首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   278篇
  免费   0篇
安全科学   2篇
废物处理   6篇
环保管理   8篇
综合类   128篇
基础理论   42篇
污染及防治   67篇
评价与监测   11篇
社会与环境   12篇
灾害及防治   2篇
  2021年   3篇
  2018年   8篇
  2017年   4篇
  2015年   7篇
  2014年   13篇
  2013年   7篇
  2012年   6篇
  2011年   5篇
  2010年   12篇
  2009年   10篇
  2008年   8篇
  2007年   9篇
  2006年   8篇
  2005年   7篇
  2004年   6篇
  2003年   8篇
  2002年   6篇
  1998年   7篇
  1996年   7篇
  1995年   3篇
  1993年   4篇
  1975年   3篇
  1971年   2篇
  1969年   2篇
  1966年   3篇
  1965年   5篇
  1964年   2篇
  1963年   7篇
  1962年   4篇
  1961年   3篇
  1960年   3篇
  1959年   5篇
  1958年   5篇
  1957年   3篇
  1956年   10篇
  1955年   7篇
  1954年   3篇
  1953年   3篇
  1952年   2篇
  1950年   2篇
  1949年   2篇
  1947年   2篇
  1942年   2篇
  1940年   2篇
  1939年   4篇
  1934年   3篇
  1933年   2篇
  1929年   2篇
  1925年   2篇
  1918年   2篇
排序方式: 共有278条查询结果,搜索用时 15 毫秒
71.
The study of the fetal platelet count and size can, according to the literature, be used for the prenatal diagnosis of the Wiskott-Aldrich syndrome (WAS). So far, no affected fetuses have been identified by this method. All pregnancies in which this method had been applied to resulted, as correctly predicted, in the birth of normal children. Here we report on a familial case of WAS where the haematological parameters failed to reveal the affected second child. Hence we assume that the platelet count and size of platelets remain normal in fetuses with WAS to the gestational age of 22 weeks and cannot be used for prenatal diagnosis.  相似文献   
72.
73.
74.
75.
76.
77.
Soil functional responses to excess nitrogen inputs at global scale   总被引:4,自引:0,他引:4  
There is little evidence that nitrogen (N) cycling in the highly weathered, low-phosphorus (P), acidic soils found in Southern Hemisphere continents will differ greatly from that in North America and Europe. Evidence from the 'south' shows: the similarity in forms and temporal patterns in losses of N from different land uses; that the C:N ratios of the forest floor/litter layer from different continents are strongly predictive of a range of processes on a global scale; that generalizations based on Northern Hemisphere experience of the impact of N additions to 'P-limited' ecosystems are likely to fail for southern ecosystems where anatomical and physiological adaptation of native plants to low-P soils makes questionable the concept of 'P-limitation'; that the greatest threats in the 'south' are probably changes in land use that may greatly increase N inputs and turnover; that localized increases in N inputs produce similar effects to those seen in the 'north'.  相似文献   
78.
Transport experiments with colloids and radionuclides in a shear zone were conducted during the Colloid and Radionuclide Retardation experiment (CRR) at Nagra's Grimsel Test Site. Breakthrough curves of bentonite colloids and uranine, a non-sorbing solute, were measured in an asymmetric dipole flow field. The colloid breakthrough is earlier than that of uranine. Both breakthrough curves show anomalously long late time tails and the slope of the late time tails for the colloids is slightly higher. Anomalous late time tails are commonly associated with matrix diffusion processes; the diffusive interaction of solutes transported in open channels with the adjacent porous rock matrix or zones of stagnant water. The breakthrough curves for different colloid size classes are very similar and show no signs of fractionation due to their (size-dependent) diffusivity. It is proposed that tailing of the colloids is mainly caused by the structure of the flow field and that for the colloid transport, matrix diffusion is of minor importance. This has consequences for the interpretation of the uranine breakthrough. Comparisons of experimental results with numerical studies and with the evaluation of the colloid breakthrough with continuous time random theory imply that the tailing in the conservative solute breakthrough in this shear zone is not only caused by matrix diffusion. Part of the tailing can be attributed to advective transport in fracture networks and advection in low velocity regions. Models based on the advection-dispersion equation and matrix diffusion do not properly describe the temporal and spatial evolution of colloid and solute transport in such systems with a consistent set of parameters.  相似文献   
79.
In the North Tyrolean Limestone Alps a site was investigated over a four-year period (1998–2001) in order to assess the nitrogen saturation status, the nitrogen budget (quantification of the net uptake of nitrogen by the canopy and of the nitrogen mineralization, nitrogen uptake from roots and N2O emission rates, proof of the origin of nitrate in the soil water with stable isotope analyses), and the effects of the actual nitrogen input on ground water quality. The main goals were to quantify the nitrogen input rate, the nitrogen pools in above-ground and below-ground compartments, nitrogen turnover processes in the soil as well as the output into the groundwater and into the atmosphere. The findings are based on continuous and discontinuous field measurements as well as on model results.While nitrogen input exceeded the Critical Loads of the WHO (1995), nitrogen deficiency and nutrient imbalances were verified by needle analyses. The atmospheric input of inorganic nitrogen was higher than the nitrogen output in 50 cm soil depth. A tracer experiment with15N helped to prove that not more than half of the applied nitrate could be discharged. This allows the conclusion that nitrogen is stored in the system and that the site cannot yet be said to be saturated with nitrogen. The same result was also obtained by modelling. In addition, it was proved that the nitrogen discharge did not stem from deposition but from processes within the system.  相似文献   
80.

Stable isotope analysis of15N/14N and18O/16O - nitrate was used to investigate the nitrate dynamics and potential groundwater pollution in an Alpine forest stand in Tyrol/Austria. The dynamics of δ15−Nnitrate values were followed in a forest ecosystem. The stable isotopic values of the throughfall are comparable with other studies. The completely decoupled dynamics of the δ15−Nnitrate of the precipitation and the surface water was observed. High variations in δ15-N - nitrate values in rainfall indicate that nitrate of different sources is deposited at that site. A significant correlation between the δ15Nnitrate values of the surface water and soil water was obtained, while no significant correlation between the δ15Nnitrate values of any precipitation sample with the surface water could be found. This suggests that the main source of nitrate in soil water originates from microbiological activity such as nitrification reactions and less from nitrate input by deposition. The results of δ18Onitrate measurements strongly supported the microbiological origin of nitrate in the surface and soil water. In an additional lysimeter experiment,15N - labelled nitrate was applied to study nitrate transport in soil. After 130 days and the collection of 300 L leachate, a total of 52% of the applied nitrate was detected in seepage water.

  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号