全文获取类型
收费全文 | 7502篇 |
免费 | 1454篇 |
国内免费 | 1995篇 |
专业分类
测绘学 | 1382篇 |
大气科学 | 1092篇 |
地球物理 | 1877篇 |
地质学 | 4054篇 |
海洋学 | 627篇 |
天文学 | 147篇 |
综合类 | 666篇 |
自然地理 | 1106篇 |
出版年
2024年 | 48篇 |
2023年 | 149篇 |
2022年 | 333篇 |
2021年 | 363篇 |
2020年 | 339篇 |
2019年 | 415篇 |
2018年 | 336篇 |
2017年 | 312篇 |
2016年 | 378篇 |
2015年 | 455篇 |
2014年 | 456篇 |
2013年 | 498篇 |
2012年 | 530篇 |
2011年 | 551篇 |
2010年 | 464篇 |
2009年 | 486篇 |
2008年 | 453篇 |
2007年 | 526篇 |
2006年 | 505篇 |
2005年 | 425篇 |
2004年 | 385篇 |
2003年 | 314篇 |
2002年 | 303篇 |
2001年 | 266篇 |
2000年 | 231篇 |
1999年 | 236篇 |
1998年 | 238篇 |
1997年 | 185篇 |
1996年 | 149篇 |
1995年 | 115篇 |
1994年 | 117篇 |
1993年 | 95篇 |
1992年 | 95篇 |
1991年 | 36篇 |
1990年 | 35篇 |
1989年 | 40篇 |
1988年 | 24篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 6篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 7篇 |
1977年 | 1篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
用一种新方法研究了三对角方程组及对称三对角方程组计算解的最佳向后扰动分析。由于这两类方程组的系数矩阵具有特殊结构 ,因而本文结果不能从已有结果直接导出。所用方法亦可用于研究 KKT及 SQD等结构线性系统的最佳向后扰动分析。 相似文献
42.
Biochemical mechanism of forming the red tide is discussed in this paper.The existence of a large number of nitrates and phosphates in the eutrophic water is the prerequisite of explosive increase of algae and the forming of red tide.Reduction of eutrophication is an important approach to preventing the red tide.The method of deep treatment of the waste water and its denitrification and dephosphorization are introduced,and a new opinion on the red tide formation and fundamental prevention is put forward. 相似文献
43.
厄尔尼诺(El Ni(?)o)现象是海-气耦合系统异常变化的表现,其起因可能不是唯一的,行星运动对地球运动的影响可能会导致El Ni(?)o的发生。根据4个半世纪内El Ni(?)o发生的历史资料,分析其发生和行星运动的关系,得出的结论是:木星赤纬的变化和火星大冲与El Ni(?)o。的发生有显著的关系,表明这2颗行星的运动可能影响El Ni(?)o的发生。文中还根据分析结桌和El Ni(?)o混沌机制的观点,探讨了行星运动对海-气系统变化的影响机制。 相似文献
44.
45.
对煤炭资源勘查资源量与客观物质量之间差值的误差理论探讨,提出误差由真值误差、系统误差和离差3个基本部分组成,其中真值误差是不可消除的观测误差、系统误差是控制网度所决定的准确度标准、而离差是由地质构造及矿床形态的多解性产生的资源量波动。在此基础上,构筑了一个关于误差的数学模型,最后应用误差理论对现行勘查工作中常见的错误进行分析,并就如何避免错误及减少误差提出了见解。 相似文献
46.
47.
48.
To look for gas hydrate, 22 multi-channel and 3 single-channel seismic lines on the East China Sea (ECS) shelf slope and at the bottom of the Okinawa Trough were examined. It was found that there was indeed bottom simulating reflector (BSR) occurrence, but it is very rare. Besides several BSRs, a gas seepage was also found. As shown by the data, both the BSR and gas seepage are all related with local geological structures, such as mud diapir, anticline, and fault-controlled graben-like structure. However, similar structural "anomalies" are quite common in the tectonically very active Okinawa Trough region, but very few of them have developed BSR or gas seepage. The article points out that the main reason is probably the low concentration of organic carbon of the sediment in this area. It was speculated that the rare occurrence of gas hydrates in this region is governed by structure-controlled fluid flow. Numerous faults and fractures form a network of high-permeability channels in the sediment and highly fractured igneous basement to allow fluid circulation and ventilation. Fluid flow in this tectonic environment is driven primarily by thermal buoyancy and takes place on a wide range of spatial scales. The fluid flow may play two roles to facilitate hydrate formation:to help gather enough methane into a small area and to modulate the thermal regime. 相似文献
49.
针对现有3维地形模型简化方法中的不足,提出了一种基于小波变换与滤波的规则格网简化方法。同时还在大量实验的基础上,给出了一般情况下需要的变换层数,分析了滤波门限与简化效果之间的关系。这里的研究不仅为3维地形的多分辨率合理建模与精度评估提供了理论和方法,而且也为今后开展类似研究及进行建模质量控制提供了科学的依据。 相似文献
50.
Lü Xixue 《中国地质大学学报(英文版)》2008,19(6):675-684
Jiyang (济阳) sag is an oil rich basin,consisting of Huimin (惠民),Dongying (东营),Zhanhua (沾化),and Chezhen (车镇) depressions.The elastic rock of Paleogene has undergone early and middle diagenetic stages and now the main clastic reservoir is in the middle diagenetic stage.Primary and secondary pores are developed in Paleogene sandstone,the latter is generated from the dissolution of feldspar and calcite cement in rocks owing to the organic acid from the maturated source rock,but the materials dissolved are different in different depressions.The reservoir secondary pores of Dongying depression are generated from the dissolution of calcite cement,the ones of Zhanhua and Huimin depressions from the dissolution of feldspar,the secondary pores of Chezhen depression from the dissolution of feldspar in upper section,and the dissolution of calcite cement in the lower section of Paleogene,respectively.The secondary pores are developed in two depths and the depth goes down from west to east,from south to north in Jiyang sag.The major controlling factors for secondary pore development are maturity and location of source rock.Lastly,the favorable reservoirs are evaluated according to reservoir buried depth,sedimentation,and diagenesis.The reservoir with high quality is located in the northern and central parts in Dongying depression; there are some good reservoirs in Gndao (孤岛),Gudong (孤东),and Gunan (孤南) areas in Zhanhua depression,and the favorable reservoirs are located in the north steep slope and the south gentle slope of Chezhen depression and central uplift,south gentle slope of Huimin depression. 相似文献