全文获取类型
收费全文 | 36373篇 |
免费 | 3151篇 |
国内免费 | 5298篇 |
专业分类
测绘学 | 2837篇 |
大气科学 | 3504篇 |
地球物理 | 4372篇 |
地质学 | 9258篇 |
海洋学 | 3494篇 |
天文学 | 17224篇 |
综合类 | 1565篇 |
自然地理 | 2568篇 |
出版年
2024年 | 177篇 |
2023年 | 401篇 |
2022年 | 751篇 |
2021年 | 764篇 |
2020年 | 943篇 |
2019年 | 1114篇 |
2018年 | 784篇 |
2017年 | 922篇 |
2016年 | 939篇 |
2015年 | 1151篇 |
2014年 | 1127篇 |
2013年 | 1316篇 |
2012年 | 1331篇 |
2011年 | 1287篇 |
2010年 | 1158篇 |
2009年 | 2594篇 |
2008年 | 2633篇 |
2007年 | 3019篇 |
2006年 | 2996篇 |
2005年 | 2692篇 |
2004年 | 2641篇 |
2003年 | 2241篇 |
2002年 | 1988篇 |
2001年 | 1675篇 |
2000年 | 1606篇 |
1999年 | 1485篇 |
1998年 | 1538篇 |
1997年 | 586篇 |
1996年 | 382篇 |
1995年 | 470篇 |
1994年 | 473篇 |
1993年 | 312篇 |
1992年 | 231篇 |
1991年 | 183篇 |
1990年 | 140篇 |
1989年 | 199篇 |
1988年 | 130篇 |
1987年 | 113篇 |
1986年 | 105篇 |
1985年 | 61篇 |
1984年 | 41篇 |
1983年 | 33篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1977年 | 8篇 |
1954年 | 4篇 |
1897年 | 7篇 |
1877年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
K. Holub 《Pure and Applied Geophysics》1997,150(3-4):435-450
—Mining-induced seismicity associated with longwall face operations in the Ostrava- Karviná coal mines, Czech Republic, has
been investigated in order to establish the conditions leading to a focal zone generation. The study, based on macroseismic
and instrumental observations, proved that seismicity is influenced by natural as well as mining conditions. The first group
includes the influence of faults, washouts and red beds, while the second one is represented by shaft and/or crosscut safety
pillars and various types of remnant pillars. All the cases discussed show that many focal zones are generated in overstressed
strata as a consequence of interaction of natural conditions and/or old workings with the active coal face.
Received June 18, 1996, accepted March 10, 1997 相似文献
83.
基于GIS的攀西地区铂族元素成矿地质条件初步分析 总被引:2,自引:1,他引:2
攀西地区以良好的铂族元素(PGE)成矿地质背景,而成为我国铂族元素找矿热点地区之一。本文在建立攀西地区铂族元素矿床地质概念模型的基础上,用地理信息系统(GIS)分析了该地区的铂族元素成矿地质条件,包括地质构造、峨眉山玄武岩、基性一超基性岩和铂族元素地球化学异常特征。指出研究区的深大断裂对铂族元素的富集表现出很好的控制作用,峨眉山玄武岩为铂族元素的矿源层之一,岩浆岩为铂族元素的富集提供了成矿物质及成矿能量。 相似文献
84.
LIU Xiangwen YANG Guangming ZOU Huamin QU Jing & ZHAO Wenxia . Graduate School China University of Geosciences Wuhan China . Test Center China University of Geosciences Wuhan China . Physics Technology College Wuhan University Wuhan China . Test Center Zhongshan University Guangzhou China 《中国科学D辑(英文版)》2004,47(3)
Sakhaite was first discovered by Ostrovskaya, Pertsev and Nikitina at Siberia in the former Soviet Union. By using the X-ray diffraction technique, they proved that the crystal system of sakhaite was cubic (a = 1.464 nm), its possible space groups were Fm3m, F432, F43m, Fm3, F23, and its crystal chemical for-mula was Ca48Mg16(CO3)16(BO3)28Cl4(OH)8 4H2O[1]. Chichagov, Simonov and Belov studied the crystal structure of synthetic sakhaite and determined that its space group was F4132, … 相似文献
85.
86.
87.
The Zhangjiakou–Penglai seismotectonic zone (ZPSZ) lies in the northern part of North China and extends along the Zhangjiakou–Beijing–Tianjin–Bohai Bay–Penglai–Yellow Sea. It is about 900 km long and some 250 km wide in a northwest direction. The great Sanhe-Pinggu (MS=8.0) earthquake occurred on September 1679 and the Tangshan (MS=7.8) earthquake on July 1976 caused serious economic and life losses. According to some differences in crust structure and regional tectonic stress field, the ZPSZ is divided into western and eastern segment by the 117°E line for study on long-term seismic hazard analysis. An analysis of Gutenberg–Richter's empirical relation of earthquake-frequency and time process of historic and recent earthquakes along the eastern and western segments shows that the earthquake activity obeys a Poisson process, and these calculations indicate that the earthquake occurrence probability of MS=6.0–6.9 is 0.77–0.83 in the eastern segment and the earthquake occurrence probability of MS=7.0–7.9 is 0.78–0.80 in the western segment of the ZPSZ during a period from 2005 to 2015. 相似文献
88.
NEKVASIL H.; DONDOLINI A.; HORN J.; FILIBERTO J.; LONG H.; LINDSLEY D. H. 《Journal of Petrology》2004,45(4):693-721
Experimental simulation of incremental crystal fractionationof a hy-normative hawaiite indicates that the spectrum of compositionsfrom mildly alkalic hawaiite to sodic rhyolite found in silica-saturatedalkalic suites of the ocean islands and continental hotspotsand rifts can be produced by fractionation at 9·3 kbarwith bulk water contents > 相似文献
89.
Sensitive high-resolution ion microprobe UPb dating showsthat a biotite orthogneiss from the Hercynian belt of westerncentral Iberia contains 1000300 Ma zircon. Older, 1000570Ma ages within this range represent inherited, detrital materialamong which four age components may be recognized: 相似文献
90.
A Reflection on Mg, Cd, Ca, Li and Si Isotopic Measurements and Related Reference Materials 总被引:6,自引:1,他引:6
Jean Carignan Damien Cardinal Anton Eisenhauer Albert Galy Mark Rehkamper Frank Wombacher Nathalie Vigier 《Geostandards and Geoanalytical Research》2004,28(1):139-148
This contribution aims to report the reflections we had with the scientific community during two international workshops on reference materials for stable isotopes in Davos (2002) and Nice (2003). After evaluating the isotopic homogeneity of some existing reference materials, based on either certificates, literature data or specific inter-laboratory rounds, we confirm these as primary reference materials or propose new ones relative to which stable isotope compositions should be reported. We propose DSM-3 for Mg, NIST SRM 915a for Ca, L-SVEC for Li and NBS28 for Si. Cadmium does not yet have a well identified delta zero material, although three commercial mono-elemental Cd solutions have yielded the same isotopic composition relative to one another. In order to scale the linearity of any mass spectrometer, some secondary reference materials are also proposed: Cambridge-1 solution for Mg, the "Münster-Cd" and JEPPIM Cd solutions for Cd and the "Big Batch" silicate for Si. The team from Nancy propose to prepare a mixed spike solution for Li isotopes. Well-characterised natural samples such as ocean or continental waters, diatoms, sponges, rocks and minerals are needed to validate the entire analytical procedure, particularly to take into account the effect of sample mineralisation and of chemical manipulations for elemental separation prior to analysis. 相似文献