全文获取类型
收费全文 | 10390篇 |
免费 | 1351篇 |
国内免费 | 1130篇 |
专业分类
测绘学 | 2957篇 |
大气科学 | 769篇 |
地球物理 | 1761篇 |
地质学 | 2412篇 |
海洋学 | 614篇 |
天文学 | 52篇 |
综合类 | 1741篇 |
自然地理 | 2565篇 |
出版年
2024年 | 28篇 |
2023年 | 136篇 |
2022年 | 440篇 |
2021年 | 512篇 |
2020年 | 479篇 |
2019年 | 501篇 |
2018年 | 319篇 |
2017年 | 494篇 |
2016年 | 449篇 |
2015年 | 484篇 |
2014年 | 603篇 |
2013年 | 645篇 |
2012年 | 727篇 |
2011年 | 738篇 |
2010年 | 610篇 |
2009年 | 514篇 |
2008年 | 581篇 |
2007年 | 661篇 |
2006年 | 613篇 |
2005年 | 525篇 |
2004年 | 494篇 |
2003年 | 422篇 |
2002年 | 341篇 |
2001年 | 332篇 |
2000年 | 221篇 |
1999年 | 195篇 |
1998年 | 183篇 |
1997年 | 137篇 |
1996年 | 87篇 |
1995年 | 91篇 |
1994年 | 92篇 |
1993年 | 61篇 |
1992年 | 39篇 |
1991年 | 27篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 20篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1977年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
251.
论数字城市工程及其技术体系 总被引:16,自引:0,他引:16
分析了数字城市的内涵 ,基于数字工程思想 ,总结了数字城市的工程结构与技术体系 ,进而阐述了数字城市的意义与建设策略。 相似文献
252.
253.
254.
Black Holes and Loose Connections in a Global Urban Network 总被引:1,自引:0,他引:1
John Rennie Short 《The Professional geographer》2004,56(2):295-302
This paper introduces the concept of black holes and loose connections in a global urban hierarchy. Black holes are defined as large cities, with a population of over 3 million, that are not classified as world cities. The paper draws upon a classification that uses advanced producer services as an indicator of world city status. Large, nonworld cities are identified, and provisional ideas about explaining their position are outlined. Connectivity and population data are used in a simple regression analysis to identify loose connections: cities whose connectivity is less than that predicted by their population. 相似文献
255.
256.
Underground coal and copper ore exploitation in two Polish mining regions causes mining tremors and a series of other negative phenomena in the environment. Although these tremors are strictly connected with human activity, they differ considerably from other paraseismic vibrations. The moment of their occurrence is not to be foreseen likewise for earthquakes. The main problem discussed in the paper was formulated as the neural network evaluation of a relation between mining tremor energies, epicentral distances and acceleration response spectra. Back-propagation neural networks with Resilient back-propagation learning method were used. Each input vector included information about the mining tremor energy and the epicentral distance. Values of acceleration response spectrum were expected as the outputs of neural networks. Neurally evaluated spectra were compared with spectra computed on the basis of experimental data. After the network is trained and tested, it can be used for mapping of new data of mining tremor energies and epicentral distances into the spectra. Then, what is the substantial advantage of neural approach, the prediction of acceleration response spectra can be performed without recording of surface vibrations. In the light of the results, it is visible that the presented way of computation of acceleration response spectra can be peculiarly applied to prognosis of mining tremors influences on structures. 相似文献
257.
建立能够反映储层孔隙结构、流体特征的逾 渗网络模型,通过数值模拟研究了储层孔隙尺寸、 孔隙形状、连通性、微孔隙的发育状况等对I-Sw曲 线影响的定性规律,研究了地层水矿化度对岩石电 阻率的影响。分析讨论了不同因素对电阻率影响的 相对强度。最后,通过曲线拟合定量地研究了不同 因素对I-Sw曲线的影响规律。研究表明,在上述影 响因素中连通性和微孔隙对I-Sw曲线的影响很大, 其它因素的影响强度较小。地层水矿化度对岩石电 阻率绝对值的影响很大。“非阿尔奇”现象普遍存在, 在低渗透(低连通性)储层岩石中更为明显。 相似文献
258.
Based on the land surface temperature (LST), the land cover classification map,vegetation coverage, and surface evapotranspiration derived from EOS-MODIS satellite data, and by the use of GIS spatial analytic technique and multivariate statistical analysis method, the urban heat island (UHI) spatial distribution of the diurnal and seasonal variabilities and its driving forces are studied in Beijing city and surrounding areas in 2001. The relationships among UHI distribution and landcover categories, topographic factor, vegetation greenness, and surface evapotranspiration are analyzed. The results indicate that: (i) The significant UHI occur in Beijing city areas in the four seasons due to high heat capacity and multi-reflection of compression building, as well as with special topographic features of its three sides surrounded by mountains,especially in the summer. The UHI spatial distribution is corresponding with the urban geometry structure profile. The LST difference is approximately 4-6℃ between Beijing city and suburb areas, comparatively is 8- 10℃ between Beijing city area and outer suburb area in northwestern regions. (ii) The UHI distribution and intensity in daytime are different from nighttime in Beijing city area, the nighttime UHI is obvious. However, in the daytime, the significant UHI mainly appears in the summer, the autumn takes second place, and the UHI in the winter and the spring seem not obvious. The surface evapotranspiration in suburb areas is larger than that in urban areas in the summer, and high latent heat exchange is evident, which leads to LST difference between city area and suburb area. (iii) The reflection of surface landcover categories is sensitive to the UHI, the correlation between vegetation greenness and UHI shows obviously negative.The scatterplot shows that there is the negative correlation between NDVI and LST (R2 = 0.6481).The results demonstrate that the vegetation greenness is an important factor for reducing the UHI,and large-scale construction of greenbelts can considerably reduce the UHI effect. 相似文献
259.
260.