全文获取类型
收费全文 | 2845篇 |
免费 | 567篇 |
国内免费 | 658篇 |
专业分类
测绘学 | 203篇 |
大气科学 | 507篇 |
地球物理 | 780篇 |
地质学 | 1481篇 |
海洋学 | 396篇 |
天文学 | 88篇 |
综合类 | 279篇 |
自然地理 | 336篇 |
出版年
2024年 | 20篇 |
2023年 | 74篇 |
2022年 | 150篇 |
2021年 | 179篇 |
2020年 | 121篇 |
2019年 | 136篇 |
2018年 | 173篇 |
2017年 | 144篇 |
2016年 | 164篇 |
2015年 | 156篇 |
2014年 | 151篇 |
2013年 | 165篇 |
2012年 | 145篇 |
2011年 | 161篇 |
2010年 | 169篇 |
2009年 | 144篇 |
2008年 | 115篇 |
2007年 | 125篇 |
2006年 | 80篇 |
2005年 | 96篇 |
2004年 | 74篇 |
2003年 | 102篇 |
2002年 | 117篇 |
2001年 | 121篇 |
2000年 | 133篇 |
1999年 | 137篇 |
1998年 | 79篇 |
1997年 | 110篇 |
1996年 | 91篇 |
1995年 | 57篇 |
1994年 | 59篇 |
1993年 | 83篇 |
1992年 | 54篇 |
1991年 | 46篇 |
1990年 | 26篇 |
1989年 | 19篇 |
1988年 | 15篇 |
1987年 | 16篇 |
1986年 | 12篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1973年 | 2篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4070条查询结果,搜索用时 15 毫秒
801.
802.
严重风蚀穴(群众称之为风剥板)不均匀分布于流动沙地中,坚硬紧实,单一生物措施难以治理。经采取环坡深耥大垄,运用豆科牧草沙打旺与禾本科谷子混播的方法,使风蚀穴得到了治理,方法简单易行,并取得明显的生态效益和经济效益 相似文献
803.
周期—频度谱方法在大庆台网数字化地震记录分析中的应用 总被引:2,自引:0,他引:2
论述了周期-频率谱方法在分析数字化地震记录中的应用。结果表明该方法对识别各类振动的性质较为有效,所形成的一整套分析流程适用于各种地震数字记录分析。 相似文献
804.
Guocheng Pan 《Natural Resources Research》1997,6(4):285-293
A fundamental task for petroleum exploration decision-making is to evaluate the uncertainty of well outcomes. The recent development
of geostatistical simulation techniques provides an effective means to the generation of a full uncertainty model for any
random variable. Sequential indicator simulation has been used as a tool to generate alternate, equal-probable stochastic
models, from which various representations of uncertainties can be created. These results can be used as input for the quantification
of various risks associated with a wildcat drilling program or the estimation of petroleum resources. A simple case study
is given to demonstrate the use of sequential indicator simulation. The data involves a set of wildcat wells in a gas play.
The multiple simulated stochastic models are then post-processed to characterize various uncertainties associated with drilling
outcomes. 相似文献
805.
河东煤田地史—热史模拟与煤变质演化 总被引:13,自引:0,他引:13
河东煤田是华北石炭二叠纪重要煤田之一.本文采用盆地数值模拟方法,建立了煤田地史一热史模型,恢复了煤变质演化历程,总结出煤级分布规律。 相似文献
806.
This study is essentially an experiment on the control experiment in the August 1975 catastrophe which was the heaviest rainfall in mainland China with a maximum 24-h rainfall of 1060.3 mm, and it significantly demonstrates that the limited area model can still skillfully give reasonable results even only the conventional data are available. For such a heavy rainfall event, a grid length of 90 km is too large while 45 km seems acceptable. Under these two grid sizes, the cumulus parameterization scheme is evidently superior to the explicit scheme since it restricts instabili-ties such as CISK to limited extent, The high resolution scheme for the boundary treatment does not improve fore-casts significantly.The experiments also revealed some interesting phenomena such as the forecast rainfall being too small while af-fecting synoptic system so deep as compared with observations. Another example is the severe deformation of synoptic systems both in initial conditions and forecast fields in the presence of complicated topography. Besides, the fixed boundary condition utilized in the experiments along with current domain coverage set some limitations to the model performances. 相似文献
807.
808.
809.
A new multidimensional scaling (MS) technique, referred to as the Pijk model, is formulated on the basis of associations among triple objects (samples or variables), instead of pairs of objects as used in the usual MS methods, such as factor analysis. The computational scheme provided for this method is the reduction of an original problem to a standard eigenvalue-eigenvector problem. The major goal of the technique is simplification and reduction of data structures and the rescaling of original objects into a new and reduced space, so that patterns and relations of the original objects can be conventiently examined in two-dimensional “factor” plots. The Pïjk method is illustrated and tested by using a set of geochemical data related to the epithermal gold and silver vein deposits in the Walker Lake quadrangle of Nevada and California. The characteristics of element associations suggested in the Pijk analysis are consistent with field observations. A preliminary comparison between the new method and the ordinary factor analysis also is made on the basis of the same data set. Results are encouraging in that analysis by the Pijk model captures triple-object associations that might be missed by the ordinary factor analysis which considers only pair-variable correlations 相似文献
810.
延边地区闹枝金矿为一破碎蚀变岩型金矿床,产于中生代火山盆地外缘的早海西期花岗闪长岩出露区,矿体严格受构造破碎带控制。本文从矿床产出的地质地球化学特征入手对区内岩浆岩与成矿的关系进行了系统研究,揭示出闹枝金矿与中生代火山杂岩有密切的成因联系.闹枝金矿为—燕山期钙碱性火山岩浆活动所形成的火山—次火山热液矿床.矿床形成于中温、pH值为弱酸—弱碱性、Eh值较低的弱还原—还原条件.成矿作用具有多阶段性。金主要以氯金络合物和硫金络合物形式迁移. 相似文献