全文获取类型
收费全文 | 3305篇 |
免费 | 457篇 |
国内免费 | 963篇 |
专业分类
安全科学 | 409篇 |
废物处理 | 23篇 |
环保管理 | 442篇 |
综合类 | 2303篇 |
基础理论 | 480篇 |
污染及防治 | 65篇 |
评价与监测 | 212篇 |
社会与环境 | 456篇 |
灾害及防治 | 335篇 |
出版年
2024年 | 44篇 |
2023年 | 114篇 |
2022年 | 253篇 |
2021年 | 296篇 |
2020年 | 257篇 |
2019年 | 198篇 |
2018年 | 200篇 |
2017年 | 245篇 |
2016年 | 227篇 |
2015年 | 242篇 |
2014年 | 190篇 |
2013年 | 201篇 |
2012年 | 289篇 |
2011年 | 232篇 |
2010年 | 180篇 |
2009年 | 146篇 |
2008年 | 117篇 |
2007年 | 180篇 |
2006年 | 159篇 |
2005年 | 151篇 |
2004年 | 102篇 |
2003年 | 101篇 |
2002年 | 76篇 |
2001年 | 90篇 |
2000年 | 67篇 |
1999年 | 60篇 |
1998年 | 60篇 |
1997年 | 62篇 |
1996年 | 39篇 |
1995年 | 37篇 |
1994年 | 18篇 |
1993年 | 18篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1972年 | 4篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有4725条查询结果,搜索用时 288 毫秒
961.
有风时空气环境影响的最简化预测模式,遵循高斯方程,过程的推导严密而具有科学性,适用于高架点源下风向地面污染最大浓度及距离的确定,计算方法删繁就简,预测结果较为准确,对三级环境评价中的空气环境影响预测具有广泛的实践意义。 相似文献
962.
新组建的北京市地震局迫切需要建成一个比较完善的地震业务工作体系,首都圈防震减灾示范区系统工程建设为北京市地震工作实现"三大工作体系"带来了契机.本文重点介绍北京市防震减灾示范区系统工程中的预报、通讯、指挥、现场部分,为了提高效率、节省资金,项目组还在硬件、信息和资源共享、网络平台、虚拟专网、各系统间的联接、可持续发展等方面进行了整合. 相似文献
963.
964.
分形及其在地震研究中的应用 总被引:1,自引:0,他引:1
本文简要介绍了分形的基本理论,对分形在地震研究中的应用进行了阐述.着重介绍了近年来地震分形在地震预报中应用的一些成果.在此基础上,提出了作者对于开展进一步工作的意见,认为应该对区域和全球的地震分形进行全局性、系统性的研究,逐渐探索地震分形的物理机制和动力学机制,从而在地震研究上取得新进展. 相似文献
965.
966.
Dale Virginia H. Brown Sandra Calderón Magnolia O. Montoya Arizmendis S. Martínez Raúl E. 《Mitigation and Adaptation Strategies for Global Change》2003,8(4):323-348
To participate in the potential market for carbon credits based on changes in the use and management of the land, one needs to identify opportunities and implement land-use based emissions reductions or sequestration projects. A key requirement of land-based carbon (C) projects is that any activity developed for generating C benefits must be additional to business-as-usual. A rule-based model was developed and used that estimates changes in land-use and subsequent carbon emissions over the next twenty years using the Eastern Panama Canal Watershed (EPCW) as a case study. These projections of changes in C stocks serve as a baseline to identify where opportunities exist for implementing projects to generate potential C credits and to position Panama to be able to participate in the emerging C market by developing a baseline under scenarios of business-as-usual and new-road development. The projections show that the highest percent change in land use for the new-road scenario compared to the business-as-usual scenario is for urban areas, and the greatest cause of C emission is from deforestation. Thus, the most effective way to reduce C emissions to the atmosphere in the EPCW is by reducing deforestation. In addition to affecting C emissions, reducing deforestation would also protect the soil and water resources of the EPCW. Yet, under the current framework of the Clean Development Mechanism (CDM), only credits arising from reforestation are allowed, which after 20 years of plantation establishment are not enough to offset the C emissions from the ongoing, albeit small, rate of deforestation in the EPCW. The study demonstrates the value of spatial regional projections of changes in land cover and C stocks: The approach helps a country identify its potential greenhouse gas (GHG) emission liabilities into the future and provides opportunity for the country to plan alternative development pathways. It could be used by potential project developers to identify which types of projects will generate the largest C benefits and provide the needed baseline against which a project is then evaluated. Spatial baselines, such as those presented here, can be used by governments to help identify development goals. The development of such a baseline, and its expansion to other vulnerable areas, well positions Panama to respond to the future market demand for C offsets. It is useful to compare the projected change in land cover under the business-as-usual scenario to the goals set by Law 21 for the year 2020. Suggested next steps for analysis includeusing the modeling approach to exploreland-use, C dynamics and management ofsecondary forests and plantations, soilC gains or losses, sources ofvariability in the land use and Cstock projections, and other ecologicalimplications and feedbacks resulting fromprojected changes in land cover. 相似文献
967.
968.
Thirty-nine deep subsurface soils( 150—180 cm depth) near the outskirts of Beijing were investagated. The concentrations including n-alkanes from C13 to C36, pristane and phytane were in the range of 0.60 to 170.10μg/g, with a median value of 4.26. Carbon preference index values for n-alkanes ranged from 1.08 to 2.98, with a median value of 1.48. The percentage contribution of “wax” nalkanes was in the range of 6.03%--46.22%. A predominance of odd/even carbon n-alkanes and unresolved complex mixtures with different shapes and ranges were frequently observed. Factor analysis reduced the data set into three principal components and confirming contributions from low ( 19.58% ), medium ( 20.49% ) molecular weight species and long-chain n-alkanes (43.41% ), respectively.Molecular biomarkers such as pristane, phytane, hopanes and steranes were detected. Based on the principal component analysis, the concentration profiles and molecular markers, it was found that the aliphatic hydrocarbons were from both biogenic and anthropogenic sources. 相似文献
969.
塔里木是与华北、杨子齐名的中国三大块体之一,是连接中亚与太平洋西岸(中国东部)的桥■,一直为世人所瞩目。作者认为,塔里木板块是在前震旦系结品基底的基础上,主体部分经历了古生代稳定的陆台,中、新生代陆内盆地的演化阶段;边缘部分经历了新元古代一古生代一小生代的陆完增生和相邻洋壳的消亡。在局部地区和某些阶段,由于地壳发展的不均衡,曾发牛过裂谷、裂陷柏和扭壳断裂带。依据这一构造认识划分了赋存于塔里木板块基底构造层、中间构造层、上都构造层、古生代裂谷系、中一新生代超壳断裂排、被动边缘和陆壳增生区小的成矿系列。其中,石油、天然气、钾盐、金刚石、铜、稀有金属、铅、铸和宝玉石等多种矿产均具有非常巨大的找矿潜力。 相似文献
970.
Blasing T. J. Broniak Christine Marland Gregg 《Mitigation and Adaptation Strategies for Global Change》2005,10(4):659-674
Time series of fossil fuel carbon emissions from 1960–2000 for each of the U.S. states and the District of Columbia are presented
and discussed. Comparison of the nationally summarized results with other national datasets shows generally good agreement,
usually within 2%, and gives insight into the quality of all the data series. Our extension of the state-by-state emissions
estimates back to 1960 reveals patterns of change that are coherent across states and can be related to historic events such
as energy crises and federal legislation. Most notable is the changing pattern of coal usage, as coal-producing states produce
increasingly more energy (mostly for electricity) for other states so that per capita CO2 emissions diverge for states that import as opposed to those that export electricity. The decline in carbon emissions from
petroleum products following the 1970s is also evident. Per capita emissions range over an order of magnitude for the different
states. The data suggest that differences in per capita emissions arise from differences in many technological, physical,
resource, social, and economic factors. The data presented here and the few correlations briefly noted pose a challenge for
trying to use per capita emissions as a measure of equity or to provide mitigation targets. 相似文献