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991.
The blue mussels Mytilus edulis L. and M. galloprovincialis Lmk. hybridize in western Europe. Within hybrid populations nuclear alleles specific to M. galloprovincialis increase in frequency with age and size. This relationship changes with tidal height; alleles from M. galloprovincialis occur more frequently high in the intertidal zone, while M. edulis alleles predominate in the low intertidal zone. We tested the hypotheses that larvae with M. galloprovincialis alleles tend to settle higher in the intertidal zone, or that mussels redistribute themselves with respect to tidal height
after initial larval settlement. We sampled recently metamorphosed mussels every 2 weeks in a hybrid mussel population at
Whitsand Bay in southwest England throughout the summer of 1996. We observed four cohorts of newly settled mussels. There
was no evidence of differential settlement of mussels with different genotypes in connection with tidal height, or into shaded
versus unshaded microsites. Therefore, we rejected the preferential settlement hypothesis. There was substantial movement
of juvenile mussels in the first 4 weeks following initial settlement, but this “secondary settlement” did not result in genetic
differentiation with respect to tidal height. Further, significant differences in allele frequencies were found between primary
and secondary spat. This allele frequency change was in the opposite direction of that seen in the adult population, suggesting
newly settled larvae may be experiencing different selective pressures than adults. We propose that the genetic structure
of hybrid mussel populations with respect to tidal height is the consequence of differences in selection intensity.
Received: 30 April 1999 / Accepted: 5 May 2000 相似文献
992.
Multi-scale landscape factors influencing stream water quality in the state of Oregon 总被引:8,自引:0,他引:8
Nash MS Heggem DT Ebert D Wade TG Hall RK 《Environmental monitoring and assessment》2009,156(1-4):343-360
Enterococci bacteria are used to indicate the presence of human and/or animal fecal materials in surface water. In addition to human influences on the quality of surface water, a cattle grazing is a widespread and persistent ecological stressor in the Western United States. Cattle may affect surface water quality directly by depositing nutrients and bacteria, and indirectly by damaging stream banks or removing vegetation cover, which may lead to increased sediment loads. This study used the State of Oregon surface water data to determine the likelihood of animal pathogen presence using enterococci and analyzed the spatial distribution and relationship of biotic (enterococci) and abiotic (nitrogen and phosphorous) surface water constituents to landscape metrics and others (e.g. human use, percent riparian cover, natural covers, grazing, etc.). We used a grazing potential index (GPI) based on proximity to water, land ownership and forage availability. Mean and variability of GPI, forage availability, stream density and length, and landscape metrics were related to enterococci and many forms of nitrogen and phosphorous in standard and logistic regression models. The GPI did not have a significant role in the models, but forage related variables had significant contribution. Urban land use within stream reach was the main driving factor when exceeding the threshold (> or =35 cfu/100 ml), agriculture was the driving force in elevating enterococci in sites where enterococci concentration was <35 cfu/100 ml. Landscape metrics related to amount of agriculture, wetlands and urban all contributed to increasing nutrients in surface water but at different scales. The probability of having sites with concentrations of enterococci above the threshold was much lower in areas of natural land cover and much higher in areas with higher urban land use within 60 m of stream. A 1% increase in natural land cover was associated with a 12% decrease in the predicted odds of having a site exceeding the threshold. Opposite to natural land cover, a one unit change in each of manmade barren and urban land use led to an increase of the likelihood of exceeding the threshold by 73%, and 11%, respectively. Change in urban land use had a higher influence on the likelihood of a site exceeding the threshold than that of natural land cover. 相似文献
993.
A. L. Moran 《Marine Biology》2000,137(5-6):893-898
A nontoxic method of marking juvenile animals is a prerequisite for many field studies investigating growth and survivorship
in marine invertebrates. This study investigates the effectiveness of low concentrations of calcein in marking hatchling snails
(Nucella ostrina), the durability of the calcein mark, and the effects of marking on survivorship and growth. I also describe an inexpensive
means of visualizing the calcein mark under a dissecting microscope. Results demonstrate that calcein provides a long-lasting,
readily detected fluorescent shell mark that can be used to measure shell growth accurately. In addition, marking with calcein
did not affect survivorship or growth, and had no size-dependent effects on growth or survivorship.
Received: 13 October 1999 / Accepted: 18 June 2000 相似文献
994.
《Atmospheric environment (Oxford, England : 1994)》2007,41(3):655-665
This paper examines the use of Moderate Resolution Imaging Spectroradiometer (MODIS) observed active fire data (pixel counts) to refine the National Emissions Inventory (NEI) fire emission estimates for major wildfire events. This study was motivated by the extremely limited information available for many years of the United States Environmental Protection Agency (US EPA) NEI about the specific location and timing of major fire events. The MODIS fire data provide twice-daily snapshots of the locations and breadth of fires, which can be helpful for identifying major wildfires that typically persist for a minimum of several days. A major wildfire in Mallory Swamp, FL, is used here as a case study to test a reallocation approach for temporally and spatially distributing the state-level fire emissions based on the MODIS fire data. Community Multiscale Air Quality (CMAQ) model simulations using these reallocated emissions are then compared with another simulation based on the original NEI fire emissions. We compare total carbon (TC) predictions from these CMAQ simulations against observations from the Inter-agency Monitoring of Protected Visual Environments (IMPROVE) surface network. Comparisons at three IMPROVE sites demonstrate substantial improvements in the temporal variability and overall correlation for TC predictions when the MODIS fire data is used to refine the fire emission estimates. These results suggest that if limited information is available about the spatial and temporal extent of a major wildfire fire, remotely sensed fire data can be a useful surrogate for developing the fire emissions estimates for air quality modeling purposes. 相似文献
995.
Goldstein RM Carlisle DM Meador MR Short TM 《Environmental monitoring and assessment》2007,130(1-3):495-510
The environmental setting (e.g., climate, topography, geology) and land use affect stream physical characteristics singly
and cumulatively. At broad geographic scales, we determined the importance of environmental setting and land use in explaining
variation in stream physical characteristics. We hypothesized that as the spatial scale decreased from national to regional,
land use would explain more of the variation in stream physical characteristics because environmental settings become more
homogeneous. At a national scale, stepwise linear regression indicated that environmental setting was more important in explaining
variability in stream physical characteristics. Although statistically discernible, the amount of variation explained by land
use was not remarkable due to low partial correlations. At level II ecoregion spatial scales (southeastern USA plains, central
USA plains, and a combination of the western Cordillera and the western interior basins and ranges), environmental setting
variables were again more important predictors of stream physical characteristics, however, as the spatial scale decreased
from national to regional, the portion of variability in stream physical characteristics explained by basin land use increased.
Development of stream habitat indicators of land use will depend upon an understanding of relations between stream physical
characteristics and environmental factors at multiple spatial scales. Smaller spatial scales will be necessary to reduce the
confounding effects of variable environmental settings before the effects of land use can be reliably assessed. 相似文献
996.
Species are often composed of discrete breeding units (i.e. populations or stocks) which, while not reproductively isolated
from other such groups, may have limited opportunities to exchange genetic material because of geographic distance, barriers
to migration, or spawning asynchrony. Low levels of gene flow between stocks may result, over time, in their genetic divergence,
and species that are subdivided into morphologic or genetically distinct stocks are said to be structured. The aim of our
investigation was to test whether or not Penaeus stylirostris from the Gulf of California (Mexico) was structured into genetically distinct populations. Shrimp samples were collected
in 1996 from six regions of the Gulf where specimens with distinct morphologic characteristics had previously been identified.
Statistical analysis of 324 RAPD loci (randomly amplified polymorphic DNA), resolved through polyacrylamide gels and scored
for each of 78 specimens, permitted the quantification and comparison of between-stock genetic differences. The finding that
genetically discrete stocks of P. stylirostris can be found in a small portion of the geographic distribution range of the species, disagrees with the long-held perception
that this resource is panmictic in nature. This new evidence is not only of interest for selective breeding programs in the
shrimp aquaculture industry, but is also relevant to the management of the Mexican shrimp fishery which, at present, is perceived
and managed as a single stock.
Received: 10 May 1999 / Accepted: 27 July 2000 相似文献
997.
Economic Development and Conservation of Biological and Cultural Diversity in Yunnan Province, China
Rey C. Stendell Richard L. Johnson John P. Mosesso Xia Zhang 《Environment, Development and Sustainability》2000,2(3-4):333-345
Chinese and American scientists are co-operating to develop concepts, strategies, agreements, and proposals in support of an economic development and sustainable ecosystems project in Yunnan Province, People's Republic of China. Yunnan's Provincial Government has initiated a major programme to develop and further utilise its biological resources to help improve economic conditions for its citizens. They are co-operating with the US Geological Survey (USGS) on evaluation and management of biological resources so economic development will be compatible with sustainable ecological systems. Scientists from the USGS and co-operating universities will provide expertise on synthesising biological data, conducting a Gap Analysis for the Province, evaluating innovative economic opportunities, and designing an effective education, training, and outreach programme. 相似文献
998.
Depth and muscle temperature of Pacific bluefin tuna examined with acoustic and pop-up satellite archival tags 总被引:1,自引:0,他引:1
David J. Marcinek Susanna B. Blackwell Heidi Dewar Ellen V. Freund Charles Farwell Daniel Dau Andrew C. Seitz Barbara A. Block 《Marine Biology》2001,138(4):869-885
Six Pacific bluefin tuna were tracked with ultrasonic telemetry and two with pop-up satellite archival tags (PSATs) in the
eastern Pacific Ocean in 1997, 1998, and 1999. Both pressure and temperature ultrasonic transmitters were used to examine
the behavior of the 2- to 4-year-old bluefin tuna. The bluefin spent over 80% of their time in the top 40 m of the water column
and made occasional dives into deeper, cooler water. The mean slow-oxidative muscle temperatures of three fish instrumented
with pressure and temperature transmitters were 22.0–26.1 °C in water temperatures that averaged 15.7–17.5 °C. The thermal
excesses in slow-oxidative muscle averaged 6.2–8.6 °C. Variation in the temperature of the slow-oxidative muscle in the bluefin
was not correlated with water temperature or swimming speeds. For comparison with the acoustic tracking data we examined the
depth and ambient temperature of two Pacific bluefin tagged with pop-up satellite archival tags for 24 and 52 days. The PSAT
data sets show depth and temperature distributions of the bluefin tuna similar to the acoustic data set. Swimming speeds calculated
from horizontal distances with the acoustic data indicate the fish mean speeds were 1.1–1.4 fork lengths/s (FL s−1). These Pacific bluefin spent the majority of their time in the top parts of the water column in the eastern Pacific Ocean
in a pattern similar to that observed for yellowfin tuna.
Received: 4 April 2000 / Accepted: 25 October 2000 相似文献
999.
Juveniles of the planehead filefish Stephano-lepishispidus (Pisces: Monacanthidae) (Linnaeus, 1766) are a major component of the Sargassum spp. community, yet little is known of their ecology. In this study, the otolith record of age, growth, and ontogeny in S.
hispidus was examined. Juveniles caught off Beaufort Inlet, North Carolina (USA) on 30 June 1996 were marked with alizarin complexone
and reared in a flow-through, outdoor tank for up to 19 days. Examination of marked otoliths at several time intervals showed
that increment formation was not significantly different than one increment per day, and thus, increment number was used to
estimate age. Depth-distribution, morphology, and meristics of larvae and juveniles collected (1990–1992) between Cape Romain,
South Carolina, and Cape Hatteras, North Carolina, were examined to identify the timing of the larval to juvenile transition.
All indicators suggested the transition occurred between 17 and 20 days. Mean otolith increment widths exhibited a marked
change at about 20 days, coinciding with the timing of the larval to juvenile transition and a change in the depth distribution
from bottom to surface waters. Increment width of individual juveniles, however, did not exhibit the same pattern; only 40%
conformed to the pattern identified for all fish. Thus, the record of the larval to juvenile transition is clear at the population
level, but unresolved at the individual level.
Received: 1 November 1999 / Accepted: 18 December 2000 相似文献
1000.
L. Hughes B. Siew-Woon Chang D. Wagner N. E. Pierce 《Behavioral ecology and sociobiology》2000,47(3):119-128
The mating system of the Australian lycaenid butterfly, Jalmenus evagoras, is highly unusual compared to most other Lepidoptera. Characteristics of this system, which has been termed an ’explosive
mating strategy,’ include the formation of an intensely competitive mating aggregation of males, a highly male biased operational
sex ratio, a lack of discrimination and mate choice by both sexes, a high variance in male mating success, and female monogamy.
In this study, we tested the hypothesis that multiple mating by males imposes physiological costs resulting in smaller spermatophores,
and that this results in a fitness cost to females. We found that male J. evagoras transferred only 2.2% of their eclosion weight during their first mating, consistent with the hypothesis that males of monandrous
species produce a relatively small investment. The wet weight of the ejaculate declined by an average of 27% at the second
mating and the dry weight by 29%, and an intermating interval of 5–9 days was needed for the ejaculate to return to the size
at the first mating, regardless of male size or age. Wet ejaculate mass increased proportionally with male size, though dry
mass was proportionally larger in smaller males. Ejaculate mass tended to increase with male age at both first and second
matings. Female characteristics, in general, did not affect ejaculate mass, although the wet weight of the ejaculate was positively
associated with female weight at the second mating. Copulation duration increased from 2.4 h to approximately 3 h at the second
mating, and to over 4 h at the third and fourth matings. Fecundity was positively correlated with female size but not with
mating history, copulation duration, or any other characteristics measured for either males or females. Female longevity declined
significantly as the number of times the male partner had previously mated increased. We conclude that despite the small male
investment in ejaculate, the costs of multiple mating may nonetheless be significant, as indicated by the reduction in ejaculate
mass, an increase in copulation duration, and reduction in female lifespan with increasing mating number.
Received: 22 January 1999 / Received in revised form: 28 July 1999 / Accepted: 18 September 1999 相似文献