全文获取类型
收费全文 | 1711篇 |
免费 | 209篇 |
国内免费 | 260篇 |
专业分类
测绘学 | 722篇 |
大气科学 | 213篇 |
地球物理 | 369篇 |
地质学 | 370篇 |
海洋学 | 152篇 |
天文学 | 52篇 |
综合类 | 180篇 |
自然地理 | 122篇 |
出版年
2024年 | 11篇 |
2023年 | 21篇 |
2022年 | 48篇 |
2021年 | 53篇 |
2020年 | 80篇 |
2019年 | 81篇 |
2018年 | 58篇 |
2017年 | 91篇 |
2016年 | 104篇 |
2015年 | 126篇 |
2014年 | 103篇 |
2013年 | 126篇 |
2012年 | 100篇 |
2011年 | 107篇 |
2010年 | 96篇 |
2009年 | 103篇 |
2008年 | 113篇 |
2007年 | 113篇 |
2006年 | 116篇 |
2005年 | 86篇 |
2004年 | 57篇 |
2003年 | 44篇 |
2002年 | 47篇 |
2001年 | 44篇 |
2000年 | 35篇 |
1999年 | 27篇 |
1998年 | 29篇 |
1997年 | 19篇 |
1996年 | 15篇 |
1995年 | 16篇 |
1994年 | 21篇 |
1993年 | 15篇 |
1992年 | 7篇 |
1991年 | 12篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 6篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有2180条查询结果,搜索用时 0 毫秒
51.
The study quantifies the environmental risk factors for two diseases with different vectors and cycles of transmission: malaria
and Chagas' disease in N.W. Argentina near the Bolivian border. This is the area within Argentina where malaria is still a
serious health problem. Chagas' disease is to some extent present in many parts of the country. The field work for the study
concerned 5903 people in 1466 dwellings. The study resulted in detailed maps of risk factors: particularly water quality and
contacts with migrants from Bolivia in the case of malaria; and thatched roofs and dogs in the case of Chagas' disease.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
52.
采用正交设计、三维数值模拟、遗传算法与支持向量机,建立了清江水布垭电站地下厂房的智能反分析流程。按照上述流程,利用前6层开挖的现场监测信息对有关岩层的力学参数进行反分析,根据反分析的参数对后续的机窝施工进行数值模拟计算和方案优化。推荐的机窝施工方案采用槽挖方式,同时应用锚桩、软岩置换、锚喷支护等措施,兼顾了高边墙和机窝岩台的稳定性。优化结果对厂房施工具有重要的指导作用。 相似文献
53.
The basic concepts of spectral and multiscale selective reconstruction of (geophysically relevant) vector fields on the sphere from error-affected data is outlined in detail. The reconstruction mechanism is formulated under the assumption that spectral as well as multiscale approximation is well-representable in terms of only a certain number of expansion coefficients at the various resolution levels. It is shown that spectral denoising by means of orthogonal expansions in terms of vector spherical harmonics reflects global a priori information of the noise (e.g., in form of a covariance tensor field), whereas multiscale signal-to-noise thresholding can be performed under locally dependent noise information within a multiresolution analysis in terms of spherical vector wavelets. An application of the multiscale formalism to Earth's magnetic field determination is presented. 相似文献
54.
常用的确定岩土力学参数的方法有原位测试和室内试验两种,但都存在一定的局限性,参数选择的合理与否,对设计计算及数值模拟分析结果的有效性影响很大。支持向量机法在理论基础和求解算法方面都具有明显优势,为确保岩土力学参数取值的合理性,采用支持向量机法对岩土力学参数进行反演。先通过小波分析理论构造出支持向量机的核函数,再用粒子群算法(PSO)分别优化Morlet小波、Mexico小波和RBF函数的支持向量机模型参数,通过小波支持向量机模型建立反演参数与沉降值间的非线性映射关系。根据正交试验和均匀试验对需反演的岩土力学参数进行设计,结合有限元软件进行计算分析,得到学习样本和测试样本。分别采用Morlet小波、Mexico小波和RBF函数得出的预测结果和原始数据进行对比分析,发现采用Morlet小波核函数预测效果更佳。使用Morlet小波核函数预测的参数输入到Midas模型中计算建筑物最终沉降量,比较计算值与实际监测值,其相对误差不超过8.1%。研究结果表明,该方法在岩土工程参数的反演中具有良好的应用价值,对今后岩土力学参数的确定及校核提供了一种新方法。 相似文献
55.
本文介绍了用计算机辅助设计软件AUTOCAD与三维动画软件3DMAX来绘制峨嵋山地区块体图的方法,以此为例子讲述了将地形图改画面三维图的具体操作步骤,并进一步论述了用计算机绘制块体图的方法有着广泛的应用及其实用价值。 相似文献
56.
A model with rigid rotations and slip deficits for the GPS-derived velocity field in Southwest Japan
We interpret the GPS-derived velocity field in southwest Japan by a superposition of the elastic deformation caused by fault interactions (slips or slip deficits) on the rigid motion of tectonic blocks (or plates). Based on the strain rate field and crustal seismicity, we apply a model with three blocks (Inner Arc, Outer Arc, and the northern Ryukyu block) and slip deficits along the block boundaries.Several characteristics of the synthesized contributions are found:
- (1) Westward motion of the outer arc relative to the Amurian plate and the inner arc,
- (2) southeastward motion of the northern Ryukyu block relative to the Amurian plate,
- (3) 2−4 mm/yr deficits of left lateral slip rates along the boundary at 32°N in southern Kyushu,
- (4) 0−8 mm/yr deficits of right lateral slip rates along the Median Tectonic Line and the Beppu-Shimabara Graben,
- (5) slip deficit rates on the plate interface smaller than those in the case without any consideration for rigid block motions,
- (6) clockwise deflection of slip deficit rate vector on the plate interface from that estimated when not taking rigid block motions into consideration.
Keywords: Oblique subduction; Sliver motion; Backarc spreading; Interplate coupling; Euler vector 相似文献
57.
地下水资源系统多目标管理模型与模糊带权二次规划方法 总被引:2,自引:0,他引:2
谢新民 《水文地质工程地质》1993,20(4):17-21,43
本文以济南地下水资源系统保泉供水管理课题为例,分析研究地下水资源系统多目标管理问题。首先建立起地下水资源系统多目标管理模型;然后利用模糊数学理论和权重概念,提出一种求解多目标决策问题的模糊带权二次规划方法,此方法可以同时解决互为竞争、互为矛盾的各目标之间的不可公度性和主次性问题。实际计算表明,所建立的模型和提出的方法具有较强的实用性和通用性。 相似文献
58.
E. Haber 《Computational Geosciences》2000,4(4):323-336
This paper present a new a mixed finite element method for the simulation of magnetostatic problems with highly discontinuous permeability. The method is derived from the well studied mixed formulation for the div-grad system that is known to be accurate for very large discontinuities. The method robustness is demonstrated on a test model problem. 相似文献
59.
Vector-raster conversion is one of the classic research topics in the field of Geographical Information Systems (GIS). The algorithms commonly used in GIS are devoted to maintaining the vector polygons' shape characteristics, but neglect the gain and loss of a polygon's area, which is another important attribute. This paper proposes an equal-area conversion model based on an area compensation optimization principle. According to the topological relationship among polygons and boundary grids, a neighborhood compensation principle was adopted to assign the attributes of boundary grids and a global optimization algorithm was developed to minimize area distortion in the whole data set. Two experiments were designed and the results indicated that this algorithm not only guaranteed the area error is as small as possible, but also has the advantage as being adaptive to polygon shape and spatial structure. 相似文献
60.
A Diagnostic Study of Explosive Development of Extratropical Cyclone over East Asia and West Pacific Ocean 总被引:9,自引:0,他引:9
ADiagnosticStudyofExplosiveDevelopmentofExtratropicalCycloneoverEastAsiaandWestPacificOcean¥JiaYiqin(贾逸勤)andZhaoSixiong(赵思雄)(... 相似文献