全文获取类型
收费全文 | 1752篇 |
免费 | 206篇 |
国内免费 | 972篇 |
专业分类
测绘学 | 62篇 |
大气科学 | 110篇 |
地球物理 | 217篇 |
地质学 | 1605篇 |
海洋学 | 261篇 |
天文学 | 524篇 |
综合类 | 73篇 |
自然地理 | 78篇 |
出版年
2024年 | 6篇 |
2023年 | 48篇 |
2022年 | 85篇 |
2021年 | 70篇 |
2020年 | 86篇 |
2019年 | 81篇 |
2018年 | 28篇 |
2017年 | 32篇 |
2016年 | 61篇 |
2015年 | 49篇 |
2014年 | 68篇 |
2013年 | 63篇 |
2012年 | 104篇 |
2011年 | 161篇 |
2010年 | 157篇 |
2009年 | 164篇 |
2008年 | 159篇 |
2007年 | 173篇 |
2006年 | 166篇 |
2005年 | 126篇 |
2004年 | 121篇 |
2003年 | 123篇 |
2002年 | 81篇 |
2001年 | 104篇 |
2000年 | 85篇 |
1999年 | 81篇 |
1998年 | 79篇 |
1997年 | 60篇 |
1996年 | 48篇 |
1995年 | 45篇 |
1994年 | 28篇 |
1993年 | 43篇 |
1992年 | 30篇 |
1991年 | 31篇 |
1990年 | 20篇 |
1989年 | 9篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有2930条查询结果,搜索用时 0 毫秒
341.
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been applied to determine the elemental composition of the surface layer, as well as of the first interior layer, of quartz grains from the mine tailings from Kristineberg (northern Sweden) in order to determine concentration gradients between these two layers. The quartz grains were collected from the oxidized and unoxidized zones within the tailings. The aim of this study is to assess the role of quartz surfaces as sites for the attenuation of solutes from the mine-tailings porewater. Concentrations of Cu, Ag, Sb, Pb and Bi are highest near the surface of each grain and decrease towards the interior. The surface concentration of Cu, Zn and Pb is more pronounced within the unoxidized than within the oxidized zone of the tailings. Cu exhibits a distinct concentration peak at the surface of the quartz grains below the pre-remediation oxidation front. For Zn and Ce the trend of high surface concentration is less pronounced than for Cu or Pb. Silver, Bi and As are preferably adsorbed within the uppermost layers of the oxidized zone where the pH is as high as 6.2. The conversion of intensity signals of the elements to concentration values in ppm was done by using external standards (NIST silicate glass). 相似文献
342.
343.
M. A.Bautista T. R.Gull K.Ishibashi † H.Hartman K.Davidson 《Monthly notices of the Royal Astronomical Society》2002,331(4):875-879
We study the nature of the peculiar [Sr ii ] and Sr ii emission filament found in the ejecta of Eta Carinae. To this purpose we carry out ab initio calculations of radiative transition probabilities and electron impact excitation rate coefficients for Sr ii . Then we build a multilevel model for the system which is used to investigate the physical condition of the filament and the nature of the observed allowed and forbidden Sr ii optical emission. It is found that the observed spectrum is consistent with the lines being pumped by the continuum radiation field in a mostly neutral region with electron density near 107 cm−3 . Under these conditions, the observed emission can be explained without the need for a large Sr overabundance. 相似文献
344.
345.
346.
电感耦合等离子体原子发射光谱法测定黄铁矿中微量元素 总被引:5,自引:7,他引:5
采用电感耦合等离子体原子发射光谱法检测了黄铁矿中Cd,Co,Cu,Mn,Pb,Zn和Ni。用干扰系数校正法消除黄铁矿中铁对上述元素的干扰,采用HCl-HNO3体系溶解矿样,不需化学分离,直接测定。方法已应用于国家标准物质GBW07267的测定。结果与标准值相符,相对标准偏差(n=8)为1.5%-7.3%。 相似文献
347.
作为大气中最重要的含氮有机化合物,有机胺易与硫酸、硝酸气体生成胺盐,促进新颗粒的形成,同时也可与臭氧、OH自由基、NO3自由基发生氧化反应,是二次气溶胶的前体物.综述了国内外关于大气有机胺检测技术的研究进展,对常规的离线检测技术和在线质谱技术进行了介绍和对比,重点介绍了质谱法工作原理以及测定大气有机胺的优越性,并对其未来发展进行了展望. 相似文献
348.
Flux-energy spectra of precipitating electrons are derived from electron density profiles measured by the EISCAT radar during auroral absorption events in the morning/noon local-time sector. The inversion technique uses effective recombination coefficient profiles computed on the basis of a previously validated theoretical model of the lower ionosphere. It is shown that flux-energy spectra for the energy range 30–200 keV are in reasonable agreement with those derived for the same events using trapped flux-energy spectra from geosynchronous satellite data and a model for diffusion of trapped electrons into the loss cone by scattering on whistler waves. During individual events, strongly varying precipitating fluxes are found to be due primarily to varying pitch-angle diffusion. 相似文献
349.
350.
采用盐酸-硝酸混合酸(盐酸-硝酸-水体积比3∶1∶4)水浴浸取地质样品,在样品消解后的母液中直接加入硫脲-抗坏血酸混合溶液,以氢化物发生-原子荧光光谱法同时测定地质样品中的痕量砷和汞。方法检出限为砷0.033 6 ng/mL,汞0.003 7 ng/mL;相对标准偏差(RSD,n=1)为砷1.1%,汞3.0%。对国家一级标准物质GBW 07109~GBW 07114、GBW 07301~GBW 07312、GBW 07401~GBW 07408中的砷和汞进行测定,测定值与标准值相吻合。 相似文献