全文获取类型
收费全文 | 846篇 |
免费 | 193篇 |
国内免费 | 170篇 |
专业分类
测绘学 | 35篇 |
大气科学 | 186篇 |
地球物理 | 241篇 |
地质学 | 469篇 |
海洋学 | 47篇 |
天文学 | 14篇 |
综合类 | 101篇 |
自然地理 | 116篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 51篇 |
2021年 | 49篇 |
2020年 | 39篇 |
2019年 | 38篇 |
2018年 | 57篇 |
2017年 | 51篇 |
2016年 | 57篇 |
2015年 | 47篇 |
2014年 | 61篇 |
2013年 | 48篇 |
2012年 | 47篇 |
2011年 | 50篇 |
2010年 | 48篇 |
2009年 | 45篇 |
2008年 | 48篇 |
2007年 | 40篇 |
2006年 | 46篇 |
2005年 | 46篇 |
2004年 | 30篇 |
2003年 | 28篇 |
2002年 | 15篇 |
2001年 | 14篇 |
2000年 | 24篇 |
1999年 | 25篇 |
1998年 | 31篇 |
1997年 | 24篇 |
1996年 | 24篇 |
1995年 | 17篇 |
1994年 | 18篇 |
1993年 | 14篇 |
1992年 | 20篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 10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1209条查询结果,搜索用时 468 毫秒
991.
Ke-cun Zhang Jian-jun Qu Qing-he Niu Qing-jie Han 《Environmental Earth Sciences》2011,64(8):2039-2046
Based on the detailed wind data and in situ observation of wind-blown sand in the section of Wudaoliang-Tuotuo River along
the Qinghai-Tibet Railway, the dynamic environment of sand flow, involving sand-laden wind, drift potential, sand transport
and their time variation were investigated. The prevailing direction of sand-laden wind obviously varies seasonally. Sand-laden
wind presents unidirectional characteristics from winter to the next spring and its prevailing direction is westerly. In summer,
northeasterly wind begins to increase and lasts for a short period. The annual drift potential along the Qinghai-Tibet Railway
reaches 970.54 Vector Units (VU), which belongs to a high-energy wind environment. Directional variability of wind regime
(RDP/DP, RDP is the resultant drift potential (RDP) and DP is drift potential) is 0.88. The RDP is 854.31VU in the direction
of 89.7°, which indicates that westerly sand-laden wind prevails in this region. Sand transport is well correlated to the
frequency of sand-laden wind and increases with drift potential logarithmically. 相似文献
992.
Analytic solution of long wave propagation over a submerged hump 总被引:1,自引:0,他引:1
A new analytical solution of the long wave refraction by a submerged circular hump is presented. The geometry of the hump is assumed to be axisymmetric and be described by a power function in the radial direction with arbitrary values of both the exponent and the scaling factor. The submergence of the hump is also variable. The water surface elevation governed by the long wave version of the mild slope wave equation is solved by separation of variables, and a series solution of the Frobenius type is obtained. The solution is shown to be valid when the hump is sufficiently submerged or is of a relatively small height. Matching method is employed to illustrate the refraction of long waves under given conditions of incidence. Effects of the shape, the scale, and the submergence of the hump on wave refraction are discussed. 相似文献
993.
四川冕宁稀土矿床脉石矿物的微量及稀土元素地球化学特征 总被引:7,自引:0,他引:7
包裹体地球化学研究表明,四川冕宁稀土矿床中存在着岩浆成因的萤石、重晶石和方解石,它们的微量元素地球化学特征与热液成因对应矿物有明显差别:岩浆成因重晶石相对富集亲石元素,贫亲硫元素;无论是岩浆成因重晶石,还是萤石均明显富集挥发分。稀土元素地球化学研究显示,不同成因萤石、重晶石在稀土元素总量、LREE/HREE、(La/Yb)N、δEu及δCe等一系列稀土元素地球化学参数上都存在明显的差异。该项研究还揭示了岩浆成因萤石、重晶石是在相对还原和酸性体系内结晶而成的。 相似文献
994.
A multi-functional solar and skylight spectrophotometer has been developed for the study of atmosphericconstituents and aerosols. The instrument and its performance are described. Due to telescope structure andlock-in amplification technique adopted,the sensitivity of the instrument is high enough to conduct direct sunmoon and twilight measurement for several atmospheric species and the degree of polarization and intensityobservation for sky light. From measured results, the total column abundance of atmospheric species and theoptical characteristics of aerosol can be retrieved. In this paper, the daily averaged column abundance of O_3measured in Beijing by direct sun was compared with Dobson spectrophotometer nearby. The two did notshow significant difference. 相似文献
995.
江汉-洞庭盆地构造特征和地震活动的初步分析 总被引:16,自引:1,他引:16
本文根据地质、地球物理和地震等资料,初步分析了江汉-洞庭盆地构造及其演化和地震活动的基本特征。此盆地由江汉坳陷、华容隆起和洞庭湖坳陷组成,整个盆地呈现二坳一隆、多凹多凸的构造特征。盆地之下是低缓的北东向莫霍面隆起带,埋深30—31km。自早白垩世至第四纪盆地经历了裂陷、强烈裂陷和区域性沉降等复杂过程,第四纪仍存在一定程度的断裂活动和断块差异活动。盆地区有中强地震和小震活动,地震带基本位于第四纪差异活动较明显的地区和莫霍面隆起的斜坡带 相似文献
996.
湘西江南型金矿床流体包裹的研究 总被引:11,自引:0,他引:11
流体包裹体研究表明:湘西江南型金矿床为中~低温热液矿床,成矿流体为地下热水与变质水混合而成的中等盐度、密度的弱还原性热液,成矿作用是在弱碱性条件下进行的。流体包裹体研究同时还表明:断裂构造对湘西江南型金矿床的矿化具有明显的控制作用。 相似文献
997.
中国大陆主要强震区(带)地震危险性的灰色预测 总被引:1,自引:0,他引:1
本文根据我国大地构造背景和强震震中分布特征,划分出主要强震区(带)。通过对各区地震时间分布不均匀性的分析,划分出各区的强震集发时段。分别以各区强震集发时段的起、止时间为基本数据,运用灰色理论的基本方法,建立灰色预测模型。给出各强震区(带)本次和下次集发时段的灰色预测结果。 相似文献
998.
The problem involving soil mass supported by a retaining wall and subjected to the load exerted by a rigid footing is considered. The collapse load of the system is determined using progressively more advanced plasticity formulations. It is demonstrated that the estimates based on elastoperfect plasticity differ very substantially from those obtained by admitting locally unstable strain softening response. 相似文献
999.
In this paper, the two metnods, rectangular spectrum (RS) and maximum entropy power spectrum (MES), have been used in calculating
the geomagnetic structures of the crust in Haicheng and its adjacent areas and carrying out the geomagnetic stratification
of the crust. The result of the research indicates that the crust can be devided into such three layers as nonmagnetic layer,
magnetic layer and regressive magnetic layer from the top to the bottom. It is also found the distribution of the geomagnetic
bottom interface (Curie surface) is consistent with the lower interface of the upper crust and the top interface of the middle
crust of the velocity structure of the crust. It is very interesting that the Haicheng earthquake of Feb. 4, 1975,M 7.3 occurred at the depth gradient belt of the Curie isotherm surface. So, to research on the geomagnetic layers and the
distribution characteristics of the Curie isotherm surface is meaningful in judging potential seismic foci.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 448–454, 1993.
The data of velocity and electricity materials used in this paper are as reference from the related materials of the maps
and directions etc. of Donggou-Haicheng-Dong Ujimqin Qi Geoscience Transect by Prof. Zao-Xun LU, Huai-Kuan XIA and others. 相似文献
1000.
测量研究了锆石、黄石、石榴石、羟硅铍石和符山石的形态和微形貌,并分别列出了这些晶体的化学成分和其它鉴定参数,观察到的生长和溶蚀螺纹证实螺旋生长机制在硅酸盐矿物晶体生长中具有重要意义。 相似文献