全文获取类型
收费全文 | 16853篇 |
免费 | 4157篇 |
国内免费 | 5982篇 |
专业分类
测绘学 | 2858篇 |
大气科学 | 2669篇 |
地球物理 | 3056篇 |
地质学 | 10432篇 |
海洋学 | 3882篇 |
天文学 | 299篇 |
综合类 | 1519篇 |
自然地理 | 2277篇 |
出版年
2024年 | 131篇 |
2023年 | 377篇 |
2022年 | 1050篇 |
2021年 | 1308篇 |
2020年 | 1087篇 |
2019年 | 1280篇 |
2018年 | 1203篇 |
2017年 | 1047篇 |
2016年 | 1090篇 |
2015年 | 1223篇 |
2014年 | 1234篇 |
2013年 | 1489篇 |
2012年 | 1600篇 |
2011年 | 1525篇 |
2010年 | 1497篇 |
2009年 | 1341篇 |
2008年 | 1386篇 |
2007年 | 1294篇 |
2006年 | 1147篇 |
2005年 | 950篇 |
2004年 | 745篇 |
2003年 | 490篇 |
2002年 | 575篇 |
2001年 | 529篇 |
2000年 | 405篇 |
1999年 | 256篇 |
1998年 | 104篇 |
1997年 | 109篇 |
1996年 | 95篇 |
1995年 | 74篇 |
1994年 | 53篇 |
1993年 | 41篇 |
1992年 | 46篇 |
1991年 | 35篇 |
1990年 | 29篇 |
1989年 | 23篇 |
1988年 | 13篇 |
1987年 | 17篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1979年 | 7篇 |
1973年 | 3篇 |
1964年 | 3篇 |
1954年 | 10篇 |
1933年 | 3篇 |
1925年 | 4篇 |
1923年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Study of the flood control scheduling scheme for the Three Gorges Reservoir in a catastrophic flood 下载免费PDF全文
The Three Gorges Project is the world's largest water conservancy project. According to the design standards for the 1,000‐year flood, flood diversion areas in the Jingjiang reach of the Yangtze River must be utilized to ensure the safety of the Jingjiang area and the city of Wuhan. However, once these areas are used, the economic and life loss in these areas may be very great. Therefore, it is vital to reduce this loss by developing a scheme that reduces the use of the flood diversion areas through flood regulation by the Three Gorges Reservoir (TGR), under the premise of ensuring the safety of the Three Gorges Dam. For a 1,000‐year flood on the basis of a highly destructive flood in 1954, this paper evaluates scheduling schemes in which flood diversion areas are or are not used. The schemes are simulated based on 2.5‐m resolution reservoir topography and an optimized model of dynamic capacity flood regulation. The simulation results show the following. (a) In accord with the normal flood‐control regulation discharge, the maximum water level above the dam should be not more than 175 m, which ensures the safety of the dam and reservoir area. However, it is necessary to utilize the flood diversion areas within the Jingjiang area, and flood discharge can reach 2.81 billion m3. (b) In the case of relying on the TGR to impound floodwaters independently rather than using the flood diversion areas, the maximum water level above the dam reaches 177.35 m, which is less than the flood check level of 180.4 m to ensure the safety of the Three Gorges Dam. The average increase of the TGR water level in the Chongqing area is not more than 0.11 m, which indicates no significant effect on the upstream reservoir area. Comparing the various scheduling schemes, when the flood diversion areas are not used, it is believed that the TGR can execute safe flood control for a 1,000‐year flood, thereby greatly reducing flood damage. 相似文献
2.
3.
隧道工程地质评价的内容和方法 总被引:2,自引:0,他引:2
结合工程隧道实际,首先阐述了隧道工程的基本地质环境和工程地质条件,然后针对隧道工程可能出现的不良地质现象和可采取的工程措施,从大气降水、围岩稳定、围岩压力、洞口稳定、隧道比选等角度探讨隧道工程地质评价的主要方法和一般内容,进行隧道工程地质评价,为隧道施工、支护提供了依据. 相似文献
4.
The Tamtsag Basin is located in the extreme eastern portion of the Mongolia. The Basin and its counterpart in China (the Hailar Basin) are united a whole basin on the structural setting. In recent years, the Tamtsag Basin attracts more and more attention with the important exploration discovered in the 19th block by SOCO and in Hailar Basin of China. This paper discusses the exploration potential of Tamtsag Basin from the viewpoint of petroleum geology. 相似文献
5.
本文用简单的宇宙学模型 ,在标准烛光和均匀分布的假设下计算了γ射线暴的logN(>P)~logP分布 (大小谱 ) .在考虑了探测效率修正和死时间修正后 ,由宇宙学模型计算的理论结果和BATSE实测的大小谱没有显著的偏离 相似文献
6.
7.
8.
The effect of ocean wave breaking as a non-Bragg mechanism on backscattering cross-section and modulation transfer functions (MTF) of radar was investigated based on Bragg resonance theory and parametric method. The result showed that the additional effect of wave breaking on backscattering cross-section is not more than 20% except for the small incident angle of VV polarized electromagnetic (e.m.) wave but is significant for HH polarized e.m. wave. Breaking waves lead to increase in the modulus of tilt modulation MTF and the larger the wind speed, the faster the increase. For large incident angle, the modulus of tilt modulation MTF with wave breaking decreases quickly with incident angle for HH polarization and approach to that without wave breaking for VV polarization. The hydrodynamic MTF increases 30%-60% when considering wave breaking and the increase is larger for HH polarization than for VV polarization. 相似文献
9.
The actual penetration depth of the Shoemaker-Levy 9 fragments into the Jovian atmosphere is still an open question. From fundamental equations of meteoric physics with variable cross-section, a new analytic model of energy release of the fragments is presented. In use of reasonable parameters, a series of results are calculated for different initial mass of the fragments. The results show that the largest fragment explodes above pressure levels of 3 bars and does not penetrate into the H2O cloud layer of the Jovian atmosphere, and that airburst of smaller fragments occur even above the upper cloud layer. 相似文献
10.