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排序方式: 共有158条查询结果,搜索用时 15 毫秒
101.
永德梯子坡剖面丁家寨组发现早二叠世牙形石 总被引:4,自引:0,他引:4
测制永德县梯子坡剖面时,首次于丁家寨组顶部灰色亮晶生物碎屑灰岩层中发现丰富的早二叠世牙形石。根据牙形石组合,提出丁家寨组上部(至少顶部)存在下二叠统沉积。 相似文献
102.
Y. Shimada M. Okuno Y. Syono M. Kikuchi K. Fukuoka N. Ishizawa 《Physics and Chemistry of Minerals》2002,29(4):233-239
The densification and structural changes in SiO2 glass compressed up to 43.4 GPa by shock experiments are investigated quantitatively by the X-ray diffraction technique.
Direct structural data (average Si–O and Si–Si distances and Si–O–Si angles, coordination number of the Si atom) of these
shock-densified SiO2 glasses have been obtained by analyzing the radial distribution function curves, RDF(r), calculated with X-ray diffraction data. The coordination number of all densified glasses is about 4 and shows almost no
pressure variation. The SiO2 glass has shown density increase of 11% at a shock compression of 26.3 GPa. This density evolution could not be explained
by the coordination change. The reduction of the average Si–O–Si angle (144° at 0 GPa to 136° at 26.3 GPa) obtained from RDF(r) data may account for this density increase. This Si–O–Si angle change may be caused by shrinkage of the network structure
and the increase of small rings of SiO4 tetrahedra. For higher shock pressure, a decrease in the Si–O–Si angle to 140° was observed. This is consistent with the
decrease in density at 32.0 and 43.2 GPa. This decrease in the Si–O–Si angle and density could be attributed to an annealing
effect due to high after-shock residual temperature. This pressure dependence of average Si–O–Si angles in shock-densified
SiO2 glass agrees with the results of our previous Raman spectroscopic study. On the other hand, the pressure variation for the
first sharp diffraction peak (FSDP) was analyzed to estimate the evolution of intermediate range structures. It is suggested
that the mean d value (d
m
) obtained from the position of FSDP strongly depends on the shock and residual temperature, as well as shock pressure.
Received: 29 June 2001 / Accepted: 14 November 2001 相似文献
103.
Bulk, first-order and turbulent kinetic energy (TKE) closure schemes are used to parameterise the boundary-layer physics in a high resolution, limited area model. The model was used to simulate the summer monsoon circulations over India. The domain selected included the monsoon trough over northern India, a region of mesoscale convection. A monsoon depression was present at the time of the simulation. The results indicate that the TKE closure scheme combined with the Monin–Obukhov surface-layer similarity relation provided the best 48-hour simulation of the circulation and the rainfall associated with the monsoon depression. 相似文献
104.
研究了云南地区各类型地震序列的早期地震波动力学特征——地震波垂直分量P波初动和P、S波最大振幅比,结果表明:前震序列振幅比为过原点的直线,比值稳定,P波初动一致;双震型地震序列在第一主震后P波初动出现一组时,仍有一类波形(“大头波”或“小头波”)的振幅比保持为过原点的直线,第一主震后P波初动出现两组时,仍有初动相同的一组地震振幅比保持为过原点的直线,或者两组初动的地震振幅比分别、共同成过原点的直线;主余震地震序列在非大震孕育期间,地震振幅比离散,与大震孕育有关的主余震地震序列振幅比仍可为过原点的直线。地震波动力学特征在上述三类地震序列的早期判断能力分别为75%、55%—73%、90%。 相似文献
105.
变密度界面模型重力异常反演的B样条函数法 总被引:3,自引:0,他引:3
重力异常反演是一个求解第一类非线性积分方程的问题。当三维界面起伏满足│Δh│〈0.414h0和二维界面起伏满足-h0〈Δh〈0.414h0时,积分方程的被积函数可Δh的级级数形式。 相似文献
106.
107.
一个以遗传算法为基础的结构可靠性分析方法 总被引:5,自引:0,他引:5
本文首先总结了一次二阶矩法在结构可靠性分析时的五个弱点。针对其在寻求验算点时需要求极限状态函数的导数以及在处理多峰性极限状态函数时存在的不收敛或收敛于局部验算点等弱点,探讨了将遗传算法应用于结构可靠性分析的可能性,并在分析其应用时存在的具体问题的基础上提出了一个以智能生物为基础的遗传算法。本文的分析计算表明:遗传算法在结构可靠性分析中是适用的,它可以克服一次二阶矩法在求解验算点时存在的几个弱点。本 相似文献
108.
L. Jones 《Stochastic Environmental Research and Risk Assessment (SERRA)》1989,3(3):179-190
The expected head and standard deviation of the head from the first order Taylor series approximation is compared to Monte Carlo simulation, for steady flow in a confined aquifer with transmissivity as a random variable. Emphasis is on the effect of changes in the covariance structure of the transmissivity, and pumping rates, on the errors in the first order Taylor series approximation. The accuracy of the first order Taylor series approximation is found to be particularly sensitive to pumping rates. With significant pumping the approximation is found to under estimate both the expected drawdown and head variance, and the error increases as the pumping rate increases. This can lead to large errors in probability constraints based on moments from the first order Taylor series approximation. 相似文献
109.
First-motion analyses of digital seismic records and an assessment of damage provided conclusive evidence that a fault-slip source mechanism was responsible for a Richter magnitude 2 that occurred at the Lucky Friday Mine on April 13, 1990. This event was the first time that movement along an argillite bed had been observed after the macroseismic monitoring system had been installed. The physical evidence of a shear-slip type failure established confidence in using double-couple, first-motion analyses for the macroseismic system. The U.S. Bureau of Mines is conducting this research as part of its mission to enhance safety by reducing rockburst hazards in mines. 相似文献
110.
地面地震初至波层析反演复杂表层速度结构方法 总被引:1,自引:0,他引:1
针对复杂表层结构的反演问题,作者研究了一套利用地面地震初至波层析反演表层速度结构的理论、方法和软件系统。该方法利用了地面地震直达波、迥折波、折射波以及三者组合的初至波,并采用具有空间变速优势的层析反演,可获得任意介质类型的表层速度结构。该方法的优点是野外施工简单(不需要在井中激发、接收),反演精度高,适应性强,反演所得到的表层速度结构可直接用于环境与工程项目的表层地质结构调查和评价。 相似文献