全文获取类型
收费全文 | 39267篇 |
免费 | 1460篇 |
国内免费 | 2122篇 |
专业分类
测绘学 | 1391篇 |
大气科学 | 3898篇 |
地球物理 | 7214篇 |
地质学 | 18412篇 |
海洋学 | 2935篇 |
天文学 | 6204篇 |
综合类 | 901篇 |
自然地理 | 1894篇 |
出版年
2024年 | 35篇 |
2023年 | 173篇 |
2022年 | 337篇 |
2021年 | 406篇 |
2020年 | 347篇 |
2019年 | 368篇 |
2018年 | 3830篇 |
2017年 | 3562篇 |
2016年 | 2378篇 |
2015年 | 653篇 |
2014年 | 685篇 |
2013年 | 853篇 |
2012年 | 1776篇 |
2011年 | 3661篇 |
2010年 | 3485篇 |
2009年 | 3630篇 |
2008年 | 2898篇 |
2007年 | 3587篇 |
2006年 | 687篇 |
2005年 | 1123篇 |
2004年 | 928篇 |
2003年 | 997篇 |
2002年 | 704篇 |
2001年 | 489篇 |
2000年 | 483篇 |
1999年 | 472篇 |
1998年 | 460篇 |
1997年 | 433篇 |
1996年 | 403篇 |
1995年 | 312篇 |
1994年 | 303篇 |
1993年 | 258篇 |
1992年 | 214篇 |
1991年 | 182篇 |
1990年 | 148篇 |
1989年 | 154篇 |
1988年 | 129篇 |
1987年 | 137篇 |
1986年 | 103篇 |
1985年 | 86篇 |
1984年 | 91篇 |
1983年 | 87篇 |
1982年 | 85篇 |
1981年 | 90篇 |
1980年 | 81篇 |
1979年 | 57篇 |
1977年 | 50篇 |
1976年 | 54篇 |
1975年 | 41篇 |
1973年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
V. B. Titov 《Water Resources》2005,32(1):23-30
Seasonal evolution of the vertical thermal, halininc, and density structure of water in the phases of warming and heat loss is shown. The annual cycle of variability of seasonal and deep-water thermo-, halo-, and pycnocline is discussed. It is revealed that variations in the seasonal (subsurface) thermo-, halo-, and pycnocline depend on the surface environmental factors (air temperature, river runoff, and precipitation), while variations in the deep-water thermo-, halo-, and pycnocline depend on the dynamic factor impact (seasonal variations in the intensity of the general cyclonic circulation in the Black Sea).Translated from Vodnye Resursy, Vol. 32, No. 1, 2005, pp. 28–34.Original Russian Text Copyright © 2005 by Titov. 相似文献
992.
Determining the maximum degree of harmonic coefficients in geopotential models by Monte Carlo methods 总被引:1,自引:0,他引:1
K. R. Koch r 《Studia Geophysica et Geodaetica》2005,49(3):259-275
Random errors for the harmonic coefficients of a geopotential model are generated from the matrix of normal equations by a parallel computer applying the Gibbs sampler. This leads to random values for the harmonic coefficients. They are transformed by nonlinear, quadratic transformations to random values for the square roots of degree variances, of mean squares of geoid undulations and gravity anomalies. The expected values of these quantities are not equal to the values of these quantities computed by the estimated harmonic coefficients, due to correlations and errors in the estimation. By hypothesis tests estimated harmonic coefficients distorted by correlations and errors are detected. Applying the tests to the geopotential model ITG-CHAMP01 of the Institute of Theoretical Geodesy in Bonn it is concluded that above the degree 62 the harmonic coefficients cannot add any information to the geopotential model. 相似文献
993.
V. V. Boulion 《Water Resources》2005,32(3):327-336
A mass-balance model was developed for the prediction of the biomass and annual production of phytoplankton, macrophytes, epiphytes, and phytobenthos (primary producers), bacterioplankton and bacteriobenthos (reducers), herbivorous and predator zooplankton, zoobenthos, planktivorous fish, benthivorous fish, and predatory fish (consumers). The model is controlled by a small number of parameters.__________Translated from Vodnye Resursy, Vol. 32, No. 3, 2005, pp. 361–370.Original Russian Text Copyright © 2005 by Boulion. 相似文献
994.
The numerical model of convection in magma sills is developed. The model is based on a full system of equations of fluid dynamics and includes heat transfer, buoyancy effects and diffusion of some minor component (marker). Solidification is treated as a phase transition. The results indicate that there are some qualitative differences between very thin sills with Rayleigh number Ra = 105 and thin sills with Ra = 106. For a basaltic magma the first case corresponds to the thickness of the sills of approximately 30 cm and the second case corresponds to the thickness of 60 cm. In the first case mixing is inefficient and conduction is the dominant form of heat transfer. In the second case mixing is efficient and convection is the dominant form of heat transfer. Some of the results can be scaled for the more viscous magmas in thicker sills. 相似文献
995.
V. Grechka 《Studia Geophysica et Geodaetica》2005,49(3):365-381
All methods of seismic characterization of fractured reservoirs are based on effective media theories that relate geometrical and material properties of fractures and surrounding rock to the effective stiffnesses. In exploration seismology, the first-order theory of Hudson is the most popular. It describes the effective model caused by the presence of a single set of thin, aligned vertical fractures in otherwise isotropic rock. This model is known to be transversely isotropic with a horizontal symmetry axis (HTI). Following the theory, one can invert the effective anisotropy for the crack density and type of fluid infill of fractures, the quantities of great importance for reservoir appraisal and management.Here I compute effective media numerically using the finite element method. I deliberately construct models that contain a single set of vertical, ellipsoidal, non-intersecting and non-interconnected fractures to check validity of the first-order Hudson’s theory and establish the limits of its applicability. Contrary to conventional wisdom that Hudson’s results are accurate up to crack density e ≈ 0.1, I show that they consistently overestimate the magnitudes of all effective anisotropic coefficients ε(V), δ(V), and γ(V). Accuracy of theoretically derived anisotropy depends on the type of fluid infill and typically deteriorates as e grows. While the theory gives | ε(V)|, |δ(V)|, |γ(V)| and close to the upper bound of the corresponding numerically obtained values for randomly distributed liquid-filled fractures, theoretical predictions of ε(V), δ(V) are not supported by numerical computations when the cracks are dry. This happens primarily because the first-order Hudson’s theory makes no attempt to account for fracture interaction which contributes to the final result much stronger for gas- than for liquid-filled cracks. I find that Mori-Tanaka’s theory is superior to Hudson’s for all examined crack densities and both types of fluid infill.The paper was presented at the 11th International Workshop on Seismic Anisotropy (11IWSA) held in St. John’s, Canada in 2004. 相似文献
996.
We study the mineralogical changes suffered by specimens of natural miocene red and green continental sandstones (from Pozuelos Formation and Tiomayo Formation) cropping out in the Argentine Puna that increase their bulk magnetic susceptibility and change color when thermally treated. We hypothesize that on heating siderite, which is present in small quantities as cement in the studied sandstones, would oxidize and decompose into maghemite and/or magnetite. Subsequent heating to higher temperatures sometimes would bring about the conversion of maghemite and/or magnetite to hematite. Mössbauer spectroscopy proved to be a very valuable tool for the determination of the presence of siderite in small amounts in the studied samples. The present results show that further work is needed in order to fully understand the mineralogical changes suffered by continental sandstones during heating. The characterization of such changes occurred during laboratory routines is relevant, since they can help to better understand natural processes. 相似文献
997.
J. Plomerova L. Vecsey V. Babuska M. Granet U. Achauer 《Studia Geophysica et Geodaetica》2005,49(4):541-560
We present results of an array study of seismic anisotropy beneath the Bohemian Massif (BM) showing distinct lateral and directional
variations of the fast shear-wave polarization and split-delay time consistent with variations in the P-residual spheres,
in which directional means of relative residuals are subtracted. Our analysis of the S- and P-wave anisotropy suggests that
the mantle lithosphere of the BM consists of at least three large domains with different orientation of the large-scale fabric
separated by sutures cutting most likely the whole lithosphere. Boundaries of the units are characterised by a null or small
shear-wave splitting, as well as by smaller values in the P-residual spheres. We present self-consistent 3D anisotropic models
of the lithosphere domains of the BM resulting from joint inversion of anisotropic parameters searching for a 3D orientation
of mantle fabric. While in the Saxothuringian and Sudetes parts of the BM the (a, c) foliations dip prevailingly to the N-NW,
they dip to the S and SW in the southern and eastern parts of the Moldanubian. 相似文献
998.
Z. Nadenik 《Studia Geophysica et Geodaetica》2005,49(3):277-288
In modern geodesy the triaxial ellipsoid as a generalisation of the ellipsoid of revolution has a significant position in studying the figure of the Earth. Lame surfaces represent a generalisation of the triaxial ellipsoid. The following paragraphs are devoted to curvatures of the Lame surfaces. 相似文献
999.
The importance of sampling frequency in the course of monitoring of mutagenic pollution of small rivers is shown, the Kotorosl River (a tributary of the Volga River) being taken as an example. In working out a sampling program, due consideration should be given for seasonal variations of the river hydrological regime and input of pollutants. Incorrect choice of sampling frequency may lead to one of the principal reasons for improper assessment of toxicogenetic situation. A water sampling program has been proposed for the Kotorosl River studies based on monitoring.__________Translated from Vodnye Resursy, Vol. 32, No. 3, 2005, pp. 347–351.Original Russian Text Copyright © 2005 by Fomicheva, Prokhorova. 相似文献
1000.
A Possible Detection of the 26 December 2004 Great Sumatra-Andaman Islands Earthquake with Solution Products of the International GNSS Service 总被引:1,自引:0,他引:1
J. Kouba 《Studia Geophysica et Geodaetica》2005,49(4):463-483
The main goal of this work is to critically review the IGS solution products and Precise Point Positioning (PPP) in order
to demonstrate their potential to contribute to studies of large earthquakes such as the one that devastated Southeast Asia
on December 26th, 2004. In view of a possible detection of the Mw 9.0 Sumatra-Andaman Islands Earthquake of December 26, 2004,
position solutions, ranging from intervals of years to one second, of four International GNSS Service (IGS) stations within
3000 km of the epicenter were examined. The IGS combined, cumulative solution product (IGS04P51), consisting of epoch and
station velocity solutions and based on data spans of several years prior to the earthquake, was used as a reference. Four
IGS combined weekly position solutions (igs04P1301-4), two weeks before and after the earthquake, were utilized for the weekly
solution resolution. PPP static and kinematic solutions with IGS Final combined orbits and clocks were used for the mean daily
and instantaneous 5-min and 1-sec epoch solutions, respectively. The most significant changes, detected by both weekly and
daily solutions occurred in longitude. The nearest IGS station ntus, about 1000 km east of the epicenter, moved westward about
15 mm, while the more distant Indian station iisc (∼ 2300 km NW from the epicenter), shifted about 15 mm eastward. In spite
of position errors caused by interpolation of the 5-min IGS clocks, the 1-sec solutions, based on separate data sets, available
only for two stations (iisc, dgar), still showed seismic surface waves, in particular at the Indian station iisc. Precise
daily IGS combined polar motion and length-of-day products, after correcting for the atmospheric effects, also likely detected,
statistically significant, anomalistic excitations on December 26, 2004 that could be caused by this great earthquake. 相似文献