全文获取类型
收费全文 | 43616篇 |
免费 | 617篇 |
国内免费 | 241篇 |
专业分类
测绘学 | 935篇 |
大气科学 | 2216篇 |
地球物理 | 9320篇 |
地质学 | 16902篇 |
海洋学 | 3871篇 |
天文学 | 9693篇 |
综合类 | 139篇 |
自然地理 | 1398篇 |
出版年
2022年 | 536篇 |
2021年 | 827篇 |
2020年 | 880篇 |
2019年 | 937篇 |
2018年 | 2156篇 |
2017年 | 1894篇 |
2016年 | 2025篇 |
2015年 | 884篇 |
2014年 | 1728篇 |
2013年 | 2435篇 |
2012年 | 1934篇 |
2011年 | 2224篇 |
2010年 | 2091篇 |
2009年 | 2317篇 |
2008年 | 2028篇 |
2007年 | 2166篇 |
2006年 | 1931篇 |
2005年 | 1064篇 |
2004年 | 965篇 |
2003年 | 966篇 |
2002年 | 860篇 |
2001年 | 862篇 |
2000年 | 731篇 |
1999年 | 482篇 |
1998年 | 534篇 |
1997年 | 553篇 |
1996年 | 397篇 |
1995年 | 434篇 |
1994年 | 419篇 |
1993年 | 326篇 |
1992年 | 332篇 |
1991年 | 328篇 |
1990年 | 389篇 |
1989年 | 314篇 |
1988年 | 295篇 |
1987年 | 297篇 |
1986年 | 233篇 |
1985年 | 341篇 |
1984年 | 333篇 |
1983年 | 338篇 |
1982年 | 316篇 |
1981年 | 286篇 |
1980年 | 298篇 |
1979年 | 239篇 |
1978年 | 275篇 |
1977年 | 237篇 |
1976年 | 200篇 |
1975年 | 217篇 |
1974年 | 196篇 |
1973年 | 241篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
I. N. Tomson O. P. Polyakova V. Yu. Alekseev V. A. Baskina 《Geology of Ore Deposits》2006,48(1):74-76
Two types of metalliferous carbonaceous rocks that differ in associated metals are considered. One of them is characterized by gold occurring in finely dispersed arsenopyrite and arsenic-bearing pyrite, and the other, by finely impregnated native metals in carbonaceous matter. Rocks of the first type also contain elements of the platinum group, while those of the second type bear rhenium, silver, iron, molybdenum, and other metals. Graphitic mineralization is usually localized in the shear zone associated with alkaline basalts. 相似文献
952.
953.
Yu. V. Plotkina E. B. Sal’nikova A. B. Kotov M. D. Tolkachev M. R. Pavlov 《Petrology》2006,14(2):201-208
The paper reports results obtained by the complex studying of zircon crystals from rocks of various genesis. Zircon is one of the minerals most often used as geochronometers. It also provides genetic information on superimposed processes that is “recorded” in the external and internal morphology of its crystals. This mineral is thoroughly examined to select its unaltered crystals for U-Pb dating by the single-grain method. Zircon grains are selected with the use of optical and electron microscopy and cathodoluminescence. This publication presents the first results obtained by examining zircon by computer microtomography (μCT) and the results of the studying of the external and internal structure by conventional techniques ([optical microscopy and SEM (SE and CL)]. The paper demonstrates the advantages of the application of the μCT techniques to the selection of targets for U-Pb zircon dating: there is no need for the special preparation of the samples and no material is destructed. However, this technique may be not informative enough if the zircon contains inherited core whose density does not differ from the density of the surrounding mineral. 相似文献
954.
955.
The authors identify and describe the following global forces of nature driving the Earth’s climate: (1) solar radiation as a dominant external energy supplier to the Earth, (2) outgassing as a major supplier of gases to the World Ocean and the atmosphere, and, possibly, (3) microbial activities generating and consuming atmospheric gases at the interface of lithosphere and atmosphere. The writers provide quantitative estimates of the scope and extent of their corresponding effects on the Earth’s climate. Quantitative comparison of the scope and extent of the forces of nature and anthropogenic influences on the Earth’s climate is especially important at the time of broad-scale public debates on current global warming. The writers show that the human-induced climatic changes are negligible. 相似文献
956.
We present three-dimensional hydrodynamical modeling of mass transfer in the close binary system β Lyr taking into account explicitly radiative cooling and the stellar wind of the accretor. Our computations show that flow forces wind out from the orbital plane, where an accretion disk with a radius of 0.4–0.5 and a height of about 0.15–0.17 (in units of orbital separation) is formed. Gas motions directed upward from the orbital plane are initiated in the region of interaction of the flow from L1 and the accretor wind (x = 0.91, y = ?0.17); i.e., a jetlike structure forms. This structure has the shape of a gas pillar above the orbital plane, where gas moves with the velocity of stellar wind. The number density of the gas in this structure is about 1014 cm?3, and its temperature is 20 000–45 000 K. At heights of about 0.15–0.20 above the orbital plane, in the region between the jetlike structure and the disk, two spiral shocks form. It is possible that the emission lines observed in the spectrum of β Lyr binary originate in this region. 相似文献
957.
958.
959.
Summary Crust-derived xenoliths hosted by Miocene basaltic diatremes in the Hyblean Plateau (south-eastern Sicily, Italy) provide
new information regarding the nature of a portion of the central Mediterranean lower crust. These xenoliths can be divided
into three groups: gabbros (plagioclase + clinopyroxene + Fe–Ti oxides ± apatite ± amphibole ± Fe-rich green spinel), diorites
(An-poor plagioclase, clinopyroxene ± Fe–Ti oxides ± orthopyroxene) and mafic granulites (plagioclase + clinopyroxene + green
spinel ± orthopyroxene ± Fe–Ti oxides). Gabbros form the main subject of this paper. They represent cumulates whose igneous
texture has been locally obliterated by metamorphic recrystallization and shearing. They were permeated by Fe–Ti-rich melts
related to tholeiitic-type fractional crystallisation. Incompatible element ratios (Zr/Nb = 5–26; Y/Nb = 1.4–11) indicate
that these cumulate gabbros derived from MORB liquids. Late-stage and hydrothermal fluids caused diverse, sometimes important,
metasomatic trasformations. Petrographic and geochemical comparison with gabbroids from well-known geodynamic settings show
that the Hyblean lower crustal xenoliths were probably formed in an oceanic or oceanic-continent transition environment. 相似文献
960.
Environmental and health risk assessment in abandoned mining area, Zlata Idka, Slovakia 总被引:1,自引:0,他引:1
The Zlata Idka village is a typical mountainous settlement. As a consequence of more than 500 years of mining activity, its environment has been extensively affected by pollution from potentially toxic elements. This paper presents the results of an environmental-geochemical and health research in the Zlata Idka village, Slovakia. Geochemical analysis indicates that arsenic (As) and antimony (Sb) are enriched in soils, groundwater, surface water and stream sediments. The average As and Sb contents are 892 mg/kg and 818 mg/kg in soils, 195 mg/kg and 249 mg/kg in stream sediments, 0.028 mg/l and 0.021 mg/l in groundwater and 0.024 mg/l and 0.034 mg/l in surface water. Arsenic and Sb concentrations exceed upper permissible limits in locally grown vegetables. Within the epidemiological research the As and Sb contents in human tissues and fluids have been observed (blood, urine, nails and hair) in approximately one third of the village’s population (120 respondents). The average As and Sb concentrations were 16.3 μg/l and 3.8 μg/l in blood, 15.8 μg/l and 18.8 μg/l in urine, 3,179 μg/kg and 1,140 μg/kg in nails and 379 μg/kg and 357 μg/kg in hair. These concentrations are comparatively much higher than the average population. Health risk calculations for the ingestion of soil, water, and vegetables indicates a very high carcinogenic risk (>1/1,000) for as content in soil and water. The hazard quotient [HQ=average daily dose (ADD)/reference dose (RfD)] calculation method indicates a HQ>1 for groundwater As and Sb concentrations. 相似文献