全文获取类型
收费全文 | 297篇 |
免费 | 11篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 5篇 |
地球物理 | 83篇 |
地质学 | 163篇 |
海洋学 | 13篇 |
天文学 | 17篇 |
综合类 | 2篇 |
自然地理 | 23篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 3篇 |
2019年 | 8篇 |
2018年 | 19篇 |
2017年 | 18篇 |
2016年 | 29篇 |
2015年 | 12篇 |
2014年 | 28篇 |
2013年 | 22篇 |
2012年 | 18篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 11篇 |
2008年 | 22篇 |
2007年 | 8篇 |
2006年 | 15篇 |
2005年 | 6篇 |
2004年 | 5篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1977年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有317条查询结果,搜索用时 31 毫秒
171.
DEPTH-AVERAGE ANALYSIS OF HYSTERESIS BETWEEN FLOW AND SEDIMENT TRANSPORT UNDER UNSTEADY CONDITIONS 总被引:1,自引:0,他引:1
Weiming WU Mustafa ALTINAKAR Sam S. Y. WANG 《国际泥沙研究》2006,21(2):101-112
1 INTRODUCTION Flow and sediment transport in natural rivers are generally unsteady, and exhibit temporal and spatial lags. Traditionally, in most hydraulic engineering problems the unsteady flow and sediment transport are approximately treated as steady … 相似文献
172.
Grain size and mineral composition of core sediments were used to investigate influences of various terrestrial and marine conditions, which have prevailed on the southwestern Black Sea shelf during the Holocene. Siliciclastic mud with small amounts of sand and gravel from nearby coastal hinterland is the principal sediment type, whereas sediments deposited near the shelf edge and the Istanbul Strait and off the Duru Lake (a paleo-river mouth) constitued large quantities of sand and gravel of both biogenic and terrigenic origin. Variable amounts of aragonite, 1 nmmicas, quartz, feldspars, calcite and dolomite constitute the dominant non-clay minerals in bulk sediments. The clay mineral assemblage in the 〈 2 μm fraction is made up of smectite, illite, kaolinite and chlorite. Aragonite and calcite are mainly derived from benthic accumulations, whereas feldspars (mainly plagioclase) and smectite reflect magmaticvolcanic provenance and the distribution of 1 nm-micas and chlorite correlate with nearby metamorphic sources onland. Nevertheless, grain size and mineral distribution generally indicate a combination of effects of wind and wave climate, longshore and offshore cyclonic currents, changing sea-level stands and nearby source rock and morphological conditions. It is also suggested that at least part of clay minerals could be derived from the northwesterly Danube River input. 相似文献
173.
Spatial assessment of salinity and nitrate pollution in Amman Zarqa Basin: a case study 总被引:1,自引:0,他引:1
Mustafa Al Kuisi Mohammed Al-Qinna Armin Margane Taiseer Aljazzar 《Environmental Earth Sciences》2009,59(1):117-129
Intensive use of land resources in arid and semi-arid regions exert serious pressures on groundwater resources and jeopardize
further socio-economical developments. The Amman-Zarqa Basin (AZB), the most vital basin in Jordan, is facing recent groundwater
deterioration due to a very large increase in water demands for domestic, agricultural, and industrial uses. The objectives
of this paper were to quantify the degree of contamination in the basin by evaluating the characteristics, distribution and
seasonal variations of two pollution indicators (nitrate concentration and salinity) and to determine the impacts of human
activities (land use) on groundwater quality. Based upon long-term data (1970–2005) of groundwater samples collected from
538 wells across the AZB, spatial analyses indicated that both indicators have a strong spatial dependence and are anisotropically
distributed. Prediction maps of Ordinary Kriging and Indicator Kriging provided detailed indications of the major and minor
sources of pollution in the basin. Inefficient wastewater treatment plants, industrial activities and agricultural practices
were responsible for 91, 85, and 25% salinization of nearby wells, respectively. Nitrate pollution had reached 73% above threshold
(50 mg/L) in some cases. The temporal analyses estimated the salinity buildup rate to be around 8 × 10−2 μS/cm per day, while nitrate buildup rate was estimated to be around 6 × 10−2 mg/L per day. Remote sensing and spatial analyses helped greatly in groundwater quality assessment not only in providing
the environmental status of the AZB but also in delineating the potential of contamination risk zones and their correlation
to human activities. Furthermore, the paper suggests some environmental protection strategies that should be adopted to protect
the vital groundwater resources of the basin from further deterioration. 相似文献
174.
175.
176.
177.
Berina Mina Kilicarslan Ismail Yucel Heves Pilatin Eren Duzenli Mustafa Tugrul Yilmaz 《水文研究》2021,35(9):e14338
This study investigates the impact of the spatio-temporal accuracy of four different sea surface temperature (SST) datasets on the accuracy of the Weather Research and Forecasting (WRF)-Hydro system to simulate hydrological response during two catastrophic flood events over the Eastern Black Sea (EBS) and the Mediterranean (MED) regions of Turkey. Three time-variant and high spatial resolution external SST products (GHRSST, Medspiration and NCEP-SST) and one coarse-resolution and time-invariant SST product (ERA5- and GFS-SST for EBS and MED regions, respectively) already embedded in the initial and the boundary conditions datasets of WRF model are used in deriving near-surface atmospheric variables through WRF. After the proper event-based calibration is performed to the WRF-Hydro system using hourly and daily streamflow data in both regions, uncoupled model simulations for independent SST events are conducted to assess the impact of SST-triggered precipitation on simulated extreme runoff. Some localized and temporal differences in the occurrence of the flood events with respect to observations depending on the SST representation are noticeable. SST products represented with higher cross-correlations (GHRSST and Medspiration) revealed significant improvement in flood hydrographs for both regions. The GHRSST dataset shows a substantial improvement in NSE (~70%), RMSE reduction up to 20%, and an increase in correlation from 0.3 to 0.8 with respect to the invariable SST (ERA5) in simulated runoffs over the EBS region. The use of both GHRSST and Medspiration SST data characterized with high spatio-temporal correlation resulted in runoff simulations exactly matching the observed runoff peak of 300 m3/s by reducing the overestimation seen in invariable SST (GFS) in the MED region. Improved precipitation simulation skills of the WRF model with the detailed SST representation show that the hydrographs of GHRSST and Medspiration simulations show better performance compared to the simulated hydrographs by observed precipitation. 相似文献
178.
An alternative method for estimating densification point velocity based on back propagation artificial neural networks 总被引:1,自引:0,他引:1
Mevlüt Güllü İbrahim Yilmaz Mustafa Yilmaz Bayram Turgut 《Studia Geophysica et Geodaetica》2011,55(1):73-86
The establishment of Turkish National Fundamental GPS Network (TNFGN) was completed in 2001 and Large Scale Map and Map Information
Production Regulation (LSMMIPR) came into force in 2005 in parallel with the establishment of TNFGN and the increase in the
use of GPS applications. TNFGN has been designed as first order GPS network and it comprises second-, third- and fourth-order
GPS densification networks. LSMMIPR has required determining the positions of first-, second- and third-order GPS densification
(C1, C2 and C3) points with the reference epoch besides the measurement epoch. Therefore, it is necessary to estimate the
velocity vectors of the densification points. In practise, the velocity vectors of C1, C2 and C3 points are estimated from
TNFGN points or higher-order densification points velocity vectors by interpolation methods but LSMMIPR did not specify the
interpolation method for this procedure. The objective of this study is to use a back propagation artificial neural network
(BPANN) that has been more widely applied in engineering among all other neural network models for estimating the velocity
of the densification point as an alternative to the interpolation methods. BPANN and selected ten interpolation methods are
evaluated over a test area, in terms of root mean square error (RMSE). The results showed that the employment of BPANN estimated
the densification point velocity (VX,Y,Z) with a better accuracy (±5.0 mm, ±4.0 mm, ±3.9 mm, respectively) than the interpolation methods in the test area and indicated
that BPANN can be a useful tool for estimating point velocity in the densification networks as a real alternative to the interpolation
methods. 相似文献
179.
Hakan Alcik Oguz Ozel Yih-Min Wu Nurcan M. Ozel Mustafa Erdik 《Soil Dynamics and Earthquake Engineering》2011
Two recent catastrophic earthquakes that struck the Marmara Region on 17 August 1999 (Mw=7.4) and 12 November 1999 (Mw=7.2) caused major concern about future earthquake occurrences in Istanbul and the Marmara Region. As a result of the preparations for an expected earthquake may occur around Istanbul region, an earthquake early warning system has been established in 2002 with a simple and robust algorithm, based on the exceedance of specified thresholds of time domain amplitudes and the cumulative absolute velocity (CAV) levels (Erdik et al., 2003 [1]). In order to improve the capability of Istanbul earthquake early warning system (IEEWS) for giving early warning of a damaging earthquake in the Marmara Region, we explored an alternative approach with the use of a period parameter (τc) and a high-pass filtered vertical displacement amplitude parameter (Pd) from the initial 3 s of the P waveforms as proposed by Kanamori (2005) [2] and Wu and Kanamori (2005) 3 and 4. The empirical relationships both between τc and moment magnitude (Mw), and between Pd and peak ground velocity (PGV) for the Marmara Region are presented. These relationships can be used to detect a damaging earthquake within seconds after the arrival of P waves, and can provide on-site warning in the Marmara Region. 相似文献
180.
A two-dimensional (2D) numerical model has been developed to solve shallow water equations for simulation of dam-break flows. The spatial derivatives are discretized using a well-balanced explicit central upwind conservative scheme. The scheme is Riemann solver free and guarantees the positivity of the flow depth over complex topography if the Courant number is kept less than 0.25. The time integration is performed by Euler’s scheme. The model is verified against analytical results for water surface elevation and discharge for three benchmark test cases. A good agreement between analytical solutions and computed results is observed. The property of well-balancing in still water over an uneven bottom is also confirmed. The model is then validated by simulating a laboratory experiment in which a dam break flow propagates over a triangular obstacle. The model performance was found to be satisfactory. A dam break laboratory experimental test case on a frictionless horizontal bottom is also simulated for 2D validation of the model, and good agreement between simulation and the experimental data is observed. The suitability of the proposed model for real life applications is demonstrated by simulating the Malpasset dam-break event, which occurred in 1959 in France. The computed arrival time of the flood wave front and the maximum flow depths at various observation points matched well with the measurements on a 1/400 scale physical model. The overall performance indicates that this model can be applied for simulation of dam-break waves in real life cases. 相似文献