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221.
Introduction C arbon dioxide, m ethane and nitrous oxide play im portant roles in the radiation balance of the earth contributing to the greenhouse effect (Rodhe, 1990). N 2O also takes part in the destruction of stratospheric ozone (W ang, 1999). N atura… 相似文献
222.
本项研究系统分析了资源与经济发展的基本关系特点。提出中国持续发展的核心问题是处理资源与发展的关系 ,并认为关键是建立适应市场机制的资源供需体系。总结了中国跨世纪面临的资源四大挑战与存在的五大问题 ,概括了我国资源与发展的若干规律 ,首次提出中国存在资源国际贸易逆差 ,中国国际贸易的顺差是依靠资源国际贸易的逆差、牺牲紧缺资源而换取的。因此 ,中国应该实行双向式自然资源发展战略。并提出了该战略的核心思想及若干政策性建议 相似文献
223.
产品碳足迹以碳标签的形式日益广泛地应用于产品供应链,通过影响企业和消费者行为而有效地促进全球碳减排.然而产品碳足迹核算标准种类繁多,不同标准对产品碳足迹的核算规定存在差异,致使其核算结果难于有效对比.本文以胶版印刷纸为例,对比分析了目前最权威的3个国际标准PAS2050、GHG Protocol和ISO14067,识别了三者对于8点产品碳足迹核算要素的不同规定,定量解析了标准差异对产品碳足迹核算的影响.结果表明,3个标准规定的差异可导致产品碳足迹核算结果产生较大的不确定性,GHG Protocol和ISO14067结果分别比PAS2050高61%和49%,其中,"碳存储、消费者交通、固定资产和延迟排放加权影响"4个方面的差异对案例产品碳足迹影响最为显著.因此,按照产品类别制定统一的核算要求是碳标签交流对比的基本前提,明晰的标准规定是降低核算结果不确定性的必要途径. 相似文献
224.
225.
We study how the combination of tides and freshwater buoyancy affects the marine organisms accumulation and horizontal transport
in the ROFI system of the eastern English Channel. The Princeton Ocean Model coupled with a particle-tracking module is used
to study the migration of fish eggs and larvae under different forcing conditions. Results of modeling are validated against
observed concentrations of Flounder (Pleuronectes flesus) larvae. Numerical Lagrangian tracking experiments are performed with passive and active particles, representing sea-water
organisms. Passive particles are neutrally buoyant whereas active particles are able to exercise light dependent vertical
migrations equating to the swimming behavior of larvae. The experiments reveal that the strongest accumulation of particles
occurs along the French coast on the margin of the ROFI. This happens because the interaction between the turbulence, the
freshwater buoyancy input, and tidal dynamics, produces particle trapping and vertical spreading within the frontal convergence
zone. Tides and freshwater input induce net alongshore horizontal transport toward the North. Tidal currents modulate the
magnitude of horizontal transport whereas the fresh water input controls more the location of accumulation zones. Tracking
experiments with active particles indicate that the vertical migration leads to a significant departure from the passive particle
transport pattern. Differences lie in the shape of the particle transport pattern and the rate of the northward migration.
In particular, vertically migrating particles travel slower. To find possible Flounder migration pathways, particles are released
within the assumed spawning area of Flounder. The model predicts larvae drift routes and demonstrates that throughout the
entire particle-tracking period the horizontal structure of the particle distribution is consistent with the larvae concentrations
observed during the field experiments. 相似文献
226.
227.
河口潮汐湿地沉积物电子受体和盐度的变化将对间隙水、沉积物的地球化学参数及有机碳厌氧矿化途径产生重要影响.本研究于闽江河口塔礁洲淡水野慈姑(Sagittaria trifolia L.)湿地原位施加人造海水及Fe(III)溶液,模拟研究了盐水入侵及径流Fe(III)浓度增强对河口潮汐湿地沉积物、间隙水的地球化学参数(溶解性CH4、DOC、DOC∶DON、Fe2+和ΔSO2-4)和沉积物各形态固相铁(非硫Fe(II)、无定形Fe(III)、晶质Fe(III)、Fe S和Fe S2)含量的影响.结果表明,模拟盐水入侵及径流Fe(III)浓度增强均可降低间隙水溶解性CH4和DOC浓度,径流Fe(III)浓度增强增加了非硫Fe(II)和晶质Fe(III)含量,盐水入侵可减小间隙水ΔSO2-4含量.间隙水ΔSO2-4与DOC、DOC∶DON、溶解性CH4及Fe2+浓度相关.模拟盐水入侵及径流Fe(III)浓度增强可分别促进硫酸盐异化还原和铁异化还原速率,同时减小间隙水CH4浓度,改变河口潮汐湿地土壤有机质厌氧矿化优势途径. 相似文献
228.
中外清洁生产背景的比较及其对我国的启示 总被引:3,自引:0,他引:3
清洁生产是实施可持续发展战略的重要途径。本文从中外比较的角度,分析了国外清洁生产的成功经验和中外实施清洁生产的背景差异,提出了今后我国在实施清洁生产战略时,应重视的几个方面,即完善实施前提,发挥政府与产业部门的作用,加强科学研究与教育培训 相似文献
229.
An infinite-horizon model of dynamic membership of international environmental agreements 总被引:3,自引:0,他引:3
Santiago J. Rubio Alistair Ulph 《Journal of Environmental Economics and Management》2007,54(3):296-310
Much of the literature on international environmental agreements (IEAs) uses static models, although most important transboundary pollution problems involve stock pollutants. The few papers that study IEAs using models of stock pollutants do not allow for the possibility that membership of the IEA may change endogenously over time. In this paper we analyse a simple infinite-horizon version of the static model of self-enforcing IEAs, in which damage costs increase with the stock of pollution, and countries decide each period whether to join an IEA. Using a quadratic approximation of the value function of the representative country we show that there exists a steady-state stock of pollution with corresponding steady-state IEA membership, and that as the stock rises towards steady state the IEA membership falls. Moreover, we find that the greater is the cost of damage, and hence the greater are the potential gains from cooperation, the smaller is the membership of a self-enforcing IEA. 相似文献
230.
Prehistoric Decline in Freshwater Mussels Coincident with the Advent of Maize Agriculture 总被引:1,自引:0,他引:1
Abstract: During late prehistory, high population densities and intensive agricultural practices of Native American societies had profound effects on the pre-Columbian landscape. The degree to which Native American land use affected aquatic ecosystems is unknown. Freshwater mussels are particularly sensitive harbingers of modern-day ecosystem deterioration. We used data from prehistoric Native American shell middens to examine prehistoric trends in abundance of freshwater mussels of the genus Epioblasma in North America during the last 5000 years. The relative abundance of Epioblasma declined steadily during this period, a result that could be explained either by an increase in human impacts to streams or by long-term climatic changes unrelated to human activities. The rate of decline of Epioblasma increased significantly, however, after the advent of large-scale maize agriculture in the southeastern United States about 1000 years before the present. Our results suggest that human land-use activities in prehistory caused changes in freshwater mussel communities that were lower in magnitude but similar in direction to changes caused by recent activities. 相似文献