全文获取类型
收费全文 | 2763篇 |
免费 | 188篇 |
国内免费 | 173篇 |
专业分类
测绘学 | 131篇 |
大气科学 | 197篇 |
地球物理 | 671篇 |
地质学 | 1092篇 |
海洋学 | 347篇 |
天文学 | 406篇 |
综合类 | 63篇 |
自然地理 | 217篇 |
出版年
2023年 | 33篇 |
2022年 | 57篇 |
2021年 | 81篇 |
2020年 | 75篇 |
2019年 | 90篇 |
2018年 | 116篇 |
2017年 | 101篇 |
2016年 | 130篇 |
2015年 | 112篇 |
2014年 | 132篇 |
2013年 | 156篇 |
2012年 | 142篇 |
2011年 | 168篇 |
2010年 | 162篇 |
2009年 | 160篇 |
2008年 | 129篇 |
2007年 | 102篇 |
2006年 | 118篇 |
2005年 | 84篇 |
2004年 | 102篇 |
2003年 | 72篇 |
2002年 | 83篇 |
2001年 | 50篇 |
2000年 | 50篇 |
1999年 | 41篇 |
1998年 | 35篇 |
1997年 | 33篇 |
1996年 | 35篇 |
1995年 | 32篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 28篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 23篇 |
1988年 | 11篇 |
1987年 | 32篇 |
1986年 | 11篇 |
1985年 | 14篇 |
1984年 | 15篇 |
1983年 | 26篇 |
1982年 | 29篇 |
1981年 | 26篇 |
1980年 | 21篇 |
1979年 | 12篇 |
1978年 | 18篇 |
1976年 | 15篇 |
1975年 | 9篇 |
1974年 | 10篇 |
1973年 | 8篇 |
排序方式: 共有3124条查询结果,搜索用时 15 毫秒
991.
992.
Erwan Le Guerrou Philip A. Allen Andrea Cozzi James L. Etienne Mark Fanning 《地学学报》2006,18(2):147-153
Sedimentary rocks deposited during the Ediacaran period (~630–542 Ma) contain carbonates whose carbon isotopic ratios show a marked negative excursion consisting of a precipitous drop from +5‰ to ?12‰, followed by a sub‐linear recovery to positive δ13C values. Isotopic ages (U/Pb) and thermal subsidence modelling are combined to constrain the excursion in time and indicate an onset at ~600 Ma, and duration of recovery of approximately 50 Myr. The excursion is widely recognized in Oman and has potential correlatives in Ediacaran strata elsewhere, and may thus represent a characteristic feature of the Ediacaran period. The amplitude of this carbon isotope excursion far exceeds those of other Neoproterozoic anomalies. The isotopic trend of negative excursion and long‐term recovery spanned at least one short‐lived glacial episode (at 580 Ma), but appears unrelated to glaciation, which indicates that negative anomalies in the Neoproterozoic marine carbon isotope record are not directly or uniquely linked to ice ages. 相似文献
993.
Pierre North 《Astrophysics and Space Science》2006,304(1-4):219-221
35 Eclipsing binaries presenting unambiguous total eclipses were selected from a subsample of the list of Wyrzykowski et al. (2003). The photometric elements are given for the I curve in DiA photometry, as well as approximate teff and masses of the components. The interest of these systems is stressed in view of future spectroscopic observations. 相似文献
994.
995.
Pierre Guillaume 《Celestial Mechanics and Dynamical Astronomy》1975,11(4):449-467
This paper extends Breakwell and Perko's ‘first order’ matching theory (1965, 1966) to a more general matching theory which is applicable to a wider class of second species solutions. In a first stage, the matching theory is elaborated on the basis of new assumptions on the orders of magnitude of the small parameters. In a second stage, we construct a matching theory which takes into account general assumptions which include our assumptions and Breakwell-Perko's. 相似文献
996.
An analytic radiative-equilibrium model is formulated where both short- and longwave radiation are treated as two-stream
(down- and upward) fluxes. An equilibrium state is defined in the model by the vertical temperature profile. The sensitivity
of any such state to the model atmosphere’s optical properties is formulated analytically. As an example, this general formulation
is applied to a single-column 11-layer model, and the model’s optical parameters are obtained from a detailed radiative parametrization
of a general circulation model. The resulting simple column model is then used to study changes in the Earth-atmosphere system’s
radiative equilibrium and, in particular, to infer the role of greenhouse trace gases, water vapor and aerosols in modifying
the vertical temperature profile. Multiple equilibria appear when a positive surface-albedo feedback is introduced, and their
stability is studied. The vertical structure of the radiative fluxes (both short- and longwave) is substantially modified
as the temperature profile changes from one equilibrium to another. These equilibria and their stability are compared to those
that appear in energy-balance models, which heretofore have ignored the details of the vertical temperature and radiation
profiles.
Received: 22 December 1995/Accepted: 17 January 1997 相似文献
997.
998.
J.A. Ramos-Leal J. Moran-Ramírez U. Rodríguez-Robles G. Santacruz-De León P.D. Roy R.M. Fuentes-Rivas R.M.G. Fonseca-Montes de Oca 《Chemie der Erde / Geochemistry》2022,82(2):125872
This work addresses hydrogeochemical processes in shallow aquifers, represented by the Quaternary alluvial deposits, from a part of the semi-arid Mexican Highlands through the evaluations of physicochemical parameters as well as the δ18O and δ2H compositions of groundwater. Mifflin diagram separates the Na-bicarbonate, sulphate and mixed groundwater into one group showing interactions with volcanic lithology in the recharge zones and another group interacting with the evaporite rich sedimentary formation. In the Gibbs diagram, the samples with Cl?/(Cl? + HCO3?) < 0.4 showed higher influence of ion exchange and the samples with Cl?/(Cl? + HCO3?) > 0.4 showed higher effects of evaporation. All of them were oversaturated with carbonate minerals (i.e., calcite and dolomite) and unsaturated with evaporites (i.e., gypsum and halite). Evaporation (earlier stage) occurred before the water-rock interactions (later stage). Evolution occurs through three different routes such as up to 7.5‰ enrichment in δ18O caused by the infiltration with a certain delay and subsequently, the water-rock interaction became dominant. Ternary mixing models revealed dominant influence of local recharge (C1) on the water system, contributing 70.4%. Water-rock interaction (C3) with 18% and evaporation (C2) with 11.6% had comparatively less influences. The presence of nitrate (2–60 mg/L) in the groundwater indicated variable degrees of anthropogenic pollution. 相似文献
999.
Binh Thai Pham Abolfazl Jaafari Tran Van Phong Hoang Phan Hai Yen Tran Thi Tuyen Vu Van Luong Huu Duy Nguyen Hiep Van Le Loke Kok Foong 《地学前缘(英文版)》2021,12(3):101105
Improving the accuracy of flood prediction and mapping is crucial for reducing damage resulting from flood events. In this study, we proposed and validated three ensemble models based on the Best First Decision Tree (BFT) and the Bagging (Bagging-BFT), Decorate (Bagging-BFT), and Random Subspace (RSS-BFT) ensemble learning techniques for an improved prediction of flood susceptibility in a spatially-explicit manner. A total number of 126 historical flood events from the Nghe An Province (Vietnam) were connected to a set of 10 flood influencing factors (slope, elevation, aspect, curvature, river density, distance from rivers, flow direction, geology, soil, and land use) for generating the training and validation datasets. The models were validated via several performance metrics that demonstrated the capability of all three ensemble models in elucidating the underlying pattern of flood occurrences within the research area and predicting the probability of future flood events. Based on the Area Under the receiver operating characteristic Curve (AUC), the ensemble Decorate-BFT model that achieved an AUC value of 0.989 was identified as the superior model over the RSS-BFT (AUC = 0.982) and Bagging-BFT (AUC = 0.967) models. A comparison between the performance of the models and the models previously reported in the literature confirmed that our ensemble models provided a reliable estimate of flood susceptibilities and their resulting susceptibility maps are trustful for flood early warning systems as well as development of mitigation plans. 相似文献
1000.