全文获取类型
收费全文 | 8633篇 |
免费 | 1027篇 |
国内免费 | 1432篇 |
专业分类
测绘学 | 469篇 |
大气科学 | 1231篇 |
地球物理 | 1761篇 |
地质学 | 4188篇 |
海洋学 | 1019篇 |
天文学 | 1095篇 |
综合类 | 465篇 |
自然地理 | 864篇 |
出版年
2024年 | 45篇 |
2023年 | 139篇 |
2022年 | 304篇 |
2021年 | 302篇 |
2020年 | 292篇 |
2019年 | 312篇 |
2018年 | 445篇 |
2017年 | 386篇 |
2016年 | 490篇 |
2015年 | 362篇 |
2014年 | 499篇 |
2013年 | 505篇 |
2012年 | 449篇 |
2011年 | 494篇 |
2010年 | 511篇 |
2009年 | 552篇 |
2008年 | 466篇 |
2007年 | 410篇 |
2006年 | 391篇 |
2005年 | 309篇 |
2004年 | 272篇 |
2003年 | 246篇 |
2002年 | 233篇 |
2001年 | 220篇 |
2000年 | 219篇 |
1999年 | 247篇 |
1998年 | 208篇 |
1997年 | 208篇 |
1996年 | 170篇 |
1995年 | 137篇 |
1994年 | 99篇 |
1993年 | 132篇 |
1992年 | 86篇 |
1991年 | 82篇 |
1990年 | 56篇 |
1989年 | 68篇 |
1988年 | 57篇 |
1987年 | 65篇 |
1986年 | 71篇 |
1985年 | 48篇 |
1984年 | 54篇 |
1983年 | 55篇 |
1982年 | 56篇 |
1981年 | 35篇 |
1980年 | 37篇 |
1979年 | 39篇 |
1976年 | 22篇 |
1975年 | 24篇 |
1974年 | 20篇 |
1973年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
101.
灰色系统在地面沉降分析中的应用 总被引:4,自引:0,他引:4
该文将灰色系统理论引入地面沉降的研究之中。根据上海地面沉降的历史数据建立了上海地面沉降发展的GM(1,1)模型以及地面沉降与地下水位变化的映射GM(1,2)模型,最后运用所建立的模型对地面沉降的发展态势进行了预测。 相似文献
102.
103.
104.
This paper proposes a simple lattice model for collapse analysis of RC bridges subjected to earthquakes by using the extended distinct element method (EDEM). In the model, a concrete element consists of lumped masses connected to one another by springs, and a reinforcement bar is represented by a discrete model or an integrated model. The proposed lattice model is simple but its parameters are reasonably defined. It has fewer element nodes and connecting springs, which will be of benefit by shortening the CPU time. The processes to determine the initial stiffness of concrete and steel springs, the parameters of the constitutive model and the fracture criteria for springs are described. A re‐contact spring model is also proposed to simulate the re‐contact of the concrete after fracture of springs; and a general grid searching method is used to decrease the CPU time for judging re‐contact after fracture. The lattice model is assessed by numerical simulations and experiments. As an application, a damaged single‐column pier subjected to the Kobe Earthquake in 1995 is analysed by EDEM with the proposed model. The simulation results indicate that the proposed model predicts well qualitatively the collapse process of RC bridges. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
105.
106.
The Northward Shift of Climatic Belts in China During the Last 50 Years and the Corresponding Seasonal Responses 总被引:29,自引:0,他引:29
Along the meridian of 105°E, the Chinese region are divided into two parts, east and west. The results show that in the east part of China the temperate extratropical belt, the warm extratropical belt,and the northern subtropical belt shift northward significantly, whereas the middle subtropical belt and the southern subtropical belt have less or no change. As for the northern subtropical belt, the maximal northward shift can reach 3.7 degrees of latitude. As for the warm extratropical belt, along the meridian of 120°-125°E, the maximal northward shift can reach 3-4 degrees. In the west part of China, each climatic belt changes little. Only in the Xinjiang area are the significant northward shifts. Correspondingly, it is found that in the last 50 years the traditional seasons have changed. For Beijing, Hailar, and Lanzhou, in general, summer becomes longer and winter shorter over the last 50 years. Summer begins early and ends late with respect to early 1950s. Contrary to the summer, winter begins la 相似文献
107.
Construction of Green's function to the external Dirichlet boundary-value problem for the Laplace equation on an ellipsoid of revolution 总被引:1,自引:0,他引:1
Green's function to the external Dirichlet boundary-value problem for the Laplace equation with data distributed on an ellipsoid
of revolution has been constructed in a closed form. The ellipsoidal Poisson kernel describing the effect of the ellipticity
of the boundary on the solution of the investigated boundary-value problem has been expressed as a finite sum of elementary
functions which describe analytically the behaviour of the ellipsoidal Poisson kernel at the singular point ψ = 0. We have
shown that the degree of singularity of the ellipsoidal Poisson kernel in the vicinity of its singular point is of the same
degree as that of the original spherical Poisson kernel.
Received: 4 June 1996 / Accepted: 7 April 1997 相似文献
108.
“平面图形演化方法”是利用无量刚的异常信息量来反映震前异常空间分布及其随时间的演化,从而预报发震时间和地点的一种方法,这种方法μ值等值线图法,μ值异常平面图法组成,它是通过绘制不同的时间上述二种平面图,通过分析水位,水化异常于震前在时间上,空间上的演化规律,寻找μ值异常集中区或高值区,异常丛集图像分布区,条带图像分布带及条带交叉图像地区,并考虑异常分布图像与活动构造带和地震带的关系,从而对强震发生 相似文献
109.
本文考虑液固耦联及底板几何非线性与土壤弹性,建立了液-固-土耦合的储液罐翘离分析力学模型。算例表明,恢复力矩与翘离角之间的关系可以表达为分段线性,翘离将使地震响应增大。 相似文献
110.
井间电阻率层析成象的某些进展 总被引:7,自引:2,他引:7
用有限元法作电阻率层析成象的核心问题是Jacobi矩阵的求取和反演成象算法的研究。本文主要论述了这两方面的最新进展,即求取Jacobi矩阵的格林函数法,用于反演成象计算的平滑度约束反演。文中通过理论模型的成象计算,比较了两种反演算法的成象效果。 相似文献