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991.
On experimental setup in bioelectromagnetics 总被引:1,自引:1,他引:0
Bioeffects created by electromagnetic field (EMF) are the subject of intensive studies. This paper critically considers estimations
of exposure to EMF in bioelectromagnetic experiments. Results of calculations presented herein show the significant role of
the presence of conducting bodies (the exposure system) near an object under test on EMF energy absorption as well as mutual
interactions between simultaneously exposed objects. Our aims herein are twofold: firstly to find a way to refer measurement
results to free-space conditions in order to enable comparison of results obtained in different laboratories, and secondly
to show that EMF energy absorption in any exposed object is different and that this difference is a function of the size of
the exposure system, the number of exposed objects, and the particular properties (i.e., the electromagnetic structure) of
the objects. In the authors’ opinion the existence of interactions caused by the presence of the exposure system and other
exposed objects is a reason why remarkable differences are observed between experiments performed even under supposedly identical
conditions. The presented considerations and conclusion suggest wider participation of physicists and engineers in bioelectromagnetic
experiments in order to ensure the correctness of metrological aspects of these experiments. 相似文献
992.
Forest ecosystems may be actively managed toward heterogeneous stand structures to provide both economic (e.g., wood production
and carbon credits) and environmental benefits (e.g., invasive pest resistance). In order to facilitate wider adoption of
possibly more sustainable forest stand structures, defining growth expectations among alternative management scenarios is
crucial. To estimate the effect of tree size and spatial distributions on growth for forest structures commonly considered
in uneven-aged forest stand management, large (0.2 ha+) plots were established in 14 uneven-aged ponderosa pine stands in
eastern Montana. All study trees were stem-mapped and measured for diameter and 10-year sapwood and basal area increment.
A generalized growth model was developed to predict both total and merchantable 10-year basal area increment for nine hypothetical
stand structures [three diameter distributions (reverse-J, irregular, flat) × three spatial distributions (clumpy, partial
clumpy, uniform)]. Results indicate that the size and spatial distributions of individual trees have a considerable effect
on overall stand growth. The greatest total stand growth was in stands with reverse “J” shaped tree size distributions, while
the greatest merchantable stand growth was in stands with “flat” diameter distributions and uniform spatial distributions.
Through better comprehension of generalized uneven-aged stand growth dynamics, forest managers may better assess the effects
of alternative stand structures on stand growth while providing forest stand structures that may be more resilient in a changing
climate. 相似文献
993.
Urbanization and its impact on groundwater: a remote sensing and GIS-based assessment approach 总被引:1,自引:0,他引:1
The perils of unplanned urbanization and increasing pressure of human activities on hydro-geomorphologic system often result
in modification of the existing recharge mechanism, which leads to many environmental consequences. In the present research,
an attempt has been made to investigate the applicability of remote sensing and geographical information system (GIS) in dealing
with spatial and temporal variability of dynamic phenomena, like urbanization and its impact on groundwater. This paper covers
primarily, quantitative and qualitative impacts of urban growth on the behavior of aquifer in Ajmer city (India). Urban growth
of the Ajmer city in last 17 years has been estimated from the satellite images. Database related to urbanization and groundwater
has been created in GIS. Groundwater recharge has been computed using a water balance approach known as Water Level Fluctuation
Methodology. Recharge estimation methodology has been implemented in GIS to introduce the spatial variability of hydro-geological
characteristics. Further, temporal and spatial variations in groundwater quality and quantity have been correlated with urban
growth using overlay analysis in GIS. The study reveals a general decline in water table and quality with urbanization. Further,
remote sensing and GIS technologies have been found useful in assessment of spatial and temporal phenomena of urbanization
and its impact on groundwater system. 相似文献
994.
Kelley L. Arbogast Brian C.P. Kane Jeffrey L. Kirwan Bradley R. Hertel 《Journal of environmental psychology》2009
Empirical and anecdotal evidence suggests that landscapes with more vegetation have a positive impact on children's focus, attention, and cognitive development. In school, children are able to regain focus, suppress impulses, and pay attention in class longer after exposure to natural settings. Because children spend much of their time in school, the amount and types of vegetation on school grounds may influence their development. Public elementary schools in the Commonwealth of Virginia (N = 988) were surveyed to examine correlations between school ground vegetation and outside recess. The number of trees on school grounds, the size of the school grounds, and the presence of sports fields were modestly correlated with greater outside recess time. These correlations support common sense because sports fields facilitate supervised play and larger school grounds provide space for sports fields and playgrounds and additional opportunities for free play. More trees on school grounds provide a welcoming environment for students and teachers, and encourage outside play. These results may help school personnel design and maintain school grounds that increase outdoor recess time. 相似文献
995.
996.
Heavy metals in the aquatic environment have, to date, come essentially from naturally occurring geochemical resources. However,
this has been enhanced by anthropogenic activities such as crude oil exploration and exploitation activities, resulting in
pollution in the Taylor Creek aquatic ecosystem. The catfish species Bagrus bayad and other environmental segments were collected from five selected sites along Taylor Creek, southern Nigeria, and total
metal concentration determined. The concentration levels of the metals in B. bayad were higher than the values reported in the literature for fresh fish and may lead to a higher risk of harmful effects. The
bivariate regression models relating metals in B. bayad and metals in the surface waters were significant (R
2 ≥ 0.9002). The log (bio-concentration factor; BCF) values of Cr and Zn in B. bayad were the highest, whereas the lowest was found for Ni. The ecological distribution of the log (BCF) values was, for all the
heavy metals, moderately stable over the creek. All log-transformed bio-magnification factors (BMF) in the creek were positive,
which indicates that the metal concentration was greater in B. bayad than in suspended particulate matter (SPM). The absolute log (BMF) values of heavy metals can, therefore, be ranked in order
of decreasing magnitude: Cr (3.26) > Zn (2.99) > Cd (2.93) > Fe (2.76) > Pb (2.66) > Mn (2.36) > Ni (2.24). This sequence
indicates that toxic metals such as Cd, Cr and Pb are undergoing significant bio-reduction from SPM to B. bayad. The degree of correlation between the metals was different in B. bayad, which suggests that the sources of the metals polluting Taylor Creek were diverse. 相似文献
997.
F. Boukhoubza A. Jail F. Korchi L. Loukili Idrissi H. Hannache J.C. Duarte L. Hassani A. Nejmeddine 《Journal of environmental management》2009,91(1):124-132
The application of hypochlorite for the removal of soluble COD, phenolic and polyphenolic like compounds, and other organic compounds responsible for the olive mill wastewater (OOWW) colour has been experimentally studied. After the OOWW filtration on a sand column, the effluent was subjected to a fast liming under optimal conditions. Lime application reduced polyphenols, COD and SS contents to half of their initial values but an important blackening of the treated OOWW was observed, especially when adding high concentrations of lime (10% (W/V) and 15% (W/V)).A second stage of treatment was applied using calcium hypochlorite. In this stage, removal of the studied compounds reached as much as 95% at higher concentrations, and particularly the colouring of OOWW which is generally difficult to eliminate was greatly reduced. The OOWW hypochloration acted through coagulation–flocculation and a rapid oxidation of the organic matter proceeded from the first 5 min. The kinetic study of the degradation of the waste polluting compounds from liming showed that Ca(ClO)2 reacts similarly in the elimination of organic compounds, polyphenols, SS and colouration. The analysis of the organochloride compounds generated by the reaction between hypochlorite and the organic compounds showed that DDD, DDT and the heptachlor contents exceeded the values recommended by the International and European drinking water standards. 相似文献
998.
Jimmie C. Oxley James L. Smith Carolyn Higgins Patrick Bowden Jesse Moran Joe Brady Carol E. Aziz Evan Cox 《Journal of environmental management》2009,90(11):3629-3634
When an explosive detonates or a propellant or flare burns, consumption of the energetic filler should be complete but rarely is, especially in the presence of large amounts of non-combustible materials. Herein we examine three types of perchlorate-containing devices to estimate their potential as sources of contamination in their normal mode of functioning. Road flares, rocket propellants and ammonium nitrate (AN) emulsion explosives are potentially significant anthropogenic sources of perchlorate contamination. This laboratory evaluated perchlorate residue from burning of flares and propellants as well as detonations of ammonium nitrate emulsion explosives. Residual perchlorate in commercial products ranged from 0.094 mg perchlorate per gram material (flares) to 0.012 mg perchlorate per gram material (AN emulsion explosives). The rocket propellant formulations, prepared in this laboratory, generated 0.014 mg of perchlorate residue per gram of material. 相似文献
999.
Water availability, use and quality in a rural watershed of the Colombian Andes were investigated through participatory research involving local youth. Research included the quantification of disaggregated water use at the household level; comparison of water use with availability; monitoring water quality of streams, community water intakes and household faucets; and the determination of land use – water quality interactions. Youth were involved in all aspects of the research from design to implementation, dissemination of results and remediation options. Quantification of domestic and on-farm water use, and water availability indicated that water availability was sufficient during the study period, but that only an 8% decrease in dry season supply would result in shortages. Elevated conductivity levels in the headwaters were related to “natural” bank erosion, while downstream high conductivity and coliform levels were associated with discharges from livestock stalls and poorly maintained septic tanks in the stream buffer zone. Through the involvement of youth as co-investigators, the knowledge generated by the research was appropriated at the local level. Community workshops led by local youth promoted water conservation and water quality protection practices based on research, and resulted in broader community participation in water management. The approach involving youth in research stimulated improved management of both land and water resources, and could be applied in small rural watersheds in developed or developing countries. 相似文献
1000.