全文获取类型
收费全文 | 891篇 |
免费 | 4篇 |
国内免费 | 16篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 32篇 |
地球物理 | 141篇 |
地质学 | 340篇 |
海洋学 | 155篇 |
天文学 | 210篇 |
综合类 | 4篇 |
自然地理 | 22篇 |
出版年
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 20篇 |
2020年 | 22篇 |
2019年 | 34篇 |
2018年 | 64篇 |
2017年 | 30篇 |
2016年 | 36篇 |
2015年 | 15篇 |
2014年 | 37篇 |
2013年 | 54篇 |
2012年 | 53篇 |
2011年 | 53篇 |
2010年 | 41篇 |
2009年 | 36篇 |
2008年 | 44篇 |
2007年 | 54篇 |
2006年 | 40篇 |
2005年 | 14篇 |
2004年 | 26篇 |
2003年 | 25篇 |
2002年 | 21篇 |
2001年 | 15篇 |
2000年 | 9篇 |
1999年 | 9篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 5篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1981年 | 5篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 4篇 |
1970年 | 4篇 |
1966年 | 2篇 |
1965年 | 3篇 |
排序方式: 共有911条查询结果,搜索用时 62 毫秒
181.
Cu concentrations in surface (river and lake) and subsurface waters are determined. The geographic pattern of Cu distribution in natural water is identified. This pattern is controlled by the difference between its concentrations in drained rocks and soils and the geochemical redox conditions of its migration. Territories with low, medium, and elevated Cu concentrations in natural waters are identified. The concentrations of Cu in natural waters of the region are found to be generally lower than the Clarke values. 相似文献
182.
Authigenic carbonates in methane seeps from the Norwegian sea: Mineralogy, geochemistry, and genesis
A. Yu. Lein A. I. Gorshkov N. V. Pimenov Yu. A. Bogdanov P. Vogt O. Yu. Bogdanova V. M. Kuptsov N. V. Ul’yanova A. M. Sagalevich M. V. Ivanov 《Lithology and Mineral Resources》2000,35(4):295-310
Authigenic carbonates in the caldera of an Arctic (72°N) submarine mud volcano with active CH4bearing fluid discharge are formed at the bottom surface during anaerobic microbial methane oxidation. The microbial community
consists of specific methane-producing bacteria, which act as methanetrophic ones in conditions of excess methane, and sulfate
reducers developing on hydrogen, which is an intermediate product of microbial CH4 oxidation. Isotopically light carbon (δ13Cav =−28.9%0) of carbon dioxide produced during CH4 oxidation is the main carbonate carbon source. Heavy oxygen isotope ratio (δ18Oav = 5%0) in carbonates is inherited from seawater sulfate. A rapid sulfate reduction (up to 12 mg S dm−3 day−1) results in total exhausting of sulfate ion in the upper sediment layer (10 cm). Because of this, carbonates can only be
formed in surface sediments near the water-bottom interface. Authigenic carbonates occurring within sediments occur do notin situ. Salinity, as well as CO
3
2−
/Ca and Mg/Ca ratios, correspond to the field of nonmagnesian calcium carbonate precipitation. Calcite is the dominant carbonate
mineral in the methane seep caldera, where it occurs in the paragenetic association with barite. The radiocarbon age of carbonates
is about 10000 yr. 相似文献
183.
Joseph F. Whelan Leonid A. Neymark Richard J. Moscati Brian D. Marshall Edwin Roedder 《Applied Geochemistry》2008
Secondary calcite, silica and minor amounts of fluorite deposited in fractures and cavities record the chemistry, temperatures, and timing of past fluid movement in the unsaturated zone at Yucca Mountain, Nevada, the proposed site of a high-level radioactive waste repository. The distribution and geochemistry of these deposits are consistent with low-temperature precipitation from meteoric waters that infiltrated at the surface and percolated down through the unsaturated zone. However, the discovery of fluid inclusions in calcite with homogenization temperatures (Th) up to ∼80 °C was construed by some scientists as strong evidence for hydrothermal deposition. This paper reports the results of investigations to test the hypothesis of hydrothermal deposition and to determine the temperature and timing of secondary mineral deposition. Mineral precipitation temperatures in the unsaturated zone are estimated from calcite- and fluorite-hosted fluid inclusions and calcite δ18O values, and depositional timing is constrained by the 207Pb/235U ages of chalcedony or opal in the deposits. Fluid inclusion Th from 50 samples of calcite and four samples of fluorite range from ∼35 to ∼90 °C. Calcite δ18O values range from ∼0 to ∼22‰ (SMOW) but most fall between 12 and 20‰. The highest Th and the lowest δ18O values are found in the older calcite. Calcite Th and δ18O values indicate that most calcite precipitated from water with δ18O values between −13 and −7‰, similar to modern meteoric waters. 相似文献
184.
Soil layers at the Tunguska event site may have accumulated infalling extraterrestrial matter derived from the Tunguska Cosmic
Body (TCB). Using mineralogical, textural, and chemical criteria, a set of metal and silicate spherules of probably cosmic
origin was identified in the collection of spherules and rounded particles recovered from sites with high concentrations of
magnetic spherules on a terrace above the floodplain of the Chunya River. The metal spherules consist of Ni(Cr)-bearing wüstite
and magnetite with Ni-rich metal inclusions. The silicate spherules are glassy, cryptocrystalline, barred, and porphyritic
melted micrometeorites, some of which contain metal droplets. The number of spherules counted in our samples is higher than
the background level, indicating the possible presence of the TCB material. 相似文献
185.
Authigenic carbonate precipitates from the NE Black Sea: a mineralogical,geochemical, and lipid biomarker study 总被引:1,自引:0,他引:1
A. Bahr T. Pape G. Bohrmann A. Mazzini M. Haeckel A. Reitz M. Ivanov 《International Journal of Earth Sciences》2009,98(3):677-695
Carbonate precipitates recovered from 2,000 m water depth at the Dolgovskoy Mound (Shatsky Ridge, north eastern Black Sea)
were studied using mineralogical, geochemical and lipid biomarker analyses. The carbonates differ in shape from simple pavements
to cavernous structures with thick microbial mats attached to their lower side and within cavities. Low δ13C values measured on carbonates (−41 to −32‰ V-PDB) and extracted lipid biomarkers indicate that anaerobic oxidation of methane
(AOM) played a crucial role in precipitating these carbonates. The internal structure of the carbonates is dominated by finely
laminated coccolith ooze and homogeneous clay layers, both cemented by micritic high-magnesium calcite (HMC), and pure, botryoidal,
yellowish low-magnesium calcite (LMC) grown in direct contact to microbial mats. δ18O measurements suggest that the authigenic HMC precipitated in equilibrium with the Black Sea bottom water while the yellowish
LMC rims have been growing in slightly 18O-depleted interstitial water. Although precipitated under significantly different environmental conditions, especially with
respect to methane availability, all analysed carbonate samples show lipid patterns that are typical for ANME-1 dominated
AOM consortia, in the case of the HMC samples with significant contributions of allochthonous components of marine and terrestrial
origin, reflecting the hemipelagic nature of the primary sediment. 相似文献
186.
D. V. Alekseev V. A. Ivanov E. V. Ivancha V. V. Fomin L. V. Cherkesov 《Russian Meteorology and Hydrology》2013,38(4):248-255
An effectiveness of the storm wave attenuation by protective piers in the Sevastopol Bay of the Black Sea is studied on the basis of numerical simulation using the SWAN spectral model. Analyzed are the parameters of waves generated by winds of four main directions as well as by the southern cyclone during the storm on November 11, 2007. It is obtained that waves from the northwest part of the Black Sea penetrate most intensively into the Sevastopol Bay in case of western wind and, to a lesser degree, in case of northern and southern winds. A protective effect of the piers is observed in the west part of the bay only and the wave attenuation near the southern coast is more significant than near the northern one. The area of the southern coast directly behind the southern pier is completely protected from the storm waves and, as moving away from the pier, the danger of intensive wave effect on the coast is kept. 相似文献
187.
Peter Nojarov Peter Ivanov Ivo Kalapov Ilia Penev Mirolujba Drenska 《Theoretical and Applied Climatology》2009,98(1-2):201-208
Connection between ozone concentration and atmosphere circulation is investigated based on measurements at BEO station, peak Moussala (2,925 m a.s.l.), for the period 09 August 2006 to 29 January 2008. Ozone concentration data are collected with UV-analyzer “Environnement O3 42” and meteo data with weather station “Vaisala”. There are measurements of 7Be. Data from NOAA HYSPLIT model for particle trajectories are also used. Eight wind directions and three ranges of wind velocities are employed in the analysis. A comparison of ozone concentrations in upward and downward air transport according to HYSPLIT model is made. The number of cases with ozone concentration above 63 ppb has been counted. Mann–Whitney nonparametric test is employed as a basic statistical method. Correlation between atmosphere pressure and tropospheric ozone content is made. The same is done for 7Be and ozone. The main conclusion is that there is not any local or regional pollution effect detectable at peak Moussala, but most of the ozone measured is due to emissions of hydrocarbons and NO x over a larger region. There could be some regional sources of ozone building substances in southwest direction from peak Moussala. Air transported from the north quarter has higher ozone concentrations compared to the south quarter. In vertical direction, upward transport of air masses shows higher values of ozone concentration. Higher wind velocity is associated with low ozone concentrations at peak Moussala. The annual course of ozone concentration has summer maximum and winter minimum. There is right connection between air pressure and ozone concentration. The same is valid for the correlation between 7Be and ozone. Diurnal ozone course shows daytime maximum in winter and nighttime maximum in summer. 相似文献
188.
Argo floats revealing bimodality of large-scale mid-depth circulation in the North Atlantic 总被引:1,自引:1,他引:0
Analysis of Argo float trajectories at 1 000 m and temperature at 950 m in the North Atlantic between November 2003 and January 2005 demonstrates the existence of two different circulation modes with fast transition between them. Each mode has a pair of cyclonic - anticyclonic gyres. The difference is the location of the cyclonic gyre. The cyclonic gyre stretches from southeast to northwest in the first mode and from the southwest to the northeast in the second mode. The observed modes strongly affect the heat and salt transport in the North Atlantic. In particular, the second mode slows down the westward transport of the warm and saline water from the Mediterranean Sea. 相似文献
189.
190.
Solar flare-generated interplanetary clouds are proposed to be treated as oblate spheromaks (oblamaks) with predominantly force-free magnetic field. The solution found for a force-free field equation in spheroidal coordinates makes it possible to describe the spheromak magnetic fields by a series of spheroidal wave functions. Comparison between theoretical and experimental results is shown in the case of the hydromagnetic cloud from the November 22, 1977 flare (STIP Interval IV). 相似文献