全文获取类型
收费全文 | 1933篇 |
免费 | 50篇 |
国内免费 | 337篇 |
专业分类
安全科学 | 87篇 |
废物处理 | 117篇 |
环保管理 | 122篇 |
综合类 | 681篇 |
基础理论 | 374篇 |
污染及防治 | 640篇 |
评价与监测 | 147篇 |
社会与环境 | 86篇 |
灾害及防治 | 66篇 |
出版年
2023年 | 27篇 |
2022年 | 81篇 |
2021年 | 73篇 |
2020年 | 43篇 |
2019年 | 45篇 |
2018年 | 73篇 |
2017年 | 71篇 |
2016年 | 91篇 |
2015年 | 89篇 |
2014年 | 142篇 |
2013年 | 211篇 |
2012年 | 158篇 |
2011年 | 163篇 |
2010年 | 120篇 |
2009年 | 103篇 |
2008年 | 117篇 |
2007年 | 111篇 |
2006年 | 100篇 |
2005年 | 60篇 |
2004年 | 43篇 |
2003年 | 45篇 |
2002年 | 44篇 |
2001年 | 32篇 |
2000年 | 27篇 |
1999年 | 22篇 |
1998年 | 25篇 |
1997年 | 23篇 |
1996年 | 20篇 |
1995年 | 19篇 |
1994年 | 12篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1982年 | 6篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1967年 | 3篇 |
1965年 | 2篇 |
1964年 | 4篇 |
1961年 | 3篇 |
1960年 | 4篇 |
1959年 | 6篇 |
1958年 | 12篇 |
1957年 | 5篇 |
1956年 | 7篇 |
1955年 | 2篇 |
排序方式: 共有2320条查询结果,搜索用时 296 毫秒
791.
Ji?í Dole?al Zuzana MaškováJan Lepš Daniela SteinbachováFrancesco de Bello Jitka KlimešováOliver Tackenberg František ZemekJan Květ 《Agriculture, ecosystems & environment》2011,145(1):10-28
Oligotrophic mountain meadows are threatened biodiversity hotspots throughout Europe. The traditional summer hay-making followed by autumn grazing is no longer economic and question is whether alternative managements can maintain both plant species and functional diversity typical of these habitats. In the Bohemian Forest Mts., we applied three treatments (mowing once a year - i.e., cutting and removing the biomass, mulching once a year - cutting and leaving the crushed biomass to decompose in situ, fallowing - no cutting) in order to assess temporal changes in meadow vegetation, plant trait composition and biomass production in a 13-year experiment. We recorded for each species twenty-five traits as to be most informative of plant strategies related to growth, resource acquisition and carbon-water economy. We compared different components of trait composition (community averages that mostly reflect traits of dominant species vs. the Rao index of functional diversity that reflects trait dissimilarity among species) and their impact on biomass production. We show that mulching promotes species and functional diversity by facilitating heliophilous forbs and legumes with more acquisitive strategies in resource use and release, e.g., higher foliar N and P content. This occurs at the expense of tall grasses (with resource-retentive strategies, e.g., high leaf dry matter content) which dominate the mown and fallow plots. The divergence in most quantitative traits indicates that niche complementarity is the dominant assembly process in mulched plots, which can prevent competitive exclusion and enable species coexistence. The divergent development was detected only after 5-6 years. This slow floristic and functional response is caused by acidity of soil and severe mountain climate that preclude rapid responses of vegetation to land-use changes. We conclude that mulching represents a good compromise maintaining both plant species and functional diversity as well as a relatively high biomass production. Mowing without grazing leads to gradual nutrient loss and thus reduces the productivity and diversity in these oligotrophic ecosystems. Fallowing causes gradual loss in diversity by increased grass competition and litter accumulation. 相似文献
792.
793.
794.
795.
东北老工业基地不同土地利用类型土壤重金属污染特点 总被引:1,自引:0,他引:1
以东北老工业基地北部城市群为例,对其重点区域及周边的不同土地利用类型中Hg,Pb,Cr,Zn4种元素进行测定分析,利用单因子污染评价和多因子污染评价方法进行评价。结果表明,4种元素在不同利用类型土壤中,汞和铅在土壤中的迁移能力较弱,且汞元素在土壤中积累程度不高,只是在个别区域其含量有所波动;铅在农田和工业用地土壤中都有一定的积累,但向其他利用类型土壤的迁移效果不明显;铬在个别区域的旱田,蔬菜地中的积累略高,并迁移威胁到了其周围的林地土壤;锌在某些地区的工业用地,旱田,蔬菜地的污染程度相比其他几种元素污染更为严重。 相似文献
796.
During the Mesozoic, one of the most significant evolutionary processes was the secondary adaptation of tetrapods to life
in water. Several non-related lineages invaded from the terrestrial realms and from the oceans of the entire world. Among
these lineages, ichthyosaurs were particularly successful. Advance parvipelvian ichthyosaurs were the first tetrapods to evolve
a fish-shaped body profile. The deep skeletal modifications of their bodies, as well as their biology, depict advance ichthyosaurs
as the paradigm of secondary adaptation of reptiles to marine life. Functional inferences point to them as off-shore cruising
forms, similar to a living tuna, and some of them were capable of deep diving. Bone histology of some genera such as Temnodontosaurus, Stenopterygius, Ichthyosaurus, and Caypullisaurus, characterized by overall cancellous bone, is consistent with the idea of a fish-shaped ichthyosaurs as fast and far cruisers.
Here, we provide histological examination of the ribs of the Middle Jurassic parvipelvian Mollesaurus. Contrasting with the bone histology of other parvipelvian, Mollesaurus ribs are characterized by a compact and thick cortex. Our data indicate that the rib cage was heavy and suggest that not
all advanced ichthyosaurs were fast cruisers. The compact and dense ribs in these parvipelvian show that advance ichthyosaurs
were ecologically more diverse than previously thought and that the lightening of the skeleton reversed, as also occurred
in the evolution of cetacean, at least once along the evolutionary history of ichthyosaurs. 相似文献
797.
Veterinary antibiotics can enter the environment due to the common practice of land application of manure from treated animals. The environmental fate of tetracyclines in swine manure after composting and field application remains largely unknown. This study analyzed the concentrations of tetracyclines in manure, manure-based compost and compost amended soil in selected swine farms from Beijing, Jiaxing and Putian, China to determine the dilution effects of antibiotics when released into the soil environment. The results demonstrate that residues of antibiotics were detected in all samples and chlortetracycline as well as its degradation products should be regarded critically concerning their potential ecotoxicity. Application of manure-based compost to soil could reduce the possible risk posed by antibiotic contamination, but the trigger value of 100 μupg/kg was still exceeded in soil samples (776.1 μupg/kg dw) from Putian City after application of compost. Field studies such as the present one can help to improve the routine administration of antibiotic-containing composted manure. 相似文献
798.
谈地磁观测中的温度效应 总被引:1,自引:0,他引:1
地磁场各要素的绝对数值是通过基线值来确定的,而基线值又与温度相关,是一条大致随温度变化的曲线。本文选取通海、贵阳、邵阳、天水等地磁台的基线值资料,计算各分量基线值与记录室温度的相关系数,判定基线值与温度之间的相关关系,掌握在不同记录室温度条件下,温度变化对地磁基线值以及地磁观测仪器的影响程度。以供其他地磁台站新建、改造观测记录室时借鉴。 相似文献
799.
民国初年,我国救灾的成效方面存在着相当的不足,并直接引起连带性恶性效果。影响民国初年救灾成效不佳的原因主要可以归纳为三点,即:施政重点倾斜、社会动荡不安、政府救灾功能减弱等。 相似文献
800.
Katarina Kova? Marta Diez-Valcarce Peter Raspor Marta Hernández David Rodríguez-Lázaro 《Food and environmental virology》2012,4(4):209-212
The application of plant essential oils (EOs) (hyssop and marjoram) was evaluated for inactivation of non-enveloped viruses using murine norovirus and human adenovirus as models. No significant reduction of virus titres (TCID50) was observed when EOs were used at different temperatures and times. 相似文献