全文获取类型
| 收费全文 | 935篇 |
| 免费 | 41篇 |
| 国内免费 | 2篇 |
专业分类
| 测绘学 | 35篇 |
| 大气科学 | 66篇 |
| 地球物理 | 252篇 |
| 地质学 | 255篇 |
| 海洋学 | 86篇 |
| 天文学 | 171篇 |
| 综合类 | 6篇 |
| 自然地理 | 107篇 |
出版年
| 2024年 | 7篇 |
| 2021年 | 13篇 |
| 2020年 | 14篇 |
| 2019年 | 17篇 |
| 2018年 | 14篇 |
| 2017年 | 26篇 |
| 2016年 | 22篇 |
| 2015年 | 8篇 |
| 2014年 | 40篇 |
| 2013年 | 29篇 |
| 2012年 | 26篇 |
| 2011年 | 39篇 |
| 2010年 | 47篇 |
| 2009年 | 54篇 |
| 2008年 | 41篇 |
| 2007年 | 45篇 |
| 2006年 | 37篇 |
| 2005年 | 40篇 |
| 2004年 | 30篇 |
| 2003年 | 42篇 |
| 2002年 | 33篇 |
| 2001年 | 22篇 |
| 2000年 | 20篇 |
| 1999年 | 21篇 |
| 1998年 | 23篇 |
| 1997年 | 14篇 |
| 1996年 | 15篇 |
| 1995年 | 13篇 |
| 1994年 | 11篇 |
| 1993年 | 12篇 |
| 1992年 | 11篇 |
| 1991年 | 6篇 |
| 1990年 | 10篇 |
| 1989年 | 11篇 |
| 1988年 | 10篇 |
| 1987年 | 9篇 |
| 1986年 | 9篇 |
| 1985年 | 11篇 |
| 1984年 | 14篇 |
| 1983年 | 11篇 |
| 1982年 | 13篇 |
| 1981年 | 7篇 |
| 1980年 | 4篇 |
| 1979年 | 11篇 |
| 1978年 | 7篇 |
| 1977年 | 13篇 |
| 1976年 | 6篇 |
| 1975年 | 10篇 |
| 1974年 | 8篇 |
| 1973年 | 6篇 |
排序方式： 共有978条查询结果，搜索用时 15 毫秒
931.
932.
The Baram Delta System, Brunei, NW Borneo, is a Tertiary delta system located on an active continental margin. Delta top regions in many Tertiary delta systems (e.g. Niger Delta) are thought to exhibit a normal‐fault stress regime and margin‐parallel maximum horizontal stress orientations. However, unlike in passive margin Tertiary delta systems, two present‐day stress provinces have been previously identified across the Baram Delta System: an inner shelf inverted province with a margin‐normal (NW–SE) maximum horizontal stress orientation and an outer shelf extension province with a margin‐parallel (NE–SW) maximum horizontal stress orientation. Before this study, there were few data constraining the inverted province other than in the vicinity of the Champion Fields. New data from 12 petroleum wells in the western inner shelf and onshore west Brunei presented herein confirm the margin‐normal maximum horizontal stress orientations of the inverted province. A total of 117 borehole breakouts, all documented in shale units, and one drilling‐induced tensile fracture (in a sandstone interval) reveal a mean maximum horizontal stress orientation of 117 with a standard deviation of 19°. This orientation is consistent with contemporary margin‐normal maximum horizontal stress orientations of the inverted province described previously in the vicinity of the Champion Fields that have been linked to basement tectonics of the Crocker–Rajang accretionary complex and associated active margin. However, stress magnitudes calculated using data from these 12 petroleum wells indicate a borderline strike–slip fault to normal fault stress regime for the present day; combined with the absence of seismicity, this suggests that the studied part of the NW Borneo continental margin is currently tectonically quiescent. 相似文献
933.
934.
Selection of bioindicators for monitoring marine environmental quality in the Bay of Fundy,Atlantic Canada 总被引：2，自引：0，他引：2
Distribution of metals, PAH's and PCB's in lobsters, mussels, and sediments were used to assess marine environmental quality of the Bay of Fundy. This study demonstrates that the lobster (Homarus americanus) is a better bioindicator for monitoring contaminants in the marine environment and has a greater capacity for the uptake and accumulation of contaminants than the mussel (Mytilus edulis) and sediments. A definite pattern in the spatial distribution of lobster Cu, Cd, and Ag was evident. The distribution of organic contaminants for both mussels and lobsters in the Bay of Fundy lacked a spatial trend, and organic contaminants were undetectable in sediments from all sites. The Gulf Watch Programme, which monitors chemicals in mussels in the Bay of Fundy, did not indicate a problem with high levels of Cu, Cd, and Zn in the ecosystem. Analytes below the detection limit, such as in mussels and sediments, increase the difficulties of chemical analysis and detection for environmental monitoring. Deficiencies of mussels in monitoring the Bay of Fundy were discussed. 相似文献
935.
936.
Asymmetric dipole-flow test in a fractured carbonate aquifer 总被引：1，自引：0，他引：1
In this study, a new method-the asymmetric dipole-flow test-is proposed and tested for characterization of conductive properties and structure of fractured aquifers. Analytical solutions were developed and then used for interpretation of a modification of the dipole-flow test with a single packer at the Bissen Quarry test site (Wisconsin, USA). The asymmetric dipole-flow tests were conducted by packing a well at various elevations, and fluids were pumped from the upper section (chamber) of the well to the lower section (chamber). The head was then monitored at 11 observation points and in both sections of the well, and the conductivities of the well segments were determined. The tests at seven packer elevations in the well were rapid (less than one hour to reach steady state). The asymmetric dipole-flow test demonstrates the potential to quantify heterogeneities of a fractured aquifer and delineate the applicability of the continuum and discrete approaches for conceptualization of ground water flow. 相似文献
937.
938.
An analysis of coupled heat and moisture movement in unsaturated soil in terms of the fundamental potentials for flow is examined. The approach adopted is based on the assumption that the total potential for liquid flow consists of two components, the elevation and the capillary potential. The fundamental potentials employed in the work are, therefore, temperature and capillary potential. The full theoretical formulation of the problem is presented, together with full details of the solution algorithm employed. Spatial discretization is achieved via the use of the finite element method, with the time-varying behaviour described by a finite difference technique. Soil parameter variations as functions of both temperature and moisture content are included in a one-dimensional approach. The work is applied to a practical engineering problem, namely heat and mass transfer in the upper layers of a soil stratum. This problem is of importance to the utilities, since many services are buried in this zone. Material parameters obtained from an associated programme of experimental work are employed. Moisture content and temperature profiles indicating the extent and rate of penetration of drying and heating fronts are produced. 相似文献
939.
Sediment cores were taken at three locations in Narragansett Bay, Rhode Island, USA in 1997 and analyzed for a variety of organic contaminants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlordanes, linear alkyl benzenes (LABs), benzotriazoles (BZTs) and dichlorodiphenyltrichloroethanes (DDTs) and metabolites. The distributions of these chemicals at Apponaug Cove and in the Seekonk River indicate that there was a disturbance in the depositional environment relative to cores collected at these locations in 1986 demonstrating the potential for buried contaminants to be remobilized in the environment even after a period of burial. Sharp breaks in the concentration of several organic markers with known dates of introduction were successfully used to determine the sedimentation rate at Quonset Point. Both the Quonset Point and Seekonk River cores had subsurface maximums for DDTs, PCBs, PAHs and BZTs, which are consistent with expected inputs to the environment. The Apponaug Cove core showed an increase of most contaminants at the surface indicating a recent event in which more contaminated sediments were deposited at that location. 相似文献
940.