全文获取类型
收费全文 | 480篇 |
免费 | 60篇 |
国内免费 | 35篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 58篇 |
地球物理 | 137篇 |
地质学 | 238篇 |
海洋学 | 46篇 |
天文学 | 45篇 |
综合类 | 19篇 |
自然地理 | 21篇 |
出版年
2024年 | 2篇 |
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 15篇 |
2018年 | 3篇 |
2017年 | 15篇 |
2016年 | 7篇 |
2015年 | 20篇 |
2014年 | 25篇 |
2013年 | 22篇 |
2012年 | 15篇 |
2011年 | 30篇 |
2010年 | 16篇 |
2009年 | 33篇 |
2008年 | 49篇 |
2007年 | 33篇 |
2006年 | 35篇 |
2005年 | 19篇 |
2004年 | 29篇 |
2003年 | 16篇 |
2002年 | 11篇 |
2001年 | 17篇 |
2000年 | 14篇 |
1999年 | 16篇 |
1998年 | 20篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1984年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有575条查询结果,搜索用时 15 毫秒
21.
基于Matlab的水准点稳定性分析 总被引:1,自引:0,他引:1
通过使用Matlab功能强大的数学软件,应用于测量工程的数据处理。具体解决变形监测中水准点是否稳定的判定问题。并通过计算实例说明其可行性和优越性。 相似文献
22.
In late-June, 1998, a series of thunderstorms dropped 16.5 cm (6.5 in.) of rain in a 72-h period over southeastern Ohio, causing extensive flooding, six deaths, and 179 million dollars in property damage. The storms also triggered more than 60 shallow landslides along a 64 km (40-mi) stretch of Interstate 77 between Buffalo and Marietta, Ohio. Almost all of the landslides were translational, occurring along the contact between colluvial soils and the underlying bedrock (shales, claystones, mudstones). Six sites were selected in the affected area for a detailed study of the shallow landslides. At each site, a record was made of the stratigraphy, slope geometry, number of landslides, landslide dimensions, hydrologic conditions, and influence of vegetation on landslide distribution. Both colluvial soils and underlying bedrock were sampled for laboratory investigations, which included determination of natural water content, grain size distribution, Atterberg limits, permeability, slake durability, and shear-strength parameters. Data from laboratory tests were used to perform sensitivity and stability analyses with respect to varying slope angles, strength parameters, and thicknesses of saturated colluvial soil. The results of the study indicate that the shallow landslides along Interstate 77 occurred when the colluvial soils reached 90% to 100% saturation, depending upon the slope angles. 相似文献
23.
Snow load on mesh systems is complicated by many factors. This paper presents field instrumentation data on snow load variation with temperature, snowfall and snow depth on a mesh system. It was found that snow load pattern on mesh systems changed with temperature even without variation in snow depth. It reached its maximum value when the temperature rose just above freezing to melt the interface. The field data was used to formulate appropriate snow load models for the various conditions of temperature in the field. The snow load models were used to study the performance of a number of mesh systems in North America and estimate the interface friction that was prevalent for the different surface conditions. 相似文献
24.
东亚夏季风成员的相互作用,构成了东亚夏季风高、低层环流的“多齿轮耦合”形态。本文利用多变量主成分分析(MV-EOF)等方法诊断分析了东亚夏季风多齿轮耦合的变化特征、耦合机制、时间稳定性、空间稳定特征及其对中国夏季降水的影响机制,并在此基础上构建了典型多齿轮耦合形态影响夏季降水的概念模型。结果表明,多齿轮耦合受到垂直温、压场的强迫和青藏高原大地形的影响,主要表现在年际变化上(周期为2~6年)。其前两个模态稳定地反映了东亚夏季风成员典型联动作用。在第一模态中,北方气旋、南亚高压和西太平洋副热带高压为主要耦合系统。其中北方气旋为正压结构,在高层通过南侧偏西气流与南亚高压耦合,南亚高压则通过中纬东部地区下沉辐散气流与西太平洋副热带高压联动。当该耦合模态增强时,有利于中国夏季降水呈自北向南“+-+-”分布。第二模态主要反映中高纬气旋、东亚副热带西风气流、南亚高压、西北太平洋反气旋系统和西太平洋副热带高压耦合特征。其中,中高纬气旋和西北太平洋反气旋为正压系统,两者通过其间的东南气流联动。气旋系统在高层通过南侧西风与东亚副热带西风急流和南亚高压联动。反气旋在中低层通过南侧的偏东气流影响副热带高压强度和面积。当该耦合模态增强时,中国黄河以北及河套地区降水偏多,黄河以南降水偏少。 相似文献
25.
26.
石崆山Ⅱ段岩质高边坡稳定性的工程地质系统分析研究 总被引:1,自引:1,他引:0
岩质高边坡稳定性的分析评价涉及工程地质学、岩体力学、计算科学等多学科交汇的问题,是一较为复杂的系统工程问题。在系统分析岩质高边坡赋存的地质背景和环境条件的基础上,采用系统分析评价、综合集成的方法应是研究分析和解决该问题的有效和最佳方法。针对漳龙高速公路石崆山Ⅱ段岩质高边坡工程,在系统分析边坡工程地质特性的基础上,采用赤平极射投影法和有限单元(FEM)法等,进行综合评价和系统分析,获得的稳定性结论,已正常运营使用若干年,反映了系统分析,综合评价方法是成功和有效的。它表明,综合评价、系统分析应是岩质高边坡稳定性评价分析的重要途径;它的综合内容和集成方式及其完善与工程实用性,有待进一步深入的研究和工程实践的运用及其经验的积累。 相似文献
27.
28.
This study presents a probabilistic neural network (PNN) technique for predicting the stability number of armor blocks of breakwaters. The PNN is prepared using the experimental data of Van der Meer. The predicted stability numbers of the PNN are compared with those of previous studies, i.e. by an empirical formula and a previous neural network model. The agreement index between the measured and predicted stability numbers by PNN are better than those by the previous studies. The PNN offers a way to interpret the network's structure in the form of a probability density function and it is easy to implement. Therefore, it can be an effective tool for designers of rubble mound breakwaters. 相似文献
29.
Pasquale Crea Concetta De Stefano Demetrio Milea Silvio Sammartano 《Marine Chemistry》2008,112(3-4):142-148
The results of a potentiometric investigation (by ISE-H+, glass electrode) on the speciation of phytate ion (Phy12−) in an ionic medium simulating the major components (Na+, K+, Ca2+, Mg2+, Cl− and SO42−) of natural seawater, at different salinities and t = 25 °C, are reported. The work was particularly aimed at determining the possible formation of mixed Ca2+–Mg2+–phytate ion pairs, and to establish how including the formation of these mixed species would affect the speciation modeling in seawater media. After testing various speciation models, that considering the formation of the MgCaH3Phy5−, MgCaH4Phy4−, Mg2CaH3Phy3− and Mg2CaH4Phy2− species was accepted, and corresponding stability constants were determined at two salinities (S = 5, 10). A discussion is reported both on the choice of the experimental conditions and on the possibility to extend these results to those typical of real seawater. A detailed procedure is also described to demonstrate that the stability of these species is higher than that statistically predicted. As reported in literature, a parameter, namely log X, has been determined in order to quantify this extra stability for the formation of each mixed species at various salinities. For example, at S = 10, log X113 = 2.67 and log X114 = 1.37 for MgCaH3Phy5− and MgCaH4Phy4− (statistical value is log Xstat = 0.60), and log X213 = 6.11 and log X214 = 2.15 for Mg2CaH3Phy3− and Mg2CaH4Phy2− (log Xstat = 1.43), respectively. Results obtained also showed that the formation of these species may occur even in conditions of low salinity (i.e. low concentration of alkaline earth cations) and low pH (i.e., more protonated ligand). 相似文献
30.