全文获取类型
收费全文 | 786篇 |
免费 | 33篇 |
国内免费 | 34篇 |
专业分类
安全科学 | 95篇 |
废物处理 | 18篇 |
环保管理 | 86篇 |
综合类 | 183篇 |
基础理论 | 389篇 |
污染及防治 | 23篇 |
评价与监测 | 23篇 |
社会与环境 | 30篇 |
灾害及防治 | 6篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 13篇 |
2019年 | 8篇 |
2018年 | 8篇 |
2017年 | 16篇 |
2016年 | 22篇 |
2015年 | 15篇 |
2014年 | 17篇 |
2013年 | 29篇 |
2012年 | 34篇 |
2011年 | 49篇 |
2010年 | 45篇 |
2009年 | 48篇 |
2008年 | 68篇 |
2007年 | 70篇 |
2006年 | 70篇 |
2005年 | 51篇 |
2004年 | 40篇 |
2003年 | 29篇 |
2002年 | 17篇 |
2001年 | 18篇 |
2000年 | 24篇 |
1999年 | 30篇 |
1998年 | 19篇 |
1997年 | 20篇 |
1996年 | 20篇 |
1995年 | 18篇 |
1994年 | 12篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有853条查询结果,搜索用时 31 毫秒
791.
Stephen C. Newbold 《Environmental Modeling and Assessment》2005,10(3):251-263
Most landscape design models have been applied to the problem of maximizing species richness in a network of nature reserves.
This paper describes a combined hydrologic simulation and landscape design model designed to prioritize sites for wetlands
restoration, where the objective is to maximize the amount of nutrients in non-point-source runoff attenuated in the restored
wetlands. Targeted site selection in four small watersheds in the Central Valley resulted in predicted levels of nitrogen
attenuation two to eight times greater than that from maximizing wetland area without consideration of the location of the
restoration sites.
Disclaimer The views expressed in this paper are those of the author and do not necessarily represent those of the US Environmental Protection
Agency. No official Agency endorsement should be inferred. 相似文献
792.
The Hamilton-Zuk hypothesis states that females choosing males with more developed secondary sexual traits, i.e. brighter males, achieve greater fitness if variability in brightness reflects heritable variation in resistance to parasites. However, several factors will affect the likelihood that parasites play a role in sexual selection in given species. Here, using simple models, we show that because of parasite aggregation on a few hosts, only few breeding males would suffer from reductions in brightness due to parasites. Only in cases where parasites are abundant and show low levels of aggregation among their hosts would there be sufficient variability in brightness among breeding males for female choice of bright, resistant males to evolve. In addition, sufficient parasite-induced variability in brightness among breeding males will only occur in host-parasite systems where pathology is linearly related to the number of parasites per host. The presence of males that are uninfected and bright but genetically susceptible to parasites will also influence the fitness advantages obtained by females choosing bright males. If genetic immunity against parasites is rare in the host population, females can probably only benefit from choosing bright males if parasites are common and little aggregated among males. These results greatly limit the generality of the Hamilton-Zuk hypothesis, and suggest that only a small fraction of host-parasite associations could promote the evolution of host mate choice for resistance based on brightness.
Correspondence to: R. Poulin 相似文献
793.
The real option valuation method is often presented as an alternative to the traditional discounted cash flow (DCF) approach because it is able to quantify the additional asset value arising from flexible asset management. However, these two valuation methods differ on a more fundamental level: their approach to determining the effects of cash flow uncertainty on asset value. Real option valuation adjusts for risk within the cash flow components while the DCF method discounts for risk at the aggregate net cash flow. This seemingly small difference allows the real option method to differentiate assets according to their unique risk characteristics, while the conventional DCF approach cannot.This paper presents an overview of the real options and conventional DCF frameworks for valuing uncertain cash flows. To emphasize the approaches' different treatment of risk we assume an absence of managerial flexibility. Using simple algebra, this paper demonstrates that the traditional DCF method fails to adequately discount net cash flow risk, no matter what discount rate is used. Finally, in a stylized mining example we show that DCF rules would lead a developer to forego $24.5 million in value creation, at a profitability index of 1.49, by making a poor investment decision. 相似文献
794.
795.
本文论证了环境保护在实施新型工业化战略中的地位和作用,提出了在推进新型工业化中构筑环保支持系统的意见。 相似文献
796.
797.
Sex linkage among genes controlling sexually selected traits 总被引:8,自引:0,他引:8
Klaus Reinhold 《Behavioral ecology and sociobiology》1998,44(1):1-7
Using literature data on reciprocal crosses I estimated the influence of sex-chromosomal genes on morphological and behavioral
traits. To determine a special role of the sex chromosomes for sexually selected traits, I compared the estimated influence
of X-chromosomal genes on sexually selected traits with their estimated influence on traits not under sexual selection. About
one-third of the phenotypic variation in sexually selected traits is caused by X-chromosomal genes. There was, in contrast,
no significant influence of X-chromosomal genes on traits that were classified as not sexually selected. Sexually selected
traits thus seem to be influenced significantly more by X-chromosomal genes than traits not under sexual selection. Though
this differential influence of X-chromosomal genes cannot readily be explained with current theoretical knowledge, it may
shed some light on X-linked hybrid sterility and on the discussion between arbitrary and good-gene models for the evolution
of female choice.
Received: 30 January 1998 / Accepted after revision: 20 June 1998 相似文献
798.
Area-Based Refinement for Selection of Reserve Sites with the Benefit-Function Approach 总被引:1,自引:0,他引:1
Abstract: Optimization of resource use is necessary for efficient conservation planning. Many reserve-selection algorithms aim to identify representative but inexpensive networks, which may lead to selecting small sites due to their lower costs and collectively higher species richness. Nevertheless, larger sites would be preferable regarding species' long-term persistence. An area-based refinement can be used to overcome this problem. We used a reserve-planning framework in which continuous benefit functions valued representation (numbers of populations), and differential species weights were based on a species' local rarity and threatened status. We introduced a refinement based on the species-area relationship that provides relatively higher values for larger sites. We applied the proposed method to rich fen vegetation in southern Finland. The species-area refinement resulted in a network of significantly larger sites with minor trade-offs with representation (numbers of populations). Giving endangered species higher weights ensured that the trade-off occurred mostly between site size and representation of low-priority species. We recommend using a species-area refinement for practical, maximum-coverage conservation planning. 相似文献
799.
为构建科学的应急救援体系,基于气象服务信息制定更合理的应急物资配送路径方案。将突发灾害下典型的"单出救点、单受灾点"应急物资配送网络结构作为研究对象。运用衰减系数反映气象条件对物资配送速度的实时影响。构建以满足时间限制和需求量要求为前提的应急物资配送路径选择模型。设计算例进行数值仿真和参数分析,将求解结果与传统最短路径法所选路径方案进行对比分析。结果表明:气象服务提供的衰减系数和途经各区域灾害强度等关键信息对配送路径的优化决策有重要影响。 相似文献
800.