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281.
Based on a phenomenology that is rather frequent in the Gulf of Trieste (Northern Adriatic Sea), we analytically model the short time evolution of the temperature field inside a shallow layer of coastal water induced by a sudden offshore wind. In particular, we reproduce in a very simple way the unsteady surfacing of the isotherms forced by the marine current circulating in a vertical plane perpendicular to the coastline. The model is in agreement with the observations of a significant event recorded on 25 June, 2002 in the Gulf of Trieste. 相似文献
282.
Lúdvík Elíasson Stephen J. Turnovsky 《Journal of Environmental Economics and Management》2004,48(3):1018
We introduce a renewable resource sector into an endogenous growth model of a small economy, deriving the transitional dynamic equilibrium. The model generates a long-run equilibrium in which a resource sector of limited size can coexist with constant ongoing growth elsewhere. The key feature of the model is the allocation of labor between harvesting the resource and its use in the final output sector. This naturally generates the empirically observed negative relationship between resource abundance and growth. We examine both the dynamic and long-run responses of the economy to various shocks pertaining to technological production conditions and resource sector parameters. 相似文献
283.
水体表面微层中酞酸酯的光降解研究 总被引:30,自引:0,他引:30
研究了水体表面微层中酞酸酯化合物光降解的动力学,指出光催化降解符合一级动力学过程,实验证明:催化剂TiO2为2g.l^-1,pH为6,并有H2O2存在时,是DBP,DEHP光降解的最佳条件,溶解氧增加有利于光降解,实际表面微层水样的光催化降解速率比模拟水样快。 相似文献
284.
A palaeoecological study was conducted to investigate past environmental conditions and vegetation dynamics around the southwestern Ljubljana Moor. In order to find potential regularities and/or dependencies among co-existent plant species through time, different machine learning methods were applied to pollen records from the cores taken at Bistra and Ho?evarica. The data comprised relative pollen frequencies of the most common plant genera/families at particular core depths that correspond to particular ages in the Early and Mid Holocene periods. The applied methods include equation discovery and hierarchical clustering. Both methods have found plausible and explainable relationships among identified plant genera/families. 相似文献
285.
广州白云山次生常绿阔叶林的群落结构动态 总被引:11,自引:0,他引:11
根据对广州白云山次生常绿阔叶林群落相隔6a的两次植被调查,分析了广州白云山次生常绿阔叶林在保护条件下,自然演变过程中的群落结构动态.群落的垂直结构变化主要以大量幼树进入第一层成树为特点;水平结构则以密度和盖度的增长为特点.在种类组成方面,6a前群落中居多的阳性树种现已逐渐为耐阴性较强的种类所代替.在组织结构水平上,乔木层的物种多样性指数、群落均匀度指标趋于增加,而生态优势度指标趋于降低,反映了群落向着组成结构复杂、物种多样性增高的方面演变,且前期变化速度较快,后期较慢并趋于稳定. 相似文献
286.
区域地球化学表明 ,第三系泉水及直接被第三系覆盖的灰岩泉水的SIC在雨季小于 0 ,在旱季大于 0。在祭白龙洞 ,地表被第三系覆盖洞段滴水的暂时硬度比地表无此覆盖层的滴水小 1 .6~ 3mmol/L ,pH值也较低。第三系盖层中空气CO2 浓度为 1 0 0 0 0~ 1 4 0 0 0mg/m3,随深度下降。第三系的裂隙最大渗透张量为 0 .0 2~ 0 .0 5m/d,高于石灰岩。野外溶蚀试验结果 ,第三系盖层中石灰岩的溶蚀速率为 1 .5mg/ 1 0 0d,且垂直溶蚀速率与水平溶蚀速率相当。上述特征表明 ,较高的裂隙渗透张量及随裂隙下渗的富侵蚀性的水是石芽、石林发育的两个重要因素。这也是为什么发育好的石林常常伴随残留的小面积第三系出现的原因 相似文献
287.
288.
289.
辽东湾海冰漂移的动力要素分析 总被引:5,自引:3,他引:5
利用辽东海JZ20-2海域冰期气象、水文和海冰的实测资料和海冰数值模拟结果,对海冰漂移过程中风和流的拖曳力、海冰内力、科氏力和海面倾斜力要素的基本特征进行了分析;采用海冰热力-动力模式对1999年2月3日6:50至2月5日6:50间辽东湾海冰进行了48h数值模拟,对并JZ20-2海域的海冰动力要素进行了对比分析。发现海冰内力、风和流的拖曳力为同一量级,海面倾斜力和科氏力明显较小,其均值的比例关系依次为14.7:18.8:32.6:1.5:1.0;海冰各动力要素相互影响,共同决定了海冰的漂移速度和运动轨迹。 相似文献
290.
Carbon Management in Agricultural Soils 总被引:11,自引:0,他引:11
R. Lal 《Mitigation and Adaptation Strategies for Global Change》2007,12(2):303-322
World soils have been a major source of enrichment of atmospheric concentration of CO2 ever since the dawn of settled agriculture, about 10,000 years ago. Historic emission of soil C is estimated at 78 ± 12 Pg
out of the total terrestrial emission of 136 ± 55 Pg, and post-industrial fossil fuel emission of 270 ± 30 Pg. Most soils
in agricultural ecosystems have lost 50 to 75% of their antecedent soil C pool, with the magnitude of loss ranging from 30
to 60 Mg C/ha. The depletion of soil organic carbon (SOC) pool is exacerbated by soil drainage, plowing, removal of crop residue,
biomass burning, subsistence or low-input agriculture, and soil degradation by erosion and other processes. The magnitude
of soil C depletion is high in coarse-textured soils (e.g., sandy texture, excessive internal drainage, low activity clays
and poor aggregation), prone to soil erosion and other degradative processes. Thus, most agricultural soils contain soil C
pool below their ecological potential. Adoption of recommend management practices (e.g., no-till farming with crop residue
mulch, incorporation of forages in the rotation cycle, maintaining a positive nutrient balance, use of manure and other biosolids),
conversion of agriculturally marginal soils to a perennial land use, and restoration of degraded soils and wetlands can enhance
the SOC pool. Cultivation of peatlands and harvesting of peatland moss must be strongly discouraged, and restoration of degraded
soils and ecosystems encouraged especially in developing countries. The rate of SOC sequestration is 300 to 500 Kg C/ha/yr
under intensive agricultural practices, and 0.8 to 1.0 Mg/ha/yr through restoration of wetlands. In soils with severe depletion
of SOC pool, the rate of SOC sequestration with adoption of restorative measures which add a considerable amount of biomass
to the soil, and irrigated farming may be 1.0 to 1.5 Mg/ha/yr. Principal mechanisms of soil C sequestration include aggregation,
high humification rate of biosolids applied to soil, deep transfer into the sub-soil horizons, formation of secondary carbonates
and leaching of bicarbonates into the ground water. The rate of formation of secondary carbonates may be 10 to 15 Kg/ha/yr,
and the rate of leaching of bicarbonates with good quality irrigation water may be 0.25 to 1.0 Mg C/ha/yr. The global potential
of soil C sequestration is 0.6 to 1.2 Pg C/yr which can off-set about 15% of the fossil fuel emissions. 相似文献