全文获取类型
收费全文 | 2427篇 |
免费 | 427篇 |
国内免费 | 519篇 |
专业分类
测绘学 | 155篇 |
大气科学 | 481篇 |
地球物理 | 549篇 |
地质学 | 1123篇 |
海洋学 | 259篇 |
天文学 | 91篇 |
综合类 | 305篇 |
自然地理 | 410篇 |
出版年
2024年 | 9篇 |
2023年 | 39篇 |
2022年 | 125篇 |
2021年 | 130篇 |
2020年 | 132篇 |
2019年 | 115篇 |
2018年 | 129篇 |
2017年 | 120篇 |
2016年 | 150篇 |
2015年 | 131篇 |
2014年 | 143篇 |
2013年 | 143篇 |
2012年 | 128篇 |
2011年 | 121篇 |
2010年 | 141篇 |
2009年 | 135篇 |
2008年 | 119篇 |
2007年 | 118篇 |
2006年 | 90篇 |
2005年 | 81篇 |
2004年 | 56篇 |
2003年 | 70篇 |
2002年 | 66篇 |
2001年 | 68篇 |
2000年 | 60篇 |
1999年 | 111篇 |
1998年 | 86篇 |
1997年 | 81篇 |
1996年 | 81篇 |
1995年 | 62篇 |
1994年 | 80篇 |
1993年 | 54篇 |
1992年 | 38篇 |
1991年 | 34篇 |
1990年 | 36篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1969年 | 2篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1958年 | 2篇 |
排序方式: 共有3373条查询结果,搜索用时 15 毫秒
941.
Risks of airborne pollution accidents in a major conurbation: case study of Zhangjiakou,a host city for the 2022 Winter Olympics 总被引:1,自引:0,他引:1
Renzhi?LiuEmail authorView authors OrcID profile Jing?Liu Zhijiao?Zhang Alistair?G.?L.?Borthwick Yanpeng?Cai Lei?Dong Xi?Du 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(11):3257-3272
The number of airborne pollution accidents is second only to that of water-borne pollution accidents, in recorded environmental disasters. Acute casualties and public health costs have prompted many airborne pollution risk analyses. To date, few assessment methods have been carried out at regional-scale to quantify acute airborne pollution risk. Herein, a Hybrid Simulation and Risk Analysis approach, involving a systematic combination of simulation, risk ranking, and standardized analysis, is proposed at regional scale. Gaussian and heavy-gas models are utilized in the simulation process, and acute exposure limits preferentially adopted in the risk analysis. The case study shows that 34 of 243 townships in Zhangjiakou City of north China, one of the twin cities selected to host the 2022 Winter Olympics, are threatened by airborne risk sources. It is found that the accidental air pollution risk is comparatively higher in the Xuanhua and Wanquan conurbations. High-risk chemical enterprises (312–432 risk scores) are mostly located near urban areas with high population density where many people are vulnerable receptors to potential air pollution accidents. The resulting risk map indicates that acute airborne pollution from Zhangjiakou would not be a threat either to the proposed Olympic site at Chongli or to downwind Beijing. 相似文献
942.
Amplitude scaling is commonly used to select ground motions matching a target response spectrum. In this paper, the effect of scaling limits on ground motion selection, based on the conditional spectrum framework, is investigated. Target spectra are computed for four probabilistic seismic hazard cases in Western United States, and 16 ground motion suites are selected using different scaling limits (ie, 2, 5, 10, and 15). Comparison of spectral acceleration distributions of the selected ground motion suites demonstrates that the use of a scaling limit of 2 yields a relatively poor representation of the target spectra, because of the small limit leading to an insufficient number of available ground motions. It is also shown that increasing scaling limit results in selected ground motions with generally increased distributions of Arias intensity and significant duration Ds5-75, implying that scaling limit consideration can significantly influence the cumulative and duration characteristics of selected ground motions. The ground motion suites selected are then used as input for slope displacement and structural dynamic analyses. Comparative results demonstrate that the consideration of scaling limits in ground motion selection has a notable influence on the distribution of the engineering demand parameters calculated (ie, slope displacement and interstory drift ratio). Finally, based on extensive analyses, a scaling limit range of 3 to 5 is recommended for general use when selecting ground motion records from the NGA-West2 database. 相似文献
943.
利用高频GPS数据长基线双差精密定位技术,获取2011年3月日本Mw9.0强震近场和远场GPS连续参考站的瞬时动态形变。分析表明:距震源较近的IGS站(USUD)的同震动态形变水平方向幅度超过60 cm,震后水平形变达到30 cm;位于远场的GPS连续参考站(JLYJ)的动态形变,清晰地给出了地震面波引起的地表形变波形。对JLYJ站的谱分析表明,地震面波引起的动态形变周期为10~17 s,并出现了两次峰值,东西向和垂向上的动态位移量远大于北南向,说明JLYJ站的形变主要由Rayleigh波及其谐波所主导,Rayleigh波的传播速度为3.5 km/s,波长约50 km。 相似文献
944.
945.
从20世纪90年代起,研究人员就开始探索活动断层探察数据的制作、存储与管理。迄今为止,已经获得了大量的活动断层探察数据,建成了一套系统的数据组织体系,为减轻地震灾害的相关研究提供了数据和技术支撑。近年来,随着活动断层数据库信息的扩充,初期设计的部分属性信息编码已不适用。为了形成适应当前工作的属性信息编码体系,本文以活动断层数据库建设体系为基础,对数据库属性值代码进行信息分类和编码优化。文章将数据库属性值代码分为字符型单一含义值、数值型单一含义值及复合含义值,分别进行编码规则设计,最终优化了数据库属性信息编码体系,提高了从建库到数据应用的数据录入、检测、制图自动化、数据分析等环节的效率。 相似文献
946.
To study the impact of modern coal mining on the overlying formation, a full‐life‐cycle four‐dimensional seismic monitoring study has been carried out. Four seismic data campaigns have been performed using flexi‐bin geometry with square bins, with total duration of 171 days. The four seismic datasets have been processed with the same processing workflow and parameters; major problems such as statics correction, signal‐to‐noise ratio, resolution, and consistency processing are addressed taking into account the geological features of the research area. This guarantees that remaining four‐dimensional differences between the time‐lapse datasets show mostly geological factors due to the coal mining and effects such as surface subsidence. Our four‐dimensional seismic monitoring of modern coal mining shows that mined and unmined areas have significant zoning characteristics; coal mining has a direct impact on the overlying formation. The mining leads to obvious event subsidence, which reflects that overlying formations undergo subsidence during the mining process. The overlying formation appears as two zones called caving zone and fractured zone. We determine the fault dip of the overlying formation at one end of the working face to be 56°or so by calculation and conversion. We also see that, during the coal mining process, over time, the overlying formation has a self‐recovery capability, which gradually strengthens from the roof siltstone upward to the Aeolian sandstone near the surface. The stability of 20‐m coal pillars between working faces displays a strengthening trend and remains safe during the mining process due to both coal seam supporting and formation compaction effects. 相似文献
947.
948.
从安丘地震台数据跟踪分析工作实际出发,详述数据跟踪分析平台软件安装与使用,探讨日常数据分析常见问题及解决办法,分享数据跟踪分析工作经验,以期为地震前兆台站数据跟踪分析工作提供参考。 相似文献
949.
采用双差定位法对2013年7月22日甘肃岷县—漳县交界地区M 6.6地震及主震后48小时内388次余震序列进行重新定位,得到350个精定位地震数据。结果表明,余震优势展布以北东向较大倾角的铲状结构为特征,长约12 km,以主震为中心两侧对称分布;震源深度主要集中在4—10 km范围内,但余震震级由10 km左右深度的3—4级向3 km深度之上近地表的2—3级迁移变化;余震分布清晰呈现双层结构,较深层分布在4—10 km深度,而较浅层分布3 km深度之上,2层之间地震分布较少。分析认为,浅层地震可能为本次地震地表破坏较强原因之一。震源深度剖面显示,破裂面向NE倾斜,推测此次地震的发震断裂为临潭—宕昌断裂。 相似文献
950.
通过测量辽宁省鞍山-海城地区地震重点监测区地下水离子浓度和氢、氧同位素组成,讨论了该区地下水化学类型的时空变化及其成因。测量结果表明,取样点水温变化范围为11.0~97.0℃,水样的总固溶物(TDS)在197.89~829.99mg/L之间,水样分为8种化学类型。大部分水样的δD、δ18O值均沿中国东北地区大气降水线分布,少数有所偏离,表明该区的地下水主要接受大气降水的补给,并可能有深部水的供给。研究区Ca-HCO3和Ca·Mg-HCO3型水主要是岩石风化溶解和阳离子交换作用的结果;Ca-HCO3·Cl和Ca·Na-Cl·SO4型水主要受岩石风化溶解、阳离子交换作用、深部卤水混入或人类活动影响;Ca-HCO3·SO4和Ca-SO4·HCO3型水与岩石风化溶解以及深部流体混入有关;Na-SO4·HCO3和Na-HCO3·SO4型水主要是深部来源水体的混入造成的。采样期间研究区发生2次ML≥3.0地震,采样点在地震发生月份出现了明显的离子浓度异常变化;Na+、Mg2+、Ca2+、Cl-和SO42-浓度变化明显,对地震活动响应较灵敏。 相似文献