首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   18601篇
  免费   3272篇
  国内免费   4257篇
测绘学   1045篇
大气科学   3722篇
地球物理   5187篇
地质学   8883篇
海洋学   2615篇
天文学   788篇
综合类   1776篇
自然地理   2114篇
  2024年   99篇
  2023年   353篇
  2022年   815篇
  2021年   960篇
  2020年   770篇
  2019年   829篇
  2018年   942篇
  2017年   889篇
  2016年   1024篇
  2015年   841篇
  2014年   1015篇
  2013年   1104篇
  2012年   972篇
  2011年   1017篇
  2010年   1077篇
  2009年   994篇
  2008年   835篇
  2007年   887篇
  2006年   655篇
  2005年   639篇
  2004年   465篇
  2003年   523篇
  2002年   509篇
  2001年   493篇
  2000年   614篇
  1999年   908篇
  1998年   760篇
  1997年   761篇
  1996年   727篇
  1995年   648篇
  1994年   570篇
  1993年   489篇
  1992年   409篇
  1991年   288篇
  1990年   233篇
  1989年   189篇
  1988年   180篇
  1987年   102篇
  1986年   110篇
  1985年   68篇
  1984年   58篇
  1983年   57篇
  1982年   55篇
  1981年   40篇
  1980年   47篇
  1979年   36篇
  1978年   14篇
  1977年   9篇
  1974年   9篇
  1958年   16篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
以HDR隔震梁桥多自由度(MDOF)模型和等效双线性单自由度(SDOF)模型为研究对象,以典型近场地震动作为输入,研究HDR支座双向耦合效应对HDR隔震梁桥地震响应的影响。研究结果表明:不考虑双向耦合效应的HDR支座滞回曲线呈典型双线性;考虑双向耦合效应的HDR支座滞回曲线面积小于不考虑双向耦合效应的HDR支座滞回曲线面积。不考虑双向耦合效应的顺桥向HDR支座位移峰值db大于考虑双向耦合效应时,但横桥向的结果相反。近场地震作用下,对梁桥进行HDR支座隔震设计时,忽略双向耦合效应计算得到的墩底剪力峰值和弯矩峰值均偏于保守。可忽略HDR支座双向耦合效应对HDR隔震梁桥近场地震能量的影响。  相似文献   
92.
93.
定点潮汐形变观测与GPS大地测量   总被引:2,自引:5,他引:2  
论述了我国定点潮汐形变观测与GPS在观测周期,物理量,频域,实测精度,监测优势者方面的异同,认为定点潮汐形变观测是测震学与大地测量(含GPS)的必要补充,介绍了我国定点潮汐形变观测技术的发展与台网观测技术,以及它在我国10多次中强震测报中的应用。  相似文献   
94.
This paper presents a case study on the Mogangling landslide and its characteristics and geological mechanism. The Mogangling landslide is a giant rock landslide located at the intersection of Dadu river and Moxi river. It is a landslide triggered by an earthquake with large magnitude that occurred in 18th century. Based on detailed site investigation, it shows the Mogangling landslide developed in the Kangding complex strata, composed of completely decomposed aggregates of massive-block stone, debris and soil with some gravels, pebbles and sand layer found distributed in front of the landslide. The control factor of the deformation of this landslide is the combined effect of Detuo fault which is located under the slope, and the regional stress formed along structural planes as well as the free surfaces formed by river cutting. Therefore, when the Kangding-Moxi earthquake (Ms =7.7) occurred on 1st June, 1786, due to seismic shaking, topographic amplification effects and back slope effects, the Mogangling landslide occurred. The Dadu River is the most important river for hydropower development in China; large-scale seismic landslides along the Dadu River are the most important geological issue during the construction of hydropower stations. Therefore, this research is important from the point of view of economic and social benefits.  相似文献   
95.
In this age of modern biology, aquatic toxicological research has pursued mechanisms of action of toxicants. This has provided potential tools for ecotoxicologic investigations. However, problems of biocomplexity and issues at higher levels of biological organization remain a challenge. In the 1980s and 1990s and continuing to a lesser extent today, organisms residing in highly contaminated field sites or exposed in the laboratory to calibrated concentrations of individual compounds were carefully analyzed for their responses to priority pollutants. Correlation of biochemical and structural analyses in cultured cells and tissues, as well as the in vivo exposures led to the production and application of biomarkers of exposure and effect and to our awareness of genotoxicity and its chronic manifestations, such as neoplasms, in wild fishes. To gain acceptance of these findings in the greater environmental toxicology community, “validation of the model” versus other, better-established often rodent models, was necessary and became a major focus. Resultant biomarkers were applied to heavily contaminated and reference field sites as part of effects assessment and with investigations following large-scale disasters such as oil spills or industrial accidents.

Over the past 15 years, in the laboratory, small aquarium fish models such as medaka (Oryzias latipes), zebrafish (Danio rerio), platyfish (Xiphophorus species), fathead minnow (Pimephales promelas), and sheepshead minnow (Cyprinodon variegatus) were increasingly used establishing mechanisms of toxicants. Today, the same organisms provide reliable information at higher levels of biological organization relevant to ecotoxicology. We review studies resolving mechanisms of toxicity and discuss ways to address biocomplexity, mixtures of contaminants, and the need to relate individual level responses to populations and communities.  相似文献   

96.
石圣  赵德军  蒋祥  翁新海  陈伟 《矿物岩石》2021,41(1):106-115
西藏山南地区洛扎县雄曲河拉康段在600 m距离内出露温泉4处,仅1处位于河谷右岸;平硐勘查显示两岸岩性、产状、构造一致,地热异常却仅在左岸平硐内部显著,右岸平硐地热异常不明显.本次研究以此异常为出发点,通过片麻状花岗岩不同切面导热实验、片麻状花岗岩与板岩相同切面导热实验,温泉水δ2H,δ18O同位素测试分析等方法,探究...  相似文献   
97.
This paper presents the applications of the differential evolution (DE) algorithm in back analysis of soil parameters for deep excavation problems. A computer code, named Python‐based DE, is developed and incorporated into the commercial finite element software ABAQUS, with a parallel computing technique to run an FE analysis for all trail vectors of one generation in DE in multiple cores of a cluster, which dramatically reduces the computational time. A synthetic case and a well‐instrumented real case, that is, the Taipei National Enterprise Center (TNEC) project, are used to demonstrate the capability of the proposed back‐analysis procedure. Results show that multiple soil parameters are well identified by back analysis using a DE optimization algorithm for highly nonlinear problems. For the synthetic excavation case, the back‐analyzed parameters are basically identical to the input parameters that are used to generate synthetic response of wall deflection. For the TNEC case with a total of nine parameters to be back analyzed, the relative errors of wall deflection for the last three stages are 2.2, 1.1, and 1.0%, respectively. Robustness of the back‐estimated parameters is further illustrated by a forward prediction. The wall deflection in the subsequent stages can be satisfactorily predicted using the back‐analyzed soil parameters at early stages. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
98.
Based on classic iterative computation results, new equations to calculate the surface turbulent transfer coefficients are proposed, which allow for large ratios of the momentum and heat roughness lengths. Compared to the Launiainen scheme, our proposed scheme generates results closer to classical iterative computations. Under unstable stratification, the relative error in the Launiainen scheme increases linearly with increasing instability, even exceeding 15%, while the relative error of the present scheme is always less than 8.5%. Under stable stratification, the Launiainen scheme uses two equations, one for 0 < Ri B ≤ 0.08 and another for 0.08 < Ri B ≤ 0.2, and does not consider the condition that Ri B > 0.2, while its relative errors in the region 0 < Ri B ≤ 0.2 exceed 31 and 24% for momentum and heat transfer coefficients, respectively. In contrast, the present scheme uses only one equation for 0 < Ri B ≤ 0.2 and another equation for Ri B > 0.2, and the relative error of the present scheme is always less than 14%.  相似文献   
99.
气候序列的层次结构   总被引:11,自引:4,他引:11  
刘式达  荣平平  陈炯 《气象学报》2000,58(1):110-114
一个气候时间序列含有多个时间尺度 ,形成不同尺度的气候层次。气候是冷还是暖是随着尺度而变化的。文中用北半球地表月平均气温气候资料的子波变换分析表明 :气候突变点既随尺度有规律的变化 ,也具有随尺度变化而不变的性质 ,即标度不变性。不论什么尺度 ,气候总是有冷暖之分 ,这种自相似性可以帮助笔者从气候资料的子波变换中建立一个一维映射动力系统 ,它反映出气候突变时间的演变规律和气候的层次结构。  相似文献   
100.
为在露天矿山恢复治理过程监督管理中提供技术支撑,通过文献阅读,结合重庆实际,提出了基于多源遥感技术的露天矿山恢复治理综合监测方法,主要包括:利用高分辨率遥感影像结合矿山遥感样本特征以及其他专题数据,识别矿山损毁土地范围;利用中分辨率遥感影像(Landsat数据、高分数据)对植被光谱的响应特征,构建植被指数进行矿山恢复治理植被动态监测;利用星载雷达数据(哨兵数据)通过干涉分析,对矿山范围内地表形变动态监测。此外,还可结合无人机采集数据,开展矿山恢复治理倾斜摄影数据查看和分析。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号