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排序方式: 共有92条查询结果,搜索用时 476 毫秒
41.
Ami Nishri Alon Rimmer Udi Wagner Zvi Rosentraub Peter Yeates 《Aquatic Geochemistry》2011,17(3):195-207
High resolution chemical data collected during summer 2003 indicate that the lower water mass (LWM) of the thermally stratified
Lake Kinneret (LK) can be subdivided into three layers: a benthic boundary layer (BBL), overlain by the hypolimnion (HYP),
and on top, the lower part of the metalimnion (ME-L). After onset of thermal stratification, the BBL is the first layer that
turns anoxic, followed shortly afterward by the ME-L, while the HYP remains oxic and has relatively higher pH until later
in summer. Thus, during the early summer, the HYP forms an oxygen-containing layer in-between two DO-deficient layers. Somewhat
later, the HYP is characterized by still having significant levels of nitrate NO3, while in both adjacent layers nitrate is already removed through denitrification. The mechanisms controlling the gradual
decline of dissolved oxygen (DO) in the HYP during the summer were studied. The seasonal mean lake-wide vertical eddy diffusion
coefficient in this layer, evaluated from heat flux measurements, is approximately 4 × 10−6 m2 s−1. The vertical oxygen flux due to diffusion from within the HYP toward its oxygen-deficient upper and lower boundaries accounts
for most of the slow summer decline in DO in this layer. A smaller portion of this decline can be attributed to in-layer respiratory
processes. The low turbidity, relatively high pH, and slow accumulation rate of NH4 in the HYP support the notion that the slower mineralization processes occurring in this layer result from relatively low
ambient concentrations of biodegradable organic matter, most probably due to the short residence time of the particles settling
through this layer. 相似文献
42.
Y. Ueda K. Yamaoka J.E. Grove M. McCollough P. Durouchoux J. Rodriguez F. Mirabel J. Swank M. Feroci P. Casella A.J. Castro-Tirado C. Sánchez-Fernández S. Chaty H. Castaneda K. Kohno V. Dhawan S.A. Trushkin K. Ebisawa T. Kotani H. Inoue 《Astrophysics and Space Science》2001,276(1):25-28
We report results from multiwavelength observations of the microquasarGRS 1915+105 performed during the 2000 April campaign. This is one ofthe biggest campaigns ever made for this source covering the broadband from radio to γ-rays. Multiwavelength light curves compiledfrom all the data reduced up to date and broad band spectra obtainedwith ASCA and RXTE are presented. 相似文献
43.
Tomofumi Kozono Hideki Ueda Taku Ozawa Takehiro Koyaguchi Eisuke Fujita Akihiko Tomiya Yujiro J Suzuki 《Bulletin of Volcanology》2013,75(3):1-13
We present precise geodetic and satellite observation-based estimations of the erupted volume and discharge rate of magma during the 2011 eruptions of Kirishima-Shinmoe-dake volcano, Japan. During these events, the type and intensity of eruption drastically changed within a week, with three major sub-Plinian eruptions on January 26 and 27, and a continuous lava extrusion from January 29 to 31. In response to each eruptive event, borehole-type tiltmeters detected deflation of a magma chamber caused by migration of magma to the surface. These measurements enabled us to estimate the geodetic volume change in the magma chamber caused by each eruptive event. Erupted volumes and discharge rates were constrained during lava extrusion using synthetic aperture radar satellite imaging of lava accumulation inside the summit crater. Combining the geodetic volume change and the volume of lava extrusion enabled the determination of the erupted volume and discharge rate during each sub-Plinian event. These precise estimates provide important information about magma storage conditions in magma chambers and eruption column dynamics, and indicate that the Shinmoe-dake eruptions occurred in a critical state between explosive and effusive eruption. 相似文献
44.
Scott C. Brooks Carrie L. Miller Ami L. Riscassi Kenneth A. Lowe Johnbull O. Dickson Grace E. Schwartz 《水文研究》2021,35(8):e14344
East Fork Poplar Creek (EFPC) is a mercury (Hg) contaminated creek in east Tennessee, USA. Stream restoration activities included the initiation of a flow management programme in 1996 in which water from a nearby lake was pumped to the head of the creek. We conducted regular water sampling for 2 years along the length of EFPC during active flow management and for 5 years after flow management stopped. Total Hg and total monomethylmercury (MMHg) concentration and flux decreased in the uppermost reaches of EFPC that were closest to the point of water addition. Most water quality parameters, including DOC concentration, remained unchanged after flow management termination. Nevertheless, SUVA254, a measure of dissolved organic matter (DOM) composition, increased and coincided with increased dissolved Hg (HgD) concentration and flux and decreased Hg solid-water partitioning coefficients throughout EFPC. Higher SUVA254 and HgD concentration have potential implications for bioavailability and MMHg production. Total and dissolved MMHg concentrations increased in lower reaches of EFPC after the end of flow management and these increases were most pronounced during spring and early summer when biota are more susceptible to exposure and uptake. A general warming trend in the creek after active flow management ended likely acted in concert with higher HgD concentration to promote higher MMHg concentration. Total and dissolved MMHg concentrations were positively correlated with water temperature above a threshold value of 10°C. Concentration changes for Hg and MMHg could not be accounted for by changes in creek discharge that accompanied the cessation of flow management. In addition to the changing DOM composition in-stream, other watershed-scale factors likely contributed to the observed patterns, as these changes occurred over months rather than instantaneously after flow management stopped. Nevertheless, similar changes in MMHg have not been observed in a tributary to EFPC. 相似文献
45.
Consideration of fabric anisotropy is crucial to gaining an improved understanding of the behavior of granular materials. This paper presents a constitutive model to describe the sand behavior associated with fabric anisotropy within a framework of a strain space multiple mechanism model. In the proposed model, a second-order fabric tensor is extended by incorporating a new function that represents the effect of inherent (or initial fabric) anisotropy, along with three additional parameters: two of them, a1 and a2 , control the degree of anisotropy, and the second mode of inherent anisotropy can be expressed by introducing the parameter a2 as well as the first mode by the parameter a1 . The third parameter, θ0 , expresses the principal direction of inherent anisotropy (eg, the normal vector direction of bedding planes relative to horizontal axis). The formulation of the dilative component of dilatancy (ie, positive dilatancy) is also extended to consider the effect of inherent anisotropy based on the interlocking mechanism. Experimental data on the complex anisotropic responses of Fraser River sand and Toyoura sand under monotonic loading is used to validate this model. The proposed model is shown to successfully capture anisotropic responses, which become contractive or dilative depending on different principal-stress directions, with a single set of anisotropy parameters; thus, the model is considered to possess the capability to simulate the anisotropic behaviors of granular materials. In addition to different loadings on the same fabric, the effects of different fabric anisotropies upon the sand behavior under the same loadings are also investigated. 相似文献
46.
Kenichiro Hamada Naoko Ueda Machiko Yamada Kuninao Tada Shigeru Montani 《Journal of Oceanography》2012,68(1):173-182
Biologically important nutrient concentrations in Dokai Bay have declined as a result of reductions in anthropogenic inputs
of total nitrogen and total phosphorus. A decrease in nutrient concentrations affects phytoplankton growth, thereby changing
the biochemical characteristics of autochthonous particulate matter. We therefore investigated changes in the C/N/P molar
ratio of suspended particulate matter (SPM) in the summer, when phytoplankton growth is vigorous, before environmental quality
standards (EQSs) were attained (1995–1998) and afterward (2006–2009). We found that the ratio of particulate organic nitrogen
(PON) to particulate phosphorus (PP) changed in conjunction with changes in the ratio of dissolved inorganic nitrogen to dissolved
inorganic phosphorus (DIP) that resulted from reductions in nutrient loading. Furthermore, we suggest that because the DIP
concentration in seawater was high before EQSs were attained, inorganic phosphorus was possibly adsorbed onto SPM. After the
attainment of EQSs, however, the DIP concentration fell, and PON/PP was high. Phosphorus limitation of phytoplankton growth
in the mouth of the bay may explain the high PON/PP ratios after EQS attainment. 相似文献
47.
Koichiro Doi Hideaki Hayakawa Takahito Kazama Toshihiro Higashi Shingo Osono Yoichi Fukuda Jun Nishijima Yuichi Aoyama Junichi Ueda 《极地研究(英文版)》2013,(4):339-343
Abstract This paper reports the results of field-based absolute gravity measurements aimed at detecting gravity change and crustal displacement caused by glacial isostatic adjustment. The project was initiated within the framework of the 53rd Japanese Antarctic Research Expedition (JARE53). Absolute gravity measurements, together with GPS measurements, were planned at several outcrops along the Prince Olav Coast and S6ya Coast of East Antarctica, including at Syowa Station. Since the icebreaker Shirase (AGB 5003) was unable to moor alongside Syowa Station, operations were somewhat restricted during JARE53. However, despite this setback, we were able to complete measurements at two sites: Syowa Station and Langhovde. The absolute gravity value at the Syowa Station IAGBN (A) site, observed using an FG-5 absolute gravimeter (serial number 210; FG-5 #210), was 982 524 322.7+0.1 ktGal, and the gravity change rate at the beginning of 2012 was -0.26 gGal.a-1. An absolute gravity value of 982 535 584.2~0.7 ktGal was obtained using a portable A-10 absolute gravimeter (serial number 017; A-10 #017) at the newly located site AGS01 in Langhovde. 相似文献
48.
2009年11月10-12日河南北部暴雪天气诊断分析 总被引:4,自引:2,他引:2
利用常规观测资料和FY2C卫星产品,对2009年11月10-12日河南北部地区暴雪天气过程进行诊断分析,结果表明:500 hPa图上在中高纬地区形成稳定的"两槽一脊"环流形势,出现"南槽北脊"结构,低空急流显著发展,850 hPa盛行偏东气流,地面图上河套倒槽与回流形势同时发展,触发了这次暴雪天气;深厚的湿层和持续的水汽辐合为暴雪产生提供了充沛的水汽条件;低层辐合、高层辐散是触发不稳定能量释放的重要启动机制,中低空正涡度平流中心和温度冷平流中心先于暴雪出现,对暴雪天气预报有指示作用;低层冷空气较强,高层暖湿空气较强,这种"冷垫"与"暖盖"稳定形势是这次连续性区域暴雪产生的重要热力条件。 相似文献
49.
50.
Microphenocrystic pyrrhotites were observed in the glassy groundmass of two dacite rocks from Satsuma-Iwojima, southwest Kyushu, Japan. It suggests that the dacite magma was saturated with respect to pyrrhotite at the time of eruption, and thus the sulfur contents in the groundmass can be taken as the solubility of sulfur in the dacite magma. The solubility of sulfur in the dacite rocks thus calculated is 65 to 72 ppm sulfur at the estimated conditions of T=900±50°C,
and
atm. 相似文献