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281.
由深源远震体波记录反演华北北部地壳上地幔速度结构 总被引:5,自引:2,他引:5
重点研究的地区为河北省北部包括京津地区,以及山西、内蒙的部分地区,在此区选取了29个台站;在向东延伸的背景区,选取了6个台站。利用这些台站的深源远震体波记录资料,通过选取介质结构模型,计算理论地震图,与观测图进行拟合,以确定地震台下介质结构的可接受模型。在拟合时,对每个地震台站都选择若干次深源远震的体波记录作为观测图。对每个地震台站一般都算出60个不同模型的理论图。实际上做出的结果比地壳深,为大约80km(即大致相当于岩石层或称岩石圈)厚度内的地壳上地幔介质结构,它们大都由10层左右的介质组成。通过波形拟合共给出了上述35个台站下的壳幔介质分层结构。并由此给出了Moho面的轮廓。 相似文献
282.
对华北地区韧性剪切带几种代表上、中、下地壳深度的糜棱岩及其围岩在高温高压条件下进行纵波速度测定及各向异性研究.对实验样品的纵波速度测定得到以下结果:1.沿糜棱岩面理方向的纵波速度大于与面理垂直方向的纵波速度,差值为0.15-0.30km/s,各向异性为3%-5%;2.糜棱岩的纵波速度低于其围岩的纵波速度,差值为0.10-0.45km/s;3.中地壳角闪岩相糜棱岩的纵波速度各向异性高于上地壳绿片岩相糜棱岩和下地壳麻粒岩相糜棱岩的各向异性;4.地震波速各向异性与糜棱岩矿物优选定向有关. 相似文献
283.
284.
Roberto Scarpa 《Pure and Applied Geophysics》1982,120(3):583-606
Jeffreys-Bullen P and PKP travel-time residuals observed at more than 50 seismic stations distributed along Italy and surrounding areas in the time interval 1962–1979, indicate the complex velocity pattern of this region. Strong lateral velocity inhomogeneities and low velocity zones are required to explain the observed pattern of residuals. In particular, late arrivals of about 1 sec are observed in the Apenninic mountain range, requiring both greater crustal thickness and low velocity layers, coherent with seismic refraction data and surface wave dispersion measurements. The seismic stations located in the Western and Eastern Alps indicate the presence of high velocities. In the Western Alps the strong azimuthal variation of residuals and the high values of early arrivals have a close relationship to the Ivrea body, an intrusive crustal complex characterized by a velocity as high as 7–7.2 km/sec.A travel-time inversion performed with theAki
et al. (1977) block model, confirms the peculiar characteristics and the sharp variations in the lithosphere of the whole Italian region, with values of velocity perturbations between many adjacent blocks, ranging in size from 50 to 100 km, and independent from the earth parametrization chosen, reaching values up to 10% in the lithospheric part and 5% in the asthenosphere. 3-D inversion requires also high velocity along the Tyrrhenian coastal margin, equivalent to an uprise of major crustal and lithospheric discontinuities along this part of the Italian peninsula. Moreover low velocity material must be present in the northern part of the Adriatic foreland, in the lithosphere-asthenosphere system, closely related to the stress and seismicity pattern, and the lateral bending of the lithosphere in the same region. 相似文献
285.
286.
287.
第三系红层中石膏溶蚀特性及其对工程的影响 总被引:2,自引:0,他引:2
第三系红层中石膏分布比较广泛,大量的实验证明,石膏发生溶蚀的主要是含Ca2 的物质,并且溶蚀速率和与水接触的方式以及水头压力大小有直接关系。结合现场资料,将渗透系数K=10-5cm s作为石膏在第三系红层泥岩封闭下发生溶蚀的判据。同时针对水利工程中石膏溶蚀以及对砼的腐蚀性提出了相应的防治措施。 相似文献
288.
Summary. Conventional blasting causes cracks and fractures in the rock. Controlled blasting techniques produce the macrocrack in a
desired direction and eliminate microcrack in the remaining rock. Macrocrack development in desired direction is required
for extraction of dimensional stone and at the same time there is need to reduce microcrack development in the block and remaining
rock. To achieve the objectives, experimental work in the quarries was carried out for separating marble block from the in
situ strata as practiced in some of the Indian mines by using detonating cord of 30 to 50 g/m by varying hole spacing, hole
diameter, air cushioning, water and sand filled blast-holes. Blasthole notching was carried out. Further, tests were carried
out by using various liners inside the blasthole to determine the damages in the extracted block and remaining rock. The designed
experimental work was undertaken and rock samples were collected by coring before and after blasting for quantification of
microcrack in the rock. P-wave velocity and microscopic studies were conducted for quantification of damages. Experiments
were also conducted at laboratory scale for the quantification of damages in single circular and notched holes with variation
of stemming and liners. The P-wave velocity close to hole always reduces after blast and in case of NG-based charge and detonating
cord it decreases up to 1/3rd. With PVC pipe and paper tube liners decrease is negligible. Thus, by using notched hole with paper tube, decrease in P-wave
is minimum indicating least damage. 相似文献
289.
Sokrat Amataj Todor Anovski Ralf Benischke Romeo Eftimi Laurence L. Gourcy Liliana Kola Ioannis Leontiadis Eftim Micevski Alqiviadis Stamos Jovan Zoto 《Environmental Geology》2007,51(5):749-753
Prespa Lake and Ohrid Lake constitute a hydraulic system shared between Albania, FYR of Macedonia and Greece. Karst rocks
separate both lakes. The elevation of Prespa Lake is about 150 m higher than that of Ohrid Lake. Considering these facts,
Cvijić formulated in 1906 the hypothesis that Prespa Lake recharges the St. Naum and Tushemisht springs at Ohrid lakeside.
Environmental isotopes demonstrated that Prespa Lake recharges about 37–42 and 52–54% of water emerging in St. Naum, and Tushemisht
springs, respectively. An artificial tracer experiment carried out in 2002 physically demonstrated the underground connection
between both lakes. This experiment confirmed the supposed underground connection and brought important information about
the groundwater velocity, transit time, and karst water conduits development. 相似文献
290.
M. D. Sharma 《Journal of Earth System Science》2007,116(4):357-367
Anisotropic wave propagation is studied in a fluid-saturated porous medium, using two different approaches. One is the dynamic
approach of Biot’s theories. The other approach known as homogenisation theory, is based on the averaging process to derive
macroscopic equations from the microscopic equations of motion. The medium considered is a general anisotropic poroelastic
(APE) solid with a viscous fluid saturating its pores of anisotropic permeability. The wave propagation phenomenon in a saturated
porous medium is explained through two relations. One defines modified Christoffel equations for the propagation of plane
harmonic waves in the medium. The other defines a matrix to relate the relative displacement of fluid particles to the displacement
of solid particles. The modified Christoffel equations are solved further to get a quartic equation whose roots represent
complex velocities of the four attenuating quasi-waves in the medium. These complex velocities define the phase velocities
of propagation and quality factors for attenuation of all the quasi-waves propagating along a given phase direction in three-dimensional
space. The derivations in the mathematical models from different theories are compared in order to work out the equivalence
between them. The variations of phase velocities and attenuation factors with the direction of phase propagation are computed,
for a realistic numerical model. Differences between the velocities and attenuations of quasi-waves from the two approaches
are exhibited numerically. 相似文献