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711.
In spite of the important relationship between sediment particle size and the transport/deposition of adsorbed pollutants in fluvial systems, little information regarding the size characteristics of suspended sediment transported by southern Ontario Great Lakes tributaries is currently available. This paper examines long-term sediment and hydrometric data collected by the Water Resources Branch of Environment Canada in order to provide information on (1) typical particle size distributions of suspended sediment, (2) relationships between source material and particle size characteristics of suspended sediment, and (3) temporal variation in the particle size characteristics of suspended sediment from six southern Ontario rivers. Results illustrate the complex behaviour and variability of sediment particle size transport in these rivers and demonstrate the need for a better understanding of seasonal effects on sediment availability and conveyance processes in fluvial systems. 相似文献
712.
陈伯舫 《地震地磁观测与研究》1996,17(2):44-49
地面Sq磁场的分析在一定程度上揭示场向电流的存在,在赤道电射流区和低纬地区,某些日子的Y分量或D分量Sq变化可明显地显示午间场向电流的存在,1990年12月11日Baclieu,琼中,河内,Chapa,通海和成都等台的Sq(I)曲线清楚表明由冬季半球流向夏季半球的午间场向电流的影响,此外,本文还用(夏-冬)/2法分析了Sq(Z)的资料,从中也可观察到午间及清晨场向电流的踪迹。 相似文献
713.
714.
Evolution of the Earth's principal axes and moments of inertia: the canonical form of solution 总被引:4,自引:0,他引:4
Harmonic coefficients of the 2nd degree are separated into the invariant quantitative (the 2nd-degree variance) and the qualitative
(the standardized harmonic coefficients) characteristics of the behavior of the potential V
2(t). On this basis the evolution of the Earth's dynamical figure is described as a solution of the time-dependent eigenvalues–eigenvectors
problem in the canonical form. Such a canonical quadratic form is defined only by temporal variations of the harmonic coefficients
and always remains finite, even within an infinite time interval. An additional condition for the correction or the determination
of temporal variations of the 2nd degree is obtained. Temporal variations of the fully normalized sectorial harmonic coefficients
are estimated in addition to ˙Cˉ
20, ˙Cˉ
21, and ˙Sˉ
21 of the EGM96 gravity model. In addition, a non-linear hyperbolic model for Cˉ
2m
(t), Sˉ
2m
(t) is constructed. The trigonometric form of the hyperbolic model leads to the consideration of the potential V
2(ψ) instead of V
2(t) within the closed interval −π/2≤ψ≤+π/2. Thus, it is possible to evaluate the global trend of V
2(t), the Earth's principal axes and the differences of the moments of inertia within the whole infinite time interval.
Received: 25 September 1998 / Accepted: 28 June 2000 相似文献
715.
In this paper seven of the ten Water Control Zones (WCZs) in Hong Kong’s coastal waters with monthly or bi-weekly sampling
data of 17 parameters collected at 37 monitoring stations from 1988 to 1999 were selected to analyze the spatial and temporal
variations of chlorophyll-a and its influencing factors. Cluster analysis was employed to group the monitoring stations based
on the structure of the data set. Multiple step regression was employed to determine the significant influencing factors of
chlorophyll-a level. The results suggest that all the monitoring stations could be grouped into two clusters. Cluster I with
frequent red tide incidents comprises two WCZs which are semi-enclosed bays. Cluster II with less red tide occurrence comprises
the other five WCZs in an estuarine environment in the west. For both clusters, the organic contents indicator, BOD5, was
a common significant influencing factor of the chlorophyll-a level. Nitrogen and light penetration condition related to turbidity,
total volatile solids and suspended solids had more influence on the cholophyll-a level in Cluster I than in Cluster II, while
phosphorus and oceanographic conditions associated with salinity, temperature, dissolved oxygen and pH were more important
in Cluster II than in Cluster I. Generally, there was a higher average chlorophyll-a level in winter and autumn in a year.
The chlorophyll-a level was much higher in Cluster I than in Cluster II among all seasons. Although the chlorophyll-a concentration
had great variations from place to place in Hong Kong’s coastal waters, it seemed to have a common long term fluctuation period
of 8–10 years with a high-low-high variation in the period in the whole region, which might be influenced by other factors
of global scale. 相似文献
716.
717.
718.
本文选取了汾渭地震带从1970年至1989年二十年的地震资料,对所发生地震的时间分维结构进行了研究。文中分别以两个月为一个单位和一年为一个单位计算了时间分维数,绘出了每两个月D_t随时间t的变化曲线和二十年中每年D_t随t的变化曲线。经过计算发现,多数较强地震前D_t值明显降低,在大同一阳高地震中表现较明显,震前1988年的时间分维值为0.1944,1989年9月计算出的分维值为0.1312。 相似文献
719.
Fourier analysis of the monthly mean northern hemispheric geopotential heights for the levels 700 mb and 300 mb are undertaken for the months of April through to August. The wave to wave and wave to zonal mean flow kinetic energy interactions are computed for specified latitude bands of the northern hemisphere during the pre-monsoon period (April to May) and monsoon period (June through to August) for bad monsoon years (1972, 1974, 1979) and for years of good monsoon rainfall over India (1967, 1973, 1977). Planetary scale waves (waves 1 to 4) are the major kinetic energy source in the upper atmosphere during the monsoon months. Waves 1 and 2 in particular are a greater source of kinetic energy to other waves via both wave to wave interactions as well as wave to zonal mean flow interactions in good monsoon years than in bad monsoon years. The zonal mean flow shows significantly larger gains in the kinetic energy with a strengthening of zonal westerlies in good monsoon years than in bad monsoon years. 相似文献
720.