全文获取类型
收费全文 | 19387篇 |
免费 | 4214篇 |
国内免费 | 3912篇 |
专业分类
测绘学 | 711篇 |
大气科学 | 1092篇 |
地球物理 | 7099篇 |
地质学 | 10647篇 |
海洋学 | 2206篇 |
天文学 | 2023篇 |
综合类 | 1250篇 |
自然地理 | 2485篇 |
出版年
2024年 | 113篇 |
2023年 | 365篇 |
2022年 | 665篇 |
2021年 | 732篇 |
2020年 | 732篇 |
2019年 | 907篇 |
2018年 | 742篇 |
2017年 | 767篇 |
2016年 | 848篇 |
2015年 | 867篇 |
2014年 | 1025篇 |
2013年 | 985篇 |
2012年 | 1087篇 |
2011年 | 1096篇 |
2010年 | 952篇 |
2009年 | 1352篇 |
2008年 | 1262篇 |
2007年 | 1276篇 |
2006年 | 1304篇 |
2005年 | 1107篇 |
2004年 | 1141篇 |
2003年 | 1066篇 |
2002年 | 880篇 |
2001年 | 837篇 |
2000年 | 816篇 |
1999年 | 649篇 |
1998年 | 738篇 |
1997年 | 484篇 |
1996年 | 463篇 |
1995年 | 440篇 |
1994年 | 402篇 |
1993年 | 344篇 |
1992年 | 293篇 |
1991年 | 160篇 |
1990年 | 119篇 |
1989年 | 135篇 |
1988年 | 93篇 |
1987年 | 92篇 |
1986年 | 45篇 |
1985年 | 29篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 29篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1954年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
带"人字"支撑的新型复合结构体系动力特征研究 总被引:6,自引:0,他引:6
探讨了一种新型复合结构——带“人字”支撑的梁柱体系的动力特征问题。在满足静力荷载作用下承载力要求的基础上,根据结构动力学原理,推导了该结构体系的动力特征方程,分析了复合结构体系的支撑截面和型式的变化对动力特征的影响,计算显示,增加支撑对提高结构的频率即抗侧刚度有明显作用,且随支撑截面尺寸增大,固有频率单调增加。支撑倾角在一定范围内变化时,对频率影响较大,而超过该范围时,其影响明显减小,由此说明“人字”支撑为较合理的支撑型式。结果表明,所研究的具有“人字”支撑的复合结构体系具有较高的抗侧能力。 相似文献
62.
63.
64.
Geometric form of Haiyuan fault zone in the crustal interior and dynamics implications 总被引:1,自引:0,他引:1
The deep seismic reflection data on profile HY2 are reprocessed by the method of simultaneous inversion of velocity distribution
and interface position. By the travel-time inversion with the data of the diving wave Pg and fault plane reflection wave,
we determine the geometric form and velocity of Haiyuan fault zone interior and surrounding rock down to 10 km depth. The
measured data show that the amplitudes have strong attenuation in the range of stake number 37–39 km, suggesting the fault
zone has considerable width in the crustal interior. The results of this paper indicate that to the north of the fault zone
the crystalline basement interface upheaves gradually from southwest to northeast and becomes shallow gradually towards northeast,
and that to the south of the fault zone, within the basin between Xihua and Nanhua mountains, the folded basement becomes
shallow gradually towards southwest. The obliquity of the fault zone is about 70° above the 3 km depth, about 60° in the range
of the 3–10 km depths. From the results of this paper and other various citations, we believe that Haiyuan fault zone is in
steep state from the Earth’s surface to the depth of 10 km.
Foundation item: Joint Seismological Science Foundation of China (201001) and State Key Basic Research Development and Programming Project
(95-13-02-02).
Contribution No. RCEG200308, Exploration Geophysical Center, China Earthquake Administration. 相似文献
65.
ZHAGN Yijun DONG Wansheng ZHAO Yang ZHANG Guangshu Zhang Hongfa CHEN Chengpin ZHANG Tong 《中国科学D辑(英文版)》2004,47(Z1)
The comprehensive observations on lightning discharges were conducted in Naqu area of Qinghai-Tibet Plateau in summer of 2002. The electric structures of thunderstorms and the characteristics of lightning discharges at initial stage were analyzed by using the observation data. The results show that most of intracloud (IC) lightning flashes were polarities inverted in thunderstorms with tripole electric charge structure and occurred between negative charge region located in the middle of the thunderstorm and positive charge region located at the bottom of the thunderstorm. The radiation characteristics of discharge processes in cloud with longer lasting time involved in Cloud-to-Ground (CG) lightning flashes were similar to that of IC discharges.A lot of radiation pulses were produced in these discharge processes. Because the IC discharges took place at the bottom of thundercloud and were near the ground, they may produce more serious damage to equipment on the ground therefore should not be neglected in lightning protection. 相似文献
66.
67.
南秦岭十里坪锑矿床成矿时代及成因的初步研究 总被引:1,自引:1,他引:1
十里坪锑矿床受赵川陆缘隆_滑构造的主滑脱拆离带的控制。矿体呈脉状赋存于韧_脆性主滑脱带上部的脆性次级断层_节理中,矿石类型主要为萤石石英辉锑矿型。围岩为太古宙_元古宙变质岩系,围岩蚀变弱。成矿流体属H2O_CO2_NaCl体系,流体包裹体盐度w(NaCleq)为3.6%~11.3%,均一温度为109~232℃,形成压力大致为800×105Pa。硫、铅同位素研究表明,矿质主要来源于变火山岩围岩;氢、氧同位素显示,成矿流体以大气降水为主,初步将该矿床定为变质岩源就地式大气降水热液矿床。矿石中萤石Sm_Nd等时线年龄为(392±24)Ma,与南秦岭北部晚古生代拗陷区热水喷流_沉积成矿时代相一致,它们都形成于秦岭微板块泥盆纪非造山裂解阶段。 相似文献
68.
Tectonic and hydrodynamic control of landslides in the northern area of the Central Rif, Morocco 总被引:1,自引:0,他引:1
The northern edge of the Central Rif (Morocco) is subject to numerous landslides where mechanisms do not correspond to the classical models used by geomechanics specialists. It is necessary to adopt a multidisciplinary approach that combines geomorphology, geology, hydrogeology, and geotechnics in order to understand how such slope failures are generated, especially in a region with a heterogeneous structure characterised by significant lithological differences, severe fracturing, and thrust sheets where tectonic contacts play a major role in groundwater circulation. This report shows that these failures are essentially controlled by the tectonic contact separating the Tisirene and Chouamat thrust sheets and by subsurface hydrodynamic conditions. A model of spatial and temporal variations in the factor of safety is proposed. 相似文献
69.
The active faults known and inferred in the area where the major Pacific, North American and Eurasian plates come together group into two belts. One of them comprises the faults striking roughly parallel to the Pacific ocean margin. The extreme members of the belt are the longitudinal faults of islands arcs, in its oceanic flank, and the faults along the continental margins of marginal seas, in its continental flank. The available data show that all these faults move with some strike-slip component, which is always right-lateral. We suggest that characteristic right-lateral, either partially or dominantly, kinematics of the fault movements has its source in oblique convergence of the Pacific plate with continental Eurasian and North American plates. The second belt of active faults transverses the extreme northeast Asia as a continental extension of the active mid-Arctic spreading ridge. The two active fault belts do not cross but come close to each other at the northern margin of the Sea of Okhotsk marking thus the point where the Pacific, North American and Eurasian plates meet. 相似文献
70.