全文获取类型
收费全文 | 16553篇 |
免费 | 2975篇 |
国内免费 | 3990篇 |
专业分类
测绘学 | 853篇 |
大气科学 | 3731篇 |
地球物理 | 4378篇 |
地质学 | 8299篇 |
海洋学 | 1680篇 |
天文学 | 873篇 |
综合类 | 1677篇 |
自然地理 | 2027篇 |
出版年
2024年 | 60篇 |
2023年 | 243篇 |
2022年 | 728篇 |
2021年 | 794篇 |
2020年 | 658篇 |
2019年 | 767篇 |
2018年 | 932篇 |
2017年 | 826篇 |
2016年 | 958篇 |
2015年 | 763篇 |
2014年 | 964篇 |
2013年 | 940篇 |
2012年 | 818篇 |
2011年 | 912篇 |
2010年 | 921篇 |
2009年 | 884篇 |
2008年 | 832篇 |
2007年 | 824篇 |
2006年 | 672篇 |
2005年 | 586篇 |
2004年 | 488篇 |
2003年 | 526篇 |
2002年 | 532篇 |
2001年 | 467篇 |
2000年 | 573篇 |
1999年 | 781篇 |
1998年 | 683篇 |
1997年 | 706篇 |
1996年 | 603篇 |
1995年 | 513篇 |
1994年 | 532篇 |
1993年 | 397篇 |
1992年 | 324篇 |
1991年 | 247篇 |
1990年 | 186篇 |
1989年 | 164篇 |
1988年 | 180篇 |
1987年 | 105篇 |
1986年 | 84篇 |
1985年 | 71篇 |
1984年 | 53篇 |
1983年 | 56篇 |
1982年 | 44篇 |
1981年 | 41篇 |
1980年 | 24篇 |
1979年 | 20篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1958年 | 16篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
331.
It has been proved through experiments that the electromagnetic radiation energy of a substance will vary when stress acts on the substance. This moment, the electromagnetic radiation energy (observation value) received by the remote sensor is triggered not only by the substance temperature and also by the stress. Separating quantitatively these two kinds of electromagnetic radiation energy and then inversing the actual temperature state and stress state of a medium is a matter with practical significance in earthquake prediction and stability monitoring for the large-scale geotechnical engineering. In this paper the principle and the mathematical method for inversing stress by using multiband remote sensing data are discussed in detail. A calculation example is listed. 相似文献
332.
Zhao-Dong Xu Ya-Peng Shen Hong-Tie Zhao 《Soil Dynamics and Earthquake Engineering》2003,23(8):683-689
The paper introduces a synthetic optimization analysis method of structures with viscoelastic (VE) dampers, namely the simplex method. The optimal parameters and location of VE dampers can be determined by this method. Numerical example and a shaking table test about reinforced concrete structures with VE dampers show that the seismic responses of structures will be reduced more effectively when the parameters and location of VE dampers are designed in accordance with the results calculated by the simplex method. 相似文献
333.
Zhao Jinren Zhang Xiankang Zhang Chengke Ren Qingfang Cheng Shuangxi Zhang Jianshi Nie Wenying PAN Shuzhen 《中国地震研究》2003,17(2):103-112
The data from two deep seismic sounding profiles was processed and studied comprehensively. The results show that crnst-mantle structures in the investigated region obviously display layered characteristics and velocity structures and tectonic features have larger distinction in different geological structure blocks. The boundary interface C between the upper and lower crust and Moho fluctuate greatly. The shallowest depths of C (30.0km) and Moho (45.5km) under Jiashi deepen sharply from Jiashi to the western Kunlun mountain areas, where the depths of C and Moho are 44.0km and 70.0km, respectively. The higher velocity structures in the Tarim massif determine its relatively “stable“ characteristics in crust tectonics. The phenomenon in the Jiashi region, where the distribution of earthquake foci mostly range from 20kin to 40kin in depth, may infer that the local uplift of C and Moho interface, anomalonsly lower velocity bodies and deep large faults control earthquake occurrence and seismogenic processes in the Jiashi strong earthquake swarm. 相似文献
334.
This paper proposes a simple lattice model for collapse analysis of RC bridges subjected to earthquakes by using the extended distinct element method (EDEM). In the model, a concrete element consists of lumped masses connected to one another by springs, and a reinforcement bar is represented by a discrete model or an integrated model. The proposed lattice model is simple but its parameters are reasonably defined. It has fewer element nodes and connecting springs, which will be of benefit by shortening the CPU time. The processes to determine the initial stiffness of concrete and steel springs, the parameters of the constitutive model and the fracture criteria for springs are described. A re‐contact spring model is also proposed to simulate the re‐contact of the concrete after fracture of springs; and a general grid searching method is used to decrease the CPU time for judging re‐contact after fracture. The lattice model is assessed by numerical simulations and experiments. As an application, a damaged single‐column pier subjected to the Kobe Earthquake in 1995 is analysed by EDEM with the proposed model. The simulation results indicate that the proposed model predicts well qualitatively the collapse process of RC bridges. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
335.
336.
Absence of Archean basement in the South Kunlun Block: Nd-Sr-O isotopic evidence from granitoids 总被引:3,自引:0,他引:3
Abstract The West Kunlun mountain range along the northwestern margin of the Tibetan Plateau is crucial in understanding the early tectonic history of the region. It can be divided into the North and South Kunlun Blocks, of which the former is considered to be part of the Tarim Craton, whereas consensus was not reached on the nature and origin of the South Kunlun Block. Samples were collected from the 471 Ma Yirba Pluton, the 405 Ma North Kudi Pluton and the 214 Ma Arkarz Shan Intrusive Complex. These granitoids cover approximately 60% of the Kudi area in the South Kunlun Block. Sr, Nd, and O isotope compositions preclude significant involvement of mantle-derived magma in the genesis of these granitoids; therefore, they can be used to decipher the nature of lower–mid crust in the area. All samples give Mesoproterozoic Nd model ages (1.1–1.5 Ga) similar to those of the exposed metamorphic complex of this block but significantly different from those of the basement of the North Kunlun Block (2.8 Ga). This indicates that the South Kunlun Block does not have an Archean basement, and, thus, does not support the microcontinent model that suggests the South Kunlun Block was a microcontinent once separated from and later collided back with the North Kunlun Block. 相似文献
337.
338.
0.7Ma以来的念青唐古拉山脉隆升过程——来自冰川剥蚀作用的证据 总被引:1,自引:0,他引:1
通过对念青唐古拉山冰碛地层划分及冰碛物同位素测年,发现最早一期冰碛物形成于0.7~0.6MaBP,指示自中更新世以来念青唐古拉山脉开始隆升,主峰地区发生了大规模的冰川剥蚀作用,形成了大面积分布的冰碛高平台;0.2~0.14MaBP念青唐古拉山又快速隆升,并堆积了刚刚伸出各大沟谷口的高侧碛;0.07~0.03MaBP念青唐古拉山再次小规模隆起,形成各大沟谷内的侧碛和终碛垄;0.01Ma BP还有小规模冰川活动。念青唐古拉山主峰地区的冰川剥蚀作用反映出的山脉隆升过程,可较好地与青藏高原的隆起过程相对比,它应是青藏高原隆升的响应。 相似文献
339.
SHRIMP U-Pb zircon age, geochemical and Nd isotopic data are reported for the Neo-proterozoic Guandaoshan pluton in the Yanbian region, SW Sichuan. This pluton is of typical I-type granite and emplaced at (857 ± 13) Ma. Geochemical and Nd isotopic characters suggest that the pluton was generated by partial melting of pre-existing, young (late Mesoproterozoic to early Neo-proterozoic) low-K tholeiitic protolith within an intraplate anorogenic setting. The Guandaoshan pluton probably records the earliest magmatism induced by the proposed ca. 860–750 Ma mantle superplume beneath the supercontinent Rodinia. 相似文献
340.