全文获取类型
收费全文 | 6475篇 |
免费 | 1547篇 |
国内免费 | 1849篇 |
专业分类
测绘学 | 79篇 |
大气科学 | 244篇 |
地球物理 | 2016篇 |
地质学 | 6192篇 |
海洋学 | 857篇 |
天文学 | 63篇 |
综合类 | 238篇 |
自然地理 | 182篇 |
出版年
2024年 | 65篇 |
2023年 | 135篇 |
2022年 | 298篇 |
2021年 | 290篇 |
2020年 | 295篇 |
2019年 | 378篇 |
2018年 | 325篇 |
2017年 | 374篇 |
2016年 | 451篇 |
2015年 | 371篇 |
2014年 | 458篇 |
2013年 | 455篇 |
2012年 | 426篇 |
2011年 | 485篇 |
2010年 | 358篇 |
2009年 | 462篇 |
2008年 | 440篇 |
2007年 | 385篇 |
2006年 | 410篇 |
2005年 | 384篇 |
2004年 | 308篇 |
2003年 | 314篇 |
2002年 | 293篇 |
2001年 | 231篇 |
2000年 | 234篇 |
1999年 | 170篇 |
1998年 | 200篇 |
1997年 | 150篇 |
1996年 | 142篇 |
1995年 | 122篇 |
1994年 | 100篇 |
1993年 | 76篇 |
1992年 | 63篇 |
1991年 | 43篇 |
1990年 | 32篇 |
1989年 | 21篇 |
1988年 | 39篇 |
1987年 | 11篇 |
1986年 | 20篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有9871条查询结果,搜索用时 15 毫秒
1.
鄂尔多斯盆地黄陵、东胜地区地温场对比 总被引:2,自引:0,他引:2
鄂尔多斯盆地黄陵、东胜铀矿区分别处于盆地南部渭北隆起的北侧边缘和盆地北部伊盟隆起的东部,赋矿层位都是中侏罗统直罗组。盆地南、北铀矿区在现今地温场及古地温场都存在明显差异,南部现今大地热值及热演化程度明显高于北部。对于下侏罗统延安组和石炭—二叠系煤层,黄陵地区镜质体反射率都高于东胜地区。通过镜质体反射率资料得出同一埋深的一套地层经历的最大古地温和对应的古地温梯度也有南部高于北部的现象。由于早白垩世后期盆地普遍整体抬升使得现今地温相对古地温降低,南部黄陵地区抬升剥蚀量大于北部东胜地区,导致古、今地温差异也大于后者。盆地南部庆阳—富县一带局部构造热运动,导致南部异常地温场的形成,使得南部热演化程度高于北部。 相似文献
2.
3.
Absorption of solar radiation within the thermal molecular sublayer of the ocean can modify the temperature difference across the cool skin as well as the air-sea gas transfer. Our model of renewal type is based on the assumption that the thermal and diffusive molecular sublayers below the ocean surface undergo cyclic growth and destruction, the heat and gas transfer between the successive burst events are performed by molecular diffusion. The model has been upgraded to include heating due to solar radiation. The renewal time is parameterized as a function of the surface Richardson number and the Keulegan number. A Rayleigh number criterion characterizes the convective instability of the cool skin under solar heating. Under low wind speed conditions, the solar heating can damp the convective instability, strongly increasing the renewal time and correspondingly decreasing the interfacial gas exchange. In the ocean, an additional convective instability caused by salinity flux due to evaporation becomes of importance in such cases. The new parameterization is compared with the cool skin data obtained in the western equatorial Pacific during the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment in February 1993. In combination with a model of the diurnal thermocline it describes main features of the field data both in nighttime and daytime. Under low wind speed conditions (< 5 m s-1) diurnal variations of the sea surface temperature due to the formation of a diurnal thermocline were substantially larger than those across the cool skin. Under wind speeds > 5 m s-1, diurnal variations of the surface temperature due to the variations of the thermal molecular sublayer become more important. 相似文献
4.
F. Bella P. F. Biagi M. Caputo G. Della Monica A. Ermini P. V. Manjgaladze V. Sgrigna D. O. Zilpimiani 《Pure and Applied Geophysics》1995,144(2):277-300
Daily averaged tilt component data from two sites of the Central Apennines (Italy) and of the Southern Caucasus (Georgia), respectively, revealed intermediate-term tilts as possible precursors to earthquakes (M=3.0÷4.7) which occurred in the above-mentioned seismic areas within a distance of 50 km from the sites. A good temporal correlation as well as a fair spatial correspondence between these residual tilts (with amplitude and duration of some microradians and months, respectively) and main shocks were pointed out, by removing both secular trends and seasonal thermoelastic effects from the raw tilts. An attempt was made to justify the above-mentioned results, based on the assumption that the observed intermediate-term preseismic tilts are the manifestation of aseismic creep episodes of comparable duration in the fault materials of thrust faults close to the tilt sites. The mechanism refers to a strain field slowly propagating from the preparation focal area to the tilt site, through crustal blocks separated by weak transition zones. This propagation is thought to be the cause of the local aseismic fault slip recorded by the tiltmeters. Previously, both discrete structures and strain propagation effects were revealed in the Central Apennines and are thought also to exist in the Southern Caucasus. As in the past, the rheological properties of fault materials are revealed as viscoelastic ones. In fact, creep equations obtained by applying several viscoelastic models on our data, proved to fit quite well some of the observed tilt precursors, producing viscosity and rigidity values very similar to those reported in literature.Professor Petr Viktorovich Manjgaladze died during the writing of this paper 相似文献
5.
矿井瓦斯危险程度与煤层中瓦斯赋存状况及其泄出方式有关,并取决于多种地质条件和采掘工艺。其中,煤特征条件特别重要。本文分析了湖南省的5种矿井瓦斯危险类型以及相应的煤特征条件,提出了“煤特征指数(I_c)”这一概念。I_c是一项评价矿井瓦斯危险程度的综合指标。研究表明,矿井瓦斯危险愈严重,则其I_c值愈高。应用该项成果预测了16对矿井的瓦斯危险类型,取得了满意的效果。 相似文献
6.
This paper reviews the data concerning the fracture network and the hydraulic characteristics of faults in an active zone of the Gulf of Corinth. Pressure gap measured through fault planes shows that in this area the active normal faults (Aigion, Helike) act, at least temporarily and locally, as transversal seal. The analysis of the carbonate cements in the fractures on both the hangingwall and the footwall of the faults also suggests that they have acted as local seals during the whole fault zone evolution. However, the pressure and the characteristics of the water samples measured in the wells indicate that meteoric water circulates from the highest part of the relief to the coast, which means it goes through the fault zones. Field quantitative analysis and core studies from the AIG-10 well have been performed to define both regional and fault-related fracture networks. Then laboratory thin section observations have been done to recognize the different fault rocks characterizing the fault zone components. These two kinds of approach give information on the permeability characteristics of the fault zone. To synthesize the data, a schematic conceptual 3D fluid flow modeling has been performed taking into account fault zone permeability architecture, sedimentation, fluid flow, fault vertical offset and meteoric water influx, as well as compaction water flow. This modeling allows us to fit all the data with a model where the fault segments act as a seal whereas the relays between these segments allow for the regional flow from the Peloponnese topographic highs to the coast. 相似文献
7.
lvaro Gonzlez Miguel Vzquez-Prada Javier B. Gmez Amalio F. Pacheco 《Tectonophysics》2006,424(3-4):319
Numerical models are starting to be used for determining the future behaviour of seismic faults and fault networks. Their final goal would be to forecast future large earthquakes. In order to use them for this task, it is necessary to synchronize each model with the current status of the actual fault or fault network it simulates (just as, for example, meteorologists synchronize their models with the atmosphere by incorporating current atmospheric data in them). However, lithospheric dynamics is largely unobservable: important parameters cannot (or can rarely) be measured in Nature. Earthquakes, though, provide indirect but measurable clues of the stress and strain status in the lithosphere, which should be helpful for the synchronization of the models.The rupture area is one of the measurable parameters of earthquakes. Here we explore how it can be used to at least synchronize fault models between themselves and forecast synthetic earthquakes. Our purpose here is to forecast synthetic earthquakes in a simple but stochastic (random) fault model. By imposing the rupture area of the synthetic earthquakes of this model on other models, the latter become partially synchronized with the first one. We use these partially synchronized models to successfully forecast most of the largest earthquakes generated by the first model. This forecasting strategy outperforms others that only take into account the earthquake series. Our results suggest that probably a good way to synchronize more detailed models with real faults is to force them to reproduce the sequence of previous earthquake ruptures on the faults. This hypothesis could be tested in the future with more detailed models and actual seismic data. 相似文献
8.
This paper presents results of high-resolution deep seismic reflection profiling of the Proterozoic Vindhyan basin of the
Rajasthan area along the Chandli-Bundi-Kota-Kunjer profile. Seismic images have been used to estimate the thickness of Vindhyan
strata as well as to understand the tectonic framework of the basin. The results are constrained by gravity, magnetic and
magnetotelluric data. The study reveals gentle SE-dipping reflection bands representing the Vindhyan strata. The seismic sections
depict gradual thickening of the Vindhyan succession towards southeast from Bundi. The velocities of the upper and lower Vindhyans
are identified as 4.6-4.8 km/s and 5.1-5.3 km/s. The NW limit of the Vindhyan basin is demarcated by the Great Boundary Fault
(GBF) that manifests as a 30 km wide NW dipping thrust fault extending to a depth of 30 km. 相似文献
9.
库车坳陷侏罗系煤成气动力学模拟研究 总被引:1,自引:0,他引:1
应用黄金管—高压釜封闭体系热模拟实验与GC、GC-IRMS分析技术,结合KINETICS专用软件,对库车坳陷侏罗系煤成气进行了动力学模拟研究。库车坳陷侏罗系煤具有高的产气性,在高演化阶段主要产甲烷气;侏罗系煤热解气甲烷碳同位素为-36‰~-25‰,乙烷碳同位素为-28‰~-16‰;甲烷、C2-C5气态烃的生成活化能分别为(47~64k)calm/ol、(55~72k)calm/ol,频率因子各为5.265×1013s-1、5.388×1018s-1。在此基础上,进一步探讨了克拉2气田天然气的成因。研究认为,克拉2气田天然气属阶段捕获的煤成气,主要聚集了5~1Ma时期的天然气,其成熟度Ro分布范围为1.3%~2.5%。 相似文献
10.
山西沁水盆地煤层气成藏的微观动力能条件研究 总被引:2,自引:4,他引:2
煤层气成藏的微观动力能条件主要包括煤储层的孔隙—裂隙系统、煤储层的生气作用和储气作用两个方面。以山西沁水盆地为例,深入剖析了煤储层的孔隙—裂隙系统及其发育历程、煤储层的生气作用与能量聚散,阐明了煤层气成藏的微观动力能对成藏效应的控制作用。结果表明:构造作用对储层渗透率具有明显的控制作用,成烃增压致使能量聚集,成为盖层突破作用的主要驱动力,而能量放散则主要是通过煤储层孔隙—裂隙系统的产生、发展。根据上述研究成果,沁水盆地煤层气成藏的地质区划结果为:盆地南部的有利区带为阳城和晋城的北部地区,包括潘庄、樊庄、郑庄等地区;盆地中部的有利区带为安泽—沁源地区,位于盆地西斜坡的中南部;盆地北部的可能有利区带为寿阳东南部地区,位于榆次东北部和阳泉西南部之间。 相似文献