全文获取类型
收费全文 | 1076篇 |
免费 | 89篇 |
国内免费 | 268篇 |
专业分类
测绘学 | 289篇 |
大气科学 | 18篇 |
地球物理 | 160篇 |
地质学 | 524篇 |
海洋学 | 138篇 |
天文学 | 144篇 |
综合类 | 125篇 |
自然地理 | 35篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 21篇 |
2021年 | 17篇 |
2020年 | 27篇 |
2019年 | 23篇 |
2018年 | 19篇 |
2017年 | 42篇 |
2016年 | 42篇 |
2015年 | 45篇 |
2014年 | 37篇 |
2013年 | 44篇 |
2012年 | 54篇 |
2011年 | 72篇 |
2010年 | 49篇 |
2009年 | 65篇 |
2008年 | 64篇 |
2007年 | 84篇 |
2006年 | 72篇 |
2005年 | 65篇 |
2004年 | 54篇 |
2003年 | 48篇 |
2002年 | 43篇 |
2001年 | 44篇 |
2000年 | 38篇 |
1999年 | 44篇 |
1998年 | 42篇 |
1997年 | 19篇 |
1996年 | 31篇 |
1995年 | 26篇 |
1994年 | 37篇 |
1993年 | 33篇 |
1992年 | 20篇 |
1991年 | 43篇 |
1990年 | 36篇 |
1989年 | 5篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1433条查询结果,搜索用时 616 毫秒
361.
Li Bing Ma Xinrong Han Lirong Yang Hongxia 《Geostandards and Geoanalytical Research》2004,28(2):317-323
A simple sample treatment method for the accurate and precise determination of iodine in soil, sediment and biological samples by inductively coupled plasma-mass spectrometry (ICP-MS) is described. Iodine in samples was extracted in screw top PTFE-lined stainless steel bombs using a 10% v/v ammonia solution at 185 C for 18 hours (overnight), after which the extract was introduced into the ICP-MS for direct measurement. 126 Te was employed as the internal standard to compensate for matrix effects and instrument drift. The limit of detection (LOD, three times the standard deviation of the procedural blank solution, expressed as the concentration in the sample solution) was 0.003 ng ml--1 . The limit of quantitation (LOQ, ten times the standard deviation of the procedural blank solution, expressed as the concentration in the solid samples, dilution factor DF = 100) was 0.01 μg g--1 (dry mass). The accuracy and precision of the method were demonstrated by analysing different Chinese geological certified reference materials (soils, stream sediments and a hair sample). The measured concentrations were in a good agreement with the certified values indicating that bias in the method was not significant. The precision (n = 10) for different concentrations ranged from 1.82% to 4.32% RSD. Comparison of the ammonia extraction procedure with a "sintering" method indicated that there was no significant difference in results obtained with the two methods for geological soil and stream sediment samples. However, for biological samples, such as hair, kelp, tea etc., the results obtained by the sintering method were far below those of the ammonia extraction method. The ammonia extraction has advantages, as it is simpler than the "sintering" method, and has a lower procedural blank, better detection limits and reproducibility. Due to the simplicity of the method, a high rate of sample throughput is possible. 相似文献
362.
We aim to constrain the lower mantle geotherm and average composition from 1D seismic models and experimental mineralogy data, explicitly accounting for possible sources of uncertainty. We employ an isentropic third-order Birch-Murnaghan equation of state, which is in excellent agreement with recent ab initio calculations of density and bulk modulus for Mg-perovskite. Furthermore, ab initio and experimental data are reasonably consistent with each other. Modelling the shear modulus is not as straightforward, but is needed because density and the bulk modulus alone do not sufficiently constrain temperature and composition. To correctly predict ab initio calculations for the shear modulus of Mg-perovskite, we needed to prescribe a cross-derivative at zero pressure, which we determined by trial and errors. Unless this ad hoc cross-derivative is confirmed by further experimental results, there seems to be an inconsistency between ab initio and experimental data. Purely experimental data most likely require a non-adiabatic temperature profile, but it is difficult to infer the number and location(s) of the non-adiabatic increase(s). If ab initio data are used, at least one thermal boundary layer seems reasonable, but its location depends on the modelling of the iron content. A strong chemical density contrast in the mid-mantle (≥2%) is not supported by ab initio data, but is possible with experimental data. Other major sources of uncertainty are the trade-off between thermal and compositional effects, the possible influence of aluminium perovskite, and poorly understood frequency effects. 相似文献
363.
给出了双星姿态测量的两种算法,并从几何和代数两个方面证实其存在双值问题;探讨了双值问题与精度衰减因子(DOP)之间的关系,并提出了双值问题的解决方案。 相似文献
364.
辽河断陷以碳酸盐岩和砂页岩为主的古潜山地层一直全部划归中、新元古界。由于在该套地层的部分岩石薄片中发现交代残余的动物化石碎片,因此提出辽河断陷有古生界存在的新观点。通过牙形石、微古植物、动物化石和岩性组合的研究,对这套地层进行了重新厘定,建立了古生代寒武纪、奥陶纪、石炭纪和二叠纪地层层序。研究成果表明,辽河断陷存在古生界储层,古生代潜山并非单斜.而是由被断裂改造的褶皱组成的断块。这一成果为重新认识潜山的内幕构造特征和油气储层分布规律奠定了基础。 相似文献
365.
366.
Yi Yong Park Suong Oh Lee Tam Tran Seong Jun Kim Myong Jun Kim 《International Journal of Mineral Processing》2006,80(2-4):126-132
A simple process to produce fine and low soda α-alumina (α-Al2O3) from a commercial grade aluminium trihydroxide (gibbsite, Al(OH)3) produced by KC Corporation Ltd was developed. There are two options for this process with the first one producing low soda α-alumina (< 0.05% Na2O) having a mean particle size of 50 μm. The second option yields a fine product with a mean size of less than 10 μm. In the first option, a plant aluminium trihydroxide containing 0.20% Na2O was first fluidized with nitrogen at 400–600 °C to yield an amorphous activated alumina. This intermediate product was then treated with acetic or oxalic acid, washed with water and heated to 1200 °C to form calcined α-alumina, having a Na2O content of less than 0.05%. A 20 min leaching using 0.2 M acetic or oxalic acid could yield an alumina product containing 0.04% Na2O. In the second option, a new technique for the preparation of fine and low soda α-alumina was evaluated using an attrition mill working also as a leaching vessel at 80 °C. Fine (< 10 μm in mean particle size) and low soda (< 0.04% Na2O) alumina was produced by a 20 min leaching step with 0.2 M acetic acid and concurrent attrition milling. 相似文献
367.
百色机场大型地接地电阻测试经验与总结 总被引:4,自引:0,他引:4
对百色机场大型地网接地电阻进行了认真的测试,通过分析比较,选出正确的测试方法和仪器,确保测试结果的准确,并作了经验总结。 相似文献
368.
369.
额济纳旗胡杨根区水分运动参数的确定--利用Richard方程和气象资料推算 总被引:2,自引:0,他引:2
利用Richard方程和气象资料相结合的办法,确定了中国典型的干旱内陆河流──黑河下游额济纳旗地区主要成林的干旱荒漠天然乔木树种──胡杨林地的水分运动参数,主要有导水系数K、比水容量C和水分扩散率D。 相似文献
370.