全文获取类型
收费全文 | 30480篇 |
免费 | 6338篇 |
国内免费 | 8003篇 |
专业分类
测绘学 | 4492篇 |
大气科学 | 6225篇 |
地球物理 | 8892篇 |
地质学 | 12233篇 |
海洋学 | 6256篇 |
天文学 | 379篇 |
综合类 | 2324篇 |
自然地理 | 4020篇 |
出版年
2024年 | 109篇 |
2023年 | 383篇 |
2022年 | 1020篇 |
2021年 | 1253篇 |
2020年 | 1434篇 |
2019年 | 1551篇 |
2018年 | 1362篇 |
2017年 | 1559篇 |
2016年 | 1653篇 |
2015年 | 1840篇 |
2014年 | 1962篇 |
2013年 | 2215篇 |
2012年 | 2089篇 |
2011年 | 2146篇 |
2010年 | 1723篇 |
2009年 | 1964篇 |
2008年 | 1969篇 |
2007年 | 2189篇 |
2006年 | 2035篇 |
2005年 | 1806篇 |
2004年 | 1645篇 |
2003年 | 1415篇 |
2002年 | 1274篇 |
2001年 | 1083篇 |
2000年 | 1033篇 |
1999年 | 935篇 |
1998年 | 879篇 |
1997年 | 739篇 |
1996年 | 653篇 |
1995年 | 637篇 |
1994年 | 552篇 |
1993年 | 455篇 |
1992年 | 309篇 |
1991年 | 262篇 |
1990年 | 161篇 |
1989年 | 133篇 |
1988年 | 124篇 |
1987年 | 76篇 |
1986年 | 40篇 |
1985年 | 40篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 13篇 |
1979年 | 11篇 |
1978年 | 14篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1954年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
71.
当前,由于缺乏对气象服务投入量与产出量准确而完整的统计,要对气象服务的各种经济效益作出总体评价是困难的。然而,在专项气象服务中,却不乏原始、完整而准确的资料。作者从此出发,讨论了专项气象服务经济效益评价的理论。并通过实地调查,以彭州市气象局几项专项气象服务为例探讨了评价技术。 相似文献
72.
介绍建立大地构造内波假说的根据,即:(1)全球海陆分布的低阶球谐特征;(2)全球大洋中脊体系的存在;(3)大陆永存及生长的事实;(4)地壳均衡及莫霍面的化学分界面性质;(5)地槽活动的现象、规律等。在分析以在事实的基础上,研究了大地构造运动中主要的物质运动过程,认为从薄地壳底部向厚地壳底部迁移的地壳物质流,引起地壳厚度的自激波动,推动地槽运动和大陆生长。 相似文献
73.
74.
75.
This paper considers the problem of estimatingm, the number of components in a finite mixture of distributions from a parametric family. A step-up procedure using the bootstrap method is proposed. Some properties of the procedure are illustrated with simulation studies. An example of the method, applied to orientation of beach clasts, is given. 相似文献
76.
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
77.
Summary. Multiparameter inversions of multimode dispersion data are performed for two large regions: the Pacific Ocean and North America. Anisotropy is taken into account by considering transversely isotropic structures with a vertical axis of symmetry. Two fundamental questions are studied in detail: (1) how to make the inverted models consistent when using different sets of parameters, (2) what is the significance of transversely isotropic inversion for the actual Earth's structure? It is proved that full consistency of the inverted models can be achieved by properly taking into account some a priori informations on the model and it is shown that the use of transversely isotropic models with vertical axis of symmetry does not cause severe limitations when interpreting the data. The models we have obtained are discussed in the light of these investigations. Considering an olivine-rich upper mantle, we make a tentative interpretation of these models in terms of preferred orientation of the a -axis of the crystals in one fixed horizontal direction. 相似文献
78.
笔者曾对广西芒场锡多金属矿田的稳定同位素进行研究。本文根据硫、铅、氢、氧、碳等稳定同位素组成和锶的初始值提供的信息.探讨了矿床成因。并结合矿田矿床地质特征、控矿条件及有关统计参数,参考前人对矿床认识的基础上,修正提出了该矿田混合热液成矿模式,可供类似矿床研究和找矿的参考。 相似文献
79.
This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
80.
Simulation of double cold cores of the 35°N section in the Yellow Sea with a wave-tide-circulation coupled model 总被引:1,自引:0,他引:1
Based on the MASNUM wave-tide-circulation coupled numerical model, the temperature structure along 35°N in the Yellow Sea
was simulated and compared with the observations. One of the notable features of the temperature structure along 35°N section
is the double cold cores phenomena during spring and summer. The double cold cores refer to the two cold water centers located
near 122°E and 125°E from the depth of 30m to bottom. The formation, maintenance and disappearance of the double cold cores
are discussed. At least two reasons make the temperature in the center (near 123°E) of the section higher than that near the
west and east shores in winter. One reason is that the water there is deeper than the west and east sides so its heat content
is higher. The other is invasion of the warm water brought by the Yellow Sea Warm Current (YSWC) during winter. This temperature
pattern of the lower layer (from 30m to bottom) is maintained through spring and summer when the upper layer (0 to 30m) is
heated and strong thermocline is formed. Large zonal span of the 35°N section (about 600 km) makes the cold cores have more
opportunity to survive. The double cold cores phenomena disappears in early autumn when the west cold core vanishes first
with the dropping of the thermocline position.
Supported by the National Basic Research Program of China (No. G1999043809) and the National Science Foundation of China (No.
49736190). 相似文献