全文获取类型
收费全文 | 1233篇 |
免费 | 329篇 |
国内免费 | 502篇 |
专业分类
测绘学 | 106篇 |
大气科学 | 1134篇 |
地球物理 | 163篇 |
地质学 | 356篇 |
海洋学 | 94篇 |
天文学 | 5篇 |
综合类 | 102篇 |
自然地理 | 104篇 |
出版年
2024年 | 7篇 |
2023年 | 17篇 |
2022年 | 44篇 |
2021年 | 40篇 |
2020年 | 82篇 |
2019年 | 65篇 |
2018年 | 51篇 |
2017年 | 56篇 |
2016年 | 67篇 |
2015年 | 76篇 |
2014年 | 114篇 |
2013年 | 102篇 |
2012年 | 118篇 |
2011年 | 98篇 |
2010年 | 51篇 |
2009年 | 130篇 |
2008年 | 90篇 |
2007年 | 122篇 |
2006年 | 94篇 |
2005年 | 121篇 |
2004年 | 75篇 |
2003年 | 62篇 |
2002年 | 34篇 |
2001年 | 55篇 |
2000年 | 44篇 |
1999年 | 45篇 |
1998年 | 36篇 |
1997年 | 26篇 |
1996年 | 26篇 |
1995年 | 32篇 |
1994年 | 23篇 |
1993年 | 23篇 |
1992年 | 8篇 |
1991年 | 9篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有2064条查询结果,搜索用时 15 毫秒
71.
在自然界与人类系统水分平衡概念的基础上,提出了作降水评价的供需平衡模式。该模式对全面发挥由降水所形成的各种主要水资源成分的潜力是有用的。用此模式作了个例试验,并提出在水分不足地区缓解水分欠缺的途径。 相似文献
72.
差巴嘎蒿繁殖若干问题的探讨 总被引:9,自引:0,他引:9
差巴嘎蒿(Artemasiahalodendron)营养繁殖的最佳材料是当年生带根基部营养枝;降水量是影响营养繁殖成活率的主导因子,栽植后5日内降水之和(x)与成活率(y)的相关系数为0.9701,回归方程为:y=34.0236+41.04671gx。营养繁殖应在有一定降水的条件下及时进行,最佳时间在6月中旬。不宜利用种子繁殖建立人工植被。 相似文献
73.
Peng Wang Lei Liu Xichuan Liu Shuai Hu Shijun Zhao Wenming Ji Taichang Gao 《地球科学进展》1986,35(7):704-714
The accurate observation of the microphysical structure of cloud and precipitation plays an important role in understanding the formation of clouds and precipitation. In-situ measurement using measuring instruments carried by meteorological balloons is an effective way to obtain the microphysical properties of cloud and precipitation particles, which is a supplementary means for aircraft to observe cloud and precipitation particles. This observation method plays a more and more important role in in-situ measurement. According to the difference of the working principle of the existing balloon-borne cloud and precipitation particles probes, the detectors can be divided into particle impact-sampling sensors, particle imaging sensors, light-scattering sensors, light intensity attenuation sensors and charge measurement sensors. The working principles, key technologies and main advantages and disadvantages of typical instruments were summarized, and their applications to detailed cloud structure acquisition, cloud remote sensing method establishment, cloud and precipitation physical process research and parameterization, and scientific observation of thunderstorm clouds were briefly introduced. Finally, the development trend of balloon-borne cloud precipitation particle detectors was prospected, which will provide reference for related technical research and equipment development. 相似文献
74.
甘肃省铜矿床主要类型及其找矿潜力分析 总被引:1,自引:0,他引:1
通过对甘肃铜矿资源现状的分析以及对主要铜矿类型特征的总结,结合铜矿形成的地质背景和时空分布规律,对我省找矿潜力作出合理评价,并提出了找矿方向。研究表明,甘肃找矿的第一主攻类型为火山岩型铜矿,其次为硫化铜镍型;主攻地区为北祁连和碧口地区,其次为北山和龙首山。 相似文献
75.
云南省40年降水的基本特征 总被引:5,自引:0,他引:5
根据云南省1951-1990年18个站的降水资料,用正交函数展开,由方差贡献最大的前三个特征向量场分析了云南省降水距平均的典型分布,指出云南省全省范围内的降水距平同号较少发生,而是较多的发一降水距平异号。进而分析了四十年降水的年际变化特征,并分析了青藏高原积雪对云南降水的影响。 相似文献
76.
On the relationship of thunderstorm ice hydrometeor characteristics and total lightning measurements 总被引:1,自引:0,他引:1
Wiebke Deierling John Latham Walter A. Petersen Scott M. Ellis Hugh J. Christian Jr. 《Atmospheric Research》2005,76(1-4):114
Satellite-borne and ground-based devices for the detection of lightning offer the opportunity to explore relationships–on all significant scales up to global–between lightning frequency, f, and other thundercloud parameters. Calculations predict that f is proportional to the product of the downflux p of solid precipitation and the upward mass flux, I, of ice crystals. This prediction has received support from limited computational studies. The physical reasons for such a relationship are explained in terms of the paramount role of ice in the electrification of thunderstorms. Herein, this prediction is subjected to further, preliminary examination through analysis of lightning and dual-polarimetric radar data collected during the STERAO experiment conducted in Northern Colorado during the summer of 1996. The analysis has yielded some highly provisional support for this flux hypothesis. Computed trends of radar derived hydrometeor fractions of solid precipitation and small ice show correlation to the total lightning frequency and raise the possibility of determining values of p and/or I from lightning measurements.It is shown that the extent to which the observed correlations between f and both solid precipitation and small ice trends are or are not strong can provide an indication as to whether the lightning activity is limited by the available concentrations of precipitating or non-precipitating ice in the upper regions of the charging zone of the thundercloud, where most of the charge transfer occurs. It is demonstrated that the most accurate determinations of precipitation rate p from measurements of lighting frequency f are likely to be for conditions where the field-growth is limited by the availability of graupel pellets. It is shown that the simultaneous time variations of f and solid precipitation trends of the type obtained in the STERAO experiment could enable us to determine the nature of the dominant glaciation process operative in the thunderclouds studied. 相似文献
77.
Short-term risk forecasts of point precipitation are obtained with COTREC/RainCast, a technique for extrapolation of radar images. The risk forecasts are updated every 5 min for the next 0–2 h. Risk levels are defined for moderate, heavy and extreme precipitation. Warning messages are generated if, at the locations of 23 rain gauges, these risk levels are reached or exceeded. The time-resolved gauge data are used to judge if the warning messages are in time, early or late.Data over a period of 4 months (summer 2002) are used for verification. The largest number of warnings (1790) was obtained for moderate precipitation. About 55% of these warnings were in time, 23% were early and 22% were late. This finding is in a good agreement with the defined risk level for warnings (50%), indicating that the model for calculating the risk factors is reliable. Less warnings in time, and more late warnings were found for heavy and extreme precipitation. Hence, the risk levels need to be lowered for heavy and extreme precipitation, in order to reduce the number of late warnings. 相似文献
78.
79.
Fadong Li Xianfang Song Changyuan Tang Changming Liu Jingjie Yu Wanjun Zhang 《Environmental Geology》2007,53(3):687-696
The groundwater in headwater region is an important recharge source for the adjacent mountain-front plain. In order to reveal
the relationship among precipitation, soil water and groundwater, from June to September in 2004, stable isotopes (deuterium
and oxygen-18) in precipitation and soil waters at the depths of 10, 20, 30, 50, 70, 90, and 110 cm were analyzed at two sites
covered by black locust (Robinia Pseudoacia L.) (Site A) and grass predominated by Themeda triandra (T. japonica (Willd.) Tanaka) and Bothriochloa ischaemum (B. ischaemum (L.) Keng) (Site B) in an experimental catchment at Taihang Mt., North China, respectively. The δ18O of precipitation in daily rain events shows large variations (−13.3 to −4.3‰) with a mean of 8.1‰. The δ18O and δ D of soil waters along profiles in two sites suggest that the influence of canopy cover was just up to 10 cm in top
soil water. The soil water moved over the zero flux plane at 70 cm in-depth is expected to escape the evaporative effect at
the end of September in both sites. The results show that the stable isotope, instead of tritium as tradition, can be used
to trace the soil water behaviors based on the movement of isotopic peak along the vertical profiles in this semi-arid and
semi-humid mountainous region. The infiltration depths of soil water in Taihang Mt. are 12 and 10 mm/day from June to September
in 2004 in Site A and Site B, respectively. Tracing by stable isotope, recharge fluxes of soil water to local groundwater
are of 3.8 and 3.2 mm/day in Site A and Site B, respectively. The results provide desirable information for assessment of
local groundwater resources.
An erratum to this article can be found at 相似文献
80.
The stable isotopes of oxygen and hydrogen were used to determine the seasonal contributions of precipitation to groundwater
recharge at a forested catchment area in the upper North Han River basin, Korea. A comparison of the stable isotopic signatures
of groundwater and precipitation indicates that the precipitations which occurred during both the dry and rainy seasons are
the important source of groundwater recharge in this region. A stable isotopic signature shown in the stream waters at the
upstream reaches is similar to that of groundwaters, indicating that stream waters are mostly fed by groundwater discharge.
Reservoir waters in the downstream flood control dams have lower deuterium excess values or d-values compared with those of the upstream waters, indicating a secondary evaporative enrichment. These results can provide
a basis for the effective management of groundwater and stream water resources in the North Han River basin. 相似文献