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241.
本文提出了新中国医院建设的三个阶段和特征,并根据国家有关规划和统计年鉴提供的数据,对我国城镇医院的发展进行预测,提出了到2020年各种情况下医院床位数增加的预测值,可供有关部门参考。 相似文献
242.
Thomas LUCKNER Ulrich ZANKE 《国际泥沙研究》2007,22(2):87-102
This paper presents an analytical solution for calculating the initiation of sediment motion and the risk of river bed movement. It thus deals with a fundamental problem in sediment transport, for which no complete analytical solution has yet been found. The analytical solution presented here is based on forces acting on a single grain in state of initiation of sediment motion. The previous procedures for calculating the initiation of sediment motion are complemented by an innovative combination of optical surface measurement technology for determining geometrical parameters and their statistical derivation as well as a novel approach for determining the turbulence effects of velocity fluctuations. This two aspects and the comparison of the solution functions presented here with the well known data and functions of different authors mainly differ the presented solution model for calculating the initiation of sediment motion from previous approaches. The defined values of required geometrical parameters are based on hydraulically laboratory tests with spheres. With this limitations the derivated solution functions permit the calculation of the effective critical transport parameters of a single grain, the calculation of averaged critical parameters for describing the state of initiation of sediment motion on the river bed, the calculation of the probability density of the effective critical velocity as well as the calculation of the risk of river bed movement. The main advantage of the presented model is the closed analytical solution from the equilibrium of forces on a single grain to the solution functions describing the initiation of sediment motion. 相似文献
243.
Semi-diurnal and fortnightly surveys were carried out to quantify the effects of wind- and navigation-induced high-energy events on bed sediments above intertidal mudflats. The mudflats are located in the upper fluvial part (Oissel mudflat) and at the mouth (Vasière Nord mudflat) of the macrotidal Seine estuary. Instantaneous flow velocities and mudflat bed elevation were measured at a high frequency and high resolution with an acoustic doppler velocimeter (ADV) and an ALTUS altimeter, respectively. Suspended particulate matter concentrations were estimated by calibrating the ADV acoustic backscattered intensity with bed sediments collected at the study sites. Turbulent bed shear stress values were estimated by the turbulent kinetic energy method, using velocity variances filtered from the wave contribution. Wave shear stress and maximum wave–current shear stress values were calculated with the wave–current interaction (WCI) model, which is based on the bed roughness length, wave orbital velocities and the wave period (TS). In the fluvial part of the estuary, boat passages occurred unevenly during the surveys and were characterized by long waves (TS>50 s) induced by the drawdown effect and by short boat-waves (TS<10 s). Boat waves generated large bottom shear stress values of 0.5 N m−2 for 2–5 min periods and, in burst of several seconds, larger bottom shear stress values up to 1 N m−2. At the mouth of the estuary, west south-west wind events generated short waves (TS<10 s) of HS values ranging from 0.1 to 0.3 m. In shallow-water environment (water depth <1.5 m), these waves produced bottom shear stress values between 1 and 2 N m−2. Wave–current shear stress values are one order of magnitude larger than the current-induced shear stress and indicate that navigation and wind are the dominant hydrodynamic forcing parameters above the two mudflats. Bed elevation and SPM concentration time series showed that these high energy events induced erosion processes of up to several centimetres. Critical erosion shear stress (τce) values were determined from the SPM concentration and bed elevation measurements. Rough τce values were found above 0.2 N m−2 for the Oissel mudflat and about 1 N m−2 for the Vasière Nord mudflat. 相似文献
244.
J. S. dos SANTOS A. H. CARDOSO Civil Engineer M. Sc. in Hydraulics Water Resources Project Engineer ExxonMobil Production Company U.S. East P.O. Box New Orleans Louisiana - U.S.A. E-mail: ahc@civil.ist.utl.pt Associate 《国际泥沙研究》2001,16(4)
1 mnCnONLocal scour close to bridge piers and abUtInnts has long been a subect of concem for engineers, sinceit can We total or partial collapse of bridges. Until to the Present, local scour has been assessed, moshy,on the basis of resultS of labOratOry stodis. These sthes were cwhed out for steady flows lashng longenough as to gUarantee the develoPment of equlllbrium scour i.e., the develoPmen of scour holes whosedePth and 8haPe no lOnger significanti evolve with hme.In nta, such long l… 相似文献
245.
《国际泥沙研究》2020,35(3):237-248
This study presents the implementation and validation of a new sediment-scour model with a strict vertex-based,terrain conformal,moving-mesh technique within the framework of OpenFOAM.OpenFOAM lacks the ability to simulate large-amplitude motion needed for analysis of sediment-scour problems,and,thus,its application normally is restricted to small-amplitude cases to prevent computational divergence due to mesh deterioration.The proposed simple,moving-mesh technique in OpenFOAM is implemented to overcome the shortcomings of the conventional automatic mesh-motion techniques in handling large-amplitude moving geometries.The model is used to simulate a simple case of prescribed boundary motion,a previous experiment in the literature,and a new laboratory experiment for local scour due to submerged wall jets.The results are compared with both the experimental and other numerical results.The comparisons demonstrate that the proposed model has the novel advantage of allowing for more severe topographic variations,and can provide more reliable predictions for the key characteristics and evolution of the bed profiles in wall jet scour problems.Furthermore,to improve the practice of modeling wall jet scour,various turbulence modeling approaches and bedload equations also are evaluated and compared. 相似文献
246.
Over the last several decades,various sediment transport capacity formulations have been used by geomorphologists and engineers to calculate fluvial morphological changes.However,it remains poorly understood if the adaptation to capacity could be fulfilled instantly in response to differing inflow discharges and sediment supplies,and thus if the calculation of morphological changes in rivers based on the assumed capacity status is fully justified.Here we present a numerical investigation on this issue.The distance required for sediment transport to adapt to capacity(i.e.,adaptation-to-capacity length) of both bed load and suspended sediment transport is computationally studied using a coupled shallow water hydrodynamic model,in line with varied inlet sediment concentrations.It is found that the adaptation-to-capacity length generally decreases as the Rouse number increases,irrespective of whether the inlet sediment concentration increases or reduces.For cases with vanishing inlet sediment concentration a unified relationship is found between the adaptation-to-capacity length and the Rouse number.Quantitatively,the adaptation-to-capacity length of bed load sediment is limited to tens of times of the flow depth,whilst that of suspended sediment increases substantially with decreasing Rouse number and can be up to hundreds of times of the flow depth.The present finding concurs that bed load sediment transport can adapt to capacity much more rapidly than suspended sediment transport,and it facilitates a quantitative criterion on which the applicability of bed load or suspended sediment transport capacity for natural rivers can be readily assessed. 相似文献
247.
Bed sediment-associated trace metals in an urban stream, Oahu, Hawaii 总被引:78,自引:0,他引:78
R. A. Sutherland 《Environmental Geology》2000,39(6):611-627
Of the 117 stream and lake systems sampled nationwide, fish from Manoa Stream on Oahu, Hawaii, have consistently shown the
highest Pb concentrations. Therefore a detailed study was conducted to examine total metal contents in bed sediments from
a 5.8-km stretch of Manoa Stream. A total of 123 samples (<63 μm) were examined for 18 elements and 14 samples for 21 elements.
Selected samples were also examined using different leach solutions to examine metal phase associations. All trace metal data,
computations of enrichment ratios and the modified index of geoaccumulation point to mineralogical control for Cr and Ni;
minor anthropogenic contamination for Ba, Cd, Cu, Hg and Zn; and a very strong contamination signal for Pb. Maximum Pb contents
(up to 1080 mg kg−1) were associated with anthropogenic material dumping in minor tributaries, storm sewer sediments and sediments in the “lower”
section of the basin. Proportionally Pb had the highest non-residual component of elements examined; dominantly in the reducible
phase associated with Mn and amorphous Fe oxyhydroxides. The contamination signal was typically lowest in the “undisturbed”
headwater reach of the basin (above 5.1 km) with significant increases throughout the “residential” and “commercial-institutional”
zones of the mid-basin. The spatial pattern of bed sediment contamination and evidence from storm sewer-outlet sediments strongly
indicates that Pb, and to a lesser degree some other metals, is still being transported to the stream and the primary agent
is soil erosion and transport of metals sorbed to sediments. The primary source of sediment-associated metals is considered
to be the automobile, though other minor sources can not be ruled out.
Received: 3 November 1998 · Accepted: 26 January 1999 相似文献
248.
Numerical resolution of well-balanced shallow water equations with complex source terms 总被引:3,自引:0,他引:3
This paper presents a well-balanced numerical scheme for simulating frictional shallow flows over complex domains involving wetting and drying. The proposed scheme solves, in a finite volume Godunov-type framework, a set of pre-balanced shallow water equations derived by considering pressure balancing. Non-negative reconstruction of Riemann states and compatible discretization of slope source term produce stable and well-balanced solutions to shallow flow hydrodynamics over complex topography. The friction source term is discretized using a splitting implicit scheme. Limiting value of the friction force is derived to ensure stability. This new numerical scheme is validated against four theoretical benchmark tests and then applied to reproduce a laboratory dam break over a domain with irregular bed profile. 相似文献
249.
1962年,苏联学者М.Г.Баляшко提出了干盐湖晶间卤水分异的成因理论一“重力垂直分异”说,后来,此理论被我国盐矿地质学家引用到察尔汗盐湖。本文首次在“系统论”思想指导下,及数理统计方法深入细致地研究了该湖S_3盐层晶间卤水分异特征,提出了新的晶间卤水分异成因理论—“阶段性淡化”说,具有重要的经济和理论意义。 相似文献