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331.
332.
应用时域边界元法 ,研究了单侧接触埋置结构与瞬态SH液 (剪切横波 )的动力相互作用 ,当入射SH波足够强时 ,界面会出现局部滑移并假设摩擦遵守库仓定理。笔者从实际情况出发 ,提出了新的数学模型和计算方法 ,计算了埋置矩形结构与瞬态SH波的动力相互作用问题 ,由于对此类问题的深入研究 ,为评估和预测埋置结构在动荷载下的安全性及疲劳寿命提供了重要的理论价值 相似文献
333.
何瑛 《防灾科技学院学报》2007,9(2):104-106
翻译是一项十分复杂的工作.中外翻译理论界流派林立,成果颇丰.但由于这一语言现象涉及因素太杂,理论体系的构建难度较大.尤金·奈达在当代翻译理论界因其不断创新的意识而成绩斐然.本文旨在通过对奈达博士翻译理论的介绍和探究,来谈一些自己的认识和看法,从而在翻译教学中加以借鉴. 相似文献
334.
在建立城市污水处理厂毒物归宿模型的基础上,继续探讨了固液相吸附分配系数Kp,生物降解速率系数Kb,挥发及吹脱速率系数KvKst等模型参数的估计方法,并就模型的检验,模拟及其在风险评价中的应用作了案例研究。 相似文献
335.
A two-dimensional simulation model of phosphorus uptake including crop growth and P-response 总被引:2,自引:0,他引:2
Alain Mollier Peter De Willigen Marius Heinen Christian Morel Andr Schneider Sylvain Pellerin 《Ecological modelling》2008,210(4):453-464
Modelling nutrient uptake by crops implies considering and integrating the processes controlling the soil nutrient supply, the uptake by the root system and relationships between the crop growth response and the amount of nutrient absorbed. We developed a model that integrates both dynamics of maize growth and phosphorus (P) uptake. The crop part of the model was derived from Monteith's model. A complete regulation of P-uptake by the roots according to crop P-demand and soil P-supply was assumed. The soil P-supply to the roots was calculated using a diffusion equation and assuming that roots behave as zero-sinks. The actual P-uptake and crop growth were calculated at each time step by comparing phosphate and carbohydrate supply–demand ratios. Model calculations for P-uptake and crop growth were compared to field measurements on a long term P-fertilization trial. Three P-fertilization regimes (no P-fertilization, 42.8 kg P ha−1 year−1 and 94.3 kg P ha−1 year−1) have led to a range of P-supply. Our model correctly simulated both the crop development and growth for all P-treatments. P-uptake was correctly predicted for the two non-limiting P-treatments. Nevertheless, for the limiting P-treatment, P-uptake was correctly predicted during the early period of growth but it was underestimated at the last sampling date (61 day after sowing). Several arguments for under-prediction were considered. However, most of them cannot explain the observed magnitude in discrepancy. The most likely reason might be the fact that biomass allocation between shoot and root must be modelled more precisely. Despite this mismatch, the model appears to provide realistic simulations of the soil–plant dynamic of P in field conditions. 相似文献
336.
We develop a dynamic groundwater model that incorporates both groundwater pumping and investment in deeper wells and apply the model to the arid, alluvial aquifer region of Northern India that is experiencing rapid depletion. We compute the potential benefits of regulating groundwater use by comparing the net benefits of groundwater under optimal management to the net benefits under a common pool regime with two different cost structures: one with flat electricity tariffs, which are widespread in India, and a second with full marginal cost electricity pricing. Using numerical simulation, we find that the opportunity to invest in deeper wells significantly exacerbates the common pool problem and suggests the potential for large benefits (66% of common pool benefits) from optimally managing groundwater use or new drilling. Flat tariffs exacerbate the problem, but large gains (almost 23%) remain even if farms are charged the full marginal cost of electricity. 相似文献
337.
Xue Shen Lei Lu Baoyu Gao Xing Xu Qinyan Yue 《Frontiers of Environmental Science & Engineering》2019,13(1):9
338.
A system can undergo rapid regime shift in which the growth of natural resources suddenly and permanently declines. We examine how the threat of such a shift alters the strategic management of a common pool renewable resource. We consider exogenous and endogenous threats and examine their effects on both incentives to join a coalition and harvest decisions. We find that an exogenous threat of reduced resource growth may cause the coalition to grow in size, and, perhaps of most interest, we identify conditions under which members of the stable coalition reduce harvest while non-members increase harvest in response to the threat. In contrast, an exogenous threat of total stock collapse may destabilize coalitions, resulting in higher harvest from former members, but reduced harvest by non-members. When the threat of either type of shift is endogenous, the threat of regime shift can induce stable coalitions with more than two members. In particular, we identify cases in which the first best (full cooperation) is sustained as an equilibrium outcome. Finally, we find that the relation between the magnitude of the shift and the size of stable coalitions may be negative. 相似文献
339.
340.
An investigation was conducted to estimate mercury emission to the atmosphere from different environmental surfaces and to assess its contribution to the local mercury budget in Chongqing, China. Mercury flux was measured using dynamic flux chamber (DFC) at six soil sites of three different areas (mercury polluted area, farmland and woodland) and four water surfaces from August 2003 to April 2004. The mercury emission fluxes were 3.5 ± 1.2–8.4 ± 2.5 ng m−2 h−1 for three shaded forest sites, 85.8 ± 32.4 ng m−2 h−1 for farming field, 12.3 ± 9.8–733.8 ± 255 ng m−2 h−1 for grassland sites, and 5.9 ± 12.6–618.6 ± 339 ng m−2 h−1 for water surfaces. Mercury exchange fluxes were generally higher from air/water surfaces than from air/soil surfaces. The mercury negative fluxes were found in tow soil sites at overcast days (mean = −6.4 ± 1.5 ng m−2 h−1). The diurnal and seasonal variations of mercury flux were observed in all sites. The mercury emission responded positively to the solar radiation, but negatively to the relative humidity. The mercury flux from air/soil surfaces was significantly correlated with soil temperature, which was well described by an Arrhenius-type expression with activation energy of 31.1 kcal mol−1. The annual mercury emission to the atmosphere from land surface is about 1.787 t of mercury in Chongqing. 相似文献