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481.
482.
Microstructural growth in otoliths of conger eel (Conger myriaster) leptocephali during the metamorphic stage 总被引:1,自引:1,他引:1
Otolith growth during metamorphosis and some aspects of the early life history of conger eel (Conger myriaster) were determined as indicated from microstructure in otoliths of the leptocephali collected from Cheonsu Bay, Korea during May and June 1988. The leptocephali occurred from early May to late June in the study area. Larvae collected in early May were in the late leptocephalus stage, and the proportion of the metamorphosing leptocephali increased over time. Otoliths in the late leptocephalus stage showed a translucent zone only. Although the fish did not feed and the body length diminished during metamorphosis, the otolith continued to grow and, consequently, the opaque zone was formed outside the translucent zone. The inner translucent zone can be considered a leptocephalus zone, and the outer opaque zone a metamorphic zone. Assuming that the growth increments were deposited daily from hatching, the conger eel can be considered to have hatched between September and February. The number of increments in the inner hyaline zone ranged from 124 to 239, and was assumed to represent the number of days from hatching to the onset of metamorphosis. The duration of metamorphosis was estimated as 51 to 75 d based on the number of increments in the opaque zone at the end of the metamorphic stage. 相似文献
483.
Direct measurement technique for determining ventilation rate in the deposit feeding clam Macoma nasuta (Bivalvia,Tellinaceae) 总被引:1,自引:0,他引:1
An exposure chamber, the clambox, was developed to measure ventilation rate, sediment processing rate, and efficiency of pollutant uptake by Macoma nasuta conrad, a surface deposit-feeding clam. Clams, collected from Yaquina Bay, Oregon, USA, were cemented into a hole in a piece of rubber dental dam so that the inhalant and exhalant siphons were separated by a membrane. The dental dam was then clamped between two glass chambers. The inhalant and exhalant siphons were thus directed into separate chambers of the device so that the amounts of water or feces discharged into the exhalant chamber provided direct measures of ventilation rate and sediment processing rate, respectively. Clams exhibited no stress from the procedure. Ventilation rate was not affected by the imposition of a 5 mm hydraulic head in the exhalant chamber, by having sediment only in the inhalant chamber, or by exposure to organic-free sediment. The mean weight-specific ventilation rate for M. nasuta was 7.3 ml g-1 h-1 on a wet-flesh basis. This low rate, compared to rates for filter-feeding bivalves, supports the contention that deposit-feeding is the dominant feeding mode for M. nasuta. The short-term pattern was for ventilation to be intermittenly interrupted, essentially ceasing for 12 to 120 min, followed by a short period of active ventilation and then a resumption of the normal rate. Less than 3% of the total water flux could be attributed to water which entered the body cavity across the mantle margin. Water exhaled from the inhalant siphon during the ejection of pseudofeces was <10% of the ventilation rate. The clambox technique should be adaptable to studies on other tellinid bivalves. 相似文献
484.
Raphael D. Sagarin Richard F. Ambrose Bonnie J. Becker John M. Engle Janine Kido Steven F. Lee C. Melissa Miner Steven N. Murray Peter T. Raimondi Dan Richards Christy Roe 《Marine Biology》2007,150(3):399-413
Here long-term monitoring data taken at 33 sites in southern and central California coast and islands were used to evaluate the size structure of the large intertidal limpet, Lottia gigantea in restricted-access and in easily accessible intertidal zones that encompass a wide range of ecological variables. Using multi-dimensional analysis of population size structures, we found that sites on islands and strictly protected mainland sites have significantly larger median limpet sizes and a greater range of limpet sizes than unprotected mainland sites, while no pattern occurs in latitudinal or regional comparison of sites. Although intertidal predators such as oystercatchers were not the primary focus of the monitoring efforts, extensive natural history notes taken during sampling visits support the argument that predation was not a primary cause for the size structure differences. Finally, substratum differences were determined not to have biased the observation of larger limpets in protected sites. In regard to human interactions with limpets, we conclude that the degree of enforcement against poaching is the better predictor of limpet size structure than proximity to population centers or visitation to intertidal sites. 相似文献
485.
Jung JM Lee YJ Park HG Jung EY Jang MH Ha K Shin PS Joo GJ 《Journal of environmental biology / Academy of Environmental Biology, India》2005,26(1):97-103
Cyanobacterial blooms and associated microcystins in hypertrophic stagnant West-Nakdong River were investigated at weekly intervals from April to August, 1999. Microcystis spp. accounted for over 85% of the numeric abundance of total phytoplankton. Microcystins were present in the blooms sampled between May and August. The peak of total microcystin (microcystin-LR + -RR) levels (maximum level; 612 microg g(-1)) was detected in the initial stage of the bloom (mid May), at the same time as high N/P ratio and high Microcystis biomass. This study indicated that total microcystins of this regulated river was positively correlated to Microcystis biomass, absolute nutrient concentration and TN/TP ratio. 相似文献
486.
Groundwater, used in this study, contaminated predominantly with aromatic compounds, was biologically treated in a fluidized-bed reactor (FBR) with immobilized cells. The aromatics were completely decomposed, while cis-1,2-dichloroethylene (cis-DCE) and trichloroethylene (TCE) were decomposed only approximately 20% and 5%, respectively. In these studies a significant improvement of the decomposition efficiency for chlorinated ethylenes was achieved by utilizing cometabolism. Methanol (MeOH) and toluene were used as the substrate in the case of one-stage reactor (Single Reactor). MeOH (187 mg l(-1)) increased the decomposition efficiency up to 40% and 60% for cis-DCE and TCE, respectively, while toluene (20 mg l(-1)) increased the decomposition efficiency of cis-DCE to 92% and the decomposition efficiency of TCE to 76%. In the case of two-stage reactor system (Reactor 1 and Reactor 2), MeOH and methane (CH4) were used as the substrate. In this system, cells grown on MeOH or CH4 in the Reactor 1 were continuously fed into Reactor 2 and groundwater was fed into Reactor 2 only. When MeOH (384 mg l(-1) d(-1)) was used as substrate the decomposition efficiency of cis-DCE and TCE were 60% and 70%, respectively. Similar decomposition efficiency was observed for a small amount of CH4 (19.3 mg l(-1) d(-1)). 相似文献
487.
Persistent organic pollutants in mangrove food webs in Singapore 总被引:1,自引:0,他引:1
In this study, persistent organic pollutants were quantified in sediments, subsurface seawater, sea-surface microlayer and twenty-four biota species collected at two separate mangrove habitats in Singapore. Data confirmed the ubiquity of POPs, including polybrominated diphenyl ethers (PBDEs), in the marine environment of Singapore. A biomagnification phenomenon was observed amongst the species collected and analysed from both mangrove sites studied. Thunder crabs and fish displayed the highest POP levels. Congener profiles of PBDEs varied amongst mangrove biota species and suggested different metabolic pathways exist for flame retardants. Similarly, crab species showed an ability to metabolize chlordane insecticide. 相似文献
488.
Szefe P Frelek K Szefer K Lee ChB Kim BS Warzocha J Zdrojewska I Ciesielski T 《Environmental pollution (Barking, Essex : 1987)》2002,120(2):423-444
Concentrations of Hg, Cd, Pb, Ag, Cu, Zn, Cr, Ni, Co, Mn, and Fe in soft tissues, shells and byssus of blue mussel (Mytilus edulis trossulus) from 23 sites along the Polish coast of the Baltic Sea were determined by AAS method. Byssus, as compared with the soft tissue, concentrated more effectively Pb, Cu, Cr, and especially Ag, Ni, Mn and Fe, moderately Hg and Zn and less effectively Cd. Significant inter-regional and inter-size differences in metal concentrations in both soft tissues and byssus were recorded. Highly significant correlations (P<0.01, P<0.05) were observed between tissue and byssal concentrations of Cd, Pb, Ni and Ag. Factor analysis showed clear separation of both the tissue and byssi samples based on their geographic distribution, possibly reflecting a different rate of deposition of clay minerals at the head of the Pomeranian Bay and the Gulf of Gdańsk. The Pomeranian Bay differs from the Gulf of Gdańsk in respect to geological structure of bottom sediments as a substrata for the M. edulis trossulus as well as in relation to various sources of metallic pollutants. From the data obtained in the present study and those reported previously the soft tissue and especially byssus of M. edulis, in contrast to shells, appear to be a significantly better bioindicator for identification of coastal areas exposed to metallic contaminants. 相似文献
489.
Laboratory experiments were conducted to determine environmental variables that affect the affinities and persistence of the nerve agent O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX) at dilute concentrations in environmental matrices. Quantitative analyses of VX and its degradation products were performed using LC-MS. Batch hydrolysis experiments demonstrated an increasing hydrolysis rate as pH increased, as shown in previous studies, but also indicated that dissolved aqueous constituents can cause significant differences in the absolute hydrolysis rate. Adsorption isotherms from batch aqueous experiments revealed that VX has a high affinity for hydrophobic organics, a moderate affinity for montmorillonite clay, and a very low affinity for an iron-oxyhydroxide soil mineral, goethite. The adsorption on goethite was increased with the presence of dissolved organic matter in solution. VX degraded rapidly when dried onto goethite, when specific adsorption was forced. No enhanced degradation occurred with goethite in small amounts of water. These results suggest that aqueous conditions have important controls on VX adsorption and degradation in the environment and a more mechanistic understanding of these controls is needed in order to enable accurate predictions of its long-term fate and persistence. 相似文献
490.
In this study, a fluidized-bed reactor (FBR) was employed to treat copper-containing wastewater by mean of copper precipitation on the surface of sand grains. The conditions for optimum copper removal efficiency were also investigated. This technology was controlled so as to keep supersaturation low to induce the nucleated precipitation of copper coating on the sand surface in an FBR. The effects of relevant parameters, such as the pH value, the molar ratio of [C(T)] to [Cu(2+)], hydraulic loading and the types of chemical reagents used, were examined. The experimental results indicated that 96% copper removal efficiency could be achieved when the influent copper concentration was 10mg l(-1). The optimum chemical reagent was Na(2)CO(3); the molar ratio of [C(T)]/[Cu(2+)] was 2, and the optimal hydraulic loading was not be more than 25m h(-1). In addition, preventing homogeneous nucleation in the FBR was an important operation parameter. Homogeneous nucleation and molecular growth would lead to undesirable microparticle formation in the effluent. A good mixture of carbonate and copper in the presence of sand grains could reduce the level of homogeneous nucleation in the bottom of the reactor. Energy dispersive analysis (EDS) of X-rays provided insight into the copper coating on the sand surface, and element analysis indicated the weight percentages of CuCO(3) and Cu(OH)(2) in precipitate. 相似文献