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81.
The River Ganga in the central Gangetic plain shows the incision of 20 m of Late Quaternary sediments that form a vast upland terrace (T2). The incised Ganga River Valley shows two terraces, namely the river valley (terrace-T1) and the present-day flood plain (terrace-T0). Terrace-T1 shows the presence of meander scars, oxbow lakes, scroll plains, which suggests that a meandering river system prevailed in the past. The present-day river channel flows on terrace-T0 and is braided, sensu stricto. It is thus inferred that the River Ganga experienced at least two phases of tectonic adjustments: (1) incision and (2) channel metamorphosis from meandering to braided.Optical dating of samples from three different terraces has bracketed the phase of incision to be <6 and 4 ka. Different ages of the top of terrace-T2 show that this surface experienced differential erosion due to tectonic upwarping in the region, which also caused the river incision. River metamorphosis occurred some time during 4 and 0.5 ka. 相似文献
82.
Accidental spills of hydrocarbons, such as Light Non-Aqueous Phase Liquids (LNAPLs), are one of the most common sources of subsurface contamination. Migration of LNAPL in a porous medium is influenced by various factors such as the number of fluids present in the unsaturated/saturated zones and the proportion of pores occupied by each fluid. The results for relationship between matric suction and degree of saturation are presented in this paper for water–air, water–LNAPL and LNAPL–air systems in a sand. A simple and reliable setup using Buchner funnel was designed to obtain these relations. It was found that the relationship between matric suction head and degree of saturation is hysteretic for all the fluid systems (water–air, water–LNAPL and LNAPL–air). Furthermore, the amount of hysteresis depended upon the fluid system, with the maximum hysteresis occurring for water–air system. The results suggest that the amount of trapped air depends upon the reversal degree of saturation from drying to wetting. 相似文献
83.
Coda of local earthquakes that occurred during 2006–2007 are used to study the attenuation characteristics of the Garhwal–Kumaun
Himalayas. The coda attenuation characteristics are represented in terms of coda Q or Q
c
. It is observed that Q
c
increases with frequency. Q
c
also varies with increase in lapse time of coda waves. Q
c
increases up to an 85-s average lapse time. This is similar to observations around the world reported by many workers who
have interpreted this as a manifestation of the fact that heterogeneity decreases with depth. However, around a 90-s average
lapse time Q
c
is lower than its values for lower and higher average lapse times. This is interpreted as an indication of possible presence
of a fluid-filled medium or a medium having partial melts at around a 160-km depth. Q
0, i.e., Q
c
at 1 Hz, increases, and frequency parameter n decreases with increasing lapse time, barring around a 90-s lapse time. This
again shows that in general, heterogeneity decreases with increasing depth. The Q
0 and n values for smaller lapse times are similar to those for tectonically active areas. By comparing Q
c
values obtained in this study with those obtained by us using the 1999 Chamoli earthquake aftershocks, it is concluded that
the crust is turbid and the mantle is more transparent. However, whether the variation in Q
c
values between 1999 and 2006–2007 is temporal or not cannot be definitely established from the available data set. 相似文献
84.
A finite element analysis of a reinforced embankment-foundation system has been conducted using a coupled formulation and elastoplasticity theory. Such important factors as type of reinforcement, the type of clay, depth of foundation and drainage condition affecting the system have been systematically investigated using appropriate constitutive models to depict various components of the system and material parameters of two typical soft clay deposits found in India. The displacements, reinforcement force and maximum heights of the embankments are among the aspects presented and discussed. It is shown that the effectiveness of the reinforcement is dependent on its stiffness and the shear strength of the clay deposit. The foundation depth has significant effect on the nature and magnitude of displacement, the reinforcement force and the height of embankment. Drainage conditions are shown to markedly influence the effectiveness of reinforcement. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
85.
Abstract As the quest for deep-sea mineral resources is gaining momentum, environment and ocean mining have become important aspects of study. Because many of these deposits occur in international waters, the concern for environmental conservation in view of the effects of deep-sea mining is resulting in these effects being studied in different oceans, and efforts to develop regulations governing this exploitation are also underway at national and international levels. The impact assessment of deep-sea mining needs to encompass a variety of subjects, including environmental, socioeconomic, technological, and legal aspects. At the same time, effects of in situ environmental conditions on mining activities also need to be considered for effecient performance by the mining system. Differences in the degree of impact have been noticed during the mining simulation experiments by different investigating agencies. Therefore, interparameter comparisons, standardization of methods, and improvement in mining design are important considerations for proper utilization of resources, conservation of environment, and cost efficiency of the mining operations. 相似文献
86.
Closed form analytic expressions for displacement and stresses at any point of either of the two homogeneous, isotropic, perfectly
elastic half-spaces in welded contact due to very long strike-slip dislocations are obtained. Both cases of vertical and horizontal
strike-slip dislocations are discussed in detail. Variation of the displacement with horizontal distance from the fault and
with vertical distance from the interface for a vertical strike-slip fault is studied numerically. 相似文献
87.
Response of low latitude ionosphere to the geomagnetic storm of May 30, 2005 in the Indian longitude sector has been investigated
by using the GPS data recorded at three stations namely, Udaipur, Hyderabad and Bengaluru. The event is noteworthy due to
the fact that the Z component of interplanetary magnetic field (IMF Bz) remained southward for about 10 hours, coincident
with the local day time for the Indian longitude sector, along with significantly higher values of AE and ASY-H indices. However,
we neither found any evidence for the presence of long lasting storm time electric fields nor could we infer episodes of eastward-westward
penetration of electric fields under steady southward IMF Bz and unsteady ring current conditions. On the storm day, the maximum
enhancement in the total electron content has been found to be about 60%. The ionosonde observations also showed increased
critical frequency (foF2) and the height (hPF2) of the F layer. The foF2 was enhanced by ∼60% which is consistent with the enhancement in total electron content. The slow rise and long duration
enhancement of hPF2 and foF2 have been attributed to the upwelling by the meridional neutral winds, caused by continuous energy inputs at higher latitudes.
The poleward expansion of the equatorial ionization anomaly has also been observed on May 30. On May 31, the following day
of the storm, significantly suppressed anomaly with near absence of its northern crest in the Indian longitude sector, revealed
the effect of storm induced disturbance dynamo electric fields. 相似文献
88.
The Oso Bay, Texas, sediments from nine sites were analyzed by GC-MS for organics to measure contamination in the bay. In most of the sites sediments contained tetrachloroethene (87–1433 g/kg), bis (2-ethylhexyl)phthalate (40–193 g/kg), and aliphatic hydrocarbons, C8-C13 (720–2491 g/kg). Sources of these contaminants include a landfill, military facilities, and municipal and industrial discharges. Size analysis of the sediments indicates they contain a high percentage of muddy sand (50–75 percent), which suggests that Oso Bay consists of common bay margin sediments. 相似文献
89.
Koushik Sen Ruchika Sharma B. R. Arora Vikram Gupta 《Journal of the Geological Society of India》2010,76(4):322-330
Anisotropy of Magnetic Susceptibility (AMS) and seismic wave velocity studies of some paramagnetic Himalayan granitoids show good correlation between magnetic fabric anisotropy and P wave velocity (Vp). Vp shows strong positive correlation with magnetic lineation (L) and degree of magnetic anisotropy (P′) having correlation coefficient (r) values of 0.93 and 0.89 respectively. Both Vp and Vs show positive correlation with the SiO2 content of Proterozoic and Paleozoic granitoids. Velocity of S wave (Vs) shows negative correlation with mean magnetic susceptibility (Km) having ‘r’ value of 0.86. The correlation between Vs-Km, Vp-P′, Vp-L also shows >95% probability in Spearman’s rank correlation. Based on the results from the present sample size it is suggested that, in paramagnetic granites, Vp is proportional to intensity of deformation and preferred orientation of minerals as well as the mineralogy. On the other hand, Vs is more dependent on the mineralogy alone. 相似文献
90.
A catalog for northeast India and the adjoining region for the period 1897–2009 with 4,497 earthquakes events is compiled
for homogenization to moment magnitude M
w,GCMT in the magnitude range 3–8.7. Relations for conversion of m
b and M
s magnitudes to M
w,GCMT are derived using three different methods, namely, linear standard regression, inverted standard regression (ISR) and orthogonal
standard regression (OSR), for different magnitude ranges based on events data for the catalog period 1976–2006. The OSR relations
for M
s to M
w,GCMT conversion derived in this paper have significantly lower errors in regression parameters compared to the relations reported
in other studies. Since the number of events with magnitude ≥7 for this region is scanty, we, therefore, considered whole
India region to obtain the regression relationships between M
w,GCMT and M
s,ISC. A relationship between M
w,GCMT and M
w,NEIC is also obtained based on 17 events for the range 5.2 ≤ magnitude ≤ 6.6. A unified homogeneous catalog prepared using the
conversion relations derived in this paper can serve as a reference catalog for seismic hazard assessment studies in northeast
India and the adjoining region. 相似文献