全文获取类型
收费全文 | 4808篇 |
免费 | 96篇 |
国内免费 | 75篇 |
专业分类
安全科学 | 215篇 |
废物处理 | 242篇 |
环保管理 | 1288篇 |
综合类 | 404篇 |
基础理论 | 1110篇 |
环境理论 | 5篇 |
污染及防治 | 1155篇 |
评价与监测 | 338篇 |
社会与环境 | 173篇 |
灾害及防治 | 49篇 |
出版年
2023年 | 24篇 |
2022年 | 22篇 |
2021年 | 48篇 |
2020年 | 30篇 |
2019年 | 61篇 |
2018年 | 70篇 |
2017年 | 89篇 |
2016年 | 111篇 |
2015年 | 109篇 |
2014年 | 105篇 |
2013年 | 546篇 |
2012年 | 176篇 |
2011年 | 254篇 |
2010年 | 190篇 |
2009年 | 187篇 |
2008年 | 257篇 |
2007年 | 258篇 |
2006年 | 239篇 |
2005年 | 165篇 |
2004年 | 182篇 |
2003年 | 190篇 |
2002年 | 170篇 |
2001年 | 82篇 |
2000年 | 106篇 |
1999年 | 99篇 |
1998年 | 73篇 |
1997年 | 66篇 |
1996年 | 77篇 |
1995年 | 77篇 |
1994年 | 65篇 |
1993年 | 65篇 |
1992年 | 74篇 |
1991年 | 46篇 |
1990年 | 55篇 |
1989年 | 42篇 |
1988年 | 35篇 |
1987年 | 43篇 |
1986年 | 47篇 |
1985年 | 40篇 |
1984年 | 45篇 |
1983年 | 50篇 |
1982年 | 38篇 |
1981年 | 56篇 |
1980年 | 46篇 |
1979年 | 23篇 |
1978年 | 26篇 |
1977年 | 18篇 |
1976年 | 12篇 |
1975年 | 20篇 |
1971年 | 15篇 |
排序方式: 共有4979条查询结果,搜索用时 15 毫秒
821.
The cuticle of the American horseshoe crab, Limulus polyphemus, is largely free of the macroscopic epibionts that rapidly colonize most solid surfaces exposed to sea water. Here, we describe
a viscous surface secretion that coats the carapace of the horseshoe crab. We report methods for stimulating production of
the substance, identify hemolytic and liposome-permeabilizing activities and provide a partial biochemical characterization.
We propose that this secretion functions as an anti-fouling agent protecting the chitinized epithelium of the cuticle from
colonization by deleterious epibionts. 相似文献
822.
Erin H. Gillam Gary F. McCracken John K. Westbrook Ya-Fu Lee Michael L. Jensen Ben B. Balsley 《Behavioral ecology and sociobiology》2009,64(1):69-79
Bats alter their echolocation in response to changes in ecological and behavioral conditions, but little is known about how
they adjust call structure in response to changes in altitude. We examined altitudinal variation in the echolocation of Brazilian
free-tailed bats, Tadarida brasiliensis, a species known to fly to altitudes of 3,000 m above the ground. From 50.2 h of recordings, we analyzed 113 high-quality
echolocation call sequences recorded from 0 to 862 m above ground level. Bats flying near the ground used shorter, higher-frequency,
broader-bandwidth calls compared to bats at higher altitudes, an effect likely due to the greater levels of echo-producing
clutter (i.e., vegetation, buildings) found near the ground. When ground-level recordings are excluded, bats continue to shift
towards the use of longer-duration, lower-frequency, narrower-bandwidth calls with increasing altitude. We propose that the
observed high-altitude changes in call structure are a response to changing acoustic attenuation rates and/or decreasing insect
densities at higher altitudes. 相似文献
823.
Crystal D. Havey A. John Dane Christy Abbas-Hawks Kent J. Voorhees 《Environmental Chemistry Letters》2009,7(4):331-336
For the first time, we show the presence of nitro substituted naphthalenes in both mainstream and sidestream tobacco smoke
using electron monochromator-mass spectrometry. Only one mainstream smoke sample showed the presence of 1-nitronaphthalene
(1-NN) at 20 pg/cigarette, while all of the sidestream smoke samples showed the presence of 1-NN at levels ranging from 0.40
to 0.60 ng/cigarette and 2-NN at quantities ranging from 1 to 2 ng/cigarette. Additionally, these levels showed a ratio of
~1:3 for 1-NN to 2-NN which demonstrates that the formation of 2-NN is favored under sidestream combustion conditions. No
larger ring structure (>2) nitro-aromatics were identified. 相似文献
824.
Villy Christensen Carl J. Walters Robert Ahrens Jacqueline Alder Joe Buszowski Line Bang Christensen William W.L. Cheung John Dunne Rainer Froese Vasiliki Karpouzi Kristin Kaschner Kelly Kearney Sherman Lai Vicki Lam Maria L.D. Palomares Aja Peters-Mason Chiara Piroddi Jorge L. Sarmiento Jeroen Steenbeek Rashid Sumaila Reg Watson Dirk Zeller Daniel Pauly 《Ecological modelling》2009
We present a new methodology for database-driven ecosystem model generation and apply the methodology to the world's 66 currently defined Large Marine Ecosystems. The method relies on a large number of spatial and temporal databases, including FishBase, SeaLifeBase, as well as several other databases developed notably as part of the Sea Around Us project. The models are formulated using the freely available Ecopath with Ecosim (EwE) modeling approach and software. We tune the models by fitting to available time series data, but recognize that the models represent only a first-generation of database-driven ecosystem models. We use the models to obtain a first estimate of fish biomass in the world's LMEs. The biggest hurdles at present to further model development and validation are insufficient time series trend information, and data on spatial fishing effort. 相似文献
825.
Henri E.Z. Tonnang Lev V. Nedorezov John O. Owino Horace Ochanda Bernhard Löhr 《Ecological modelling》2009
The performance of discrete mathematical models to describe the population dynamics of diamondback moth (DBM) (Plutella xylostella L.) and its parasitoid Diadegma semiclausum was investigated. The parameter values for several well-known models (Nicholson–Bailey, Hassell and Varley, Beddington, Free and Lawton, May, Holling type 2, 3 and Getz and Mills functional responses) were estimated. The models were tested on 20 consecutive sets of time series data collected at 14 days interval for pest and parasitoid populations obtained from a highland cabbage growing area in eastern Kenya. Model parameters were estimated from minimized squared difference between the numerical solution of the model equations and the empirical data using Powell's method. Maximum calculated DBM growth rates varied between 0.02 and 0.07. The carrying capacity determined at 16.5 DBM/plant by the Beddington et al. model was within the range of field data. However, all the estimated parameter values relating to the parasitoid, including the instantaneous searching rate (0.07–0.28), per capita searching efficiency (0.20–0.27), search time (5.20–5.33), handling time (0.77–0.90), and parasitism aggregation index (0.33), were well outside the range encountered empirically. All models evaluated for DBM under Durbin–Watson criteria, except the May model, were not autocorrelated with respect to residuals. In contrast, the criteria applied to the parasitoid residuals showed strong autocorrelations. Thus, these models failed to estimate parasitoid dynamics. We conclude that the interactions of the DBM with its parasitoid cannot be explained by any of the models tested. Two factors may be associated with this failure. First, the parasitoid in this integrated biological control system may not be playing a major role in regulating DBM population. Second, and perhaps more likely, poor correlations reflect gross inadequacies in the theoretical assumptions that underlie the existing models. 相似文献
826.
Risk to humans of consuming metals in anchovy (<Emphasis Type="Italic">Coilia</Emphasis> sp.) from the Yangtze River Delta 总被引:1,自引:0,他引:1
Fengyan Liu Jiachun Ge Xin Hu Teng Fei Yuehua Li Yuan Jiang Zhiqiang Xu Shuyan Ding John P. Giesy 《Environmental geochemistry and health》2009,31(6):727-740
Concentrations of metals were determined in four species of anchovy (Coilia sp.) from the Yangtze River, Taihu Lake, and Hongze Lake in Jiangsu Province, China. Concentrations of Cr in anchovy fish
muscle ranged from 2.6 × 10−2 to 5.0 mg/kg ww, and Coilia nasus taihuensis in Jiaoshan, Taihu Lake contained the highest concentrations of Cr, which was almost 111-fold higher than the mean value
at other locations. Concentrations of Pb ranged from 1.5 × 10−2 to 1.3 × 10−1 mg/kg ww. Comparisons of concentrations of lead (Pb) among the four species indicated that anadromous species contained higher
concentrations of Pb than did freshwater species. However, concentrations of Pb in C. nasus from the Nanjing and Haimen locations in the Yangtze River were not significant higher than those of two freshwater species:
C. nasus taihuensis from Taihu Lake and C. brachygnathus from Hongze Lake (Duncan’s test, α = 0.05). While concentrations of Cd and Zn ranged from 7.0 × 10−4 to 3.6 × 10−3 mg/kg ww and 3.4 to 4.8 mg/kg ww, respectively, there were no significant differences in concentrations among the eight locations.
The only concentration of the metals studied that exceeded the Chinese National Standard was Cr in Coilia from Jiaoshan, Taihu Lake, which was 2.5-fold higher than the standard. These results indicate that people who consume the
genus Coilia are not at risk due to concentrations of metals, except Cr in C. nasus taihuensis from Jiaoshan in Taihu Lake. Concentrations of all of the metals studied except for Cr were similar to or less than those
of metals in most other areas in the world. 相似文献
827.
828.
Jana S. Stewart Lizhu Wang John Lyons Judy A. Horwatich Roger Bannerman 《Journal of the American Water Resources Association》2001,37(6):1475-1487
ABSTRACT: Multivariate analyses and correlations revealed strong relations between watershed and riparian‐corridor land cover, and reach‐scale habitat versus fish and macroinvertebrate assemblages in 38 warmwater streams in eastern Wisconsin. Watersheds were dominated by agricultural use, and ranged in size from 9 to 71 km2 Watershed land cover was summarized from satellite‐derived data for the area outside a 30‐m buffer. Riparian land cover was interpreted from digital orthophotos within 10‐, 10‐to 20‐, and 20‐to 30‐m buffers. Reach‐scale habitat, fish, and macroinvertebrates were collected in 1998 and biotic indices calculated. Correlations between land cover, habitat, and stream‐quality indicators revealed significant relations at the watershed, riparian‐corridor, and reach scales. At the watershed scale, fish diversity, intolerant fish and EPT species increased, and Hilsenhoff biotic index (HBI) decreased as percent forest increased. At the riparian‐corridor scale, EPT species decreased and HBI increased as riparian vegetation became more fragmented. For the reach, EPT species decreased with embeddedness. Multivariate analyses further indicated that riparian (percent agriculture, grassland, urban and forest, and fragmentation of vegetation), watershed (percent forest) and reach‐scale characteristics (embeddedness) were the most important variables influencing fish (IBI, density, diversity, number, and percent tolerant and insectivorous species) and macroinvertebrate (HBI and EPT) communities. 相似文献
829.
ABSTRACT: A spatial linear program that strategically arranges and schedules forest treatments so as to meet peak stormflow objectives is formulated and demonstrated. The approach uses simulated spatial routing of stormflows nested as short‐term time schedules within longer‐term forest planning time periods. A simple case example is used to demonstrate the formulation and explore its spatial sensitivity. 相似文献
830.