全文获取类型
收费全文 | 449篇 |
免费 | 15篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 28篇 |
地球物理 | 124篇 |
地质学 | 157篇 |
海洋学 | 36篇 |
天文学 | 76篇 |
综合类 | 1篇 |
自然地理 | 33篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 20篇 |
2017年 | 20篇 |
2016年 | 24篇 |
2015年 | 27篇 |
2014年 | 17篇 |
2013年 | 23篇 |
2012年 | 27篇 |
2011年 | 24篇 |
2010年 | 17篇 |
2009年 | 35篇 |
2008年 | 23篇 |
2007年 | 25篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 7篇 |
2003年 | 9篇 |
2002年 | 15篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 8篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1971年 | 2篇 |
1968年 | 1篇 |
1951年 | 1篇 |
1922年 | 1篇 |
排序方式: 共有467条查询结果,搜索用时 15 毫秒
191.
Leone Melluso Ciro Cucciniello Chiara M. Petrone Michele Lustrino Vincenzo Morra Massimo Tiepolo Lopo Vasconcelos 《Journal of African Earth Sciences》2008,52(4-5):139-151
The Karoo volcanic sequence in the southern Lebombo monocline in Mozambique contains different silicic units in the form of pyroclastic rocks, and two different basalt types. The silicic units in the lower part of the Lebombo sequence are formed by a lower unit of dacites and rhyolites (67–80 wt.% SiO2) with high Ba (990–2500 ppm), Zr (800–1100 ppm) and Y (130–240 ppm), which are part of the Jozini–Mbuluzi Formation, followed by a second unit, interlayered with the Movene basalts, of high-SiO2 rhyolites (76–78 wt.%; the Sica Beds Formation), with low Sr (19–54 ppm), Zr (340–480 ppm) and Ba (330–850 ppm) plus rare quartz-trachytes (64–66 wt.% SiO2), with high Nb and Rb contents (240–250 and 370–381 ppm, respectively), and relatively low Zr (450–460 ppm). The mafic rocks found at the top of the sequence are basalts and ferrobasalts belonging to the Movene Formation. The basalts have roughly flat mantle-normalized incompatible element patterns, with abundances of the most incompatible elements not higher than 25 times primitive mantle. The ferrobasalt has TiO2 4.7 wt.%, Fe2O3t = 16 wt.%, and high Y (100 ppm), Zr (420 ppm) and Ba (1000 ppm). The Movene basalts have initial (at 180 Ma) 87Sr/86Sr = 0.7052–0.7054 and 143Nd/144Nd = 0.51232, and the Movene ferrobasalt has even lower 87Sr/86Sr (0.70377) and higher 143Nd/144Nd (0.51259). The silicic rocks show a modest range of initial Sr-(87Sr/86Sr = 0.70470–0.70648) and Nd-(143Nd/144Nd = 0.51223–0.51243) isotope ratios. The less evolved dacites could have been formed after crystal fractionation of oxide-rich gabbroic cumulates from mafic parental magmas, whereas the most silica-rich rhyolites could have been formed after fractional crystallization of feldspars, pyroxenes, oxides, zircon and apatite from a parental dacite magma. The composition of the Movene basalts imply different feeding systems from those of the underlying Sabie River basalts. 相似文献
192.
193.
Evolution of an early Eocene pull‐apart basin in the Central Pontides (Northern Turkey): New insights into the origin of the North Anatolian Shear Zone
下载免费PDF全文
![点击此处可从《地学学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Giuseppe Ottria Luca Pandolfi Rita Catanzariti Simone Da Prato Alessandro Ellero Chiara Frassi Mehmet Cemal Göncüoğlu Michele Marroni Leonardo Ruffini Kaan Sayit 《地学学报》2017,29(6):392-400
Although the North Anatolian Shear Zone is one of the main lithospheric‐scale strike‐slip deformation zone in the world, playing a prominent role in the complex geodynamic interaction among the Eurasian, Anatolian and Arabian plates, the onset time of its activity remains highly controversial. Here, we tackle this issue by utilizing nannofossil biostratigraphy on deposits from the Ta?cilar basin, a pull‐apart basin that we have identified inside the North Anatolian Shear Zone overprinting the Intra‐Pontide suture zone. The syn‐tectonic sedimentary succession of the Ta?cilar basin developed completely during the early Eocene (Ypresian; CNE4–CNE5 Zones). The strike‐slip faulting related to the initial onset of the North Anatolian Shear Zone can likely be constrained within the Ypresian, suggesting that the westward escape of the Anatolian plate along the North Anatolian Shear Zone started in the early Eocene. 相似文献
194.
195.
Chiara Origliasso Marilena Cardu Vladislav Kecojevic 《Rock Mechanics and Rock Engineering》2014,47(2):757-770
The purpose of this research was to evaluate the production rate (PR) and cutting performance of surface miners (SM) based on rock properties and specific energy (SE). We use data from equipment manufacturers and experimental data in this study and propose a new method and equations to determine both the PR and the cutting speed of SM. The unconfined compressive strength (UCS) of the rock, its abrasivity, and the machine’s engine power are the three most important factors influencing the PR. Moreover, the cutting depth, UCS, and engine power have a significant impact on the cutting speed. We propose a new method and equations to determine the energy required to cut a volume unit and a surface unit, i.e., specific energy, and establish the relationship between SE, UCS, and PR. The results of this study can be used by surface miner operators to evaluate the applicability of the machines to a specific mine site. 相似文献
196.
Validation of theoretical footprint models using experimental measurements of turbulent fluxes over maize fields in Po Valley 总被引:1,自引:0,他引:1
Representative source area of turbulent fluxes measured by eddy covariance stations is an important issue which has not yet been fully investigated. In particular, the validation of the analytical footprint models is generally based on the comparison with Lagrangian model predictions, while experimental results are not largely diffused in literature. In this work, spatial distribution of carbon dioxide, latent and sensible heat fluxes across two different maize fields in Po Valley, is used to validate two theoretical footprint models. Experiments are performed in two totally different scenarios at bare and vegetated soils using two eddy covariance systems: one fixed station which is located about in the middle of the field and a mobile station which is placed at various distances from the field edge to investigate the horizontal variation of the vertical scalar fluxes. The first objective of this work is to provide detailed information about the spatial distribution of turbulent fluxes across Po Valley characteristic fields at bare and vegetated soils, highlighting peculiarities and uniqueness. The second objective consists in the comparison between mobile measurements of carbon dioxide, latent and sensible heat fluxes and the predictions of two analytical footprint models widely used in literature. Contemporaneously, the latter objective will permit to understand what is the best footprint model which, under typical Po Valley atmospheric turbulent conditions, describes a representative source area compatible with the field dimensions and the turbulent flux distributions. The results show that both models are in good agreement with experimental measurements. The results also show that the spatial distribution of turbulent fluxes is strongly influenced by the presence of vegetation in the field. Moreover, the representative source area is different for different scalar fluxes. Another result is about 10:1 fetch-to-height obtained for both field situations. 相似文献
197.
Orogens and rift zones have a finite number of regional faults. The accretionary prisms analysed here have a number of thrusts < 50, whereas extensional areas have a number of normal faults ranging between six and 44. The average spacing of thrusts is between 5 and 25 km; spacing of normal faults is more restricted into two peaks, at 25–29 km and 4–6 km, in which the latter is the most common. The number and spacing of faults appear to be mainly controlled by the depth of the decollement plane, which seems to be more variable in compressive settings with respect to rift zones. Basement‐involved orogens present fewer and more spaced thrusts; by contrast, a greater number of thrusts with shorter spacing characterize thin‐skinned thrust belts. The shallower the decollement is, the stronger it appears to control the palaeogeography, in the sense of rheological lateral variations in the sedimentary cover. 相似文献
198.
199.
Riccardo Campana Mauro Orlandini Ettore Del Monte Marco Feroci Filippo Frontera 《Experimental Astronomy》2014,37(3):599-613
Low-inclination, low altitude Earth orbits (LEO) are of increasing importance for astrophysical satellites, due to their low background environment. Here, the South Atlantic Anomaly (SAA) is the region with the highest amount of radiation. We study the radiation environment in a LEO (500–600 km altitude, 4° inclination) through the particle background measured by the Particle Monitor (PM) experiment onboard the BeppoSAX satellite, between 1996 and 2002. Using time series of particle count rates measured by PM we construct intensity maps and derive SAA passage times and fluences. The low-latitude SAA regions are found to have an intensity strongly decreasing with altitude and dependent on the magnetic rigidity. The SAA extent, westward drift and strength vs altitude is shown. 相似文献