全文获取类型
收费全文 | 12848篇 |
免费 | 1647篇 |
国内免费 | 1999篇 |
专业分类
测绘学 | 606篇 |
大气科学 | 2111篇 |
地球物理 | 2940篇 |
地质学 | 6587篇 |
海洋学 | 1341篇 |
天文学 | 825篇 |
综合类 | 991篇 |
自然地理 | 1093篇 |
出版年
2024年 | 30篇 |
2023年 | 129篇 |
2022年 | 434篇 |
2021年 | 488篇 |
2020年 | 391篇 |
2019年 | 487篇 |
2018年 | 711篇 |
2017年 | 667篇 |
2016年 | 738篇 |
2015年 | 526篇 |
2014年 | 727篇 |
2013年 | 829篇 |
2012年 | 748篇 |
2011年 | 775篇 |
2010年 | 825篇 |
2009年 | 761篇 |
2008年 | 669篇 |
2007年 | 684篇 |
2006年 | 521篇 |
2005年 | 401篇 |
2004年 | 293篇 |
2003年 | 326篇 |
2002年 | 407篇 |
2001年 | 425篇 |
2000年 | 385篇 |
1999年 | 438篇 |
1998年 | 350篇 |
1997年 | 353篇 |
1996年 | 305篇 |
1995年 | 274篇 |
1994年 | 254篇 |
1993年 | 208篇 |
1992年 | 186篇 |
1991年 | 141篇 |
1990年 | 120篇 |
1989年 | 99篇 |
1988年 | 86篇 |
1987年 | 48篇 |
1986年 | 46篇 |
1985年 | 40篇 |
1984年 | 31篇 |
1983年 | 33篇 |
1982年 | 20篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1969年 | 5篇 |
1958年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
162.
163.
164.
165.
166.
167.
SOHO/MDI magnetograms are used to analyze the time variations in the magnetic parameters of the active region (AR) NOAA 10486, which was part of a large activity complex that passed over the solar disk from October 26 to 31, 2003, during solar cycle 23. The results are compared with X-ray flares in the AR and the parameters of coronal mass ejections associated with the AR. The time variations in the distributions of themagnetic-field strengths associated with the total magnetic flux (Fa), the flux imbalance between the northern and southern polarities (Im), the complexity of the field, as a measure of the mutual overlapping of the opposite polarities (Co), and the tilt angle of the magnetic axis (An) are considered. The time variations in the free energy accumulated in current sheets of ARs were traced using a parameter introduced for this purpose (Sh). The following results were obtained. First, the parameters Fa, Im, Co, An, and Sh quantitatively describe the current state of the AR and can be used to trace and analyze the dynamical evolution of its magnetic field. Second, variations in the magnetic-field-strength distributions and the mean values of Fa, Im, Co, An, and Sh are associated with flares and coronal mass ejections, and the variations have considerable amplitudes. Third, the parameter Sh characterizing the degree to which the magnetic field is non-potential in regions adjacent to the main neutral line increases before eruptive events, and is thus particular interest for monitoring the states of ARs in real time. Fourth, the magnetic field of the AR manifests a sort of quasi-elasticity, so that the field structure is restored after active events, on average, within 1–3 h. 相似文献
168.
The statistical dependence of τ/(DM)2 (the ratio of the broadening of a pulsar pulse due to scattering in the interstellar medium to the square of the pulsar’s dispersion measure) on the pulsar’s dispersionmeasure, Galactic coordinates, age, and the angular distance to the nearest supernova remnant are studied. This parameter describes the relative level of electron density fluctuations in the turbulent interstellar plasma. It is shown that the interstellar plasma turbulence level is three orders of magnitude higher in the spiral arms of the Galaxy than outside the arms. The plasma turbulence level is approximately an order of magnitude higher in the Galactic arms, in regions within ?0.3° of supernova remnants, than outside these regions. We conclude that the source of energy for the turbulence in the Galactic arms is supernova explosions in the denser medium there. 相似文献
169.
170.
Based on the determination of composition of volcanic volatiles and petrologic estimation of the total mass of volatiles erupted,
we showed important advances in the study of the impact of Mesozoic and Cenozoic volcanic activities on paleo-environmental
changes in China. The volcanic activities include western Liaoning and Zhangjiakou Mesozoic intermediate-acidic explosive
eruptions, southern Tibet and Shanwang Cenozoic volcanism, and Mt. Changbai volcanic eruption around one thousand years ago.
The paper predominantly discusses the earth’s surface temperature changes, ozone depletion, acidic rain formation and mass
mortalities of vertebrate induced by the Mesozoic and Cenozoic volcanism in China.
__________
Translated from Bulletin of Mineralogy, Petrology and Geochemistry, 2007, 26(4): 319–322 [译自: 矿物岩石地球化学通报] 相似文献