全文获取类型
收费全文 | 10333篇 |
免费 | 1709篇 |
国内免费 | 2548篇 |
专业分类
测绘学 | 927篇 |
大气科学 | 2325篇 |
地球物理 | 2688篇 |
地质学 | 2932篇 |
海洋学 | 2534篇 |
天文学 | 1047篇 |
综合类 | 551篇 |
自然地理 | 1586篇 |
出版年
2024年 | 47篇 |
2023年 | 111篇 |
2022年 | 279篇 |
2021年 | 363篇 |
2020年 | 384篇 |
2019年 | 511篇 |
2018年 | 414篇 |
2017年 | 455篇 |
2016年 | 424篇 |
2015年 | 469篇 |
2014年 | 580篇 |
2013年 | 769篇 |
2012年 | 519篇 |
2011年 | 587篇 |
2010年 | 528篇 |
2009年 | 748篇 |
2008年 | 773篇 |
2007年 | 834篇 |
2006年 | 707篇 |
2005年 | 593篇 |
2004年 | 578篇 |
2003年 | 506篇 |
2002年 | 474篇 |
2001年 | 366篇 |
2000年 | 362篇 |
1999年 | 344篇 |
1998年 | 312篇 |
1997年 | 226篇 |
1996年 | 247篇 |
1995年 | 170篇 |
1994年 | 154篇 |
1993年 | 151篇 |
1992年 | 125篇 |
1991年 | 103篇 |
1990年 | 88篇 |
1989年 | 63篇 |
1988年 | 45篇 |
1987年 | 41篇 |
1986年 | 23篇 |
1985年 | 24篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 4篇 |
1980年 | 20篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
51.
52.
Jorge Luis De Souza 《Pure and Applied Geophysics》1991,136(2-3):245-264
The Rayleigh wave phase and group velocities in the period range of 24–39 sec, obtained from two earthquakes which occurred in northeastern brazil and which were recorded by the Brazilian seismological station RDJ (Rio de Janeiro), have been used to study crustal and upper mantle structures of the Brazilian coastal region. Three crustal and upper mantle models have been tried out to explain crustal and upper mantle structures of the region. The upper crust has not been resolved, due basically to the narrow period range of the phase and group velocities data. The phase velocity inversions have exhibited good resolutions for both lower crust and upper mantle, with shear wave velocities characteristic of these regions. The group velocity data inversions for these models have showed good results only for the lower crust. The shear wave velocities of the lower crust (3.86 and 3.89 km/sec), obtained with phase velocity inversions, are similar to that (=3.89 km/sec) found byHwang (1985) to the eastern South American region, while group velocity inversions have presented shear velocity (=3.75 km/sec) similar to that (=3.78 km/sec) found byLazcano (1972) to the Brazilian shield. It was not possible to define sharply the crust-mantle transition, but an analysis of the phase and group velocity inversions results has indicated that the total thickness of the crust should be between 30 and 39 km. The crustal and upper mantle model, obtained with phase velocity inversion, can be used as a preliminary model for the Brazilian coast. 相似文献
53.
Influence of Structural Non-Stationarity of Surface Roughness on Morphological Characterization and Mechanical Deformation of Rock Joints 总被引:2,自引:2,他引:0
N. Fardin 《Rock Mechanics and Rock Engineering》2008,41(2):267-297
Summary Structural non-stationarity of surface roughness affects accurate morphological characterization as well as mechanical behaviour
of rock joints at the laboratory scale using samples with a size below the stationarity threshold. In this paper, the effect
of structural non-stationarity of surface roughness is investigated by studying the scale dependence of surface roughness
and mechanical behaviour of rock joints. The results show that the structural non-stationarity mainly affects the accurate
characterization of the surface roughness of the fracture samples. It also controls the amount and location of the contact
areas during shear tests, which in turn affects the mechanical properties and asperity degradation of the samples. It is concluded
that for accurate determination of the morphological and mechanical properties of rock joints at laboratory and field scales,
samples with size equal to or larger than the stationarity threshold are required.
Author’s address: Nader Fardin, Rock Mechanics Group, Department of Mining Engineering, Faculty of Engineering, University
of Tehran, P.O. Box: 11365/4563, Tehran, Iran 相似文献
54.
本文以赤道东太平洋海温作为主导因子,分析其与东亚温带气旋的关系。得出:高海温多气旋,低海温少气旋的对应关系较为明显。并进一步对不符合这种主要关系的年份从环流型。下垫面海温等作了分类鉴别分析。 相似文献
55.
物质海 -气通量计算新建议中将物质海 -气通量计算公式 F=K(CL- b Cg)中的 CL 用CL ( SML ) 代替。本文着重于对公式中质量迁移系数 K的讨论。在测定了海水微表层、次表层水粘度并同时测定了其它一些化学参量基础上 ,得出如下结论 :海水粘度与盐度、碱度有一定相关性 ;微表层与次表层海水的粘度变化小于 3%。因此 ,海水微表层效应影响 K值 ,与海水微表层效应影响物质浓度相比 ,可以不考虑。 相似文献
56.
57.
In this study, we investigate two internal wave generation methods in numerical modeling of time-dependent equations for water wave propagation, i.e., delta source function method and source term addition method, the latter of which has been called the line source method in literatures. We derive delta source functions for the Boussinesq-type equations and extended mild-slope equations. By applying the fractional step splitting method, we show that the delta source function method is equivalent to the source term addition method employing the energy velocity. This suggests that the energy velocity should be used rather than the phase velocity for the transport of incident wave energy in the source term addition method. Finally, the performance of the delta source function method is verified by accurately generating nonlinear cnoidal waves as well as linear waves for horizontally one-dimensional cases. 相似文献
58.
A.F. Velegrakis M.I. VousdoukasA.M. Vagenas Th. KarambasK. Dimou Th. Zarkadas 《Coastal Engineering》2007
This short contribution reports the results of a field study on the nearshore characteristics of waves generated by both conventional and high speed passenger ferries. The field observations took place in the late summer of 2005, at a beach close to the port of Mytilene (Island of Lesbos, Greece), and involved the visual observation of ship waves, using digital video recordings and image processing techniques. The results showed that passage of the fast ferry was associated with a longer, more complex and energetic nearshore event; this event not only did include higher nearshore waves (up to 0.74 m) and was organised in different wave packets, but it was also an order of magnitude longer (∼ 680 s) than the conventional ferry event. Regarding the effects on beach sediment dynamics, the fast ferry waves were estimated to be very efficient in mobilising the nearshore sediments in contrast to those of the conventional ferry. The fast ferry service appears to generate daily prolonged nearshore events, which contain waves with higher energy than those expected from the normal summer wind wave regime of the area; these events also include some high and very steep waves, which can be particularly erosive. Therefore, fast ferry wakes may have considerable impacts on the seasonal beach sediment dynamics/morphodynamics and the nearshore benthic ecology, as well as they may pose significant risks to bathers, affecting the recreational use of the beaches exposed to fast ferry traffic. Finally, the study has shown that satisfactory field observations of the nearshore characteristics of ship-generated (and wind) waves can be obtained using inshore deployments of calibrated poles, digital video cameras and appropriate image processing algorithms. 相似文献
59.
We develop techniques of numerical wave generation in the time-dependent extended mild-slope equations of Suh et al. [1997. Time-dependent equations for wave propagation on rapidly varying topography. Coastal Engineering 32, 91–117] and Lee et al. [2003. Extended mild-slope equation for random waves. Coastal Engineering 48, 277–287] for random waves using a source function method. Numerical results for both regular and irregular waves in one and two horizontal dimensions show that the wave heights and the frequency spectra are properly reproduced. The waves that pass through the wave generation region do not cause any numerical disturbances, showing usefulness of the source function method in avoiding re-reflection problems at the offshore boundary. 相似文献
60.