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991.
A theoretical model, based on linear stability analysis, is proposed to predict the onset of natural convection in lakes and
reservoirs due to night time cooling. To such purpose, the system was modelled as a initially quiescent deep Boussinesq fluid
reservoir, whose upper boundary temperature changes sinusoidally. From scaling analysis, it is found that critical onset times
for convection are proportional to R
−2/7, where R is a Rayleigh number including fluid properties and forcing frequency. The proportionality constant was found, from the solution
of an eigenvalue problem, as a function of the Prandtl number. The onset time for convection was easily observed from experiments
and quantitatively detected as a rapid increase of the RMS of the computed velocity field obtained using PIV. In this controlled
conditions, differences close to 10% between predicted and observed times for the start of the convective flow was found.
It is apparent from the present set of results that predictions are reasonable. 相似文献
992.
Diogo Rúben Neves Sara Rodrigues Concei??o Juana Fortes Maria Teresa Reis Jo?o Alfredo Santos Rui Capit?o 《Journal of Coastal Conservation》2012,16(4):489-501
This paper describes a first approach on the risk assessment in port navigation using GUIOMAR, an integrated system for port and coastal engineering modelling developed at the National Civil Engineering Laboratory (LNEC), Portugal, using a GIS software environment. A set of automatic procedures was designed to include a new methodology based on the amplitude of the wave-induced vertical movement of a ship along its trajectory. In this methodology, the risk in port navigation is assessed on the basis of a combination of the probability of exceedance of a pre-set threshold for the ship??s vertical movements and its consequences. To test the new procedures, a set of sea wave records obtained at the Sines wave-buoy from 1988 to 2002 was transferred into Sines Port using two numerical models of sea wave propagation and deformation (SWAN and DREAMS), included in the GUIOMAR system. The numerical model WAMIT was used for estimating the wave-induced ship??s vertical movements inside the port. By applying the new procedures, automatic generation of risk maps was carried out for navigation in the vicinity of the West breakwater of the Port of Sines. The recent developments contribute towards a more versatile and efficient GUIOMAR system, which results in a more adequate tool to support decision-making processes in port and coastal management. 相似文献
993.
The relative importance of chemical, nematocyst, and nutritional defenses was examined for 18 species of Caribbean sea anemones
(actinarians), zoanthids, and mushroom polyps (corallimorpharians) from the Florida Keys and the Bahamas Islands, 2008–2010.
Feeding assays were performed using the fish Thalassoma bifasciatum with artificial foods containing crude organic extracts of cnidarian tissues. A novel behavioral assay using brine shrimp
nauplii was used to assess nematocyst defenses. The nutritional quality of cnidarian tissues was examined using bomb calorimetry
and soluble protein assays. In general, actinarians invested in nematocyst defenses, zoanthids in either nematocyst or chemical
defenses, and corallimorpharians lacked both, except for 1 of 3 species that was chemically defended. Relative to other coral
reef invertebrates, cnidarian tissues had similar caloric values but lower soluble protein concentrations. Trade-offs between
chemical and nematocyst defenses were observed for 65% of species, while habitat and behavior provided a likely explanation
for undefended species. 相似文献
994.
Seung?Hyeon?Kim Young?Kyun?Kim Sang?Rul?Park Wen-Tao?Li Kun-Seop?LeeEmail author 《Marine Biology》2012,159(2):255-267
Seagrass species in the genus Halophila are usually distributed in tropical or subtropical areas, but a Halophila species identified as H. nipponica was first observed in temperate coastal regions of Korea in 2007. Since this species mainly occurs in warm temperate regions
influenced by warm currents, we hypothesized that H. nipponica may exhibit different growth patterns from those of other temperate seagrass species in Korea, instead showing similar growth
dynamics to tropical/subtropical species. The growth and morphology of H. nipponica in relation to coincident measurements of environmental factors were investigated from July 2008 to September 2009 to examine
the growth dynamics of this species. Water temperature at the study site ranged from 9.7°C in January to 25.1°C in August.
Shoot density, biomass, and productivity exhibited significant seasonal variation, increasing during summer and decreasing
during winter. Productivity was severely restricted to nearly ceasing at water temperatures less than 15°C, and winter minimum
growth lasted until May. The optimal temperature for H. nipponica growth was approximately 25°C, which was the maximum water temperature at the study site, and no growth reduction in high
summer water temperature was observed. Thus, H. nipponica on the temperate coast of Korea exhibited a distinctly different growth pattern from those of temperate seagrass species
in Korea, which have shown great reductions in growth at water temperatures higher than 20°C. Higher below- to above-ground
ratio and leaf burial into sediments with shorter leaf petioles during winter might be overwintering strategies in this species.
The growth patterns of H. nipponica at the study site imply that this species still possess the tropical characteristics of the genus Halophila. 相似文献
995.
This study developed an objective quantitative method for detecting small-scale temporal or spatial differences in gametogenesis
in echinoderms. The method was applied to conventional monthly samples of the planktotrophic brittle star, Ophiopholis aculeata, collected at a single site in Newfoundland (eastern Canada) at 10–15 m depth. The samples were analysed to determine gonad
index, oocyte size and gonadal stage using histology. The maturity stage index (MSI) was developed to integrate a measure
of brittle star size (disc diameter), oocyte size and oocyte density. The MSIs ranged from 0 to 800 and had significantly
different means among the four gametogenic stages (early growth, growth, mature and spent). The MSI was more sensitive in
revealing significant differences between consecutive stages than any of its individual constituents. The MSI was also applied
to gametogenic data from the lecithotrophic holothuroid, Mesothuria lactea, again revealing significant differences between successive oogenic stages. This method is expected to be useful in field
and experimental studies of gametogenesis in echinoderms (and possibly other taxa), where it is important to detect not just
the timing of annual peaks in reproduction but small differences in reproductive status among individuals or populations (e.g.
from different habitats or feeding regimes). 相似文献
996.
The fatty acid and alcohol composition of the pelagic amphipod, Themisto libellula, was monitored during the 5 first months of its life cycle (4–20 mm length) in an Arctic fjord, Kongsfjorden, Svalbard. Fatty
acids of the three major lipid classes, polar lipids (PL), triacylglycerol (TAG), and wax esters (WE), were analyzed to highlight
ontogenic changes in their diet and metabolism. The PL composition of T. libellula did not show any strong variations along their growth except during the first month where an important increase of 20:5(n-3)
(EPA) and 22:6(n-3) (DHA) was observed. The TAG composition revealed a clear gradient corresponding to a diet shift from omnivorous
juveniles toward carnivorous sub-adults and adults. Indeed, fatty acid trophic markers of diatoms were dominant in the juveniles,
whereas 20:1(n-9) and 22:1(n-11), the Calanus sp. trophic markers, overwhelmed in the older stages. The WE composition highlighted the same general trend, however, differences
were found with the TAG and are discussed as a result of differences in turnover rates and assimilation pathways between the
two lipid classes. 相似文献
997.
The preference of the hermit crab, Calcinus
californiensis, among six species of shells, was tested by two different experiments. The first experiment used pair-wise trials, analyzing
the preference by Chi-square tests using two different constructions of the null hypothesis. One hypothesis was based on a
no-preference among shell species, the second on comparing the number of crabs changing for a particular shell species when
two options were given versus the changing when no options were offered. The second experiment was a multiple-alternative
test based on a rank ordering of the shell preference. This method has both statistical and resource-saving advantages over
the traditional pair-wise comparisons. The sequence of shell preference was similarly independent of the procedure used. The
preferred shell species are heavy and might be associated with hydrodynamic advantages and with the protection against predation.
The shell preference matches with the pattern of shell occupancy indicating that the shell use in nature is determined by
the crab’s preference. The information generated may be used for further research on shell preference as a methodological
alternative. 相似文献
998.
M.?KoskiEmail author L.?Yebra J.?Dutz S.?H.?J?nasd?ttir C.?Vidoudez H.?H.?Jakobsen G.?Pohnert J.?C.?Nejstgaard 《Marine Biology》2012,159(3):643-660
We studied the effect of a developing Skeletonema marinoi/Phaeocystis spp. bloom on Calanus finmarchicus hatching success, early naupliar survival and metabolism. Our focus was (1) on the development of reproductive rates during
a bloom initiation, peak and decline in relation to the production of potentially toxic algal metabolites and (2) on the proportional
importance of female nutrition versus naupliar food environment for the production of viable nauplii. Despite polyunsaturated
aldehyde (PUA) production by both S. marinoi and Phaeocystis sp., we did not observe any harmful effects on hatching success or naupliar survival and condition in any stages of the short-term
(<1 week) algal bloom. Hatching success appeared to be controlled by egg lipid composition, while the beneficial effect of
a high food concentration was reflected in naupliar RNA:DNA ratio, protein content and total production of viable nauplii.
The egg lipids reflected seston lipids, indicating that the egg fatty acid composition was not modified by the females. Our
results suggest that unselective feeding and/or retention of specific lipids can induce qualitative food limitation, although
recruitment during the S. marinoi/Phaeocystis sp. bloom was high. 相似文献
999.
Sílvia?SantosEmail author Joana?F.?M.?F.?Cardoso Valeska?Borges Rob?Witbaard Pieternella?C.?Luttikhuizen Henk?W.?van der?Veer 《Marine Biology》2012,159(3):601-611
This study analyzed the isotopic profiles of four aragonitic shells of Scrobicularia plana in conjunction with measured seawater temperatures and salinities. Comparison of δ18OSHELL with expected values revealed fractionation of δ18O in near equilibrium with the ambient environment. Growth cessation occurred between November and March. Carbonate deposition
stopped when temperatures were <12°C. Analysis of δ13CSHELL values suggested that carbon in the shell does not reflect the DIC in ambient water, likely due to the incorporation of metabolic
carbon. An ontogenetic trend of increasing δ13C values over time was observed, likely related to changes in metabolic activity. Annual growth patterns were inferred from
δ18OSHELL profiles and compared with internal and external growth lines. Estimations of age based on external lines were unreliable,
resulting in overestimation of age and underestimation of growth rates, likely due to the disturbance lines being wrongly
identified as annual. Analysis of internal lines may lead to over- or underestimation of age and was more reliable in recent
portions of the shell. 相似文献
1000.
Alistair?ChealEmail author Michael?Emslie Ian?Miller Hugh?Sweatman 《Marine Biology》2012,159(5):1143-1154
The composition and functionality of ecologically important herbivorous fish assemblages were examined throughout much of
Australia’s Great Barrier Reef (GBR). Diversity and abundance of surgeonfishes (Acanthuridae), parrotfishes (Labridae) and
rabbitfishes (Siganidae) were strongly associated with position on the continental shelf, whilst effects of latitude were
weaker and inconsistent. Species distributions varied considerably amongst taxonomic groups; parrotfishes were mostly widespread
whilst distributions of surgeonfishes were often restricted. Most inshore environments supported depauperate herbivore assemblages
dominated by different taxa and functional groups compared with assemblages in offshore environments. There were also strong
cross-shelf transitions in the main taxa performing each functional role. Overall, this study show that the functional contributions
of herbivorous fish assemblages to important ecosystem processes and the contributing taxa vary considerably amongst different
GBR environments. Additionally, the two most numerically dominant herbivores actively select detritus, not algae, supporting
increasing evidence for the importance of detritus in coral reef ecology. 相似文献