全文获取类型
收费全文 | 1240篇 |
免费 | 145篇 |
国内免费 | 92篇 |
专业分类
测绘学 | 497篇 |
大气科学 | 85篇 |
地球物理 | 248篇 |
地质学 | 331篇 |
海洋学 | 115篇 |
天文学 | 17篇 |
综合类 | 138篇 |
自然地理 | 46篇 |
出版年
2024年 | 8篇 |
2023年 | 12篇 |
2022年 | 22篇 |
2021年 | 51篇 |
2020年 | 51篇 |
2019年 | 58篇 |
2018年 | 36篇 |
2017年 | 66篇 |
2016年 | 63篇 |
2015年 | 73篇 |
2014年 | 70篇 |
2013年 | 63篇 |
2012年 | 77篇 |
2011年 | 106篇 |
2010年 | 53篇 |
2009年 | 74篇 |
2008年 | 68篇 |
2007年 | 67篇 |
2006年 | 58篇 |
2005年 | 44篇 |
2004年 | 39篇 |
2003年 | 29篇 |
2002年 | 27篇 |
2001年 | 28篇 |
2000年 | 29篇 |
1999年 | 21篇 |
1998年 | 27篇 |
1997年 | 30篇 |
1996年 | 12篇 |
1995年 | 19篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 14篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1477条查询结果,搜索用时 15 毫秒
921.
922.
《Chemie der Erde / Geochemistry》2015,75(3):335-343
In the Iberian Chains of northeastern Spain, the Hirnantian Orea Shale comprises three erosive glaciogenic unconformities punctuating two transgressive glaciomarine sequences. These sequences represent ice retreat episodes of grounded ice on a North Gondwanan region of 50–60°S of estimated palaeolatitude. In contrast, the same formation recorded in the Hesperian Chains repeated episodes of extensional tectonic activity: diamictites were associated with slope-related debris flows and slumps commonly interrupted by truncating discontinuities.An analysis of δ13Corg in the Orea Shale has revealed that the lower Orea sequence displays isotopically light baseline values (∼ −27‰) punctuated by minor (2–3‰) shifts. In distal parts, the upper sequence is characterised by a rapid rise in δ13Corg values, which mark a positive excursion, in the range of 2.5‰ to 7‰ over 40 cm of thickness. The stratigraphic gap involved in the intra-Orea erosive unconformity appears to be greater both in proximal exposures and slope-related (Hesperian) areas, where the chemostratigraphic shift was not recorded. Upsection in the three studied sections, the δ13C values display upsection a sharp return to baseline values of −26‰ to −28‰.The Hirnantian strata of the Iberian and Hesperian Chains have recorded three major correlatable events: (i) a the karstic surface that caps upper Katian limestones and reflects the maximum glacial extension; (ii) a single δ13Corg positive peak of ∼6‰ that is recognisable in distal ramp settings, marking the beginning of the second ice retreat episode and probably representing the late Hirnantian HICE shift; and (iii) the erosive unconformity marked by the progradation of the Los Puertos shoreline complexes. 相似文献
923.
?????BP??????????????????Kalman????????????????????????????????????BP???????÷????????BP?????????????????????????????????????????????÷??????????????????????Ч?????? 相似文献
924.
基于大量文本信息过滤系统的实现 总被引:1,自引:0,他引:1
提出一种分布式的垃圾短信过滤系统的实现方法,适合于移动网络。过滤系统接受从短信中心传来的大量手机短信,然后在最短的时间内检索这些短信是否为垃圾短信,将检索结果返回短信中心。算法主要针对大量信息的检索而提出的,试验表明,在短信过滤方面具有处理时间短和性能更好的特点。 相似文献
925.
A complication of finite-volume triangular C-grid methods is the numerical emergence of horizontal divergence errors that lead to grid-scale oscillations in vertical velocity. Nonlinear feedback via advection of momentum can lead to numerical instability in velocity modes via positive feedback with spurious vertical velocities induced by horizontal divergence truncation error. Existing strategies to mitigate divergence errors such as direct divergence averaging and increased diffusion do not completely mitigate horizontal vertical velocity oscillations. We present a novel elliptic filtering approach to mitigate this spurious error and more accurately represent vertical velocities via improved calculation of horizontal divergences. These results are applied to laminar curved channel flows, demonstrating the applicability of the method to reproduce secondary flow features. 相似文献
926.
K. Eckhardt 《水文研究》2005,19(2):507-515
Recursive digital filtering of hydrographs is a baseflow separation method that can easily be automated and has been recommended for providing reproducible results. In the past, different formulations of the most simple filter type, the so‐called one‐parameter filter, have been proposed. In this paper, a theoretical framework is developed for filter algorithms that were constructed under the assumption that the outflow from an aquifer is linearly proportional to its storage. It is shown that these one‐parameter filters describing an exponential baseflow recession are all special cases of a two‐parameter filter whose equation is specified. Its parameters are the recession constant—which can be objectively determined by a recession analysis—and BFImax, the maximum value of the baseflow index that can be modelled by the algorithm. This introduces a subjective element into the baseflow calculation, since BFImax is not measurable. A preliminary analysis based on the results of conventional separation techniques shows that it might be possible to find typical BFImax values for classes of catchments that can be unequivocally distinguished by their hydrological and hydrogeological characteristics. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
927.
This paper deals wiah a new method for identification of long-term slip behavior of a conceaiedfault in a plain area from tectono-stratigraphic and chronological data obtained by drilling.Chronological determination and lithological analysis and correlation of sediments in stratigraphic colunms of drills NO.1 and No.2 at Dongliuhe Village on the hanging and foot walls ofXiadian fault allow us to quantitatively reconstruct the differential sedimentary history and vertical dislocation process on the hanging and foot walls of the fault since 26 ka BP and to set upa tectono-stratigraphic indicators for identifying paleoearthquakes.On this basis,taking theaccumulative vertical displacement of both sides of a fault to be a quantitative constraint,thestate before an abrupt dislocation in surface-rupturing earthquake can be reconstructed(de-ducting the later coseismic vertical displacement),then 11 surface-rupturing paleoseismic even-ts can be identified.A close correlation between recurrence behavior of surface 相似文献
928.
介绍了二值图像的顺序形态变换基本概念,定义了两种基于顺序形滤波的广义边缘算子,重点讨论了百分位p=1/2时的边缘算子抑制噪声、提取边缘的理论和方法。实验表明,同传统的边缘检测算子相比,该方法具有良好的噪声抑制、边缘提取特性。 相似文献
929.
Kate Moore 《Journal of Geographical Systems》2000,2(4):375-398
Received: 18 July 1999 / Accepted: 30 December 1999 相似文献
930.
本文采用“位场解释的奇点法和滤波”反演活对浙江境内4条长剖面的重力资料进行了解释。奇点法定义了归一化总矢量的相位的概念。重力场奇点处相位曲线发生反转,即从-~+或从+~-。利用相位图上的反转点可准确地确定构造位置。计算结果表明:江山~绍兴深大断裂在诸暨附近从应店街通过;江山-绍兴断裂和苏州-开化断裂均向南倾,可能是反映了一个巨大推覆体的南北边界。 相似文献