全文获取类型
收费全文 | 1052篇 |
免费 | 259篇 |
国内免费 | 243篇 |
专业分类
测绘学 | 75篇 |
大气科学 | 207篇 |
地球物理 | 286篇 |
地质学 | 607篇 |
海洋学 | 108篇 |
天文学 | 15篇 |
综合类 | 119篇 |
自然地理 | 137篇 |
出版年
2024年 | 6篇 |
2023年 | 27篇 |
2022年 | 96篇 |
2021年 | 90篇 |
2020年 | 67篇 |
2019年 | 60篇 |
2018年 | 83篇 |
2017年 | 73篇 |
2016年 | 78篇 |
2015年 | 64篇 |
2014年 | 76篇 |
2013年 | 62篇 |
2012年 | 50篇 |
2011年 | 66篇 |
2010年 | 62篇 |
2009年 | 47篇 |
2008年 | 53篇 |
2007年 | 41篇 |
2006年 | 45篇 |
2005年 | 46篇 |
2004年 | 32篇 |
2003年 | 33篇 |
2002年 | 14篇 |
2001年 | 18篇 |
2000年 | 24篇 |
1999年 | 23篇 |
1998年 | 32篇 |
1997年 | 26篇 |
1996年 | 29篇 |
1995年 | 20篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 23篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 12篇 |
1987年 | 1篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有1554条查询结果,搜索用时 0 毫秒
881.
Niu Zhiren 《地震工程学报》1985,7(1):102-120
The article has made a simple exposition of the dilation-creep modelof earthquake source development(abbreviated DC).Inelastic volumetricdilation of rock masses and fault creep are considered as two basic phys-ical processes in the DC model.The physical mechanism of precursors ofthe M=7.8 Tangshan earthquake has also been analysed and discussed inthis paper.The results show that the precursors of the Tangshan earth-quake were not caused by only one factor and the precursors observed in-and around the epicentral area prior to this earthquake can be grouped into three types.TypeⅠprecursors may be causally related to rock dilata-ncy.TypeⅡprecursors result from fault creep.TypeⅢprecursors maybe associated with some sort of upward migration of mass in the crust orthe upper mantle,and/or may be attributed to large scale stressing processaccommodated by some combination of stable slippage and discontinuousbrittle rupture(namely small earthquake)along the faults.It was sug-gested that repeated dilation and discontinuous creep occurred during theprocess of source development of the Tangshan earthquake and the prepa-ratory process of the Tangshan earthquake can be divided into the follo-wing six phases:elastic stress accumulation(from 1954 to 1967);earlyinelastic dilation(from 1968 to 1969);early fault creep(from 1970 to1973);the second dilation(from the end of 1973 to the first half of 1975);the second evident fault creep(from the second half of 1975 to the end ofApr.1976);and fault creep just before the main shock(from the end ofApr.1976 to the occurrence of the Tangshan earthquake).It is regardedhat the preparatory process of the Tangshan earthquake,as one of the intraplate events,may be controlled jointly by the upward migration ofdeep mass and large scale intraplate stress field.This characteristic prob-ably is different from that of earthquake along plate boundary. 相似文献
882.
883.
观测环境的破坏对地磁观测的影响是严重的,用仪器如实地记录环境的变化,用实际观测的数据来研究外界干扰的影响很有意义。利用郑州地震台的地磁资料,采用趋势分析、相关分析等方法,对高速公路施工期间的观测资料进行研究。最后得出高速公路施工的不同时期,对地磁观测的影响情况,和相同影响情况下模拟仪器和数字化仪器记录的差异。 相似文献
884.
885.
Permafrost covers a significant area of the Qinghai-Tibet Plateau. Slope instability problem in the region was often neglected, though it plays important roles in engineering construction and landform processes. In this paper, the slope instability phenomena in the permafrost regions on the plateau are discussed. The slope failures often occur in the forms of thaw-induced landslides and gelifluction. Thaw-induced landslides are closely related to active layer detachment and changes of permafrost conditions. Such landslides include retrogressive flow and thaw slump and are hazardous to engineering constructions. Gelifluction includes deep-seated movement and surface movement. It is an important factor in landform planation because it may spread over a large area and remain active for a long period of time. 相似文献
886.
887.
888.
通过对地震波在近地表附近双源传递机理的研究,论述了品质因数与激发井深的关系,并根据不同地区、不同品质因数,其地震波最大激发能量、最大信噪比与激发井深的关系曲线,给出了相应的激发深度.三维地震实例表明,地震波在近地表附近的双源传递与品质因数是选择地震波激发井深的重要因素,另外激发频率的增大,对激发井深的影响程度随之增大;观测同样频率的地震信号,存在小Q值地震波激发井深较大Q值激发井深相应变小的特点. 相似文献
889.
Xiao Yi Li Shuang Niu Shengli Li Yanhua Ke Shizhen Deng Hongwen 《Environmental Earth Sciences》2011,64(4):1059-1070
Dielectric measurements, in the frequency range from 100 Hz to 15 MHz, were carried out using an insulating film method, on
shaly and clean sandstone samples, dry, oil-impregnated, partially or fully saturated with fresh water or solutions of NaCl,
at different concentrations. The results show that two kinds of polarization relating to interface dominate: the inner surface
polarization (ISP) at the pore surface in rocks and the outer surface polarization (OSP) on the outer surface of the rock
sample. Both ISP and OSP are of the Debye type and can be fitted very well using the Cole–Cole equation. The dielectric spectra
of ISP reflect the length scale of pore size or throat size, whereas the relaxation strength depends heavily on the inner
pore surface area. Clay contributes to dispersion in rocks, mainly through increasing the inner surface. When the effect of
water content is minimized, the dielectric properties measured on brine-wetted rock samples show great salinity dependence.
The increase in salinity shifts the relaxation spectra to the high frequency end; it also enhances the relaxation strength.
In the frequency range studied, no dispersion in dry and oil-saturated samples has been observed, which underscores the key
role played by water in dielectric polarization in rocks. 相似文献
890.
海南岛大规模二叠-三叠纪侵入岩的形成是与古特提斯洋有关,还是与古太平洋俯冲闭合有关还存在巨大争议。本文对琼中金波两处辉绿岩脉及其围岩花岗岩的研究显示,露头1辉绿岩脉的锆石U-Pb年龄为245.4±3.8Ma,TiO_(2)含量(1.07%~1.18%)低,而MgO(8.60%~9.41%)和Mg^(#)值(62.31~65.02)较高,为钙碱性系列,球粒陨石和原始地幔标准化配分曲线中具有明显的Eu、Nb、Ta、Ti和Ba负异常,以及显著Th、U、Zr、Rb和Pb等正异常,(^(87)Sr/^(86)Sr)_(i)=0.707138~0.712797,(^(143) Nd/^(144)Nd)_(i)=0.511884~0.511965,ε_(Nd)(t)值为-7.01~-8.58,指示其形成于大陆岛弧环境。相比之下,露头2辉绿岩锆石U-Pb年龄为242.8±3.1Ma,但其TiO_(2)(2.65%~3.06%)含量较高,而MgO(4.24%~5.39%)和Mg^(#)值(40.09~45.86)较低,具有Eu、Rb、Pb、Nb、Ta和Ti弱正异常和Th负异常,(^(87)Sr/^(86)Sr)_(i)=0.690244~0.717031,(^(143) Nd/^(144)Nd)_(i)=0.512886~0.512915,ε_(Nd)(t)值为+6.41~+7.93,具有板内玄武岩的特征,指示其形成于板内裂解环境。辉绿岩脉围岩二长花岗岩的锆石U-Pb年龄为255.3±3.0Ma和255.7±3.2Ma,含少量角闪石和黑云母,具有较高的SiO_(2)(71.62%~73.72%)、Na_(2)O+K_(2)O(6.60%~9.17%)和Al_(2)O_(3)(平均14.88%)含量,A/CNK值(0.97~1.03)较低,亏损Nb、Ta、Ti、Sr和Ba,富集Rb、Th、U和Pb,为高分异I型岛弧花岗岩。总的来看,二长花岗岩和辉绿岩形成于大陆岛弧挤压向伸展过渡的构造环境。对比二叠-三叠纪侵入岩体的走向、碰撞前-同碰撞-碰撞后岩浆岩的时代以及榴辉岩的变质年龄等,发现海南岛侵入岩与哀牢山-松马造山带明显不同,而与日本和朝鲜半岛的岛弧岩浆岩类似,由此我们认为海南岛大规模晚二叠-早三叠世岩浆岩为古太平洋板片向欧亚板块俯冲后撤的产物,后撤过程受到古特提斯俯冲板片的影响。 相似文献