全文获取类型
收费全文 | 27516篇 |
免费 | 5000篇 |
国内免费 | 5716篇 |
专业分类
测绘学 | 1127篇 |
大气科学 | 2022篇 |
地球物理 | 5267篇 |
地质学 | 16719篇 |
海洋学 | 4089篇 |
天文学 | 2204篇 |
综合类 | 1877篇 |
自然地理 | 4927篇 |
出版年
2024年 | 132篇 |
2023年 | 379篇 |
2022年 | 910篇 |
2021年 | 1202篇 |
2020年 | 1103篇 |
2019年 | 1310篇 |
2018年 | 1055篇 |
2017年 | 1121篇 |
2016年 | 1109篇 |
2015年 | 1256篇 |
2014年 | 1513篇 |
2013年 | 1803篇 |
2012年 | 1504篇 |
2011年 | 1663篇 |
2010年 | 1486篇 |
2009年 | 1782篇 |
2008年 | 1702篇 |
2007年 | 1810篇 |
2006年 | 1937篇 |
2005年 | 1603篇 |
2004年 | 1554篇 |
2003年 | 1451篇 |
2002年 | 1295篇 |
2001年 | 1127篇 |
2000年 | 1043篇 |
1999年 | 899篇 |
1998年 | 857篇 |
1997年 | 665篇 |
1996年 | 567篇 |
1995年 | 493篇 |
1994年 | 466篇 |
1993年 | 348篇 |
1992年 | 269篇 |
1991年 | 206篇 |
1990年 | 152篇 |
1989年 | 134篇 |
1988年 | 86篇 |
1987年 | 62篇 |
1986年 | 42篇 |
1985年 | 37篇 |
1984年 | 23篇 |
1983年 | 19篇 |
1982年 | 13篇 |
1981年 | 15篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 10篇 |
1973年 | 1篇 |
1971年 | 3篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
V. Castellani S. Degl'Innocenti P. G. Prada Moroni 《Monthly notices of the Royal Astronomical Society》2001,320(1):66-72
We compare theoretical stellar models for main sequence (MS) stars with the Hipparcos data base for the Hyades cluster to give a warning against the uncritical use of available theoretical scenarios and to show how formal MS fittings can be fortuitous if not fictitious. Moreover, we find that none of the current theoretical scenarios appears able to account for an observed mismatch between theoretical predictions and observations of the coolest Hyades MS stars. Finally, we show that current theoretical models probably give too faint He burning luminosities unlike the case of less massive He burning models, with degenerate progenitors, which have been suggested to suffer the opposite discrepancy. 相似文献
73.
74.
Yanjun ZHANG Fenglong ZHANG Full QI Fuquan NI 《东北亚地学研究》2006,9(2):199-203
In view of the situation of excavation of open coal mine for the underground water disaster,we should carry out simulation studies for the numerical value of the water lowering project and improve the accuracy and the level of the water lowering project.On the basis of the hydrological geological conditions of certain open mine digging,a more reasonable seepage numerical model was built according to MODFLOW.It was simulated in advance that the process of the confined water level descending with the time,and combining with the actual observations to test the correctness of the model.The calculation showed that the results coincided well with the results of actual measurement.Based on this,different water lowering numerical simulations were built for the open coal mine digging.It could be simulated and forecast that the changes of the groundwater level in drainage process within and outside the mine pit,and it was quantitatively assessed that the possible water lowering result of the opencast water drainage process,which provide an important basis for the actual water lowering project and the possible project disposal. 相似文献
75.
We investigate the evolution of rotation period and spindown age of a pulsar whose surface magnetic field undergoes a phase
of growth. Application of these results to the Crab pulsar strongly indicates that its parameters cannot be accounted for
by the field growth theories. 相似文献
76.
Natural and agricultural wetlands are considered to be the major sources of global atmospheric methane (CH4). A one‐dimensional model was developed to simulate methane emission and used to examine the influence of various physical processes on the rate of methane emission. Three processes involved in the methane emission are implemented in the model: production, reoxidation and transport. Three transport pathways were considered: diffusion across water–air or soil–air interfaces, ebullition and diffusion through plants. These pathways are influenced by soil properties, plant growth, water‐table conditions, temperature and external inputs (e.g. fertilizer). The model was used to examine the seasonal variation of the methane emission at a rice field in Hunan, China, which was observed during a field experiment for consecutive (early and late) rice seasons in 1992. The observed seasonal variations of methane emission, and role of plants in transporting methane to the atmosphere, are captured by the model simulation. Further model applications were conducted to simulate effects of fertilizer and water‐level condition on the methane emission. The results indicate that unfermented organic fertilizer produces a higher methane emission rate than mineral fertilizer. The simulations with treatments of a deep‐water covering and constant moisture reduced the methane emission. The rice field study provides a framework for further development of the model towards simulations based on spatially distributed variables (e.g. water table, soil temperature and vegetation) at a regional scale. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
77.
试论城市地貌环境与城市道路系统的关系*——以四川省几个城市为例 总被引:5,自引:0,他引:5
本文分析了城市地貌环境对城市道路系统的影响,认为地貌过程不仅影响了城市道路的建设和管理,而且是城市道路系统布局和发展的重要控制因素。以四川省几个城市为例,分析了山地城市、丘陵城市和平原城市道路系统的不同特点。 相似文献
78.
通过对美国地下空间开发利用的考察,认为有如下特点,第一,结合城市建设,构筑地下铁道,第二立足于战略,建立水下通路,第三,地下空间的开发利用平战结合.这些方法对我国的地下空间开发利用值得借鉴. 相似文献
79.
80.
IMPACTS OF FUTURE SEA LEVEL RISE ON SALT WATER INTRUSION IN THE CHANGJIANG RIVER ESTUARY 总被引:1,自引:0,他引:1
杨桂山 《中国地理科学(英文版)》1992,2(1):30-41
Sea level rise could increase the salinity of an estuary by altering the balance between fresh water and salt water. The implications of sea level rise for increasing salinity have been examined in the Changjiang (Yangtze) River estuary. By correlative analysis of chlorinity, discharge and tidal level and calculation of two-dimensional chlorinity, distribution of the Changjiang River estuary, the changes of the intensity and lasting hours of salt water intrusion at Wusong Station and the changes of chlorinity distribution in the South Branch of the Changjiang River estuary have been estimated when future sea level rises 50-100 cm. The intensity of salt water intrusion in the future will be far more serious than current trend. 相似文献