全文获取类型
收费全文 | 265224篇 |
免费 | 5003篇 |
国内免费 | 3367篇 |
专业分类
测绘学 | 6981篇 |
大气科学 | 19551篇 |
地球物理 | 55386篇 |
地质学 | 92868篇 |
海洋学 | 22208篇 |
天文学 | 57408篇 |
综合类 | 1042篇 |
自然地理 | 18150篇 |
出版年
2021年 | 2263篇 |
2020年 | 2598篇 |
2019年 | 2863篇 |
2018年 | 4425篇 |
2017年 | 4151篇 |
2016年 | 6188篇 |
2015年 | 4228篇 |
2014年 | 6913篇 |
2013年 | 14198篇 |
2012年 | 6859篇 |
2011年 | 8633篇 |
2010年 | 7739篇 |
2009年 | 10257篇 |
2008年 | 8944篇 |
2007年 | 8634篇 |
2006年 | 9708篇 |
2005年 | 7917篇 |
2004年 | 7780篇 |
2003年 | 7272篇 |
2002年 | 6813篇 |
2001年 | 6026篇 |
2000年 | 5969篇 |
1999年 | 5224篇 |
1998年 | 5244篇 |
1997年 | 5032篇 |
1996年 | 4680篇 |
1995年 | 4434篇 |
1994年 | 4108篇 |
1993年 | 3859篇 |
1992年 | 3640篇 |
1991年 | 3594篇 |
1990年 | 3769篇 |
1989年 | 3523篇 |
1988年 | 3306篇 |
1987年 | 3849篇 |
1986年 | 3409篇 |
1985年 | 4224篇 |
1984年 | 4740篇 |
1983年 | 4409篇 |
1982年 | 4315篇 |
1981年 | 3928篇 |
1980年 | 3637篇 |
1979年 | 3512篇 |
1978年 | 3489篇 |
1977年 | 3281篇 |
1976年 | 3046篇 |
1975年 | 2960篇 |
1974年 | 2914篇 |
1973年 | 3078篇 |
1972年 | 2025篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
751.
752.
Lithostratigraphical and lithofacies approaches used to interpret glacial sediments often ignore deformation structures that can provide the key to environment of formation. We propose a classification of deformation styles based on the geometry of structures rather than inferred environment of formation. Five styles are recognised: pure shear (P), simple shear (S), compressional (C), vertical (V) and undeformed (U). These dictate the first letter of the codes; the remaining letters conveying the evidence. This information can be used to reconstruct palaeostress fields and to infer physical properties of sediments when they deformed. Individual structures are not diagnostic of particular environments but the suite of structures, their relative scale, stratigraphical relationships, and orientation relative to palaeoslopes and to palaeoice‐flow directions can be used to infer the environment in which they formed. This scheme is applied at five sites in west Wales. The typical succession is interpreted as subglacial sediments overlain by meltout tills, flow tills and sediment flows. Paraglacial redistribution of glacial sediments is widespread. Large‐scale compressional deformation is restricted to sites where glaciers readvanced. Large‐scale vertical deformation occurs where water was locally ponded near the ice margin. There is no evidence for glaciomarine conditions. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
753.
754.
We present the results of our analysis of the RXTE observations for two transient sources, IGR J17091-3624 and IGR J18539+0727, in April 2003. The derived energy spectra of the sources and the power-density spectra of their light curves make it possible to classify them as low/hard-state X-ray binaries. The parameters of the power spectrum for IGR J18539+0727 lead us to tentatively conclude that the compact object in this binary is a black hole. 相似文献
755.
In this paper we show that a change in the signs of some of the metric components of the solution of the field equations for
the classical cosmic string results in a solution which we interpret as a time-dependent wall composed of tachyons. We show
that the walls have the property of focusing the paths of particles which pass through them. As an illustration of this focusing,
we demonstrate the results of a simple simulation of the interaction between one such tachyon wall and a rotating disk of
point masses. This interaction leads to the temporary formation of spiral structures. These spiral structures exist for a
time on the order of one galactic rotation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
756.
An additional investigation has been carried out of the rational model (Aslanov, 2000) of the separation of drops from the tops of the unstable wave formation on the molten surface of a meteoroid. The ratio of the wavelength of unstable hydrodynamic disturbances to the diameter of drops has been calculated in a mathematically closed form. Particular theoretical estimates of the size of the region of spraying of molten drops agree with prevailing sizes given in the known classification of the forms of meteoroid fragmentation. 相似文献
757.
Flux pile-up magnetic reconnection is traditionally considered only for incompressible plasmas. The question addressed in this paper is whether the pile-up scalings with resistivity are robust when plasma compressibility is taken into account. A simple analytical argument makes it possible to understand why the transition from a highly compressible limit to the incompressible one is difficult to discern in typical simulations spanning a few decades in resistivity. From a practical standpoint, however, flux pile-up reconnection in a compressible plasma can lead to anomalous electric resistivity in the current sheet and flare-like energy release of magnetic energy in the solar corona. 相似文献
758.
Late Cretaceous-Paleogene Palynostratigraphy from the Arkhara-Boguchan Brown Coal Mine of Zeya-Bureya Depression, Russia 总被引:1,自引:1,他引:0
Tatyana V. Kezina 《东北亚地学研究》2003,(2)
1IntroductionThe Arkhara-Boguchan brown coal mine is lo-cated in the western Arkhara depression,southeast-ern part of the Zea-Bureya Basin (Fig.1). Late Creta-ceous-Paleogene coal-bearing strata are well out-cropped at the Arkhara-Boguchan quarry. It contains four coal-bearing beds (in descending order): “Ve-likan”, “Promezhutochny”,“Dvoinoy”and “Nyzhny”, and composed of three sedimentary cycles (Fig.2). The lower cycle can be divided into two sub-cycles:the lowest sub-cycle is … 相似文献
759.
The present-day chemical and dynamical properties of the Milky Way are signatures of the Galaxy's formation and evolution.
Using a self consistent chemodynamical evolution code we examine these properties within the currently favoured paradigm for
galaxy formation – hierarchical clustering within a CDM cosmology. Our Tree N-body/Smoothed Particle Hydrodynamics code includes
a self-consistent treatment of gravity, hydrodynamics, radiative cooling, star formation, supernova feedback and chemical
enrichment. Two models are described which explore the role of small-scale density perturbations in driving the evolution
of structure within the Milky Way. The relationship between metallicity and kinematics of halo stars are quantified and the
implications for galaxy formation discussed. While high-eccentricity halo stars have previously been considered a signature
of `rapid collapse', we suggest that many such stars may have come from recently accreted satellites.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
760.
In the 19th century De la Rue, Stewart, and Loewy carried out a compilation of drawings and photographs of the solar sunspots corresponding to the interval 1832–1868. Using these drawings and photographs, they determined fortnightly values of the percentage of the solar photosphere covered by the sunspots. In this work, we have performed a spectral analysis of these data in order to determine possible periodic signals. In addition to the 11-year solar cycle, short cycles of about 330 days and 30–50 days have been recovered, lacking the 150–160 days period discovered by other authors using several solar activity indicators. 相似文献