全文获取类型
收费全文 | 3652篇 |
免费 | 638篇 |
国内免费 | 938篇 |
专业分类
测绘学 | 355篇 |
大气科学 | 823篇 |
地球物理 | 690篇 |
地质学 | 2256篇 |
海洋学 | 349篇 |
天文学 | 26篇 |
综合类 | 297篇 |
自然地理 | 432篇 |
出版年
2024年 | 22篇 |
2023年 | 41篇 |
2022年 | 108篇 |
2021年 | 138篇 |
2020年 | 129篇 |
2019年 | 151篇 |
2018年 | 136篇 |
2017年 | 128篇 |
2016年 | 205篇 |
2015年 | 199篇 |
2014年 | 256篇 |
2013年 | 203篇 |
2012年 | 270篇 |
2011年 | 273篇 |
2010年 | 234篇 |
2009年 | 286篇 |
2008年 | 227篇 |
2007年 | 334篇 |
2006年 | 286篇 |
2005年 | 211篇 |
2004年 | 203篇 |
2003年 | 152篇 |
2002年 | 139篇 |
2001年 | 121篇 |
2000年 | 122篇 |
1999年 | 109篇 |
1998年 | 70篇 |
1997年 | 94篇 |
1996年 | 61篇 |
1995年 | 67篇 |
1994年 | 59篇 |
1993年 | 55篇 |
1992年 | 46篇 |
1991年 | 26篇 |
1990年 | 21篇 |
1989年 | 16篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有5228条查询结果,搜索用时 15 毫秒
1.
STUDY ON GIS FOR YIELD ESTIMATION BY REMOTE SENSING IN JILIN MAIZE BELTSTUDYONGISFORYIELDESTIMATIONBYREMOTESENSINGINJILINMAIZ... 相似文献
2.
In this paper the second order characteristic (discontinuous bifurcation) condition is derived for the granular flow (fully plastic) equations. This second order bifurcation equation is shown to be formally identical to the first order localization requirement during steady elastoplastic deformation provided the elastic compliance tensor is substituted for the product of the plastic multiplier with the flow Hessian. For isotropic yield and flow functions the invariant form of the characteristic condition is given in detail, as well as an alternative expression in adapted co‐ordinates. The characteristic condition can be regarded as defining a hardening function which is maximized to identify the critical angles. When the method is applied to 3D Coulomb flow, Mohr's 3D fracture plane conditions are obtained uniquely. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
3.
在△T异常解释课题中,一个新的角度参量─—视磁化特征角的拟定,最大限度地简化了球体磁场表达式。从而才有可能通过特殊解法,给出了球体磁场的极值与拐点公式。作者据此建立了四种不受正常场制约、仅需异常的局部持征曲线即可全面解释三度异常的解释方法。屏障分解、叠加判别、三元迭代的设计,为解释三度体叠加异常给出了简单而易行的途径。 相似文献
4.
In view of rapid developments in iterative solvers, it is timely to re‐examine the merits of using mixed formulation for incompressible problems. This paper presents extensive numerical studies to compare the accuracy of undrained solutions resulting from the standard displacement formulation with a penalty term and the two‐field mixed formulation. The standard displacement and two‐field mixed formulations are solved using both direct and iterative approaches to assess if it is cost‐effective to achieve more accurate solutions. Numerical studies of a simple footing problem show that the mixed formulation is able to solve the incompressible problem ‘exactly’, does not create pressure and stress instabilities, and obviate the need for an ad hoc penalty number. In addition, for large‐scale problems where it is not possible to perform direct solutions entirely within available random access memory, it turns out that the larger system of equations from mixed formulation also can be solved much more efficiently than the smaller system of equations arising from standard formulation by using the symmetric quasi‐minimal residual (SQMR) method with the generalized Jacobi (GJ) preconditioner. Iterative solution by SQMR with GJ preconditioning also is more elegant, faster, and more accurate than the popular Uzawa method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
5.
Tidal inundation mapping under enhanced land subsidence in Semarang,Central Java Indonesia 总被引:3,自引:0,他引:3
Tidal inundation by high tide under enhanced land subsidence is a damaging phenomenon and a major threat to the Semarang urban
area in Indonesia. It impacts on economic activities, as well as the cost of an emergency program and causes interruption
of pubic services, danger of infectious diseases and injury to human lives. This study examines a spatial analysis tool on
the GIS-raster system for the tidal inundation mapping based on the subsidence-benchmark data and modified detail digital
elevation model. Neighborhood operation and iteration model as a spatial analysis tool have been applied in order to calculate
the encroachment of the tidal inundation on the coastal area. The resulting map shows that the tidal flood spreads to the
lowland area and causes the inundation of coastal settlement, infrastructure, as well as productive agricultural land, i.e.,
the fish-pond area. The monitoring of the vulnerable area due to the tidal inundation under the scenario of extended land
subsidence plays an important role in long-term coastal zone management in Semarang. 相似文献
6.
7.
8.
赤潮生物种类特征光谱获取技术 总被引:1,自引:0,他引:1
较为系统地研究了赤潮生物水体反射率曲线获取方法。通过对 2类反射率反演方法得出的反射率曲线与实际反射率曲线进行比较 ,得出在不具备大气环境参数的情况下 ,经验线性法的反演结果与实际反射率曲线最接近的结论 ,并进一步对正常海水和赤潮生物水体的光谱特性进行分析 ,提取出赤潮生物水体的特征光谱。这是进行赤潮监测和识别的重要前提 相似文献
9.
Fishing, selection, and phenotypic evolution 总被引:10,自引:9,他引:10
10.
刘新国 《中国海洋大学学报(自然科学版)》1996,(2)
本文系统地研究具二次约束最小二乘问题的敏度分析。首先给出长期方程唯一正根的上界和下界;然后证明割线法用于计算拉格朗日乘子时全局收敛;最后给出解的扰动界。 相似文献