全文获取类型
收费全文 | 122813篇 |
免费 | 1558篇 |
国内免费 | 1303篇 |
专业分类
测绘学 | 3335篇 |
大气科学 | 8971篇 |
地球物理 | 24060篇 |
地质学 | 44584篇 |
海洋学 | 10713篇 |
天文学 | 27066篇 |
综合类 | 466篇 |
自然地理 | 6479篇 |
出版年
2021年 | 964篇 |
2020年 | 1090篇 |
2019年 | 1198篇 |
2018年 | 4448篇 |
2017年 | 4142篇 |
2016年 | 4158篇 |
2015年 | 1903篇 |
2014年 | 2990篇 |
2013年 | 5597篇 |
2012年 | 3937篇 |
2011年 | 6131篇 |
2010年 | 5465篇 |
2009年 | 6762篇 |
2008年 | 5749篇 |
2007年 | 6220篇 |
2006年 | 4221篇 |
2005年 | 3617篇 |
2004年 | 3486篇 |
2003年 | 3356篇 |
2002年 | 3171篇 |
2001年 | 2672篇 |
2000年 | 2573篇 |
1999年 | 2230篇 |
1998年 | 2212篇 |
1997年 | 2140篇 |
1996年 | 1831篇 |
1995年 | 1729篇 |
1994年 | 1550篇 |
1993年 | 1415篇 |
1992年 | 1339篇 |
1991年 | 1316篇 |
1990年 | 1325篇 |
1989年 | 1190篇 |
1988年 | 1147篇 |
1987年 | 1255篇 |
1986年 | 1164篇 |
1985年 | 1424篇 |
1984年 | 1656篇 |
1983年 | 1450篇 |
1982年 | 1414篇 |
1981年 | 1288篇 |
1980年 | 1198篇 |
1979年 | 1121篇 |
1978年 | 1135篇 |
1977年 | 971篇 |
1976年 | 908篇 |
1975年 | 909篇 |
1974年 | 850篇 |
1973年 | 917篇 |
1971年 | 594篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
142.
Phillip S. Toms 《第四纪科学杂志》2003,18(8):815-816
143.
Himalayan magmatism and porphyry copper–molybdenum mineralization in the Yulong ore belt, East Tibet
Summary ?The NW–SE-trending Yulong porphyry Cu–Mo ore belt, situated in the Sanjiang0 area of eastern Tibet, is approximately 400 km
long and 35 to 70 km wide. Complex tectonic and magmatic processes during the Himalayan epoch have given rise to favorable
conditions for porphyry-type Cu–Mo mineralization.
Porphyry masses of the Himalayan epoch in the Yulong ore belt are distributed in groups along regional NW–SE striking tectonic
lineaments. They were emplaced mainly into Triassic and Lower Permian sedimentary-volcanic rocks. K–Ar und U–Pb isotopic datings
give an intrusion age range of 57–26 Ma. The porphyries are mainly of biotite monzogranitic and biotite syenogranitic compositions.
Geological and geochemical data indicate that the various porphyritic intrusions in the belt had a common or similar magma
source, are metaluminous to peraluminous, Nb–Y–Ba-depleted, I-type granitoids, and belong to the high-K calc-alkaline series.
Within the Yulong subvolcanic belt a number of porphyry stocks bear typical porphyry type Cu–Mo alteration and mineralization.
The most prominent porphyry Co–Mo deposits include Yulong, Malasongduo, Duoxiasongduo, Mangzong and Zhanaga, of which Yulong
is one of the largest porphyry Cu (Mo) deposits in China with approximately 8 × 106 tons of contained Cu metal. Hydrothermal alteration at Yulong developed around a biotite–monzogranitic porphyry stock that
was emplaced within Upper Triassic limestone, siltstone and mudstone. The earliest alteration was due to the effects of contact
metamorphism of the country rocks and alkali metasomatism (potassic alteration) within and around the porphyry body. The alteration
of this stage was accompanied by a small amount of disseminated and veinlet Cu–Mo sulfide mineralization. Later alteration–mineralization
zones form more or less concentric shells around the potassic zone, around which are distributed a phyllic or quartz–sericite–pyrite
zone, a silicification and argillic zone, and a propylitic zone.
Fluid inclusion data indicate that three types of fluids were involved in the alteration–mineralization processes: (1) early
high temperature (660–420 °C) and high salinity (30–51 wt% NaCl equiv) fluids responsible for the potassic alteration and
the earliest disseminated and/or veinlet Cu–Mo sulfide mineralization; (2) intermediate unmixed fluids corresponding to phyllic
alteration and most Cu–Mo sulfide mineralization, with salinities of 30–50 wt% NaCl equiv and homogenization temperatures
of 460–280 °C; and (3) late low to moderate temperature (300–160 °C) and low salinity (6–13 wt% NaCl equiv) fluids responsible
for argillic and propylitic alteration. Hydrogen and oxygen isotopic studies show that the early hydrothermal fluids are of
magmatic origin and were succeeded by increasing amounts of meteoric-derived convective waters. Sulfur isotopes also indicate
a magmatic source for the sulfur in the early sulfide mineralization, with the increasing addition of sedimentary sulfur outward
from the porphyry stock.
Received August 29, 2001; revised version accepted May 1, 2002
Published online: November 29, 2002 相似文献
144.
The role of biology in astronomical phenomena and processes was first discussed extensively by us in the period from 1979-1982.
The two sections reproduced below are the concluding chapters of `Space Travellers' which we published in 1981. The ideas
discussed here have turned out to be forerunners to several recent developments in astrobiology.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
145.
146.
147.
Gopal C. Kilambi Praveen Nagar N. Kameswara Rao 《Journal of Astrophysics and Astronomy》1992,13(2):175-194
Mid-ultraviolet and optical photometric analysis of helium stars are presented. A linear relation exists between the effective
temperature derived from model atmospheres and (1965-V)0 index. The effective temperatures derived from (1965-V)0 index are somewhat higher than that of MK spectral type estimates especially for late B-type helium objects. 相似文献
148.
Zhang Qing Wang Li-fan Hu Jing-yao P. A. Mazzali Wang Zhen-ru 《Chinese Astronomy and Astrophysics》1995,19(4):426-431
We present the modeling of the ultraviolet and optical spectra obtained simultaneously on 1993 April 15 with the HST and at Lick Observatory. A Monte Carlo code is employed in the modeling and a comparison is made between models reported by different groups. With an atmosphere similar to the Sun in chemical composition, the observed spectral lines are well reproduced by a power law density structure of index around 20 except the strong H and HeI λ5876 lines which have peculiar absorption profiles. The photospheric velocity is found to be 9500 km/s and the blackbody temperature of the spectrum is 7990 K. For H and HeI λ5876, we suggest a two-component density structure which has a smoother layer located immediately outside the steeply decreasing inner envelope. The power law indices are most probably 20 and 3, respectively, with the transition point at about 13 000 km/s. In addition, this outer smooth layer serves to flatten the far UV spectrum as observed. 相似文献
149.
150.