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991.
Recovery by riffle macroinvertebrates in a river after a major accidental spillage of chlorpyrifos 总被引:2,自引:0,他引:2
The impact of a major spillage of the insecticide 'Dursban' on the riffle macroinvertebrates along 19 km of the River Roding, Essex, is described. Five affected riffles and an upstream control were kick-sampled at approximately 10-week intervals for two years following the spill, and the results are compared with species composition and relative abundance data collected from the same sites during the previous six years. Initial concentrations of the active ingredient, chlorpyrifos, in river water (up to 2.5 mg litre(-1)) exceeded the level lethal to all the aquatic arthropods present by at least 10-fold, and this group of macroinvertebrates was eliminated. Molluscs and annelids, which are relatively tolerant of chlorpyrifos, survived. Since these groups already dominated the lowermost urban reaches, the impact of the spill was greatest further upstream, where reaches with a better water quality previously supported a more diverse and abundant arthropod fauna. Chlorpyrifos residues in water declined below 1 microg litre(-1) within 11 weeks, but sediment within 5 km of the spillage site remained highly contaminated for considerably longer. Of ten arthropod taxa previously common to all sites, chironomid larvae were first to recolonise affected reaches, 13 weeks after the spill. The isopod Asellus aquaticus, was also quick to recover. Although other arthropods had recolonised most sites within 79 weeks, the coleopteran Oulimnius tuberculatus and the epheremeropteran Caenis moesta had failed to return to the lowermost reaches after 108 weeks. Downstream drift was probably the principal factor influencing the pattern of arthropod recolonisation, with the location and aquatic fauna of tributary streams entering the affected reaches being particularly important. 相似文献
992.
993.
Prenatal specimens were received from a fetus with abnormalities noted on ultrasound. A supernumerary marker chromosome (SMC) was detected: 47,XY,+mar. Fluorescence in situ hybridisation (FISH) further classified this to be partial tetrasomy for chromosome 14. We compare this finding with other cases of SMC (14) and further classify phenotype with karyotype. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
994.
995.
George A. Sacher 《Environment international》1978,1(6):381-389
The theory of competing risks cannot be based entirely on the analysis of postmortem pathology data. It is necessary also to know the prevalence and residence times of the diseases in question, separately and jointly, in the living population at risk. It is also necessary to have a conceptual model of the transition process from health to disease, or from one disease state to another, within the organism, so that the formal transition probabilities estimated from epidemiological data can be interpreted in biophysical terms as arising from changes in the physico-chemical state of the organism. This paper offers such a model for transition processes arising from fluctuations of physiological state (for example, lapse into diabetic coma or insulin shock as a result of extreme high or low excursions of the blood sugar level). A Gaussian fluctuation process is postulated, and the transition probability, or incidence rate, is calculated as the frequency with which the state variable fluctuates beyond a specified distance, Λ, from the mean state. An explicit solution is given for the limiting, but biologically reasonable, case that such an excursion is a rare event. In this case, the transition probability varies exponentially for linear displacement of Λ or of the dispersion of fluctuations, σ. If Λ decreases, and/or σ increases, as a linear function of age, this model yields an exponential (Gompertzian) relation of disease incidence to age. Generalization to more than one variable is accomplished by introducing the concept of a mortality potential surface, in which the disease transitions are geometrized as saddle points, or “passes”, on the surface. 相似文献
996.
A resident population of 13 black rhinoceros ( Diceros bicornis ) persist in Ngorongoro Crater, Tanzania. The effective population size ( N e ) may be as few as 5 animals. Projected growth for this population suggests that the effective population size will remain small for the near future, threatening this Iocal population with extinction due to the stochastic factors associated with small population size. A summary of historic and recent demographic data for this population reveals a population crash during the period of heavy poaching that affected this species throughout its range. Although poaching of this species has been brought under control the population remains small. These data and models of projected population growth argue for consideration of more-intensive management within the framework of the small population paradigm. This case is an example of applied conservation resulting from this paradigm used in conjunction with rather than competing with the declining population paradigm. We identify additional monitoring, particularly of density-dependent behaviors, that will be necessary for designing a successful management program. Finally, the use of molecular markers for developing an accurate pedigree for this population is suggested in order to maintain a genetically healthy population. These strategies have broad applicability to black rhinoceros conservation throughout Africa. 相似文献
997.
At the new Marais des Cygnes National Wildlife Refuge in Linn County, Kansas, and Bates County, Missouri, USA, we evaluated
long-lived contaminants before acquisition of the land for the refuge. We sampled sediments at 16 locations and fish at seven
locations. The samples were analyzed for metals and for chlorinated hydrocarbon compounds. Selected sediment samples also
were analyzed for aliphatic hydrocarbons. Arsenic concentrations in sediment samples from six locations were elevated compared
to US norms, but arsenic was not detected in any fish composite. Mercury concentrations in largemouth bass from two locations
were comparable to the 85th percentile concentrations in nationwide fish collections. Most sediment concentrations of other
metals were unlikely to have detrimental effects on biota. No chlorinated hydrocarbons were detected in any sediment sample.
Chlordane compound concentrations in fish composites from two sites at the eastern end of the sampling area were 0.127 and
0.228 μg/g wet weight, respectively, which are high enough to cause concern. Most aliphatic hydrocarbons detected were found
at low concentrations and probably were natural in origin. We concluded that there are no serious contaminants concerns within
the project area, but past use of arsenical pesticides may mean a legacy of elevated soil arsenic levels in parts of the area
and some use of banned pesticides such as chlordane and DDT likely is still occurring near the refuge. 相似文献
998.
Albert Rango Arlen Feldman Thomas S. George III Robert M. Ragan 《Journal of the American Water Resources Association》1983,19(2):165-174
ABSTRACT: In a cooperative demonstration project, NASA and the U.S. Army Corps of Engineers (Corps) compared conventional and Landsat-derived land-use data for use in hydrologic models, and the resulting discharge frequency curves were analyzed. When a grid-based data-management system was used on a cell-by-cell basis (size about 1.1 acres or 0.45 hectare), Landsat classification accuracy was only 64 percent, but, when the grid cells were aggregated into watersheds, the classification accuracy increased to about 95 percent. When both conventional and Landsat land-use data were input to the HEC-1 model for generating discharge frequency curves, the differences in calculated discharge were judged insignificant for subbasins as small as 1.0mi2 (2.59 km2). For basins larger than 10mi2 (25.9km2), use of the Landsat approach is more cost-effective than use of conventional methods. Digital Landsat data can also be used effectively by local and regional agencies for hydrologic analysis by incorporating the data into grid-based data-management systems. The transfer of this new technology is well under way through inclusion in some Corps training courses and through use by both county government personnel and private consultants. 相似文献
999.
In this paper we study optimal harvesting of the Norwegian spring-spawning herring stock. The biological model is described
by a discrete time age-structured model. The optimal harvesting patterns are studied numerically and the results show that
when using a linear cost function and constant price in the optimisation model, the optimal harvesting pattern is pulse fishing.
However, optimal constant fishing effort gives only slightly lower profit. Moreover, when price is made responsive to harvest
the optimal harvesting strategy is substantially smoothed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
1000.
George F. Ray 《Resources Policy》1984,10(2):75-80
This article analyses the lifetimes of reserves of three dozen important minerals. Despite the high rate of their extraction in the past 30 years, the recorded reserves of these non-renewable materials were higher in 1981 than in 1950 and they seem to meet foreseeable demand for a long time to come, as indicated by the estimated static lifetime for each of the minerals covered. The dynamic nature of ‘reserves’ is emphasized: further exploration and scientific and technological advance will add to the present proven reserves, and at a higher price further resources will be ‘upgraded’ into commercially exploitable reserves. Apparent long-term security can be disturbed by natural disasters, political events or other factors, especially in the case of minerals whose reserves and production are highly concentrated in one country. However, any such interruption in the continuity of supply is likely to be short-lived. 相似文献