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491.
Although linear binding isotherms of hydrophobic organic chemicals (HOCs) with dissolved organic matter (DOM) are widely reported, several studies showed nonlinear HOC-DOM interactions. This study pointed out that fluorescence static quenching modeling (FSQM), which often uses a Stern-Volmer type plot to process the data from fluorescence quenching experiments, is conceptually different from the classic Stern-Volmer equation. We also emphasized that although linear Stern-Volmer plots are generally observed in literature, it does not necessarily indicate a linear HOC-DOM interaction. According to both mathematical simulation and laboratory sorption experiments in this study, nonlinear interactions could be concealed by the use of Stern-Volmer plot. Moreover, this study tested the two assumptions for applying FSQM to process binding data. Our results showed that binding coefficient (K(DOC)) for phenanthrene is neither independent of free solute concentration, nor DOM concentration, which is a critical limitation for using FSQM in a form of Stern-Volmer equation to examine HOC-DOM interactions. Therefore, the true characteristics of HOC-DOM interactions need to be examined using different ways of experimental design and data processing. 相似文献
492.
A method for the measurement of the relative toxicity of Cu2+ in aquatic environments is proposed. It is based on the quantitative measurement on the shape change of the supercoiled DNA after it is contacted with different levels of Cu2+ for various time intervals. In the absence of any redox reagents, all supercoiled DNA degraded into other forms of DNA after 24h incubation in the presence of 5.13 x 10(-3), 5.08 x 10(-4) and 5.35 x 10(-5)mol/L Cu2+. At a lower Cu2+ concentration (10(-6)mol/L), 44% of supercoiled DNA retained its original supercoiled form after 24 h, and 29% after 48 h. The concentration of RC50, i.e. concentration of pollutants at which 50% of the supercoiled DNA was relaxed compared to control samples, can be obtained from the does-response curves at different exposure time, which may provide a rapid and convenient approach to assess the relative toxicity of environmental pollutants. 相似文献
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Rea WJ Fenyves EJ Seba D Pan Y 《Journal of environmental biology / Academy of Environmental Biology, India》2001,22(3):163-169
The blood levels of organochlorine pesticides and chlorinated hydrocarbon solvents were measured in 200 and 114 chemically sensitive patients respectively, and compared with blood concentrations of standard medication (non- chlorinated substances. Clonidine, Haloperidol) of comparable toxicity after therapeutically effective dosage, and with reference levels of highly potent chemicals in the blood such as hormones. It was shown that the average blood levels of the most toxic environmental pollutants are comparable with the therapeutic steady state average blood levels of medications which have similar toxicities in the animal model. In addition the toxicity levels of xenoestrogens are at least an order of magnitude higher than normal plasma estrogen or progesterone levels. These findings suggest the possibility of additive or synergistic effects of these chlorinated compounds and the aforementioned medications. Also, these findings suggest the possibility of hormone deregulation from exposure to the aforementioned toxic chlorinated compounds. 相似文献
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潘奋 《中国安全科学学报》2000,10(5):9-12
阐述安全工程学的基本内容和“安全第一 ,预防为主”的方针。针对当前企业安全生产所面临的道德、心理、安全系统、责任制、监督监察及培训教育等问题 ,探讨了安全工程学与法学、经济学的关系 ,阐明了笔者的观点和研究的思路。 相似文献
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介绍了配电线路在运行中发生短路、过负荷以及导线或电缆接头处接触电阻过大而引起导线过热、产生火花和电弧引起火灾事故的原因。并针对上述原因 ,提出安全用电 ,预防配电线路发生火灾事故的安全技术措施 相似文献
500.
Primary production and rain use efficiency across a precipitation gradient on the Mongolia Plateau 总被引:25,自引:0,他引:25
Understanding how the aboveground net primary production (ANPP) of arid and semiarid ecosystems of the world responds to variations in precipitation is crucial for assessing the impacts of climate change on terrestrial ecosystems. Rain-use efficiency (RUE) is an important measure for acquiring this understanding. However, little is known about the response pattern of RUE for the largest contiguous natural grassland region of the world, the Eurasian Steppe. Here we investigated the spatial and temporal patterns of ANPP and RUE and their key driving factors based on a long-term data set from 21 natural arid and semiarid ecosystem sites across the Inner Mongolia steppe region in northern China. Our results showed that, with increasing mean annual precipitation (MAP), (1) ANPP increased while the interannual variability of ANPP declined, (2) plant species richness increased and the relative abundance of key functional groups shifted predictably, and (3) RUE increased in space across different ecosystems but decreased with increasing annual precipitation within a given ecosystem. These results clearly indicate that the patterns of both ANPP and RUE are scale dependent, and the seemingly conflicting patterns of RUE in space vs. time suggest distinctive underlying mechanisms, involving interactions among precipitation, soil N, and biotic factors. Also, while our results supported the existence of a common maximum RUE, they also indicated that its value could be substantially increased by altering resource availability, such as adding nitrogen. Our findings have important implications for understanding and predicting ecological impacts of global climate change and for management practices in arid and semiarid ecosystems in the Inner Mongolia steppe region and beyond. 相似文献