全文获取类型
收费全文 | 35158篇 |
免费 | 4749篇 |
国内免费 | 3272篇 |
专业分类
测绘学 | 2832篇 |
大气科学 | 4173篇 |
地球物理 | 6810篇 |
地质学 | 18556篇 |
海洋学 | 2981篇 |
天文学 | 1998篇 |
综合类 | 3126篇 |
自然地理 | 2703篇 |
出版年
2025年 | 23篇 |
2024年 | 438篇 |
2023年 | 513篇 |
2022年 | 913篇 |
2021年 | 950篇 |
2020年 | 840篇 |
2019年 | 925篇 |
2018年 | 5496篇 |
2017年 | 4737篇 |
2016年 | 3410篇 |
2015年 | 1078篇 |
2014年 | 966篇 |
2013年 | 872篇 |
2012年 | 1919篇 |
2011年 | 3563篇 |
2010年 | 2871篇 |
2009年 | 3081篇 |
2008年 | 2555篇 |
2007年 | 2931篇 |
2006年 | 526篇 |
2005年 | 579篇 |
2004年 | 679篇 |
2003年 | 628篇 |
2002年 | 483篇 |
2001年 | 286篇 |
2000年 | 285篇 |
1999年 | 269篇 |
1998年 | 217篇 |
1997年 | 177篇 |
1996年 | 134篇 |
1995年 | 147篇 |
1994年 | 105篇 |
1993年 | 115篇 |
1992年 | 92篇 |
1991年 | 66篇 |
1990年 | 45篇 |
1989年 | 45篇 |
1988年 | 36篇 |
1987年 | 31篇 |
1986年 | 22篇 |
1985年 | 15篇 |
1984年 | 13篇 |
1983年 | 15篇 |
1982年 | 11篇 |
1981年 | 24篇 |
1980年 | 27篇 |
1979年 | 5篇 |
1976年 | 7篇 |
1958年 | 7篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Hani N. Khoury 《Arabian Journal of Geosciences》2018,11(4):72
The Azraq basin (the Badia region in NE-Jordan) is rich in its industrial rocks and minerals. Most of the commodities are concentrated in one area, which is the Azraq depression (El-Qa’). The climatic changes (wet and dry) of Azraq closed lake contributed in the formation of industrial rocks and minerals in the El-Qa’. Basalt, pyroclastics, zeolites, diatomaceous earth, bentonite, palgorskite, porcelanite, saline brines, chalk, limestone, and gypsum are the potential industrial commodities. The basaltic rocks are of high alkalis content and good homogeneity and are of good potential use in constructions and cast basalt. The scoriaceous pyroclastic material proved to be of excellent properties for use as lightweight aggregates, cultivation purposes, and for the production of pozzolanic cement. Smectite-rich beds (bentonite) from Ein El Badia could be used as binder, absorbent, and additives for feeding farm animals. Palygorskite is potential for use in drilling mud, paint, pharmaceuticals, and as a filtering medium. The diatomaceous earth deposits are Moler type and could be used as filter aid and absorbent. Zeolites are efficient for agricultural purposes, animal waste, and wastewater treatment plants. Saline brine is exploited in the Azraq mudflat area for table salt. Porcelanite could be used as an absorbent of hazardous elements, abrasive, and filler. The softness and high purity of chalk enable its use as filler and in the lime production. The large limestone concretions are of high quality for use as a building stone. Gypsum (gypcrete) could be used after the removal of the undesired chert impurities. The Badia region is a highly potential area for future exploration and mining industry in a manner that achieves the required outcomes and minimizes impacts on ecosystems. 相似文献
92.
Kazutaka Yamaoka Yoshihiro Ueda Hajime Inoue Fumiaki Nagase Ken Ebisawa Taro Kotani Yasuo Tanaka 《Astrophysics and Space Science》2001,276(1):19-22
We summarize the ASCA observations of the two Galactic superluminal sources GRO J1655–40 and GRS 1915+105, focusing on theabsorption line features.The high spectroscopic capability of ASCA enabled us to detectiron-K absorption line features from both objects. This is direct evidence for the presence of highly ionized plasma in a non-spherical configuration around a black hole, and is considered to be a unique signature of superluminal jet systems. The candidate of the line-absorber would be a part of an accretion disk at a distance of 109-11 cm from the central X-ray source. 相似文献
93.
Analyses of 72 samples from Upper Panjhara basin in the northern part of Deccan Plateau, India, indicate that geochemical
incongruity of groundwater is largely a function of mineral composition of the basaltic lithology. Higher proportion of alkaline
earth elements to total cations and HCO3>Cl + SO4 reflect weathering of primary silicates as chief source of ions. Inputs of Cl, SO4, and NO3 are related to rainfall and localized anthropogenic factors. Groundwater from recharge area representing Ca + Mg–HCO3 type progressively evolves to Ca + Na–HCO3 and Na–Ca–HCO3 class along flow direction replicates the role of cation exchange and precipitation processes. While the post-monsoon chemistry
is controlled by silicate mineral dissolution + cation exchange reactions, pre-monsoon variability is attributable chiefly
to precipitation reactions + anthropogenic factors. Positive correlations between Mg vs HCO3 and Ca + Mg vs HCO3 supports selective dissolution of olivine and pyroxene as dominant process in post-monsoon followed by dissolution of plagioclase
feldspar and secondary carbonates. The pre-monsoon data however, points toward the dissolution of plagioclase and precipitation
of CaCO3 supported by improved correlation coefficients between Na + Ca vs HCO3 and negative correlation of Ca vs HCO3, respectively. It is proposed that the eccentricity in the composition of groundwater from the Panjhara basin is a function
of selective dissolution of olivine > pyroxene followed by plagioclase feldspar.
The data suggest siallitization (L < R and R
k) as dominant mechanism of chemical weathering of basalts, stimulating monosiallitic (kaolinite) and bisiallitic (montmorillonite)
products. The chemical denudation rates for Panjhara basin worked out separately for the ground and surface water component
range from 6.98 to 36.65 tons/km2/yr, respectively. The values of the CO2 consumption rates range between 0.18 × 106 mol//km2/yr (groundwater) and 0.9 × 106 mol/km2/yr (surface water), which indicates that the groundwater forms a considerable fraction of CO2 consumption, an inference, that is, not taken into contemplation in most of the studies. 相似文献
94.
首次应用具有我国自主知识产权的中巴资源卫星影像数据对煤矿矿区采煤地面塌陷进行遥感调查研究。煤矿采空区地面塌陷随着时间日趋严重,面积不断扩大,兼有渐变和突变的特点,用常规方法定点观测难以适应其发展,确定其边界分布非常困难。文章应用中巴资源卫星HR高分辨率影像数据,以六道湾一铁厂沟煤矿矿区为例,通过已知塌陷区的基本特点,建立塌陷区的遥感影像地物解译标志体系,通过人机交互遥感影像解译,圈定地面塌陷的边界并获得塌陷区的有关数据,为该地区环境地质灾害治理提供依据。 相似文献
95.
Amin Naboureh Mohammad Hossein Rezaei Moghaddam Bakhtiar Feizizadeh Thomas Blaschke 《Arabian Journal of Geosciences》2017,10(12):259
The present paper is an attempt to integrate a semi-automated object-based image analysis (OBIA) classification framework and a cellular automata-Markov model to study land use/land cover (LULC) changes. Land use maps for the Sarab plain in Iran for the years 2000, 2006, and 2014 were created from Landsat satellite data, by applying an OBIA classification using the normalized difference vegetation index, salinity index, moisture stress index, soil-adjusted vegetation index, and elevation and slope indicators. The classifications yielded overall accuracies of 91, 93, and 94% for 2000, 2006, and 2014, respectively. Finally, using the transition matrix, the spatial distribution of land use was simulated for 2020. The results of the study revealed that the number of orchards with irrigated agriculture and dry-farm agriculture in the Sarab plain is increasing, while the amount of bare land is decreasing. The results of this research are of great importance for regional authorities and decision makers in strategic land use planning. 相似文献
96.
基于ArcGIS Runtime SDK for Android离线编辑关键技术应用研究 总被引:1,自引:0,他引:1
近年来,传统的外业调绘模式逐渐向内外业一体化模式转变。本文以地理国情内外业一体化系统为依托,重点研究了ESRI的离线编辑关键技术,介绍了基于ArcGIS Runtime SDK for Android实现的离线编辑功能,以面修形算法为例,在细粒度的几何编辑基础上实现了常见的外业编辑业务。 相似文献
97.
98.
99.
100.
Pasargadae complex had been the main center of Persian history during the Achaemenian period (560–330 bc), registered as one of the world heritage sites by UNESCO in 2004. This research is an attempt to recognize the natural setting
and landscape of Pasargadae during the Achaemenian period, in Iran. The method is based on the application of a multi-layer
technique. Collected data by fieldwork, especially in geology, hydrology, and hydrogeology, along with the analysis of aerial
data and satellite information provided the baseline information for preparing historic and environmental layers and have
made it possible to recognize a natural lakelet in the this area. The results show that the geometry of lakelet together with
the ancient river of Pasargadae had been the main elements that formed the character of the site; they were also important
in the locations of buildings in the Pasargadae complex. 相似文献