全文获取类型
收费全文 | 9556篇 |
免费 | 1736篇 |
国内免费 | 1860篇 |
专业分类
测绘学 | 315篇 |
大气科学 | 1315篇 |
地球物理 | 3037篇 |
地质学 | 5399篇 |
海洋学 | 1115篇 |
天文学 | 65篇 |
综合类 | 474篇 |
自然地理 | 1432篇 |
出版年
2024年 | 61篇 |
2023年 | 153篇 |
2022年 | 289篇 |
2021年 | 379篇 |
2020年 | 392篇 |
2019年 | 407篇 |
2018年 | 365篇 |
2017年 | 390篇 |
2016年 | 447篇 |
2015年 | 443篇 |
2014年 | 617篇 |
2013年 | 713篇 |
2012年 | 537篇 |
2011年 | 606篇 |
2010年 | 542篇 |
2009年 | 648篇 |
2008年 | 685篇 |
2007年 | 672篇 |
2006年 | 660篇 |
2005年 | 470篇 |
2004年 | 451篇 |
2003年 | 389篇 |
2002年 | 367篇 |
2001年 | 320篇 |
2000年 | 300篇 |
1999年 | 283篇 |
1998年 | 232篇 |
1997年 | 223篇 |
1996年 | 184篇 |
1995年 | 166篇 |
1994年 | 140篇 |
1993年 | 138篇 |
1992年 | 117篇 |
1991年 | 83篇 |
1990年 | 76篇 |
1989年 | 49篇 |
1988年 | 50篇 |
1987年 | 19篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1978年 | 17篇 |
1977年 | 5篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
C. Kranenburg 《Applied Ocean Research》1984,6(1):23-30
The rupture of a submarine oil pipeline starts various mechanisms leading to an oil spill. Among these mechanisms the leakage of oil driven by the difference in specific gravities of oil and sea-water is difficult to estimate. A simple mathematical model has been developed and laboratory experiments have been carried out to obtain an insight into the density-driven exchange flow and to determine the leak rate. The mathematical model is predictive and takes account of the effects of friction, inclination of the pipeline, and inertia of the fluid. The experiments were done in a horizontal model pipeline. Theoretical and experimental results are in satisfactory agreement. 相似文献
82.
AbstractLarge reserves of natural gas hydrates exist, and the depressurization method has the greatest potential for gas hydrate reservoir recovery. Currently, the most commonly adopted depressurization simulation method is a constant bottom-hole pressure production scheme. This study proposes a new depressurization mode with decreasing bottom-hole pressure. The production characteristic was numerically investigated using this method. The results show the following: (1) As the depressurization exponent (n) decreases, the development effect improves, and production indexes including cumulative gas production/dissociation and gas-water ratio increase. However, the reservoir energy consumption is higher and the hydrate reformation is more severe. (2) Compared to the proposed depressurization mode, the hydrate production index of the constant bottom-hole pressure production (n?=?0) is better. However, the hydrate reservoir energy consumption is higher and the hydrate reformation is more severe using constant bottom-hole pressure production. (3) To achieve a balance between production and reservoir energy consumption during depressurization production, the bottom-hole pressure should be controlled by selecting a suitable depressurization exponent between nmin and nmax, which can be determined through numerical simulations. 相似文献
83.
84.
85.
根据中、日合作黑潮调查研究期间(1987-1993年)在九州西侧海域获得的水文资料,计算了129°E断面的地转流速和流量。着重提出129°E断面北侧存在一支较稳定的西向流;分析这支西向流的去向,指出它是向对马暖流输送黑潮水的重要途径;给出了这支西向流及黑潮通过该断面的流速、流轴、流幅及流量的变化特征。 相似文献
86.
87.
The permeability of faults within siliciclastic petroleum reservoirs of the North Sea and Norwegian Continental Shelf 总被引:1,自引:0,他引:1
Faulting in Middle Jurassic reservoirs occurred at shallow depth during regional extension. Clean sandstones (<15% clay) deformed without significant grain fracturing and permeability reduction. Faults in impure sandstones (15–40% clay) experienced significant syn-deformation compaction and permeability reduction. Enhanced compaction during deeper burial reduced their permeabilities further from an average of 0.05 mD at <2.5 km to 0.001 mD at >4 km. Clay-rich sediments (>40% clay) deformed to produce clay smears with very low permeabilities (<0.001 mD). Faulting in the Rotliegendes occurred at greater depth during both basin extension and inversion. Extensional faulting produced cataclasites with permeability reductions of <10–>106; their permeabilities range from 0.2 to 0.0001 mD and are inversely related to their maximum burial depth. Faults formed or reactivated during inversion experienced permeability increase. These results can be extrapolated to other hydrocarbon reservoirs if differences in stress and temperature history are taken into account.The permeability of most (>80%) faults is not sufficiently low, compared to their wallrock, to retard single-phase fluid flow on a km-scale. Nevertheless, most faults could retard the flow of a non-wetting phase if present at low saturations. It may be necessary to incorporate the two-phase fluid flow properties of fault rocks into reservoir simulators using upscaling or pseudoisation techniques. Fault property data should be calibrated against production data before it can be used confidently. 相似文献
88.
Estimation of Land Subsidence Based on Groundwater Flow Model 总被引:8,自引:0,他引:8
This article presents an approach for estimating land subsidence due to withdrawal of groundwater. The proposed method calculates the groundwater seepage in 3-D-condition and calculates the land subsidence one-dimensionally. The governing equation on groundwater seepage is based on the three-dimensional mass conservation law and the principle of effective stress. The land subsidence calculation method is derived based on the following assumptions: (1) displacements occur only in the vertical direction, and (2) in vertical direction the total stresses do not change. The governing equation is solved by numerical method, i.e., finite element method (FEM) in spatial discretization and finite difference method (FDM) in time series discretization. In FEM Galerkin method is adopted and in FDM, lumped matrix method is employed. The proposed method is calibrated via analyzing 1-D consolidation problem and the results are compared with those from Terzaghi's one-dimensional consolidation theory and oedometer test. The proposed method is employed to analyze the consolidation of a soft layer due to withdrawal of groundwater from an aquifer under it. Moreover, this method is also applied to a field case of land subsidence due to groundwater pumping in a gas production field in Japan. The analytical results are compared with the field observed data. The results show that this approach simulates the field case well. 相似文献
89.
90.
1 .IntroductionTheglobalairtemperatureroseabout 0 .5~ 0 .6°Coverthepast 2 0thcentury ,andtheglobalmeansealevelincreasedbyabout2 0cmduringtheperiod .Theregionalmeansealevelriseswiththerisingglobalmeansealevel.Zuoetal.( 1 997)indicatedthatthemeanrisingrateofabsolutemeansealevelalongtheChinacoastontheassumptionofunifiedisostaticdatumis 2mm a .Woodworth( 1 999)analyzedsealevelspanning 1 76 8tothepresentinLiverpool,andobtainedaseculartrendforheperiodupto 1 880of0 .39± 0 .1 7mm a ,andatrendfort… 相似文献