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161.
Phase relations in the system KAlSi3O8-NaAlSi 3O8 have been examined at pressures of 5–23 GPa and temperatures of 700–1200° C. KAlSi3O8 sanidine first dissociates into a mixture of wadeite-type K2Si4O9, kyanite and coesite at 6–7 GPa, which further recombines into KAlSi3O8 hollandite at 9–10 GPa. In contrast, NaAlSi3O8 hollandite is not stable at 800–1200° C near 23 GPa, where the mixture of jadeite plus stishovite directly changes into the assemblage of calcium ferrite-type NaAlSiO4 plus stishovite. Phase relations in the system KAlSi3O8-NaAlSi3O8 at 1000° C show that NaAlSi3O8 component gradually dissolves into hollandite with increasing pressure. The maximum solubility of NaAlSi3O8 in hollandite at 1000° C was about 40 mol% at 22.5 GPa, above which it decreases with pressure. Unit cell volume of the hollandite solid solution decreases with increasing NaAlSi3O8 component. The hollandite solid solution in this system may be an important candidate as a host mineral of K and Na in the uppermost lower mantle 相似文献
162.
Titanochondrodite and titanoclinohumite derived from the upper mantle in the Buell Park Kimberlite,Arizona, USA 总被引:2,自引:0,他引:2
Ken-ichiro Aoki Kiyoshi Fujino Masaki Akaogi 《Contributions to Mineralogy and Petrology》1976,56(3):243-253
Kimberlite from Buell Park, Arizona, which was intruded into Permian sediments about 30 m.y. ago, is characterized by the hydrous silicates titanochondrodite and titanoclinohumite. Titanochondrodite is the first finding in kimberlites. Optical properties, chemical compositions and cell dimensions of these two minerals are determined.Titanochondrodite and titanoclinohumite are considered to crystallize from kimberlite magma at a depth of about 100 km and at 1,000° C, on the basis of kimberlite mineralogy, petrography and high pressure experimental work. Although there is no direct evidence, the importance of these two minerals in peridotite wedges above sinking lithosphere at the continental margins is also discussed. 相似文献
163.
Sinzo Masaki 《GeoJournal》1983,7(6):483-490
The two species groups of ground cricket previously known as P. taprobanensis and P. fascipes are widely distributed from the tropical to temperate regions of East Asia. In the Japanese Islands they show parallel variations along a latitudinal gradient in both developmental and morphometric traits. The ovipositor length varies continuously from 44 to 28°N, but this cline is disrupted by an abrupt shortening farther south. The disruption is associated with changes in the life cycle from the presence to virtual absence of egg diapause and from a short-day to long-day type of nymphal photoperiodic response. It is inferred that the two different types of life cycle were selected for in the temperate and subtropical climates, respectively, and that this differential selection resulted in speciation. Since climatic adaptation seems to be the primary factor involved, this sort of divergence may be called “climatic speciation”. 相似文献
164.
Infrared absorption spectra are presented for four hydrous magnesian silicates which are stable at high pressures and high temperatures characteristic of the earth's mantle: phase A (Mg7Si2O14H6), phase B (approx. Mg23Si8O42H6), chondrodite (Mg5Si2O10H2), clinohumite (Mg9Si4O18H2). The results show that phase B as well as phase A, chondrodite and clinohumite contain hydroxyl groups in their structures. It is also suggested that phase B, in addition to phase A, could be of potential importance in the upper mantle and transition zone as a dense host mineral for hydroxyl ions. Chemical composition of phase A was reexamined by microprobe analysis: it agrees well with Mg7Si2O14H6, estimated by Yamamoto and Akimoto (1974, 1977), but disagrees with a newly proposed formula Mg2SiO5H2 by Benimoff and Sclar (1984). 相似文献
165.
166.
The decorrelation length (Lcf) has been widely used to describe the behavior of vertical overlap of clouds in general circulation models (GCMs); however, it has been a challenge to associate Lcf with the large-scale meteorological conditions during cloud evolution. This study explored the relationship between Lcf and the strength of atmospheric convection in the tropics based on output from a global cloud-resolving model. Lcf tends to increase with vertical velocity in the mid-troposphere (w500) at locations of ascent, but shows little or no dependency on w500 at locations of descent. A representation of Lcf as a function of vertical velocity is obtained, with a linear regression in ascending regions and a constant value in descending regions. This simple and dynamic-related representation of Lcf leads to a significant improvement in simulation of both cloud cover and radiation fields compared with traditional overlap treatments. This work presents a physically justifiable approach to depicting cloud overlap in the tropics in GCMs. 相似文献
167.
Focused infiltration of snowmelt water in partially frozen soil under small depressions 总被引:5,自引:0,他引:5
Ephemeral puddles in small closed depressions can play an important role in the hydrology and ecology of many landscapes, by storing runoff water, recharging soil moisture and shallow groundwater, and by providing food and habitat for many organisms. Infiltration of snowmelt water under small depressions (<1000 m2) has been studied in the St. Denis National Wildlife Area in Saskatchewan, Canada, located within the northern glaciated prairie of North America where numerous depressions of varying sizes exist. The depressions stored most of the snowmelt runoff generated within their respective watersheds. The water level in a typical depression declined at 0.6 mm/h while the underlying frozen soil was thawing. This rate was likely limited by the rate of downward movement of the thawing front, which was functioning as a moving impermeable boundary. The rate of thawing was controlled by the external energy input from the ground surface. Standing water in depressions efficiently trapped incoming radiation and conducted it to the thawing front. The recession rate increased to 1.1 mm/h when the soil under the depression thawed completely. The recession rate at this later stage appears to be limited by the hydraulic conductivity of the subsoil (0.04–4 mm/h), which is much smaller than the topsoil conductivity (10–20 mm/h). 相似文献
168.
Masaki Yoshida 《Physics of the Earth and Planetary Interiors》2004,147(1):67-85
In a traditional analytical method, the convective features of Earth’s mantle have been inferred from surface signatures obtained by the geodynamic model only with depth-dependent viscosity structure. The moving and subducting plates, however, bring lateral viscosity variations in the mantle. To clarify the effects of lateral viscosity variations caused by the plate-tectonic mechanism, I have first studied systematically instantaneous dynamic flow calculations using new density-viscosity models only with vertical viscosity variations in a three-dimensional spherical shell. I find that the geoid high arises over subduction zones only when the vertical viscosity contrast between the upper mantle and the lower mantle is O(103) to O(104), which seems to be much larger than the viscosity contrast suggested by other studies. I next show that this discrepancy may be removed when I consider the lateral viscosity variation caused by the plate-tectonic mechanism using two-dimensional numerical models of mantle convection with self-consistently moving and subducting plates, and suggest that the observed geoid anomaly on the Earth’s surface is significantly affected by plate-tectonic mechanism as a first-order effect. 相似文献
169.
In teleost sPeCies, it is well accepted that estradiol--l75 (E2 )is generated from ovarian fOl-licles stimulated by pituitary gonadOtropins (GTH) (Nagahama, l987). FUrthermore, E2 canstimulate hepatic vitellngenesis and elevate plasrna yOlk protein precursor vite1lOgenin, totalCa and W levels in several teleosts (KorSgaard and Petersen, l976, l978; Whiteheadet al., l978; Elliott et al., l979; Pertersen et al., l983; Wallace, 1985; tapigliati etal., 1999). On the other hand, many stud… 相似文献
170.
Conditions for the formation of large meander (LM) of the Kuroshio are inferred from observational data, mainly obtained in the 1990s. Propagation of the small meander of the Kuroshio from south of Kyushu to Cape Shiono-misaki is a prerequisite for LM formation, and three more conditions must be satisfied. (1) The cold eddy carried by small meander interacts with the cold eddy in Enshu-nada east of the cape. During and just after the propagation of small meander, (2) the Kuroshio axis in the Tokara Strait maintains the northern position and small curvature, and (3) current velocity of the Kuroshio is not quite small. If the first condition is not satisfied, the Kuroshio path changes little. If the first condition is satisfied, but the second or third one is not, the Kuroshio transforms to the offshore non-large-meander path, not the LM path. All three conditions must be satisfied to form the large meander. For continuance of the large meander, the Kuroshio must maintain the small curvature of current axis in the Tokara Strait and a medium or large range of velocity and transport. These conditions for formation and continuance may be necessary for the large meander to occur. Moreover, effects of bottom topography on position and structure of the Kuroshio are described. Due to topography, the Kuroshio changes horizontal curvature and vertical inclination of current axis in the Tokara Strait, and is confined into either of two passages over the Izu Ridge at mid-depth. The former contributes to the second condition for the LM formation. 相似文献