全文获取类型
收费全文 | 1225篇 |
免费 | 206篇 |
国内免费 | 446篇 |
专业分类
测绘学 | 87篇 |
大气科学 | 88篇 |
地球物理 | 282篇 |
地质学 | 1059篇 |
海洋学 | 130篇 |
天文学 | 17篇 |
综合类 | 68篇 |
自然地理 | 146篇 |
出版年
2024年 | 6篇 |
2023年 | 21篇 |
2022年 | 47篇 |
2021年 | 52篇 |
2020年 | 69篇 |
2019年 | 75篇 |
2018年 | 70篇 |
2017年 | 58篇 |
2016年 | 68篇 |
2015年 | 69篇 |
2014年 | 88篇 |
2013年 | 103篇 |
2012年 | 67篇 |
2011年 | 96篇 |
2010年 | 63篇 |
2009年 | 84篇 |
2008年 | 74篇 |
2007年 | 97篇 |
2006年 | 73篇 |
2005年 | 80篇 |
2004年 | 69篇 |
2003年 | 44篇 |
2002年 | 67篇 |
2001年 | 40篇 |
2000年 | 42篇 |
1999年 | 31篇 |
1998年 | 40篇 |
1997年 | 38篇 |
1996年 | 37篇 |
1995年 | 20篇 |
1994年 | 13篇 |
1993年 | 20篇 |
1992年 | 11篇 |
1991年 | 7篇 |
1990年 | 14篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1877条查询结果,搜索用时 15 毫秒
131.
核电厂项目设计接口管理分析 总被引:1,自引:0,他引:1
介绍了核电厂项目中的设计接口关系,以及我国应用接口控制手册(ICM)进行设计接口管理的工程实践,并对ICM的有效管理提出了新的看法。 相似文献
132.
Spatiotemporal variations of maximum seasonal freeze
depth in 1950s–2007 over the Heihe River Basin,
Northwest China 总被引:1,自引:0,他引:1
Investigation on spatiotemporal variations of maximum seasonal freeze depth (MSFD) over the Heihe River Basin is of great importance for systematic understanding of regional climate and environmental change, ecological-hydrological processes, water resources assessment, construction and resource development. Based on soil and air temperatures at the meteorological stations of the China Meteorological Administration (CMA) over the Heihe River Basin, MSFDs time series are structured into a composite time series over the 1960-2007 period. Evaluating the averaged MSFD time series for 1960 2007 reveals a statistically significant trend of 4.0 cm/decade or a net change of-19.2 cm for the 48-year period over the basin. The MSFD had significantly negative correlation with mean annual air temperature (MAAT), winter air temperature, mean annual ground surface temperature (MAGST), degree days of thawing for the air (DDTa) as well as for the surface (DDTs), and degree days of freezing for the surface (DDFs). While there was significantly positive correlation between DDF,. and MSFD time series, MSFD was deeper and changed greatly in the Heihe River source area. It was shallower in the east-central basin and gradually deepened in other sections of the basin. The MSFD distribution pattern in 2003-2005 is consistent with that of averaged degree days of freezing for air (DDFa) in 1960-2007. However, the maximum of MSFD may not be accurate, because there is no long term observation data in the deep seasonally frozen ground regions near the lower boundary of permafrost. With increasing elevation, averaged DDFa increased at a rate of 51.6 ℃-day/100m, therefore, the MSFG and the date reaching MSFG became deeper and later, respectively. 相似文献
133.
近年来分布式光纤感测技术在岩土与地质工程领域的应用研究已成为一个研究热点,但工程实践表明,埋入式传感光纤与被测岩土体之间的变形协调性会对监测结果产生显著的影响,该问题一直制约着光纤感测技术在工程监测中的推广。本文通过一系列室内拉拔试验,对比了3种预埋于砂土中的单模光纤在不同上覆压力的作用下的拉拔力-拉拔位移曲线,并建立了一个用于描述光纤-砂土界面力学性质的三段式的拉拔模型,分析峰值拉拔力、残余拉拔力、有效拉拔位移和残余拉拔位移4个参数在不同上覆压力作用下的变化情况。分析结果揭示传感光纤-砂土界面的力学特性和应力传递规律,为分布式光纤传感技术在岩土体变形监测中的应用,尤其在变形监测光纤的选用标准方面,提供了参考依据。 相似文献
134.
135.
以1981—2018年内蒙古典型草原季节性冻土为研究对象,通过气候倾向率、Mann-Kendall法、多元线性回归等方法,分析最大冻土时空分布特征、年际、年代际变化,研究影响最大冻土深度变化的气象因子。结果表明:(1) 内蒙古典型草原季节性冻土冻结初日在9—11月,终日在4—6月,年内最大冻土深度出现在2—3月,深度在100~280 cm之间。(2) 最大冻土深度年际变化分为下开口抛物线型、上开口抛物线型、正弦曲线型,从最大冻土深度气候倾向率看呈现减小趋势的站点有68%。(3) 最大冻土深度年代际变化分为逐年代递减、减-增型和无明显变化规律,50%的站点在1989年以后最大冻土深度发生突变。(4) 多元线性回归表明气温冻结指数、年平均风速、年极端最低气温对最大冻土深度产生显著影响。该研究揭示了最大冻土深度存在退化的事实,为草原应对气候变化提供指导,为陆地土壤和大气碳循环交换的研究给出提示。 相似文献
136.
随着计算机技术的不断进步,用户界面设计---有效的人机交互策略变得更加重要。地理信息系统的发展要求其系统软件的设计者与开发者设计开发出更加人性化的用户界面,以提高不同领域、不同层次软件使用者的满意度。 相似文献
137.
A. P. S. Selvadurai 《国际地质力学数值与分析法杂志》2011,35(6):639-651
In this paper, we develop an exact closed form solution for a circular entry point located at the interface between an impermeable material and a stratified porous medium, where the principal plane of hydraulic isotropy is inclined to the interface. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
138.
Lanzhou Valley Basin is composed of two smaller diamond-shaped basins striking from NW to SE and including 6 river terraces.
The lower terraces remaining even and smooth are main sites for city buildings. The main function of Lanzhou urban settlement
is a ferry and transport centre. Lanzhou used to be an important crossing site and post on the “silk road”, and then became
a transport and trade centre in Northwest China. In the middle part of the 17th century, Lanzhou became the capital of Gansu,
a new province. The development process of Lanzhou urban settlement indicates that urban settlement is a system consisting
of natural environment and human society based on the former. 相似文献
139.
Jerome B. Johnson 《水文研究》2004,18(1):53-64
A theory of pressure sensor response in snow is derived and used to examine the sources of measurement errors in snow water equivalent (SWE) pressure sensors. Measurement errors in SWE are caused by differences in the compressibility of the pressure sensor and the adjacent snow layer, which produces a shear stress along the perimeter of the sensor. When the temperature at the base of the snow cover equals 0 °C, differences in the snowmelt rate between the snow–SWE sensor interface and the adjacent snow–soil interface may also produce a shear stress along the sensor's perimeter. This shear stress perturbs the pressure field over the sensor, producing SWE measurement errors. Snow creep acts to reduce shear stresses along the SWE sensor's perimeter at a rate that is inversely proportional to the snow viscosity. For sustained periods of differential snowmelt, a difference in the mass of snow over the sensor compared with the surrounding soil will develop, producing additional permanent errors in SWE measurements. The theory indicates that SWE pressure sensor performance can be improved by designing a sensor with a high Young's modulus (low compressibility), low aspect ratio, large diameter and thermal properties that match those of the surrounding soil. Simulations of SWE pressure sensor errors using the theory are in close agreement with observed errors and may provide a means to correct historical SWE measurements for use in hydrological hindcast or climate studies. Published in 2003 by John Wiley & Sons, Ltd. 相似文献
140.
Interface damage and delamination is usually accompanied by frictional slip at contacting interfaces under compressive normal stress. The present work is concerned with an analysis of progressive interface failure using the cohesive crack model with the critical stress softening and frictional traction present at the contact. Both monotonic and cyclic loadings are considered for anti‐plane shear of an elastic plate bonded to a rigid substrate by means of cohesive interface. An analytical solution can be obtained by neglecting the effect of minor shear stress component. The analysis of progressive delamination process revealed three solution types, namely: short, medium and long plate solutions. The long plate solution was obtained under an assumption of quasistatic progressive growth of the delamination zone. In view of snap back response, the quasistatic deformation process cannot be executed by either traction or displacement control. The states of frictional slip accompanied by shake down or incremental failure are distinguished in the case of cyclic loading, related to load amplitude and structural dimensions. The analysis provides a reference solution for numerical treatment of more complex cases. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献