全文获取类型
收费全文 | 16883篇 |
免费 | 3131篇 |
国内免费 | 4439篇 |
专业分类
测绘学 | 1547篇 |
大气科学 | 3240篇 |
地球物理 | 3849篇 |
地质学 | 9041篇 |
海洋学 | 2578篇 |
天文学 | 829篇 |
综合类 | 1543篇 |
自然地理 | 1826篇 |
出版年
2024年 | 90篇 |
2023年 | 363篇 |
2022年 | 715篇 |
2021年 | 905篇 |
2020年 | 790篇 |
2019年 | 863篇 |
2018年 | 869篇 |
2017年 | 834篇 |
2016年 | 978篇 |
2015年 | 866篇 |
2014年 | 1010篇 |
2013年 | 1026篇 |
2012年 | 1055篇 |
2011年 | 1054篇 |
2010年 | 1131篇 |
2009年 | 966篇 |
2008年 | 1006篇 |
2007年 | 831篇 |
2006年 | 731篇 |
2005年 | 671篇 |
2004年 | 556篇 |
2003年 | 595篇 |
2002年 | 640篇 |
2001年 | 631篇 |
2000年 | 548篇 |
1999年 | 685篇 |
1998年 | 562篇 |
1997年 | 493篇 |
1996年 | 486篇 |
1995年 | 417篇 |
1994年 | 353篇 |
1993年 | 347篇 |
1992年 | 274篇 |
1991年 | 217篇 |
1990年 | 173篇 |
1989年 | 142篇 |
1988年 | 148篇 |
1987年 | 73篇 |
1986年 | 65篇 |
1985年 | 54篇 |
1984年 | 35篇 |
1983年 | 24篇 |
1982年 | 39篇 |
1981年 | 32篇 |
1980年 | 23篇 |
1979年 | 22篇 |
1978年 | 7篇 |
1976年 | 9篇 |
1973年 | 5篇 |
1958年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
银川市初夏气溶胶粒子谱分布特征 总被引:4,自引:5,他引:4
利用美制APS—3310A型激光粒谱仪,在中国西北城市银川对大气气溶胶粒子进行现场观测,结合气象条件,并通过理论计算分析,给出了银川市初夏大气气溶胶的日变化特征、3种不同粒径粒子分布特点及飘尘谱分布特征,以期为银川市大气污染总量控制方案及对策提供科学依据。 相似文献
142.
143.
根据野外实地考察,综合前人的工作资料,从地层结构、层位、沉积体系、岩性及形成砂岩型铀矿的条件出发,概括了公婆泉盆地中生代地层的主要特征;确定了目的层并浅要分析了砂岩型铀成矿条件,对下一步铀矿找矿工作具有一定的现实意义。 相似文献
144.
145.
测井资料交会图法在火山岩岩性识别中的应用 总被引:22,自引:1,他引:22
在火山岩储层研究中,岩性识别显得越来越重要。在评述目前常用的岩性识别方法后,重点以测井资料交会图法为例,以松辽盆地徐家围子断陷升平气田深层白垩系营城组火山岩为对象,优选出密度测井、自然伽玛测井、声波测井、电阻率、钍铀等测井项目的数据进行交会,编制出测井曲线交会图版,并以此为依据识别出该区的火山岩主要岩性有:安山岩、玄武岩、流纹岩和凝灰岩等。识别结果与实际情况相吻合。 相似文献
146.
147.
岫岩-海城5.4级地震前小震震源机制解与记录特征分析 总被引:4,自引:2,他引:4
采用Pn、Pg初始波初动符号,利用乌尔夫网上半球投影,用作图方法求解了岫岩-海城震区(1999年1月-1999年11月29日)主震前辽宁数字地震台网记录(ML≥2.5)的41个小震的震源机制参数。结合前震记录的某些特征,对主震前应力方向的时空变化,震源错动性质进行分析和讨论。 相似文献
148.
Introduction Receiver function has been extensively applied in studying S wave velocity of crust and up-per mantle for about 20 years (Owens, et al, 1987; LIU, et al, 1996), which is a time series ob-tained by the deconvolution of vertical component from horizontal component for teleseismic P waveform. Receiver function represents the teleseismic P plane wave response of crust and upper mantle beneath seismic station, from which the source and propagation effects are removed. Receiver funct… 相似文献
149.
Crustal structure beneath the Songpan—Garze orogenic belt 总被引:2,自引:0,他引:2
The Benzilan-Tangke deepseismic sounding profile in the western Sichuan region passes through the Song-pan-Garze orogenic belt with trend of NNE.Based on the travel times and the related amplitudes of phases in the record sections,the 2-D P-wave crustal structure was ascertained in this paper.The velocity structure has quite strong lateral variation along the profile.The crust is divided into 5layers,where the first,second and third layer belong to the upper crust,the forth and fifth layer belong to the lower crust.The low velocity anomaly zone gener-ally exists in the central part of the upper crust on the profile,and it integrates into the overlying low velocity basement in the area to the north of Ma‘erkang.The crustal structure in the section can be divided into 4parts:in the south of Garze-litang fault,between Garze-Litang fault and Xianshuihe fault,between Xianshuihe fault and Longriba fault and in the north of Longriba fault,which are basically coincided with the regional tectonics division.The crustal thickness decreases from southwest to northeast along the profile,that is ,from62km in the region of the Jinshajiang River to 52km in the region of the Yellow River.The Moho discontinuity does not obviously change across the Xianshuihe fault basesd on the PmP phase analysis.The crustal average velocity along the profile is lower,about 6.30 km/s.The Benzilan-Tangke profile reveals that the crust in the study area is orogenic.The Xianshuihe fault belt is located in the central part of the profile,and the velocity is positive anomaly on the upper crust,and negative anomaly on the lower crust and upper mantle.It is considered as a deep tectonhic setting in favor of strong earthquake‘s accumulation and occurrence. 相似文献
150.
Wave Propagation, Scattering and Imaging Using Dual-domain One-way and One-return Propagators 总被引:4,自引:0,他引:4
R.-S. Wu 《Pure and Applied Geophysics》2003,160(3-4):509-539
— Dual-domain one-way propagators implement wave propagation in heterogeneous media in mixed domains (space-wavenumber domains). One-way propagators neglect wave reverberations between heterogeneities but correctly handle the forward multiple-scattering including focusing/defocusing, diffraction, refraction and interference of waves. The algorithm shuttles between space-domain and wavenumber-domain using FFT, and the operations in the two domains are self-adaptive to the complexity of the media. The method makes the best use of the operations in each domain, resulting in efficient and accurate propagators. Due to recent progress, new versions of dual-domain methods overcame some limitations of the classical dual-domain methods (phase-screen or split-step Fourier methods) and can propagate large-angle waves quite accurately in media with strong velocity contrasts. These methods can deliver superior image quality (high resolution/high fidelity) for complex subsurface structures. One-way and one-return (De Wolf approximation) propagators can be also applied to wave-field modeling and simulations for some geophysical problems. In the article, a historical review and theoretical analysis of the Born, Rytov, and De Wolf approximations are given. A review on classical phase-screen or split-step Fourier methods is also given, followed by a summary and analysis of the new dual-domain propagators. The applications of the new propagators to seismic imaging and modeling are reviewed with several examples. For seismic imaging, the advantages and limitations of the traditional Kirchhoff migration and time-space domain finite-difference migration, when applied to 3-D complicated structures, are first analyzed. Then the special features, and applications of the new dual-domain methods are presented. Three versions of GSP (generalized screen propagators), the hybrid pseudo-screen, the wide-angle Padé-screen, and the higher-order generalized screen propagators are discussed. Recent progress also makes it possible to use the dual-domain propagators for modeling elastic reflections for complex structures and long-range propagations of crustal guided waves. Examples of 2-D and 3-D imaging and modeling using GSP methods are given. 相似文献