全文获取类型
收费全文 | 327篇 |
免费 | 13篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 9篇 |
地球物理 | 84篇 |
地质学 | 142篇 |
海洋学 | 22篇 |
天文学 | 61篇 |
综合类 | 5篇 |
自然地理 | 20篇 |
出版年
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 16篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 18篇 |
2012年 | 22篇 |
2011年 | 16篇 |
2010年 | 16篇 |
2009年 | 21篇 |
2008年 | 17篇 |
2007年 | 16篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 8篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1995年 | 4篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 6篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1975年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 4篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1967年 | 1篇 |
1965年 | 3篇 |
1964年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有353条查询结果,搜索用时 15 毫秒
121.
V. V. Emel’yanenko O. P. Popova N. N. Chugai M. A. Shelyakov Yu. V. Pakhomov B. M. Shustov V. V. Shuvalov E. E. Biryukov Yu. S. Rybnov M. Ya. Marov L. V. Rykhlova S. A. Naroenkov A. P. Kartashova V. A. Kharlamov I. A. Trubetskaya 《Solar System Research》2013,47(4):240-254
Various observational data including infrasound, seismic, optical (onboard) monitoring, ground video and photo records, and evidence from witnesses of the Chelyabinsk event on February 15, 2013, have been analyzed. The extensive material gathered has provided a base for investigations of the physical properties of the object, the results of which are discussed. A bolide light curve is constructed, which shows a multiplicity of flashes. Estimations of the energy of the meteoroid explosion, which took place in the atmosphere at an altitude of about 23 km, show evidence of the formation of a high-power shock wave equivalent to 300–500 kilotons of TNT. The object diameter corresponding to this energy falls within the range 16–19 m. The trajectory of the meteor is outlined. It is preliminarily concluded that the Chelyabinsk meteorite was a representative the Apollo asteroid family. 相似文献
122.
Penelope J. WOZNIAKIEWICZ Anton T. KEARSLEY Hope A. ISHII Mark J. BURCHELL John P. BRADLEY Nick TESLICH Mike J. COLE Mark C. PRICE 《Meteoritics & planetary science》2012,47(4):660-670
Abstract– Samples returned by the Stardust mission from comet 81P/Wild 2 provide an unequaled opportunity to investigate cometary formation and evolution. Crystalline silicates have been identified in impact craters in Stardust Al foil, yet their origin is ambiguous. They may be original cometary components, or they may have grown from melt generated by impact. We have now studied experimental impacts of the calcium silicate mineral wollastonite, using scanning and transmission electron microscopy to document the relationship between impact feature shape and crystal lattice orientation in impact residue. Wollastonite can have a characteristic acicular habit, forming crater shapes that indicate crystal orientation upon impact. From extracted impact residue, we determined the lattice orientation of crystalline material for comparison with the whole particle orientation. We assume that crystallization from melt, without surviving seed nuclei, should result in randomly oriented crystallite growth, with no preferred direction for individual crystals. However, we find that the majority of crystalline material in the residue retains b‐axis orientation parallel to the long axis of the crater form. This, together with impact parameter calculations and lack of Al incorporation by the residue (suggesting melting did not occur), indicates that these crystals and, by analogy, the majority of Al‐free crystalline silicates in Stardust foil, are surviving remnants of the impactor. Furthermore, amorphous wollastonite residue probably did not form via melting and subsequent quenching, but instead by high‐pressure amorphization or degradation of unquenchable phases. Finally, one crystal studied appears to be a new high‐pressure/temperature polymorph of CaSiO3, indicating that such polymorphs may be observed in Stardust residues in craters. 相似文献
123.
The interplay between streamwise flow,curvature-induced secondary flow,sediment transport and bed morphology leads to the formation of a typical bar-pool bed morphology in open-channel bends.The associated scour at the outer bank and deposition at the inner bank may endanger the outer bank’s stability or reduce the navigable width of the channel.Previous preliminary laboratory experiments in a sharply curved flume with a fixed horizontal bed have shown that a bubble screen located near the outer bank can generate an additional secondary flow located between the outer bank and the curvature-induced secondary flow and with a sense of rotation opposite to the latter.This bubble-induced secondary flow redistributes velocities and bed shear stresses.The reported study investigates the implications of a bubble screen on the flow and the morphology in configurations with mobile bed.Velocity measurements show that the bubble-induced secondary flow shifts the curvature-induced secondary flow in inwards direction and reduces its strength.The bubble screen considerably reduces morphological gradients.Maximum bend scour is reduced by about 50%and occurs further away from the outer bank where it does not endanger the bank stability anymore.The location of maximum scour coincides with the junction of the curvature-induced and bubble-induced secondary flows.At this same location,the maximum streamwise velocities and maximum vertical velocities impinging on the bed also occur,which indicates their importance with respect to the formation of bend scour.The bubble screen also substantially reduced deposition at the inner bank.These preliminary experiments show the potential of a bubble screen to influence and modify the bed morphology. 相似文献
124.
A model with short computational time has previously been developed to predict the rate-dependent gas/oil ratio (GOR) from
a horizontal well. The oil flow towards the wellbore is based on a one-dimensional model by Konieczek. The model performs
remarkably well for medium-time production optimization (weeks, months), while the predictions during the first days after
a large change in the production can be poor. An improved one-dimensional model for the flow towards the wellbore is proposed,
where the oil flow is treated as a superposition of three terms:
1) |
Radial flow towards the wellbore and towards a mirror well. 相似文献
125.
126.
Yuanming Pan Mao Mao Zucheng Li Sanda M. Botis Rudolf I. Mashkovtsev Anton Shatskiy 《Physics and Chemistry of Minerals》2012,39(8):627-637
Single-crystal electron paramagnetic resonance spectra of electron-irradiated stishovite, measured at temperatures from 3.5 to 294?K, reveal three S?=?1/2 radiation-induced defects: an aluminum-associated oxygen hole center and two nd 1 centers (Ti3+ and W5+). The aluminum-associated oxygen hole center, characterized by an orthorhombic site symmetry, coaxial matrices of the electronic Zeeman g, nuclear hyperfine A(27Al) and nuclear quadrupole P(27Al), and the orientation of the g-minimum axis along an O–O direction and those of the unique A(27Al) and P(27Al) axes perpendicular to the O–O direction, is an Al–O2 3? center, with the unpaired electron equally distributed on two equatorial oxygen atoms of a substitutional Al3+ ion at the octahedral Si site. Fully optimized Al-doped structure, theoretical 27Al nuclear hyperfine and quadrupole coupling constants and directions, and 3D spin densities from periodic hybrid density functional theory calculations provide further support for this structural model. Spin Hamiltonian parameters of the Ti3+ and W5+ centers, which are confirmed by their diagnostic 47Ti, 49Ti and 183W hyperfine structures, arise from electron trapping on substitutional Ti4+ and W6+ ions at the octahedral Si site. 相似文献
127.
A. I. Zakharov A. V. Mironov M. E. Prokhorov A. V. Biryukov O. Yu. Stekol’shchikov M. S. Tuchin 《Astronomy Reports》2013,57(3):195-211
We describe goals and principles for the realization the Lyra-B space experiment onboard the International Space Station, which is currently being prepared at the Sternberg Astronomical Institute. The main goal of the experiment is to carry out a high-accuracy, multicolor all-sky survey of stars down to 16 m –17 m . The detailed structure of the expected observational data, their possible scientific use, and a number of technical problems are discussed. 相似文献
128.
Orange, ochre-coloured, light green and dark blue varieties of kyanite, ideally Al2SiO5, from Loliondo, Tanzania, have been characterised by electron microprobe analysis and polarised infrared and optical absorption spectroscopy. All colour varieties show elevated Fe contents of 0.39 to 1.31 wt.% FeO, but Ti contents only in the range of the EMP detection limit. Orange and ochre-coloured crystals have Mn contents of 0.23 and 0.06 wt.% MnO, respectively, the dark blue kyanite contains 0.28 wt.% Cr2O3, while the light green sample is nearly free from transition metal cations other than Fe. Polarised infrared spectra reveal OH defect concentrations of 3 to 17 wt.ppm H2O with structural OH defects partially replacing the OB (O2) oxygen atoms. Polarised optical absorption spectra show that the colour of all four varieties is governed by crystal field d-d transitions of trivalent cations, i.e. Fe3+ (all samples), Mn3+ (orange and ochre) and Cr3+ (blue kyanite), replacing Al in sixfold coordinated triclinic sites of the kyanite structure. Intervalence charge transfer, the prevalent colour-inducing mechanism in ‘usual’ (Cr-poor) blue kyanites, seems to play a very minor, if any, role in the present samples. Crystal field calculations in both a ‘classic’ tetragonal and in the semiempirical Superposition Model approach, accompanied by distance- and angle-least-squares refinements, indicate that Fe3+ preferably occupies the Al4 site, Cr3+ prefers the Al1 and Al2 sites, and Mn3+ predominantly enters the Al1 site. In each case specific local relaxation effects were observed according to the crystal chemical preferences of these transition metal cations. Furthermore, the high values obtained in the calculations for the interelectronic repulsion parameter Racah B correspond to a high ionic contribution to Me3+–O bonding in the kyanite structure. In the particular case of the blue sample, band positions specifically related to the high Racah B value enable this ‘unusual’ type of blue colouration of kyanite solely due to Cr3+ cations. 相似文献
129.
岩溶表层带水生动物研究进展 总被引:2,自引:1,他引:1
本文旨在介绍岩溶表层带水生生态研究中微小甲壳类生物的最新研究进展,相关研究国内还少有涉及。岩溶表层带不仅仅是岩溶地下含水层的一个重要组成,而且是岩溶发育的活跃地带,同时也是大量地下生物生存的栖息地。目前,岩溶表层带内甲壳类主要采自洞穴滴水,残留的滴水水洼以及裂隙中的水体。这些甲壳类主要是桡足类,也有其他甲壳类,如端足目和介形虫,它们主要为暗层生物(stygobiont),也包括一些陆生物种。以斯洛文尼亚为例,在所调查的洞穴中平均每个洞穴有近9个暗层桡足类物种,为了适应表层带特殊的地质环境,这些物种在形体上存在适当的进化。表层带的众多地质因子如顶板厚度、栖息地的连通性、及栖息地的大小等,以及水文因子包括水文动态特征、水化学特征等,都对这些物种的组成与分布有较大的影响。虽然岩溶表层带及其水生动物的独特性和重要性已逐步得到了许多地质学家和生物学家的认可,但还有很多问题有待进一步的解答,譬如邻近群落间差异性,以及桡足类对非饱和带水流指示作用等。 相似文献
130.
|