全文获取类型
收费全文 | 5672篇 |
免费 | 1275篇 |
国内免费 | 1596篇 |
专业分类
测绘学 | 825篇 |
大气科学 | 881篇 |
地球物理 | 1428篇 |
地质学 | 3258篇 |
海洋学 | 749篇 |
天文学 | 245篇 |
综合类 | 509篇 |
自然地理 | 648篇 |
出版年
2024年 | 55篇 |
2023年 | 155篇 |
2022年 | 402篇 |
2021年 | 497篇 |
2020年 | 380篇 |
2019年 | 445篇 |
2018年 | 429篇 |
2017年 | 375篇 |
2016年 | 386篇 |
2015年 | 384篇 |
2014年 | 394篇 |
2013年 | 396篇 |
2012年 | 398篇 |
2011年 | 398篇 |
2010年 | 384篇 |
2009年 | 377篇 |
2008年 | 307篇 |
2007年 | 295篇 |
2006年 | 280篇 |
2005年 | 233篇 |
2004年 | 160篇 |
2003年 | 137篇 |
2002年 | 141篇 |
2001年 | 153篇 |
2000年 | 134篇 |
1999年 | 143篇 |
1998年 | 113篇 |
1997年 | 89篇 |
1996年 | 70篇 |
1995年 | 66篇 |
1994年 | 83篇 |
1993年 | 64篇 |
1992年 | 42篇 |
1991年 | 37篇 |
1990年 | 28篇 |
1989年 | 22篇 |
1988年 | 25篇 |
1987年 | 9篇 |
1986年 | 17篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1958年 | 6篇 |
1957年 | 4篇 |
1954年 | 1篇 |
排序方式: 共有8543条查询结果,搜索用时 15 毫秒
151.
152.
XU Jianming XU Xiangde LIU Yu DING Guoan CHEN Huailiang HU Jiangkai ZHANG Jianchun WU Hao LI Weiliang HE Jinhai YANG Yuanqin WANG Jiahe 《中国科学D辑(英文版)》2005,48(Z2)
Based on analysis of the air pollution observational data at 8 observation sites in Beijing including outer suburbs during the period from September 2004 to March 2005, this paper reveals synchronal and in-phase characteristics in the spatial and temporal variation of air pollutants on a city-proper scale at deferent sites; describes seasonal differences of the pollutant emission influence between the heating and non-heating periods, also significantly local differences of the pollutant emission influence between the urban district and outer suburbs, i.e. the spatial and temporal distribution of air pollutant is closely related with that of the pollutant emission intensity. This study shows that due to complexity of the spatial and temporal distribution of pollution emission sources, the new generation Community Multi-scale Air Quality (CMAQ) model developed by the EPA of USA produced forecasts, as other models did, with a systematic error of significantly lower than observations, albeit the model has better capability than previous models had in predicting the spatial distribution and variation tendency of multi-sort pollutants. The reason might be that the CMAQ adopts average amount of pollutant emission inventory, so that the model is difficult to objectively and finely describe the distribution and variation of pollution emission sources intensity on different spatial and temporal scales in the areas, in which the pollution is to be forecast. In order to correct the systematic prediction error resulting from the average pollutant emission inventory in CMAQ, this study proposes a new way of combining dynamics and statistics and establishes a statistically correcting model CMAQ-MOS for forecasts of regional air quality by utilizing the relationship of CMAQ outputs with corresponding observations, and tests the forecast capability. The investigation of experiments presents that CMAQ-MOS reduces the systematic errors of CMAQ because of the uncertainty of pollution emission inventory and improves the forecast level of air quality. Also this work employed a way of combining point and area forecasting, i.e. taking the products of CMAQ for a center site to forecast air pollution for other sites in vicinity with the scheme of model products "reanalysis" and average over the "area". 相似文献
153.
Based on the land surface temperature (LST), the land cover classification map,vegetation coverage, and surface evapotranspiration derived from EOS-MODIS satellite data, and by the use of GIS spatial analytic technique and multivariate statistical analysis method, the urban heat island (UHI) spatial distribution of the diurnal and seasonal variabilities and its driving forces are studied in Beijing city and surrounding areas in 2001. The relationships among UHI distribution and landcover categories, topographic factor, vegetation greenness, and surface evapotranspiration are analyzed. The results indicate that: (i) The significant UHI occur in Beijing city areas in the four seasons due to high heat capacity and multi-reflection of compression building, as well as with special topographic features of its three sides surrounded by mountains,especially in the summer. The UHI spatial distribution is corresponding with the urban geometry structure profile. The LST difference is approximately 4-6℃ between Beijing city and suburb areas, comparatively is 8- 10℃ between Beijing city area and outer suburb area in northwestern regions. (ii) The UHI distribution and intensity in daytime are different from nighttime in Beijing city area, the nighttime UHI is obvious. However, in the daytime, the significant UHI mainly appears in the summer, the autumn takes second place, and the UHI in the winter and the spring seem not obvious. The surface evapotranspiration in suburb areas is larger than that in urban areas in the summer, and high latent heat exchange is evident, which leads to LST difference between city area and suburb area. (iii) The reflection of surface landcover categories is sensitive to the UHI, the correlation between vegetation greenness and UHI shows obviously negative.The scatterplot shows that there is the negative correlation between NDVI and LST (R2 = 0.6481).The results demonstrate that the vegetation greenness is an important factor for reducing the UHI,and large-scale construction of greenbelts can considerably reduce the UHI effect. 相似文献
154.
山东省泰安朱家庄自然硫矿床,赋存于鲁西断隆古近纪汶东陆相盆地。自然硫矿层在汶口组二段上亚段,泥质灰岩-含泥灰岩-含云灰岩-石膏岩韵律层中的白云岩-石膏岩层段发育。自然硫以胶态、晶态、土态3种形态产出,可划分为顺层型、准顺层型、斑杂型及不顺层型4大类10余种矿石类型。从矿区去膏化作用普遍、自然硫与石膏-硬石膏分别富集轻-重同位素的特征、油气显示明显及地下水主要径流方向自然硫矿化最强等各种证据,表明该矿属生物后生成因的矿床。 相似文献
155.
论述了华蓥山隧道的岩溶发育特征,根据岩溶发育强度的划分依据和划分标准,结合岩溶发育的历史,采用类比判别法、主因素判别法和综合判别法对岩溶发育强度作了垂直分带,据此预测的溶洞规模与实际情况吻合。 相似文献
156.
珠江口盆地白云凹陷新生代构造演化动力学 总被引:42,自引:0,他引:42
白云凹陷构造演化史的研究对在白云凹陷开展油气勘探和深水沉积研究具有重要的意义。通过对断裂与沉积结构平面和剖面特点的分析,结合岩浆活动特点,文中提出白云凹陷是一个复式地堑,推测这种结构特点与凹陷下地壳的强烈韧性减薄和颈缩变形有关,表现为热岩石圈的伸展。其发育机制推测与白云凹陷位于构造转换带上有关,特殊的构造位置使白云凹陷成为强烈构造变形区,岩石圈地壳强烈减薄,伴随伸展过程和地幔上涌,脆性地壳或上地幔中部分熔融物质的出现导致岩石圈强度的急剧降低,在区域伸展应力场下以韧性流变方式减薄。岩浆在构造转换带下聚集并发育主岩浆房,由于白云凹陷南北边缘没有发育正断裂系统,岩浆主要沿垂直伸展的方向运移,因此在珠琼运动一幕和二幕南南东向伸展应力作用下,岩浆向白云凹陷的东部和西部运移至北西向基底深大断裂处,那里由于北西向断裂表现为左行张剪性质而成为压力较低的地区,从而成为岩浆上涌和侵位的地方。在岩浆聚集的地区,活动岩浆体附近的脆性变形被分散的韧性变形所取代,因此在凹陷的东北和西南两个角上,发育了张性和张剪性小断裂群,由于热岩石圈弹性较差,白云凹陷长期持续沉降。白云凹陷的断裂活动和沉积演化史还受到南海海盆扩张活动的影响。 相似文献
157.
试图从台站产出的原始地形变前兆数据出发,提出一些实际操作性较强的预处理方法,从已编制好的软件中给出处理实例,从而达到提高台站观测人员的科研能力,填补资料预处理方面的某些空白的目的,这对于台站人员集观测、科研于一体有着十分重要的意义。从95-01-02项目厦门地震台前兆数据预处理的实践表明:这些方法取得了明显的实效,直到今天仍然具有很大的使用价值。 相似文献
158.
Multi-dimensional Seismic Response Analysis of Base-Isolated Frame Structure with 3D Isolator 总被引:1,自引:0,他引:1
XiongShishu HuangLiting ChenJinfeng SuJingsu 《中国地质大学学报(英文版)》2005,16(1):66-71,78
INTRODUCTIONAs a new and effective method for withstandingthe horizontal component of earthquake motion on abuilding structure, the base isolation technique hascome to the engineering application phase ( Hu,1988). However, for some important buildings andfoundation facilities in an earthquake region, it is im portant to consider the effects of 3D aseismatic analy sis, including the vertical component, due to themulti dimensional characteristics of earthquakes (Suand … 相似文献
159.
Zhu Yu Wei Jun Yang Manjuan Li Hao Liu Hongqing 《中国地质大学学报(英文版)》2005,16(3):277-282
INTRODUCTION Tunnel typeanchoragehasobviousadvantages inbearingcapacityversusinvestment(LiuandHu,1996).However,itisrarelyusedinapracticalpro jectbecauseofitsrequirementofgoodrockcondi tions.Siduhebridge(Fig.1),whichliesintheBa dongmountainsinthewestplatea… 相似文献
160.
Xiong Xiong* Institute of Geodesy Geophysics Chinese Academy of Sciences Wuhan China Institute of Geology Geophysics Chinese Academy of Sciences Beijing China Wang Jiye Institute of Geodesy Geophysics Chinese Academy of Sciences Wuhan China Graduate School Chinese Academy of Sciences Beijing China Teng Jiwen Institute of Geology Geophysics Chinese Academy of Sciences Beijing China 《中国地质大学学报(英文版)》2005,16(4)
INTRODUCTION Volcanoesaremostlyobservedinoceanicridges,hotspotsandcontinentalriftzones(Hongetal.,2003),andarerarelyobservedincontinentalinteri ors.However,sincethevolcanoeswithintheconti nentinteriorscannotbeattributedtotheplate/block marginprocess,theydr… 相似文献