全文获取类型
收费全文 | 18119篇 |
免费 | 3378篇 |
国内免费 | 4571篇 |
专业分类
测绘学 | 1545篇 |
大气科学 | 3864篇 |
地球物理 | 4401篇 |
地质学 | 8751篇 |
海洋学 | 2815篇 |
天文学 | 853篇 |
综合类 | 1783篇 |
自然地理 | 2056篇 |
出版年
2024年 | 82篇 |
2023年 | 281篇 |
2022年 | 789篇 |
2021年 | 908篇 |
2020年 | 808篇 |
2019年 | 830篇 |
2018年 | 946篇 |
2017年 | 854篇 |
2016年 | 1024篇 |
2015年 | 890篇 |
2014年 | 1090篇 |
2013年 | 1136篇 |
2012年 | 1053篇 |
2011年 | 1135篇 |
2010年 | 1058篇 |
2009年 | 1065篇 |
2008年 | 952篇 |
2007年 | 914篇 |
2006年 | 775篇 |
2005年 | 757篇 |
2004年 | 561篇 |
2003年 | 497篇 |
2002年 | 545篇 |
2001年 | 583篇 |
2000年 | 572篇 |
1999年 | 768篇 |
1998年 | 666篇 |
1997年 | 633篇 |
1996年 | 618篇 |
1995年 | 494篇 |
1994年 | 488篇 |
1993年 | 424篇 |
1992年 | 378篇 |
1991年 | 307篇 |
1990年 | 236篇 |
1989年 | 205篇 |
1988年 | 176篇 |
1987年 | 104篇 |
1986年 | 96篇 |
1985年 | 64篇 |
1984年 | 57篇 |
1983年 | 35篇 |
1982年 | 65篇 |
1981年 | 27篇 |
1980年 | 24篇 |
1979年 | 20篇 |
1978年 | 9篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1958年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
21.
同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数,研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度,结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近,叠积后实际重力观测与极移重力信号理论值之间的差异分别为0.4%和3.9%,说明超导重力仪可有效监测极移导致的重力变化。 相似文献
22.
23.
ImooUonONSCCisoneofthemosttwortantcausoffailureofstaiuleSsstalequipmentandfacilitieS.Studiesonunh0refacilitiesshowedthatanaddicchloridesolutionfilmcouldbefo~onthescheeofstalandthatstaiuleSSstalisinaCtivedissolutionstateinaedicchloridesolutionopinetal.,l99O;Gnanamoorthyetal.,l99O).ltisgenerallythoughtxthatSCCcannotoimrwhenthematerialisinaCtiveanodicdissolutionstate,soitsomcewithresultingcasualties(0ldfieldetal.,l99O)arousedattentiont0it.SomeSCCmeCanisrnsproposedpeuang,l988,Newmanctal.,… 相似文献
24.
概略地叙述了西宁地区的泥石流形成条件和形成机理,并将西宁地区泥石流划分为稀性泥石流类及泥石质泥石流种类。在此基础上提出防治泥石流灾害的意见。 相似文献
25.
26.
Hong-Guang Wang Guo-Jun Qiao Ren-Xin XuDepartment of Astronomy Peking University Beijing 《中国天文和天体物理学报》2003,3(5):443-452
The inner vacuum gap model has become the foundation stone of most theories on pulsar radio emission. The fundamental picture of this model is the sparking, which was conjectured to be induced by magnetic absorption of background gamma photons. However, a question is, can the sparking be triggered in the millisecond pulsars (MSPs) with magnetic fields (B) only about 108 G? We investigate this problem by including the pair production above the inner gap. Under the assumption that the magnetic field is dipolar, our results show the background gamma-ray emission can not be the key factor that triggers the sparking, at least not in MSPs with B - 108 G, if the temperature in the polar cap region is only so high as is observed (< 4 × 106 K). Some other mechanisms are required. 相似文献
27.
H. L. Xu S. Svanberg R. D. Cowan P.-H. Lefèbvre P. Quinet E. Biémont 《Monthly notices of the Royal Astronomical Society》2003,346(2):433-440
Radiative lifetime measurements were performed with time-resolved laser-induced fluorescence techniques for 24 levels of Nd ii in the energy range 20 500–32 500 cm−1 . For 17 levels, no previous experimental data exist. These results have allowed the testing of new theoretical calculations with the relativistic Hartree–Fock method taking configuration interactions and core-polarization effects into account, and a satisfying agreement has been found for this complex ion. A new set of calculated oscillator strengths, accurate within a few per cent for the strongest transitions, is presented for 107 lines of astrophysical interest appearing in the wavelength range 358.0–1100.0 nm. These results will be useful to evaluate abundance values of neodymium in chemically peculiar stars in relation with cosmochronology. 相似文献
28.
The dunes in estuary of Tumen River in China lie to the area between the Jiushaping and Fangchuan in the left bank of Tumen River (Fig.1). The dis-tance is about 15~20 km between the dunes and the coast. It ranges from China to D. P. R. Korea and Russia. The range of the height of dunes is about 15~20 m and the width is 100~200 m. By the re-connaissance, we protracted 9 section planes of the dunes and collected 40 sand samples of the dunes, and identified the sedimentary environment … 相似文献
29.
Hong-Qi Zhang Xing-Ming Bao Yin Zhang Ji-Hong Liu Shu-Dong Bao Yuan-Yong Deng Wei Li Jie Chen Jin-Ping Dun Jiang-Tao Su Juan Guo Xiao-Fan Wang Ke-Liang Hu Gang-Hua Lin Dong-Guang WangNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(6):491-494
We analyze the magnetic configurations of three super active regions, NOAA 10484, 10486 and 10488, observed by the Huairou Multi-Channel Solar Telescope (MCST) from 2003 October 18 to November 4. Many energetic phenomena, such as flares (including a X-28 flare) and coronal mass ejections (CMEs), occurred during this period. We think that strong shear and fast emergence of magnetic flux are the main causes of these events. The question is also of great interest why these dramatic eruptions occurred so close together in the descending phase of the solar cycle. 相似文献
30.