排序方式： 共有14条查询结果，搜索用时 234 毫秒
1.
1 INTRODUCTION Agricultural use of pesticides has been recognized as one of the important non-point pollution sources in the world, and the pesticide application to agricultural lands has led to large amounts of residues discharged into surface water through runoff (Leonard, 1990). There have been growing concerns about the fate and transport of pesticides in agricultural lands, due to the associated adverse impacts on water environment and human health (Agassi et al., 1995; Ng and Clegg… 相似文献
2.
3.
WOLFRAM SCHÜßLER ROLF NEUBERT INGEBORG LEVIN NATALIE FISCHER CHRISTIAN SONNTAG 《Tellus. Series B, Chemical and physical meteorology》2000,52(3):909-918
The amounts of microbial and root‐respired CO2 in a maize/winter wheat agricultural system in south western Germany were investigated by measurements of the CO2 mixing ratio and the 13 C/12 C ratio in soil air. CO2 fluxes at the soil surface for the period of investigation (1993–1995) were also determined. Root respired CO2 shows a strong correlation with the plant mass above ground surface of the respective vegetation (R2 ≥0.88); the maximum CO2 release from roots was in August for the maize (2.0±0.5 mmol m−2 h−1 ) and in June for winter wheat (1.5±0.5 mmol m−2 h−1 ). Maximum CO2 production by roots correlate well with the maximum amount of plant root matter. Integrating the CO2 production over the whole growing season and normalizing to the dry root matter yields, the CO2 production per gram dry organic root matter (DORM) of maize was found to be 0.14±0.03 gC (g DORM)−1 . At the sites investigated, root‐produced CO2 contributed (16±4)% for maize, and (24±4)% for winter wheat, respectively, to the total annual CO2 production in the soil (450±50 gC m−2 for maize, 210±30 gC m−2 for winter wheat). 相似文献
4.
5.
JANOS FISCHER 《水文科学杂志》2013,58(2):157-159
Abstract Digital mapping techniques are used increasingly in hydrology. One of the constraints on the application of those techniques is the digitizing process, which can be costly and time consuming. This paper describes the background and development of a low cost, easy-to-use system for digitizing maps, based on the use of a video camera as a scanner, and goes on to discuss the application of this system to the task of digitizing the hydrological soil maps of Europe. 相似文献
6.
G. FISCHER 《Geophysical Prospecting》1985,33(5):716-722
The magnetotelluric phase in the medium of incidence over a good conductor varies from its value at the conductor surface, usually close to 45°, to the characteristic standing-wave phaseshift of 90° over a distance of a few conductor skin-depths, much shorter than the vacuum wavelength at the frequencies considered. Over the top of a graben or at the surface of a two-layer structure the basement can be looked upon as the matrix. If the graben or the overburden is a better conductor it will carry an extra current density in phase with the electric field, thus giving rise to an additional magnetic field also in phase with the electric field. This drives the argument of the surface impedance toward smaller values. For a more resistive graben or overburden the current is depressed, corresponding to a reduction of the surface magnetic field by an amount in phase with the electric field. This effect drives the phase of the impedance to values above the characteristic 45° of a uniform conductor. 相似文献
7.
8.
The suitability of VLF ground surveys in the investigation of shallow two-dimensional structures is analyzed. For such structures the polar formalism is derived, necessary in practice since the transmitters are generally not in the structural strike or profile. A simple vertical dike is considered to demonstrate the striking anisotropy which can be expected over such a structure, in particular the high apparent resistivity along the direction of a well-conducting dike and the low resistivity across it. The theory is then confronted with the practical example of an asymmetrical vertical dike resulting from a strike-slip fault. Modelling of the survey results is very successful and yields good confirmation of the polar behaviour. VLF ground surveys thus provide a quick and powerful tool for the study of geological accidents within about 100 m of the surface. 相似文献
9.
10.