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521.
Validity of Performance Criteria and a Tentative Model for Regulatory Use in Compensatory Wetland Mitigation Permitting 总被引:1,自引:1,他引:0
The purpose of this paper is to develop the principles for a manageable and practical set of performance criteria that will
reasonably assure no net loss in a situation in which it cannot be absolutely assured. To this end, the performance criteria
proposed for 116 compensatory wetland projects on file with the Army Corps of Engineers in San Francisco, between 1988 and
1995, were examined. The trends discerned in the project proposals were analyzed and evaluated in light of the current state
of wetland science. Specific suggestions for the development of uniform criteria in each of four major wetland types—riparian,
perennial tidal, perennial nontidal, and seasonal—are discussed, and a system of regulation tying qualitative assessment with
quantitative requirements is outlined as a reasonable solution to the enforcement of the no-net-loss policy. 相似文献
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Biological Control of Water Hyacinth Under Conditions of Maintenance Management: Can Herbicides and Insects Be Integrated? 总被引:1,自引:0,他引:1
Ted D. Center F. Allen Dray Jr. Greg P. Jubinsky Michael J. Grodowitz 《Environmental management》1999,23(2):241-256
Neochetina eichhorniae and N. bruchi. We therefore sampled water hyacinth and weevil populations at 54 sites distributed statewide. Half were under maintenance
control, half were not treated with herbicides. General site conditions were assessed, demographic data were collected on
weevil and plant populations, the reproductive condition of the weevils was determined, and plant nutrient and proximate composition
of water hyacinth leaves were analyzed. Water hyacinth infestations under maintenance control were minimal when compared to
unmanaged sites. Likewise, on a population basis, all weevil cohorts were much lower due to the paucity of plants. Plants
at unmanaged sites, where weevil intensities were much higher, suffered high levels of stress and showed low growth potential.
Lower percentages of the female weevils were reproductive at unmanaged sites when compared to managed sites, so densities
of reproductives and immatures were similar at both site types. Reproductive status of the weevils improved with increased
plant quality. Plant quality, in turn, declined as stresses arising from weevil feeding increased. Plant quality was positively
correlated with plant growth potential and flower production. Thus, maintenance control improved plant nutritive quality thereby
inducing reproductive vigor of the weevils, but ensuring plant regrowth and the need for future control. This suggests that
biological and herbicidal controls should be integrated, using herbicides to maintain water hyacinth infestations below management
thresholds but in a manner that conserves biological control agent populations. This approach would lead to improved plant
nutritional quality that would, in turn, stimulate reproduction in biological control agent populations. 相似文献
524.
Thomas Hruby 《Environmental management》1999,23(1):75-85
/ Many methods have been developed over the last two decades to provide information about wetland functions, but there has been little discussion of the models and algorithms used. Methods for generating information about wetlands were analyzed to understand their similarities, differences, and the type of information provided. Methods can first be grouped by the type of information they provide-classifications, characterizations, ratings, assessments, and evaluations. Methods that characterize, rate, or assess wetlands may generate information using one of two conceptual approaches-logic and mechanistic. Most methods that generate a numeric assessment of performance or value of wetland functions rely on the mechanistic approach to constructing models. Rapid assessment methods based on mechanistic models, however, do not assess the rates or dynamics of ecological processes occurring in wetlands. Rather, they provide a clear and concise way of organizing our current, and often subjective, knowledge about wetland functions. This is one limitation of current methods that is often misunderstood both by wetland managers and the scientific community. The advantages and limitations of the assumptions and the computational elements inherent in these approaches are discussed to provide wetland managers and regulators a better understanding of the information they are using. KEY WORDS: Wetlands; Functions; Assessment; Models; Methods 相似文献
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527.
污染稻、麦籽实中Cd、Cu、Pb的分布及其存在形态初探 总被引:31,自引:0,他引:31
采用组织化学及溶剂提取法研究了污染水稻、小麦籽实中Cd、Cu、Pb的分布及存在形态.结果表明,3种金属元素在水稻、小麦籽实各形态结构中的浓度具有明显不均一性,胚中浓度显著高于胚乳,颖壳,皮层中浓度也较高;糙米、麦粒中的Cd、Cu、Pb在去离子水、0.1mol EDTA、1%醋酸、2.5% NaCl、0.2%NaOH、70%乙醇中的溶出比例有显著差异;综合2项试验结果可以看出Cd、Cu、Pb在籽实中主要与谷物成分结合形成配合物,其优势形态是蛋白质结合态. 相似文献
528.
通过用氧化铝柱层析和等梯度呷醇:水=85%:15%)反相高效液相色谱(C18硅烷柱)紫外检测器254nm,测定30多种油品和我国海洋环境油类样品中的多环芳烃(PAHs),建立了溢油PAHs模糊指数结果表明,油类PAHs响应因子和相对保留值的变异系数分别在8.4%-16.5%和0.00%-5.4%之间,回收率在74.6%-111.2%之间,精密度和准确度较好;海洋环境油类的多环芳烃模糊指数值(0.00383-0.01839)与润滑油类的值(0.00106-0.00942)接近,较石油及其它产品油的值(0.06983-1.00000)低;用润滑油类作为标准油,PAHs模糊指数作为溢油芳烃类监测的指示物(指标),可提高监测海洋环境油类的代表性和可靠性 相似文献
529.
常压非平衡态等离子体降解挥发性烃类污染物 总被引:30,自引:1,他引:29
采用无声放电产生的非平衡态等离子体,对含有易挥发性有机化合物正己烷、环己烷、苯和甲苯4种典型的烃类废气的空气进行了处理.结果表明,对于一个大气压下正己烷含量(体积分数)为0.26%、0.79%、13%的宁气,在12kV的电压下放电ls,正己烷的降解率分别为88%、81.8%、64.9%.含有环己洗、苯及甲苯浓度为0.26%的空气,在同样的条件下,放电ls后,环己烷、苯及甲苯降解率分别为87.4%、8l%和70.3%,其主要降解产物为CO2和H2O.还研究了污染物浓度与氧含量对非平衡态等离子体法降解挥发性烃类污染物的影响 相似文献
530.