全文获取类型
收费全文 | 37155篇 |
免费 | 254篇 |
国内免费 | 216篇 |
专业分类
测绘学 | 721篇 |
大气科学 | 1705篇 |
地球物理 | 7050篇 |
地质学 | 14629篇 |
海洋学 | 3529篇 |
天文学 | 8796篇 |
综合类 | 99篇 |
自然地理 | 1096篇 |
出版年
2022年 | 488篇 |
2021年 | 708篇 |
2020年 | 754篇 |
2019年 | 826篇 |
2018年 | 1696篇 |
2017年 | 1544篇 |
2016年 | 1638篇 |
2015年 | 615篇 |
2014年 | 1414篇 |
2013年 | 2035篇 |
2012年 | 1619篇 |
2011年 | 1898篇 |
2010年 | 1790篇 |
2009年 | 1986篇 |
2008年 | 1765篇 |
2007年 | 1978篇 |
2006年 | 1735篇 |
2005年 | 898篇 |
2004年 | 815篇 |
2003年 | 808篇 |
2002年 | 741篇 |
2001年 | 764篇 |
2000年 | 630篇 |
1999年 | 417篇 |
1998年 | 437篇 |
1997年 | 474篇 |
1996年 | 337篇 |
1995年 | 358篇 |
1994年 | 335篇 |
1993年 | 281篇 |
1992年 | 284篇 |
1991年 | 290篇 |
1990年 | 337篇 |
1989年 | 272篇 |
1988年 | 258篇 |
1987年 | 260篇 |
1986年 | 192篇 |
1985年 | 301篇 |
1984年 | 302篇 |
1983年 | 295篇 |
1982年 | 274篇 |
1981年 | 248篇 |
1980年 | 265篇 |
1979年 | 203篇 |
1978年 | 242篇 |
1977年 | 204篇 |
1976年 | 177篇 |
1975年 | 184篇 |
1974年 | 171篇 |
1973年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Integrating lysimeter drainage and eddy covariance flux measurements in a groundwater recharge model
Vicente Vásquez Anton Thomsen Bo V. Iversen Rasmus Jensen Rasmus Ringgaard 《水文科学杂志》2013,58(9):1520-1537
AbstractField-scale water balance is difficult to characterize because controls exerted by soils and vegetation are mostly inferred from local-scale measurements with relatively small support volumes. Eddy covariance flux and lysimeters have been used to infer and evaluate field-scale water balances because they have larger footprint areas than local soil moisture measurements. This study quantifies heterogeneity of soil deep drainage (D) in four 12.5-m2 repacked lysimeters, compares evapotranspiration from eddy covariance (ETEC) and mass balance residuals of lysimeters (ETwbLys), and models D to estimate groundwater recharge. Variation in measured D was attributed to redirection of snowmelt infiltration and differences in lysimeter hydraulic properties caused by surface soil treatment. During the growing seasons of 2010, 2011 and 2012, ETwbLys (278, 289 and 269 mm, respectively) was in good agreement with ETEC (298, 301 and 335 mm). Annual recharge estimated from modelled D was 486, 624 and 613 mm for three calendar years 2010, 2011 and 2012, respectively. In summary, lysimeter D and ETEC can be integrated to estimate and model groundwater recharge.
Editor D. Koutsoyiannis 相似文献
962.
Ramesh S. V. Teegavarapu 《水文科学杂志》2013,58(11):2009-2026
AbstractNew optimal proximity-based imputation, K-nearest neighbour (K-NN) classification and K-means clustering methods are proposed and developed for estimation of missing daily precipitation records. Mathematical programming formulations are developed to optimize the weighting, classification and clustering schemes used in these methods. Ten different binary and real-valued distance metrics are used as proximity measures. Two climatic regions, Kentucky and Florida, (temperate and tropical) in the USA, with different gauge density and network structure, are used as case studies to evaluate the new methods. A comprehensive exercise is undertaken to compare the performances of the new methods with those of several deterministic and stochastic spatial interpolation methods. The results from these comparisons indicate that the proposed methods performed better than existing methods. Use of optimal proximity metrics as weights, spatial clustering of observation sites and classification of precipitation data resulted in improvement of missing data estimates.
Editor D. Koutsoyiannis; Associate editor C. Onof 相似文献
963.
Electrical imaging provides important subsurface information for the construction of hypervelocity impact models. We here provide an overview and evaluation of the current electrical imaging methods used in impact cratering studies. Although apparent resistivity models are commonly used in the geoelectrical imaging of impact structures, the reliability of these models has not hitherto been determined. In order to assess these imaging approaches in impact cratering, we investigate for the first time the discrepancies between the apparent resistivity and true resistivity models of an impact structure. To this end, we present (1) a new true resistivity model of the Araguainha impact structure in central Brazil by applying L2-norm inversion to previously published data, (2) apparent resistivity model of the impact structure, and (3) models obtained from different stages of the iterative tomographic inversions. Our results show that changes in vertical resistivity gradient are significantly better defined in the true resistivity models than in the apparent resistivity model. On the basis of these results, we outline a new approach that true resistivity models can be effectively assessed by applying both L1- and L2-norm inversion schemes together with the monitoring of intermediate models from iterative inversion. The results of our study highlight the importance of tomographic inversion of resistivity data in impact cratering studies, and they provide a data modeling framework and foundation for cost-effective subsurface imaging of impact structures in the future. 相似文献
964.
V. V. Alpatov V. I. Badin I. A. Grebnev M. G. Deminov D. S. Faermak 《Geomagnetism and Aeronomy》2012,52(6):793-796
The results of a theoretical analysis of the radial distribution of electron temperature T e in the area of heating of the lower ionosphere by intense shortwave radiation are presented. It was established that effective radius r eff of heating at a certain height may differ significantly from the characteristic radius of illumination of the ionosphere (a) by radiation at this height. At the boundary of the heating area (r = r eff ), the characteristic radial scale of T e changes is less than the corresponding scale of changes in the squared amplitude of the radiation electric field, and it is almost independent of the amplitude value; i.e., the formation of a relatively strong T e gradient at such a boundary is a common feature of heating of the lower ionosphere by intense shortwave radiation. 相似文献
965.
Water Resources - The short-term, seasonal, and interannual variations in the abundance and species composition of the Black Sea metazoan microzooplankton have been analyzed at the open coastal... 相似文献
966.
Water Resources - The average concentrations of elements Fe, Mn, Zn, Pb, Cu, Cr, V, Co, Cd, Ni, As, and Mo in the subcolloidal fraction of bottom sediments were determined in the northern and... 相似文献
967.
Water Resources - Chlorophyll a concentration, the total abundance of bacteria, the number of bacterial cells with active metabolism, and the abundance of saprotrophic bacteria were studied in the... 相似文献
968.
Geomagnetism and Aeronomy - A global dynamic model of the F2 layer of the ionosphere GDMF2 is designed to calculate foF2 in both quiet and geomagnetically disturbed conditions. The term... 相似文献
969.
Geomagnetism and Aeronomy - The magnetic fields of a subterranean source observed on the Earth’s surface or from the orbit of a satellite are studied. We analyze the space of all harmonic... 相似文献
970.
Vasil’ev G. I. Konstantinov A. N. Kudryavtsev I. V. Ogurtsov M. G. Ostryakov V. M. Pavlov A. K. Frolov D. A. 《Geomagnetism and Aeronomy》2019,59(8):1075-1080
Geomagnetism and Aeronomy - The causes of a sharp increase in the radiocarbon content in the Earth’s atmosphere for periods with abnormally low solar modulation of galactic cosmic rays (GCRs)... 相似文献