全文获取类型
收费全文 | 3837篇 |
免费 | 753篇 |
国内免费 | 1132篇 |
专业分类
测绘学 | 327篇 |
大气科学 | 920篇 |
地球物理 | 889篇 |
地质学 | 2086篇 |
海洋学 | 478篇 |
天文学 | 90篇 |
综合类 | 331篇 |
自然地理 | 601篇 |
出版年
2024年 | 28篇 |
2023年 | 68篇 |
2022年 | 198篇 |
2021年 | 220篇 |
2020年 | 212篇 |
2019年 | 216篇 |
2018年 | 236篇 |
2017年 | 208篇 |
2016年 | 242篇 |
2015年 | 250篇 |
2014年 | 256篇 |
2013年 | 262篇 |
2012年 | 254篇 |
2011年 | 260篇 |
2010年 | 274篇 |
2009年 | 226篇 |
2008年 | 203篇 |
2007年 | 183篇 |
2006年 | 167篇 |
2005年 | 149篇 |
2004年 | 144篇 |
2003年 | 162篇 |
2002年 | 255篇 |
2001年 | 216篇 |
2000年 | 155篇 |
1999年 | 132篇 |
1998年 | 79篇 |
1997年 | 83篇 |
1996年 | 60篇 |
1995年 | 68篇 |
1994年 | 57篇 |
1993年 | 48篇 |
1992年 | 30篇 |
1991年 | 26篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1972年 | 1篇 |
1958年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有5722条查询结果,搜索用时 15 毫秒
961.
Hydrochemistry of geothermal water in Tianshui and adjacent area, Gansu province, China 总被引:1,自引:1,他引:0
A geochemical study on thermal water has been carried out in Tianshui and its adjacent area, Gansu province, China. Chemical and isotopic contents were employed in the investigation on the origin and evolution of thermal water and the evaluation of reservoir temperature in the geothermal systems. Thermal waters in Wushan and Tianshui are characterized by outlet temperatures from 15 to 38°C and low TDS (226?C255?mg/L), defined as bicarbonate water. Its origin may be attributed to the interaction between meteoric rain, biotite plagioclase gneiss and carbonate reservoir rocks. In contrast, thermal waters in Tongwei and Qingshui have higher outlet temperatures of 25?C54.2°C and a moderate TDS of 915?C1,793?mg/L, regarded as sulfate waters. These sulfate waters may arise from the interaction between meteoric water, granite and amphogneiss. Isotopic data presented here suggest that thermal waters in the study area have a meteoric origin without being significantly effected by water?Crock isotope exchange. Chemical geothermometry indicates the existence of a deep geothermal reservoir of low-to-medium enthalpy (70?C111°C) in the Tianshui study area. 相似文献
962.
963.
Xingping Wen Xiaofeng Yang Guangdao Hu 《Journal of the Indian Society of Remote Sensing》2011,39(2):193-201
Urban heat island (UHI) effect has a close relation to land covers type. This paper investigates the relationship between
land cover ratio and UHI in Guangzhou, south of China using remote sensing and automatic weather stations data. The temperature
data were obtained by Automatic weather stations (AWS) of Guangzhou in October, 2004, at the same time with the CBERS remote
sensing image acquired. Firstly, the hourly mean temperature was computed from hourly AWS data. Secondly, the CBERS remote
sensing image was classified using support vector machine (SVM) and land covers classification were output. Thirdly, the classification
result was overlapped with a round buffer with 1.5 KM radius centered on the AWS, and then the land cover ratio, Edge Density
(ED) and Mean Fractal Dimension (MFRACT) of buffers were computed out. Finally, the correlation coefficient between hourly
mean temperature and land cover ratio, ED and MFRACT was calculated. It concluded that UHI intensity was heavier during nighttime
than daytime. Stations with higher vegetation ratio and higher ED had lower heat island effect. On the contrary, stations
with higher impervious ratio and lower ED had more serious heat island effect. The positive–negative of correlation coefficient
between hourly mean temperature and vegetation ratio during 11:00–17:00 h (local time) was opposite to that during other time.
ED was negatively correlated with hourly mean temperature except during 11:00–17:00 h. On the contrary, MFRACT was positively
correlated with hourly mean temperature. It implied that fragmentations of patches were favorable to UHI alleviation, and
complexities of patch were unfavorable factors. 相似文献
964.
遥感影像亮度和反差分布不均匀性校正算法的效果比较 总被引:1,自引:1,他引:0
提出能同时消除亮度和反差分布不均匀现象的分块均值方差变换法, 重点对插值匀光法、MASK 匀光
法、同态滤波匀光法、Retinex 匀光法以及分块均值方差变换法的校正效果进行了实验比较。研究表明: 分块均值
方差变换法既能消除亮度分布不均匀现象, 又能消除反差分布不均匀现象, 而MASK 匀光法、插值匀光法、Retinex
匀光法只能解决亮度分布不均匀问题, 同态滤波匀光法仅能减弱亮度分布不均匀现象; 在匀光效果方面, 分块均
值方差变换法最好, MASK 匀光法次之, 插值匀光法紧随其后, 接下来是Re 相似文献
965.
966.
967.
968.
当前数字城管系统良莠不齐,在建设中存在较多问题,制约了城市管理信息化水平快速提高,应用RFID技术和3DGIS技术可以较好地解决这些问题。文章介绍了RFID技术和3DGIS技术在数字城管系统中的应用,为城市管理的信息化、数字化开拓了新的发展方向。 相似文献
969.
Diagnostic analysis of the evolution mechanism for a vortex over the Tibetan Plateau in June 2008 总被引:2,自引:0,他引:2
Based on the final analyses data (FNL) of the Global Forecasting System of the NCEP and the obser- vational radiosonde data, the evolution mechanism of an eastward-moving low-level vortex over the Tibetan Plateau in June 2008 was analyzed. The results show that the formation of the vortex was related to the convergence between the northwesterly over the central Tibetan Plateau from the westerly zone and the southerly from the Bay of Bengal at 500 hPa, and also to the divergence associated with the entrance re- gion of the upper westerly jet at 200 hPa. Their dynamic effects were favorable for ascending motion and forming the vortex over the Tibetan Plateau. Furthermore, the effect of the atmospheric heat source (Q1) is discussed based on a transformed potential vorticity (PV) tendency equation. By calculating the PV budgets, we showed that Q1 had a great inffuence on the intensity and moving direction of the vortex. In the developing stage of the vortex, the heating of the vertically integrated Q1 was centered to the east of the vortex center at 500 hPa, increasing PV tendency to the east of the vortex. As a result, the vortex strengthened and moved eastward through the vertically uneven distribution of Q1. In the decaying stage, the horizontally uneven heating of Q1 at 500 hPa weakened the vortex through causing the vortex tubes around the vortex to slant and redistributing the vertical vorticity field. 相似文献
970.
Cloud droplet dispersion is an important parameter in estimating aerosol indirect effect on climate in general circulation
models (GCMs). This study investigates droplet dispersion in shallow cumulus clouds under different aerosol conditions using
three-dimensional large eddy simulations (LES). It is found that cloud droplet mean radius, standard deviation, and relative
dispersion generally decrease as aerosol mixing ratio increases from 25 mg−1 (clean case) to 100 mg−1 (moderate case), and to 2000 mg−1 (polluted case). Under all the three simulated aerosol conditions, cloud droplet mean radius and standard deviation increase
with height. However, droplet relative dispersion increases with height only in the polluted case, and does not vary with
height in the clean and moderate cases. 相似文献