全文获取类型
收费全文 | 4148篇 |
免费 | 904篇 |
国内免费 | 1133篇 |
专业分类
测绘学 | 381篇 |
大气科学 | 335篇 |
地球物理 | 2074篇 |
地质学 | 2097篇 |
海洋学 | 558篇 |
天文学 | 121篇 |
综合类 | 346篇 |
自然地理 | 273篇 |
出版年
2024年 | 8篇 |
2023年 | 39篇 |
2022年 | 85篇 |
2021年 | 153篇 |
2020年 | 170篇 |
2019年 | 190篇 |
2018年 | 178篇 |
2017年 | 153篇 |
2016年 | 220篇 |
2015年 | 231篇 |
2014年 | 231篇 |
2013年 | 274篇 |
2012年 | 252篇 |
2011年 | 312篇 |
2010年 | 262篇 |
2009年 | 278篇 |
2008年 | 282篇 |
2007年 | 335篇 |
2006年 | 293篇 |
2005年 | 265篇 |
2004年 | 244篇 |
2003年 | 192篇 |
2002年 | 183篇 |
2001年 | 141篇 |
2000年 | 150篇 |
1999年 | 141篇 |
1998年 | 134篇 |
1997年 | 124篇 |
1996年 | 116篇 |
1995年 | 109篇 |
1994年 | 108篇 |
1993年 | 73篇 |
1992年 | 59篇 |
1991年 | 54篇 |
1990年 | 33篇 |
1989年 | 36篇 |
1988年 | 24篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有6185条查询结果,搜索用时 781 毫秒
71.
The 2004 Chuetsu earthquakes of Niigata (Japan) triggered numerous landslides, and the most widespread types of landslides
were highly disrupted, relatively shallow slides and soil (debris) flows. This paper presented a method to evaluate slope
instability using Newmark displacement on a pixel-by-pixel basis in a given area. The proposed method was able to integrate
Newmark displacement modeling and Monte Carlo simulations within geographical information systems. In the modeling, an empirical
attenuation relationship was utilized to calculate Arias intensity over this study area, and the variability of geotechnical
parameters was taken into account to calculate coseismic landslide displacement. Before deriving the displacement from related
inputs, the Monte Carlo simulations ran 1,500 times and generated 1,500 displacement values for each grid cell, and then means
and standard deviations of displacement were calculated and probabilistic distributions can be obtained. Finally, given 10 cm
as a threshold value of displacement, estimated probabilities of displacement exceeding 10 cm were shown as a map of seismic
landslide hazards. The resulting hazard map was classified into four categories from very low to high level. 相似文献
72.
73.
针对野外数据采集参数对分辨率的影响,对资料处理过程中静校正、反褶积、速度分析、Q补偿及谱白化等几个重要模块原理进行分析,指出在高速岩层中数据采集,应采用小药量激发,小道距,小排列,全三维,不组合、单点数字检波器接收。高密度多点采集,能够充分保护有效地质信息的高频成份,在更大范围内满足高分辨地震勘探的要求。资料处理过程中,在保证同相叠加和高信噪比的前提下,采用提高分辨率的模块以弥补地震波在传播过程中损失的高频成份。实践证明通过高保真、宽频带数据采集和高信噪比前提下的高分辨率数据处理,完全能够为矿井采掘提供高精度地震勘探资料。 相似文献
74.
利用傅立叶变换红外光谱(FTIR)分析技术,对乌达矿区低温氧化和新鲜煤样进行了红外光谱测试,通过两类煤样的特征官能团吸光度的对比分析.揭示了煤在氧化前后特征官能团的变化规律:氧化后的煤样中脂肪族和芳烃CH减少,酸酐C=O从无到有,芳烃骨架C=C基本不变,进而研究了其对煤自燃倾向性的影响。结果表明脂肪族和羟基含量越高,煤自燃倾向性越大。 相似文献
75.
76.
Hitoshi Oda 《Pure and Applied Geophysics》1996,147(4):719-727
By applying the perturbation theory to theXYZ algorithm (a kind of variational method), the difference f in free vibration frequencies between sphere and ellipsoid was approximated as
, where i and
i
(i = x,y andz) (i=x, y andz) are aspherical coefficients and asphericities of the ellipsoid, respectively. We developed an analytic method to compute the aspherical coefficients719-4 by using theXYZ algorithm. A numerical example was given for an ellipsoidal olivine, and an attempt was made to estimate the asphericities of the specimen by a least-squares method, based on the relationship between frequency shift and asphericity. 相似文献
77.
Rabindra Kumar Bhattacharyya 《Pure and Applied Geophysics》1996,146(3-4):677-688
In this paper the smooth perturbation technique is employed to investigate the problem of reflection of waves incident on the plane boundary of a semi-infinite elastic medium with randomly varying inhomogeneities. Amplitude ratios have been obtained for various types of incident and reflected waves. It has been shown that an incidentSH orSV type of wave gives rise to reflectedSH, P andSV waves, the main components beingSH andP, SV in the respective cases. The reflected amplitudes have been calculated depending upon the randomness of the medium to the square of the small quantity , where measures the deviation of the medium from homogeneity. An incidentP-type wave produces mainly aP component and also a weakSH component to the order of 2. The reflected amplitudes obtainable for elastic media are also altered by terms of the same order. The direction of the reflected wave is influenced by randomness in some cases. 相似文献
78.
We numerically study the dynamic interaction of propagating cracks. It is assumed that propagating cracks can nucleate and drive subsidiary cracks because of shear strain enhancement near the propagating crack tips. The critical strain fracture criterion is assumed in the analysis. Intense interaction is expected to occur among the cracks. All the cracks are assumed to be parallel and antiplane strain deformation is assumed in the computation.In the interaction of two non-coplanar cracks, a strain shadow is formed in the neighborhood of each crack because of the strain release by the introduction of the crack. The growth of each crack is accelerated when the propagating tips of each crack are outside of the strain shadow of the other crack. In general, the crack tips enter the strain shadow, and the crack tips decelerate. The calculation shows that only one of the two cracks can continue to grow, and the other's growth is decelerated and arrested. If we can assume that the suite of cracks interact in a pairwise manner only, then this may suggest that only a limited number of cracks can continue to grow during the final stage of the rupture process. Hence the crack interaction causes complexity in dynamic earthquake faulting. The concepts of barrier and asperity have been employed by many researchers for the interpretation of complex seismic wave data. However, the physical realities of such concepts are obscure. Our calculations show that dynamic crack interactions can produce barriers and asperities in some cases; the crack tip deceleration or arrest due to the interactions among non-coplanar cracks can be interpreted as being due to a barrier. The dynamic coalescence among the coplanar cracks can be regarded as an asperity.Umeda found a localized area that strongly radiates high-frequency seismic waves in the epicentral areas of some large shallow earthquakes. He defined this as an earthquake bright spot. Our analysis implies that only a limited number of cracks continue to grow when many interactive cracks nucleate, and that all other cracks stop extending soon after nucleation. Hence, if the nucleation and termination of several cracks occur in a localized area, it will be observed seismologically as an earthquake bright spot. This is because it is theoretically known that the sudden termination of crack growth and dynamic crack coalescence efficiently emits high-frequency elastic waves. 相似文献
79.
Donald G. Isaak Earl K. Graham Jay D. Bass Hong Wang 《Pure and Applied Geophysics》1993,141(2-4):393-414
We present new elasticity measurements on single-crystal fayalite and combine our results with other data from resonance, pulse superposition interferometry, and Brillouin scattering to provide a set of recommended values for the adiabatic elastic moduliC
ij and their temperature variations. We use a resonance method (RPR) with specimens that were previously investigated by pulse superposition experiments. The nineC
ij of fayalite are determined from three new sets of measurements. One set of our newC
ij data is over the range 300–500 K. We believe that the relatively large discrep ncies found in someC
ij are due in large part to specimen inhomogeneities (chemical and microstructural) coupled with differences in the way various techniques sample, rather than only systematic errors associated with experimental procedures or in the preparations of the specimens.Our recommendeaC
ij's (GPa) and (C
ij/T)
p
(GPa/K) are:
The resulting values for the isotropic bulk and shear moduli,K
s and , and their temperature derivatives are:K
s=134(4) GPa; =50.7(0.3) GPa; (K
s/T)
p
=–0.024(0.005) GPa/K; and (/T)
p
=–0.013(0.001) GPa/K. An important conclusion is thatK
s increases as the Fe/(Fe+Mg) ratio in olivine is increased. 相似文献
80.