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311.
1IntroductionThe quantity and quality of cropland guarantees the grain production (Feng, 2000), and the essence of cropland security is food security. Cropland security means the stability of total quantity of cropland, which also means stable quality, potential productivity and regional balance (Feng, 2000). With the development of urbanization and industrialization, more and more cropland is encroached, especially the cropland with great market-value (Cai, 2000; Ge, 2002; Richard, 2002), w… 相似文献
312.
313.
Co-seismic and cumulative offsets of the recent earthquakes along the Karakax left-lateral strike-slip fault in western Tibet 总被引:3,自引:0,他引:3
Haibing Li Jérôme Van der WoerdZhiming Sun Jialiang Si Paul Tapponnier Jiawei Pan Dongliang Liu Marie-Luce Chevalier 《Gondwana Research》2012,21(1):64-87
The 400 km-long Karakax left-lateral strike-slip fault is the westernmost segment of the Altyn Tagh fault. It separates northwestern Tibet to the south from the Tarim basin to the north. The western section of the Karakax fault exhibits clear co-seismic surface ruptures of past large earthquakes. Geomorphic offset measurements from the field and high-resolution Ikonos images along 1.5 km across the Sanshiliyingfang fan and along 55 km of the fault, range from 3 to 28 m, with distinct clusters at 6 ± 2(3), 14 ± 2, 19 ± 2 and 24 ± 3 m. The cluster of the smallest offsets around 6 m (full range from 3 to 10 m) distributed over a minimum length of 55 km, is attributed to the last largest surface rupturing event that testifies of the occurrence of a magnitude Mw 7.4-7.6 earthquake along the Karakax fault. We interpret the other offset clusters as the possible repetition of similarly sized events thus favoring a characteristic slip model for the Karakax fault. In a 3 m-deep trench dug across the active trace of the fault we can identify the main rupture strands of the last and penultimate events. The penultimate event horizon, a silty-sand layer, has been radiocarbon dated at 975-1020 AD (AMS 14C age). It is proposed that large Mw 7.4-7.6 events with co-seismic slip of about 6 m rupture the Karakax fault with a return time of about 900 years implying an average slip-rate of about 6-7 mm/years during the late Holocene. These results suggest that the Karakax fault is the largest left-lateral strike-slip fault at the rim of northwestern Tibet accommodating eastward movement of Tibet due to the India-Eurasia collision. 相似文献
314.
安徽牯牛降A型花岗岩的年代学、地球化学和构造意义 总被引:9,自引:6,他引:3
皖南地区牯牛降岩体位于扬子板块东南缘,江南隆起带内。本文报道了牯牛降花岗岩体新的锆石U-Pb年龄和地球化学数据,并对岩体成因及其构造意义进行了探讨。锆石原位LA-ICP-MS U-Pb定年表明牯牛降岩体的形成年龄为130.1±1.3Ma (95% confidence, MSWD=0.55)。结合己发表的其他高质量锆石U-Pb同位素年龄数据表明皖南地区花岗岩的形成年龄主要集中在125~130Ma。牯牛降花岗岩为高钾钙碱性、准铝质岩石,SiO2 含量为72.21%~74.85%,具有高K2O含量(>5.11%)、高铁值(FeOT/(FeOT+MgO)>0.91)和K2O/Na2O比值(>1.61),低MgO和CaO含量的特征。微量元素地球化学性质上表现为强烈亏损Ba、Sr、Eu(Eu*/Eu=0.29~0.30),富集REE(>419×10-6)、Rb、Th 和U,较高的高场强元素Zr、Nb、Y和Ga含量。主量和微量元素均表现为A型花岗岩的特征。非常低的Mg#值(0.14~0.16)和较低Cr含量(Cr=10×10-6),高Yb(7.08×10-6~9.02×10-6)、Y(78.7×10-6~90.8×10-6)含量和较高的Th/U比值(5.17~7.79)说明古老地壳物质的部分熔融可能是牯牛降岩体主要形成机制。牯牛降A2型花岗岩特征代表了拉张的碰撞后构造环境。 相似文献
315.
本文分析了地质实验室在测量设备期间核查工作中存在的问题,依据测量设备定义及评审准则要求,明确了期间核查对象。提出了符合地质实验室特点的期间核查方法,其内容包括核查标准和测量参数的选择、核查时机和频次的确定、核查结果的评价方法。文中所提出的期间核查评价方法—控制图法,经济、简便易行,直观地监控测量设备校准状态。确保了测量结果的准确度、精密度能够满足质量规范要求和评审准则要求。本文对地质实验室正确、有效地开展期间核查工作,具有一定指导作用。 相似文献
316.
Chen Si Cui Kaixuan Zhang Wenyan Zhao Yicong Xiao Tian Pan Hongmiao Zhang Wuchang Wu Long-Fei 《中国海洋湖沼学报》2021,39(6):2053-2062
Journal of Oceanology and Limnology - Magnetotactic bacteria(MTB) are a group of prokaryotes having the ability to orient and swim along geomagnetic fi eld lines because they contain intracellular... 相似文献
317.
综合运用钻井、测井、地震等资料,将黄骅坳陷目前的勘探热点地区——歧北次凹的主要勘探目的层段,即沙一下亚段划分为4个四级层序和8个五级层序,建立了沙一下亚段高精度层序地层格架。结合属性提取和测井约束反演等地球物理方法技术,在高精度层序地层格架约束下对歧北次凹目标层内单个地质体进行多层次多角度的精细刻画,研究其空间展布,并剖析其内部结构特征,分析地质体的控制因素。研究发现:物源供给、断裂陡坡带及断裂转换带对地质体的发育具有重要的控制作用,最后提炼出地质体发育模式,为研究区隐蔽油气藏的勘探和开发提供科学依据。 相似文献
318.
歧口凹陷东营组沉降特征及其成因分析 总被引:2,自引:1,他引:1
运用区域三维资料和EBM盆地模拟软件,对歧口凹陷三维连片区东营组沉积时期的沉降史进行了模拟分析,并探讨了沉降中心迁移的原因。结果表明,歧口凹陷东营组发育于同裂陷阶段晚期的断拗转换期,沉降特征具有时空差异性,沉降速率时快时慢,不同次凹之间差异较大。从东三段到东一上段,NE-NNE向主干断层控制作用逐渐减弱,沉降中心逐渐减少,并沿东北方向向歧口深凹逐渐迁移。通过对区域断层和沉降特征研究,认为区域断层的差异性活动控制着沉降中心的发育部位,而区域应力场的改变则控制着沉降中心的迁移。 相似文献
319.
Haiyang Xi Qi Feng Wei Liu JianHua Si Zongqiang Chang Yonghong Su 《Environmental Earth Sciences》2010,60(5):953-963
Water resources is a primary controlling factor for economical development and ecological environmental protection in the
inland river basins of arid western China. Groundwater, as the important component of total water resources, plays a dominant
role in the development of western China. In recent years, with the utilization ratio of surface water raised, the groundwater
recharge rate has been reduced by surface water, and groundwater was exploited on a large-scale. This has led to the decline
of groundwater levels and the degradation of eco-environments in the lower reaches of Heihe watershed, especially. Therefore,
the study on the groundwater-level change in recent years, as well as simulating and predicting groundwater levels changes
in the future is very significant to improve the ecological environment of the Heihe River Basin, coordinate the water contradiction,
and allocate the water resources. The purpose of this study is to analyze the groundwater-level variations of the Ejina region
basin on a large-scale, to develop and evaluate a conceptual groundwater model in Ejina Basin; according to the experimental
observation data, to establish the groundwater flow model combining MODFLOW and GIS Software; simulated the regional hydrologic
regime in recent 10 years and compared with various delivery scenarios from midstream; determined which one would be the best
plan for maintaining and recovering the groundwater levels and increasing the area of Ejina Oasis. Finally, this paper discusses
the possible vegetation changes of Ejina Basin in the future. 相似文献
320.
Sun K.Si Y. 《世界地理研究》2023,(9):109-119
The geographical flow of talents is affecting innovation activities worldwide, so the research on the spatial structure evolution of talent flows is particularly important. This article uses the 2014-2015 global list of highly cited scientists as raw data to retrieve the study and work experience of scientists, uses cities as the research scale, and uses the P-space model to build a highly cited Chinese scientist flow network. At the same time, uses quantile regression analyzes the impact of whether scientists in core cities are more productive. We found that: (1) The city network of highly cited Chinese scientists has the characteristics of a small-world network, and the network space structure presents a "Y-shaped" structure. China-U. S., China-Europe, and China-Australia are the main sides. (2) This article analyzes the source cities and the target cities in which scientists move, and finds that Beijing, Cambridge(UStates), Shanghai are the city with a high degree. (3) The distribution of scientists shows a trend of spreading with the development of the stage. (4) Scientists in core cities have more high-quality paper output. The increase in the degree of centrality of scientists' target cities has a greater impact on the output of scientists. © 2023 World Regional Studies. 相似文献