全文获取类型
收费全文 | 62801篇 |
免费 | 10163篇 |
国内免费 | 13887篇 |
专业分类
测绘学 | 5252篇 |
大气科学 | 7184篇 |
地球物理 | 11702篇 |
地质学 | 35484篇 |
海洋学 | 7794篇 |
天文学 | 4794篇 |
综合类 | 4143篇 |
自然地理 | 10498篇 |
出版年
2024年 | 335篇 |
2023年 | 935篇 |
2022年 | 1860篇 |
2021年 | 2118篇 |
2020年 | 2210篇 |
2019年 | 2505篇 |
2018年 | 2033篇 |
2017年 | 2290篇 |
2016年 | 2553篇 |
2015年 | 2691篇 |
2014年 | 3315篇 |
2013年 | 3210篇 |
2012年 | 3693篇 |
2011年 | 3859篇 |
2010年 | 3325篇 |
2009年 | 4160篇 |
2008年 | 3990篇 |
2007年 | 4435篇 |
2006年 | 4352篇 |
2005年 | 3760篇 |
2004年 | 3598篇 |
2003年 | 3385篇 |
2002年 | 2969篇 |
2001年 | 2576篇 |
2000年 | 2307篇 |
1999年 | 2180篇 |
1998年 | 1915篇 |
1997年 | 1639篇 |
1996年 | 1513篇 |
1995年 | 1256篇 |
1994年 | 1252篇 |
1993年 | 1083篇 |
1992年 | 869篇 |
1991年 | 622篇 |
1990年 | 529篇 |
1989年 | 462篇 |
1988年 | 322篇 |
1987年 | 219篇 |
1986年 | 140篇 |
1985年 | 93篇 |
1984年 | 39篇 |
1983年 | 29篇 |
1982年 | 37篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1979年 | 34篇 |
1978年 | 41篇 |
1977年 | 25篇 |
1975年 | 4篇 |
1954年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Janis Britals 《Celestial Mechanics and Dynamical Astronomy》1992,54(4):305-316
It is shown in this paper how to build a canonical transformation of variables, so that the eccentric anomaly becomes the new independent variable. In the case of eccentric elliptical orbits it changes the equations of motion so, that they can be integrated analytically to any order of approximation comparatively easy. 相似文献
2.
3.
4.
5.
6.
中国古生教授学会微体古生物学分会举行代表大会和学术年会中国古竽物学会微体古物学分会第五次会员代表大分暨第六次不术年会于1996年1月24日到30日在福州市召开。来自全国地质、石油、煤炭的和产、科研和大学的100多位代表参加了这次大会和学术研讨。大会共... 相似文献
7.
8.
R. PALMERI M. L. FREZZOTTI G. GODARD R. J. DAVIES 《Journal of Metamorphic Geology》2009,27(9):685-705
Monocrystalline quartz inclusions in garnet and omphacite from various eclogite samples from the Lanterman Range (Northern Victoria Land, Antarctica) have been investigated by cathodoluminescence (CL), Raman spectroscopy and imaging, and in situ X‐ray (XR) microdiffraction using the synchrotron. A few inclusions, with a clear‐to‐opalescent lustre, show ‘anomalous’ Raman spectra characterized by weak α‐quartz modes, the broadening of the main α‐quartz peak at 465 cm?1, and additional vibrations at 480–485, 520–523 and 608 cm?1. CL and Raman imaging indicate that this ‘anomalous’α‐quartz occurs as relicts within ordinary α‐quartz, and that it was preserved in the internal parts of small quartz inclusions. XR diffraction circular patterns display irregular and broad α‐quartz spots, some of which show an anomalous d‐spacing tightening of ~2%. They also show some very weak, hazy clouds that have d‐spacing compatible with coesite but not with α‐quartz. Raman spectrometry and XR microdiffraction characterize the anomalies with respect to α‐quartz as (i) a pressure‐induced disordering and incipient amorphization, mainly revealed by the 480–485 and 608‐cm?1 Raman bands, together with (ii) a lattice densification, evidenced by d‐spacing tightening; (iii) the cryptic development of coesite, 520–523 cm?1 being the main Raman peak of coesite and (iv) Brazil micro‐twinning. This ‘anomalous’α‐quartz represents the first example of pressure‐induced incipient amorphization of a metastable phase in a crustal rock. This issue is really surprising because pressure‐induced amorphization of metastable α‐quartz, observed in impactites and known to occur between 15 and 32 GPa during ultrahigh‐pressure (UHP) experiments at room temperature, is in principle irrelevant under normal geological P–T conditions. A shock (due to a seism?) or a local overpressure at the inclusion scale (due to expansion mismatch between quartz and its host mineral) seem the only geological mechanisms that can produce such incipient amorphization in crustal rocks. This discovery throws new light on the modality of the quartz‐coesite transition and on the pressure regimes (non‐lithostatic v. lithostatic) during high‐pressure/UHP metamorphism. In particular, incipient amorphization of quartz could favour the quartz‐coesite transition, or allow the growth of metastable coesite, as already experimentally observed. 相似文献
9.
10.
根据印度洋西北部鸢乌贼(Sym plectoteuthis oualaniensis)作业渔场的现场调查数据.分析了作业水深、作业时段、摄食等级和月相等因子对手钓上钩率的影响。统计表明.晚上、午夜和凌晨3个不同时段和不同作业水深对手钓上钩率均有显著性影响。3个时段中,其摄食等级呈先低后高再低的现象。午夜和凌展,上钩率的变化趋势与摄食等级的变化趋势呈显著的负相关。在月相的影响下.离朔日三四天之前,手钓产量呈上升趋势;离望日五六天之前。手钓产量呈明显的下降趋势。 相似文献