全文获取类型
收费全文 | 71281篇 |
免费 | 1132篇 |
国内免费 | 660篇 |
专业分类
测绘学 | 1714篇 |
大气科学 | 5039篇 |
地球物理 | 14216篇 |
地质学 | 25254篇 |
海洋学 | 6165篇 |
天文学 | 16337篇 |
综合类 | 208篇 |
自然地理 | 4140篇 |
出版年
2022年 | 396篇 |
2021年 | 704篇 |
2020年 | 777篇 |
2019年 | 825篇 |
2018年 | 1895篇 |
2017年 | 1759篇 |
2016年 | 2237篇 |
2015年 | 1319篇 |
2014年 | 2179篇 |
2013年 | 3766篇 |
2012年 | 2277篇 |
2011年 | 3119篇 |
2010年 | 2607篇 |
2009年 | 3510篇 |
2008年 | 3255篇 |
2007年 | 3046篇 |
2006年 | 2877篇 |
2005年 | 2356篇 |
2004年 | 2255篇 |
2003年 | 2111篇 |
2002年 | 1932篇 |
2001年 | 1800篇 |
2000年 | 1716篇 |
1999年 | 1377篇 |
1998年 | 1476篇 |
1997年 | 1390篇 |
1996年 | 1101篇 |
1995年 | 1142篇 |
1994年 | 964篇 |
1993年 | 874篇 |
1992年 | 856篇 |
1991年 | 760篇 |
1990年 | 858篇 |
1989年 | 719篇 |
1988年 | 650篇 |
1987年 | 815篇 |
1986年 | 664篇 |
1985年 | 856篇 |
1984年 | 922篇 |
1983年 | 862篇 |
1982年 | 831篇 |
1981年 | 707篇 |
1980年 | 663篇 |
1979年 | 606篇 |
1978年 | 603篇 |
1977年 | 552篇 |
1976年 | 539篇 |
1975年 | 499篇 |
1974年 | 506篇 |
1973年 | 469篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
371.
Michael J. Steventon Christopher A.‐L. Jackson David M. Hodgson Howard D. Johnson 《Basin Research》2019,31(3):600-620
Strain style, magnitude and distribution within mass‐transport complexes (MTCs) are important for understanding the process evolution of submarine mass flows and for estimating their runout distances. Structural restoration and quantification of strain in gravitationally driven passive margins have been shown to approximately balance between updip extensional and downdip contractional domains; such an exercise has not yet been attempted for MTCs. We here interpret and structurally restore a shallowly buried (c. 1,500 mbsf) and well‐imaged MTC, offshore Uruguay using a high‐resolution (12.5 m vertical and 15 × 12.5 m horizontal resolution) three‐dimensional seismic‐reflection survey. This allows us to characterise and quantify vertical and lateral strain distribution within the deposit. Detailed seismic mapping and attribute analysis shows that the MTC is characterised by a complicated array of kinematic indicators, which vary spatially in style and concentration. Seismic‐attribute extractions reveal several previously undocumented fabrics preserved in the MTC, including internal shearing in the form of sub‐orthogonal shear zones, and fold‐thrust systems within the basal shear zone beneath rafted‐blocks. These features suggest multiple transport directions and phases of flow during emplacement. The MTC is characterised by a broadly tripartite strain distribution, with extensional (e.g. normal faults), translational and contractional (e.g. folds and thrusts) domains, along with a radial frontally emergent zone. We also show how strain is preferentially concentrated around intra‐MTC rafted‐blocks due to their kinematic interactions with the underlying basal shear zone. Overall, and even when volume loss within the frontally emergent zone is included, a strain difference between extension (1.6–1.9 km) and contraction (6.7–7.3 km) is calculated. We attribute this to a combination of distributed, sub‐seismic, ‘cryptic’ strain, likely related to de‐watering, grain‐scale deformation and related changes in bulk sediment volume. This work has implications for assessing MTCs strain distribution and provides a practical approach for evaluating structural interpretations within such deposits. 相似文献
372.
373.
Qadri S. M. Talha Islam Md. Aminul Shalaby Mohamed Ragab 《Natural Resources Research》2019,28(2):369-392
Natural Resources Research - This study addresses the three-dimensional (3D) petrophysical modelling and volumetric analysis of the Farewell Reservoir in the Kupe Field in the southern Taranaki... 相似文献
374.
Ilin N. V. Shatalina M. V. Slyunyaev N. N. 《Izvestiya Atmospheric and Oceanic Physics》2019,55(5):446-452
Izvestiya, Atmospheric and Oceanic Physics - On the basis of a parametrization of the ionospheric potential (IP), the seasonal dynamics of the diurnal IP variation for 2016–2017 is simulated... 相似文献
375.
K. M. Evans 《Geological Journal》1983,18(4):297-305
The Lynton Beds represent shallow marine sediments with a restricted fauna dominated by brachiopods. The age indicated by the brachiopod fauna is late Emsian, although the possibility of a younger date for the uppermost horizons cannot be discounted. 相似文献
376.
Elvis A. Shukla Jagdish Prasad M. S. S. Nagaraju Rajeev Srivastava D. L. Kauraw 《Journal of the Indian Society of Remote Sensing》2009,37(1):129-137
Soil resource characterization of Dhamni micro-watershed in Chandrapur district of Maharashtra was carried out using IRS-1D
LISS-III data in conjunction with field survey and ancillary data. The study indicates that nearly 84.2 per cent of the total
geographical area of the watershed is under cultivation. Forest (mainly degraded) occupy only 4.5 per cent area Whereas wasteland
with scrub cover 9.4 per cent area of the watershed. Nine soil series were tentatively identified and mapped as soil series
association in to five mapping units. These soils belong to order Inceptisol, Vertisol and Mollisol. Except the soils of wasteland
with scrub, other soils are moderately suitable for pigeonpea and soybean and have average to good productivity. 相似文献
377.
Numerical modelling of deep sea air-lift 总被引:2,自引:0,他引:2
Deep sea air-lifting of solid particles from depth of 1600 m is simulated with a mathematical model of the three-phase flow in an upward pipe. The computations are carried out for an axisymmetric domain in a transient way. Phase distributions, pressure and velocity profiles together with flow rates for all phases are presented and analysed. The influence of the pipe diameter on the air-lift efficiency was studied for air-lift pipes of different lengths and found to be significant. The lifting efficiency increases with the increase of the pipe diameter due to the reduction of the wall friction influence on the flow. In addition, the efficiency also increases with the increase of the solid particles volume fraction at the inlet. The presented numerical model can be utilized during various stages of the design of the air-lift pumps to help answer fundamental questions on the process, and during their operation to select optimal process parameters and to address possible problems. 相似文献
378.
A. Vela V. Pasqualini V. Leoni A. Djelouli H. Langar G. Pergent C. Pergent-Martini L. Ferrat M. Ridha H. Djabou 《Estuarine, Coastal and Shelf Science》2008,79(4):591-598
Mapping marine biocenoses is an efficient method for providing useful data for the management and conservation of Mediterranean lagoons. Fused images from two satellites, SPOT 5 and IKONOS, were tested as management tools for identifying specific ecosystems in the El Bibane lagoon, situated in southern Tunisia near the Libyan border. The objectives of this study were to provide a precise map of the entire El Bibane lagoon using fused images from SPOT 5 and to compare fused images from SPOT 5 and IKONOS over a test-area. After applying a supervised classification, pixels are automatically classified in four classes: low seagrass cover, high seagrass cover, superficial mobile sediments and deep mobile sediments. The maps of the lagoon revealed and confirmed an extremely wide distribution of seagrass meadows within the lagoon (essentially Cymodocea nodosa; 19 546 ha) and a large area of mobile sediments more or less parallel to the shore (3 697 ha). A direct comparison of overall accuracy between SPOT 5 over the entire area, SPOT 5 over the test-area and IKONOS over the test-area revealed that these tools provided accurate mapping of the lagoon environment (83.25%, 85.91% and 73.41% accuracy, respectively). The SPOT 5 images provided greater overall accuracy than the IKONOS image, but did not take into account the heterogeneous spatial structure of the seagrasses and sediments present in the lagoon environment. Although IKONOS imagery provided lower overall accuracy than SPOT 5, it proved a very useful tool for the mapping of heterogeneous structures as it enabled the patchiness of formations to be better taken into account. The use of SPOT 5 and IKONOS fused images appears to be very promising for completing the mapping of lagoons in other regions and countries of the Mediterranean Sea. 相似文献
379.
Aref M.O.AL-JABALI Abdo S.AL-MAQTARY Hussein AL-AKHALI Mohammed HAZAEA Fadel AL-AGHBARI 《东北亚地学研究》2009,(1)
According to topography of Yemen,most areas and villages are located at obligated crest,toe of mountain and under cliffs.Therefore Al-Huwayshah consisting of Tawilah sandstone group is characterized by steep slope reach to 90° in some areas.This area is affected by strong tectonic movements and faults that occurred during the geological epochs.This effect enhances to find out fractures and joints as well as the rocks become brittle and ready to slide depending on the position of area.And there are some frac... 相似文献
380.
A field work has been carried out to identify the occurrence of oil and oil products pollution in mangrove sediment from Red Sea of Yemen. The concentration of total petroleum hydrocarbons is from 700ng/g at Kamaran Island station to 400 ng/g at Al-Hodiedah station, and the total organic carbon (TOC) in samples ranges from 0. 07% at Dhubab station to 0. 03% at Kamaran Island station. This pollution is as a result of localized oil pollution and/or heavy ship traffic in the Red Sea and Gulf of Aden. 相似文献