全文获取类型
收费全文 | 4100篇 |
免费 | 887篇 |
国内免费 | 2255篇 |
专业分类
测绘学 | 277篇 |
大气科学 | 530篇 |
地球物理 | 1613篇 |
地质学 | 3654篇 |
海洋学 | 611篇 |
天文学 | 20篇 |
综合类 | 220篇 |
自然地理 | 317篇 |
出版年
2024年 | 10篇 |
2023年 | 82篇 |
2022年 | 191篇 |
2021年 | 156篇 |
2020年 | 253篇 |
2019年 | 342篇 |
2018年 | 290篇 |
2017年 | 202篇 |
2016年 | 310篇 |
2015年 | 314篇 |
2014年 | 401篇 |
2013年 | 405篇 |
2012年 | 396篇 |
2011年 | 428篇 |
2010年 | 345篇 |
2009年 | 389篇 |
2008年 | 353篇 |
2007年 | 325篇 |
2006年 | 350篇 |
2005年 | 294篇 |
2004年 | 243篇 |
2003年 | 196篇 |
2002年 | 155篇 |
2001年 | 118篇 |
2000年 | 96篇 |
1999年 | 102篇 |
1998年 | 97篇 |
1997年 | 78篇 |
1996年 | 69篇 |
1995年 | 57篇 |
1994年 | 54篇 |
1993年 | 39篇 |
1992年 | 35篇 |
1991年 | 16篇 |
1990年 | 21篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有7242条查询结果,搜索用时 437 毫秒
41.
42.
43.
44.
45.
Cheng-Shin Jang Chen-Wuing Liu Yeeping Chia Li-Hsin Cheng You-Ching Chen 《Hydrogeology Journal》2008,16(2):389-397
Changes in hydrogeological properties of the River Choushui alluvial fan aquifer before and after the 1999 Chi-Chi earthquake, Taiwan, have been identified using pumping tests. Three wells, SH2, YL2 and SC2, located in a compressional zone with high coseismic groundwater levels, were tested. The threshold of the aquifer deformation with respect to transmissivity (T) is greater than that with respect to storage coefficient (S). Decreases in the post-earthquake S are approximately 60% at SH2 and SC2, indicating aquifer compression after the Chi-Chi earthquake. Changes in the post-earthquake T range from 61% increase to 0.8% decrease. Moreover, results from anisotropy analysis of T at SC2 further illustrate that normal stresses induced by the Chi-Chi earthquake have consolidated soil particles. Soil particles dilated laterally after the earthquake, resulting in an increase of the equivalent T. The changes in hydrogeological properties have a considerable influence on spatiotemporal fluid pressure and horizontal groundwater movement, resulting in different amounts of drawdown during post-earthquake pumping. 相似文献
46.
47.
基于ArcGIS Engine的水下间断等高线自动连接研究 总被引:1,自引:0,他引:1
本文利用ArcGIS提供的数据分析和数据管理功能对不连续的水下等高线自动连接问题进行了研究。ArcGIS Engine作为ESRI公司最新推出的面向开发的嵌入式组件,具有高效便捷的特点,由于其开发时完全脱离了ArcGIS桌面平台,因而为用户提供了一个可供选择的,有针对性的,低成本的GIS应用选择。本文对水下地形等高线的断线自动连接问题应用ArcGIS Engine进行了研究实验,阐述了使用该技术编程的具体过程,实验结果证明了本文方法的有效性和实用价值。 相似文献
48.
An iterative inverse method, the sequential self-calibration method, is developed for mapping spatial distribution of a hydraulic
conductivity field by conditioning on nonreactive tracer breakthrough curves. A streamline-based, semi-analytical simulator
is adopted to simulate solute transport in a heterogeneous aquifer. The simulation is used as the forward modeling step. In
this study, the hydraulic conductivity is assumed to be a deterministic or random variable. Within the framework of the streamline-based
simulator, the efficient semi-analytical method is used to calculate sensitivity coefficients of the solute concentration
with respect to the hydraulic conductivity variation. The calculated sensitivities account for spatial correlations between
the solute concentration and parameters. The performance of the inverse method is assessed by two synthetic tracer tests conducted
in an aquifer with a distinct spatial pattern of heterogeneity. The study results indicate that the developed iterative inverse
method is able to identify and reproduce the large-scale heterogeneity pattern of the aquifer given appropriate observation
wells in these synthetic cases. 相似文献
49.
鉴于目前地震学综合定量预报指标的缺乏和预报工作的急需,尝试使用“对比筛选法(简称CSM方法)”进行地震学定量预报指标的提取试验。较之以往作法的进展在于:1.同时使用“有震”和“无震”两类样本对比筛选;2.对不同地区的地震学参数进行了归一化处理。这样做的显著优点是:1.可以较有效地提取“有震异常”和“正常变化”指标;2.提取的异常和预报指标具有定量化和普适性特点。 试验研究使用大华北地震区资料,研究对象取中强地震。经内符和外推检验,证明该方法提取的异常和预报指标有效性和实用性较高。 相似文献
50.
We discuss wind variability in intermediate luminosity B supergiants. Because these are not the hottest, most luminous or just about other kind of -est stars, they have not attracted much attention. However, since their wind lines are well-developed, but unsaturated, they make ideal diagnostics for time dependent wind studies. We show that their wind profiles undergo large scale variability and that this phenomenon is quite common. We also discuss a time series for the B0.5 Ib HD 64760 which suggests the long sought after connection between wind and photospheric activity. Newly developed analysis techniques needed to extract physical information from the wind lines are discussed, and results are applied to the time series. 相似文献