全文获取类型
收费全文 | 311篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 28篇 |
地球物理 | 76篇 |
地质学 | 120篇 |
海洋学 | 35篇 |
天文学 | 17篇 |
综合类 | 6篇 |
自然地理 | 19篇 |
出版年
2021年 | 4篇 |
2019年 | 2篇 |
2018年 | 12篇 |
2017年 | 18篇 |
2016年 | 15篇 |
2015年 | 9篇 |
2014年 | 15篇 |
2013年 | 19篇 |
2012年 | 18篇 |
2011年 | 18篇 |
2010年 | 17篇 |
2009年 | 12篇 |
2008年 | 18篇 |
2007年 | 12篇 |
2006年 | 12篇 |
2005年 | 6篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1984年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1954年 | 1篇 |
1953年 | 1篇 |
1951年 | 2篇 |
1949年 | 1篇 |
1948年 | 1篇 |
1940年 | 5篇 |
1937年 | 2篇 |
1926年 | 1篇 |
排序方式: 共有323条查询结果,搜索用时 15 毫秒
101.
102.
103.
In‐situ 40Ar/39Ar laser microprobe dating was carried out on the Hoping pseudotachylite from a mylonite‐fault zone in the metamorphosed basement complex of the active Taiwan Mountain Belt to determine the timing of the responsible earthquake(s). The dating results, distributed from 3.2 to 1.6 Ma with errors ranging from 0.2 to 1.1 Ma, were derived from a combination of two Ar isotopic system end‐members with inverse isochron ages of 1.55 ± 0.05 and 2.87 ± 0.07 Ma, respectively. Petrographical observations reveal fault melt containing ultracataclasites, therefore the older inverse isochron end‐member may be attributed to the relic wall rock Ar isotopic system contained in micro‐breccia. Without significant Ar loss expected, the ~1.6 Ma for the young end‐member defines the exact time of the pseudotachylite formation. Seismic faulting therefore occurred during basement rock exhumation in the Taiwanese hinterland. 相似文献
104.
The purpose of this study was to evaluate related processes of sediment consolidation and resuspension in a coastal basin and how these processes influence retention of fine sediment delivered by a river diversion. Sediment samples were collected from Lake Lery, a coastal receiving basin of the Caernarvon Diversion from the Mississippi River, Louisiana. Consolidation was tested for six initial sediment concentrations (14.0–105 kg m–3) in a settling column over 15-day periods. Mud erodibility was tested at seven shear stress regimes (0.01–0.60 Pa) using a dual-core Gust erosion microcosm system, on cores containing suspensions that consolidated for 1, 2, and 4 weeks. Consolidation rates were found to be inversely and exponentially related to initial suspension concentration, over concentrations ranging from fluid mud (10–200 kg m–3) to hydraulic dredge effluent. Consolidation is best predicted by a function consisting of two exponential terms and one asymptotic constant, describing rates of rapid initial and slower subsequent settling. Coupled resuspension and consolidation tests (concentrations of 20–21 kg m–3) show that shear stresses generating the highest turbidity peaks increase from ≤0.30 Pa after 2 weeks of consolidation to ≥0.45 Pa after 4 weeks, and this strengthening cannot be attributed solely to increasing sediment concentration over time. Comparison of measured erosion shear stresses with bed shear stresses typical of coastal lakes and bays suggests that this degree of strengthening, if given time to occur, could increase the overall retention of fine sediments deposited on lake and bay floors. 相似文献
105.
106.
This paper proposes an automatic procedure for train speed evaluation by the dominant frequency method based on the ground vibration characteristic induced by the trainload. A number of field measurements, a total of 154 runs with different train speeds of 198–303 km/h, were carried out to test the stability and accuracy of the proposed evaluation procedure. The evaluation differences of the train speed by using the opposed photoelectric sensing approaches and dominant frequency method are less than 3%, which means that the proposed procedure for automatic train speed evaluation is applicable and accurate. The advantages of the dominant frequency method for train speed calculation are in its mobility and cost-savings with regard to the installation and repair work, especially for long-term monitoring programs at elevated railway systems. Thus, the proposed procedure increases the applicability and potential of the dominant frequency method for train speed monitoring in real-time field measurement, since the evaluation work does not have to be done manually. 相似文献
107.
C. P. Lo 《The Professional geographer》1986,38(2):141-149
Shuttle Imaging Radar-A data are employed to study the settlement, population and land use in the Baoding and Dezhou areas of the North China Plain. By applying nearest neighbor and quadrat analyses, the settlements are found to exhibit a mixed random-clustering pattern which defied the application of Christaller's central place theory. The distinctly visible boundaries from the images permitted accurate estimation of population in both areas. The linear land use forms, notably transportation lines, could also be accurately mapped; the Chinese practice of lake reclamation was also revealed. It is concluded that SIR-A data are useful for much human geography research. 相似文献
108.
In this paper, we use a neural network to carry out angle-of-arrival (AOA) estimation in a multipath oceanic environment. In particular, the AOA problem is considered as a mapping from the space of AOA to the space of the sensor output. A neural network is used to determine the inverse mapping from the sensor output space to the space of AOA and this inversion is realized using a radial basis function (RBF) network. We will present the development of the RBF approach for AOA estimation. Simulations are carried out to understand the efficiency and performance of this method. Furthermore, real data are used to evaluate the RBF approach and the results demonstrate the robustness and effectiveness of this neural network method 相似文献
109.
Stefano Lo Russo Glenda Taddia Paolo Dabove Elena Cerino Abdin Ambrogio Maria Manzino 《Environmental Earth Sciences》2018,77(18):647
Thermal perturbation produced in the subsurface by open-loop groundwater heat pumps (GWHPs) represents a complex transport phenomenon that is affected by several factors, including intrinsic characteristics of the exploited aquifer, abstraction and reinjection well features, and the temporal dynamics of the accessed groundwater. Post-GWHP water may have become warmed or cooled before being reinjected into the aquifer, thereby creating a thermal plume, known as the thermal affected zone (TAZ), which can alter aquifer temperature. The TAZ is propagated mainly by advection, after which the plume tends to degrade via conductive heat transport and convection within moving water. Groundwater monitoring and multiparametric probes are used to check the dynamics of plume propagation and whether a system’s thermal plumes are generating unsuitable interference with wells, subsurface infrastructure, or land use. Analyses of time-series groundwater monitoring data can be used to monitor TAZ movement. In this paper, the thermal plume velocity was calculated by both an analytical solution and cross-correlation. Cross-correlation calculated between temperature measured in the reinjection well and control downstream piezometers can reveal plume dynamics and demonstrate the importance of advective transport in aquifer heat transfer. 相似文献
110.
Stefano Lo Russo Glenda Taddia Loretta Gnavi Vittorio Verda 《Hydrogeology Journal》2014,22(1):205-216
A fundamental aspect in groundwater heat pump (GWHP) plant design is the correct evaluation of the thermally affected zone that develops around the injection well. This is particularly important to avoid interference with previously existing groundwater uses (wells) and underground structures. Temperature anomalies are detected through numerical methods. Computational fluid dynamic (CFD) models are widely used in this field because they offer the opportunity to calculate the time evolution of the thermal plume produced by a heat pump. The use of neural networks is proposed to determine the time evolution of the groundwater temperature downstream of an installation as a function of the possible utilization profiles of the heat pump. The main advantage of neural network modeling is the possibility of evaluating a large number of scenarios in a very short time, which is very useful for the preliminary analysis of future multiple installations. The neural network is trained using the results from a CFD model (FEFLOW) applied to the installation at Politecnico di Torino (Italy) under several operating conditions. The final results appeared to be reliable and the temperature anomalies around the injection well appeared to be well predicted. 相似文献