全文获取类型
收费全文 | 15480篇 |
免费 | 3027篇 |
国内免费 | 3860篇 |
专业分类
测绘学 | 1080篇 |
大气科学 | 3424篇 |
地球物理 | 4036篇 |
地质学 | 7919篇 |
海洋学 | 1963篇 |
天文学 | 664篇 |
综合类 | 1558篇 |
自然地理 | 1723篇 |
出版年
2024年 | 57篇 |
2023年 | 245篇 |
2022年 | 670篇 |
2021年 | 814篇 |
2020年 | 640篇 |
2019年 | 760篇 |
2018年 | 876篇 |
2017年 | 793篇 |
2016年 | 893篇 |
2015年 | 734篇 |
2014年 | 930篇 |
2013年 | 878篇 |
2012年 | 826篇 |
2011年 | 923篇 |
2010年 | 904篇 |
2009年 | 875篇 |
2008年 | 740篇 |
2007年 | 751篇 |
2006年 | 639篇 |
2005年 | 610篇 |
2004年 | 428篇 |
2003年 | 425篇 |
2002年 | 479篇 |
2001年 | 469篇 |
2000年 | 510篇 |
1999年 | 739篇 |
1998年 | 608篇 |
1997年 | 604篇 |
1996年 | 578篇 |
1995年 | 480篇 |
1994年 | 441篇 |
1993年 | 433篇 |
1992年 | 345篇 |
1991年 | 275篇 |
1990年 | 208篇 |
1989年 | 180篇 |
1988年 | 156篇 |
1987年 | 87篇 |
1986年 | 87篇 |
1985年 | 54篇 |
1984年 | 41篇 |
1983年 | 27篇 |
1982年 | 49篇 |
1981年 | 16篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1962年 | 5篇 |
1958年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
11.
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
12.
13.
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
14.
15.
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
16.
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
17.
This paper proposes a multi‐level parallelized substructuring–frontal combined algorithm for the analysis of the problem of thermo/hydraulic/mechanical behaviour of unsaturated soil. Temperature, displacement, pore water pressure and pore air pressure are treated as the primary variables in a non‐linear analysis. Details are given firstly of the substructuring–frontal combined approach. The incorporation of the algorithm in a multi‐level parallel strategy is then discussed. The parallel processing can thus be carried out at different substructural levels. The method thus developed impacts, in a positive way, on both computer storage requirement and execution time. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
18.
Pco2 of air and seawater samples from the East China Sea(ECS) were measured in situ in autumn, 1994,Ocean currents,terrestrial fluviation,biological activities,etc.,Pco2 char-acters in air and seawater were investigated,CO2 flux and its character in the East China Sea are discussed on the basis of the Pco2 profiles of air and seawater,It was clear that the nearshore was the source of CO2;and tht the oulter sea area was the sink of CO2; and that the shelf area of the EXS is a net sink for atmospheric CO2 in autumn. 相似文献
19.
本文给出1993—1994年期间,用云南天文台1米望远镜折轴摄谱仪观测获得类太阳色球活动星。εEri的5个波段高分辨、高信噪比光谱,运用两种不同方法:谱线轮廓塞曼致宽分析和多重线统计分析法成功地测定了εEri的表面磁场强度和磁场的覆盖因子,并对这两种磁场测定方法作了简单的讨论. 相似文献
20.
1 INTRODUCTIONIn the previous paper (on et al. 1999, hereafter Paper I), we investigated the wavelength-dependence of four colltribution functions (CFs) derived from dmerent formal solutions andreferring to different emergellt quantities in the unpolarized case. Because one cannot generallyassign a single formation region to the whole line band in a real stellar atmosphere, e.g., the solaratmosphere, instead, the line formation region can be defined as the layers deviating farthestfrom t… 相似文献