全文获取类型
收费全文 | 413篇 |
免费 | 16篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 31篇 |
大气科学 | 22篇 |
地球物理 | 85篇 |
地质学 | 197篇 |
海洋学 | 49篇 |
天文学 | 22篇 |
综合类 | 2篇 |
自然地理 | 30篇 |
出版年
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 10篇 |
2017年 | 12篇 |
2016年 | 3篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 21篇 |
2012年 | 17篇 |
2011年 | 23篇 |
2010年 | 20篇 |
2009年 | 18篇 |
2008年 | 17篇 |
2007年 | 28篇 |
2006年 | 18篇 |
2005年 | 15篇 |
2004年 | 10篇 |
2003年 | 14篇 |
2002年 | 18篇 |
2001年 | 11篇 |
2000年 | 14篇 |
1999年 | 13篇 |
1998年 | 14篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1966年 | 4篇 |
1960年 | 2篇 |
1959年 | 2篇 |
1955年 | 2篇 |
1953年 | 3篇 |
1948年 | 1篇 |
排序方式: 共有438条查询结果,搜索用时 31 毫秒
321.
Oceanic Velocity Microstructure Measurements in the 20th Century 总被引:6,自引:0,他引:6
The science of ocean turbulence was started more than 50 years ago by a small research group using a surplus mine-sweeping
paravane to measure the velocity and temperature fluctuations in the ocean. The field has grown considerably and measurements
are now conducted by researchers in many countries. A wide variety of sophisticated instrument systems are used to profile
horizontally and vertically through the marine environment. Here we review the historical development of velocity micro-structure
profiles over the past four decades and summarize the basic requirements for successful measurements. We highlight critical
technological developments and glance briefly at some of the scientific discoveries made with these instruments.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
322.
INTRODUCTIONMicro organismsthatinhabittheintersticesandundersideofseaiceareexposedtowidevariationsofsalinity ,particularlyduringthe periodsofbrinedrainageandicemelting(Horner ,1 977;GrantandHorner ,1 976 ) .Althoughtheamountsofmarineorganisminseaicearelowerdurin… 相似文献
323.
Friedrich Lucassen Gerhard Franz Rolf L. Romer Dieter Pudlo Peter Dulski 《Contributions to Mineralogy and Petrology》2008,156(6):765-784
The isotopic composition of mafic small-volume intra-plate magmatism constrains the compositions of the sub-continental mantle
sources. The Nd, Pb, and Sr isotope signatures of widespread late Mesozoic to Quaternary intra-plate magmatism in NE Africa
(Sudan, South Egypt) are surprisingly uniform and indicate the presence of a high-μ (μ = 238U/204Pb) source in the mantle. The rocks are characterized by small ranges in the initial isotopic composition of Nd, Pb, and Sr
and most samples fall within ε Nd ca. 3–6, 206Pb/204Pb ca. 19.5–20.5, 207Pb/204Pb ca. 15.63–15.73, 208Pb/204Pb ca. 39–40 and 87Sr/86Sr ca. 0.7028–0.7034. We interpret this reservoir as lithospheric mantle that formed beneath the Pan-African orogens and magmatic
arcs from asthenospheric mantle, which was enriched in trace elements (U, Th, and light REE). Combining our new data set with
published data of intra-plate magmatic rocks from the Arabian plate indicates two compositionally different domains of lithospheric
mantle in NE-Africa–Arabia. The two domains are spatially related to the subdivision of the Pan-African orogen into a western
section dominated by reworked cratonic basement (NE-Africa; high-μ lithospheric mantle) and an eastern section dominated by
juvenile Pan-African basement (easternmost NE-Africa and Arabia; moderate μ lithospheric mantle). The compositions of the
Pan-African lithospheric mantle and the MORB-type mantle of the Red Sea and Gulf of Aden spreading centers could explain the
Nd–Pb-Sr isotopic compositions of the most pristine Afar flood basalts in Yemen and Ethiopia by mixtures of the isotopic composition
of regional lithospheric and asthenospheric sources.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
324.
Boron-isotope fractionation between tourmaline and fluid: an experimental re-investigation 总被引:2,自引:1,他引:1
Christian Meyer Bernd Wunder Anette Meixner Rolf L. Romer Wilhelm Heinrich 《Contributions to Mineralogy and Petrology》2008,156(2):259-267
The fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments
between 400 and 700°C at 200 MPa and at 500°C, 500 MPa. Tourmaline was crystallized from an oxide mix in presence of water
that contained boron in excess. In one series of experiments, [B]fluid/[B]tour was 9 after the run; in another series it was 0.1. All experiments produced tourmaline as the sole boron-bearing solid, along
with traces of quartz and talc. Powder XRD and Rietveld refinements revealed no significant amounts of tetrahedrally coordinated
boron in tourmaline. 11B always preferentially fractionated into the fluid. For experiments where [B]fluid/[B]tour was 9, a consistent temperature-dependent boron isotope fractionation curve resulted, approximated by Δ11B(tour–fluid) = −4.20 · [1,000/T (K)] + 3.52; R
2 = 0.77, and valid from 400 to 700°C. No pressure dependence was observed. The fractionation (−2.7 ± 0.5‰ at 400°C; and −0.8 ± 0.5‰
at 700°C) is much lower than that previously presented by Palmer et al. (1992). Experiments where [B]fluid/[B]tour was 0.1 showed a significant larger apparent fractionation of up to −4.7‰. In one of these runs, the isotopic composition
of handpicked tourmaline crystals of different size varied by 1.3‰. This is interpreted as resulting from fractional crystallization
of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline, thus indicating
larger fractionation than observed at equilibrium. The effect is eliminated or minimized in experiments with very high boron
excess in the fluid. We therefore suggest that values given by the above relation represent the true equilibrium fractionations. 相似文献
325.
326.
Simon?LutzEmail author Gerhard?Beutler Stefan?Schaer Rolf?Dach Adrian?J?ggi 《GPS Solutions》2016,20(2):239-250
The International GNSS Service (IGS) issues four sets of so-called ultra-rapid products per day, which are based on the contributions of the IGS Analysis Centers. The traditional (“old”) ultra-rapid orbit and earth rotation parameters (ERP) solution of the Center for Orbit Determination in Europe (CODE) was based on the output of three consecutive 3-day long-arc rapid solutions. Information from the IERS Bulletin A was required to generate the predicted part of the old CODE ultra-rapid product. The current (“new”) product, activated in November 2013, is based on the output of exactly one multi-day solution. A priori information from the IERS Bulletin A is no longer required for generating and predicting the orbits and ERPs. This article discusses the transition from the old to the new CODE ultra-rapid orbit and ERP products and the associated improvement in reliability and performance. All solutions used in this article were generated with the development version of the Bernese GNSS Software. The package was slightly extended to meet the needs of the new CODE ultra-rapid generation. 相似文献
327.
Shock-effects on the K-Ar system of plagioclase feldspar and the age of anorthosite inclusions from North-Eastern Minnesota 总被引:1,自引:0,他引:1
Artificial shock pressures up to 52.5 GPa have no influence on the K-Ar system of plagioclase feldspar. The 40Ar-39Ar analysis of feldspar (labradorite An67 from anorthosite of North-Eastern Minnesota) shocked up to 45 GPa—in vacuo, to prevent massive entrapment of atmospheric argon-shows that the age spectra and the argon diffusion properties remain unaltered. Similar feldspar samples (labradorite An51 from Nain, Labrador), shocked in air up to 52.5 GPa and dated by the conventional K-Ar method, also yield the same age as unshocked samples but with a higher atmospheric argon contribution. The Minnesota anorthosite has an 40Ar-39Ar age of 1075 ± 10 m.y. No information on a possible previous history of the anorthosite became apparent. 相似文献
328.
Oxygen Fugacity measurements were carried out on chromites from the Eastern Bushveld Complex (Maandagshoek) and are compared with former measurements on chromites from the western Bushveld Complex (Zwartkop Chrome Mine). These results together with those of Hill and Roeder (1974) yield the following conditions of formation for the massive chromitite layers: Western Bushveld Complex (Zwartkop Chrome Mine) $$\begin{gathered} Layer{\text{ }}T(^\circ C) p_{O_2 } (atm) \hfill \\ LG3{\text{ 1160}} - {\text{1234 10}}^{ - {\text{5}}} - 10^{ - 7.6} \hfill \\ LG4{\text{ 1175}} - {\text{1200 10}}^{ - 6.35} - 10^{ - 7.20} \hfill \\ LG6{\text{ 1162}} - {\text{1207 10}}^{ - 6.20} - 10^{ - 7.50} \hfill \\ \hfill \\ \end{gathered} $$ Eastern Bushveld Complex (Farm Maandagshoek) $$\begin{gathered} {\text{LXI 1115}} - {\text{1150 10}}^{ - 7.80} - 10^{ - 8.80} \hfill \\ ( = {\text{Steelpoort Seam)}} \hfill \\ {\text{LX 1125 10}}^{ - 8.25} \hfill \\ {\text{V 1120 10}}^{ - 8.55} \hfill \\ {\text{LII 1120 10}}^{ - 8.0} - 10^{ - 8.60} \hfill \\ \end{gathered} $$ The comparison of the data shows, that the chronitite layers within each particular sequence were formed under approximately identicalp o 2- andT-conditions. The chromites from the western Bushveld Complex, however, were formed at higher temperatures and higher oxygen fugacities than the chromites from the eastern Bushveld Complex. Fromp o 2-T-curves of disseminated chromites and the temperatures derived above, the following conditions of formation for the host rocks were obtained: Western Bushveld Complex $$T = 1200^\circ {\text{C; }}p_{{\text{o}}_{\text{2}} } = 10^{ - 7.25} - 10^{ - 7.50} $$ Eastern Bushveld Complex $$T = 1125^\circ {\text{C; }}p_{{\text{o}}_{\text{2}} } = 10^{ - 8.50} - 10^{ - 9.25} $$ Consequently, the host rocks in the Zwartkop-Chrome-Mine, were formed under higher temperatures and higher oxygen fugacities than the host rocks at Maandagshoek. The rock sequence in the Zwartkop-Chrome-Mine therefore originated in an earlier stage of the differentiation of the Bushveld magma. Comparison of the chromites from the host rocks with the chromites from massive layers supports Ulmer's (1969) thesis that an increase of the oxygen fugacity is responsible for the formation of massive chromitite layers. The values in this investigation show that increases of only about 0.5–1.0 log units are necessary to enhance chromitite layer formation. 相似文献
329.
The International Geographical Union Reports
International geographical union regional conference on Asian Pacific countries 相似文献330.
Rolf Thienhaus 《International Journal of Earth Sciences》1953,41(1):181-190
Ohne Zusammenfassung 相似文献