全文获取类型
收费全文 | 1319篇 |
免费 | 70篇 |
国内免费 | 14篇 |
专业分类
测绘学 | 54篇 |
大气科学 | 108篇 |
地球物理 | 343篇 |
地质学 | 484篇 |
海洋学 | 123篇 |
天文学 | 211篇 |
综合类 | 7篇 |
自然地理 | 73篇 |
出版年
2023年 | 5篇 |
2022年 | 8篇 |
2021年 | 24篇 |
2020年 | 23篇 |
2019年 | 21篇 |
2018年 | 47篇 |
2017年 | 50篇 |
2016年 | 58篇 |
2015年 | 49篇 |
2014年 | 60篇 |
2013年 | 80篇 |
2012年 | 70篇 |
2011年 | 79篇 |
2010年 | 62篇 |
2009年 | 82篇 |
2008年 | 79篇 |
2007年 | 68篇 |
2006年 | 66篇 |
2005年 | 55篇 |
2004年 | 31篇 |
2003年 | 45篇 |
2002年 | 44篇 |
2001年 | 36篇 |
2000年 | 25篇 |
1999年 | 19篇 |
1998年 | 16篇 |
1997年 | 15篇 |
1996年 | 12篇 |
1995年 | 17篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1991年 | 11篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 2篇 |
排序方式: 共有1403条查询结果,搜索用时 234 毫秒
941.
S. Ferrant C. Laplanche G. Durbe A. Probst P. Dugast P. Durand J. M. Sanchez‐Perez J. L. Probst 《水文研究》2013,27(12):1751-1763
A nitrate sensor has been set up to measure every 10 min the nitrate signal in a stream draining a small agricultural catchment dominated by fertilized crops during a 2‐year study period (2006–2008) in the south‐west of France. An in situ sampling protocol using automatic sampler to monitor flood events have been used to assume a point‐to‐point calibration of the sensor values. The nitrate concentration exhibits nonsystematic concentration and dilution effects during flood events. We demonstrate that the calibrated nitrate sensor signal gathered from the outlet is considered to be a continuous signal using the Nyquist–Shannon sampling theorem. The objectives of this study are to quantify the errors generated by a typical infrequent sampling protocol and to design appropriate sampling strategy according to the sampling objectives. Nitrate concentration signal and flow data are numerically sampled to simulate common sampling frequencies. The total fluxes calculated from the simulated samples are compared with the reference value computed on the continuous signal. Uncertainties are increasing as sampling intervals increase; the method that is not using continuous discharge to compute nitrate fluxes bring larger uncertainty. The dispersion and bias computed for each sampling interval are used to evaluate the uncertainty during each hydrological period. High underestimation is made during flood periods when high‐concentration period is overlooked. On the contrary, high sampling frequencies (from 3 h to 1 day) lead to a systematic overestimation (bias around 3%): highest concentrations are overweighted by the interpolation of the concentration in such case. The in situ sampling protocol generates less than 1% of load estimation error and sample highest concentration peaks. We consider useful such newly emerging field technologies to assess short‐term variations of water quality parameters, to minimize the number of samples to be analysed and to assess the quality state of the stream at any time. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
942.
Maider Armendáriz Idoia Rosales Beatriz Bádenas Laura Piñuela Marc Aurell José Carlos García‐Ramos 《地学学报》2013,25(6):439-445
Palaeotemperature estimates from the oxygen‐isotope compositions of belemnites have been hampered by not knowing ancient seawater isotope compositions well enough. We have tackled this problem using Mg/Ca as a proxy for temperature and here, we present a ~2 Ma record of paired Mg/Ca and δ18O measurements of Jurassic (Early Pliensbachian) belemnites from the Asturian basin as a palaeo‐proxy of seawater oxygen‐isotope composition. From the combined use of the two approaches, we suggest a δ18Ow composition of about ?0.1‰ for the Jamesoni–Ibex zones. This value may have been increased by about 0.6‰ during the Davoei Zone due to the effect of waters with a different δ18Ow composition. These findings illustrate the inaccuracy of using a globally homogeneous ice‐free value of δ18Ow = ?1‰ for δ18Ocarb‐based palaeotemperature reconstructions. Our data suggest that previous palaeotemperatures calculated in the region from δ18O values of belemnites may have been underestimated as the seawater oxygen isotopic composition could have been higher. 相似文献
943.
Marc Chaussidon 《Meteoritics & planetary science》2012,47(7):1236-1237
944.
Jason M. Dortch Lewis A. Owen Marc W. Caffee Dewen Li Thomas V. Lowell 《第四纪科学杂志》2010,25(8):1259-1269
Glacial landforms and outwash terraces in the Nenana River valley, Reindeer Hills and Monahan Flat in the central Alaska Range were dated with 60 10Be exposure ages to determine the timing of Late Pleistocene glaciation. In the Nenana River valley, glaciation occurred at 104–180 ka (Lignite Creek glaciation), ca. 55 ka (Healy glaciation), and ca. 16 ka (Carlo Creek phase); glaciers retreated in the Reindeer Hills and Monahan Flat by ca. 14 ka and ca. 13 ka, respectively. The Carlo Creek moraine is similar in age to at least six other moraines in the Alaska Range, Ahklun Mountains and Brooks Range. The new data suggest that post‐depositional geological processes limit the usefulness of 10Be methods to the latter part (≤60 ka) of the late Quaternary in central Alaska. Ages on Healy and younger landforms cluster well, with the exception of Riley Creek moraines and Monahan Flat‐west sites, where boulders were likely affected by post‐depositional processes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
945.
Ross [Ross PJ. Modeling soil water and solute transport – fast, simplified numerical solutions. Agron J 2003;95:1352–61] developed a fast, simplified method for solving Richards’ equation. This non-iterative 1D approach, using Brooks and Corey [Brooks RH, Corey AT. Hydraulic properties of porous media. Hydrol. papers, Colorado St. Univ., Fort Collins; 1964] hydraulic functions, allows a significant reduction in computing time while maintaining the accuracy of the results. The first aim of this work is to confirm these results in a more extensive set of problems, including those that would lead to serious numerical difficulties for the standard numerical method. The second aim is to validate a generalisation of the Ross method to other mathematical representations of hydraulic functions. 相似文献
946.
947.
The stiffness characteristics of a packing of granules are influenced by the particle interactions at contacts, the void ratio, the co-ordination number and the packing structure. A stress-strain relationship for the packings of spheres is presented. The relationship explicitly includes the contact force-displacement law and the parameters characterizing the packing structure. The initial moduli computed using this relationship are compared with experimental measurements and empirical equations for sands. The theoretical results are also compared with experimental results on packings of glass balls. Closed-form solutions are derived for statistically isotropic packings under initial isotropic stress conditions. Numerical solutions for the stiffness properties are obtained for anisotropic initial stress conditions and anisotropic packing structures. 相似文献
948.
949.
Theoretical and Applied Climatology - This study investigates the spatial and temporal patterns of trends and magnitude of rainfall on monthly, seasonal and annual time scales of 13 districts of... 相似文献
950.
Andrea Koschinsky Marc Van Gerven Peter Halbach 《Marine Georesources & Geotechnology》2013,31(4):375-391
Ferromanganese crusts comparable with central Pacific occurrences with respect to thickness and extension have been discovered at the Tropic Seamount in the subtropical NE Atlantic. A comparison with typical hydrogenetic crusts from a central Pacific seamount revealed lower concentration of the Mn phase with Mn, Co, Ni, Zn, and Cu but a strongly increased terrigenous input of Fe, Pb, Al, and Si in the Atlantic crusts. Growth rates are increased compared with the Pacific crusts, and crust ages average at 10 My. The old phosphatized crust generation that started to grow about 20 My ago on the Pacific seamounts is not pronounced at the Tropic Seamount. The typical hydrographic and morphological parameters for hyrogenetic crust growth have also been found at the Tropic Seamount, which implies that the Tropic Seamount crusts have developed according to the hydrogenetic growth model. There are no indications of hydrothermal influence. 相似文献