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251.
Short-term and intermediate-term geochemical precursors 总被引:2,自引:0,他引:2
Detection of precursory phenomena in observation data is essential to earthquake prediction studies. Continuous monitoring of radon concentration in groundwater in Japan in one case showed a short-term anomaly related to a nearby earthquake. With the exception of the 1978 Izu-Oshimakinkai earthquake (M7.0), however, no abnormal change has been noted. This may be due partially to difficulty in detecting insignificant precursory signals from observation data, which ordinarily contains a noise-induced fluctuations, and partially to lack of understanding of the mechanism controlling the appearance of precursory phenomena. In order to increase our knowledge of the variation pattern of precursory changes in radon concentration of groundwater, hydrologic precursors with significant features are examined in this paper. Complexity of appearance of precursory phenomena and problems in assignment of the specific earthquake are discussed. 相似文献
252.
Changping Zhang Yuji Murayama 《International journal of geographical information science》2013,27(7):681-692
The analysis of local spatial autocorrelation for spatial attributes has been an important concern in geographical inquiry. In this paper, we propose a concept and algorithm of k-order neighbours based on Delaunay's triangulated irregular networks and redefine Getis and Ord's (1992) local spatial autocorrelation statistic as Gi(k) with weight coefficient wij(k) based on k-order neighbours for the study of local patterns in spatial attributes. To test the validity of these statistics, an experiment is performed using spatial data of the elderly population in Ichikawa City, Chiba Prefecture, Japan. The difference between the weight coefficients of the k-order neighbours and distance parameter to measure the spatial proximity of districts located in the city centre and near the city limits is found by Monte-Carlo simulation. 相似文献
253.
Kondwani G. Munthali Yuji Murayama 《International journal of geographical information science》2013,27(10):1881-1895
Subsistence agriculture continues to be the mainstay activity in most tropical regions, and opinions on how it impacts tropical deforestation vary significantly. The sparse literature available on subsistence farm-based models highlights the existing methodological gap in the ability of present-day agent-based models (ABMs) to simulate the impact of subsistence production on frontier tropical deforestation. Though issues concerning agent specification and its variability have been successfully dealt with, gaps exist in the explicit incorporation and articulation of linkages of subsistence production and consumption theories on the one hand and frontier tropical deforestation on the other hand. This demands explicit determination of the decision-making process and the objective functions for subsistence farmers. Once simulated, the trajectories of deforestation and its trigger mechanisms can be understood. Overall, farm-based ABMs have the potential to allow insightful understanding of the small and slow individual homogeneous subsistence practices that have resulted in massive deforestation in the tropics. 相似文献
254.
Abstract— U, Th, and Pb isotopes and rare earth elements (REEs) in individual phosphate grains from martian meteorites Lafayette and Yamato‐000593/000749 were measured using a sensitive high‐resolution ion microprobe (SHRIMP). Observed U‐Pb data of 12 apatite grains from Yamato (Y‐) 000593/000749 are well represented by linear regressions in both “conventional” 2D isochron plots and the 3D U‐Pb plot (total Pb/U isochron), indicating that the formation age of this meteorite is 1.53 ± 0.46 Ga (2σ). On the other hand, the data of nine apatite grains from Lafayette are well represented by planar regression rather than linear regression, indicating that its formation age is 1.15 ± 0.34 Ga (2σ) and that a secondary alteration process slightly disturbed its U‐Pb systematics as discussed in the literature regarding Nakhla. The observed REE abundance patterns of the apatites in Lafayette and Yamato‐000749, normalized to CI chondrites, are characterized by a progressive depletion of heavy REEs (HREEs), a negative Eu anomaly, similarity to each other, and consistency with previously reported data for Nakhla. Considering the extensive data from other radiometric systems such as Sm‐Nd, Rb‐Sr, Ar‐Ar, and trace elements, our results suggest that the parent magmas of the nakhlites, including the newly found Y‐000593/000749, are similar and that their crystallization ages are ?1.3 Ga. 相似文献
255.
We present the rest-frame colour–magnitude diagram for 35 early-type galaxies in the Hubble Deep Field with median redshift
0.9.Although with considerable scatter, a red sequence well described by the passive evolution of an intrinsically old stellar
population is observed. Comparison with the passively evolved colour–magnitude relation of the rich Coma Cluster (z = 0.023) indicates that at least ∼1/2 of the early-type galaxies in the field at this redshift are as old as those in rich
clusters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
256.
257.
258.
Naoto Takahata Yuji Sano Keika Horiguchi Kotaro Shirai Toshitaka Gamo 《Journal of Oceanography》2008,64(2):293-301
We have collected fifty-five seawater samples at seven stations at various depths in the Yamato and Japan Basins of the Japan
Sea and measured their helium isotopic ratios. The 3He/4He ratios vary from 0.997 Ratm to 1.085 Ratm where Ratm is the atmospheric ratio. The maximum 3He excesses about 8%, are observed at mid-depth (1000 m), and these values are significantly lower than those observed in
deep Pacific waters. This implies that mantle-derived helium in deep Pacific water cannot enter the Japan Sea since it is
an almost landlocked marginal sea. The observed 8% excess 3He may be attributable to the decay product of tritium. Slightly higher 3He/4He ratios in the Bottom Water were observed in the Yamato Basin than in the Japan Basin. The ventilation ages of seawater
shallower than 1000 m are calculated as about 5 to 20 years, which is consistent with the CFC ages reported in the literature.
There is a positive correlation between the apparent oxygen utilization and 3H-3He ages. The estimated oxygen utilization rate from the correlation in a layer between 500 m and 1000 m is about 3 μmol/kg/yr, which is similar to that in the eastern subtropical North Atlantic. 相似文献
259.
从断层时间尺度、活动性、场地效应等方面阐述跨断层桥梁的定义与内涵;从"功能性"、"制约性"、"地表破裂变异性"、"设计缺陷"4方面分析跨断层桥梁"不得不"面临较大的地震破坏风险的原因;最后以1979年Imperial Valley地震中El Centro台阵收集到的强震记录为基础,对断层破裂强震记录特征及地震动传播机理进行分析,研究断层两侧地面运动分布规律,建议跨走滑断层桥梁的地震动输入方向。本文研究结果对促进跨断层桥梁抗震设防具有借鉴意义。 相似文献
260.