全文获取类型
收费全文 | 73011篇 |
免费 | 1471篇 |
国内免费 | 1359篇 |
专业分类
测绘学 | 2097篇 |
大气科学 | 5527篇 |
地球物理 | 15088篇 |
地质学 | 25561篇 |
海洋学 | 6466篇 |
天文学 | 16499篇 |
综合类 | 345篇 |
自然地理 | 4258篇 |
出版年
2022年 | 476篇 |
2021年 | 757篇 |
2020年 | 797篇 |
2019年 | 883篇 |
2018年 | 1746篇 |
2017年 | 1659篇 |
2016年 | 2077篇 |
2015年 | 1286篇 |
2014年 | 2001篇 |
2013年 | 3627篇 |
2012年 | 2355篇 |
2011年 | 3150篇 |
2010年 | 2802篇 |
2009年 | 3693篇 |
2008年 | 3182篇 |
2007年 | 3228篇 |
2006年 | 3072篇 |
2005年 | 2254篇 |
2004年 | 2225篇 |
2003年 | 2035篇 |
2002年 | 2024篇 |
2001年 | 1756篇 |
2000年 | 1660篇 |
1999年 | 1423篇 |
1998年 | 1453篇 |
1997年 | 1443篇 |
1996年 | 1176篇 |
1995年 | 1131篇 |
1994年 | 1028篇 |
1993年 | 904篇 |
1992年 | 837篇 |
1991年 | 819篇 |
1990年 | 849篇 |
1989年 | 800篇 |
1988年 | 724篇 |
1987年 | 878篇 |
1986年 | 747篇 |
1985年 | 897篇 |
1984年 | 1103篇 |
1983年 | 951篇 |
1982年 | 930篇 |
1981年 | 835篇 |
1980年 | 801篇 |
1979年 | 738篇 |
1978年 | 751篇 |
1977年 | 676篇 |
1976年 | 618篇 |
1975年 | 617篇 |
1974年 | 592篇 |
1973年 | 646篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
A. E. Volvach A. A. Berezhnoi L. N. Volvach I. D. Strepka E. A. Volvach 《Bulletin of the Crimean Astrophysical Observatory》2011,107(1):122-124
Investigations on OH maser lines in comets have been performed with the RT-22 at CrAO. The results of observations of 9P/Temper1
and Lulin C/2007 N3 comets in the OH molecule line at a wavelength of 18 cm are presented. An original technique for observation
data analysis has been developed. The gas production rate of OH molecules in these comets is estimated. 相似文献
202.
This paper, based on a real world case study (Limmat aquifer, Switzerland), compares inverse groundwater flow models calibrated with specified numbers of monitoring head locations. These models are updated in real time with the ensemble Kalman filter (EnKF) and the prediction improvement is assessed in relation to the amount of monitoring locations used for calibration and updating. The prediction errors of the models calibrated in transient state are smaller if the amount of monitoring locations used for the calibration is larger. For highly dynamic groundwater flow systems a transient calibration is recommended as a model calibrated in steady state can lead to worse results than a noncalibrated model with a well-chosen uniform conductivity. The model predictions can be improved further with the assimilation of new measurement data from on-line sensors with the EnKF. Within all the studied models the reduction of 1-day hydraulic head prediction error (in terms of mean absolute error [MAE]) with EnKF lies between 31% (assimilation of head data from 5 locations) and 72% (assimilation of head data from 85 locations). The largest prediction improvements are expected for models that were calibrated with only a limited amount of historical information. It is worthwhile to update the model even with few monitoring locations as it seems that the error reduction with EnKF decreases exponentially with the amount of monitoring locations used. These results prove the feasibility of data assimilation with EnKF also for a real world case and show that improved predictions of groundwater levels can be obtained. 相似文献
203.
Karaevskaya E. S. Demidov N. E. Kazantsev V. S. Elizarov I. M. Kaloshin A. G. Petrov A. L. Karlov D. S. Schirrmeister L. Belov A. A. Wetterich S. 《Izvestiya Atmospheric and Oceanic Physics》2021,57(10):1254-1270
Izvestiya, Atmospheric and Oceanic Physics - The archaeal composition of permafrost samples taken during the drilling of frozen marine sediments in the area of the Barentsburg coal mine on the east... 相似文献
204.
Comprehensive distribution patterns of physical and chemical characteristics have been obtained from a series of cruises in Liverpool Bay. The marked feature of these distributions was their temporal variability, suggesting that the surface residual circulation is also temporally variable. The influence of wind stress upon the circulation pattern and hence water quality of this sea area is illustrated. 相似文献
205.
206.
A. F. Morozov B. N. Khakhaev O. V. Petrov V. I. Gorbachev G. V. Tarkhanov L. D. Tsvetkov Yu. M. Erinchek A. M. Akhmedov V. A. Krupenik K. Yu. Sveshnikova 《Doklady Earth Sciences》2010,435(1):1483-1486
A thick (200 m) rock salt mass covering Late Archean granitoids was exposed for the first time in the Early Proterozoic volcanogenic-sedimentary
formations in the Onega trough of the east Baltic Shield by the Onega parametric well. The mineral composition of salts, their
geochemical features, and the isotopic composition of carbonate carbon and oxygen have been studied. After fluid inclusions
present in salts, their metamorphism temperature and isotopic composition of helium and argon were determined. The obtained
results give evidence of the fact that rock salts and magnesites associated with them were formed in an evaporate basin with
participation of deep crustal processes. The age of the underlying granitoids (2.716 ± 9 Ma) is determined using the Pb—Pb
method. 相似文献
207.
208.
A.B. Cadle B. Cairncross A.D.M. Christie D.L. Roberts 《International Journal of Coal Geology》1993,23(1-4)
The coal-bearing sediments and coal seams of the Karoo Basin, Southern Africa are described and discussed. The Karoo Basin is bounded on its southern margin by the Cape Fold Belt, onlaps onto the Kaapvaal Craton in the north and is classified as a foreland basin. Coal seams are present within the Early Permian Vryheid Formation and the Triassic Molteno Formation.The peats of the Vryheid Formation accumulated within swamps in a cool temperate climatic regime. Lower and upper delta plain, back-barrier and fluvial environments were associated with peat formation. Thick, laterally extensive coal seams have preferentially accumulated in fluvial environments. The coals are in general inertinite-rich and high in ash. However, increasing vitrinite and decreasing ash contents within seams occur from west to east across the coalfields. The Triassic Molteno coal seams accumulated with aerially restricted swamps in fluvial environments. These Molteno coals are thin, laterally impersistent, vitrinite-rich and shaly, and formed under a warm temperate climatic regime.Palaeoclimate, depositional systems, differential subsidence and basin tectonics influence to varying degrees, the maceral content, thickness and lateral extent of coal seams. However, the geographic position of peat-forming swamps within a foreland basin, coupled with basin tectonics and differential subsidence are envisaged as the primary controls on coal parameters. The Permian coals are situated in proximal positions on the passive margin of the foreland basin. Here, subsidence was limited which enhanced oxidation of organic matter and hence the formation of inertinitic coals. The coals in this tectonic setting are thick and laterally extensive. The Triassci coals are situated within the tectonically active foreland basin margin. Rapid subsidence and sedimentation rates occurred during peat formation which resulted in the preservation of thin, laterally impersistent, high ash, vitrinite-rich, shaly coals. 相似文献
209.
210.