全文获取类型
收费全文 | 3356篇 |
免费 | 368篇 |
国内免费 | 371篇 |
专业分类
测绘学 | 663篇 |
大气科学 | 159篇 |
地球物理 | 383篇 |
地质学 | 900篇 |
海洋学 | 258篇 |
天文学 | 205篇 |
综合类 | 290篇 |
自然地理 | 1237篇 |
出版年
2024年 | 28篇 |
2023年 | 47篇 |
2022年 | 198篇 |
2021年 | 211篇 |
2020年 | 183篇 |
2019年 | 218篇 |
2018年 | 151篇 |
2017年 | 192篇 |
2016年 | 187篇 |
2015年 | 143篇 |
2014年 | 142篇 |
2013年 | 217篇 |
2012年 | 174篇 |
2011年 | 161篇 |
2010年 | 133篇 |
2009年 | 147篇 |
2008年 | 158篇 |
2007年 | 166篇 |
2006年 | 144篇 |
2005年 | 130篇 |
2004年 | 154篇 |
2003年 | 128篇 |
2002年 | 114篇 |
2001年 | 89篇 |
2000年 | 92篇 |
1999年 | 63篇 |
1998年 | 58篇 |
1997年 | 48篇 |
1996年 | 34篇 |
1995年 | 32篇 |
1994年 | 33篇 |
1993年 | 24篇 |
1992年 | 16篇 |
1991年 | 24篇 |
1990年 | 10篇 |
1989年 | 17篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4095条查询结果,搜索用时 31 毫秒
941.
利用EOF相空间分析东亚梅雨旱涝长期过程的初步研究 总被引:11,自引:1,他引:11
利用非线性动力学中的相空间概念,分析了梅雨旱涝3~5年循环的长期过程.对全球热带850hPa的纬向风场距平所作的EOF,第1特征向量显示了Walker环流异常在赤道球圈上的分布;第2特征向量主要显示热带-副热带之间的环流异常的经向分布.在第1时间系数和第2时间系数所定义的2维相空间中,由相轨线分析,得到梅雨涝年主要集中于第2象限,而旱年则相对多在第4象限.说明梅雨旱涝年际变异的主导模态和热带大气环流的主要特征向量有着密切的关联.它们显示了以3~5年时间尺度的大气环流演变的长期特征性过程. 相似文献
942.
This paper investigates the nonlinear prediction of monthly rainfall time series which consists of phase space con-tinuation of one-dimensional sequence, followed by least-square determination of the coefficients for the terms of the time-lag differential equation model and then fitting of the prognostic expression is made to 1951-1980 monthly rainfall datasets from Changsha station Results show that the model is likely to describe the nonlinearity of the an-nual cycle of precipitation on a monthly basis and to provide a basis for flood prevention and drought combating for the wet season. 相似文献
943.
提出用自然正交函数分解的方法来开拓相空间,从而研究有限区域上大气系统的混沌性质。与利用时间滞后作漂移来开拓相空间方法相比较,前者充分保证了相空间各基矢量的正交性,弥补了后者只能对单点资料进行计算的不足。文中利用欧洲中期数值天气预报中心1980-1986年北半球亚洲地区的500hPa位势高度场逐日格点资料进行了EOF分解并计算得到了该地区大气系统的分维数为D=6.2,从而表明,为支撑该地区大气系统的混沌吸引子至少应取7维系统或以7个变量才能作出描述。 相似文献
944.
945.
朱元泓 《武汉大学学报(信息科学版)》1995,(2)
从屏幕色到印刷的转换方法朱元泓。是,人们感到头痛的是屏。的效果。为了达到理想的印刷色土要进行多次重复尝试(从修改荧光屏,浪费材料,特别是多色地图电子复制设计A屏幕色转换为印刷色的新方法,即逆解组纶堡方d值修正法,并说明两种方法可达到的精度。j色通过红... 相似文献
946.
947.
旅游区游憩活动地域组合研究 总被引:23,自引:3,他引:20
针对市场导向的旅游开发战略与旅游地规划设计的整合问题,从游憩角度探讨解决这一问题的方法和技术,论文分析了游憩需求与游憩活动,设施和环境之间的相互关系,认为旅游地是由游憩活动,设施和环境及其支持系统旅游地规划的中心内容是游憩规划,游憩活动地域组合具有4种类型,3种模式。 相似文献
948.
ABSTRACTReliable simulations of hydrological models require that model parameters are precisely identified. In constraining model parameters to small ranges, high parameter identifiability is achieved. In this study, it is investigated how precisely model parameters can be constrained in relation to a set of contrasting performance criteria. For this, model simulations with identical parameter samplings are carried out with a hydrological model (SWAT) applied to three contrasting catchments in Germany (lowland, mid-range mountains, alpine regions). Ten performance criteria including statistical metrics and signature measures are calculated for each model simulation. Based on the parameter identifiability that is computed separately for each performance criterion, model parameters are constrained to smaller ranges individually for each catchment. An iterative repetition of model simulations with successively constrained parameter ranges leads to more precise parameter identifiability and improves model performance. Based on these results, a more consistent handling of model parameters is achieved for model calibration. 相似文献
949.
G. Christakos C. T. Miller D. Oliver 《Stochastic Environmental Research and Risk Assessment (SERRA)》1993,7(1):14-32
This paper develops concepts and methods to study stochastic hydrologic models. Problems regarding the application of the existing stochastic approaches in the study of groundwater flow are acknowledged, and an attempt is made to develop efficient means for their solution. These problems include: the spatial multi-dimensionality of the differential equation models governing transport-type phenomena; physically unrealistic assumptions and approximations and the inadequacy of the ordinary perturbation techniques. Multi-dimensionality creates serious mathematical and technical difficulties in the stochastic analysis of groundwater flow, due to the need for large mesh sizes and the poorly conditioned matrices arising from numerical approximations. An alternative to the purely computational approach is to simplify the complex partial differential equations analytically. This can be achieved efficiently by means of a space transformation approach, which transforms the original multi-dimensional problem to a much simpler unidimensional space. The space transformation method is applied to stochastic partial differential equations whose coefficients are random functions of space and/or time. Such equations constitute an integral part of groundwater flow and solute transport. Ordinary perturbation methods for studying stochastic flow equations are in many cases physically inadequate and may lead to questionable approximations of the actual flow. To address these problems, a perturbation analysis based on Feynman-diagram expansions is proposed in this paper. This approach incorporates important information on spatial variability and fulfills essential physical requirements, both important advantages over ordinary hydrologic perturbation techniques. Moreover, the diagram-expansion approach reduces the original stochastic flow problem to a closed set of equations for the mean and the covariance function. 相似文献
950.
Mental Maps and Fuzziness in Space Preferences* 总被引:1,自引:0,他引:1
Mental maps are widely used to represent aggregate residential preferences in a population. This study examines the contention by researchers that the dominant viewpoint in a group in terms of residential desirability is not affected by the fuzziness in individual space preferences. Results indicate that a significant misrepresentation of group preferences can result when fuzziness of individual preferences is overlooked. The use of ordinal scales to generate mental maps is likely to distort the actual pattern of residential preferences that dominates in the group because of the failure of the ranking approach to account for imprecision and ambiguity in individual preferences. Because interval scales used in rating or evaluating tasks do not force individuals to give a crisp judgement of places, they are more adequate than ordinal scales for mental mapping and for behavioral analysis. 相似文献