全文获取类型
收费全文 | 216篇 |
免费 | 18篇 |
国内免费 | 40篇 |
专业分类
测绘学 | 42篇 |
大气科学 | 1篇 |
地球物理 | 47篇 |
地质学 | 132篇 |
海洋学 | 28篇 |
天文学 | 4篇 |
综合类 | 6篇 |
自然地理 | 14篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 8篇 |
2019年 | 9篇 |
2018年 | 8篇 |
2017年 | 5篇 |
2016年 | 12篇 |
2015年 | 10篇 |
2014年 | 15篇 |
2013年 | 26篇 |
2012年 | 7篇 |
2011年 | 11篇 |
2010年 | 6篇 |
2009年 | 13篇 |
2008年 | 11篇 |
2007年 | 15篇 |
2006年 | 9篇 |
2005年 | 11篇 |
2004年 | 20篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 3篇 |
2000年 | 7篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
排序方式: 共有274条查询结果,搜索用时 93 毫秒
121.
作为全站仪测量系统的重要组成部分,反射棱镜在精密工程测量中发挥着极为重要的作用。准确测定棱镜的加常数,对于提高测距精度具有重要意义。常见的测定方法对场地条件要求较高,本文提出一种改进方法,通过观测2个固定位置的360°小棱镜,即可运用最小二乘法准确求解棱镜常数。该方法场地限制条件少,能因地制宜、方便快捷地开展施测,在工程实践中更具应用潜力。 相似文献
122.
Various fracture filling minerals and secondary minerals in fracture walls were formed by fluid-rock interaction during the exhumation of the Palaeogene Shimanto Belt of Kyushu, Japan, which is located in an accretionary complex. Each mineral formed under favourable geological conditions and can be used to estimate the conditions of accretion and formation of the related rock sequences. Petrographic observations, mineralogical and geochemical analyses were made on fracture filling minerals and secondary minerals from boreholes of ca. 140 m depth, drilled in the Shimanto Belt. Results reveal that the secondary minerals were formed in three major stages distinguished by the sequential textural relationships of the minerals and the interpreted environment of mineral formation. Filling mineral assemblages show that the studied rock formation has been subducted to a depth of several km and the temperature reached was ca. 200–300 °C. After the subduction, the rock formation was uplifted and surface acidic water penetrated up to 80 m beneath the present ground surface. The acid water dissolved calcite fracture filling minerals to form the present groundwater flow-paths, which allowed recent wall rock alteration to occur. The results shown here imply that filling mineral assemblages can be an effective tool to evaluate the environmental changes during exhumation of an accretionary complex. 相似文献
123.
A series of flow induced vibration (FIV) experiments for an equilateral triangle prism elastically mounted in a water channel are performed with different system stiffness at constant damping and mass. An amplitude variation coefficient is proposed to describe FIV stationarity in the present study. The FIV of the prism can be divided into three primary regions based on the amplitude and frequency responses, which are the vortex induced vibration (VIV) branch, the transition branch from VIV to galloping, and the galloping branch. The transition branch occurs at the reduced velocity in the range of 7.8 < Ur = U/(fn,air·D) < 10.4, accompanied with a relatively rapid increase in amplitude and a precipitous drop in frequency and vibration stationarity. In addition, the reduced velocity where the transition region is initiated is independent of the system stiffness. The maximum amplitude reaches 3.17 D in the galloping branch. The ratio of the response frequency to the natural frequency of the prism in air remains locked to approximately 0.65 throughout the fully developed galloping branch. Large amplitude responses in an infinite range of flow velocities, excellent vibration stationarity and steady vibration frequencies, which are characteristics of the galloping of the prism, have a positive impact on improving energy conversion. 相似文献
124.
LP/HT metamorphism as a temporal marker of change of deformation style within the Late Palaeozoic accretionary wedge of central Chile
下载免费PDF全文
![点击此处可从《Journal of Metamorphic Geology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
T. Hyppolito C. Juliani A. Garcia‐Casco V. Meira A. Bustamante C. Hall 《Journal of Metamorphic Geology》2015,33(9):1003-1024
A Late Palaeozoic accretionary prism, formed at the southwestern margin of Gondwana from Early Carboniferous to Late Triassic, comprises the Coastal Accretionary Complex of central Chile (34–41°S). This fossil accretionary system is made up of two parallel contemporaneous metamorphic belts: a high‐pressure/low temperature belt (HP/LT – Western Series) and a low pressure/high temperature belt (LP/HT – Eastern Series). However, the timing of deformation events associated with the growth of the accretionary prism (successive frontal accretion and basal underplating) and the development of the LP/HT metamorphism in the shallower levels of the wedge are not continuously observed along this paired metamorphic belt, suggesting the former existence of local perturbations in the subduction regime. In the Pichilemu region, a well‐preserved segment of the paired metamorphic belt allows a first order correlation between the metamorphic and deformational evolution of the deep accreted slices of oceanic crust (blueschists and HP greenschists from the Western Series) and deformation at the shallower levels of the wedge (the Eastern Series). LP/HT mineral assemblages grew in response to arc‐related granitic intrusions, and porphyroblasts constitute time markers recording the evolution of deformation within shallow wedge material. Integrated P–T–t–d analysis reveals that the LP/HT belt is formed between the stages of frontal accretion (D1) and basal underplating of basic rocks (D2) forming blueschists at c. 300 Ma. A timeline evolution relating the formation of blueschists and the formation and deformation of LP/HT mineral assemblages at shallower levels, combined with published geochronological/thermobarometric/geochemistry data suggests a cause–effect relation between the basal accretion of basic rocks and the deformation of the shallower LP/HT belt. The S2 foliation that formed during basal accretion initiated near the base of the accretionary wedge at ~30 km depth at c. 308 Ma. Later, the S2 foliation developed at c. 300 Ma and ~15 km depth shortly after the emplacement of the granitoids and formation of the (LP/HT) peak metamorphic mineral assemblages. This shallow deformation may reflect a perturbation in the long‐term subduction dynamics (e.g. entrance of a seamount), which would in turn have contributed to the coeval exhumation of the nearby blueschists at c. 300 Ma. Finally, 40Ar–39Ar cooling ages reveal that foliated LP/HT rocks were already at ~350 °C at c. 292 Ma, indicating a rapid cooling for this metamorphic system. 相似文献
125.
126.
本文发表的是用北京天文台60厘米施密特望远镜进行发射线星系物端棱镜巡天结果的第四篇文章。文中的表1包括100个发射线天体,其中的96个是发射线星系;其余的对象有3个行星状星云,1个发射线星。在这些发射线星系中,属于s,sd型的有69个,d,ds型的有27个,分别占72%和28%。除了4个已知的Seyfert星系之外,至少还有5个也可能是Seyfert星系。这些发射线天体中的23个是IRAS源,它们都与具有强发射的现象相联系. 相似文献
127.
Cesare Barbieri Carlo Blanco Beatrice Bucciarelli Regina Coluzzi Andrea Di Paola Luciano Lanteri Gian Luca Li Causi Ettore Marilli Piero Massimino Vincenzo Mezzalira Stefano Mottola Roberto Nesci Alessandro Omizzolo Fernando Pedichini Francesca Rampazzi Corinne Rossi Ruggero Stagni Milcho Tsvetkov Roberto Viotti 《Experimental Astronomy》2003,15(1):29-43
There is a widespread interest to digitize the precious information contained in the astronomical plate archives, both for
the preservation of their content and for its fast distribution to all interested researchers in order to achieve their better
scientific exploitation. This paper presents the first results of our large-scale project to digitize the archive of plates
of the Italian Astronomical Observatories and of the Specola Vaticana. Similar systems, composed by commercial flat-bed retro-illuminated
scanners plus dedicated personal computers and acquisition and analysis software, have been installed in all participating
Institutes. Ad-hoc codes have been developed to acquire the data, to test the suitability of the machines to our scientific needs, and to reduce
the digital data in order to extract the astrometric, photometric and spectroscopic content. Two more elements complete the
overall project: the provision of high quality BVRI CCD sequences in selected fields with the Campo Imperatore telescopes,
and the distribution of the digitized information to all interested researchers via the Web. The methods we have derived in
the course of this project have been already applied successfully to plates taken by other Observatories, for instance at
Byurakan and at Hamburg. 相似文献
128.
129.
结合长期外业实践,阐述了施工及天气角度、仪器及棱镜工作状态、施工组织等因素对CPⅢ平面工作的影响,提出了如何避免或消减这些因素对外业工作的影响,进而更快、更高精度地进行CPⅢ的外业测量。 相似文献
130.
Claudio Vita-Finzi 《Proceedings of the Geologists' Association. Geologists' Association》2011,122(3):343-346
Tsunami intensity is poorly correlated with earthquake magnitude. The distribution of aftershocks that immediately followed the 2010 Maule (Chile), the 2004 Sumatra–Andaman and the 2005 Nias (Indonesia) events supports the view that faulting within an accretionary wedge or an outer rise can sometimes disrupt the seafloor more effectively than a megathrust even if the associated seismicity is minor. Monitoring offshore faults would thus seem an effective way to supplement modes of tsunami early warning which hinge on instrumental earthquake detection or wave height and period. 相似文献