全文获取类型
收费全文 | 3589篇 |
免费 | 1035篇 |
国内免费 | 638篇 |
专业分类
测绘学 | 153篇 |
大气科学 | 384篇 |
地球物理 | 2170篇 |
地质学 | 1285篇 |
海洋学 | 637篇 |
天文学 | 72篇 |
综合类 | 269篇 |
自然地理 | 292篇 |
出版年
2024年 | 20篇 |
2023年 | 59篇 |
2022年 | 122篇 |
2021年 | 141篇 |
2020年 | 136篇 |
2019年 | 199篇 |
2018年 | 170篇 |
2017年 | 166篇 |
2016年 | 176篇 |
2015年 | 194篇 |
2014年 | 223篇 |
2013年 | 197篇 |
2012年 | 203篇 |
2011年 | 213篇 |
2010年 | 187篇 |
2009年 | 254篇 |
2008年 | 221篇 |
2007年 | 277篇 |
2006年 | 251篇 |
2005年 | 198篇 |
2004年 | 219篇 |
2003年 | 184篇 |
2002年 | 176篇 |
2001年 | 112篇 |
2000年 | 124篇 |
1999年 | 106篇 |
1998年 | 96篇 |
1997年 | 104篇 |
1996年 | 90篇 |
1995年 | 57篇 |
1994年 | 67篇 |
1993年 | 77篇 |
1992年 | 47篇 |
1991年 | 45篇 |
1990年 | 38篇 |
1989年 | 22篇 |
1988年 | 22篇 |
1987年 | 22篇 |
1986年 | 10篇 |
1985年 | 4篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1954年 | 4篇 |
排序方式: 共有5262条查询结果,搜索用时 46 毫秒
81.
折射层析成像法测试隧道围岩松动圈 总被引:1,自引:0,他引:1
通过应用折射层析成像法在乌鞘岭特长隧道中的测试,说明该方法对于横向速度变化不均一,过渡带速度渐变的地质情况具有分辨率高、图像直观、易于解释,适合对隧道围岩松动圈的测试. 相似文献
82.
沙粒不能“远走高飞”———有关“尘暴”的一条根本原理 总被引:3,自引:0,他引:3
沙与尘虽然都是岩石物理风化的产物, 但在风力作用下, 习性截然不同。拜格诺用严格的物理实验证明, 尘粒能随风远走高飞, 而沙粒却只能在地面附近跳跃前进。从北方侵袭华北平原的所谓沙尘暴, 实质上都是尘暴。对历次重大天气事件沉积物的分析, 也完全证明了这一点。因此, 尘暴物质的源头不是来自有沙, 而是有尘的地方; 从而可以使人们采取正确的治理方法。 相似文献
83.
Results are presented from a seismic refraction survey (P-S waves) carried out in different years on recent faults of North Sakhalin. Structural features of the near-surface zone of active faults with different types of tectonic motions and their imaging in seismic fields are demonstrated. Criteria for estimating the activity of the studied tectonic disruption are proposed. 相似文献
84.
泥石流流速是难以实测和准确推算的重要参数。在分析既有各类弯道超高计算公式的基础上,探讨适用于各类泥石流的弯道超高计算模式,进而改进基于弯道超高的粘性泥石流、稀性泥石流和泥流的流速计算公式,用实例加以验证。 相似文献
85.
Summary. Conventional blasting causes cracks and fractures in the rock. Controlled blasting techniques produce the macrocrack in a
desired direction and eliminate microcrack in the remaining rock. Macrocrack development in desired direction is required
for extraction of dimensional stone and at the same time there is need to reduce microcrack development in the block and remaining
rock. To achieve the objectives, experimental work in the quarries was carried out for separating marble block from the in
situ strata as practiced in some of the Indian mines by using detonating cord of 30 to 50 g/m by varying hole spacing, hole
diameter, air cushioning, water and sand filled blast-holes. Blasthole notching was carried out. Further, tests were carried
out by using various liners inside the blasthole to determine the damages in the extracted block and remaining rock. The designed
experimental work was undertaken and rock samples were collected by coring before and after blasting for quantification of
microcrack in the rock. P-wave velocity and microscopic studies were conducted for quantification of damages. Experiments
were also conducted at laboratory scale for the quantification of damages in single circular and notched holes with variation
of stemming and liners. The P-wave velocity close to hole always reduces after blast and in case of NG-based charge and detonating
cord it decreases up to 1/3rd. With PVC pipe and paper tube liners decrease is negligible. Thus, by using notched hole with paper tube, decrease in P-wave
is minimum indicating least damage. 相似文献
86.
A good number of empirical formulae and methods dealing with the analysis of the effects of blast-induced ground vibrations have been developed. The most common approach suggested for estimating the attenuation of particle velocity on the ground is to scale the distance (scaled distance, SD). This approach makes it possible to estimate the peak particle velocity when the amount of explosive charge or the distance or both are altered.Many parameters known to have an influence on particle velocity have been used for particle velocity prediction equations. Some of these parameters are maximum charge per delay, the distance between the station and shot location, burden, inelastic attenuation factor and site factors. However, the impacts of the discontinuities existing on the benches where blasts are detonated on the propagation velocity of seismic waves have not been taken into consideration in these equations.This study aims to examine the impacts of the discontinuity frequency parameter derived through geological measurements carried out on the blasting benches or nearby in a quarry mine (Supren, Eskisehir) in Turkey on the propagation of blast-induced ground vibrations. Developed based on the geological observations carried out on the benches, the model was formed by adding discontinuity frequency parameter to the particle velocity prediction model suggested by Nicholls et al. [Nicholls HR, Johnson CF, Duvall WI. Blasting vibrations and their effects on structures. Bulletin no. 656. Washington, DC: US Bureau of Mines; 1971]. In order to research the effect of the discontinuity frequency in the bench on the blast-induced ground vibrations, the relationship between the recorded peak particle velocity, scaled distance and discontinuity frequency was statistically evaluated for the site. The established relationship and the results of the study are presented. 相似文献
87.
88.
基于对非饱和多孔介质的研究成果,考虑孔隙中的液相和气相的相互影响,研究非饱和土地基中剪切S波的传播特性。通过非饱和土中固相、液相和气相的质量平衡方程、动量平衡方程和非饱和土有效应力原理,建立问题的弹性波动方程,经过理论推导给出非饱和土中剪切S波的弥散特征方程。通过数值算例分析剪切S波的波速和衰减系数随饱和度、频率和固有渗透系数等因素的变化规律。结果表明,剪切S波的波速几乎不受饱和度的影响,但其随着频率的增大而减小,随着固有渗透系数的增大先不变后增大;剪切S波的衰减系数随着饱和度和频率的增加均增大,而随着固有渗透系数的增大先不变后增大最后减小。 相似文献
89.
90.
Han Wenliang Gao Guoming Wang Guangqian Hui Yujia Department of Hydraulic Engineering Tsinghua University Beijing China 《国际泥沙研究》2000,(3)
I INTRODUCTIONThe settlement of particles in fluid has been studied in many fields such as hydraulics, metallurgy andchemistry since the middle of 19 century because of its great importance. Although the settlement ofsingle particle and group settling velocity of uniform particles in still water are relatively well-studied, yetthe settlement of non-uniform particles in flowing water lacks understanding. For instance, Cunningham(1910), Richardson (1954) and Batchelor (1972), have obtained… 相似文献