全文获取类型
收费全文 | 105088篇 |
免费 | 1651篇 |
国内免费 | 1439篇 |
专业分类
测绘学 | 3241篇 |
大气科学 | 8136篇 |
地球物理 | 20941篇 |
地质学 | 39743篇 |
海洋学 | 8082篇 |
天文学 | 19635篇 |
综合类 | 2289篇 |
自然地理 | 6111篇 |
出版年
2021年 | 399篇 |
2020年 | 537篇 |
2019年 | 536篇 |
2018年 | 7356篇 |
2017年 | 6693篇 |
2016年 | 4907篇 |
2015年 | 1329篇 |
2014年 | 1583篇 |
2013年 | 3378篇 |
2012年 | 3212篇 |
2011年 | 6593篇 |
2010年 | 5790篇 |
2009年 | 6874篇 |
2008年 | 5773篇 |
2007年 | 6447篇 |
2006年 | 2558篇 |
2005年 | 2781篇 |
2004年 | 2915篇 |
2003年 | 2778篇 |
2002年 | 2354篇 |
2001年 | 1834篇 |
2000年 | 1819篇 |
1999年 | 1518篇 |
1998年 | 1514篇 |
1997年 | 1481篇 |
1996年 | 1275篇 |
1995年 | 1209篇 |
1994年 | 1091篇 |
1993年 | 995篇 |
1992年 | 944篇 |
1991年 | 801篇 |
1990年 | 1012篇 |
1989年 | 850篇 |
1988年 | 752篇 |
1987年 | 926篇 |
1986年 | 818篇 |
1985年 | 1022篇 |
1984年 | 1183篇 |
1983年 | 1125篇 |
1982年 | 1016篇 |
1981年 | 992篇 |
1980年 | 851篇 |
1979年 | 816篇 |
1978年 | 867篇 |
1977年 | 789篇 |
1976年 | 754篇 |
1975年 | 695篇 |
1974年 | 703篇 |
1973年 | 709篇 |
1972年 | 442篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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
62.
63.
We study the self-consistent, linear response of a galactic disc to vertical perturbations, as induced, say, by a tidal interaction. We calculate the self-gravitational potential corresponding to a non-axisymmetric, self-consistent density response of the disc using the Green's function method. The response potential is shown to oppose the perturbation potential because the self-gravity of the disc resists the imposed potential, and this resistance is stronger in the inner parts of a galactic disc. For the m = 1 azimuthal wavenumber, the disc response opposes the imposed perturbation up to a radius that spans a range of 4–6 disc scalelengths, so that the disc shows a net warp only beyond this region. This physically explains the well known but so far unexplained observation that warps typically set in beyond this range of radii. We show that the inclusion of a dark matter halo in the calculation only marginally changes (by ∼10 per cent) the radius for the onset of warps. For perturbations with higher azimuthal wavenumbers, the net signature of the vertical perturbations can only be seen at larger radii – for example, beyond 7 exponential disc scalelengths for m = 10 . Also, for the high- m cases, the magnitude of the negative disc response due to the disc self-gravity is much smaller. This is shown to result in corrugations of the mid-plane density, which explains the puzzling scalloping with m = 10 detected in H i in the outermost regions ∼30 kpc in the Galaxy. 相似文献
64.
Stress wave attenuation across fractured rock masses is a great concern of underground structure safety. When the wave amplitude is large, fractures experience nonlinear deformation during the wave propagation. This paper presents a study on normal transmission of P‐wave across parallel fractures with nonlinear deformational behaviour (static Barton–Bandis model). The results show that the magnitude of transmission coefficient is a function of incident wave amplitude, nondimensional fracture spacing and number of fractures. Two important indices of nondimensional fracture spacing are identified, and they divide the area of nondimensional fracture spacing into three parts (individual fracture area, transition area and small spacing area). In the different areas, the magnitude of transmission coefficient has different trends with nondimensional fracture spacing and number of fractures. In addition, the study reveals that under some circumstances, the magnitude of transmission coefficient increases with increasing number of fractures, and is larger than 1. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
65.
AGGLOMERATION AND RADIATION EFFECT OF THE PULL OF URBANIZATION 总被引:2,自引:1,他引:1
QIJin-li 《中国地理科学(英文版)》2003,13(3):224-227
In order to explore the train of thought for China‘s urbanizing development and coordinated rural eco-nomic development, and to find good ways of solving rural problems through urbanization, this paper absorbs the push-and-pull forces theory and the systematic dynamic theory in the traditional population migration theories, views urbanization as a dynamic system, makes research on the push-and-pull mechanism of urbanization. The pulling power of urbanization is analyzed according to two aspects, the agglomeration effect and the radiation effect of cities. The agglomeration effect provides continuous propelling force for urbanization, and the radiation effect further accelerates the urbanization process by pushing forward the development of rural economy. Of course, the slow de-velopment of urbanization can result in the hindrance to rural economic development. 相似文献
66.
Carlos J.A.P. Martins 《Astrophysics and Space Science》2003,283(4):439-444
I briefly present the Organizing Committee's and my own motivation for organizing this workshop, and I suggest a few key questions
for which we will try to find possible answers in the coming days.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
67.
68.
HUXue-lian CHENGCheng-qi WUDe-wen MAAi-nai 《中国地理科学(英文版)》2003,13(1):84-90
Based on the analysis of the development of GIS technology and application,this paper brought forward the concept of GoGIS,namely Cooperative GIS ,CoGIS is GIS facing group-users and supporting human-human interaction,which makes it differ from the former GISs,Then,the characteristics of general Computer Spport Cooperative Work (CSCW)applications and the complexity of Geographic Information Science were analyzed,and the conclusion the CoGIS was not a simple GIS layer on CSCW was reached,Further,this paper gaver the hierarchical architecture of CoGIS,and analyzed the coperative platform in detail from the following:1)basic elements;2) collaboration patterns;3) cooperation control mechanism;4) synchronization mechanism;5) security and 6) group communication and so on.With those,the problems about GIS applications are discussed,such as 1)distributed multi-source GIS information and knowledge sharing platform;2)the fusion and visualization of GIS information;3)virtual reality cooperative modeling;4) dymamic simulation;5)expert system and 6) decision-making.Finally,this paper analyzed CoGIS application mode in brief. 相似文献
69.
70.