全文获取类型
收费全文 | 2315篇 |
免费 | 577篇 |
国内免费 | 441篇 |
专业分类
测绘学 | 232篇 |
大气科学 | 436篇 |
地球物理 | 862篇 |
地质学 | 723篇 |
海洋学 | 536篇 |
天文学 | 112篇 |
综合类 | 186篇 |
自然地理 | 246篇 |
出版年
2024年 | 3篇 |
2023年 | 27篇 |
2022年 | 42篇 |
2021年 | 55篇 |
2020年 | 66篇 |
2019年 | 86篇 |
2018年 | 57篇 |
2017年 | 82篇 |
2016年 | 91篇 |
2015年 | 89篇 |
2014年 | 112篇 |
2013年 | 162篇 |
2012年 | 133篇 |
2011年 | 152篇 |
2010年 | 141篇 |
2009年 | 150篇 |
2008年 | 149篇 |
2007年 | 211篇 |
2006年 | 170篇 |
2005年 | 138篇 |
2004年 | 136篇 |
2003年 | 113篇 |
2002年 | 109篇 |
2001年 | 94篇 |
2000年 | 77篇 |
1999年 | 99篇 |
1998年 | 77篇 |
1997年 | 72篇 |
1996年 | 72篇 |
1995年 | 58篇 |
1994年 | 65篇 |
1993年 | 55篇 |
1992年 | 51篇 |
1991年 | 42篇 |
1990年 | 17篇 |
1989年 | 31篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3333条查询结果,搜索用时 15 毫秒
41.
42.
Researches on breaking-induced currents by waves are summarized firstly in this paper. Then, a combined numerical model in orthogonal curvilinear coordinates is presented to simulate wave-induced current in areas with curved boundary or irregular coastline. The proposed wave-induced current model includes a nearshore current module established through orthogonal curvilinear transformation form of shallow water equations and a wave module based on the curvilinear parabolic approximation wave equation. The wave module actually serves as the driving force to provide the current module with required radiation stresses. The Crank-Nicolson finite difference scheme and the alternating directions implicit method are used to solve the wave and current module, respectively. The established surf zone currents model is validated by two numerical experiments about longshore currents and rip currents in basins with rip channel and breakwater. The numerical results are compared with the measured data and published numerical results. 相似文献
43.
44.
45.
本文研究了1类具梯度项的次线性椭圆型方程大解和完全有界解的存在性问题。运用上下解方法和极值原理分别得到了Rn上方程存在完全大解的充分必要条件和存在完全有界解的充分条件,并且证明了该方程在Rn中光滑有界区域Ω上不存在大解。 相似文献
46.
Deep excavations particularly in deep deposits of soft clay can cause excessive ground movements and result in damage to adjacent buildings. Extensive plane strain finite element analyses considering the small strain effect have been carried out to examine the wall deflections for excavations in soft clay deposits supported by retaining walls and bracing. The excavation geometry, soil strength and stiffness properties, and the wall stiffness were varied to study the wall deflection behavior. Based on these results, a simple Polynomial Regression (PR) model was developed for estimating the maximum wall deflection. Wall deflections computed by this method compare favorably with a number of field and published records. 相似文献
47.
本文基于GRAPES全球模式的短期预报误差样本,利用赤道波动正规模态研究了热带风、压场平衡特征,并根据这些特征分析了线性平衡方程(LBE)在该区域应用时存在的问题。结果表明:(1)赤道波动能成功解释热带短期预报误差样本的大部分分量,对流层中层为60%~80%,对流层顶和平流层低层为80%以上。(2)在可解释的误差方差中,赤道罗斯贝波(ER)占比仅为30%~55%,其他赤道波动的作用不可忽视。(3)在ER模态基础上引入其他赤道波动会大幅削弱原有风、压场平衡约束,重力惯性波与Kelvin波的作用最为显著。此时,对流层中层位势高度h与u风、v风间的约束接近于零,而平流层低层h-u的平衡特征由Kelvin波主导。(4)LBE主要表达了ER模态下的风、压场平衡特征,与实际情形相比高估了热带风、压场的耦合程度,进一步的改进中需削弱这一虚假平衡,使得热带风、压场分析变得更加独立。 相似文献
48.
采用Ronge-Kutta射线追踪法对地震勘探中几个典型地质模型的地震波射线路径和旅行时计算的实例和效果进行分析。将Ronge-Kutta射线追踪模拟的结果与程函方程计算的时距曲线结果进行对比,验证了Ronge-Kutta射线追踪法的易实现性和程函方程有限差分旅行时算法的强稳定性,表明Ronge-Kutta射线追踪法在复杂构造区域进行地震射线路径和旅行时计算时能得到较好的模拟效果。 相似文献
49.
地表温度是反映地表环境的一个重要参数,精确获取地表温度的方法对研究城市热岛效应、进行生态环境监测评价是必不可少的。利用遥感手段进行地表温度的反演是一种较新颖的方法,相对成熟的反演算法主要有单通道算法、辐射传输方程法及单窗算法。本文以山东省威海市Landsat TM数据为例,分别利用辐射传输方程法和单窗算法进行地表温度反演,通过遥感目视解译的方法提取研究区各类典型地物对应的地表温度,进行统计分析,结果表明,两者反演得到的地表温度具有一致的变化趋势,其中单窗算法中不同典型地物的地表温度整体标准差较小,如建设用地为0.530,起伏波动小,算法精度略优于辐射传输方程法。 相似文献
50.
Nine organic-rich shale samples of Lower Cambrian black shales were collected from a recently drilled well in the Qiannan Depression, Guizhou Province where they are widely distributed with shallower burial depth than in Sichuan Basin, and their geochemistry and pore characterization were investigated. The results show that the Lower Cambrian shales in Qiannan Depression are organic rich with TOC content ranging from 2.81% to 12.9%, thermally overmature with equivalent vitrinite reflectance values in the range of 2.92–3.25%, and clay contents are high and range from 32.4% to 53.2%. The samples have a total helium porosity ranging from 2.46% to 4.13% and total surface area in the range of 9.08–37.19 m2/g. The estimated porosity in organic matters (defined as the ratio of organic pores to the volume of total organic matters) based on the plot of TOC vs helium porosity is about 10% for the Lower Cambrian shales in Qiannan Depression and is far lower than that of the Lower Silurian shales (36%) in and around Sichan Basin. This indicates that either the organic pores in the Lower Cambrian shale samples have been more severely compacted than or they did not develop organic pores as abundantly as the Lower Silurian shales. Our studies also reveal that the micropore volumes determined by Dubinin–Radushkevich (DR) equation is usually overestimated and this overestimation is closely related to the non-micropore surface area of shales (i.e. the surface area of meso- and macro-pores). However, the modified BET equation can remove this overestimation and be conveniently used to evaluate the micropore volumes/surface area and the non-micropore surface areas of micropore-rich shales. 相似文献