全文获取类型
收费全文 | 9632篇 |
免费 | 1895篇 |
国内免费 | 2750篇 |
专业分类
测绘学 | 1334篇 |
大气科学 | 1458篇 |
地球物理 | 2132篇 |
地质学 | 5241篇 |
海洋学 | 1848篇 |
天文学 | 399篇 |
综合类 | 763篇 |
自然地理 | 1102篇 |
出版年
2024年 | 70篇 |
2023年 | 217篇 |
2022年 | 497篇 |
2021年 | 568篇 |
2020年 | 469篇 |
2019年 | 530篇 |
2018年 | 534篇 |
2017年 | 544篇 |
2016年 | 573篇 |
2015年 | 616篇 |
2014年 | 582篇 |
2013年 | 720篇 |
2012年 | 781篇 |
2011年 | 770篇 |
2010年 | 783篇 |
2009年 | 725篇 |
2008年 | 781篇 |
2007年 | 645篇 |
2006年 | 597篇 |
2005年 | 525篇 |
2004年 | 388篇 |
2003年 | 349篇 |
2002年 | 378篇 |
2001年 | 340篇 |
2000年 | 304篇 |
1999年 | 196篇 |
1998年 | 145篇 |
1997年 | 114篇 |
1996年 | 86篇 |
1995年 | 84篇 |
1994年 | 57篇 |
1993年 | 63篇 |
1992年 | 38篇 |
1991年 | 36篇 |
1990年 | 28篇 |
1989年 | 22篇 |
1988年 | 21篇 |
1987年 | 6篇 |
1986年 | 13篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1973年 | 4篇 |
1957年 | 6篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
1998年5月29日皮山县发生6.2级地震,震中距皮山县城约39km,震源深度为32km,烈度分布区为北西-南东走向的椭圆形,极震区烈度为Ⅶ度,个别点为Ⅷ度,地震使皮山县县城,9个乡,2个镇,2个农场,墨玉县部分地区遭到不同程度的损失。共计受伤人数为26人,其中重伤为2人,无家可归者人数为5566人,1392户,牲畜死亡4454头。地震造成的直接经济损失达5486.75万元。 相似文献
992.
QuanLian Li NingLian Wang XiaoBo Wu JianChen Pu JianQiao He Jun Xie 《中国科学D辑(英文版)》2009,52(11):1803-1812
We report on the concentration and compositional features of n-alkanes of natural and anthropogenic origins in the snow samples collected from the Qiyi glacier in the Qilian Mountains,
the Yuzhufeng glacier in eastern Kunlun Mountains, the Xiaodongkemadi glacier in the Tanggula Mountains, and the Gurenhekou
glacier in the Nyainqêntanglha Range. The results indicate a decrease in the total n-alkane concentration (T-HCs) from the northeast to the south over the Tibetan Plateau. The T-HCs in these studied areas were
close to those in the Belukha and Sofiyskiy glacier, Russian Alati Mountains and the Dasuopu glacier in the Himalaya but were
much higher than those in the Greenland ice sheet, suggesting that the mountain glaciers in the Asian continent may receive
a higher loading of n-alkanes than the Greenland ice core. Moreover, the compositional characteristics of n-alkanes indicated that the n-alkanes in the studied areas were probably originated from the plant waxes as well as the fossil-fuel combustion exhaust,
whereas the contribution from the lower organisms was small. In addition, the plant wax (Cn(wax)) and anthropogenic (non-Cn(wax)) contributions revealed that fast industrialization may have significant effects on the organic pollutant composition
in glacier over the Tibetan Plateau and its circumference environment. Particularly, except for the Yuzhufeng glacier, the
ΣnC21
−/ΣnC22
+ and (nC15+nC17+nC19)/(nC27+nC29+nC31) ratio decreased from the Qiyi glacier to the Gurenhekou glacier over the Tibetan Plateau, while the carbon preference index
(CPI) values increased. These results indicate a decrease in terrigenous input while an increase in marine input from the
northeast to the south over the Tibetan Plateau. These two ratios can be used as the climatic and environmental change indicators. 相似文献
993.
Reflection and transmission of seismic waves at an interface betwen two saturated soils 总被引:2,自引:0,他引:2
ReflectionandtransmisionofseismicwavesataninterfacebetwentwosaturatedsoilsJUNYANG(杨峻)SHIMINGWU(吴世明)ZhejiangUniversity,Hangz... 相似文献
994.
Jian Zeng Tian-Chang Chen Wei-Bin Han Jun Fan Si-Hua Zheng Akira Hasegawa Shigeki Horiuchij Satoshi Matsumoto 《地震学报(英文版)》1997,10(3):313-320
Based on the single scattering model of coda power spectrum analysis, digital waveform data of 50 events recorded by the real-time
processing system of the Chengdu telemetry network are analyzed to estimate the Q
c values of earth medium beneath the Chengdu telemetry network for several specified frequencies. It is found that the Q
c shows the frequency dependency in the form of Q
c = Q
0
f
n in the range of 1.0 to 20.0Hz. Estimated Q
0 ranges from 60.83 to 178.05, and n is found to be 0.713 to 1.159. The average value of Q
0 and n are 117 and 0.978 respectively. This result indicates the strong frequency dependency of the attenuation of coda waves beneath
the Chengdu telemetry network. Comparing with the results obtained in other regions of the world, it is found that Q
0
−1 value and its change with frequency are similar to those in regions with strong tectonic activity.
This subject is supported by the Ministry of Personnel, China for partly sponsoring. 相似文献
995.
在前文模型试验的基础上 ,本文总结归纳了隔震桥梁的设计方法与设计流程 ,着重论述探讨了隔震桥梁的概念设计与细部构造设计应注意的问题 相似文献
996.
A new probabilistic analytical approach to evaluate seismic system reliability of large lifeline systems is presented in this paper. The algorithm takes the shortest path from the source to the terminal of a node weight or edge weight network as decomposition policy, using the Boolean laws of set operation and probabilistic operation principal, a recursive decomposition process then could be constructed. For a general weight network, the modified Torrieri method (NTR/T method) is introduced to combine with the suggested algorithm. Therefore, the recursive decomposition algorithm may be applied to evaluate the seismic reliability of general lifeline systems. A series of case studies, including a practical district electric power network system and a large urban water supply system, show that the suggested algorithm supplies a useful probabilistic analysis means for the seismic reliability evaluation of large lifeline systems. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
997.
慢地震慢前兆的机制研究 总被引:12,自引:1,他引:12
通过岩石高温高压破裂实验与有机玻璃破裂试验的应力—应变曲线对比、地震波形记录(观测资料)与试样破裂波形(实验资料)对比、地震前后定点应变与主破裂前后应变形态变化的对比,认为慢地震是临界或亚临界破裂或预先滑动所致,是低频应变波动。它是材料屈服、弱化或塑性变化的必然结果。而慢前兆则是临近大地震(大破裂)前出现的诸如形变、低频地震波(破裂弹性波)等的短期及临震前兆现象,它比较可靠。但由于许多岩石主破裂前并无明显的临界破裂或预滑动现象,也并非所有岩石都一定出现明显屈服,所以也并非每个地震前都有慢地震,因此,也就不一定都出现低频波动。从而,也并不一定都出现相同的短期、临震前兆现象。 相似文献
998.
Characteristics and genesis of maghemite in Chinese loess and paleosols: Mechanism for magnetic susceptibility enhancement in paleosols 总被引:4,自引:0,他引:4
Tianhu Chen Huifang Xu Qiaoqin Xie Jun Chen Junfeng Ji Huayu Lu 《Earth and Planetary Science Letters》2005,240(3-4):790-802
Morphological characteristics and microstructures of magnetic minerals extracted from Chinese loess and paleosols were investigated using powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Our results indicate that maghemite in loess–paleosol sequences was transformed from magnetite through oxidation of magnetite. Maghemite transformed from eolian magnetite during chemical weathering has low-angle grain boundaries among maghemite nano-crystals. Some nano-crystalline maghemites with nanoporous texture resulted from microbe-induced precipitation of magnetite or transformation of poorly crystalline ferric Fe (oxy)hydroxides in presence of Fe-reducing bacteria. Aggregates of euhedral maghemite nano-crystals were transformed from magnetite magnetosomes. Both microbe-induced nanoporous magnetite and microbe-produced magnetite magnetosomes are directly related to microbial activities and pedogenesis of the paleosols. It is proposed that the formation of nano-crystalline maghemite with superparamagnetic property in paleosol results in the enhancement of magnetic susceptibility, although the total amount (weight percent) of magnetic minerals in both paleosol and loess units is similar. Our results also show that nano-crystalline and nanoporous magnetite grains prefer to transform into maghemite in semi-arid soil environments instead of hematite, although hematite is a thermodynamically stable phase. This result also indicates that a decrease in crystal size will increase stability of maghemite. It is also inferred that surface energy of maghemite is lower than that of hematite. 相似文献
999.
1000.