全文获取类型
收费全文 | 485篇 |
免费 | 6篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 26篇 |
地球物理 | 116篇 |
地质学 | 112篇 |
海洋学 | 83篇 |
天文学 | 113篇 |
综合类 | 5篇 |
自然地理 | 38篇 |
出版年
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 8篇 |
2014年 | 14篇 |
2013年 | 19篇 |
2012年 | 12篇 |
2011年 | 15篇 |
2010年 | 16篇 |
2009年 | 22篇 |
2008年 | 27篇 |
2007年 | 34篇 |
2006年 | 21篇 |
2005年 | 18篇 |
2004年 | 22篇 |
2003年 | 12篇 |
2002年 | 18篇 |
2001年 | 15篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 14篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1988年 | 11篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 11篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1973年 | 8篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1969年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有497条查询结果,搜索用时 15 毫秒
121.
To understand the fundamental chemical processes of fluid–rock interaction during the pulverization of quartz grains in fault zones, quartz grains were crushed within pure water. The crushing experiments were performed batch style using a shaking apparatus. The crushing process induced a decrease in pH and an increase in hydrogen gas with increased shaking duration. The amount of hydrogen ions generated was five times larger than that of the hydrogen gas, which was consistent with the amount of Si radicals estimated from electron spin resonance measurements by Hochstrasser and Antonini (1972). This indicates that hydrogen gas was generated by consuming most of the Si radicals. The generation of hydrogen ions was most likely related to the presence of silanols on the newly formed mineral surface, implying a change of proton activities in the fluid after pulverization of quartz. 相似文献
122.
Water and sediment quality, partial mass budget and effluent N loading in coastal brackishwater shrimp farms in Bangladesh 总被引:2,自引:0,他引:2
Shahidul Islam M Jahangir Sarker M Yamamoto T Abdul Wahab M Tanaka M 《Marine pollution bulletin》2004,48(5-6):471-485
The present study aimed to quantify the water and sediment quality and growth and production parameters and to establish nutrient budgets for an average of five selected semi-intensive shrimp ponds in Bangladesh over a growing cycle. Physico-chemical parameters of water and sediments were measured and analyzed by standard methods. Gross yield (kg ha-1) of shrimp was calculated from the stocking and harvesting data. Finally, a partial nutrient mass budget for N and P was calculated. Most of the parameters of water and sediments correlated significantly with each other suggesting a high degree of interactions between different parameters in the system. Significantly higher concentrations of all species of nitrogenous nutrients were recorded in the effluent waters than that entering into the ponds. Therefore, a high loading and net output of nitrogenous nutrients in effluent waters was documented. The study also indicated a net discharge of solids and minerals through effluent loading. However, significantly lower concentrations of phosphorus in the effluent water indicated a net retention and trapping of phosphatic nutrients in the environment. Total production ranged between 532.0 and 697.0 kg ha-1 cycle-1 and P. monodon production between 484.0 and 562.0 kg ha-1 cycle-1. Ponds gained nitrogen primarily from intake water (55%) and fertilizers (29%), and nitrogen was lost primarily from water exchange (78%) and harvested shrimp (12%). Phosphorus gain occurred mostly from intake water (52%) and fertilizers (25%), and phosphorus was lost primarily from water exchange (52%) and harvested shrimp (3.3%). About 10% of input nitrogen and 44% of phosphorus were not accounted for in measured losses, and presumably were fixed or metabolized in the system. On average, 78 g N was discharged to and 25 g P was removed from the surrounding water by the system for each kilogram of shrimp produced. Mean conversion of feed nitrogen and phosphorus to shrimp flesh averaged 74% and 40%, respectively. It was concluded that semi-intensive systems serve as net supplier of N to and net remover of P from the surrounding water. 相似文献
123.
Temperature dependencies of magnetic rotation were measured in micron-sized silicates dispersed in ethanol for two different samples of kaolinite. Magnetic rotation proceeded by balance between thermal agitation energy and magnetic anisotropy energy. Measurements were performed between 195 and 343 K. The field intensity required to achieve magnetic alignment of microcrystals increases with temperature, because of the temperature dependence of paramagnetic anisotropy, and the temperature dependence of thermal agitation energy. The results indicate that the values of magnetic anisotropy of nonmagnetic materials might partially derive from the paramagnetic moments, which derive from paramagnetic impurity ions. The present experiment provides a technical basis for determining the precise values of diamagnetic anisotropy ()DIA from minerals which have a concentration of paramagnetic ions and do not form a single crystal large enough to allow bulk measurements. The values of ()DIA can be obtained by extrapolating the –T relations, which follow the Curie law, to the temperature limits. 相似文献
124.
In this study, we examined the subsurface structure in the vicinity of the active Atera fault beneath at least one monogenetic volcano that forms the Sakashita body of the Ueno basalts, central Japan. Microgravity and seismic reflection surveys over an area of about 3×3 km (horizontal)×1 km (vertical from surface) revealed that (1) a low-density body interpreted as the damaged zone of the Atera fault reaches a depth more than 200 m below sea level; and (2) a weak zone of crust that may exist about 1.5 km southwest of the Atera fault in a direction parallel to it. By combining the shape of the Sakashita body and (2), we propose that a dyke extending in a NW–SE direction with several vent alignments in the same direction may exist along this weak zone. This suggests that the studied area was governed in the NW–SE compressional and NE–SW extensional stress field when the Sakashita body formed. 相似文献
125.
Abstract The fractality of fault zones of thickness T for the 248-m-long core from a borehole penetrating the northern segment of the seismic Chelungpu Fault, Taiwan, was analyzed. The frequency curve of T shows that the fractal dimension is normal when T is smaller than a characteristic thickness T c , and it becomes abnormally large when T exceeds T c . The fractal dimensions of size and spatial distributions of T increase as the mean distribution density of T increases, which is inconsistent with the evolution laws for ordinary brittle faults. This discrepancy implies that the thickening rate of T when T is more than T c is not constant, but a decreasing function of fault displacement. The slow thickening rate is related to the elastohydrodynamic lubrication which was effective on the fault when T exceeds T c . This slip instability mechanism can explain the large, fast and smooth slip on the northern segment of the Chelungpu Fault during the 1999 Chi-Chi earthquake. 相似文献
126.
Abstract The seismic slip that occurred during the 1999 Chi-Chi earthquake in Taiwan showed contrastive behaviors in different regions along the Chelungpu Fault: A large and smooth slip occurred in the north, while a relatively small slip associated with high-frequency seismic wave radiation occurred in the south. The core samples from shallow boreholes at northern (Fengyuan) and southern (Nantou) sites penetrating the seismic Chelungpu Fault were analyzed. The fault zones at the northern site are characterized by soft clayey material associated with clayey injection veins. This suggests that the fault zones were pressurized during ancient seismic slip events, and hence the elastohydrodynamic lubrication occurred effectively. In contrast, the fault rock from the southern site is old pseudotachylyte that has been shattered by repeated ancient seismic slip events. Statistical analysis of many pseudotachylyte fragments reveals that the degree of frictional melting tended to be low. In this case, the seismic slip is restrained by the mechanical barrier of a highly viscous melt layer. These contrastive fault rocks were produced by repeated ancient seismic slip events, but the two corresponding mechanisms of friction are likely to have also occurred during the 1999 Chi-Chi earthquake, thus causing the contrastive slip behaviors in the north and south. 相似文献
127.
Due to a continual rainfall, a flowslide occurred in Yamashina area, Kanazawa City, Japan on November 8, 2002 in the Tertiary
mudstone area. The sliding mass was fully fluidized during the motion and moved downward the slope for a long distance. On
December 31, 2003, slope failure was triggered by intensive rainfall and snowmelt water at the same site again, and resulted
in the second occurrence of flowslide. The total displacement of the slope was recorded with an extensometer. Through field
investigation, the difference of the sliding mechanism between the two flowslides was examined. 相似文献
128.
Tidal triggering of earthquakes in the subducting Philippine Sea plate beneath the locked zone of the plate interface in the Tokai region, Japan 总被引:5,自引:1,他引:5
We found a characteristic space–time pattern of the tidal triggering effect on earthquake occurrence in the subducting Philippine Sea plate beneath the locked zone of the plate interface in the Tokai region, central Japan, where a large interplate earthquake may be impending. We measured the correlation between the Earth tide and earthquake occurrence using microearthquakes that took place in the Philippine Sea plate for about two decades. For each event, we assigned the tidal phase angle at the origin time by theoretically calculating the tidal shear stress on the fault plane. Based on the distribution of the tidal phase angles, we statistically tested whether they concentrate near some particular angle or not by using Schuster's test. In this test, the result is evaluated by p-value, which represents the significance level to reject the null hypothesis that earthquakes occur randomly irrespective of the tidal phase angle. As a result of analysis, no correlation was found for the data set including all the earthquakes. However, we found a systematic pattern in the temporal variation of the tidal effect; the p-value significantly decreased preceding the occurrence of M ≥ 4.5 earthquakes, and it recovered a high level afterwards. We note that those M ≥ 4.5 earthquakes were considerably larger than the normal background seismicity in the study area. The frequency distribution of tidal phase angles in the pre-event period exhibited a peak at the phase angle where the tidal shear stress is at its maximum to accelerate the fault slip. This indicates that the observed small p-value is a physical consequence of the tidal effect. We also found a distinctive feature in the spatial distribution of p-values. The small p-values appeared just beneath the strongly coupled portion of the plate interface, as inferred from the seismicity rate change in the past few years. 相似文献
129.
Some global features of palaeointensity in geological time 总被引:1,自引:0,他引:1
130.