全文获取类型
收费全文 | 9129篇 |
免费 | 1672篇 |
国内免费 | 2157篇 |
专业分类
测绘学 | 461篇 |
大气科学 | 1894篇 |
地球物理 | 2488篇 |
地质学 | 4549篇 |
海洋学 | 927篇 |
天文学 | 505篇 |
综合类 | 925篇 |
自然地理 | 1209篇 |
出版年
2024年 | 36篇 |
2023年 | 126篇 |
2022年 | 399篇 |
2021年 | 424篇 |
2020年 | 377篇 |
2019年 | 484篇 |
2018年 | 530篇 |
2017年 | 466篇 |
2016年 | 551篇 |
2015年 | 456篇 |
2014年 | 563篇 |
2013年 | 514篇 |
2012年 | 483篇 |
2011年 | 566篇 |
2010年 | 531篇 |
2009年 | 499篇 |
2008年 | 457篇 |
2007年 | 473篇 |
2006年 | 359篇 |
2005年 | 291篇 |
2004年 | 281篇 |
2003年 | 278篇 |
2002年 | 285篇 |
2001年 | 259篇 |
2000年 | 306篇 |
1999年 | 390篇 |
1998年 | 330篇 |
1997年 | 340篇 |
1996年 | 275篇 |
1995年 | 244篇 |
1994年 | 291篇 |
1993年 | 219篇 |
1992年 | 171篇 |
1991年 | 129篇 |
1990年 | 103篇 |
1989年 | 76篇 |
1988年 | 99篇 |
1987年 | 50篇 |
1986年 | 44篇 |
1985年 | 40篇 |
1984年 | 35篇 |
1983年 | 32篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1978年 | 5篇 |
1975年 | 2篇 |
1958年 | 7篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Ji Wu Guang-Wu Zhu Hua Zhao Chi Wang Lei Li Yue-Qiang Sun Wei Guo Cheng-Li Huang 《Chinese Astronomy and Astrophysics》2010
Compared with other planets, Mars is a planet most similar with the earth and most possible to find the extraterrestrial life on it, and therefore especially concerned about by human beings. In recent years, some countries have launched Mars probes and announced their manned Mars exploration programs. China has become the fifth country in the world to launch independently artificial satellites, and the third country able to carry out an independent manned space program. However, China is just at the beginning of deep space explorations. In 2007, China and Russia signed an agreement on a joint Mars exploration program by sending a Chinese micro-satellite Yinghuo-1 (YH-1) to the Mars orbit. Once YH-1 enters its orbit, it will carry out its own exploration, as well as the joint exploration with the Russian Phobos-Grunt probe. This paper summarizes the scientific background and objectives of YH-1 and describes briefly its payloads for realizing these scientific objectives. In addition, the main exploration tasks of YH-1 and a preliminary prospect on its exploration results are also given. 相似文献
992.
993.
There are approximately 470,000 km(2) of karst aquifers that feed many large springs in North China. Turbulent flow often exists in these karst aquifers, which means that the classical ground water model based on Darcy's law cannot be applied here. Ground water data are rare for these aquifers. As a consequence, it is difficult to quantitatively investigate ground water flow in these karst systems. The purpose of this study is to develop a parsimonious model that predicts karst spring discharge using gray system theory. In this theory, a white color denotes a system that is completely characterized and a black color represents a system that is totally unknown. A gray system thus describes a complex system whose characteristics are only partially known or known with uncertainty. Using this theory, we investigated the karst spring discharge time series over different time scales. First, we identified three specific components of spring discharge: the long-term trend, periodic variation, and random fluctuation. We then used the gray system model to simulate the long-term trend and obtain periodic variation and random fluctuation components. Subsequently, we developed a predictive model for karst spring discharge. Application of the model to Liulin Springs, a representative example of karst springs in northern China, shows that the model performs well. The predicted results suggest that the Liulin Springs discharge will likely decrease over time, with small fluctuations. 相似文献
994.
Using 3 years of high-quality temperature measurements (2002–2004) recorded from Maui, HI (20.8°N), we have investigated the characteristics of mesospheric seasonal oscillations at low-latitudes. Measurements of the near-infrared OH (6,2) and O2 (0,1) nightglow emission layers (centered at 87 and 94 km) independently reveal a distinct semi-annual oscillation (SAO) and annual oscillation (AO) with amplitudes of 3.8 and 2.0 K, respectively. An observed asymmetry in the seasonal variation of the nocturnal mean, previously reported by Taylor et al. [2005. Characterization of the semi-annual-oscillation in mesospheric temperatures at low-latitudes. Advances in Space Research 35, doi:10.1016/j.asr.2005.05.111] from this site is shown to be due to a superposed AO of amplitude 50% of the SAO signature. Detailed investigations of the local-time variation of the SAO amplitude and phase combined with TIME-GCM simulations of the seasonal variation of the diurnal tide strongly suggest a large local-time dependence of the amplitude (but not phase) of the observed SAO. These data indicate that the true mean temperature SAO amplitude could be as high as 7 K at this latitude. 相似文献
995.
沈阳长白乡-观音阁断裂、抚顺浑河断裂的定位和活动性研究 总被引:3,自引:0,他引:3
本文基于对沈阳长白乡-观音阁断裂,以及抚顺浑河断裂开展的1:10000地质地貌填图工作,获得了这两条断裂在最老第四纪地层热释光的测年结果,它们分别为(112±6.7)ka和(150±9.0)ka。长白乡-观音阁断裂为一沿丘陵山地前缘分布的断裂,由2—3条分支断裂组成,最新的断面活动显示为压扭性正断层性质。断裂在晚更新世坡洪积扇堆积形成以来没有活动显示。3条浅层人工地震测线探测结果表明,其上断点均未错断第四系上更新统底界。断裂为中更新世活动断裂,晚更新世以来没有活动。浑河断裂为一沿丘陵山地前缘分布的断裂,由3—4条分支断裂组成,最新的断面活动显示为压扭性正断层性质。断裂在晚更新世坡洪积扇堆积形成以来没有活动显示。5条浅层人工地震测线探测结果表明,其上断点均在第四系上更新统底界以下。断裂为中更新世活动断裂,晚更新世以来没有活动。 相似文献
996.
Arctic sea-ice motion and its relation to pressure field 总被引:5,自引:0,他引:5
Daily Arctic sea-ice motion maps during the winter seasons (December–March) from December 1988 to March 2003 derived from
NSCAT, QuikSCAT, SSM/I, and AMSRE data by a wavelet analysis method have been merged with those derived from buoy data. These
merged sea-ice motion data have been used to study the circulation regimes and winter-to-winter variability of Arctic sea-ice
motion. The relation between sea-ice motion and the pressure field in the Arctic Ocean was also studied by applying Principal
Component Analysis (PCA) to the monthly merged sea-ice motion data and the monthly pressure field data from IABP. The mean
Arctic sea-ice motion map of the 15 winter seasons has two distinct features: the Beaufort Gyre and a cyclonic circulation
system in the Eurasian Basin, which moves ice from the Laptev Sea to Fram Strait. The strengths and sizes of the two features
change from one winter season to another. Seasons with a strong or normal Beaufort Gyre alternate with seasons with a weak
or no Beaufort Gyre every one to three seasons. The principal components of the first two modes of PCA of the monthly sea-ice
motion are closely correlated with their counterparts of the monthly pressure field in the Arctic Ocean. The mode-one components
of these two anomalies alternate between anticyclonic and cyclonic circulation systems. The correlation between Arctic Oscillation
indexes and the principal components of the first mode of PCA of the monthly Arctic sea-ice motion is low but statistically
significant. 相似文献
997.
Xinmiao Zhao Hongfu Zhang Xiangkun Zhu Suohan Tang Yanjie Tang 《Contributions to Mineralogy and Petrology》2010,160(1):15-14
Iron isotopes, together with mineral elemental compositions of spinel peridotite xenoliths and clinopyroxenites from Hannuoba
and Hebi Cenozoic alkaline basalts, were analyzed to investigate iron isotopic features of the lithospheric mantle beneath
the North China Craton. The results show that the Hannuoba spinel peridotite xenoliths have small but distinguishable Fe isotopic
variations. Overall variations in δ57Fe are in a range of −0.25 to 0.14‰ for olivine, −0.17 to 0.17‰ for orthopyroxene, −0.21 to 0.27‰ for clinopyroxene, and −0.16
to 0.26‰ for spinel, respectively. Clinopyroxene has the heaviest iron isotopic ratio and olivine the lightest within individual
sample. No clear linear relationships between the mineral pairs on “δ-δ” plot suggest that iron isotopes of mineral separates
analyzed have been affected largely by some open system processes. The broadly negative correlations between mineral iron
isotopes and metasomatic indexes such as spinel Cr#, (La/Yb)N ratios of clinopyroxenes suggest that iron isotopic variations in different minerals and peridotites were probably produced
by mantle metasomatism. The Hebi phlogopite-bearing lherzolite, which is significantly modified by metasomatic events, appears
to be much heavier isotopically than clinopyroxene-poor lherzolite. This study further confirms previous conclusions that
the lithospheric mantle has distinguishable and heterogeneous iron isotopic variations at the xenoliths scale. Mantle metasomatism
is the most likely cause for the iron isotope variations in mantle peridotites. 相似文献
998.
Iron isotope variations in spinel peridotite xenoliths from North China Craton: implications for mantle metasomatism 总被引:2,自引:1,他引:1
Xinmiao Zhao Hongfu Zhang Xiangkun Zhu Suohan Tang Yanjie Tang 《Contributions to Mineralogy and Petrology》2010,160(1):1-14
Iron isotopes, together with mineral elemental compositions of spinel peridotite xenoliths and clinopyroxenites from Hannuoba and Hebi Cenozoic alkaline basalts, were analyzed to investigate iron isotopic features of the lithospheric mantle beneath the North China Craton. The results show that the Hannuoba spinel peridotite xenoliths have small but distinguishable Fe isotopic variations. Overall variations in δ57Fe are in a range of ?0.25 to 0.14‰ for olivine, ?0.17 to 0.17‰ for orthopyroxene, ?0.21 to 0.27‰ for clinopyroxene, and ?0.16 to 0.26‰ for spinel, respectively. Clinopyroxene has the heaviest iron isotopic ratio and olivine the lightest within individual sample. No clear linear relationships between the mineral pairs on “δ-δ” plot suggest that iron isotopes of mineral separates analyzed have been affected largely by some open system processes. The broadly negative correlations between mineral iron isotopes and metasomatic indexes such as spinel Cr#, (La/Yb)N ratios of clinopyroxenes suggest that iron isotopic variations in different minerals and peridotites were probably produced by mantle metasomatism. The Hebi phlogopite-bearing lherzolite, which is significantly modified by metasomatic events, appears to be much heavier isotopically than clinopyroxene-poor lherzolite. This study further confirms previous conclusions that the lithospheric mantle has distinguishable and heterogeneous iron isotopic variations at the xenoliths scale. Mantle metasomatism is the most likely cause for the iron isotope variations in mantle peridotites. 相似文献
999.
新疆贝勒库都克A型花岗岩锆石U-Pb年龄、地球化学及锡成矿 总被引:1,自引:0,他引:1
新疆东准噶尔卡拉麦里地区是一个重要的锡成矿带,分布有多种类型花岗岩。贝勒库都克岩体位于锡成矿带中部,由黑云母正长花岗岩和黑云母二长花岗岩组成。本文通过精确的LA-ICP-MS锆石U-Pb测年获得贝勒库都克含锡黑云母正长花岗岩年龄为283±2Ma,MSWD=0.14(95%置信度),时代属于早二叠世,这与东准噶尔后碰撞深成岩浆活动的范围(330~265Ma)相吻合。岩石地球化学研究表明,贝勒库都克岩体富硅(SiO2=75.25%~76.67%),低铝(Al2O3=11.91%~12.86%),贫镁(MgO=0.02%~0.18%)和钙(CaO=0.39%~0.89%),富碱(Na2O+K2O=8.08%~8.97%),K2O>Na2O,NK/A=0.86~0.95(平均0.92),A/NCK=0.97~1.02,富集Rb、K等大离子亲石元素及Zr、Hf等高场强元素,Ba,Nb,Sr强烈亏损,δEu=0.01~0.11,其FeOt/MgO(12.71~84.51,平均34.55)和10000Ga/A1(2.97~4.20)值大,HFSE元素(Zr+Nb+Ce+Y=191.8×10-6~353.3×10-6)含量高,明显不同于典型的I型和S型花岗岩,基本属于典型的铝质A型花岗岩。年代学和地球化学综合研究表明,贝勒库都克铝质A型花岗岩是壳幔混合成因,是准噶尔地区后碰撞幔源岩浆底侵作用导致大陆地壳垂向生长过程的记录者。贝勒库都克铝质A型花岗岩Sn的含量高(6.0×10-6~19.5×10-6,个别为80.0×10-6),铝质A型花岗岩是成矿热液的直接母体,而富Sn的流体相最终形成了贝勒库都克锡矿床,锡矿与铝质A型花岗岩是同期地质事件的产物。 相似文献
1000.
Geochemical characteristics,cooling history and mineralization significance of Zhangtiantang pluton in South Jiangxi Province,P.R. China 总被引:1,自引:0,他引:1
The zircon SHRIMP dating of the Zhangtiantang granite gave an age of 159±7 Ma., which shows that the granite was produced
at the early Late Jurassic. The Ar-Ar plateau ages of biotite and K-feldspar from the Zhangtiantang pluton are 153.2±1.1 Ma
and 135.8±1.2 Ma, respectively. The Ar-Ar anti-isochrone ages of biotite and K-feldspar are 152.5±1.7Ma and 135.4±2.7Ma, respectively.
The ages represent the isotopic closure ages of minerals in the pluton. The Zhangtiantang granites are regarded as peraluminous
crust-derived type granites to possess the typical geochemical characteristics of calc-alkaline rocks on continental margin,
with enriched Si, K, Al (average value of A/CNK as 1.18), HREE, Rb, U, and Th, heavily depleted V, Cr, Co, Ni, Ti, Nb-Ta,
Zr, Sr, P, and Ba, strongly negative Eu and common corundum normative (average value of C as 1.84). The εNd(t) values of the Zhangtiantang granite are −5.84 to −7.79, and t
2DM values are 1.69 to 1.83 Ga, which indicates partial melting of continental-crust metamorphic sedimentary rocks during the
Middle Proterozoic.
The cooling history of the Zhangtiantang granitic pluton indicates that the cooling velocity of pluton was faster (about 67°C/Ma)
from zircon (158 Ma) to biotite (152 Ma), and was slower (about12°C/Ma) from biotite (152.5 Ma) to K-feldspar (135.8 Ma).
It can be deduced that the temporal gap (about 10 Ma) between the granite formmation and W-Sn mineralization in South China
may be related to ordinary magma-hydrothermal processes by the variational cooling curve of the pluton. The Zhangtiantang
pluton was formed in a compressive setting, with differentiation evolution and mineralization occurring in a relative relaxation
setting. 相似文献