全文获取类型
收费全文 | 103390篇 |
免费 | 1311篇 |
国内免费 | 697篇 |
专业分类
测绘学 | 2259篇 |
大气科学 | 6553篇 |
地球物理 | 20019篇 |
地质学 | 36999篇 |
海洋学 | 9337篇 |
天文学 | 24492篇 |
综合类 | 294篇 |
自然地理 | 5445篇 |
出版年
2022年 | 757篇 |
2021年 | 1282篇 |
2020年 | 1361篇 |
2019年 | 1505篇 |
2018年 | 3129篇 |
2017年 | 2894篇 |
2016年 | 3360篇 |
2015年 | 1666篇 |
2014年 | 3238篇 |
2013年 | 5393篇 |
2012年 | 3547篇 |
2011年 | 4523篇 |
2010年 | 4078篇 |
2009年 | 5179篇 |
2008年 | 4537篇 |
2007年 | 4700篇 |
2006年 | 4284篇 |
2005年 | 3027篇 |
2004年 | 2914篇 |
2003年 | 2725篇 |
2002年 | 2683篇 |
2001年 | 2401篇 |
2000年 | 2289篇 |
1999年 | 1798篇 |
1998年 | 1851篇 |
1997年 | 1747篇 |
1996年 | 1469篇 |
1995年 | 1466篇 |
1994年 | 1253篇 |
1993年 | 1187篇 |
1992年 | 1125篇 |
1991年 | 1129篇 |
1990年 | 1136篇 |
1989年 | 995篇 |
1988年 | 908篇 |
1987年 | 1071篇 |
1986年 | 910篇 |
1985年 | 1148篇 |
1984年 | 1290篇 |
1983年 | 1237篇 |
1982年 | 1140篇 |
1981年 | 1062篇 |
1980年 | 994篇 |
1979年 | 880篇 |
1978年 | 898篇 |
1977年 | 763篇 |
1976年 | 741篇 |
1975年 | 741篇 |
1974年 | 718篇 |
1973年 | 791篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Intraplate deformation and 3D rheological structure of the Rhine Rift System and adjacent areas of the northern Alpine foreland 总被引:4,自引:0,他引:4
S. Cloetingh P. A. Ziegler F. Beekman P. A. M. Andriessen N. Hardebol P. Dèzes 《International Journal of Earth Sciences》2005,94(4):758-778
The lithosphere of the Northern Alpine foreland has undergone a polyphase evolution during which interacting stress-induced intraplate deformation and upper mantle thermal perturbations controlled folding of the thermally weakened lithosphere. In this paper we address relationships among deeper lithospheric processes, neotectonics and surface processes in the Northern Alpine foreland with special emphasis on tectonically induced topography. We focus on lithosphere memory and neotectonics, paying special attention to the thermo-mechanical structure of the Rhine Graben System and adjacent areas of the northern Alpine foreland lithosphere. We discuss implications for mechanisms of large-scale intraplate deformation and links with surface processes and topography evolution. 相似文献
962.
Localization of mining-induced horizontal fractures along rock layer interfaces in overburden: field measurements and prediction 总被引:3,自引:0,他引:3
V. Palchik 《Environmental Geology》2005,48(1):68-80
The locations of mining-induced horizontal fractures along rock interfaces in the overburden of Donetsk Coal Basin were identified using an original experimental device. The device traps methane from horizontal fracture zone (100–fold coal seam thickness) over an active longwall mining excavation. Presence or absence of horizontal fractures along rock layer interfaces is correlated with physical characteristics of the overburden, such as thickness, uniaxial compressive strength of overburden rock layers, location of rock layer interfaces and thickness of extracted coal seams. As a result, a combined criterion based on these physical characteristics is proposed to predict the presence of overburden horizontal fracturing in coal mine operations. 相似文献
963.
Development of an integrated conceptual model for the rational management of the transboundary Nestos River, Greece 总被引:1,自引:0,他引:1
This paper provides a detailed analysis of the geologic, hydrologic and hydrogeologic characteristics of Nestos River basin,
which is formed within the Greek mountainous part of the river. The quantitative analysis was mainly based on the data of
the river flow in different gauging points across the rivercourse as well as on the data of groundwater discharge from karst
springs of the mountainous area while important conclusions were made regarding the hydraulic connection between the surface
waters of the river and the groundwater of the karst aquifers of the basin. The qualitative analysis has shown that the quality
of both surface waters and groundwaters of the investigated basin is high, whereas, no sources of contamination were indicated
during this research. The possible effects of the two large dams of Platanovrisi and Thesavros are also analysed as they strongly
affect the quantitative and qualitative regime of the river delta. 相似文献
964.
A. Aiuppa S. Inguaggiato M. O’Dwyer M.J. Padgett M. Valenza 《Geochimica et cosmochimica acta》2005,69(7):1861-1871
We present here new measurements of sulfur dioxide and hydrogen sulfide emissions from Vulcano, Etna, and Stromboli (Italy), made by direct sampling at vents and by filter pack and ultraviolet spectroscopy in downwind plumes. Measurements at the F0 and FA fumaroles on Vulcano yielded SO2/H2S molar ratios of ≈0.38 and ≈1.4, respectively, from which we estimate an H2S flux of 6 to 9 t · d−1 for the summit crater. For Mt. Etna and Stromboli, we found SO2/H2S molar ratios of ≈20 and ≈15, respectively, which combined with SO2 flux measurements, suggest H2S emission rates of 50 to 113 t · d−1 and 4 to 8 t · d−1, respectively. We observe that “source” and plume SO2/H2S ratios at Vulcano are similar, suggesting that hydrogen sulfide is essentially inert on timescales of seconds to minutes. This finding has important implications for estimates of volcanic total sulfur budget at volcanoes since most existing measurements do not account for H2S emission. 相似文献
965.
Calculation of the UV-visible spectra and the stability of Mo and Re oxysulfides in aqueous solution
J.A. Tossell 《Geochimica et cosmochimica acta》2005,69(10):2497-2503
Erickson and Helz (2000) established that molybdate, MoO4−2, is quickly and completely transformed to thiomolybdate, MoS4−2, by reaction with sulfide. They monitored the equilibria and kinetics of this process by measuring the UV-visible spectra of solutions containing the different oxythiomolybdate species. There is interest in the analogous reactions for the ReO4− species but little experimental data. We have therefore calculated quantum-chemically the equilibrium constants in solution for the sulfidation reactions of both MoO4−2 and ReO4−, as well as recalculating their UV-visible charge-transfer spectra. Calculations using configuration interaction singles and time-dependent hybrid Hartree-Fock density functional methods give good absolute values and trends in UV-vis energies for both series. For MoO4−2 the calculated equilibrium constants for the various sulfidation steps match reasonably well against the experimental values (within two log K units). For the ReO4− sulfidation reaction the first two steps are considerably less favorable than for MoO4−2, suggesting that the “geochemical switch” of Erickson and Helz, a rapid transformation of oxyanion to thioanion highly dependent on sulfide concentration, will be less effective in the Re case. However, both our calculations and experiment indicate that ReO4− and ReS4− are both easier to reduce than their Mo analogs, so that reduction of these Re(VII) species will be the preferred mechanism for their removal from seawater. A previous suggestion that the neutral species MoO4H2 is actually the hydrated octahedral Mo(OH)6 species is found to be incorrect, but the MoO3(OH2)3 species, a highly distorted six-coordinate complex, is almost competitive in energy with MoO4H2 plus two H2O. 相似文献
966.
967.
968.
Stephen J. Lynton Richard J. Walker Philip A. Candela 《Geochimica et cosmochimica acta》2005,69(13):3337-3347
The fractionation of lithium isotopes among quartz, muscovite, and a chloride-bearing aqueous fluid has been investigated experimentally at 400°-500°C and 50-100 MPa. Experiments were performed for 15-60 days in cold seal vessels with natural mineral specimens. Lithium was introduced primarily through the fluid, which also contained KCl and HCl. In most runs, the fluid was prepared with the L-SVEC standard (δ7Li = 0) and was 1 M in total chloride with K/Li/H = 100/10/1. In two experiments, a 6Li spike was employed. The experiments demonstrate that quartz and muscovite are susceptible to pronounced, rapid shifts in Li isotopic composition by diffusion through interaction with a Li-bearing fluid, particularly at 500°C. At 500°C, fractionation factors were determined to be Δquartz-aqueous ≅ +8 to + 12‰ and Δmuscovite-aqueous ≅ +18 to + 20‰. An intermineral fractionation factor is given by Δmuscovite-quartz ≈ +9‰. At 400°C, the results suggest Δquartz-aqueous ≈ +4 to + 6‰. The study provides evidence of systematic fractionation in lithium isotopes at the temperatures of some magmatic processes, such as those associated with porphyry-type ore systems and pegmatites. 相似文献
969.
Frank A. Podosek 《Geochimica et cosmochimica acta》2005,69(21):5147-5148
970.
Edward A. Boyle 《Geochimica et cosmochimica acta》2005,69(21):5165-5166