全文获取类型
收费全文 | 934篇 |
免费 | 31篇 |
国内免费 | 21篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 147篇 |
地球物理 | 239篇 |
地质学 | 285篇 |
海洋学 | 90篇 |
天文学 | 101篇 |
综合类 | 49篇 |
自然地理 | 58篇 |
出版年
2022年 | 8篇 |
2021年 | 6篇 |
2020年 | 17篇 |
2019年 | 9篇 |
2018年 | 25篇 |
2017年 | 18篇 |
2016年 | 26篇 |
2015年 | 12篇 |
2014年 | 48篇 |
2013年 | 46篇 |
2012年 | 36篇 |
2011年 | 252篇 |
2010年 | 36篇 |
2009年 | 28篇 |
2008年 | 27篇 |
2007年 | 26篇 |
2006年 | 27篇 |
2005年 | 18篇 |
2004年 | 20篇 |
2003年 | 20篇 |
2002年 | 28篇 |
2001年 | 18篇 |
2000年 | 10篇 |
1999年 | 13篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1973年 | 4篇 |
1971年 | 5篇 |
1969年 | 7篇 |
1965年 | 4篇 |
1963年 | 5篇 |
1959年 | 4篇 |
1914年 | 4篇 |
1912年 | 4篇 |
排序方式: 共有986条查询结果,搜索用时 62 毫秒
201.
K. Andrée 《International Journal of Earth Sciences》1912,3(5-6):324-360
Ohne Zusammenfassung 相似文献
202.
Michel Michaelovitch de Mahiques Ilson Carlos Almeida da SilveiraSilvia Helena de Mello e Sousa Marcelo Rodrigues 《Marine Geology》2002,181(4):387-400
Sedimentary and isotope data as well as 14C AMS dating on 15 box cores were used to identify the main post-Last Glacial Maximum (LGM) processes in the outer shelf and upper slope of the northernmost part of the São Paulo Bight, southeastern Brazil. Results show slight but significant variations in calcium carbonate, total sulphur and nitrogen contents as well as carbon and oxygen isotope ratios. Sedimentation rates, varying from 5 to 184 mm kyr−1 are controlled by the shelf and upper slope morphology, the Brazil Current meander dynamics, and the Coastal Water offshore motion. 相似文献
203.
Modelling of undertow by a one-equation turbulence model 总被引:1,自引:0,他引:1
204.
Wave and current experiments have been carried out with the purpose of measuring the instantaneous bed shear stress over a hydraulically smooth bed, in order to evaluate the extent of the interaction. Measurements have been carried out with a dual-component hot-film probe which, with some constraints, enables the magnitude and direction of the instantaneous bed shear stress to be measured. Results are presented as maximum obtained bed shear stress values over one cycle and the corresponding mean value in the direction of the current for various combinations of waves and current. 相似文献
205.
The problem of fitting a probability distribution, here log-Pearson Type III distribution, to extreme floods is considered from the point of view of two numerical and three non-numerical criteria. The six techniques of fitting considered include classical techniques (maximum likelihood, moments of logarithms of flows) and new methods such as mixed moments and the generalized method of moments developed by two of the co-authors. The latter method consists of fitting the distribution using moments of different order, in particular the SAM method (Sundry Averages Method) uses the moments of order 0 (geometric mean), 1 (arithmetic mean), –1 (harmonic mean) and leads to a smaller variance of the parameters. The criteria used to select the method of parameter estimation are:
These criteria are transformed into value functions or fuzzy set membership functions and then three Multiple Criteria Decision Modelling (MCDM) techniques, namely, composite programming, ELECTRE, and MCQA, are applied to rank the estimation techniques. 相似文献
| - the two statistical criteria of mean square error and bias; |
| - the two computational criteria of program availability and ease of use; |
| - the user-related criterion of acceptability. |
206.
Erwan Messager Vincent Lebreton Laurent Marquer Elda Russo-Ermolli Ronan Orain Josette Renault-Miskovsky David Lordkipanidze Jackie Despriée Carlo Peretto Marta Arzarello 《Quaternary Science Reviews》2011,30(11-12):1439-1447
The present study focuses on new palaeobotanical data (pollen, phytoliths and fruits) from three of the oldest Early Palaeolithic sites in Eurasia (Dmanisi in Georgia, Ca’ Belvedere di Monte Poggiolo in Italy and Pont-de-Lavaud in France). The main aim is to examine the ecological factors associated with the first human dispersals out of Africa into Eurasia. The palaeoecological data are discussed with regards to chronology and geographical location of the settlements. The vegetation pattern of each site consists of temperate Eurasian and Mediterranean taxa, subtropical trees being more or less recorded depending on climatic and geographic features. The new palaeobotanical data show that different vegetation structures occurred between the first human dispersal in Caucasus and the later dispersals in western Eurasia. However, in all cases hominins seemed to be adapted to temperate ecosystems. In Caucasus, human occupation took place at 1.7 Ma in a forest-steppe environment, while at ca 1 Ma human populations occupied various settings such as open landscapes or dense forests. These data suggest that during the Early Pleistocene, human populations evolved and dispersed in western Eurasia, gradually increasing their degree of adaptation to diversified environments. 相似文献
207.
The Eifelian sedimentary record in the epeiric Baltic Basin contains an extensive brecciated interval known as the Narva Breccia. During recent decades, the origin of this breccia has been attributed to (1) palaeoseismicity, (2) extraterrestrial impact event or (3) diagenetic collapse. Our studies show the presence of two different breccia types that form 11 stratigraphic horizons and contain several laterally and stratigraphically unrelated breccias. The occurrence of Type‐1 and Type‐2 breccias, together with carbonate sabkha and carbonate inter‐ to supratidal tidal flat deposits on the basin margins, indicates synsedimentary brecciation formed in a sabkha environment. Type‐2 breccia could also originate from wave‐cycling loading. 相似文献
208.
Cecelia C.S. Hannides Michael R. Landry Claudia R. Benitez-Nelson Renée M. Styles Joseph P. Montoya David M. Karl 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(1):73-88
Export processes play a major role in regulating global marine primary production by reducing the efficiency of nutrient cycling and turnover in surface waters. Most studies of euphotic zone export focus on passive fluxes, that is, sinking particles. However, active transport, the vertical transfer of material by migrating zooplankton, can also be an important component of carbon (C) and nitrogen (N) removal from the surface ocean. Here we demonstrate that active transport is an especially important mechanism for phosphorus (P) removal from the euphotic zone at Station ALOHA (Hawaii Ocean Time-series program; 22°45′N, 158°W), a P-stressed site in the North Pacific Subtropical Gyre. Migrant excretions in this region are P-rich (C51:N12:P1) relative to sinking particles (C250:N31:P1), and migrant-mediated P fluxes are almost equal in magnitude (82%) to P fluxes from sediment traps. Migrant zooplankton biomass and therefore the importance of this P removal pathway relative to sinking fluxes has increased significantly over the past 12 years, suggesting that active transport may be a major driving force for enhanced P-limitation of biological production in the NPSG. We further assess the C:N:P composition of zooplankton size fractions at Station ALOHA (C88:N18:P1, on average) and discuss migrant-mediated P export in light of the balance between zooplankton and suspended particle stoichiometries. We conclude that, because active transport is such a large component of the total P flux and significantly impacts ecosystem stoichiometry, export processes involving migrant zooplankton must be included in large-scale efforts to understand biogeochemical cycles. 相似文献
209.
Behrouz Ahmadi‐Nedushan André St‐Hilaire Taha B. M. J. Ouarda Laurent Bilodeau Élaine Robichaud Nathalie Thiémonge Bernard Bobée 《水文研究》2007,21(1):21-34
Successful applications of stochastic models for simulating and predicting daily stream temperature have been reported in the literature. These stochastic models have been generally tested on small rivers and have used only air temperature as an exogenous variable. This study investigates the stochastic modelling of daily mean stream water temperatures on the Moisie River, a relatively large unregulated river located in Québec, Canada. The objective of the study is to compare different stochastic approaches previously used on small streams to relate mean daily water temperatures to air temperatures and streamflow indices. Various stochastic approaches are used to model the water temperature residuals, representing short‐term variations, which were obtained by subtracting the seasonal components from water temperature time‐series. The first three models, a multiple regression, a second‐order autoregressive model, and a Box and Jenkins model, used only lagged air temperature residuals as exogenous variables. The root‐mean‐square error (RMSE) for these models varied between 0·53 and 1·70 °C and the second‐order autoregressive model provided the best results. A statistical methodology using best subsets regression is proposed to model the combined effect of discharge and air temperature on stream temperatures. Various streamflow indices were considered as additional independent variables, and models with different number of variables were tested. The results indicated that the best model included relative change in flow as the most important streamflow index. The RMSE for this model was of the order of 0·51 °C, which shows a small improvement over the first three models that did not include streamflow indices. The ridge regression was applied to this model to alleviate the potential statistical inadequacies associated with multicollinearity. The amplitude and sign of the ridge regression coefficients seem to be more in agreement with prior expectations (e.g. positive correlation between water temperature residuals of different lags) and make more physical sense. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
210.
Caroline Kivimäe Richard G.J. Bellerby Agneta Fransson Marit Reigstad Truls Johannessen 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(12):1532-1542
The first carbon budget constructed for the Barents Sea to study the fluxes of carbon into, out of, and within the region is presented. The budget is based on modelled volume flows, measured dissolved inorganic carbon (DIC) concentration, and literature values for dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations. The results of the budget show that ~5600±660×106 t C yr?1 is exchanged through the boundaries of the Barents Sea. If a 40% uncertainty in the volume flows is included in the error calculation it resulted in a total uncertainty of ±1600×106 t C yr?1. The largest part of the total budget flux consists of DIC advection (~95% of the inflow and ~97% of the outflow). The other sources and sinks are, in order of importance, advection of organic carbon (DOC+POC; ~3% of both in- and outflow), total uptake of atmospheric CO2 (~1% of the inflow), river and land sources (~0.2% of the inflow), and burial of organic carbon in the sediments (~0.2% of the outflow). The Barents Sea is a net exporter of carbon to the Arctic Ocean; the net DIC export is ~2500±660×106 t C yr?1 of which ~1700±650×106 t C yr?1 (~70%) is in subsurface water masses and thus sequestered from the atmosphere. The net total organic carbon export to the Arctic Ocean is ~80±20×106 t C yr?1. Shelf pumping in the Barents Sea results in an uptake of ~22±11×106 t C yr?1 from the atmosphere which is exported out of the area in the dense modified Atlantic Waters. The main part of this carbon was channelled through export production (~16±10×106 t C yr?1). 相似文献