全文获取类型
收费全文 | 1833篇 |
免费 | 80篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 35篇 |
大气科学 | 103篇 |
地球物理 | 932篇 |
地质学 | 411篇 |
海洋学 | 28篇 |
天文学 | 342篇 |
综合类 | 3篇 |
自然地理 | 66篇 |
出版年
2021年 | 29篇 |
2020年 | 33篇 |
2019年 | 27篇 |
2018年 | 44篇 |
2017年 | 68篇 |
2016年 | 82篇 |
2015年 | 65篇 |
2014年 | 88篇 |
2013年 | 100篇 |
2012年 | 43篇 |
2011年 | 48篇 |
2010年 | 65篇 |
2009年 | 64篇 |
2008年 | 52篇 |
2007年 | 39篇 |
2006年 | 36篇 |
2005年 | 20篇 |
2004年 | 28篇 |
2003年 | 29篇 |
2002年 | 31篇 |
2001年 | 26篇 |
2000年 | 23篇 |
1999年 | 22篇 |
1998年 | 28篇 |
1996年 | 32篇 |
1995年 | 19篇 |
1994年 | 27篇 |
1993年 | 25篇 |
1992年 | 27篇 |
1991年 | 20篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 29篇 |
1984年 | 28篇 |
1983年 | 29篇 |
1982年 | 34篇 |
1981年 | 23篇 |
1980年 | 21篇 |
1979年 | 36篇 |
1978年 | 27篇 |
1977年 | 23篇 |
1976年 | 17篇 |
1975年 | 20篇 |
1974年 | 23篇 |
1973年 | 23篇 |
1972年 | 24篇 |
1971年 | 24篇 |
1967年 | 16篇 |
排序方式: 共有1920条查询结果,搜索用时 15 毫秒
171.
Studia Geophysica et Geodaetica - 相似文献
172.
The formation and evolution of a large amplitude MHD perturbation propagating perpendicular to the magnetic field in a perfectly conducting low plasma is studied. The perturbation is generated by an abrupt expansion of the source region. Explicit expressions for the time and the distance needed for the transformation of the perturbation's leading edge into a shock wave are derived. The results are applied to coronal conditions and the dynamic spectra of the radio emission excited by the shock are synthesized, reproducing metric and kilometric type II bursts. The features corresponding to the metric type II burst precursor and the moving type IV burst in the case of kilometric type II bursts are identified. A specific radio signature that is sometimes observed at the onset of a metric type II burst is found to appear immediately before the shock wave formation due to the associated growth of the magnetic field gradient. Time delays and starting frequencies of bursts' onsets are calculated and presented as a function of the impulsiveness of the source-region expansion, using different values of the ambient Alfvén velocity and various time profiles of the expansion velocity. The results are confronted with the observations of metric and kilometric type II solar radio bursts. 相似文献
173.
Milan Burša Jan Kouba Viliam Vatrt Vojtěch Vítek Marie Vojtíšková 《Studia Geophysica et Geodaetica》2000,44(1):1-12
The T/P altimeter data 1993 – 1997 (cycles 11 – 194) has been analyzed with emphases on seasonal variations in sea surface topography (SST). The amplitude of the annual variations amounted to (5.9±0.3) mm when inverted barometer (IB) corrections were applied and (2.0±0.4) mm without any IB corrections. The amplitude of the semi-annual variations in SST was small with IB corrections applied: (0.6±0.3) mm. However, when no IB corrections were applied, it was (1.8±0.4) mm, i.e. the semiannual variations are at the same level as the annual variations with no IB corrections. The phase angle offset of the annual term has shifted by about 180° when IB correction was applied. The dynamics of the ocean-atmosphere system is discussed and it is concluded that it could, at least partly, be responsible for the above observed effects. 相似文献
174.
K. Pandžić I. Šimunić F. Tomić S. Husnjak T. Likso D. Petošić 《Theoretical and Applied Climatology》2006,85(1-2):107-115
Summary This paper presents an the evaluation of three mathematical models for the estimation of 10-day drain discharge using weather, pedological and phenological parameters. One model uses modified Palmer’s procedure for the calculation of
water balance components and the second two use empirical multiple linear regression. The models have been applied to data
of an amelioration experimental field in central Croatia (south-western part of the Pannonian Lowland), where a set of average
10-day air temperature and relative humidity data, average wind speed, cumulative precipitation and drain discharge amounts,
insolation and soil moisture data and vegetation indices have been collected. The experiment has been performed during the
period 1990–1992. The models have been tested by comparing estimated and observed 10-day drain discharge amounts. All models
mainly give acceptable cumulative results although their accuracy depends on the season. 相似文献
175.
This paper presents the development and utilisation of an automated image processing algorithm for detection and analysis
of grains. Using optical polarising microscopy, a set of colored images are collected from an area on a thin section. A filtering
operation, using rotation of a morphological alternating sequence filter (based on a structuring element), is used to remove
twinning features within individual grains. Filtering is followed by the watershed segmentation technique to determine grain
boundaries. The method is used for the identification of calcite grains in marble and the subsequent analysis of morphological
anisotropy. 相似文献
176.
Sea/land breeze climatological characteristics along the northern Croatian Adriatic coast 总被引:1,自引:0,他引:1
Summary Climatological characteristics along the northern Croatian Adriatic coast have been examined for nine meteorological stations
for the summertime sea/land breeze circulation. The stations considered are Pula-airport, Opatija, Rijeka, Senj, Malinska,
Rijeka-airport, Mali Lošinj, Rab and Zadar. The hourly surface measurements at each station from June to September for the
period 1991–2004 as well as the radiosoundings in Zadar (from 2002 to 2004) were used for the analysis. A dataset with the
sea/land breeze days was formed according to the several criteria.
The mean daily maxima of both air and sea surface temperatures were more influenced by the large scale disturbances toward
north (e.g. in Rijeka or Opatija) compared to the values for e.g. Zadar. Furthermore, the influence of the large scale disturbances
diminished toward the south concerning the sea–land temperature difference only at the stations placed at Rijeka Bay and Velebit
channel. The strongest sea breeze was found at Pula-airport and the most frequent ones at Opatija and Zadar. At Senj the rarest,
the weakest and the shortest sea breeze was observed. The climatological records of wind speed and air-sea temperature difference
(ΔT) showed for Opatija, Malinska and Zadar that the maximum measured wind speed is around 4.5 °C confirming the nonlinear relationship
between the sea breeze speeds and the ΔT during the day.
At most stations, the clockwise rotation of the hodographs prevails which is typical for the Northern hemisphere due to Coriolis
force, with the exception at Senj and Malinska. While the hodographs for Pula, Rijeka-airport and Mali Lošinj display a later
onset of the prevailing sea breeze because of the interaction among several sea breeze circulations, the results for Opatija,
Zadar and Senj show considerably distorted hodographs because of the nearby channeling of the air flow. 相似文献
177.
Summary “Koshava” is a gusty wind of changeable intensity, blowing from a south-easterly direction, over Serbia, Romania and Bulgaria.
It is caused by the interaction between the synoptic circulation and the orography of the Carpathian and the Balkan mountains.
This paper analyzes wind data measured at the Belgrade-Observatory during the longest period of consecutive days of “Koshava”
which occurred from 14 January to 13 February 1972. Mean hourly wind speed data has been examined using spectral analysis.
The power spectra are calculated using autocorrelation spectral analysis, the multi-taper method and wavelet transform. The
maximum of which is about 122 h (5 days) corresponds to the time span of synoptic processes. 相似文献
178.
Roša D. Vršnak B. Božić H. Brajša R. Ruždjak V. Schroll A. Wöhl H. 《Solar physics》1998,179(2):237-252
The dependence of the measured apparent synodic solar rotation rate on the height of the chosen tracer is studied. A significant error occurs if the rotation rate is determined by tracing the apparent position of an object above the photospheric level projected on the solar disc. The centre-to-limb variation of this error can be used to determine simultaneously the height of the object and the true synodic rotation rate. The apparent (projected) heliographic coordinates are presented as a function of the height of the traced object and the coordinates of its footpoint. The relations obtained provide an explicit expression for the apparent rotation rate as a function of the observed heliographic coordinates of the tracer, enabling an analytic least-squares fit expression to determine simultaneously the real synodic rotation rate and the height of the tracer. 相似文献
179.
The territory of Croatia and neighboring regions is divided into 17 seismic source zones, considering available seismological
and geological data. On this basis, seismic hazard elements (seismicity rate, maximum magnitude, b-value, probabilities of
exceedance and return periods for a predefined set of magnitudes) are computed using the maximum likelihood method appropriate
for treating data-sets with variable completeness thresholds. The values of long term expected peak horizontal acceleration
obtained by using a combination of the deterministic and the probabilistic procedure are the highest in the Dubrovnik zone,
while the Zagreb zone has the highest earthquake hazard in the continental part of the country.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
180.
The paper is concerning with the light curve analysis of an active binary system of OO Aql. Basic orbital and physical parameters of this system were estimated by analysing photometric observations by Lafta and Grainger (1985) and Essam et al. (1992). Both groups of observations gave quite different light curves with a conspicuous asymmetry arising from unequal height of successive maxima. A slightly changed programme by Djuraevi (1992a) was applied. The programme was based on the Roche model and it included an option of overcontact configuration and active (bright or dark) spotted regions on the system's components. An inverse-problem method by Djuraevi (1992b) was used to estimate the parameters of the system and active regions. The light-curve analysis suggested a significant change in the system. For Lafta and Grainger's light curves our analysis showed the presence of a dark spotted area near the polar region of the primary component. This dark area covered about 22% of the primary's hemisphere. Essam et al.'s light curves had very complex shape. In this case the mechanism of the mass transfer and the exchange of the thermal energy between the components could produce a bright-spot (bs) area on the secondary, near the Lagrange equilibrium point L1 around the neck region between the stars. To explain a sharp increase of the system's brightness in the B filter immediately after the secondary minimum, we had to introduce also a hot-spot (hs) area of a high temperature contrast on the secondary. With the increase of the brightness in the V-filter being of much lower intensity, this hot spot region could be taken as a local eruption. The behaviour of the B–V colour index with the orbital phase is in favour of this hypothesis also. The obtained results show that the light-curve changes are due to development and moving of active spot regions on the components. 相似文献