全文获取类型
收费全文 | 1881篇 |
免费 | 23篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 57篇 |
大气科学 | 43篇 |
地球物理 | 883篇 |
地质学 | 436篇 |
海洋学 | 17篇 |
天文学 | 383篇 |
综合类 | 4篇 |
自然地理 | 86篇 |
出版年
2018年 | 41篇 |
2017年 | 37篇 |
2016年 | 55篇 |
2015年 | 42篇 |
2014年 | 41篇 |
2013年 | 60篇 |
2012年 | 62篇 |
2011年 | 51篇 |
2010年 | 57篇 |
2009年 | 51篇 |
2008年 | 44篇 |
2007年 | 58篇 |
2006年 | 41篇 |
2005年 | 38篇 |
2004年 | 38篇 |
2003年 | 45篇 |
2002年 | 41篇 |
2001年 | 28篇 |
2000年 | 33篇 |
1999年 | 24篇 |
1998年 | 22篇 |
1997年 | 24篇 |
1996年 | 26篇 |
1995年 | 28篇 |
1994年 | 26篇 |
1993年 | 32篇 |
1992年 | 22篇 |
1991年 | 24篇 |
1989年 | 28篇 |
1988年 | 25篇 |
1987年 | 30篇 |
1986年 | 29篇 |
1985年 | 32篇 |
1984年 | 32篇 |
1983年 | 32篇 |
1982年 | 36篇 |
1981年 | 32篇 |
1980年 | 33篇 |
1979年 | 30篇 |
1978年 | 34篇 |
1977年 | 31篇 |
1976年 | 24篇 |
1975年 | 29篇 |
1974年 | 21篇 |
1973年 | 22篇 |
1972年 | 26篇 |
1971年 | 41篇 |
1970年 | 20篇 |
1969年 | 21篇 |
1968年 | 25篇 |
排序方式: 共有1909条查询结果,搜索用时 15 毫秒
61.
62.
Summary Approximate expressions for the Hilbert transform of the functionf(t)=exp(-
0
2
t
2/2) cos(
0
t+v) are determined. This function, given a suitable choice of the three parameters 0, and v, approximates a wide class of seismic signals very well. The approximate expressions for the Hilbert transform enable very simple formulae to be given for the elementary seismograms of the individual seismic body waves (in the zero approximation of the ray theory). This accelerates the computation of ray theoretical seismograms considerably. 相似文献
63.
64.
Hannes Konrad Malte Thoma Ingo Sasgen Volker Klemann Klaus Grosfeld Dirk Barbi Zdeněk Martinec 《Surveys in Geophysics》2014,35(6):1441-1458
We apply a coupled thermomechanical ice sheet—self-gravitating viscoelastic solid Earth model (SGVEM), allowing for the dynamic exchange of ice thickness and bedrock deformation, in order to investigate the effect of viscoelastic deformation on ice dynamics and vice versa. In a synthetic glaciation scenario, we investigate the interaction between the ice sheet and the solid Earth deformation, the glacial-isostatic adjustment (GIA), accounting for an atmospheric forcing depending on the ice sheet surface altitude. We compare the results from the coupled model to runs with the common elastic lithosphere/relaxing asthenosphere (ELRA) model, where the lithosphere is represented by a thin plate and the mantle relaxes with one characteristic relaxation time, as well as to a rigid Earth without any deformation. We find that the deformational behaviour of the SGVEM on ice dynamics (i.e. stored ice volume, ice thickness and velocity field) is comparable to the ELRA for an optimal choice of the parameters in steady state, but exhibits differences in the transient behaviour. Beyond the ice sheet, in the region of peripheral forebulge, the differences in the transient surface deformation between ELRA and SGVEM are substantial, demonstrating the inadequacy of the ELRA model for interpreting constraints on GIA in the periphery of the ice sheet, such as sea-level indicators and GPS uplift rates. 相似文献
65.
Site classification of Turkish national strong-motion stations 总被引:1,自引:0,他引:1
M. Abdullah Sandıkkaya Mustafa Tolga Yılmaz B. Sadık Bakır Özdoğan Yılmaz 《Journal of Seismology》2010,14(3):543-563
Since 1973, the General Directorate of Disaster Affairs of Turkey has deployed several strong-motion accelerographs at selected
sites. Within the framework of the project entitled Compilation of National Strong Ground Motion Database in Accordance with International Standards, site conditions were investigated within the upper 30-m depth by surface seismic and standard penetration tests. Preliminary
characterization of the sites is made by making use of both geophysical and geotechnical criteria of NEHRP Provisions and
Eurocode-8 site classification systems. The liquefaction susceptibility of those sites which comprise saturated cohesionless
deposits is also determined. Mean shear-wave velocity, mean penetration resistance, site class, and liquefaction susceptibility
of each site are tabulated. The Turkish strong-motion database supplemented by detailed information on site conditions is
a valuable source of information particularly for those studies that put emphasis on the relationship between site conditions
and strong-motion parameters. 相似文献
66.
—Approximate PP plane wave displacement coefficients of reflection and transmission for weak contrast interfaces separating weakly but arbitrarily anisotropic elastic media are presented. The PP reflection coefficient for such an interface has been derived recently by Vavry?uk and P?en?ík (1997). The PP transmission coefficient presented in this paper was derived by the same approach. The coefficients are given as a sum of the coefficient for the weak contrast interface separating two nearby isotropic media and a term depending linearly on contrasts of the so-called weak anisotropy (WA) parameters (parameters specifying deviation of properties of the medium from isotropy), across the interface. While the reflection coefficient depends only on 8 of the complete set of the WA parameters describing P-wave phase velocity in weakly anisotropic media, the transmission coefficient depends on their complete set. The PP reflection coefficient depends on "shear-wave splitting parameter" γ. Tests of accuracy of the approximate formulae are presented on several models. 相似文献
67.
Burša Milan Kouba Jan Müller Achim Raděj Karel True Scott A. Vatrt Viliam Vojtíšková Marie 《Studia Geophysica et Geodaetica》1999,43(1):1-6
Geopotential values W of the mean equipotential surfaces representing the mean ocean topography were computed on the basis of four years (1993 - 1996) TOPEX/POSEIDON altimeter data: W = 62 636 854.10m
2
s
–2
for the Pacific (P), W = 62 636 858.20m
2
s
–2
for the Atlantic (A), W = 62 636 856.28m
2s–2
for the Indian (I) Oceans. The corresponding mean separations between the ocean levels were obtained as follows: A – P = – 42 cm, I– P = – 22 cm, I – A = 20 cm, the rms errors came out at about 0.3 cm. No sea surface topography model was used in the solution. 相似文献
68.
The Arica Elbow region represents that part of Andean South America where the azimuth of the strike of the Peru-Chile trench changes from 150° to 190°. The area under study is roughly bounded by latitudes 17 °S and 23 °S, The shape of the Wadati-Benioff zone was studied in terms of the distribution of ISC hypocentres dated between 1964 and 1993. A system of 22 vertical cross-sections, perpendicular to the trench axis, and a map of epicentres was used to derive the detailed shape of the Wadati-Benioff zone of the presently descending slab. The distribution of earthquake foci indicates a fingerlike shape of the lower part of the Wadati-Benioff zone beneath the aseismic gap. The slab length shows small changes around 350 km in the northern sections, pronounced length oscillations between 350 and 750 km in the neighbouring central sections and a constant value of 650 km in the southern sections. The dip and thickness of the Wadati-Benioff zone are practically constant in all sections. Fault plane solutions, separated spatially into three zones, were used to estimate the state of stress in the slab. 相似文献
69.
The solar eclipse on August 11, 1999, observed in the region covered by many geomagnetic observatories, has offered a unique opportunity to look for an effect of the eclipse on geomagnetic pulsations. The pulsation activity digital data have been taken from Budkov Observatory in the Czech Republic (in the X component only), from observatories in Germany (Niemegk, Fürstenfeldbruck, Bad Bergzabern), in Hungary (Nagycenk), and for comparison in South Africa (Hermanus, conjugate-point station), and in Finland (Sodankylä, far from the eclipse zone). At all these stations the field in all three component has been recorded. The pulsation amplitudes in the X component exhibit a long-term minimum near the time of the eclipse. Spectral analysis of selected short intervals confirmed this decrease and also revealed a decrease of the average pulsation period during the eclipse. Such a change in the amplitude or in the period was not observed outside of the eclipse interval or in other days. Investigation in some narrower frequency bands showed that the maximal decrease occurred in the 15–20 s band. All these changes can be found in records from all the stations near the eclipse totality belt, also in records at the conjugate-point station, where no eclipse occurred. No signature has been found in records at the station situated far from the eclipse zone. 相似文献
70.
Anthropogenic global warming caused by CO2 emissions is strongly and fundamentally linked to future energy production. The Special Report on Emission Scenarios (SRES)
from 2000 contains 40 scenarios for future fossil fuel production and is used by the IPCC to assess future climate change.
Previous scenarios were withdrawn after exaggerating one or several trends. This study investigates underlying assumptions
on resource availability and future production expectations to determine whether exaggerations can be found in the present
set of emission scenarios as well. It is found that the SRES unnecessarily takes an overoptimistic stance and that future
production expectations are leaning toward spectacular increases from present output levels. In summary, we can only encourage
the IPCC to involve more resource experts and natural science in future emission scenarios. The current set, SRES, is biased
toward exaggerated resource availability and unrealistic expectations on future production outputs from fossil fuels. 相似文献