全文获取类型
收费全文 | 4539篇 |
免费 | 30篇 |
国内免费 | 25篇 |
专业分类
安全科学 | 44篇 |
废物处理 | 171篇 |
环保管理 | 162篇 |
综合类 | 2075篇 |
基础理论 | 803篇 |
环境理论 | 7篇 |
污染及防治 | 914篇 |
评价与监测 | 251篇 |
社会与环境 | 152篇 |
灾害及防治 | 15篇 |
出版年
2022年 | 52篇 |
2021年 | 39篇 |
2019年 | 33篇 |
2018年 | 70篇 |
2017年 | 57篇 |
2016年 | 76篇 |
2015年 | 65篇 |
2014年 | 97篇 |
2013年 | 195篇 |
2012年 | 128篇 |
2011年 | 98篇 |
2010年 | 125篇 |
2009年 | 135篇 |
2008年 | 148篇 |
2007年 | 171篇 |
2006年 | 119篇 |
2005年 | 113篇 |
2004年 | 96篇 |
2003年 | 117篇 |
2002年 | 89篇 |
2001年 | 88篇 |
2000年 | 86篇 |
1999年 | 91篇 |
1998年 | 62篇 |
1997年 | 59篇 |
1996年 | 42篇 |
1995年 | 56篇 |
1994年 | 60篇 |
1993年 | 37篇 |
1991年 | 40篇 |
1990年 | 44篇 |
1989年 | 34篇 |
1985年 | 39篇 |
1979年 | 38篇 |
1978年 | 34篇 |
1969年 | 37篇 |
1967年 | 57篇 |
1966年 | 50篇 |
1965年 | 57篇 |
1964年 | 64篇 |
1963年 | 64篇 |
1962年 | 64篇 |
1961年 | 69篇 |
1960年 | 59篇 |
1959年 | 70篇 |
1958年 | 61篇 |
1957年 | 74篇 |
1956年 | 57篇 |
1955年 | 55篇 |
1954年 | 51篇 |
排序方式: 共有4594条查询结果,搜索用时 343 毫秒
461.
Hans Preusting Jaap Kingma Gjalt Huisman Alexander Steinbüchel Bernard Witholt 《Journal of Polymers and the Environment》1993,1(1):11-21
WhenPseudomonas oleovorans (GPo1) is grown on sodium octanoate under ammonium limiting conditions, it is able to accumulate a copolyester consisting of medium chain length 3-hydroxyalkanoic acids (PHAm). 3-Hydroxybutyrate is only incorporated in trace amounts. WhenP. oleovorans is equipped with the PHB biosynthetic genes ofAlcaligenes eutrophus (GPo1[pVK101::PP1]), it forms a polyester containing major amounts of 3-hydroxybutyrate. The resulting polymer however is a blend of PHAm and PHB, rather than a copolymer of 3-hydroxybutyrate and medium chain length 3-hydroxyalkanoic acids [11]. To establish whether PHAm and PHB molecules are stored in the same or separate granules by this recombinantP. oleovorans strain, we studied polymer forming cells by freeze-fracture electron microscopy. This approach is possible because previous freeze-fracture electron microscopy studies on PHAm and PHB accumulating strains have shown that PHAm and PHB granules can be distinguished from each other: PHAm granules from mushroom-like structures, whereas PHB granules from needle structures during freeze-fracturing. In this paper we show that stationary phase cells of GPo1[pVK101::PP1] contained both mushroom and needle-like structures, indicating that PHAm and PHB chains were stored in separate granules. To be able to determine whether the separation of PHAm and PHB is complete, the respective granules were separated on sucrose gradients. A total cell extract of GPo1[pVK101::PP1] which was subjected to sucrose gradient centrifugation revealed two white bands of different densities: the upper band with a density of 1.05 g/mL consisted exclusively of PHAm granules, while the lower band with a density of 1.19 g/mL consisted of PHB granules only. Thus, when bacteria synthesize both PHAm and PHB, the resulting polymer chains are segregated completely and stored in separate granules. 相似文献
462.
463.
464.
465.
Behavior of dialifor, dimethoate, and methidathion in artificially fortified grape juice processed into wine. 总被引:1,自引:0,他引:1
N S Kawar Y Iwata M E Düsch F A Gunther 《Journal of environmental science and health. Part. B》1979,14(5):505-513
Dialifor and methidathion were added to diluted "Zinfandel" grape concentrate at 25 ppm and dimethoate at 1.0 and 25 ppm prior to fermentation with Saccharomyces cerevisiae. The finished wine 56 days later contained 10% (2.5 ppm) of the dialifor, 46% (12 ppm) of the methidathion and 85% (21 and 0.98 ppm) of the dimethoate added to the grape must. Residues in wine stored at 24 degrees C dissipated by hydrolysis; half-lives in wine were 7 days for dialifor and methidathion and 30 days for dimethoate. Residues were unchanged in wine in frozen storage for one year. Analysis of seven commercial wines for dimethoate indicated less than 0.03 ppm dimethoate was present; identity could not be confirmed by thin-layer chromatography at this level. 相似文献
466.
467.
468.
469.
Elements emitted to the atmosphere are partly exported to more remote areas and contribute to the regional and territorial deposition rates. This study is based on the principle that carpet-forming bryophytes (pleurocarpic mosses) absorb elements and particles from rain, melting snow and dry deposition. We compare the concentrations of 60 elements in carpets of the forest moss Pleurozium schreberi sampled in 1975 and 2000 within a sparsely inhabited area dominated by forest and bogland in south Sweden. As an average for all the 60 elements, the median concentration was 2.7 times higher in 1975 than in 2000. The greatest difference was measured for Pb, although In, Bi, Ge, V, Sn, As and Ag had more than 5 times higher concentrations in 1975 than in 2000. Somewhat lower 1975/2000 concentration ratios (3.0-3.8) were measured for U, Sb, Cd, W, Ga, Fe, Li, and Be. The rare-earth elements (Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), except Eu as well as Th, Ni, Al, Ti, Hf, Nb, and Zr, had concentration ratios around the average (2.5-2.8). Possible causes of these changes are discussed. We conclude that reductions in anthropogenic dust emissions during recent decades have decreased the atmospheric deposition over northern Europe of most elements in the periodical system, as previously reported for a limited number of transition and heavy metals. Changes in the deposition of soil dust would be of minor importance to the decreased deposition rates. 相似文献
470.
Urban areas of different land uses can be distinguished by their specific patterns of atmospheric dust and trace element precipitation. Dusts emitted from industrial areas with fossil fuel processing, for instance, are enriched in V, Ni and Co. Cluster analysis groups sampling sites based on their specific element patterns. The resulting groups correspond to the surrounding land use: Urban sampling sites were identified showing similar patterns of dust and trace element precipitation as a reference site; dusts of other urban sites were influenced by diffuse pollution (caused by non-point and dispersed pollution sources), or by specific industrial emissions. Cluster analysis was also used to characterize the chemical dust composition. Three clusters of typical element associations were distinguished. These clusters represent the dust matrix, diffuse urban pollution and pollution due to fossil fuel processing. Dust precipitation and chemical dust composition show seasonal variations. Dust precipitation and concentrations of trace elements in the precipitated dust are negatively correlated during the annual courses. The highest concentrations of trace elements occur during winter, whereas the highest precipitations of dust were found during summer. This finding stresses that both, precipitation and concentration have to be addressed for the environmental assessment of urban dusts. 相似文献