全文获取类型
收费全文 | 5684篇 |
免费 | 1048篇 |
国内免费 | 1347篇 |
专业分类
测绘学 | 342篇 |
大气科学 | 1190篇 |
地球物理 | 1556篇 |
地质学 | 2763篇 |
海洋学 | 716篇 |
天文学 | 298篇 |
综合类 | 659篇 |
自然地理 | 555篇 |
出版年
2024年 | 36篇 |
2023年 | 108篇 |
2022年 | 260篇 |
2021年 | 296篇 |
2020年 | 238篇 |
2019年 | 264篇 |
2018年 | 295篇 |
2017年 | 267篇 |
2016年 | 338篇 |
2015年 | 293篇 |
2014年 | 350篇 |
2013年 | 303篇 |
2012年 | 287篇 |
2011年 | 325篇 |
2010年 | 298篇 |
2009年 | 360篇 |
2008年 | 328篇 |
2007年 | 310篇 |
2006年 | 225篇 |
2005年 | 244篇 |
2004年 | 172篇 |
2003年 | 167篇 |
2002年 | 183篇 |
2001年 | 184篇 |
2000年 | 181篇 |
1999年 | 252篇 |
1998年 | 228篇 |
1997年 | 185篇 |
1996年 | 203篇 |
1995年 | 147篇 |
1994年 | 148篇 |
1993年 | 153篇 |
1992年 | 125篇 |
1991年 | 70篇 |
1990年 | 56篇 |
1989年 | 48篇 |
1988年 | 43篇 |
1987年 | 22篇 |
1986年 | 26篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1958年 | 4篇 |
排序方式: 共有8079条查询结果,搜索用时 15 毫秒
31.
32.
33.
川滇密西西比河谷型铅锌矿床成矿流体来源研究:流体Na-Cl-Br体系的证据 总被引:11,自引:1,他引:11
应用流体包裹体滤液分析方法,测定了川滇7个MVT铅锌矿床成矿流体的Na,Cl,Br含量,结果表明成矿流体的x(Na/Br)和x(Cl/Br)的平均值分别为185和73,并与高度蒸发浓缩的残留海水的x(Na/Br)和x(Cl/Br)相近。成矿流体的Na,Cl含量呈正相关,在lgNa-lgCl图解中呈线性分布。根据这些事实以及矿床地质特征,认为原始成矿卤水起源于蒸发浓缩的残留海水,原始含矿卤水与富含有机质的大气降水混合导致矿质沉淀而成矿。 相似文献
34.
Audrey GalvéAlfred Hirn Jiang MeiJosep Gallart Béatrice de VoogdJean-Claude Lépine Jordi DiazWang Youxue Qian Hui 《Earth and Planetary Science Letters》2002,203(1):35-43
New wide-angle reflection and refraction seismic data provide constraints on the structure of the upper lithosphere, and test models of its evolution to raise the northeastern part of the Tibetan Plateau. Amplitudes observed for reflections from the crust-mantle boundary are sufficiently large to suggest that there is no significant partial melt in the deep crust. The data show an increase of the crustal thickness between terranes from north of the Kun Lun Fault into the Qang Tang of central Tibet, and a contrast among their intracrustal images and compositions. In the north, P and S velocities are consistent with a dominantly felsic composition and show that only the upper crust thickened. South of the Kun Lun Fault a thicker crust made of two layers could result from the superposition of the originally thin crust of the Bayan Har terrane on the lower part of the crust of the domain to the north, which upper crust it shoved and thickened. Different modes of crustal thickening, either by thickening of individual layers or superpositions and imbrication among them appear to work jointly to raise the topography. 相似文献
35.
A general method is developed for optimal application of dampers and actuators by installing them at optimal location on seismic-resistant
structures. The study includes development of a statistical criterion, formulation of a general optimization problem and establishment
of a solution procedure. Numerical analysis of the seismic response in time-history of controlled structures is used to verify
the proposed method for optimal device application and to demonstrate the effectiveness of seismic response control with optimal
device location. This study shows that the proposed method for the optimal device application is simple and general, and that
the optimally applied dampers and actuators are very efficient for seismic response reduction. 相似文献
36.
Nonlinear earthquake response analysis and energy calculation for seismic slit shear wall structures
Based on the concept of structural passive control, a new type of slit shear wall, with improved seismic performance when
compared to an ordinary solid shear wall, was proposed by the authors in 1996. The idea has been verified by a series of pseudo-static
and dynamic tests. In this paper a macro numerical model is developed for the wall element and the energy dissipation device.
Then, nonlinear time history analysis is carried out for a 10-story slit shear wall model tested on a shaking table. Furthermore,
the seismic input energy and the individual energy dissipated by the components are calculated by a method based on Newmark-β
assumptions for this shear wall model, and the advantages of this shear wall are further demonstrated by the calculation results
from the viewpoint of energy. Finally, according to the seismic damage criterion on the basis of plastic accumulative energy
and maximum response, the optimal analysis is carried out to select design parameters for the energy dissipation device. 相似文献
37.
Through numerical simulation for GPS data, aseism/c negative dislocation model for crustal horizontal movement during 1999-2001 in the northeast margin of Qinghai-Xizang block is presented, combined with the spatial distri-bution of apparent strain field in this area, the characteristics of motion and deformation of active blocks and their boundary faults, together with the place and intensity of strain accumulation are analyzed. It is shown that: a) 9 active blocks appeared totally clockwise motion from eastward by north to eastward by south. Obvious sinistral strike-slip and NE-NEE relative compressive motion between the blocks separated by Qilianshan-Haiyuan fault zone was discovered; b) 20 fault segments (most of them showed compression) locked the relative motion between blocks to varying degrees, among the total, the mid-east segment of Qilianshan fault (containing the place where it meets Riyueshan-Lajishan fault) and the place where it meets Haiyuan fault and Zhuanglanghe fault, more favored accumulation of strain. Moreover, the region where Riyueshan-Lajishan fault meets north boundary of Qaidam block may have strain accumulation to some degree, c) Obtained magnitude of block velocities and locking of their boundaries were less than relevant results for observation in the period of 1993-1999. 相似文献
38.
39.
介绍了GIS在城市轨道交通建设中的应用,分析了轨道交通建设的评价要素和对GIS系统的建设要求提出了系统设计的总体思路和框架及应用前景。 相似文献
40.
介绍了蒙特卡罗法的基本步骤以及伪随机数的检验方法;结合工程控制网的设计给出了一个实际算例,算例的结果表明该方法切实有效。 相似文献