全文获取类型
收费全文 | 557篇 |
免费 | 21篇 |
国内免费 | 19篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 36篇 |
地球物理 | 120篇 |
地质学 | 199篇 |
海洋学 | 45篇 |
天文学 | 143篇 |
综合类 | 18篇 |
自然地理 | 31篇 |
出版年
2024年 | 1篇 |
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 16篇 |
2020年 | 5篇 |
2019年 | 15篇 |
2018年 | 26篇 |
2017年 | 28篇 |
2016年 | 31篇 |
2015年 | 30篇 |
2014年 | 29篇 |
2013年 | 29篇 |
2012年 | 17篇 |
2011年 | 36篇 |
2010年 | 35篇 |
2009年 | 34篇 |
2008年 | 39篇 |
2007年 | 40篇 |
2006年 | 24篇 |
2005年 | 17篇 |
2004年 | 19篇 |
2003年 | 19篇 |
2002年 | 14篇 |
2001年 | 17篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 13篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1981年 | 2篇 |
1972年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1962年 | 2篇 |
1961年 | 1篇 |
1960年 | 2篇 |
排序方式: 共有597条查询结果,搜索用时 31 毫秒
561.
Shaking table tests of a reinforced concrete waffle–flat plate structure designed following modern codes: seismic performance and damage evaluation 下载免费PDF全文
Shaking table tests were conducted on a scaled reinforced concrete waffle–flat plate structure. It represented a conventional construction design under current building codes in the Mediterranean area. The test structure was subjected to a sequence of four seismic simulations of increasing magnitude. Each simulation was associated with a seismic hazard level characterized by the mean return period PR. The test structure performed well for the simulations associated with PR = 95, 475 and 975 years but collapsed under the maximum considered earthquake of PR = 2475 years. Damage concentrated at column bases, where the maximum chord rotation reached 93% of the ultimate capacity, and at the transverse beams of the exterior plate‐to‐column connection that failed in torsion. It is shown that most (from 85% to 90%) of the energy input by the earthquake that contributes to damage is dissipated by the plate. The capacity curve of the tested structure estimated from the experimental base shear vs. top displacement relationship allowed us to compute the overstrength (1.4). It is close to the maximum established by European code EN 1998‐1 (1.5). Based on a detailed study of the test results, potential updates to current codes and design recommendations are suggested. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
562.
563.
564.
Early Cretaceous flora from coal-bearing strata of Markovsky Peninsula in South Primorye,Russia 总被引:1,自引:0,他引:1
The Early Cretaceous flora from the coal-bearing strata(Ussuri and Lipovtsy formations)in the Markovsky peninsula of South Primorye,Far East Russia,is reported in some detail in this paper.The flora containing over 80 species of about 50 genera can be divided into two assemblages.The paleofloristic characteristics and the comparisons of this flora with its coeval floras from the adjacent region of the eastern Heilongjiang of Northeast China,indicate the flora and its coal-bearing strata of the Markovsky peninsula can be compared to those of the Chengzihe and Muling formations of the Jixi area of Heilongjiang,representing probably the late Barremian and Aptian age,respectively. 相似文献
565.
Sarah E. M. Gain Yoann Grau Hadrien Henry Elena Belousova Ivars Dainis William L. Griffin Suzanne Y. O'Reilly 《Geostandards and Geoanalytical Research》2019,43(3):339-354
Zircon megacrysts from the Mud Tank carbonatite, Australia, are being used in many laboratories as a reference material for LA‐ICP‐MS U‐Pb dating and trace element measurement, and LA‐MC‐ICP‐MS determination of Hf isotopes. We summarise a database of > 10000 analyses of Mud Tank zircon (MTZ), collected from 2000 to 2018 during its use as a secondary reference material for simultaneous U‐Pb and trace element analysis, and for Hf‐isotope analysis. Trace element mass fractions are highest in dark red‐brown stones and lowest in colourless and gem‐quality ones. Individual unzoned grains can be chemically homogeneous, while significant variations in trace element mass fraction are associated with oscillatory zoning. Chondrite‐normalised trace element patterns are essentially parallel over large mass fraction ranges. A Concordia age of 731.0 ± 0.2 Ma (2s, n = 2272) is taken as the age of crystallisation. Some grains show lower concordant to mildly discordant ages, probably reflecting minor Pb loss associated with cooling and the Alice Springs Orogeny (450–300 Ma). Our weighted mean 176Hf/177Hf is 0.282523 ± 10 (2s, n = 9350); the uncertainties on this ratio reflect some heterogeneity, mainly between grains. A few analyses suggest that colourless grains have generally lower 176Hf/177Hf. MTZ is a useful secondary reference material for U‐Pb and Hf‐isotope analysis, but individual grains need to be carefully selected using CL imaging and tested for homogeneity, and ideally should be standardised by solution analysis. 相似文献
566.
567.
Vitaliy D. Rusov Vladimir N. Vaschenko Elena P. Linnik Оksana T. Myhalus Yuriy A. Bondartchuk Vladimir P. Smolyar Sergey I. Kosenko Strachimir Cht. Mavrodiev Boyko I. Vachev 《Journal of Atmospheric and Solar》2010,72(5-6):389-397
The solution of energy-balance model of the Earth global climate and the EPICA Dome C and Vostok experimental data of the Earth surface palaeotemperature evolution over past 420 and 740 kyr are compared.In the framework of proposed bifurcation model (i) the possible sharp warmings of the Dansgaard-Oeschger type during the last glacial period due to stochastic resonance is theoretically argued; (ii) the concept of climatic sensitivity of water in the atmosphere, whose temperature instability has the form of so-called hysteresis loop, is proposed, and based on this concept the time series of global ice volume over the past 1000 kyr, which is in good agreement with the time series of δ18O concentration in the sea sediments, is obtained; (iii) the so-called “CO2 doubling” problem is discussed. 相似文献
568.
Boris P. Ilyashuk Elena A. Ilyashuk Eugeny A. Makarchenko Oliver Heiri 《Journal of Paleolimnology》2010,44(2):667-676
Larvae of the genus Pseudodiamesa Goetghebuer, which includes 12 described valid species and is divided by Makarchenko and Makarchenko (1999) into two species groups, Pseudodiamesa branickii group and Pseudodiamesa
nivosa group, are widespread in lakes and running waters of cold, high-latitude and high-altitude areas of the Northern Hemisphere.
Larval remains of the genus are often found in subfossil assemblages from these cold regions, but intra-genus morphotypes
usually are not distinguished by palaeoecologists. Current knowledge of the ecology of the species indicates that the Pseudodiamesa nivosa group is more cold-adapted than the Pseudodiamesa branickii group and, therefore, these two intra-genus morphotypes cannot be amalgamated into a larger taxonomic unit without losing
substantial information. Here we present the morphological characters of head capsules of Pseudodiamesa larvae attributed to the different species-group morphotypes, which are clearly visible in subfossil specimens. The information
summarized in this paper will help provide more reliable chironomid-based palaeoclimatic inferences from lake sediment records
covering colder phases through the late Quaternary in the Northern Hemisphere. 相似文献
569.
Van Lichtervelde Marieke Grand’Homme Alexis de Saint-Blanquat Michel Olivier Philippe Gerdes Axel Paquette Jean-Louis Melgarejo Joan Carles Druguet Elena Alfonso Pura 《Mineralogy and Petrology》2017,111(1):1-21
Mineralogy and Petrology - The Cap de Creus granitic pegmatites in the eastern Catalan Pyrenees were dated using in situ U-Pb geochronology by laser ablation ICP-MS on zircon and columbite-group... 相似文献
570.
Frequency analysis of the stability of asteroids in the framework of the restricted three-body problem 总被引:1,自引:1,他引:0
Alessandra?CellettiEmail author Claude?Froeschlé Elena?Lega 《Celestial Mechanics and Dynamical Astronomy》2004,90(3-4):245-266
The stability of some asteroids, in the framework of the restricted three-body problem, has been recently proved in (Celletti
and Chierchia, 2003), by developing an isoenergetic KAM theorem. More precisely, having fixed a level of energy related to
the motion of the asteroid, the stability can be obtained by showing the existence of nearby trapping invariant tori existing
at the same energy level. The analytical results are compatible with the astronomical observations, since the theorem is valid
for the realistic mass-ratio of the primaries.
The model adopted in (Celletti and Chierchia, 2003), is the planar, circular, restricted three-body model, in which only the
most significant contributions of the Fourier development of the perturbation are retained. In this paper we investigate numerically
the stability of the same asteroids considered in (Celletti and Chierchia, 2003), (namely, Iris, Victoria and Renzia). In
particular, we implement the nowadays standard method of frequency-map analysis and we compare our investigation with the
analytical results on the planar, circular model with the truncated perturbing function. By means of frequency analysis, we
study the behaviour of the bounding tori and henceforth we infer stability properties on the dynamics of the asteroids. In
order to test the validity of the truncated Hamiltonian, we consider also the complete expression of the perturbing function
on which we perform again frequency analysis. We investigate also more realistic models, taking into account the eccentricity
of the trajectory of Jupiter (planar-elliptic problem) or the relative inclination of the orbits (circular-inclined model).
We did not find a relevant discrepancy among the different models. 相似文献