全文获取类型
收费全文 | 2499篇 |
免费 | 438篇 |
国内免费 | 647篇 |
专业分类
测绘学 | 126篇 |
大气科学 | 445篇 |
地球物理 | 713篇 |
地质学 | 1445篇 |
海洋学 | 237篇 |
天文学 | 91篇 |
综合类 | 248篇 |
自然地理 | 279篇 |
出版年
2024年 | 8篇 |
2023年 | 36篇 |
2022年 | 123篇 |
2021年 | 124篇 |
2020年 | 118篇 |
2019年 | 130篇 |
2018年 | 172篇 |
2017年 | 150篇 |
2016年 | 128篇 |
2015年 | 130篇 |
2014年 | 155篇 |
2013年 | 181篇 |
2012年 | 146篇 |
2011年 | 150篇 |
2010年 | 161篇 |
2009年 | 158篇 |
2008年 | 121篇 |
2007年 | 134篇 |
2006年 | 86篇 |
2005年 | 78篇 |
2004年 | 83篇 |
2003年 | 71篇 |
2002年 | 59篇 |
2001年 | 74篇 |
2000年 | 108篇 |
1999年 | 97篇 |
1998年 | 80篇 |
1997年 | 86篇 |
1996年 | 97篇 |
1995年 | 64篇 |
1994年 | 64篇 |
1993年 | 47篇 |
1992年 | 32篇 |
1991年 | 21篇 |
1990年 | 24篇 |
1989年 | 19篇 |
1988年 | 18篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1936年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有3584条查询结果,搜索用时 31 毫秒
991.
992.
Based on the analysis of the Asian lower-level jet stream, this paper indicates that having shifted to the Bay of Bengal, this large-scale lower-level jet (LLJ) develops into two branches: the northern branch (NB) which is a strong southwest flow moving into the inland of China along the southeast side of the Qinghai-Xizang Plateuu and then moving eastward to Japan along the north side of the subtropical high, and the southern branch (SB) which continues to he a west flow and travels into the West Pacific across the Indo-China Peninsula along the south side of the mon-soon trough. Above the two branches are two synoptic-scale transient tubular monsoon circulation systems, the northern branch being a subtropical monsoon stream tube (SMST) and the southern branch a tropical monsoon stream tube (TMST). Their ascending branches, corresponding to a subtropical monsoon rain belt and a tropical monsoon rain bell respectively, bear considerable influence on the weather over China. 相似文献
993.
In this paper the incremental nonlinear models are generally discussed, the correlation of this sort of models with others and the difference between them are interpreted, and some basic concepts are clarified. We presented a nonlinear dilatant stress-strain model for soil, which is referred to as KKG model for the sake of simplicity. The experimental results of a sand sample are used to determine the moduli for the following models KKG, KG (the deformation model), and Eν (elastoplastic model) respectively. The comparison of the calculation values of these models with the associated experimental results shows good fittings and prediction of KKG model, and its good simulation of soil dilatant behaviour in particular. The predicted pore pressure and effective stress path have a reasonably good agreement with observed results as well. 相似文献
994.
大气短波辐射传输研究中的辐射函数 总被引:1,自引:0,他引:1
研究大气短波辐射传输问题时,必需考虑多次散射,在计算各次散射光的递推方程中存在一个对光学厚度的特殊积分.为此,本文定义了“辐射函数”,并研究了它的数学性质,从而使得平面平行大气中散射光的逐次计算既准确又简便. 相似文献
995.
The International Stratigraphic Guide defined that all stratified or quasi-stratified rock bodies of the earth crust, including sedimentary, igneous, metamorphic, solidified and unsolidified ones, should be considered as research contents of stratigraphy. Traditional stratigraphy mainly involves strata formed under gravity mechanism, plus a few kinds of bedded volcanic rocks such as lava, pyroclastic rock and volcanic ash, as well as metamorphic sedimentary and volcano-sedimentary rocks. These traditional strata are regarded as Smithian strata in this paper. In modem stratigraphy, mechanism of strata formation includes not only gravity but also thermal (ophiolite), mechanic and tectonic forces (orogenic melange and tectonite). In these above-mentioned non-gravitative conditions, the strata,formed complying with their own mechanisms but not with the law of superposition of Smithian stratigraphy, are called non-Smithian strata here. In melange regions from orogenic belt, formations of nonSmithian strata could be classified into subduct-scrape-match, subduct-retm-n-match, and subduct-overthrnst twits. 相似文献
996.
The effect of the electrical anisotropy on the response of helicopter-borne frequency-domain electromagnetic systems 总被引:4,自引:0,他引:4
Helicopter electromagnetic (HEM) systems are commonly used for conductivity mapping and the data are often interpreted using an isotropic horizontally layered earth model. However, in regions with distinct dipping stratification, it is useful to extend the model to a layered earth with general anisotropy by assigning each layer a symmetrical 3 × 3 resistivity tensor. The electromagnetic (EM) field is represented by two scalar potentials, which describe the poloidal and toroidal parts of the magnetic field. Via a 2D Fourier transform, we obtain two coupled ordinary differential equations in the vertical coordinate. To stabilize the numerical calculation, the wavenumber domain is divided into two parts associated with small and large wavenumbers. The EM field for small wavenumbers is continued from layer to layer with the continuity conditions. For large wavenumbers, the EM field behaves like a DC field and therefore cannot be sensed by airborne EM systems. Thus, the contribution from the large wavenumbers is simply ignored. The magnetic fields are calculated for the vertical coaxial (VCX), horizontal coplanar (HCP) and vertical coplanar (VCP) coil configurations for a helicopter EM system. The apparent resistivities defined from the VCX, VCP and HCP coil responses, when plotted in polar coordinates, clearly identify the principal anisotropic axes of an anisotropic earth. The field example from the Edwards Aquifer recharge area in Texas confirms that the polar plots of the apparent resistivities identify the principal anisotropic axes that coincide well with the direction of the underground structures. 相似文献
997.
WebGIS的空间数据共享与互操作 总被引:4,自引:0,他引:4
WebGIS技术是目前实现空间数据共享的有效手段,但是,由于空间数据异构复杂性,空间数据共享与互操作的实现还存在大量的问题亟待解决。本文阐述了空间数据共享与互操作技术模式,介绍了地理标记语言GML及在WebGIS中应用的优势,提出了一种基于GML的WebGIS空间数据共享与互操作方案。 相似文献
998.
太湖流域洪涝灾害评估模型 总被引:3,自引:1,他引:3
在地理信息系统支持下建立了太湖流域DEM模型,并建立了全流域12类共24种土地利用类型、2194个圩区、1012个乡镇和94个报汛站点的空间数据库及属性数据库。在此基础上,根据实时报汛资料,通过插值得到各乡汛期圩外水位和降雨量。圩区采用排涝计算圩内内涝水量再与DEM叠加,非圩区用乡最高水位与DEM叠加,可获得全流域淹没水深栅格数据。统计不同乡镇、不同土地类型、不同淹没水深的淹没面积,并根据当年的社会经济数据,建立了太湖流域洪涝灾害损失评估模型。对1999年太湖流域洪涝灾害评估结果表明,模型具有一定的精度,可为流域防洪减灾决策提供依据。 相似文献
999.
Based on the three-dimensional ela stic inclusion model proposed by Dobrovolskii, we developed a three-dimensional rheologic
inclusion model and theory to study the earthquake preparation process. By using correspondence principle in the theory of
rheologic mechanics, we derived the analytic expression of the viscoelastic displacement at an arbitrary point (x, y, z) in three directions of x, y and z-axes (i.e., U(r, t), V*(r, t) and W(r, t)) produced by a three-dimension inclusion in the semi-infinite rheologic medium defined by the standard linear rheologic model.
Foundation item: Chinese Joint Seismological Science Foundation (101105) 相似文献
1000.
推进监测预报体系建设,提高地震预测预报水平 总被引:2,自引:0,他引:2
阴朝民 《地震地磁观测与研究》2003,24(5):1-6
对监测预报工作的地位和作用进行了深入的阐述,分析总结了监测预报工作取得的进展以及存在的问题,提出了未来监测预报体系建设的指导思想和总体目标。并对进一步加强监测预报体系建设,提高预测预报水平各环节的工作进行了详细的论述。 相似文献