全文获取类型
收费全文 | 9680篇 |
免费 | 1758篇 |
国内免费 | 2516篇 |
专业分类
测绘学 | 654篇 |
大气科学 | 2432篇 |
地球物理 | 2328篇 |
地质学 | 4989篇 |
海洋学 | 1091篇 |
天文学 | 415篇 |
综合类 | 914篇 |
自然地理 | 1131篇 |
出版年
2024年 | 42篇 |
2023年 | 161篇 |
2022年 | 441篇 |
2021年 | 479篇 |
2020年 | 394篇 |
2019年 | 436篇 |
2018年 | 526篇 |
2017年 | 491篇 |
2016年 | 543篇 |
2015年 | 444篇 |
2014年 | 554篇 |
2013年 | 575篇 |
2012年 | 513篇 |
2011年 | 530篇 |
2010年 | 555篇 |
2009年 | 546篇 |
2008年 | 537篇 |
2007年 | 496篇 |
2006年 | 441篇 |
2005年 | 378篇 |
2004年 | 284篇 |
2003年 | 324篇 |
2002年 | 334篇 |
2001年 | 320篇 |
2000年 | 343篇 |
1999年 | 459篇 |
1998年 | 387篇 |
1997年 | 408篇 |
1996年 | 371篇 |
1995年 | 306篇 |
1994年 | 273篇 |
1993年 | 210篇 |
1992年 | 185篇 |
1991年 | 130篇 |
1990年 | 88篇 |
1989年 | 99篇 |
1988年 | 88篇 |
1987年 | 58篇 |
1986年 | 45篇 |
1985年 | 36篇 |
1984年 | 24篇 |
1983年 | 25篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1958年 | 9篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 928 毫秒
801.
研究表明,康滇地轴及其东部地区属均衡补偿平衡区,西部属强烈上升的异常区。上升的原动力为板块碰撞的构造力与均衡调整力的综合。 相似文献
802.
803.
本文研究了镉-5-Br-PADAP-溴化十六烷基三甲基铵-peregalo显色体系的光谱特征,显色条件,络合物的组成、干扰及其消除。实验证明该法灵敏度高,ε=1.3×10~5l·mol~(-1)·cm~(-1)。选择性较好,显色酸度范围较宽pH=8.0-9.5,络合物最大吸收波长为560nm,镉在0-10μg/25ml的含量范围内服从比尔定律。经标准水样、工业废水及生活用水验证,不经分离可测定水中PPb级的微量镉。 相似文献
804.
~(218)Po法寻找隐伏铀矿体初见成效 总被引:2,自引:0,他引:2
本文介绍了一种寻找隐伏铀矿体的快速测氡方法,即~(218)Po法。作者叙述了该法的工作原理、特点以及找矿效果,并阐述了~(218)Po法寻找隐伏铀矿体的可能性。最后着重叙述了~(218)Po法测量结果的解释方法。通过野外试验,作者认为:~(218)Po法不仅可以寻找隐伏铀矿体,而且能够定量预测盲矿体的埋藏深度与规模。 相似文献
805.
806.
We have surveyed the areal and stratigraphic distribution of tonsteins in Late Permian coalfields of southwestern China over an area of several hundred thousand square kilometers. We studied the relationship between tonstein distribution and sedimentary environment. Based on mineralogical and petrographic data, we have concluded that these tonsteins originated as air-fall volcanic ashes. Following accumulation in the peat swamps, in situ alteration of the vitric and lithic components took place under acidic conditions, leading to the formation of kaolinite.Based on petrologic, mineralogic, and chemical analytical data, we have determined that the application of mineralogic and geochemical criteria for tonsteins may be useful in correlating coal beds, predicting coal qualities and reconstructing related sedimentary paleoenvironmental conditions. 相似文献
807.
This paper presets the results of simple-shear rheological tests for the shallow clay layer in Shanghai and the rheological parameters of this clay layer, such as shear parameter, viscosity and long-term strength etc. , by using the obtained relationship among stress, strain and time. The test results show that with certain density and water content of the clay and shear stress less than the yield value, the relationship between shear stress and shear strain for the same shear duration can be obtained by superposition theorem. Because of its linearity, likewise, the relationship between long-term shear flow rate and shear stress also hold true thus, from the linear portion of the curves mentioned above the shear modulus G and viscosity η can be obtained . however , when shear stress is beyond a certain yield value, the curve becomes non-linear. This yield value can be regarded as long-term strength of the soil . In rheological experiments these parameters are all functions of time. 相似文献
808.
809.
The purpose of this study is to quantify some of the parameters needed to perform near-field modelling of sites in the Kara Sea that were impacted by the disposal of radioactive waste. The parameters of interest are: the distribution coefficients (Kd) for several important radionuclides, the mineralogy of the sediment, and the relationship of Kd to liquid-to-solid ratio. Sediment from the Kara Sea (location: 73 degrees 00'N, 58 degrees 00'E) was sampled from a depth of 287 m on August 23/24, 1992. Analysis of the material included mineralogy, grain size and total organic carbon (TOC). Uptake kinetics were determined for 85Sr, 137Cs, 241Am, 99Tc, 1251, 232U and 210Pb and distribution coefficients (Kd) were determined for these radionuclides using batch type experiments. Sorption isotherms, developed for 137Cs, 85Sr and 99Tc, were linear in each case. Increasing the liquid-to-solid ratio strongly increased uptake of 137Cs and moderately increased uptake of 99Tc. Analysis for anthropogenic radionuclides indicated the presence only of 239/240Pu in the sediment with the highest activity (at the top section of the core) being 0.420 Bq kg(-1). Other anthropogenic radionuclides were below detection limits. 相似文献
810.