全文获取类型
收费全文 | 509篇 |
免费 | 20篇 |
国内免费 | 19篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 53篇 |
地球物理 | 160篇 |
地质学 | 151篇 |
海洋学 | 130篇 |
天文学 | 11篇 |
综合类 | 8篇 |
自然地理 | 20篇 |
出版年
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2018年 | 22篇 |
2017年 | 21篇 |
2016年 | 33篇 |
2015年 | 28篇 |
2014年 | 29篇 |
2013年 | 39篇 |
2012年 | 31篇 |
2011年 | 43篇 |
2010年 | 35篇 |
2009年 | 31篇 |
2008年 | 30篇 |
2007年 | 29篇 |
2006年 | 19篇 |
2005年 | 29篇 |
2004年 | 15篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1998年 | 5篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1992年 | 5篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1970年 | 1篇 |
1958年 | 1篇 |
1955年 | 1篇 |
1951年 | 4篇 |
1950年 | 1篇 |
1949年 | 2篇 |
1948年 | 3篇 |
排序方式: 共有548条查询结果,搜索用时 15 毫秒
31.
Precise, automatic and fast method for vanishing point detection 总被引:1,自引:0,他引:1
A new automated approach for vanishing point detection in images of urban scenes is described. This method is based on the theorem of Thales. The main contribution of this paper is the automatic and simultaneous detection of all vanishing points of the image, achieved by converting this problem into the detection of circles in a complex cloud of points, in which each point corresponds to a segment and is associated with an uncertainty. This extraction of circles uses a RANSAC method, modified to improve its speed by using accumulation techniques (Hough transform or otherwise). This robust estimation is then refined by least squares error propagation using the individual variances of each segment. The algorithm is robust, its accuracy is optimised and it is entirely automatic. Its successful operation has been tested on a large number of images of varied urban scenes. 相似文献
32.
Kyoung-nam Jo Kyung Sik Woo Hyoun Soo Lim Hai Cheng R. Lawrence Edwards Yongjin Wang Xiuyang Jiang Ryeon Kim Jae Il Lee Ho Il Yoon Kyu-Cheul Yoo 《Quaternary Science Reviews》2011,30(9-10):1218-1231
Textural and stable isotopic records from the absolute-dated stalagmite of the Daeya Cave (DY-1) provide new insights into the climatic evolution of the Korean Peninsula during the Holocene and Eemian climatic optima. The stalagmite yielded ages of 8572 ± 227 to 5907 ± 158 and 1,23,456 ± 535 to 1,19,837 ± 1089 years, which coincide with the Holocene and Eemian climatic optima, respectively. The stalagmite’s δ13C record closely resembles previously reported Chinese speleothem δ18O data. Thus it can be suggested that textural and geochemical results of the DY-1 reflect East Asian monsoon intensity, which is forced by summer insolation patterns in the northern hemisphere. Lighter carbon isotopic compositions, well-developed fibrous calcite crystals, and their relatively faster growth rate in the stalagmite sample are interpreted to reflect the warmest and wettest climate conditions of the Holocene and Eemian interglacials. Both climatic optima took place when insolation was decreasing from its maximum level, temperature in Greenland was highest, and sea level approached its maximum level. These climatic optima also coincide with decreasing Antarctic temperatures. Compared the DY-1 data to other proxies, it is suggested that the Holocene and Eemian climatic optima developed through a balance among boreal insolation, monsoon intensity, and sea level (also continental ice volume), which are the main climatic forcing factors in the northern hemisphere. These trends also follow the bi-polar seesaw mechanism as previously described. 相似文献
33.
This study delineated spatially and temporally variable runoff generation areas in the Sand Mountain region pasture of North Alabama under natural rainfall conditions, and demonstrated that hydrologic connectivity is important for generating hillslope response when infiltration‐excess (IE) runoff mechanism dominates. Data from six rainfall events (13·7–32·3 mm) on an intensively instrumented pasture hillslope (0·12 ha) were analysed. Analysis of data from surface runoff sensors, tipping bucket rain gauge and HS‐flume demonstrated spatial and temporal variability in runoff generation areas. Results showed that the maximum runoff generation area, which contributed to runoff at the outlet of the hillslope, varied between 67 and 100%. Furthermore, because IE was the main runoff generation mechanism on the hillslope, the data showed that as the rainfall intensity changed during a rainfall event, the runoff generation areas expanded or contracted. During rainfall events with high‐intensity short‐ to medium‐duration, 4–8% of total rainfall was converted to runoff at the outlet. Rainfall events with medium‐ to low‐intensity, medium‐duration were found less likely to generate runoff at the outlet. In situ soil hydraulic conductivity (k) was measured across the hillslope, which confirmed its effect on hydrologic connectivity of runoff generation areas. Combined surface runoff sensor and k‐interpolated data clearly showed that during a rainfall event, lower k areas generate runoff first, and then, depending on rainfall intensity, runoff at the outlet is generated by hydrologically connected areas. It was concluded that in IE‐runoff‐dominated areas, rainfall intensity and k can explain hydrologic response. The study demonstrated that only connected areas of low k values generate surface runoff during high‐intensity rainfall events. Identification of these areas would serve as an important foundation for controlling nonpoint source pollutant transport, especially phosphorus. The best management practices can be developed and implemented to reduce transport of phosphorus from these hydrologically connected areas. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
34.
35.
Summary New oxygen isotope data for metaluminous granites from the basement-dominated part of the Damara orogen (Namibia) range from
9.1 to 11.9‰. These data, together with previously published Sr, Nd and Pb isotope data indicate that these granites and associated
peraluminous granites originated from felsic meta-igneous basement sources. New and unusually low oxygen isotope data for
metaluminous granodiorites extend now the range of δ18O values from ca. 12 to 6‰ for this rock type. These low oxygen isotope values approach the values observed in mafic quartz
diorites for which a model of derivation from depleted mafic lower crust has been established. In view of the higher Pb isotope
ratios but lower oxygen isotope values of the granodiorites relative to the mafic quartz diorites, it is concluded that the
granodiorites represent partial melts of an undepleted but strongly altered mafic lower crust. Most of the peraluminous and
metaluminous granites and the metaluminous granodiorites have identical U–Pb monazite, allanite and zircon ages of ca. 510–500 Ma
implying partial melting of distinct basement rocks of Archaean to Proterozoic age at the peak of regional high-grade metamorphism. 相似文献
36.
Jong-Chan Park Woohan Kim Tae Woong Chung Chang-Eob Baag Jin-Han Ree 《Geophysical Journal International》2007,169(3):1103-1114
We evaluate the stress field in and around the southern Korean Peninsula with focal mechanism solutions, using the data collected from 71 earthquakes ( ML = 1.9–5.2) between 1999 and 2004. For this, the hypocentres were relocated and well-constrained fault plane solutions were obtained from the data set of 1270 clear P -wave polarities and 46 SH / P amplitude ratios. The focal mechanism solutions indicate that the prevailing faulting types in South Korea are strike-slip-dominant-oblique-slip faultings with minor reverse-slip component. The maximum principal stresses (σ1 ) estimated from fault-slip inversion analysis of the focal mechanism solutions show a similar orientation with E–W trend (269°–275°) and low-angle plunge (10°–25°) for all tectonic provinces in South Korea, consistent with the E–W trending maximum horizontal stress (σHmax ) of the Amurian microplate reported from in situ stress measurements and earthquake focal mechanisms. The directions of the intermediate (σ2 ) and minimum (σ3 ) principal stresses of the Gyeongsang Basin are, however, about 90 deg off from those of the other tectonic provinces on a common σ2 –σ3 plane, suggesting a permutation of σ2 and σ3 . Our results incorporated with those from the kinematic studies of the Quaternary faults imply that NNW- to NE-striking faults (dextral strike-slip or oblique-slip with a reverse-slip component) are highly likely to generate earthquakes in South Korea. 相似文献
37.
The time variation of the wind-induced flow in a homogeneous unbounded sea region has been analytically investigated. The time-dependent Ekman solution in a homogeneous, shallow open sea has been further extended by taking into account the time variation in water depth which might be caused by either tidal motion or change in the mixed layer thickness. The solution approach taken in this study is based on the Galerkin-eigenfunction method originally developed by Heaps [1972. On the numerical solution of three-dimensional hydrodynamical equations for tides and storm surges. Memoires de la Societe Royale des Sciences de Liege Serie 6(2), 143–180]. A series of calculations have been made with emphasis on the influence of the time variation in water depth upon the build-up of Ekman spirals in the presence of oscillatory variations in water depth. It has been found that two oscillations contribute to the wind drift current, the inertial oscillation and the depth-variation-induced oscillation; the inertial oscillation decays with time, but the depth-variation-induced oscillation remains undamped despite the presence of bottom friction. The presence of time-harmonic variation produces peculiar forms of hodograph with a curled or circular pattern according to the angular frequency of the water depth variation. 相似文献
38.
Yu?LiuEmail author Park?Won-Kyu Qiufang?Cai Seo?Jung-Wook Jung?Hyun-Sook 《中国科学D辑(英文版)》2003,46(10):1031-1039
Three tree-ring rainfall reconstructions from China and Korea are used in this paper to investigate the East Asian summer
monsoon-related precipitation variation over the past 160 years. Statistically, there is no linear correlation on a year-by-year
basis between Chinese and Korean monsoon rainfall, but region-wide synchronous variation on a decadal-scale was observed.
More rainfall intervals were 1860–1890, 1910–1925, and 1940–1960, and dry or even drought periods were 1890–1910, 1925–1940,
and 1960–present. Reconstructions also display that the East Asian summer monsoon precipitation suddenly changed from more
into less around mid-1920. These tree-ring precipitation records were also confirmed by Chinese historical dryness/wetness
index and Korean historical rain gauge data. 相似文献
39.
Dolomitic concretions in diatomaceous hemipelagic sediments of the Miocene Pohang Basin in the southwestern East Sea (Sea of Japan) preserve distinct signals of two independent sedimentary processes, which controlled the extents of isotopic compositions. Variable δ18O (−9.1‰ to +0.7‰) and high δ13C (+3.1‰ to +17.9‰) values suggest that the concretions formed in the methanogenic zone with alteration of the residual mid-Miocene seawater by volcanogenic sediments. Remarkable δ18O and δ13C values show a strong linear relationship, indicating that distinctly independent depositional processes operated during the formation of the concretions. The degree of methanogenesis was enhanced during rapid hemipelagic sedimentation of organic-rich particles, resulting in higher δ13C values, and the effect of volcaniclastics was diluted, maintaining the original properties of ambient mid-Miocene seawater. In contrast, lower δ18O and 87Sr/86Sr values characterize the effect of volcaniclastic sediments that were transported by intermittent gravity flows and interacted with mid-Miocene seawater. The input of volcaniclastic sediment probably degraded the role of methanogenesis by lowering the contents of organic matter and thereby decreased the δ13C values within the concretions. Isotopic signals recorded within the concretions highlight understanding of the depositional environment and evolution of the pore-water chemistry. 相似文献
40.
Summary The lower ultramafic part of the Chalkidiki Ophiolite Complex consists of a successive alternation of chromitite, dunite, and harzburgite, which is repeated periodically in a cyclic manner. This cyclic pattern is consistent with an origin as magmatic cumulates. However, the tectonic fabric superimposed on the cumulate texture of this sequence suggest a solid-state deformation at considerable depth.In the present study, the textural and chemical features of chromite are discussed. The interrelationships between the compositions of chromite, its mode of occurrence as well as the associated silicates are emphasized. It is found that the investigated chromites have properties in common with both podiforn and stratiform chromites. From a geometrical and structural point of view, they are of podiform type. On the other hand, their appreciably high iron content, the strong interdependence between the composition of chromite and the coexisting silicates together with the cryptic layering exhibited by the two mineral groups contrast markedly with podiform chromites.An alternative hypothesis is proposed involving fractional crystallization of an ultrabasic melt introduced to the magma chamber as periodic inflows of essentially the same composition. An upwelling upper-mantle that is subjected to stepwise partial fusion may fulfill these conditions.
With 11 Figures 相似文献
Chemismus und Texturen von Chromiten in ultramafischen Gesteinen des Chalkidiki Komplexes, Nordost-Griechenland
Zusammenfassung Der untere, ultramafische Teil des Chalkidiki Komplexes besteht aus einer wechselnden Abfolge von Chromititen, Duniten und Harzburgiten, die sich zyklisch wiederholt. Diese zyklische Abfolge ist in guter Übereinstimmung mit einer Entstehung als magmatische Kumulate. Das tektonische Gefüge, das auf die Kumulat-Texturen überprägt wurde, weist jedoch auf Deformationen in festem Zustand in beträchtlicher Tiefe hin.Die vorliegende Untersuchung befaßt sich mit dem Chemismus und den Texturen der Chromite. Besonderes Interesse wendet sich dabei den Wechselbeziehungen zwischen den Zusammensetzungen, der Art des Vorkommens und den assoziierten Silikaten zu. Dabei zeigt sich, daß die untersuchten Chromite in vieler Hinsicht Ähnlichkeiten sowohl mit podiformen wie mit stratiformen Vorkommen erkennen lassen. Geometrisch und texturell gesehen gehören sie dem podiformen Typ an. Nicht in Einklang damit stehen jedoch die beträchtlichen Eisengehalte sowie die deutlichen Wechselbeziehungen zwischen der Zusammensetzung von Chromit und der koexistierenden Silikate, und schließlich auch der kryptische Lagenbau, den die zwel Mineralgruppen erkennen lassen. Ein genetisches Modell wird vorgeschlagen, das fraktionierte Kristallisation einer ultrabasischen Schmelze von im wesentlichen gleichmäßiger Zusammensetzung vorsieht, die in periodischen Abständen der Magmenkammer zugeführt wurde. Eine Aufwölbung des oberen Mantels, die schrittweiser, partieller Aufschmelzung ausgesetzt ist, könnte diesen Bedingungen entsprechen.
With 11 Figures 相似文献