全文获取类型
收费全文 | 18587篇 |
免费 | 1138篇 |
国内免费 | 2876篇 |
专业分类
安全科学 | 2605篇 |
废物处理 | 312篇 |
环保管理 | 2698篇 |
综合类 | 9681篇 |
基础理论 | 2249篇 |
环境理论 | 12篇 |
污染及防治 | 1520篇 |
评价与监测 | 970篇 |
社会与环境 | 1521篇 |
灾害及防治 | 1033篇 |
出版年
2024年 | 53篇 |
2023年 | 262篇 |
2022年 | 423篇 |
2021年 | 536篇 |
2020年 | 540篇 |
2019年 | 469篇 |
2018年 | 408篇 |
2017年 | 581篇 |
2016年 | 727篇 |
2015年 | 730篇 |
2014年 | 815篇 |
2013年 | 1005篇 |
2012年 | 1226篇 |
2011年 | 1401篇 |
2010年 | 1043篇 |
2009年 | 1015篇 |
2008年 | 825篇 |
2007年 | 1262篇 |
2006年 | 1278篇 |
2005年 | 1010篇 |
2004年 | 858篇 |
2003年 | 973篇 |
2002年 | 776篇 |
2001年 | 661篇 |
2000年 | 602篇 |
1999年 | 590篇 |
1998年 | 439篇 |
1997年 | 351篇 |
1996年 | 286篇 |
1995年 | 256篇 |
1994年 | 259篇 |
1993年 | 217篇 |
1992年 | 172篇 |
1991年 | 126篇 |
1990年 | 95篇 |
1989年 | 51篇 |
1988年 | 46篇 |
1987年 | 26篇 |
1986年 | 21篇 |
1985年 | 30篇 |
1984年 | 20篇 |
1983年 | 19篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 18篇 |
1977年 | 13篇 |
1974年 | 6篇 |
1973年 | 11篇 |
1971年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
111.
Modelling land cover change from existing land cover maps is a vital requirement for anyone wishing to understand how the landscape may change in the future. In order to test any land cover change model, existing data must be used. However, often it is not known which data should be applied to the problem, or whether relationships exist within and between complex datasets. Here we have developed and tested a model that applied evolutionary processes to Bayesian networks. The model was developed and tested on a dataset containing land cover information and environmental data, in order to show that decisions about which datasets should be used could be made automatically. Bayesian networks are amenable to evolutionary methods as they can be easily described using a binary string to which crossover and mutation operations can be applied. The method, developed to allow comparison with standard Bayesian network development software, was proved capable of carrying out a rapid and effective search of the space of possible networks in order to find an optimal or near-optimal solution for the selection of datasets that have causal links with one another. Comparison of land cover mapping in the North-East of Scotland was made with a commercial Bayesian software package, with the evolutionary method being shown to provide greater flexibility in its ability to adapt to incorporate/utilise available evidence/knowledge and develop effective and accurate network structures, at the cost of requiring additional computer programming skills. The dataset used to develop the models included GIS-based data taken from the Land Cover for Scotland 1988 (LCS88), Land Capability for Forestry (LCF), Land Capability for Agriculture (LCA), the soil map of Scotland and additional climatic variables. 相似文献
112.
Environmental sociology and the sociology of natural resources are two key subdisciplines of the sociological study on the interactions between nature and human society. Previous discussion on the relationships of these two fields has largely focused on their distinctions and synthesis in western (particularly American) academia. Environmental sociology emerged as an important sociological subdiscipline in China in the early 1990s and is under vigorous disciplinary construction at present. By contrast, the sociology of natural resources is still a novel term for most Chinese researchers. This article provides a systematic review of recent literature on the relationships between environmental and natural resource sociologies, which should provide important implications for the further development of environmental sociology in China. 相似文献
113.
Typologically identical (dwarf birch-herb-dwarf shrub-moss) open and closed larch forests growing on the same altitudinal transect have proved to differ in the structural-functional organization of lower vegetation layers. Coverage, general species composition, and species richness of the herb-dwarf shrub layer are higher in the open forest than in the closed forest. Correlations between individual species of vascular plants weaken upon transition from the open to the closed forest. Conversely, the coverage of the lichen-moss layer increases in the closed forest, which contributes to its role as a factor of selection of vascular plant species against the background of the prevailing influence of the tree layer. 相似文献
114.
Specific ecogenetic features of solods in the forest-steppe zone has been studied, and the role of biotic and abiotic factors of soil formation has been estimated. Differentiation of soil horizons with respect to the physical clay fraction accounts for specific features of their moistening, which is reflected in the ratio of strongly and weakly crystallized forms of iron. Periodic changes in redox conditions results in iron segregation, and a high content of fulvic acids accounts for its eluvial migration. These processes are controlled by soil geochemical barriers. 相似文献
115.
The impact of emissions from the Siberian Chemical Plant (Tomsk oblast) on reproduction and embryonic development of the fieldfare was studied. Bird abundance, clutch size, and egg volume in the impact and background (control) zones were similar, but partial brood mortality in the impact zone proved to be significantly higher, and the frequency of embryonic pathologies (including developmental abnormalities) was also several times higher than in the control. 相似文献
116.
微量金属元素及其配合物对厨余垃圾甲烷发酵的影响 总被引:4,自引:0,他引:4
生物可利用的微量金属元素不仅能够保证污染物以最大的速率转化,而且还可以使某些特殊的转化得以发生,并提高微生物对有毒污染物质的耐受能力。在研究厨余垃圾总固体浓度(total solid, TS)、接种量和C/N比对厨余垃圾厌氧发酵影响的基础上,重点探讨微量金属元素钴及其配合物丝氨酸对厨余垃圾厌氧发酵甲烷产量及关键酶含量的影响。结果表明,当TS为0.5%、接种污泥量为100 mL/L和C/N比为20∶1时,厨余垃圾厌氧发酵的甲烷产率较高,为367 mL/g COD;添加2 μmol/L的微量金属元素钴-配合物丝氨酸时,甲烷产率则提高到432 mL/g COD,相应地,辅酶M的含量由空白实验的41.21 μmol/g VSS提高到54.64 μmol/g VSS,辅酶F420的含量由0.31 μmol/g VSS提高到0.48 μmol/g VSS。 相似文献
117.
118.
微曝气Fenton氧化法处理模拟双酚A废水的效果及其生物验证 总被引:2,自引:1,他引:1
研究了微曝气Fenton氧化法关键工艺参数对模拟双酚A(BPA)废水处理效果的影响,并从活性污泥性质和污染物去除率两方面,采用膜生物反应器(membrane bioreactor, MBR)对微曝气Fenton氧化法的处理效果进行了实验验证,为实现BPA废水的生物处理奠定基础。结果表明,初始pH值、反应时间、H2O2/COD(质量浓度比)、H2O2/Fe2+ (摩尔浓度比)、反应温度及曝气量均对预处理效果有较大影响,在最佳条件下,COD去除率可达70%,BOD/COD值则由原废水的0.02提高到0.50以上。MBR处理上述出水的结果表明,经微曝气Fenton氧化处理BPA的废水,可较好地适应后续的生化处理。 相似文献
119.
120.
This paper develops a method for identifying and assessing long-term supply risks for mineral raw materials. The method is based on a combined evaluation of past and future supply and demand trends. By analysing raw material boom and bust cycles over the past 50 years, we have quantified indicators and defined benchmarks for identifying critical market situations. By applying the method, risks for supply shortage may be identified at an early stage. In addition, a numerical evaluation model has been developed for better comparison between various mineral raw materials. Compared to other assessment methods this method uses specific benchmarks for each raw material to better assess supply risks. The method is embedded within a systematic and comprehensive analytical approach. 相似文献