全文获取类型
收费全文 | 3084篇 |
免费 | 566篇 |
国内免费 | 1191篇 |
专业分类
测绘学 | 175篇 |
大气科学 | 687篇 |
地球物理 | 593篇 |
地质学 | 2539篇 |
海洋学 | 293篇 |
天文学 | 16篇 |
综合类 | 202篇 |
自然地理 | 336篇 |
出版年
2024年 | 16篇 |
2023年 | 40篇 |
2022年 | 103篇 |
2021年 | 119篇 |
2020年 | 132篇 |
2019年 | 156篇 |
2018年 | 145篇 |
2017年 | 121篇 |
2016年 | 200篇 |
2015年 | 188篇 |
2014年 | 249篇 |
2013年 | 206篇 |
2012年 | 252篇 |
2011年 | 269篇 |
2010年 | 226篇 |
2009年 | 286篇 |
2008年 | 240篇 |
2007年 | 313篇 |
2006年 | 269篇 |
2005年 | 183篇 |
2004年 | 184篇 |
2003年 | 160篇 |
2002年 | 121篇 |
2001年 | 105篇 |
2000年 | 96篇 |
1999年 | 79篇 |
1998年 | 56篇 |
1997年 | 70篇 |
1996年 | 51篇 |
1995年 | 57篇 |
1994年 | 37篇 |
1993年 | 33篇 |
1992年 | 26篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1978年 | 1篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4841条查询结果,搜索用时 15 毫秒
11.
Shen Yang Xue Shen Hanlong Liu Huayang Ge Xiaoxi Rui 《Marine Georesources & Geotechnology》2020,38(6):706-715
AbstractConstruction of the reefs in the South China Sea is a significant foundation to the secure stability and economic development of China. The construction of an airport runway is necessary for this realization. The calcareous sand is the main primary material in the runway construction. A certain type of calcareous sand near a certain reef of the South China Sea was studied in this paper. To investigate this specific calcareous sand, quartz sand was used as a reference for comparison. Microscopic 3-D imaging, compression and triaxial tests were conducted to test the micro, squeezing and shear properties. The effect mechanism of gradation on the calcareous sand’s compressibility and shear characteristics are discussed from a mesoscopic viewpoint using 3-D morphology. Calcareous sand particles are multiangular and flatter in comparison with quartz sand. The larger the particle sizes are, the more different the two sands’ morphologies are. The compressibility of calcareous sand is greater, and the effect of the coarse fraction (5–1?mm) content in the gradation plays the most significant role in this feature. When the coarse particles’ content is less than 25% and the mass ratio of the middle and fine particles (M) is constant, there is the worst coarse fraction content causing the calcareous sand to be most likely compressed. The worst coarse fraction content decreases with the increase in M, and an empirical formula is proposed. When the gradation, relative density and confining pressure are the same, the peak shear stress and strain of calcareous sand are all at a high level. The effect of confining pressure is manifested in calcareous sand. The shear strength and dilation of calcareous sand are also most affected by the medium coarse fraction (5–0.25?mm) content. 相似文献
12.
江苏岸外辐射沙脊群东沙稳定性研究 总被引:8,自引:0,他引:8
东沙是江苏岸外辐射沙脊群中的第二大沙洲,具有独特的地形地貌和水动力条件,对它进行稳定性研究为揭示整个辐射沙洲及其邻近岸滩的动态演变都非常有益。通过利用多年遥感卫片资料、1998年取得的现场水文泥沙观测资料和东沙滩面表层沉积物资料等,对东沙的地形地貌特征、沉积特征和东沙两侧潮汐通道的水流泥沙特征等进行了详细分析。研究结果表明,东沙的沙脊偏于西侧,西侧滩面较窄、高程较高且岸线较为顺直,东侧滩面较宽、高程较低且岸线较为破碎;西洋和陈家坞槽均处于冲刷状态,净输沙的主要方向为输向槽外或输向条子泥;东沙近三十年来面积有所缩小且有外围向中央收缩的趋势,尤其以向东、向南方向的迁移最为明显。 相似文献
13.
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
14.
J. Acosta E. Uchupi A. Muñoz P. Herranz C. Palomo M. Ballesteros 《Marine Geophysical Researches》2003,24(1-2):41-57
Circular to elliptical mounds in the Canary Channel with reliefs of 75 to 375 m and diameters of 4 to 8 km partially surrounded by moats with reliefs of 25 to 75 m, were formed by piercement of the seafloor by Mesozoic evaporites. Several long gullies, < 1km wide, with abrupt terminations and pockmarks associated with these mounds were probably eroded by dense brine and hydrocarbon seeps. The salt brines that eroded the gullies were formed where salt diapirs intersect the seafloor, or in the subsurface by circulating ground water heated by igneous activity along the Canary Ridge. If the brines originated in the subsurface they reached the seafloor along faults. Displacement of the surficial sediments by sliding and creep is probably the result of the expulsion of hydrocarbons and/or vertical motion of the Mesozoic evaporites. Microtopographic features along or near the east flank of the Canary Ridge are the creation of uplift of the ridge, hydrothermal activity, mass wasting processes and turbidity currents. 相似文献
15.
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
16.
To look for gas hydrate, 22 multi-channel and 3 single-channel seismic lines on the East China Sea (ECS) shelf slope and at the bottom of the Okinawa Trough were examined. It was found that there was indeed bottom simulating reflector (BSR) occurrence, but it is very rare. Besides several BSRs, a gas seepage was also found. As shown by the data, both the BSR and gas seepage are all related with local geological structures, such as mud diapir, anticline, and fault-controlled graben-like structure. However, similar structural "anomalies" are quite common in the tectonically very active Okinawa Trough region, but very few of them have developed BSR or gas seepage. The article points out that the main reason is probably the low concentration of organic carbon of the sediment in this area. It was speculated that the rare occurrence of gas hydrates in this region is governed by structure-controlled fluid flow. Numerous faults and fractures form a network of high-permeability channels in the sediment and highly fractured igneous basement to allow fluid circulation and ventilation. Fluid flow in this tectonic environment is driven primarily by thermal buoyancy and takes place on a wide range of spatial scales. The fluid flow may play two roles to facilitate hydrate formation:to help gather enough methane into a small area and to modulate the thermal regime. 相似文献
17.
18.
为了探索海洋天然气水合物背景下有孔虫特征的响应,对综合大洋钻探计划(IODP) 311航次岩芯沉积物中底栖有孔虫Uvigerina peregrina和Bulimina mexicana进行了初步研究。通过对冷泉站位U1328和毗邻的非冷泉站位U1327沉积物中底栖有孔虫Uvigerina peregrina和Bulimina mexicana的显微形貌特征和碳、氧稳定同位素测试等,证实有孔虫壳体未受到后期成岩作用的改造和自生碳酸盐岩的交代影响,有孔虫壳体的碳稳定同位素呈现明显的负偏。其中U1327站位中U.peregrina δ13C为-0.67‰~-2.75‰(PDB),B.mexicana δ13C为-0.51‰~-1.52‰(PDB);U1328站位中U.peregrina δ13C为 -0.72‰~-2.71‰(PDB),B.mexicanaδ13C为 -0.58‰~-1.45‰(PDB)。底栖有孔虫壳体的碳稳定同位素负偏成因可能与水合物不稳定分解释放的甲烷厌氧氧化作用和食物源有关,因而可较好地指示海底天然气水合物系统地质背景。 相似文献
19.
华北安鹤煤田煤储层特征与煤层气有利区分布 总被引:3,自引:2,他引:1
通过对安鹤煤田采集煤样的煤质、显微组分、煤相、显微裂隙分析,等温吸附、低温氮比表面及孔隙结构和压汞孔隙结构测试,研究了该区煤层气赋存的地质条件、煤层气生气地质特征和煤储层物性特征。并采用基于G IS的多层次模糊数学评价方法计算了该区的煤层气资源量,预测了煤层气有利区分布。研究结果表明,该区煤层气总资源量为1 115.73×108m3,煤层气资源丰度平均为1.18×108m3/km2,具有很好的煤层气资源开发潜力。在煤田中部的四矿到八矿之间的地区以及北部的水冶镇附近地区,煤层累计有效厚度大、煤层气资源丰度高、煤层埋深适中、煤储层孔裂隙系统发育、渗透性高,是该区煤层气勘探开发的最有利目标区。 相似文献
20.
This paper studies a landfill where there are three faults running through.As serious pollution has occurred to the geological environment,the landfill is to be closed up and renovated.The paper aims to explore the role of fracture structure in leachate pollution at the landfill.The research was carried out in several stages.First,mathematical models of the pre-renovation landfill with three faults running through and the landfill after renovation were established.And then,the boundary conditions and parameters of the two mathematical models were determined.The groundwater level of the landfills was simulated in order to modify the two mathematical models.As a result,a feasible mathematical model was achieved.Based on this model,a comparison was made of the COD concentration variations in the inside leachate and outside leachate between the two landfills. Accordingly,the impacts of the fracture structure on the pollution of leachate at the landfills could be identified.The study results show that while faults contribute to the migration of leachate,they also serve as a confluence of leachate,thus further deteriorating the environment.The COD concentrations of the inside leachate and the outside leacbate of the pre-renovation landfill are respectively 800 mg/L and 220 mg/L higher than those of the post.renovation landfill.Therefore,measures must be taken to handle the leachate seepage in areas where there are faults as well as the neighboring areas so as to get the environmental pollution under control. 相似文献