全文获取类型
收费全文 | 1277篇 |
免费 | 80篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 19篇 |
大气科学 | 104篇 |
地球物理 | 394篇 |
地质学 | 494篇 |
海洋学 | 89篇 |
天文学 | 219篇 |
综合类 | 2篇 |
自然地理 | 46篇 |
出版年
2023年 | 7篇 |
2021年 | 12篇 |
2020年 | 14篇 |
2019年 | 10篇 |
2018年 | 42篇 |
2017年 | 39篇 |
2016年 | 61篇 |
2015年 | 40篇 |
2014年 | 73篇 |
2013年 | 90篇 |
2012年 | 60篇 |
2011年 | 59篇 |
2010年 | 56篇 |
2009年 | 74篇 |
2008年 | 53篇 |
2007年 | 31篇 |
2006年 | 33篇 |
2005年 | 53篇 |
2004年 | 44篇 |
2003年 | 23篇 |
2002年 | 23篇 |
2001年 | 18篇 |
2000年 | 17篇 |
1999年 | 17篇 |
1998年 | 16篇 |
1997年 | 18篇 |
1996年 | 21篇 |
1995年 | 24篇 |
1994年 | 17篇 |
1993年 | 11篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1987年 | 21篇 |
1986年 | 11篇 |
1985年 | 13篇 |
1984年 | 18篇 |
1983年 | 25篇 |
1982年 | 19篇 |
1981年 | 22篇 |
1980年 | 11篇 |
1979年 | 20篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1975年 | 11篇 |
1974年 | 8篇 |
1973年 | 9篇 |
1972年 | 7篇 |
1969年 | 7篇 |
排序方式: 共有1367条查询结果,搜索用时 328 毫秒
1.
Effects of the geometry of two‐dimensional fractures on their hydraulic aperture and on the validity of the local cubic law 下载免费PDF全文
Flow through rough fractures is investigated numerically in order to assess the validity of the local cubic law for different fracture geometries. Two‐dimensional channels with sinusoidal walls having different geometrical properties defined by the aperture, the amplitude, and the wavelength of the walls' corrugations, the corrugations asymmetry, and the phase shift between the two walls are considered to represent different fracture geometries. First, it is analytically shown that the hydraulic aperture clearly deviates from the mean aperture when the walls' roughness, the phase shift, and/or the asymmetry between the fracture walls are relatively high. The continuity and the Navier–Stokes equations are then solved by means of the finite element method and the numerical solutions compared to the theoretical predictions of the local cubic law. Reynolds numbers ranging from 0.066 to 66.66 are investigated so as to focus more particularly on the effect of flow inertial effects on the validity of the local cubic law. For low Reynolds number, typically less than 15, the local cubic law properly describes the fracture flow, especially when the fracture walls have small corrugation amplitudes. For Reynolds numbers higher than 15, the local cubic law is valid under the conditions that the fracture presents a low aspect ratio, small corrugation amplitudes, and a moderate phase lag between its walls. 相似文献
2.
Published in Astrofizika, Vol. 38, No. 4, pp. 677–680, October–December, 1995. 相似文献
3.
Arnaud M. Aubourg E. Bareyre P. Br';ehin S. Caridroit R. de Kat J. Dispau G. Djidi K. Gros M. Lachièze-Rey M. Laigneau Y. Laurent B. Lesquoy E. Lavocat Ph. Magneville C. Mazeau B. Milsztajn A. Moscoso L. Pasquaud J. Paul B. Perrin P. Petibon J. Piret Y. Queinnec F. Rich J. Spiro M. de Trogoff J. Vigroux L. Zylberajch S. Ansari R. Cavalier F. Moniez M. Beaulieu J. P. Ferlet R. Grison Ph. Vidal-Madjar A. Adrianzyk G. Berger J. P. Burnage R. Delclite J. C. Kohler D. Magnan R. Richaud A. Guibert J. Moreau O. Tajahmady F. Baranne A. Maurice E. Prévôt L. Gry C. 《Experimental Astronomy》1994,4(3-4):265-278
A 20cm
2
CCD mosaic camera has been especially built to search for dark galactic halo objects by the gravitational microlensing effect. The sensitive area is made of 16 edge-buttable CCDs developped by Thomson-CTS, with 23×23 µm
2
pixels. The 35 kg camera housing and mechanical equipment is presented. The associated electronics and data acquisition system are described in a separate paper. The camera resides at the focal plane of a 40 cm, f/10, Ferson reflector. The instrument has been in operation since December 1991 at the La Silla Observatory (ESO). 相似文献
4.
Yannick Giraud-Héraud Jean Kaplan François De Volnay Martin Charling Tao Sylvaine Turck-Chièze 《Solar physics》1990,128(1):21-33
The Saclay solar evolution code is used to check the effect of WIMPs on solar evolution. In this paper we study the effects of various types of Cosmion-matter interactions, give constraints on the crosssections compatible with the measured neutrino rate of 2 SNU on chlorine, and relate these constraints to ongoing dark matter detection experiments.Unité associée au CNRS UA 280, F-75251 Paris Cedex 05, France.On leave from LPC, Collège de France. 相似文献
5.
6.
Claude R. Duguay Greg M. Flato Martin O. Jeffries Patrick Mnard Kim Morris Wayne R. Rouse 《水文研究》2003,17(17):3465-3483
A one‐dimensional thermodynamic model for simulating lake‐ice phenology is presented and evaluated. The model can be driven with observed daily or hourly atmospheric forcing of air temperature, relative humidity, wind speed, cloud amount and snowfall. In addition to computing the energy balance components, key model output includes the temperature profile at an arbitrary number of levels within the ice/snow (or the water temperature if there is no ice) and ice thickness (clear ice and snow‐ice) on a daily basis, as well as freeze‐up and break‐up dates. The lake‐ice model is used to simulate ice‐growth processes on shallow lakes in arctic, sub‐arctic, and high‐boreal forest environments. Model output is compared with field and remote sensing observations gathered over several ice seasons. Simulated ice thickness, including snow‐ice formation, compares favourably with field measurements. Ice‐on and ice‐off dates are also well simulated when compared with field and satellite observations, with a mean absolute difference of 2 days. Model simulations and observations illustrate the key role that snow cover plays on the seasonal evolution of ice thickness and the timing of spring break‐up. It is also shown that lake morphometry, depth in particular, is a determinant of ice‐off dates for shallow lakes at high latitudes. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
Claude Jaupart 《Bulletin of Volcanology》1991,54(1):1-9
Lava contains gas bubbles and hence is a compressible liquid whose density increases as a function of pressure. After eruption at the Earth's surface, it spreads at a rate which is a function of its thickness and it is compressed under its own weight. Therefore, both thickness and spreading rate are determined by a balance between viscous and compressible effects. Theoretical equations are derived for the shape and velocity of a compressible liquid spreading on a horizontal surface. Solutions are obtained for a fixed eruption rate Q. The radial extent of the flow increases proportional to t
1/2. A dimensionless number C is defined which characterizes the importance of flow compression:
, where 0 is bubbly lava density at atmospheric pressure, compressibility, viscosity and g the acceleration of gravity. C can be thought of as the ratio of two characteristic length-scales, one for compression effects and one for viscous effects. The larger C is, the more important compressibility effects are. As C is increased, the flow becomes thinner because the liquid is compressed more and more efficiently. Compressibility acts to smooth out variations of flow thickness, which provide the driving force. Thus, all else being equal, a compressible liquid flows less rapidly than an incompressible one. When trying to infer the effective viscosity of a flow from its spreading rate, the neglect of compressibility leads to an overestimate. The various factors which act to determine the distribution of gas bubbles in lava flows are reviewed and discussed quantitatively. Comparison with data from Obsidian Dome (Eastern California) shows that disequilibrium effects are important and that bubble resorption during burial in a thick flow is not a pervasive phenomenon. The analysis is applied to the 1979 dome of Soufrière de Saint Vincent (W.I.). An effective value of compressibility for this 100-m-thick dome is 1.5x10–6 Pa–1. This implies that, all else being equal, the viscosity of this lava may be overestimated by a factor of 5 if no account is taken of the compressible nature of the flow. 相似文献
8.
Geneviève Bordeleau Richard Martel Dirk Schäfer Guy Ampleman Sonia Thiboutot 《Environmental Geology》2008,55(2):385-396
Numerical modelling was done at the Cold Lake Air Weapons Range, Canada, to test whether the dissolved RDX and nitrate detected
in groundwater come from the same sources, and to predict whether contamination poses a threat to the surface water receptors
near the site. Military live fire training activities may indeed pose a risk of contamination to groundwater resources, however
field investigations on military bases are quite recent, and little information is available on the long-term behaviour of
munition residues related contaminants. Very limited information was available about the contaminant source zones, which were
assigned based on our knowledge of current training activities. The RDX plume was well represented with the model, but the
heterogeneous distribution of nitrate concentrations was more difficult to reproduce. It was nonetheless determined that both
contaminants originate from the same areas. According to the model, both contaminants should reach the nearby river, but concentrations
in the river should remain very low if the source zone concentration does not change. Finally, the model allowed the recommendation
of a new location for the main bombing target, which would offer added protection to the river and the lake into which it
flows. 相似文献
9.
Philippe E. Raison Regis Jardin Daniel Bouëxière Rudy J. M. Konings Thorsten Geisler Claudiu C. Pavel Jean Rebizant Karin Popa 《Physics and Chemistry of Minerals》2008,35(10):603-609
The crystallographic structures of the synthetic cheralite, CaTh(PO4)2, and its homolog CaNp(PO4)2 have been investigated by X-ray diffraction at room temperature. Rietveld analyses showed that both compounds crystallize in the monoclinic system and are isostructural to monazite LnPO4 (Ln = La to Gd). The space group is P21/n (I.T. = 14) with Z = 2. The refined lattice parameters of CaTh(PO4)2 are a = 6.7085(8) Å, b = 6.9160(6) Å, c = 6.4152(6) Å, and β = 103.71(1)° with best fit parameters R wp = 4.87%, R p = 3.69% and R B = 3.99%. For CaNp(PO4)2, we obtained a = 6.6509(5) Å, b = 6.8390(3) Å, c = 6.3537(8) Å, and β = 104.12(6)° and R wp = 6.74%, R p = 5.23%, and R B = 6.05%. The results indicate significant distortions of bond length and angles of the PO4 tetrahedra in CaTh(PO4)2 and to a lesser extent in CaNp(PO4)2. The structural distortions were confirmed by Raman spectroscopy of CaTh(PO4)2. A comparison with the isostructural compounds LnPO4 (Ln = Ce and Sm) confirmed that the substitution of the large rare earth trivalent cations with Ca2+ and Th4+ introduces a distortion of the PO4 tetrahedra. 相似文献
10.
Claude Cabanne 《Ocean & Coastal Management》1992,18(2-4)
The attraction of the coast of south Vendée is mainly due to its long stretches of sandy beaches and to the mildness of the weather. Following the Second World War, the number of tourists grew rapidly this being a popular family area with camping, caravanning, renting of lodgings, staying with friends or relatives, or second homes. This tourism development not only puts growing pressure on space, but also on traditional local trades. The most disrupted is agriculture. The biological exploitation of the sea has remained at l'Aiguillon-La Faute. At La Tranche and La Faute, tourism takes first place. At l'Aiguillon, where the balance of trades is better, it would be a mistake to sacrifice the biological exploitation of the sea for tourism. 相似文献