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971.
Tectonic and geochemical characteristics and reserved conditions of a mantle source gas accumulation zone in eastern China 总被引:8,自引:0,他引:8
Along both sides of the Tancheng-Lujiang Fracture Zone in eastern China, a series of mantle source gas pools constitute a
massive-scale tectonic accumulation zone in NNE direction, with the mantle geochemical characteristics of high concentrations
of C02 and He, high3He/4He-40Ar/36Ar ratio system and high δ13Coo2 ratios (the main frequency, -3.4%— 4.6%), showing no difference from the tectonic framework of the area. In the area, the
tectonic environment is a rift formed as a result of diapiric mantle injection and crust thinning to form graben-type basins
and lithospheric fractures. The mantle-derived volcanic rocks and inclusions are well-developed and a high geothermal zone
(mantlesource) exists in the area. The characteristics of the three components (solid, liquid and gas) of mantle, concentrated
all over the same tectonic space zone, show that the rift system is of a good tectonic environment or passage for mantle degassing
and gas migration. The main types of the gas pools are volcano, fault-block, anticline, buried hill and so on, but most of
them are combination traps closely related with fracture. For the mantle source gas pools, rift is an optimum tectonic region,
and nearby lithospheric fracture, mantle source volcanic rocks or basement uplifts are a favourable structural location when
reservoir-caprock association develops. 相似文献
972.
The focal mechanism solution of the M s 6.5 Wuding earthquake in Yunnan Province of October 24, 1995
The focal mechanism of Wuding earthquake with magnitude M=6.5 on October 24, 1995 is estimated by the method of inversion of seismic tensor in this paper. The two principal axes are
nearly horizontal, the principal compressive axis is about N30°E, the nodal plane which strikes about N105°E (N75°W) is probably
consistent with the actual rupture plane. 相似文献
973.
974.
Fundamental-mode Rayleigh wave attenuation data for stable and tectonically active regions of North America, South America, and India are inverted to obtain several frequency-independent and frequency-dependentQ
models. Because of trade-offs between the effect of depth distribution and frequency-dependence ofQ
on surface wave attenuation there are many diverse models which will satisfy the fundamental-mode data. Higher-mode data, such as 1-Hz Lg can, however, constrain the range of possible models, at least in the upper crust. By using synthetic Lg seismograms to compute expected Lg attenuation coefficients for various models we obtained frequency-dependentQ
models for three stable and three tectonically active regions, after making assumptions concerning the nature of the variation ofQ
with frequency.In stable regions, ifQ
varies as , where is a constant, models in which =0.5, 0.5, and 0.75 satisfy fundamental-mode Rayleigh and 1-Hz Lg data for eastern North America, eastern South America, and the Indian Shield, respectively. IfQ
is assumed to be independent of frequency (=0.0) for periods of 3 s and greater, and is allowed to increase from 0.0 at 3 s to a maximum value at 1 s, then that maximum value for is about 0.7, 0.6, and 0.9, respectively, for eastern North America, eastern South America, and the Indian Shield. TheQ models obtained under each of the above-mentioned two assumptions differ substantially from one another for each region, a result which indicates the importance of obtaining high-quality higher-mode attenuation data over a broad range of periods.Tectonically active regions require a much lower degree of frequency dependence to explain both observed fundamental-mode and observed Lg data. Optimum values of for western North America and western South America are 0.0 if is constant (Q
is independent of frequency), but uncertainty in the Lg attenuation data allows to be as high as about 0.3 for western North America and 0.2 for western South America. In the Himalaya, the optimum value of is about 0.2, but it could range between 0.0 and 0.5. Frequency-independent models (=0.0) for these regions yield minimumQ
values in the upper mantle of about 40, 70, and 40 for western North America, western South America, and the Himalaya, respectively.In order to be compatible with the frequency dependence ofQ observed in body-wave studies,Q
in stable regions must be frequency-dependent to much greater depths than those which can be studied using the surface wave data available for this study, andQ
in tectonically active regions must become frequency-dependent at upper mantle or lower crustal depths.On leave from the Department of Geophysics, Yunnan University, Kunming Yunnan, People's Republic of China 相似文献
975.
976.
地幔交代作用 总被引:1,自引:0,他引:1
许文良 《吉林大学学报(地球科学版)》1987,(4)
地幔交代作用是地球内部的一种化学变化。从200公里深处由高速喷发带上来的地幔岩块的研究表明,在熔融之前某些含挥发组分的交代矿物已经存在。地幔交代作用的提出,是用以解释硷性岩浆的化学组成和同位素体系变化的原因。硷性岩浆作用广泛的时空分布表明,地幔交代作用是广泛的,并且是长期的一种地质作用。它不仅是引起地幔化学上和氧化还原条件变化的主要因素之一,而且是产生硷性岩浆的理想源区和引起克拉通地区陆壳抬升的动因之一。 相似文献
977.
幔汁(ACOHNS)流体的重大意义 总被引:24,自引:1,他引:24
杜乐天 《大地构造与成矿学》1989,13(1):91-99
详细探讨了幔汁及幔汁活动对地壳中各种地质作用的重大影响,分析幔汁的成分结构,运动方式和对地质作用的控制。 相似文献
978.
本文主要讨论弯窿一火山型攀西裂谷的成因,岩浆深成作用与火山作用过程;弩窿梅
造的发生、发展的演化历史,岩浆分异趋势及双峰式岩浆演化系列及其成因。
攀西裂谷曾经历了岩石圈弯窿一除壳弯窿一次火山弯窿三个发展演化阶段。碱性岩浆作用与
地壳隆开、地慢去气、热流汇聚作用有着密切的成因联系,成弯作用最盛,岩浆碱度最高。随着
陆壳破裂、开放、挥发分散逸,岩浆性质从强碱质一弱碱质一碱酸性转化。
弯窿构造的发展演化阶段有机地控制了岩浆源和二次岩浆房的深度和岩浆演化特点,随着弯
窿构造的发展演化,岩浆活动由深成慢源→中浅成慢源加嵌轻微混染→超浅成壳慢混合源逐渐
演化,因而可以认为:弯窿一火山型裂谷发育的各个阶段,存在有低位→中位→高位的二次岩浆
房.
攀西裂谷属不发育的夭折裂谷,以演化时间长为特点,有利于岩浆深源(二次岩浆房内)结
晶分异、液体不混容性分离作用和陆壳的同化混染作用等得以彻底进行,最终形成“双峰式”岩
浆组合。 相似文献
979.
Liu Guodong 《Pure and Applied Geophysics》1987,125(2-3):465-482
Based on the data from more than 200 MTS sites distributed within different areas of the Chinese continent, general characteristics of upper mantle conductivity have been described. At least two conductive layers have been found in the upper mantle of some areas. The first is thin with a resistivity of a modicum to few tens m; the second one is thicker with a resistivity of one to m. Nearly 300 heat-flow values indicate that there exists an exponential correspondent relationship between a depth of the upper mantle conductive layer with a thickness and an average value of heat flow. Based on the above results, the top depth map of this upper mantle conductive layer has been outlined for parts of the Chinese continent. This conductive layer is basically consistent with the low velocity zone in the upper mantle, and Cenozoic tectonism and current seismicity are significantly related to the variation of depth of the conductive layer in the upper mantle. The possible origins of the conductive layers in the upper mantle have been discussed here. 相似文献
980.
Substitute conductors for electromagnetic response estimates 总被引:3,自引:0,他引:3
Ulrich Schmucker 《Pure and Applied Geophysics》1987,125(2-3):341-367
Various concepts exist to define substitute conductors for empirical response estimates at singular frequencies: Chapman's shell-core model, the Cagniard-Tikhonov apparent resistivity, the Niblett-Bostick and Molochnov transformation, thep
* —z
* transformation. They are all interrelated and assign comparable resistivities to the substitute conductor at a given frequency. Applications to synthetic response data of plane and spherical conductors show under which conditions these substitutions come closest to the model and which influence of source dimensions and Earth's sphericity can be expected.p
* —z
* transformed global response data forS andDst variations demonstrate how substitute conductors may serve as useful guides in inverse procedures. 相似文献