全文获取类型
收费全文 | 15336篇 |
免费 | 5988篇 |
国内免费 | 4875篇 |
专业分类
测绘学 | 2908篇 |
大气科学 | 2562篇 |
地球物理 | 2975篇 |
地质学 | 10684篇 |
海洋学 | 3009篇 |
天文学 | 310篇 |
综合类 | 1424篇 |
自然地理 | 2327篇 |
出版年
2025年 | 14篇 |
2024年 | 566篇 |
2023年 | 676篇 |
2022年 | 1071篇 |
2021年 | 1241篇 |
2020年 | 1008篇 |
2019年 | 1120篇 |
2018年 | 1034篇 |
2017年 | 929篇 |
2016年 | 1013篇 |
2015年 | 1119篇 |
2014年 | 1099篇 |
2013年 | 1275篇 |
2012年 | 1296篇 |
2011年 | 1299篇 |
2010年 | 1271篇 |
2009年 | 1277篇 |
2008年 | 1271篇 |
2007年 | 1184篇 |
2006年 | 1135篇 |
2005年 | 869篇 |
2004年 | 765篇 |
2003年 | 582篇 |
2002年 | 581篇 |
2001年 | 518篇 |
2000年 | 483篇 |
1999年 | 288篇 |
1998年 | 174篇 |
1997年 | 152篇 |
1996年 | 114篇 |
1995年 | 107篇 |
1994年 | 82篇 |
1993年 | 87篇 |
1992年 | 79篇 |
1991年 | 63篇 |
1990年 | 48篇 |
1989年 | 46篇 |
1988年 | 30篇 |
1987年 | 41篇 |
1986年 | 31篇 |
1985年 | 17篇 |
1984年 | 22篇 |
1983年 | 18篇 |
1982年 | 25篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
大兴安岭北段阿龙山地区,发育有6个环状火山盆地,根据它们的形成、演化的地质、地球物理标志,可划分为未成熟、成熟与老年三种火山构造盆地类型.各种火山构造盆地的地质、地球物理特征与类型标志明显,又都经历了环状产生与基性火山喷发、酸性岩浆活动、晚期基性火山喷发3个演化阶段,形成了中基性-中酸性—中基性的演化过程. 相似文献
82.
This study focuses on the three‐dimensional (3‐D) characteristics of wave propagation in pipe‐pile using elastodynamic finite integration technique. First, a real 3‐D pile‐soil model in cylindrical coordinate system is presented. Then, the governing equations are established. With the boundary and initial conditions, the numerical solution is obtained. The accuracy and feasibility of the self‐written code are further verified via comparing with the measured data. Velocity histories at different angles of pile top and pile tip are illustrated, and the snapshots reflecting the 3‐D characteristics of wave propagation are given. It shows that the interferences of Rayleigh waves can confuse the result interpretation for pile integrity testing. The increase of hammer contact time can effectively mitigate the interferences, and the interferences of Rayleigh waves are weakest at an angle of 90° from where hammer hits. Besides, surrounding soil can partly mitigate the wave interferences. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
83.
84.
Fengyun-3 E(FY-3E),the world’s first early-morning-orbit meteorological satellite for civil use,was launched successfully at the Jiuquan Satellite Launch Center on 5 July 2021.The FY-3E satellite will fill the vacancy of the global early-morning-orbit satellite observation,working together with the FY-3C and FY-3D satellites to achieve the data coverage of early morning,morning,and afternoon orbits.The combination of these three satellites will provide global data coverage for numerical weather prediction(NWP)at 6-hour intervals,effectively improving the accuracy and time efficiency of global NWP,which is of great significance to perfect the global earth observing system.In this article,the background and meteorological requirements for the early-morning-orbit satellite are reviewed,and the specifications of the FY-3E satellite,as well as the characteristics of the onboard instrumentation for earth observations,are also introduced.In addition,the ground segment and the retrieved geophysical products are also presented.It is believed that the NWP communities will significantly benefit from an optimal temporal distribution of observations provided by the early morning,mid-morning,and afternoon satellite missions.Further benefits are expected in numerous applications such as the monitoring of severe weather/climate events,the development of improved sampling designs of the diurnal cycle for accurate climate data records,more efficient monitoring of air quality by thermal infrared remote sensing,and the quasicontinuous monitoring of the sun for space weather and climate. 相似文献
85.
Ping Chen Dan Xia Boyuan Chen Lin Li Xiuzhong Li Tian-lin Dong 《Journal of Applied Geophysics》2011,73(3):261-266
Ray representation of electromagnetic resonance (reverberation) mode in subsurface circular cylindrical dielectric resonator (including void) is proposed. The modal ray path must be regular polygon or polystar. Travel time formulas for fundamental resonance multiples and the detecting conditions for non-exact-backscattering rays are derived. Simulation of time–distance curves of a modal hollow concrete block is generally concurred to the measured ground penetrating radar signal pattern. The proposed modeling method can be generalized to other resonant cavities with different profiles and provide a sound base for further applications of other more complicated geophysics science and engineering fields, particularly in ray-based tomography. 相似文献
86.
本文使用1960—1980年春季的水文资料,以温度和盐度作为主要指标,根据聚类分析逼近温盐图解,结合对该海域地理环境特征的分析,对烟台、威海及石岛近海春季的水团结构演变及其和渔场、渔期的关系进行综合分析。结果表明,北黄海及青岛外海的冷水团,以及黄海暖水团的强度与位置的变动,对春季渔期的早迟以及渔场位置的变动,都有很大的影响。 相似文献
87.
Based on the mechanism study of new well stimulation method—tailored pulse loading method, the effects of initial stresses in this method is further studied. The effects of initial stresses on the propagation velocities and directions of the cracks around a hole, especially on the energy dissipation in crack extension, are obtained through theoretical analysis, dynamic photo elasticity tests, high speed photography. And large coal specimen tests. These results provide a theoretical foundation for the practical applications of the tailored pulse loading method. 相似文献
88.
松辽盆地榆树林油田下白垩统泉头组四段扶余油层沉积时期发育大型浅水三角洲沉积。本文基于12 口探井岩心与
2268 口钻井资料,通过单井岩心相分析、测井相分析、连井相对比和平面沉积微相研究,认为研究区发育浅水三角洲平原、
内前缘、外前缘和前三角洲亚相,以浅水三角洲平原亚相为主,平原分流河道和内前缘水下分流河道为主要沉积微相。在
扶三段(F Ⅲ)早期,研究区主要为浅水三角洲内前缘亚相,物源只来自北部 ;其后,三角洲向南进积,全区变为平原亚
相 ;F Ⅲ 3 小层沉积时期,南部物源进入,并与北部物源交汇,一直持续至扶一段(F Ⅰ)末期;在 F Ⅰ 3 小层沉积末期,湖
平面快速上升,南北两个三角洲退积,研究区中部依次出现浅水三角洲内前缘、外前缘和前三角洲。 相似文献
89.
90.
Fu Hongtao Wang Jun Cai Yuanqiang Jin Jinqiang Dong Quanyang Hu Xiuqing Wang Peng Geng Xueyu Zhang Dikang 《Acta Geotechnica》2020,15(11):3183-3192
Acta Geotechnica - Project Oufei is the largest individual reclamation project in Wenzhou city, China, and the main infrastructure consists of seawalls, sluices and separation dikes. These... 相似文献