mumcular Forest Sub-district in Mu?la, Turkey. The historic fire data was transferred onto the digital forest stand map of the study area, where the exact locations of ignition points are unknown; however, the exact number of ignition points in each compartment of the forest stand map is known. Different random distributions of ignition points were produced, and for each random distribution, kernel density maps were produced by applying two distinct kernel functions with several smoothing parameter options. The obtained maps were compared through correlation analysis in order to illustrate the effect of randomness, choice of kernel function and smoothing parameter. The proposed method gives a range of values rather than a single bandwidth value; however, it provides a more reliable way than comparing the maps with different bandwidths subjectively by eye. 相似文献