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991.
992.
993.
Chemical signals of epiphytic lichens in southwestern North America; natural versus man-made sources for airborne particulates 总被引:1,自引:0,他引:1
Stephen R. Getty David S. Gutzler Yemane Asmerom Charles K. Shearer Scott J. Free 《Atmospheric environment (Oxford, England : 1994)》1999,33(30):2261
Ambient airborne particulate matter (PM) in southwestern North America consists of naturally derived desert dust, plus anthropogenic inputs from several sources. Epiphytic lichens (Usnea sp.) in this region are a useful biomonitor for the airborne PM because they derive nutrients and moisture largely from incorporated atmospheric aerosols, and not by absorption from the host tree limb from which they are suspended. Using a broad-based sampling strategy from southern Chihuahua, Mexico, to northern New Mexico, USA, we show that select elemental abundance ratios and lead isotopes from epiphytic lichens are useful for distinguishing between sources of airborne PM, and for gauging anthropogenic inputs into desert ecosystems. Abundance patterns of the trace elements La, Nd, and Sm in the lichens suggest origination from continental crust, but rare earth elements display a pronounced enrichment relative to the major element Fe by a factor of about 5. This enrichment appears related to geologic weathering, aeolian transport, and grain-size biases toward trace-element-rich mineral grains in the arid setting. Using the metal Pb as an indicator of human inputs, epiphytic lichens typically show Pb enrichments by a factor of about 25–60 over typical upper crustal values. Regional-scale differences in Pb isotope ratios of these lichens relate to different pollutant sources in southwestern North America. 相似文献
994.
Mark D. E. Fellowes Steve G. Compton James M. Cook 《Behavioral ecology and sociobiology》1999,46(2):95-102
The populations of many species are structured such that mating is not random and occurs between members of local patches.
When patches are founded by a single female and all matings occur between siblings, brothers may compete with each other for
matings with their sisters. This local mate competition (LMC) selects for a female-biased sex ratio, especially in species
where females have control over offspring sex, as in the parasitic Hymenoptera. Two factors are predicted to decrease the
degree of female bias: (1) an increase in the number of foundress females in the patch and (2) an increase in the fraction
of individuals mating after dispersal from the natal patch. Pollinating fig wasps are well known as classic examples of species
where all matings occur in the local patch. We studied non-pollinating fig wasps, which are more diverse than the pollinating
fig wasps and also provide natural experimental groups of species with different male morphologies that are linked to different
mating structures. In this group of wasps, species with wingless males mate in the local patch (i.e. the fig fruit) while
winged male species mate after dispersal. Species with both kinds of male have a mixture of local and non-local mating. Data
from 44 species show that sex ratios (defined as the proportion of males) are in accordance with theoretical predictions:
wingless male species<wing-dimorphic male species<winged male species. These results are also supported by a formal comparative
analysis that controls for phylogeny. The foundress number is difficult to estimate directly for non-pollinating fig wasps
but a robust indirect method leads to the prediction that foundress number, and hence sex ratio, should increase with the
proportion of patches occupied in a crop. This result is supported strongly across 19 species with wingless males, but not
across 8 species with winged males. The mean sex ratios for species with winged males are not significantly different from
0.5, and the absence of the correlation observed across species with wingless males may reflect weak selection to adjust the
sex ratio in species whose population mating structure tends not to be subdivided. The same relationship is also predicted
to occur within species if individual females adjust their sex ratios facultatively. This final prediction was not supported
by data from a wingless male species, a male wing-dimorphic species or a winged male species.
Received: 27 July 1998 / Received in revised form: 11 January 1999 / Accepted: 16 January 1999 相似文献
995.
996.
针对某一林区,确定其林木管理目标,以及为达到此目标对林火监测与扑救系统的要求,从而确定森林防火的资金投入。分析了加大森林防火投入前后森林火灾损失与扑求费用的变化。 相似文献
997.
Xi Luo Ao Li Xue Xia Peng Liang Xia Huang 《Frontiers of Environmental Science & Engineering》2023,17(9):108
998.
提出一种基于Landsat 8 OLI影像提取水体信息的斜率比值法(SR),比对不同方法、不同类型水体和不同季节影像的数据,结果表明:SR法相比归一化差异水体指数法(NDWI)和改进的归一化差异水体指数法(MNDWI),水体信息提取精度更高,且对阈值精确度的要求低,阈值一般设定为2.0;SR法适用于清澈水体、浑浊水体、浅水河滩等水体,对河流干流和较大支流的提取精度达到99%,细小支流、沟渠的提取精度为66%,面积较小的水体提取精度为65%;在冬季太阳高度角较低时,SR也能较好地去除阴影。 相似文献
999.
1000.
硫化沉淀法处理矿山酸性废水研究 总被引:5,自引:1,他引:4
对沉淀浮选机理进行了分析 ,讨论了选择性沉淀 浮选技术 ,论述了硫化沉淀浮选法不仅能处理矿山含重金属离子废水 ,同时还能回收其中的有用金属 相似文献