全文获取类型
收费全文 | 3456篇 |
免费 | 399篇 |
国内免费 | 740篇 |
专业分类
测绘学 | 1404篇 |
大气科学 | 277篇 |
地球物理 | 661篇 |
地质学 | 1266篇 |
海洋学 | 436篇 |
天文学 | 89篇 |
综合类 | 313篇 |
自然地理 | 149篇 |
出版年
2024年 | 28篇 |
2023年 | 67篇 |
2022年 | 148篇 |
2021年 | 192篇 |
2020年 | 192篇 |
2019年 | 236篇 |
2018年 | 150篇 |
2017年 | 225篇 |
2016年 | 196篇 |
2015年 | 222篇 |
2014年 | 236篇 |
2013年 | 299篇 |
2012年 | 286篇 |
2011年 | 234篇 |
2010年 | 167篇 |
2009年 | 217篇 |
2008年 | 197篇 |
2007年 | 215篇 |
2006年 | 199篇 |
2005年 | 157篇 |
2004年 | 143篇 |
2003年 | 123篇 |
2002年 | 70篇 |
2001年 | 59篇 |
2000年 | 54篇 |
1999年 | 54篇 |
1998年 | 29篇 |
1997年 | 49篇 |
1996年 | 28篇 |
1995年 | 31篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 6篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有4595条查询结果,搜索用时 19 毫秒
41.
Bruce A. Callander 《GeoJournal》1997,42(1):55-63
IPCCs statement in its 1995 report (IPCC 1996) that a human influence was discernible in global climate has been widely quoted but often misunderstood. The character of the evidence underpinning this detection statement is explained so that its strengths and weaknesses can be better understood and the subtleties of its message better appreciated. To demonstrate the close linkage between the government-approved summary and the underlying chapters of the IPCC report the detailed evolution of the detection statement from first draft through to the form finally approved by the IPCC is described. 相似文献
42.
A centrifugal mill is a high-power intensity media mill that can be used for ultra-fine grinding, employing centrifugal forces generated by gyration of the axis of the mill tube in a circle. The mill charge motion is quite different depending on the ratio of the gyration diameter to the mill diameter (G / D ratio), varying from a motion similar to that of a conventional tumbling media mill to that of a vibration mill. In this study, a centrifugal mill was constructed with an arrangement where the gyration diameter could be readily adjusted. The batch grinding characteristics of three different minerals (limestone, talc and illite) in water with dispersing agent were investigated at various G / D ratios. It was found that the optimum G / D ratio in terms of the specific energy consumption to give a desired fineness of product was different for the three minerals. This was due to their different reactions to the breakage mechanisms provided by the mill charge motion at varying G / D ratios. The size distributions became progressively narrower at increased grinding times, and particles finer than about 0.1 μm were not detected even for prolonged grinding times. Measurement of specific surface areas indicated that this was not due to an artifact of the size measurements by laser diffractometry. This implies that there is a limitation in which particles finer than 0.1 μm are not produced under the conditions tested in this type of mill, but further investigation is needed for experimental verification of this limit of comminution. 相似文献
43.
A simplified procedure for evaluating aseismic stability of slope subjected to earthquake shaking, in which the effect of dynamic shear strength and time-history stress on the yielding angular acceleration of sliding block is taken into account, is presented. The fundamental feature of this procedure is the dynamic shear strength. The numerical computations are performed by using the proposed method. It is shown that the computed sliding displacement for a given core dam, with either method of dynamic shear strength properly considered, is more rational compared with the conventional computational results based on static shear strength. 相似文献
44.
Shubhra Goel Shalini Nihar Ranjan Patra 《Geotechnical and Geological Engineering》2006,24(6):1511-1525
Inclined anchors are widely used in a variety of civil engineering problems to resist oblique loads, most relevant being in
transmission towers and in rocks and dams for structural strengthening. In the present study, the breakout resistance of the
inclined anchors in sand has been worked out using limit equilibrium approach. The breakout resistance has been calculated
for different soil friction angles with varying relative depth ratio and anchor inclination. The break out factor increases
continuously with the inclination of the anchor. A comparison of predicted values of break out resistance of anchors by the
proposed analysis with the experimental values as reported by the other researchers showed reasonably good agreement. 相似文献
45.
46.
47.
福建平潭虎潮山滑坡成因机理分析与评价 总被引:3,自引:0,他引:3
虎潮山滑坡位于平宏公路12k 704~12k 884段北侧山坡体上,是平潭海岛通往陆地的唯一公路通道。论文通过定性的工程地质分析和定量计算评价了虎潮山坡体稳定性的变化趋势,提出改建公路超挖深切坡脚和持续长时间强降雨导致的孔隙水压力作用是边坡发生滑动破坏的主要因素。 相似文献
48.
多时相组合分类法在土地利用动态监测中的应用 总被引:16,自引:0,他引:16
介绍了土地利用遥感动态监测的基本概念,简述了遥感土地利用变化信息提取等遥感监测方法.重点探讨了多时相组合分类方法的相关技术。对广西2002年和2003年两个时相的MODIS数据.采用多时相直接分类法对土地利用变化状况进行了遥感动态监测。对不同方式波段组合的试验表明。经过差值、比值处理的波段组合具有较差的试验效果(总体精度只有30%~40%),而经过PCA变换的波段组合则具有相对较好的试验效果(总体精度超过70%)。 相似文献
49.
介绍了一个建筑物阴影检测的模型。首先利用摄影测量学原理来计算阴影坐标。即用数字表面模型(digitalsurfacemodel,缩写为DSM)和太阳高度和方位来计算建筑物阴影的空间坐标,并由相机模型计算出每个阴影单元对应的扫描行和相机空间坐标。由高度场光线跟踪判断阴影的可见性,对可见阴影计算出它在投影图像上的坐标。然后在这个结果的基础上再对图像进行阴影的细分割。 相似文献
50.