全文获取类型
收费全文 | 10771篇 |
免费 | 2092篇 |
国内免费 | 1866篇 |
专业分类
测绘学 | 2023篇 |
大气科学 | 2240篇 |
地球物理 | 2142篇 |
地质学 | 4548篇 |
海洋学 | 1241篇 |
天文学 | 568篇 |
综合类 | 984篇 |
自然地理 | 983篇 |
出版年
2024年 | 71篇 |
2023年 | 260篇 |
2022年 | 346篇 |
2021年 | 396篇 |
2020年 | 298篇 |
2019年 | 432篇 |
2018年 | 267篇 |
2017年 | 270篇 |
2016年 | 271篇 |
2015年 | 421篇 |
2014年 | 726篇 |
2013年 | 581篇 |
2012年 | 733篇 |
2011年 | 747篇 |
2010年 | 652篇 |
2009年 | 769篇 |
2008年 | 1073篇 |
2007年 | 720篇 |
2006年 | 619篇 |
2005年 | 816篇 |
2004年 | 621篇 |
2003年 | 671篇 |
2002年 | 625篇 |
2001年 | 471篇 |
2000年 | 346篇 |
1999年 | 234篇 |
1998年 | 142篇 |
1997年 | 157篇 |
1996年 | 114篇 |
1995年 | 130篇 |
1994年 | 141篇 |
1993年 | 114篇 |
1992年 | 88篇 |
1991年 | 56篇 |
1990年 | 64篇 |
1989年 | 68篇 |
1988年 | 28篇 |
1987年 | 27篇 |
1986年 | 15篇 |
1985年 | 25篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1965年 | 9篇 |
1961年 | 6篇 |
1960年 | 7篇 |
1958年 | 5篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
991.
通过对九江市地质环境的调查与客观实际情况分析,选取地质灾害、已有资源和河流侵蚀作用等作为敏感因子;选取地形坡度、斜坡高度、基岩埋深等作为重要因子;采用层次分析法确定评价因子权重,采用多目标决策的敏感因子-模糊聚类综合评判法对九江市城市建设用地地质环境质量评价。评价共划分出1277个单元,评价结果显示:建设用地环境质量优越的单元占总评价面积的65.86%,较好、简单改善后可建设的单元占15.35%,中等、一般需要一定工程措施的建设用地占1.57%,其它较差的和不适于建设用地的单元仅占17.22%。这个结果对九江市城市规划、建设、管理提供相应的地质环境信息,最大限度实现城市建设与地质资源环境的优化配置,达到城市建设安全、合理、经济的目的。从而也证明了多目标决策的敏感因子-模糊聚类综合评判法对解决城市建设用地质量评价不失为一种好的理论方法和手段。 相似文献
992.
INTRODUCTIONThe study of surface subsidence resulting fromunderground mining holds significance in view ofbeneficial effects on national economy and people’sliving conditions.As is known,a large quantity ofminerals need to be exploited for modernization con-struction.Mining leads to surface subsidence,someunderground engineering and production facilities aredestroyed accordingly,which blocks the developmentof production and retards people’s living standard.To solve this contradiction,su… 相似文献
993.
简要回顾了地球物理方法技术在国内几个油田发现过程中的作用。针对中国油气资源战略选区中普遍存在的方法技术问题,以羌塘盆地为例,进行了较为全面深入的剖析。通过对已有资料和成果的分析,认为羌塘盆地实现战略发现的时机已经成熟。而要实现战略发现,目前亟待解决的问题是打参数井、圈定局部构造和寻找合适的方法技术。鉴于羌塘盆地特殊的自然环境和地质条件,提出了高精度大地电磁法、自然电场法、特殊条件下的地震勘探、井地联合地震勘探等关键技术。具体的工作部署是:查明有利区带中最有利的局部构造和构造部位,在最有利的构造部位实施参数井钻探,围绕参数井开展地质、地球物理勘探与综合研究。这些技术和方法的应用有望使羌塘盆地的油气勘探工作迈上新台阶。 相似文献
994.
文章介绍了瞬态瑞雷面波勘探技术的理论基础和勘探原理、工作方法、资料的整理与解释,并结合工程实例说明瞬态面波勘探技术的应用效果。 相似文献
995.
996.
In this paper, the numerical simulation bias of the non-hydrostatic version GRAPES-Meso (Mesoscale of the Global and Regional Assimilation and Prediction System) at the resolution of 0.18o for a torrential rain case, which happened in May 31st to June 1st 2005 over Hunan province, are diagnosed and investigated by using the radiosondes, intensive surface observation, and the operational global analysis data, and the sensitivity experimental results as well. It is shown in the result that the GRAPES-Meso could reproduce quite well the main features of large-cale circulation and the distribution of the accumulated 24h precipitation and the key locations of the torrential rainfall are captured reasonably well by the model. However, bias exist in the simulation of the mesoscale features of the torrential rain and details of the relevant systems, for example, the simulated rainfall that is too earlier in model integration and remarkable underprediction of the peak value of rainfall rates over the heaviest rainfall region, the weakness of the upper jet simulation and the overprediction of the south-west wind in the lower troposphere etc. The investigation reveals that the sources of the simulation bias are different. The erroneous model rainfall in the earlier integration stage over the heaviest rainfall region is induced by the model initial condition bias of the wind field at about 925hPa over the torrential rainfall region, where the bias grow rapidly and spread upward to about 600hPa level within the few hours into the integration and result in abnormal convergence of the wind and moisture, and thus the unreal rainfall over that region. The large bias on the simulated rainfall intensity over the heaviest rainfall region might be imputed to the following combined factors of (1) the simulation bias on the strength and detailed structures of the upper-level jet core which bring about significant underpredictions of the dynamic conditions (including upper-level divergence and the upward motion) for heavy rainfall due to unfavorable mesoscale vertical coupling between the strong upper-level divergence and lower-level convergence; and (2) the inefficient coupling of the cumulous parameterization scheme and the explicit moisture in the integration, which causes the failure of the explicit moisture scheme in generating grid-scale rainfall in a certain extent through inadequate convective adjustment and feedback to the grid-scale. In addition, the interaction of the combined two factors could form a negative feedback to the rainfall intensity simulation, and eventually lead to the obvious underprediction of the rainfall rate. 相似文献
997.
Variables fields such as enstrophy, meridional-wind and zonal-wind variables are derived from monthly 500 hPa geopotential height anomalous fields. In this work, we select original predictors from monthly 500-hPa geopotential height anomalous fields and their variables in June of 1958 - 2001, and determine comprehensive predictors by conducting empirical orthogonal function (EOF) respectively with the original predictors. A downscaling forecast model based on the back propagation (BP) neural network is built by use of the comprehensive predictors to predict the monthly precipitation in June over Guangxi with the monthly dynamic extended range forecast products. For comparison, we also build another BP neural network model with the same predictands by using the former comprehensive predictors selected from 500-hPa geopotential height anomalous fields in May to December of 1957 - 2000 and January to April of 1958 - 2001. The two models are tested and results show that the precision of superposition of the downscaling model is better than that of the one based on former comprehensive predictors, but the prediction accuracy of the downscaling model depends on the output of monthly dynamic extended range forecast. 相似文献
998.
999.
在介绍城市室内空气污染的现状、空气污染物的主要来源种类及其对人体健康造成危害的基础上,对目前常用的控制室内空气污染、改善室内空气质量的方法进行了对比分析,并提出了一些建设性意见. 相似文献
1000.