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排序方式: 共有173条查询结果,搜索用时 93 毫秒
31.
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33.
Gravity and S-wave modelling across the Jan Mayen Ridge,North Atlantic; implications for crustal lithology 总被引:1,自引:0,他引:1
Rolf Mjelde Inger Eckhoff Ståle Solbakken Shuichi Kodaira Hideki Shimamura Karl Gunnarsson Ayako Nakanishi Hajime Shiobara 《Marine Geophysical Researches》2007,28(1):27-41
The horizontal components from fourteen Ocean Bottom Seismometers deployed along four profiles focused along the western margin
of the Jan Mayen microcontinent, North Atlantic, have been modelled with regard to S-waves, based on P-wave models obtained
earlier. The seismic models have furthermore been constrained by 2D gravity modelling. High V
p/V
s-ratios (2.3–7.9) within the Cenozoic sedimentary section are attributed to significant porosities, whereas V
p/V
s-ratios in the order of 1.9–2.2 for the Mesozoic and Paleozoic sedimentary rocks indicate shale-dominated lithology throughout
the area. The eastern side of the Jan Mayen Ridge is interpreted as a passive, volcanic margin, based on relatively high crustal
V
p/V
s-ratios (1.9), whereas lower V
p/V
s-ratios (1.75–1.8) suggest the presence of intermediate composition crust and non-volcanic margin on the western side of the
ridge. In the westernmost part of the Jan Mayen Basin, slightly increased upper mantle V
p/V
s-ratios may indicate some degree of serpentization of upper mantle peridotites. 相似文献
34.
Norihiro Kobayashi Tomomi Eriguchi Kisaburo Nakata Shigeki Masunaga Fumio Horiguchi Junko Nakanishi 《Estuarine, Coastal and Shelf Science》2006,70(4):621
A 3-D chemical fate prediction model (FATE3D) was applied to predict the dioxin concentrations in the seawater of Tokyo Bay, Japan. The simulations were carried out for a period of one year (from September 2002 to August 2003). Parameters such as meteorological data, flow field conditions, concentrations and sinking rates of organic particulate matter, initial and boundary conditions, and loading fluxes and physico-chemical properties of dioxins were used as the model inputs.The simulation results compared favorably with the field measurements of dioxin concentrations in the bay for both the particulate and dissolved phases, indicating the validity and predictive capability of the model. Furthermore, the differences in the seasonal cycles and distributions between the particulate- and dissolved-phase dioxins in the bay were estimated from the simulation results.However, the particulate-phase dioxin concentrations in the bottom layers (+1 m from the bottom) were underestimated, probably because the resuspension process was not taken into account in the model. The improvement of the model's predictive capability, including the resuspension process, shall be the focus of our next study. 相似文献
35.
36.
Ichiro Kaneoka 《Marine Geophysical Researches》1972,1(4):412-417
The subsidence of seamounts in the northwestern Pacific is suggested from the unexpected high vesicularity of submarine basaltic rocks which were dredged from great depths. There exists a tendency that the closer the seamount is situated to the trench axis, the greater the amount of subsidence becomes. 相似文献
37.
Precise Positioning of Ocean Bottom Seismometer by Using Acoustic Transponder and CTD 总被引:1,自引:0,他引:1
Shiobara Hajime Nakanishi Ayako Shimamura Hideki Mjelde Rolf Kanazawa Toshihiko Berg Eivind W. 《Marine Geophysical Researches》1997,19(3):199-209
We have obtained precise estimates of the position of Ocean Bottom Seismometers (OBS) on the sea bottom. Such estimates are usually uncertain due to their free falling deployment. This uncertainty is small enough, or is correctable, with OBS spacing of more than 10 km usually employed in crustal studies. But, for example, if the spacing is only 200 m for OBS reflection studies, estimates of the position with an accuracy of the order of 10 m or more is required.The determination was carried out with the slant range data, ship position data and a 1D acoustic velocity structure calculated from Conductivity–Temperature–Depth (CTD) data, if they are available. The slant range data were obtained by an acoustic transponder system designed for the sinker releasing of the OBS or travel time data of direct water wave arrivals by airgun shooting. The ship position data was obtained by a single GPS or DGPS. The method of calculation was similar to those used for earthquake hypocenter determination.The results indicate that the accuracy of determined OBS positions is enough for present OBS experiments, which becomes order of 1 m by using the DGPS and of less than 10 m by using the single GPS, if we measure the distance from several positions at the sea surface by using a transponder system which is not designed for the precise ranging. The geometry of calling positions is most important to determine the OBS position, even if we use the data with larger error, such as the direct water wave arrival data. The 1D acoustic velocity structure should be required for the correct depth of the OBS. Although it is rare that we use a CTD, even an empirical velocity structure works well. 相似文献
38.
39.
Simple monitoring method for precaution of landslides watching tilting and water contents on slopes surface 总被引:2,自引:2,他引:0
Taro Uchimura Ikuo Towhata Trinh Thi Lan Anh Jou Fukuda Carlos J. B. Bautista Lin Wang Ichiro Seko Taro Uchida Akira Matsuoka Yosuke Ito Yuichi Onda Sho Iwagami Min-Seok Kim Naoki Sakai 《Landslides》2010,7(3):351-357
A low-cost and simple monitoring method for early warning of landslides is proposed. To detect abnormal deformation of a slope, this method employs a tilt sensor in place of an extensometer on the slope surface. In order to examine the relevance of measuring rotation angle on a slope surface by tilt sensor, model tests were conducted, and rotation on the slope surface was observed together with slide displacement along the surface. The rotation data responded 30 min before failure in a model test, which could be useful as a signal for early warning. However, the behavior of rotation before failure varies from case to case, and thus, criteria to issue warning should be defined more carefully. For a model slope made of uniform loose sand, measurement of slide displacement along the slope surface is sensitive to failure at the toe, while the measurement of rotation on the slope surface is useful to detect the development of progressive failure upward along the slope. Wireless sensor units with microelectromechanical systems (MEMS) tilt sensor and volumetric water content sensor were also examined on a real slope in Kobe City, and a long-term monitoring was attempted. A simple but possible way to define the criteria of judgment to issue warning can be proposed based on combination of data obtained by the tilt sensors and volumetric water content sensors. 相似文献
40.
Ichiro Kaneoka 《Earth and Planetary Science Letters》1980,46(2):233-243
40Ar/39Ar dating results on seven volcanic rocks from four areas of the Deccan Traps, India, suggest that volcanic activity more than 70 Ma ago might have occurred at least in limited areas.In the Igat Puri area, the uppermost flow shows an40Ar/39Ar age of 63 Ma, whereas a lower flow has an age of around 82–84 Ma.40Ar/39Ar ages of samples from the Bombay area also seem to favor the occurrence of volcanic activity more than 70 Ma ago. One rhyolite dyke from the Osam Hill in the Girnar Hill area shows a well-defined plateau age of 68 Ma, whereas two tholeiitic basalts from the Mahabaleshwar area indicate a total40Ar/39Ar age of around 63–64 Ma, though they show the effect of secondary disturbance in the age spectra.The volcanic activity(ies) more than 70 Ma ago may correspond to precursory one(s) for the main volcanic activity around 65 Ma ago in the Deccan Traps. 相似文献