全文获取类型
收费全文 | 10001篇 |
免费 | 1887篇 |
国内免费 | 2276篇 |
专业分类
测绘学 | 609篇 |
大气科学 | 1889篇 |
地球物理 | 2567篇 |
地质学 | 5268篇 |
海洋学 | 1047篇 |
天文学 | 586篇 |
综合类 | 897篇 |
自然地理 | 1301篇 |
出版年
2024年 | 65篇 |
2023年 | 205篇 |
2022年 | 479篇 |
2021年 | 569篇 |
2020年 | 471篇 |
2019年 | 543篇 |
2018年 | 588篇 |
2017年 | 568篇 |
2016年 | 567篇 |
2015年 | 511篇 |
2014年 | 578篇 |
2013年 | 571篇 |
2012年 | 550篇 |
2011年 | 589篇 |
2010年 | 578篇 |
2009年 | 572篇 |
2008年 | 548篇 |
2007年 | 529篇 |
2006年 | 355篇 |
2005年 | 385篇 |
2004年 | 325篇 |
2003年 | 287篇 |
2002年 | 324篇 |
2001年 | 346篇 |
2000年 | 323篇 |
1999年 | 414篇 |
1998年 | 317篇 |
1997年 | 338篇 |
1996年 | 282篇 |
1995年 | 259篇 |
1994年 | 178篇 |
1993年 | 195篇 |
1992年 | 161篇 |
1991年 | 96篇 |
1990年 | 71篇 |
1989年 | 92篇 |
1988年 | 81篇 |
1987年 | 39篇 |
1986年 | 34篇 |
1985年 | 28篇 |
1984年 | 29篇 |
1983年 | 12篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 14篇 |
1979年 | 7篇 |
1978年 | 12篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1958年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
DYNAMIC VARIATIONS OF WATER QUALITY IN TAIHU LAKE AND MULTIVARIATE ANALYSIS OF ITS INFLUENTIAL FACTORS 总被引:1,自引:0,他引:1
Cai Qiming Gao Xiyun Chen Yuwei Ma Shengwei Nanjing Institute of Geography Limnology CAS Nanjing People''s Republic of ChinaMartin Dokulil Institute of Limnology Austria 《地理学报(英文版)》1997,(3)
LakeTaihuisalargeshallowlakeinChina,whichpalysanimportantroleinwater-quantityregulation,watersupply,cultivationetc.Withrapiddevelopmentofagricultureandindustryinthearea,alargenumberofpollutantshavebeendischargedintothelake,leadingtoanincreaseinnutrients… 相似文献
32.
Application of discovery process models in estimating petroleum resources at the play level in China
Discovery process modeling has gained wide acceptance in the Chinese exploration community. In recent years, a variety of
discovery process models have been applied to the prediction of undiscovered petroleum resources at the play level in sedimentary
basins in China. However, challenging problems have been encountered, particularly when one method alone has been applied
to small plays in nonmarine sedimentary basins or in plays with an unusual order of discovery wells. This paper presents results
gotten by using the lognormal discovery process model of the Geological Survey of Canada and the geoanchored method for three
petroleum plays in basins with different geologic settings. Although the predicted shapes of the parentsize distributions
which use these two models, were not always similar, the expected values of the total resources and the number of fields (pools)
to be discovered are comparable. The combined use of two discovery process models in the same play compensates for the weaknesses
in one method compared with the other and vice versa. Thus, more reliable estimates are the result. 相似文献
33.
着重介绍了CuInSe2的结构和光、电学特性;讨论了多各上薄膜沉积技术;评价了主要的合成装置及其作途;综述了制备CuInSe2太阳电池器件的工艺和材料,提出了一种能成功地生产大面积太阳电池薄膜的经济有铲的沉积技术。 相似文献
34.
丰城洛市地区推,滑覆构造特征及其成因探讨 总被引:2,自引:0,他引:2
介绍了洛市地区推、滑覆构造特征、运动学标志及其形成时期、成因模式。 相似文献
35.
In this paper,the Gutenberg-Richter model is used to generate seismic events.The events that satisfy the random distribution are also generated.With those events,the natural probability distribution of Load and Unload Response Ratio(LURR),which measures quantitatively the degree of instability of a nonlinear system,is discussed.The study is based on stress energy release,which is chosen as the response of nonlinear system F3.The comparative results from the observation catalogue and generating data are also studied.It is revealed that the natural probability of LURR is mostly stable when the sample number is sufficient.The lower the natural probability of LURR,the more the precursory is information it may contain.The influence of Y3 resulting from the sample number and the magnitude range of events is also discussed. 相似文献
36.
The Turpan-Harmi (abbreviated to Tuha below) Basin is a typical basin of coal-generated oil accumulation in China. The Middle-Lower
Jurassic coal measures are considered the main source beds. Hence, both desmocollinite and suberinite are considered the contributors
for coal-generated oil. Principal geochemical features of the crude oil in the Tuha Basin are rich in alkanes (70%—80%), high
pristane/phytane ratio (6—8), abundant heavy carbon isotope (δ13C PDB= -26%–-23%) and absolute GP sterane predominance. The hydrocarbon generation process from the coal series is characterized
by multistages, early generation and early expulsion. 相似文献
37.
Results of numerical simulation studies of processes associated with Stimulated Electromagnetic Emission (SEE) produced during ionospheric heating experiments are presented. A one-dimensional magnetized electrostatic Particle-In-Cell (PIC) simulation model with uniform plasma density is used to investigate electrostatic wave generation in the region where the pump frequency ω0 approximately equals the upper hybrid frequency ωuh. In particular, the simulation plasma is driven with a uniform oscillating electric field to represent the long wavelength pump wave and power spectra of the electrostatic waves produced are taken. The pump wave frequency and amplitude are varied to consider the effects on the simulation power spectrum. The upper hybrid frequency in the model is varied through harmonics of the electron cyclotron frequency Ωce to consider the effects of stepping the pump frequency through cyclotron harmonics. The power spectrum from the simulation plasma is richly structured. The resulting power spectra show sidebands upshifted and downshifted from the pump frequency by multiples of the lower hybrid frequency ωlh. The structure of the spectrum is highly sensitive to the proximity of the upper hybrid frequency to the cyclotron harmonic frequencies. 相似文献
38.
Budd—Chiari综合征的CT评价 总被引:2,自引:0,他引:2
回顾性分析了52例Budd-Chiari综合征的CT表现,CT显示肝尾叶增大50例(96%),肝脏呈低度密度或密度不均,42例(81%)肝静脉未明显,22例(42%)见有肝内侧枝血管,49例(94%)有肝外侧枝血管,作者认为CT检查对Budd-Chiari综合征有较高的诊断价值。 相似文献
39.
Mineralization Ages of the Jiapigou Gold Deposits,Jilin 总被引:1,自引:0,他引:1
Li Junjian Shen Baofeng Mao Debao Li Shuangbao Zhou Huifang Cheng Yuming Tianjin Institute of Geology Mineral Resources Chinese Academy of Geological Sciences Tianjin Nonferrous Metal Geological Exploration Bureau Changchun Jilin 《《地质学报》英文版》1997,71(2):180-188
The Jiapigou gold deposits are typical vein type deposits associated withArchaean greenstone belts in China. According to the crosscutting relationships between dykesand auriferous veins, single hydrothermal zircon U-Pb dating and quartz K-Ar,~(40)Ar-~(39)Ar andRb-Sr datings, the main mineralization stage of the Jiapigou deposit has been determined to be2469-2475 Ma, while mineralization superimposition on the gold deposit occurred in1800-2000 Ma and 130-272 Ma. They form a mineralization framework of one oldermetallogenic epoch (Late Archaean-Early Proterozoic) and one younger metallogenic epoch(Mesozoic) of gold deposits in Archaean greenstone belts in China. 相似文献
40.
哺乳动物群指示的气候旋回——以周口店早更新世哺乳动物群为例 总被引:2,自引:0,他引:2
文章根据对周口店地区四个哺乳动物群的分析,讨论了该区早更新世气候及生态环境的变迁。第18地点显示了约1.90MaB.P.的干凉气候和森林—草原植被。第12地点指示了1.70MaB.P.的湿热气候和茂密森林生态环境。东洞则记录了1.20MaB.P.的干冷气候和草原景观。到第9地点时(约1.00~0.90MaB.P.),气候炎热,森林和草原植被同时发育 相似文献