全文获取类型
收费全文 | 6744篇 |
免费 | 1274篇 |
国内免费 | 1609篇 |
专业分类
测绘学 | 277篇 |
大气科学 | 1429篇 |
地球物理 | 1758篇 |
地质学 | 3248篇 |
海洋学 | 1010篇 |
天文学 | 219篇 |
综合类 | 849篇 |
自然地理 | 837篇 |
出版年
2024年 | 25篇 |
2023年 | 112篇 |
2022年 | 322篇 |
2021年 | 356篇 |
2020年 | 329篇 |
2019年 | 301篇 |
2018年 | 366篇 |
2017年 | 349篇 |
2016年 | 422篇 |
2015年 | 303篇 |
2014年 | 393篇 |
2013年 | 368篇 |
2012年 | 341篇 |
2011年 | 362篇 |
2010年 | 411篇 |
2009年 | 363篇 |
2008年 | 301篇 |
2007年 | 317篇 |
2006年 | 273篇 |
2005年 | 208篇 |
2004年 | 194篇 |
2003年 | 207篇 |
2002年 | 204篇 |
2001年 | 183篇 |
2000年 | 205篇 |
1999年 | 318篇 |
1998年 | 292篇 |
1997年 | 277篇 |
1996年 | 229篇 |
1995年 | 244篇 |
1994年 | 218篇 |
1993年 | 172篇 |
1992年 | 151篇 |
1991年 | 93篇 |
1990年 | 93篇 |
1989年 | 73篇 |
1988年 | 51篇 |
1987年 | 37篇 |
1986年 | 23篇 |
1985年 | 26篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 2篇 |
1958年 | 4篇 |
排序方式: 共有9627条查询结果,搜索用时 0 毫秒
91.
Palaeo- and archaeointensity determinations of the geomagnetic field are limited by mineralogical alteration that may occur when samples are heated in the laboratory to produce a TRM ( Thellier & Thellier 1959 ; Shaw 1974 ). By using microwave excitation of the magnetic grains we have been able to create a TRM without significantly heating the bulk samples, thereby avoiding thermal alteration ( Walton et al . 1993 ; Shaw et al . 1996 ). When applied to Peruvian ceramics in a manner analogous to the standard Thellier method, the microwave technique was found to reduce the scatter dramatically in the archaeointensity results ( Shaw et al . 1996 ). In the present study we apply this microwave technique to a collection of Chinese ceramics covering the time interval 2700–7500 yr BP. These ceramics have already been investigated using adaptations of both Thellier's ( Coe 1967 ) and Shaw's ( Rolph & Shaw 1985 ) palaeointensity methods ( Yang et al . 1993a ). Although an acceptable agreement was found between those two methods, the equivalent virtual axial dipole moments (VADMs) were significantly lower than for the global model of McElhinny & Senanayake (1982 ). The present study, using the microwave technique with cooling-rate correction, has provided more consistent VADMs, and is much closer to the global model. 相似文献
92.
Particle size distribution of 12–500 nm was measured at Mt. Waliguan, China Global Atmosphere Watch Baseline Observatory, from Aug. in 2005 to May in 2007. 72-hr back-trajectories at 100-m arrival height above ground level for the same period were calculated at 6:00, 12:00, and 21:00 (Beijing Time) for each day using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT-4) model developed by NOAA/ARL. It was found that air mass sources significantly impact particle number concentration and size distribution at Mt. Waliguan. Cluster analysis of back-trajectories show that higher Aitken mode particle number concentration was observed when air masses came from or passed by the northeastern section of Mt. Waliguan, with short trajectory length. High number concentration of nucleation mode was associated with air masses from clean regions, with long trajectory length 相似文献
93.
Xiao Yang Zhao Chang Sun Yue Wang Shun Wu Huanran Chen Hui Liu Hanlong 《Acta Geotechnica》2021,16(5):1391-1400
Acta Geotechnica - One-dimensional compression tests on quartz sands treated by microbially induced carbonate precipitation (MICP) were carried out to evaluate the effects of gradation and calcium... 相似文献
94.
95.
96.
Natural Hazards - This study involved the systematic collation of historical data from local records, government records, etc., as well as disaster data compiled by contemporary researchers.... 相似文献
97.
矿山边坡稳定性研究的回顾与展望 总被引:7,自引:4,他引:7
本文阐述了露天矿边坡工程的特点, 回顾了露天矿边坡稳定性研究及其取得的理论成果和进展, 指出露天矿边坡稳定性研究的特点, 提出相应的研究技术路线与方法。 相似文献
98.
99.
The anodic stripping voltammetry with physically-coating mercury film electrode was used to investigate the complexing action
of trace heavy metals in seawater with organic ligands. The apparent copper complexing capacity of seawater was determined
by titrating the organic ligands in natural seawater with standard ionic copper solution. The complexing actions of copper
in seawater with humic acid (HA) or fulvic acid (FA) were investigated by titrating copper in seawater with HA or FA solution.
The equilibrium time, electrodeposition potential, and effect of pH etc. were investigated respectively. The results show
that the interaction of copper in seawater with organic matter is a fast process. At natural pH, HA or FA tend to act with
copper in seawater to form nonlabile complexes. During experimental electrode process, these complexes did not significantly
dissociate. The experimental results were calculated according to 1∶1 complex formation. 相似文献
100.