全文获取类型
收费全文 | 9088篇 |
免费 | 1269篇 |
国内免费 | 1653篇 |
专业分类
测绘学 | 713篇 |
大气科学 | 978篇 |
地球物理 | 1940篇 |
地质学 | 5212篇 |
海洋学 | 1312篇 |
天文学 | 603篇 |
综合类 | 490篇 |
自然地理 | 762篇 |
出版年
2024年 | 58篇 |
2023年 | 167篇 |
2022年 | 384篇 |
2021年 | 438篇 |
2020年 | 349篇 |
2019年 | 428篇 |
2018年 | 504篇 |
2017年 | 505篇 |
2016年 | 560篇 |
2015年 | 425篇 |
2014年 | 549篇 |
2013年 | 768篇 |
2012年 | 728篇 |
2011年 | 720篇 |
2010年 | 727篇 |
2009年 | 652篇 |
2008年 | 636篇 |
2007年 | 654篇 |
2006年 | 573篇 |
2005年 | 420篇 |
2004年 | 267篇 |
2003年 | 207篇 |
2002年 | 237篇 |
2001年 | 207篇 |
2000年 | 139篇 |
1999年 | 118篇 |
1998年 | 48篇 |
1997年 | 52篇 |
1996年 | 34篇 |
1995年 | 33篇 |
1994年 | 42篇 |
1993年 | 37篇 |
1992年 | 36篇 |
1991年 | 28篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 22篇 |
1987年 | 26篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1980年 | 7篇 |
1979年 | 13篇 |
1977年 | 6篇 |
1973年 | 6篇 |
1969年 | 7篇 |
1954年 | 7篇 |
1937年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
M. A. Vashkov’yak 《Astronomy Letters》2001,27(7):464-469
We consider the structural peculiarities of Uranus’s satellite system associated with its separation into two groups: inner equatorial satellites moving in nearly circular orbits and distant irregular satellites with retrograde motion in highly elliptical orbits. The intermediate region is free from satellites in a wide range of semimajor axes. By analyzing the evolution of satellite orbits under the combined effect of solar attraction and Uranus’s oblateness, we offer a celestial-mechanical explanation for the absence of equatorial satellites in this region. M.L. Lidov’s studies during 1961–1963 have served as a basis for our analysis. 相似文献
2.
Abstract Eclogites are distributed for more than 500 km along a major tectonic boundary between the Sino-Korean and Yangtze cratons in central and eastern China. These eclogites usually have high-P assemblages including omphacite + kyanite and/or coesite (or its pseudomorph), and form a high-P eclogite terrane. They occur as isolated lenses or blocks 10 cm to 300 m long in gneisses (Type I), serpentinized garnet peridotites (Type II) and marbles (Type III). Type I eclogites were formed by prograde metamorphism, and their primary metamorphic mineral assemblage consists mainly of garnet [pyrope (Prp) = 15–40 mol%], omphacite [jadeite (Jd) = 34–64 mol%], pargasitic amphibole, kyanite, phengitic muscovite, zoisite, an SiO2 phase, apatite, rutile and zircon. Type II eclogites characteristically contain no SiO2 phase, and are divided into prograde eclogites and mantle-derived eclogites. The prograde eclogites of Type II are petrographically similar to Type I eclogites. The mantle-derived eclogites have high MgO/(FeO + Fe2O3) and Cr2O3 compositions in bulk rock and minerals, and consist mainly of pyrope-rich garnet (Prp = 48–60 mol%), sodic augite (Jd = 10–27 mol%) and rutile. Type III eclogites have an unusual mineral assemblage of grossular-rich (Grs = 57 mol%) garnet + omphacite (Jd = 30–34 mol%) + pargasite + rutile. Pargasitic and taramitic amphiboles, calcic plagioclase (An68), epidote, zoisite, K-feldspar and paragonite occur as inclusions in garnet and omphacite in the prograde eclogites. This suggests that the prograde eclogites were formed by recrystallization of epidote amphibolite and/or amphibolite facies rocks with near-isothermal compression reflecting crustal thickening during continent–continent collision of late Proterozoic age. Equilibrium conditions of the prograde eclogites range from P > 26 kbar and T= 500–750°C in the western part to P > 28 kbar and T= 810–880°C in the eastern part of the high-P eclogite terrane. The prograde eclogites in the eastern part are considered to have been derived from a deeper position than those in the western part. Subsequent reactions, manifested by (1) narrow rims of sodic plagioclase or paragonite on kyanite and (2) symplectites between omphacite and quartz are interpreted as an effect of near-isothermal decompression during the retrograde stage. The conditions at which symplectites re-equilibrated tend to increase from west (P < 10 kbar and T < 580°C) to east (P > 9 kbar and T > 680°C). Equilibrium temperatures of Type II mantle-derived eclogites and Type III eclogite are 730–750°C and 680°C, respectively. 相似文献
3.
S. Maaløe 《Mineralogy and Petrology》2003,77(1-2):1-24
Summary ?Partial melting of the mantle is polybaric which implies that the phase relations change during partial melting. In addition
to the pressure the composition of the melt depends on the melting mode. Various melting models have been suggested. Here
the basic phase relations of polybaric batch, percolative, and critical melting are considered, using a simple ternary system.
The percolative melts are in equilibrium with their residua, but differ somewhat in composition from those of batch melting.
Critical melting is a fractional type of melting where the residuum contain interstitial melt. The critical melts differ in
composition from batch melts. The linear trends of peridotites from ophiolites show that the extracted melts had nearly constant
compositions, and therefore were extracted within a small pressure interval. A comparison between the trends of mantle peridotite
and experimental batch melts suggests strongly that the melt extracted from the peridotites are in equilibrium with their
residua. This could suggest that either batch or percolative melting are relevant melting modes for the mantle. However, isotopic
disequilibria favor instead a critical mode of melting. This inconsistency can be avoided if the ascending melts are accumulated
within a source region and equilibrate with the residuum before the melt is extracted from the source region. The evidence
for equilibrium suggests that multisaturation of tholeiitic compositions in PT-diagrams is relevant for estimating pressure
and temperature of generation of primary tholeiitic magmas.
Received September 2, 2001; revised version accepted March 20, 2002 相似文献
4.
5.
This review is devoted to problems in the photochemical modeling of atmospheric processes. The physicochemical and mathematical foundations underlying the construction of photochemical models are described, a classification of the atmospheric reactions is presented, and the features of photochemical modeling are considered under various irradiance conditions for various atmospheric layers and geographical regions. Atmospheric processes that are important to photochemical models are discussed. Applications involving photochemical models are outlined. Some results are presented to illustrate the capabilities of photochemical models. Special attention is given to relatively recent directions in photochemical modeling, such as data assimilation and inverse problems. The review can be used by experts in areas related to atmospheric chemistry as a basic source of knowledge on the subject and for the development of photochemical modules for atmospheric models. 相似文献
6.
珠江三角洲地质灾害种类的多样性与其所处的复杂地质环境和多变的气候条件密切相关。文章选用了地震活动、活动断裂、地壳升降运动、软土地基、地面塌陷以及冲、淤积等6个主要因素作为评价指标,并用模糊数学方法对珠江三角洲内17个小区作了计算,结果表明该区大部分地区属于轻灾害区,只有滨海沿岸地区属于较重灾害区。 相似文献
7.
The measurement of the signal to noise ratio in continuous seismic profiling systems is carried out by means of a small general purpose digital computer equipped with an analog to digital converter. The computer is programmed to compute and compare the power spectrum of a sample of noise to the power spectrum of a sample of noise plus an echo. Power spectra of some twenty to fifty shots are averaged to yield reliable estimates of the signal to noise ratio as a function of frequency. The observed spectra agree well with spectra calculated from signals measured near to an air-gun. This measurement of signal to noise ratio as a function of frequency provides unambiguous information for the adjustment of the necessary band-pass filter thus improving the operation of a continuous seismic profiler. 相似文献
8.
9.
10.
采用GPS和全站仪联合作业的数字测图方式进行了外业快速数据采集。并利用南方CASS软件对数据进行内业成图工作,最后利用大型的地理信息系统软件ArcGIS进行地理数据的入库,从而实现了阜新市区地理数据库的更新,此方式具有速度快、效率高和精度高等优点,可以借鉴到同类的地区。 相似文献