全文获取类型
收费全文 | 88604篇 |
免费 | 28997篇 |
国内免费 | 54347篇 |
专业分类
测绘学 | 12778篇 |
大气科学 | 26830篇 |
地球物理 | 21937篇 |
地质学 | 65468篇 |
海洋学 | 23718篇 |
天文学 | 1778篇 |
综合类 | 8758篇 |
自然地理 | 10681篇 |
出版年
2024年 | 611篇 |
2023年 | 1619篇 |
2022年 | 3988篇 |
2021年 | 4985篇 |
2020年 | 4955篇 |
2019年 | 8075篇 |
2018年 | 7756篇 |
2017年 | 7371篇 |
2016年 | 7386篇 |
2015年 | 7672篇 |
2014年 | 7294篇 |
2013年 | 8523篇 |
2012年 | 8861篇 |
2011年 | 8887篇 |
2010年 | 8831篇 |
2009年 | 7988篇 |
2008年 | 7483篇 |
2007年 | 7219篇 |
2006年 | 6653篇 |
2005年 | 5855篇 |
2004年 | 5144篇 |
2003年 | 4139篇 |
2002年 | 3936篇 |
2001年 | 3621篇 |
2000年 | 3096篇 |
1999年 | 2482篇 |
1998年 | 2133篇 |
1997年 | 2127篇 |
1996年 | 1758篇 |
1995年 | 1590篇 |
1994年 | 1428篇 |
1993年 | 1373篇 |
1992年 | 1193篇 |
1991年 | 889篇 |
1990年 | 851篇 |
1989年 | 686篇 |
1988年 | 578篇 |
1987年 | 428篇 |
1986年 | 371篇 |
1985年 | 277篇 |
1984年 | 316篇 |
1983年 | 182篇 |
1982年 | 235篇 |
1981年 | 158篇 |
1980年 | 121篇 |
1979年 | 134篇 |
1978年 | 61篇 |
1977年 | 55篇 |
1971年 | 54篇 |
1970年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Based on the δ13C and δ18O fluctuation of lacustrine carbonate, CaCO3 content and sporo-pollen data, a palaeoclimatic history of Bosten Lake during the Holocene has been outlined, several stages
of climatic changes are divided, and the following result es are obtained: (1) Palaeoclimatic changes revealed by carbonate
isotope around Bosten Lake are basically identical with that revealed by other geological records in Xinjiang. Environmental
changes presented apparent Westlies Style model: during cold period, relative humidity increased, δ18O, δ13C and CaCO3 appeared low; but in warm periods, the dry regime aggravated. (2) The temperature reflected by δ18O exist evident features being increase in the late period during the Holocene. Together with the δ13C, pollen and CaCO3 analyses, several cold and warm phases which are of broad regional significance can be identified. The warm peaks occurred
at about 11.0 ka B.P., 9.4 ka B.P., 7.5 ka B.P., 5.0 ka B.P., 3.0 ka B.P. and 2.0 ka B.P.; the cold peaks at 11.5 ka B.P.,
10.5 ka B.P., 8.8 ka B.P., 5.5 ka B.P., 3.3 ka B.P., 2.2 ka B.P. and 1.5 ka B.P.. (3) Several climatic events with the nature
of “abrupt climatic changes” are revealed in the periods of 11.0 ka B.P. −10.5 ka B.P., 9.4 ka B.P. −8.8 ka B.P., 5.5 ka B.P.
−5.0 ka B.P. and 2.0 ka B.P. −1.5 ka B.P.. (4) The results show that carbonate isotopic record of lacustrine sediment in arid
area is very sensitive to climatic changes, and may be play a very important role in understanding the features and mechanism
of palaeoclimatic changes. 相似文献
32.
33.
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
34.
We extrapolated the 3-D fields above the photosphere, taking the observed photospheric magnetic fields in the active regions NOAA 6659 and 7321 as the boundary conditions of a linear force-free field model, and detected the singular points of the 2-D fields in a plane at the chromospheric level. These singular points can be described with the Poincaré index. Singular points with the index of +1 correspond to concentrations of magnetic flux, and those with the index of -1 to the saddle points in the plane. All of these singular points are connected by the lanes demarcating the 2-D magnetic cells in the plane. It has been confirmed that these saddle points are the intersections between separators and planes intersecting the 3-D fields. From comparisons between kernels of flares occurring in both regions and the saddle points, we found that there is a close morphological relationship between distributions of the saddle points and flare kernels. The main results are as follows: (a) The flare kernels tend to appear in areas with concentrating 2-D saddle points. (b) The morphology of the kernels is exactly confined by the lanes in the plane at chromospheric level. These facts seem favourable for the viewpoint that solar flares are closely related to magnetic separatrices and separators. 相似文献
35.
本文在已有数据处理方法的基础上,利用近代数值逼近理论,给出了从时空域角度描述地壳垂直运动过程的一种具体的函数解析形式。最后给出了一个实际算例。 相似文献
36.
37.
Yunfei Bao Shengbo Chen 《东北亚地学研究》2006,9(1):100-108
IntroductionThe radiance leaving the earth-atmosphere sys-tem which can be sensed by a satellite borne ra-diometer is the sum of radiation emission fromtheearth surface and each atmospheric level that aretransmittedtothe top of the atmosphere.The radia-tion emissionfromthe earthsurface andthe radianceof each atmospheric level can be separated fromtheradiance at the top the atmospheric level a satellitemeasured.Thus,the earth surface parameters willbe retrieved from the surface radiance after a… 相似文献
38.
39.
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
40.
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