全文获取类型
收费全文 | 2583篇 |
免费 | 45篇 |
国内免费 | 27篇 |
专业分类
测绘学 | 245篇 |
大气科学 | 163篇 |
地球物理 | 526篇 |
地质学 | 911篇 |
海洋学 | 59篇 |
天文学 | 629篇 |
综合类 | 21篇 |
自然地理 | 101篇 |
出版年
2022年 | 23篇 |
2021年 | 29篇 |
2020年 | 34篇 |
2019年 | 29篇 |
2018年 | 139篇 |
2017年 | 111篇 |
2016年 | 152篇 |
2015年 | 76篇 |
2014年 | 130篇 |
2013年 | 150篇 |
2012年 | 105篇 |
2011年 | 115篇 |
2010年 | 98篇 |
2009年 | 110篇 |
2008年 | 88篇 |
2007年 | 62篇 |
2006年 | 59篇 |
2005年 | 56篇 |
2004年 | 32篇 |
2003年 | 41篇 |
2002年 | 54篇 |
2001年 | 36篇 |
2000年 | 39篇 |
1999年 | 44篇 |
1998年 | 34篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 27篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 31篇 |
1991年 | 40篇 |
1990年 | 28篇 |
1989年 | 41篇 |
1988年 | 48篇 |
1987年 | 52篇 |
1986年 | 36篇 |
1985年 | 35篇 |
1984年 | 61篇 |
1983年 | 58篇 |
1982年 | 34篇 |
1981年 | 21篇 |
1980年 | 27篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1976年 | 12篇 |
1974年 | 11篇 |
1973年 | 12篇 |
1972年 | 14篇 |
1971年 | 10篇 |
排序方式: 共有2655条查询结果,搜索用时 15 毫秒
1.
Water quality is often highly variable both in space and time, which poses challenges for modelling the more extreme concentrations. This study developed an alternative approach to predicting water quality quantiles at individual locations. We focused on river water quality data that were collected over 25 years, at 102 catchments across the State of Victoria, Australia. We analysed and modelled spatial patterns of the 10th, 25th, 50th, 75th and 90th percentiles of the concentrations of sediments, nutrients and salt, with six common constituents: total suspended solids (TSS), total phosphorus (TP), filterable reactive phosphorus (FRP), total Kjeldahl nitrogen (TKN), nitrate-nitrite (NOx), and electrical conductivity (EC). To predict the spatial variation of each quantile for each constituent, we developed statistical regression models and exhaustively searched through 50 catchment characteristics to identify the best set of predictors for that quantile. The models predict the spatial variation in individual quantiles of TSS, TKN and EC well (66%–96% spatial variation explained), while those for TP, FRP and NOx have lower performance (37%–73% spatial variation explained). The most common factors that influence the spatial variations of the different constituents and quantiles are: annual temperature, percentage of cropping land area in catchment and channel slope. The statistical models developed can be used to predict how low- and high-concentration quantiles change with landscape characteristics, and thus provide a useful tool for catchment managers to inform planning and policy making with changing climate and land use conditions. 相似文献
2.
The observed times of minimum light derived from the photometry of the Wolf-Rayet eclipsing binary stars CQ Cep and V444 Cyg are used to estimate the mass-loss rate of the Wolf-Rayet components in several modes of mass-loss and mass-exchange. 相似文献
3.
Similarity solutions, describing the flow of a perfect gas behind spherical shock waves, are investigated including the radiation heat flux. The shock is assumed to be propagating in a medium at rest. Shock radius varies exponentially with time and density is inversely proportional to fifth power of the shock radius immediately ahead of the shock front. 相似文献
4.
The aim of this paper is to investigate the thermal stability of a fluid layer with permeable boundaries and a variable gravitational field. It is observed that the principle of exchange of stabilities is valid when the layer is heated form below and the complex growth rate of an arbitrary oscillatory mode exists outside of a circle whose radius depends upon the permeability parameter, Prandtl number and wavelength of the mode. In the case of a layer heated from below, gravity increasing upward has a destabilizing effect whereas the permeability parameter has a stabilizing effect. 相似文献
5.
It is shown that the kinematical parameters associated with the congruence formed by tachyonic motion can be defined in the manner of Greenberg, but not that of Ehlers. The space-like counterpart of Raychaudhuri's equation has also been obtained. 相似文献
6.
An LRS Bianchi Type V bulk viscous fluid dust distribution string cosmological model in General Relativity is investigated.
It has been shown that if coefficient of bulk viscosity (ζ) is proportional to the expansion (θ) in the model then string
cosmological model for Bianchi Type V space-time is possible. In absence of bulk viscosity(ζ) i.e. when ζ → 0 then there is
no string cosmological model for Bianchi Type V space-time. The physical and geometrical aspects are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
In this paper general solutions are found for domain walls in Lyra geometry in the plane symmetric spacetime metric given
by Taub. Expressions for the energy density and pressure of domain walls are derived in both cases of uniform and time varying
displacement field β. It is also shown that the results obtained by Rahaman et al [IJMPD, 10, 735 (2001)] are particular case
of our solutions. Finally, the geodesic equations and acceleration of the test particle are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
The present work applies the method of characteristics to study the behaviour of planar and cylindrical wave-heads propagating through a perfectly electrically conducting and thermally radiating inviscid gas under the optically thin limit in the presence of a transverse magnetic field. The true nonlinear progress of the flow variable gradients at the wavefront is predicted and the critical distance at which the characteristics pile up at the wavefront to form a shock wave is obtained. It is investigated as to how the effects of radiative flux, the magnetic field strength and the specific heat ratio influence the process of steepening or flattening of the characteristic wavefront. 相似文献
9.
The oscillatory, conjugate and asymptotic behaviours of the principal and non-principal solutions of the Blasius and corresponding heat transfer equations governing the compressible laminar boundary-layer flow over a semi-infinite flat plate with heat flux have been studied; the results of the discussion being based on the asymptotic integrations of second-order linear differential equations. 相似文献
10.
Wood destruction in test panels ofShorea leprosulawas related to the percentage of fouling, types of wood borers and the number of wood borers. The natural durability ofShorea leprosulapanels was estimated to be 4–5 months in Malaysian marine waters. A higher fouling cover resulted in lower rates of wooden panel deterioration. Larger numbers of wood borers brought about greater panel deterioration. Primary wood destruction was caused by bivalve wood borers, mainlyMartesia striata, Lyrodus pedicellatus, Bankia campanellata, Teredo furciferaandTeredo bartschi. Martesia striatawas the important wood destroying agent in the intertidal zone and, together with the shipworms, was also responsible for panel destruction in the subtidal zone. 相似文献