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861.
Moisture Movement Through Cracked Clay Soil Profiles 总被引:1,自引:0,他引:1
Delwyn G. Fredlund Sandra L. Houston Quan Nguyen Murray D. Fredlund 《Geotechnical and Geological Engineering》2010,28(6):865-888
A continuum mechanics approach is used for the formulation of unsaturated hydraulic conductivity functions and the water storage
functions for fractured or cracked clay soils in this parametric study. Suggested procedures are based on available research
literature related to the behavior of cracked unsaturated porous media. The soil–water characteristic curve, hydraulic conductivity
and water storage functions take on the character of bi-modal unsaturated soil property functions. The bimodal character arises
out of the independent behavior of the cracks and the intact clay soil. Matric suction changes beneath a slab-on-grade foundation
placed on a cracked clay soil profile are modeled for varied surface flux conditions using the proposed unsaturated hydraulic
conductivity and water storage functions. The impact of various levels of surface cracking on soil suction distributions is
discussed. Suction distribution patterns are dependent on the initial soil surface suction. In particular, the results are
dependent upon whether the initial matric suction is less than or greater than the air entry of the cracked clay. There is
an extremely wide range of possible conditions that could be modeled but the parametric study results presented in this paper
are limited to a series of selected crack widths and densities for an exfiltration case and an infiltration case. 相似文献
862.
Evidence for high temperature and 18O‐enriched fluids in the Arab‐D of the Ghawar Field,Saudi Arabia
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Peter K. Swart Dave L. Cantrell Monica M. Arienzo Sean T. Murray 《Sedimentology》2016,63(6):1739-1752
Using the clumped isotope method, the temperature of dolomite and calcite formation and the oxygen isotopic composition (δ18Ow) of the diagenetic fluids have been determined in a core taken from the Arab‐D of the Ghawar field, the largest oil reservoir in the world. These analyses show that while the dolomites and limestones throughout the major zones of the reservoir recrystallized at temperatures between ca 80°C and 100°C, the carbonates near the top of the reservoir formed at significantly lower temperatures (20 to 30°C). Although the δ18O values of the diagenetic fluids show large variations ranging from ca <0‰ to ca +8‰, the variations exhibit consistent downhole changes, with the highest values being associated with the portion of the reservoir with the highest permeability and porosity. Within the limestones, dolomites and dolomites associated with the zone of high permeability, there are statistically significant different trends between the δ18Ow values and recrystallization temperature. These relationships have different intercepts suggesting that fluids with varying δ18Ow values were involved in the formation of dolomite and limestone compared to the formation of dolomite associated with the zone of high permeability. These new data obtained using the clumped isotope technique show how dolomitization and recrystallization by deep‐seated brines with elevated δ18Ow values influence the δ18O values of carbonates, possibly leading to erroneous interpretations unless temperatures can be adequately constrained. 相似文献
863.
Asia-Pacific mussel watch: monitoring contamination of persistent organochlorine compounds in coastal waters of Asian countries 总被引:27,自引:0,他引:27
Monirith I Ueno D Takahashi S Nakata H Sudaryanto A Subramanian A Karuppiah S Ismail A Muchtar M Zheng J Richardson BJ Prudente M Hue ND Tana TS Tkalin AV Tanabe S 《Marine pollution bulletin》2003,46(3):281-300
Contamination of persistent organochlorines (OCs) such as PCBs (polychlorinated biphenyls), DDT and its metabolites (DDTs), HCH (hexachlorocyclohexane) isomers (HCHs), chlordane compounds (CHLs), and HCB (hexachlorobenzene) were examined in mussels collected from coastal waters of Asian countries such as Cambodia, China, Hong Kong, India, Indonesia, Japan, Korea, Malaysia, Philippines, Far East Russia, Singapore, and Vietnam in 1994, 1997, 1998, 1999, and 2001 to elucidate the contamination status, distribution and possible pollution sources and to assess the risks on aquatic organisms and human. OCs were detected in all mussels collected from all the sampling sites investigated. Considerable residue levels of p,p(')-DDT and alpha-HCH were found in mussels and the concentrations of DDTs and HCHs found in mussels from Asian developing countries were higher than those in developed nations suggesting present usage of DDTs and HCHs along the coastal waters of Asian developing countries. On the other hand, lower concentrations of PCBs detected in mussels from Asian developing countries than those in developed countries indicate that PCBs contamination in mussels is strongly related to industrial and activities. To our knowledge, this is a first comprehensive report on monitoring OCs pollution in the Asia-Pacific region. 相似文献
864.
Marine mussels, Perna viridis, were transplanted from a reference site to various polluted sites around Hong Kong. After 30 d of exposure, antioxidative responses in the gills and hepatopancreas and tissue concentrations of chlorinated hydrocarbons [polychlorinated biphenyls (PCBs) and chlorinated pesticides (CPs)] were determined for individual mussels. Glutathione S transferase (GST) and glutathione (GSH) were positively correlated with tissue PCB concentrations. Only one of the enzymatic antioxidants, glutathione peroxidase (GPx), showed significant response to tissue PCB. No significant correlation was found between tissue concentrations of chlorinated hydrocarbons and other enzymatic antioxidants (superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR) and NADPH DT-diaphorase (DT-d). Oxidative stress, measured as thiobarbituric acid reactive substances, was correlated with chlorinated pesticide concentrations in tissues. This study demonstrated a correlation between GST/GSH and chlorinated hydrocarbons. The apparent lack of correlation between trace organic pollutants and some of the enzymatic antioxidants may be due to the inhibitory effects caused by these chemicals. The above results suggest that more investigations are needed before these enzymes can be used as biomarkers. 相似文献
865.
The disused railway cutting at Ammons Hill, Hereford and Worcester, exposes a sequence of beds belonging to the Devonian St Maughans Formation of Lochkovian (Gedinnian) age. The beds are of Old Red Sandstone facies, but contain brackish water faunas. These faunas occur at a level generally considered to be above the level of marine influence that affected the older Raglan Mudstone Formation of mainly Přídolí Series age. The section, described by King in 1934, is now overgrown, but was excavated in 1986 by the British Geological Survey during its survey of the Worcester 1:50000 sheet. The evidence of the section calls for slight amendment of Allen's (1985) model of an interrupted transition from marine deposition in Ludlow time to freshwater deposition in Gedinnian time that was complete by the time of the formation of a regionally extensive calcrete palaeosol, the Psammosteus Limestone. Subsequent transgressive events took place before the establishment of apparently wholly fluvial and floodplain environments. 相似文献
866.
In this study, we provide the first absolute ages for a Big Circle megalithic structure in Jordan, using rock surface luminescence dating of the buried surface of rocks collected from circle J4 in southern Jordan. Five rocks were used for this study. All rocks showed evidence of previous daylight exposure before being used in the construction of the circle. The exposure was sufficient to bleach the latent luminescence signal to a negligible level compared to the subsequent burial dose. Three rocks gave indistinguishable ages, and were last exposed to daylight in 1500 ± 100 BCE; this is very likely to be the date of circle construction. Two others gave younger ages, indicating later disturbance or reworking. These new results provide very strong evidence for construction during the Late Bronze Age, and refute the earlier hypothesis of construction during Umayyad period (661–750 CE) as a hunting trap. 相似文献
867.