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121.
Chow-Choong Ngeow Shashi M. Kanbur 《Monthly notices of the Royal Astronomical Society》2005,360(3):1033-1039
There is strong evidence that the period–luminosity (PL) relation for the Large Magellanic Cloud (LMC) Cepheids shows a break at a period around 10 d. Because the LMC PL relation is extensively used in distance scale studies, the non-linearity of the LMC PL relation may affect the results based on this LMC calibrated relation. In this paper we show that this problem can be remedied by using the Wesenheit function in obtaining Cepheid distances. This is because the Wesenheit function is linear, although recent data suggest that the PL and the period–colour (PC) relations that make up the Wesenheit function are not. We test the linearity of the Wesenheit function and find strong evidence that the LMC Wesenheit function is indeed linear. This is because the non-linearity of the PL and PC relations cancel out when the Wesenheit function is constructed. We discuss this result in the context of distance scale applications. We also compare the distance moduli obtained from μ0 =μ V − R (μ V −μ I ) (equivalent to Wesenheit functions) constructed with the linear and the broken LMC PL relations, and we find that the typical difference in distance moduli is ∼ ±0.03 mag . Hence, the broken LMC PL relation does not seriously affect current distance scale applications. We also discuss the random error calculated with equation μ0 =μ V − R (μ V −μ I ) , and show that there is a correlation term that exists from the calculation of the random error. The calculated random error will be larger if this correlation term is ignored. 相似文献
122.
123.
Manoj Datta G. Venkatappa Rao Shashi K. Gulhati 《Marine Georesources & Geotechnology》2013,31(4):307-341
Abstract This paper presents the results of a laboratory investigation undertaken to study the nature of two submarine carbonate soils from Bombay High off the west coast of India, as well as to study the shear and plasticity behavior of their sand and silt‐clay fractions, respectively. Scanning electron micrographs reveal that the carbonate content in both soils is comprised primarily of nonskeletal particles of various types. X‐ray diffraction and infrared absorption analyses indicate that in one soil the carbonate fraction consists of calcite and aragonite minerals, whereas in the other soil dolomite is also present. The non‐carbonate fraction of both soils is comprised primarily of quartz and feldspar, and also some clay minerals. The nature of the carbonate fraction of the two soils indicates that they were formed by different depositional processes. During drained triaxial shear the nonskeletal sand grains of both soils exhibit a lower degree of crushing when compared with that of the skeletal carbonate sands, and thus appear to be stronger foundation material. Although the carbonate contents of the silt‐clay fractions of the two soils are similar, they exhibit markedly different plasticity characteristics . This is probably because of the microlevel cementation produced by carbonate material in one soil. This study leads one to the conclusion that carbonate content alone should not be treated as a parameter which controls the engineering behavior of submarine soils; the nature and form of carbonate material must also be identified. 相似文献
124.
Landslides are very common in high-altitude Himalayan terrains. Major roads in the Himalayas are frequently blocked due to
heavy landslides and remain closed for long periods of time. Permanent mitigatory solutions to these landslides are required
to keep the highways open. Lanta Khola, located 71.2 km north of Gangtok (capital of the Indian state of Sikkim), is one of
the oldest landslides on the North Sikkim Highway and is active since 1975. The rock types on either side of the landslide
are different (augen gneiss in the east and metapelitic schist in the west), and it is believed that the Main Central Thrust
passes through the slide zone. Since the slide is invariably activated in the aftermath of heavy rainfall, it is important
to identify the subsurface structures that channel water below the landslide surface in order to understand the triggers of
slide activity. This can only be accomplished by geophysical survey; however, an appropriate geophysical technique that can
be applied in such terrains must be identified. Very low-frequency (VLF) electromagnetic survey was performed over the Lanta
Khola landside in order to delineate subsurface structures. Although a very limited number of VLF transmitters are available
worldwide, it was possible to pick up VLF signals from a number of VLF stations even in this high-altitude mountainous terrain.
VLF measurements along five profiles perpendicular to the geological strike were recorded, and a high conducting zone was
delineated from the VLF observations. This conducting zone correlates with the low resistive zone identified from gradient
resistivity profiling. The anomalies confirm that there is a water-saturated zone (soggy zone) even in the subsurface of the
slide parallel to the geological gneiss–schist contact within the Lanta Khola slide. This indicates that the conductive feature
correlates with a weak water-saturated debris layer that lies along the slide and is parallel to the geological contact. Resistive
structures on either side of the landslide zone can thus be correlated with the stable ground. It is necessary to drain out
water from the soggy zone to minimize slide activity since this zone appears to penetrate into the body of the slide. 相似文献
125.
在研究了 1 990年 4月 2 6日共和 7.0级强震前 ,青海东北部地区的小震活动和前兆异常总台频次的变化 ,以及地下流体 ,电磁 ,形变等前兆异常的时空演化特征的基础上 ,得出在大震前 1~ 7个月前兆异常台项总频次的升高和 2 .0~ 3.9级地震形成的条带和空区 ,以及 3.5级以上地震频次增加在时间上是同步的。而且 ,2 .0~ 3.9级地震形成的条带和空区对未来大震的震中位置具有指示意义。这种前兆异常在时间上的同步性可能是大震前的异常由中期向短期过渡的时间标志 ,震前 2个月出现的前兆台项总频次异常峰值以及形变前兆异常场兆变化则是异常进入短临的时间。 相似文献
126.
127.
A vertical soil column setup integrated with wetlands is developed to study the biodegradation and transport of toluene, a light non‐aqueous phase liquid (LNAPL), in the subsurface environment. LNAPL‐contaminated water is applied to infiltrate from the top of the soil column. The observed and simulated breakthrough curves show high equilibrium concentration at top ports rather than at lower ports, indicating effective toluene biodegradation with soil depth. The observed equilibrium concentration of toluene is higher in the case of unplanted wetland, asserting an accelerated biodegradation rate in the planted case. A difference in the relative concentration of toluene between input and output fluxes at 100 h is found as 13.34% and 30.86% for planted and unplanted wetland setups, respectively. Estimated biodegradation rates show that toluene degradation is 2.5 times faster in the planted wetland setup. In addition, the difference in the observed bacterial count and dissolved oxygen prove that toluene degraded aerobically at a faster rate in the planted setup. Simulations show that as time reached 80–100 h, there is no significant change in concentration profile, thereby confirming the equilibrium condition. The results of this study will be useful to frame plant‐assisted bioremediation techniques for LNAPL‐contaminated soil–water resources in the field. 相似文献
128.
Shashi Mathur 《国际地质力学数值与分析法杂志》1999,23(12):1349-1357
The settlement of soil occurs whenever there is an increase in effective confining stress. The withdrawal of water by plant roots results in a change in water pressure and moisture content in the soil. The variation in the moisture content leads to a change in the effective stress that causes a decrease in porosity which eventually results in the settlement of soil. The driving force for the uptake of water by the roots is the difference in the plant water and soil water potential existing between the soil solution adjacent to the roots and the root xylem. In case of transpiring plants, this driving force is mainly due to the tension (negative pressure) produced in the roots. A finite element solution of the governing equation yields the variation of moisture content with depth and the total settlement of the soil column due to the extraction of water by the plant roots. The simulated results indicate the damaging situation due to changes in the soil moisture content on account of transpiring trees and plants grown around the perimeter of structures. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献