全文获取类型
收费全文 | 410篇 |
免费 | 36篇 |
国内免费 | 41篇 |
专业分类
测绘学 | 37篇 |
大气科学 | 44篇 |
地球物理 | 113篇 |
地质学 | 105篇 |
海洋学 | 71篇 |
天文学 | 7篇 |
综合类 | 62篇 |
自然地理 | 48篇 |
出版年
2023年 | 3篇 |
2022年 | 15篇 |
2021年 | 13篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 20篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 17篇 |
2014年 | 17篇 |
2013年 | 25篇 |
2012年 | 20篇 |
2011年 | 32篇 |
2010年 | 17篇 |
2009年 | 19篇 |
2008年 | 25篇 |
2007年 | 26篇 |
2006年 | 23篇 |
2005年 | 18篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 12篇 |
2001年 | 8篇 |
2000年 | 10篇 |
1999年 | 17篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 17篇 |
1995年 | 11篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
排序方式: 共有487条查询结果,搜索用时 15 毫秒
101.
残余和现今应力场重迭法预测强震危险时区 总被引:3,自引:0,他引:3
以红河断裂带测区为例,用X射线法测量了测区的古构造残余应力场及其应变能密度场,用有限单元法计算了测区在两种边界条件下的水平最大剪应力场,用实验和理论证明了古构造残余主压应力大小和方向对岩石破坏、破裂扩展和震级的影响。用上述方法预测,松平—南涧、玉溪—开远、普洱为测区内强震危险区段。结合地球自转角速度相对变率的天文观测曲线在时间轴上的外延,预测得1989-1996、1999-2004、2007-2013、2016-2018年为测区内强震危险时段。 相似文献
102.
Gengxin Ou Francisco Munoz-Arriola Daniel R. Uden Derrel Martin Craig R. Allen Nancy Shank 《Climatic change》2018,151(2):303-316
This study investigates the influence of climate change on groundwater availability, and thereby, irrigation across political boundaries within the US High Plains aquifer. A regression model is developed to predict changes in irrigation according to predicted changes in precipitation and temperature from a downscaled dataset of 32 general circulation models (GCMs). Precipitation recharge changes are calculated with precipitation-recharge curves developed for prognostic representations of precipitation across the Nebraska-Colorado-Kansas area and within the Republican River Basin focal landscape. Irrigation-recharge changes are scaled with changes in irrigation. The groundwater responses to climate forcings are then simulated under new pumping and recharge rates using a MODFLOW groundwater flow model. Results show that groundwater pumping and recharge both will increase and that the effects of groundwater pumping will overshadow those from natural fluctuations. Groundwater levels will decline more in areas with irrigation-driven decreasing trends in the baseline. The methodologies and predictions of this study can inform long-term water planning and the design of management strategies that help avoid and resolve water-related conflicts, enabling irrigation sustainability. 相似文献
103.
磁流变液及结构减振智能驱动器 总被引:2,自引:0,他引:2
本文,首先通过正交试验研究了磁流变液各组分对其性能的影响作用及作用机理.试验表明,油酸的主要作用是提高磁性颗粒的溶解性,而OP乳化剂的主要作用是提高磁性颗粒的分散能力.其次,根据以上的试验结果,在大量具体对比试验的基础上,研制成功了一种剪切屈服强度高、沉降稳定性好的磁流变液.而后,根据磁流变液的流变特性,结合磁路特点,设计制作了一个额定电压为9V、电流为2A、功率为20W的磁流变减振驱动器,并测试了此驱动器的阻尼力及时间响应特性.测试表明,本减振驱动器的响应时间是0.2至0.3秒,而不是理论响应时间的10毫秒.最后,分析了响应时间的影响因素. 相似文献
104.
本文介绍了香港丰富多彩的自然旅游资源和人文旅游资源,分析了香港自50年代以来旅游业开发的进程,预测香港回归祖国之后,旅游业必将进一步稳定发展。 相似文献
105.
106.
本文对重心法则给出了一个扩展,使该法则的运用由综合指标到了全部指标,并证明了 I_G~((1))=I_G~((2))。 相似文献
107.
Poor bleaching is a significant problem for Optically Stimulated Luminescence (OSL) dating of glacial sediments. Five young glacial samples (including two modern analogues) from different depositional settings were collected beyond the Yingpu Glacier in the eastern Qinghai-Tibetan Plateau. De was determined using different OSL methods. The luminescence characteristics and dating results showed that the large aliquot quartz Blue Stimulated Luminescence (BSL) is more applicable than polymineral infrared stimulated luminescence (IRSL) method. Small aliquot quartz BSL results showed poor luminescence properties due to low luminescence sensitivity of quartz in this area. The dating results also indicated that glaciofluvial samples deposited close to ice margin (~40 m and ~700 m) and supraglacial debris dominated lateral moraine samples are relatively well-bleached, whereas samples from ground moraine and low terminal moraine were poorly bleached, probably due to containing subglacial and englacial debris. The residual doses of glaciofluvial and lateral moraine crest samples were below a few Gy and age overestimations were below a few hundred years. The ground moraine and low terminal moraine samples had residual doses as high as ~110 Gy, and ages were overestimated by ~15-17 ka. 相似文献
108.
Installation of buttress walls against diaphragm walls has been used as an alternative measure for the protection of adjacent buildings during excavation, but their mechanism in reducing movements has not yet been fully understood. This study performs three-dimensional finite element analyses of two excavation case histories, one in clay with T-shape buttress walls and another in dominant sand with rectangular buttress walls, to establish analysis model. Then, a series of parametric study were performed by varying soil types, types and length of buttress walls based on the above-mentioned excavations. Results show that the mechanism of buttress walls in reducing wall deflections mainly came from the frictional resistance between the side surface of buttress wall and adjacent soil rather than from the combined bending stiffness from diaphragm and buttress walls. The buttress wall with a length <2.0 m had a poor effect in reducing the wall deflection because the soil adjacent to the buttress wall had almost the same amount of movement as the buttress wall, causing the frictional resistance little mobilized. Since the frictional resistance of buttress walls in a deep excavation has fully been mobilized prior to the final excavation depth, the efficiency of buttress walls in reducing the wall deflection in a deep excavation was much less than that in a shallow excavation. Rectangular shape of buttress walls was of a better effect than T-shape in the shallow excavation because frictional resistance between buttress walls and adjacent soil played a major role in reducing the wall deflection rather than bearing resistance of the flange. When the excavation went deeper, the difference in reducing the wall deflection between the R-shape and T-shape became small. 相似文献
109.
110.