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721.
Weirs are low-level dams traditionally used in Louisiana's coastal marshes to improve habitat for ducks and furbearers. Currently,
some workers hope that weirs may reduce marsh loss, whereas others fear that weirs may accelerate marsh loss. Parts of Marsh
Island, Louisiana, have been weir-managed since 1958 to improve duck and furbearer habitat. Using aerial photographs, marsh
loss that occurred between 1957 and 1983 in a 2922-ha weir-managed area was compared to that in a 2365-ha unmanaged area.
Marsh loss was 0.38%/yr in the weir-managed area, and 0.35%/yr in the unmanaged area. Because marsh loss in the two areas
differed less than 0.19%/yr, it was concluded that weirs did not affect marsh loss. The increase in open water between 1957
and 1983 did not result from the expansion of lakes or bayous. Rather, solid marsh converted to broken marsh, and the amount
of vegetation within previously existing broken marsh decreased. Solid marsh farthest from large lakes and bayous, and adjacent
to existing broken marsh, seemed more likely to break up. Marsh Island has few canals; therefore, marsh loss resulted primarily
from natural processes. Weirs may have different effects under different hydrological conditions; additional studies are needed
before generalizations regarding weirs and marsh loss can be made. 相似文献
722.
The activity of four enzymes, including GOT-1, has been investigated in the erythrocytes of a 10q→24qter trisomic fetus. Analyses have been performed on a feto-maternal blood mixture sampled by fetoscopy and on red cells obtained by cardiac puncture, following therapeutic abortion. The demonstration of a 40 percent increase of GOT-1 activity, as compared to normal fetuses of similar gestational age, suggests that gene dosage studies may be a useful confirmatory technique in prenatal diagnosis of unbalanced chromosomal aberrations. Practical application of a similar diagnostic approach is conditioned by (1) precise characterization of fetal chromosome imbalance; (2) confirmed assignment of the gene locus coding for the gene product under investigation; (3) evidence of a linear proportionality between gene dose and concentration of the gene product in patients with the same chromosome imbalance detected in the fetus; (4) knowledge of the range of normal variation at different weeks of gestation of the enzyme activity to be tested in the fetus; (5) safety of fetal sampling procedure. 相似文献
723.
724.
Loss of Pesticides from Agricultural Fields in SE Norway – Runoff Through Surface and Drainage Water
G. Riise H. Lundekvam Q.L. Wu L.E. Haugen J. Mulder 《Environmental geochemistry and health》2004,26(2):269-276
Loss of two pesticides with different mobility characteristics, bentazone (Koc 34) and propiconazole (Koc 1800), were studied at three agricultural fields (Askim, Bjørnebekk and Syverud) in SE Norway. A conservative tracer (Br) was used to follow the flow of water. The loss of pesticides varied among the fields, depending on hydrological characteristics and soil properties. The loss of pesticides was higher from two artificially levelled silty clay loam soils with poor aggregate stability (Askim and Bjørnebekk) compared to a loam/silt loam soil with increased content of organic carbon and better aggregate stability (Syverud). The total accumulated loss was <0.5% from all fields. The highest pesticide concentrations were measured at the first runoff episode after application for both the mobile (bentazone) and less mobile pesticide (propiconazole) in the surface runoff. In the drainage water, the peak for the less mobile pesticide coincided with the Br tracer, while the peak for mobile pesticide appeared earlier than the Br tracer. Rapid movement of water, particles and pesticides through soils indicate flow through macropores. Larger proportions (in percent of total applied) of both the mobile and the strongly sorbed pesticides were lost through the drainage as compared to the loss through surface runoff at Askim. Here, it is suggested that macropore flow contribute to the increased loss of pesticides through the drainage. At Syverud, high infiltration capacity reduces the amount of water available for surface runoff, and somewhat higher loss of the mobile pesticide was registered in the drainage compared to the surface runoff. For the strongly sorbed pesticide, however, propiconazole was neither detected in surface nor in drainage water at Syverud. Generally, there was a higher percentage loss of the mobile compared to the strongly sorbed pesticide in both surface and drainage water, which is in agreement with the pesticides mobility characteristics in soil. An exception was, however, the erodible soil Bjørnebekk, where a higher fraction of propiconazole was lost in the surface runoff compared to bentazone. Large amounts of sediment transport from the Bjørnebekk field probably contributed to enhanced transport of the strongly sorbed pesticide. 相似文献
725.
Adam B. Munson Joseph J. Delfino 《Journal of the American Water Resources Association》2007,43(2):522-532
Abstract: Regulation of river flows can result in decreased stage fluctuations and alteration of inundation patterns of floodplain wetlands. However, floodplain inundation has historically not been addressed in most minimum flow determinations. Florida law requires the water management districts of the state to establish minimum flows and levels to protect water bodies from significant harm associated with water withdrawals. The Southwest Florida Water Management District utilizes a 15% reduction in habitat criterion as a threshold for defining significant harm to freshwater segments of rivers. Utilizing a multi‐parameter approach and different habitat measures for seasonal flow periods, the District has recommended minimum flow compliance standards for the Alafia, Myakka and middle Peace rivers. For the high‐flow period, the District utilized a 15% reduction in the number of days of floodplain inundation (a temporal loss) as a significant harm threshold. This approach yielded allowable flow reductions of 8% for the Alafia and Peace rivers during the high‐flow season and a 7% allowable reduction of natural flows on the Myakka River. Comparison of changes in flows associated with temporal and spatial loss thresholds indicated that flow reductions required to effect a 15% spatial loss of habitat on the Alafia, Myakka and middle Peace rivers are higher than those that would yield a 15% temporal loss. This indicates that with respect to natural flow protection, the District’s consideration of temporal reductions in habitat for establishing minimum river flows for seasonal high‐flow periods is more conservative than the use of a spatial loss criterion. 相似文献
726.
为揭示交通事故经济损失的变化规律,笔者研究并利用时间序列的方法,建立了ARIMA模型,对1985—2005年全国交通事故经济损失的数据进行了分析和预测。根据原始数据的特点,选择随机时间序列分析方法。通过对模型的识别和参数的选择,得到2006—2008年的交通事故损失的预测值分别为2.9559,2.9707和3.0129亿元,置信区间为95%。通过对1985—2005年交通事故经济损失的预测结果与原始数据的比较表明,预测结果接近原始数据,该方法为交通事故的预防和控制提供了技术指导和有益参考。 相似文献
727.
728.
Jing Zhang 《Water, Air, & Soil Pollution: Focus》2007,7(6):583-592
Industrialization and urbanization along the coastal population centers have brought great changes in the land cover and material
fluxes from watersheds to receiving bays and estuaries. We have embarked a multiyear research project on “Watersheds Nutrient
Loss and Eutrophication of Jiaozhou Bay” for the period of 2000 to 2004, funded by the Natural Science Foundation of China
to examine human influence on the marine sector of ecosystem. Jiaozhou Bay, located in the southern part of Shandong Peninsula,
was selected because of the existence of long-term hydrographic and meteorological records since the 1930s and recent observations
on the marine ecological variables. We have made extensive and periodic measurements on the water movement, nutrients, phytoplankton,
and microbe in water column and bottom sediments. Box and 3-dimensional hydrodynamic models were developed and utilized to
understand the evolution of eutrophic status with time. It was found that primary productivity has suffered from silica depletion
followed by phosphate, and the dominance of large phytoplankton has been replaced by small-size communities. These ecosystem
changes were brought by the changes in the relative contribution among major pathways and concentrations, owing to the human
activities in the watershed. Eight articles in this volume reported various aspects of the linkage between watershed human
activities and ecosystem for the Jiaozhou Bay as the initial outcome of this project. 相似文献
729.
Heike Pröhl 《Behavioral ecology and sociobiology》2005,58(3):310-315
Both modelling and field data from three breeding seasons show that an environmental factor, clutch loss (CL), affects the operational sex ratio (OSR) and therefore male mating frequency in strawberry poison frogs. Clutch loss affects the length of reproductive cycles of both sexes: with increasing clutch losses, males spend proportionately more time than females in parental investment activities. Because of this, males spend relatively less time in the mating pool, i.e. exhibit proportionately more time-out than females in comparison to a situation with low or no clutch loss. Hence, clutch loss leads to a less male-biased OSR, coupled with a decrease in the opportunity for sexual selection. Furthermore, this study resolves an apparent paradox, the negative correlation between mating frequency and reproductive success (=number of produced tadpoles) of individual males in one breeding season. Clutch loss decouples the correlation between mating frequency and reproductive success because females re-enter the mating pool when they lose their offspring. However, clutch loss diminishes the reproductive output. Similar consequences of clutch loss on the OSR may be true for many species where both sexes reproduce frequently in one breeding season.Communicated by J. Christensen-Dalsgaard 相似文献
730.