全文获取类型
收费全文 | 4464篇 |
免费 | 864篇 |
国内免费 | 1194篇 |
专业分类
测绘学 | 587篇 |
大气科学 | 781篇 |
地球物理 | 986篇 |
地质学 | 2286篇 |
海洋学 | 829篇 |
天文学 | 251篇 |
综合类 | 337篇 |
自然地理 | 465篇 |
出版年
2024年 | 22篇 |
2023年 | 75篇 |
2022年 | 177篇 |
2021年 | 200篇 |
2020年 | 205篇 |
2019年 | 262篇 |
2018年 | 197篇 |
2017年 | 199篇 |
2016年 | 226篇 |
2015年 | 237篇 |
2014年 | 305篇 |
2013年 | 337篇 |
2012年 | 272篇 |
2011年 | 303篇 |
2010年 | 224篇 |
2009年 | 310篇 |
2008年 | 347篇 |
2007年 | 310篇 |
2006年 | 334篇 |
2005年 | 277篇 |
2004年 | 256篇 |
2003年 | 189篇 |
2002年 | 167篇 |
2001年 | 134篇 |
2000年 | 143篇 |
1999年 | 119篇 |
1998年 | 111篇 |
1997年 | 93篇 |
1996年 | 81篇 |
1995年 | 75篇 |
1994年 | 73篇 |
1993年 | 54篇 |
1992年 | 55篇 |
1991年 | 31篇 |
1990年 | 33篇 |
1989年 | 19篇 |
1988年 | 19篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有6522条查询结果,搜索用时 375 毫秒
91.
Aierken Sidike X.-M. Wang Alifu Sawuti H.-J. Zhu I. Kusachi N. Yamashita 《Physics and Chemistry of Minerals》2006,33(8-9):559-566
Natural calcite from Kuerle, Xinjiang, China, shows orange-red fluorescence when exposed to short-wave ultraviolet (UV) light (Hg 253.7 nm). Photoluminescence (PL) emission and excitation spectra of the calcite are observed at room temperature in detail. The PL emission spectrum under 208 nm excitation consists of three bands: two UV bands at 325 and 355 nm and an orange-red band at 620 nm. The three bands are ascribed to Pb2+, Ce3+ and Mn2+, respectively, as activators. The Pb2+ excitation band is observed at 243 nm, and the Ce3+ excitation band at 295 nm. The Pb2+ excitation band is also observed by monitoring the Ce3+ fluorescence, and the Pb2+ and Ce3+ excitation bands, in addition to six Mn2+ excitation bands, are also observed by monitoring the Mn2+ fluorescence. These indicate that four types of the energy transfer can occur in calcite through the following processes: (1) Pb2+ → Ce3+, (2) Pb2+ → Mn2+, (3) Ce3+ → Mn2+ and (4) Pb2+ → Ce3+ → Mn2+. 相似文献
92.
Márian Urban Rainer Thomas Vratislav Hurai Patrik Koneèný Martin Chovan 《Mineralium Deposita》2006,40(8):867-873
CO2 inclusions with density up to 1,197 kg m−3 occur in quartz–stibnite veins hosted in the low-grade Palaeozoic basement of the Gemericum tectonic unit in the Western Carpathians. Raman microanalysis corroborated CO2 as dominant gas species accompanied by small amounts of nitrogen (<7.3 mol%) and methane (<2.5 mol%). The superdense CO2 phase exsolved from an aqueous bulk fluid at temperatures of 183–237°C and pressures between 1.6 and 3.5 kbar, possibly up to 4.5 kbar. Low thermal gradients (∼12–13°C km−1) and the CO2–CH4–N2 fluid composition rule out a genetic link with the subjacent Permian granites and indicate an external, either metamorphogenic (oxidation of siderite, dedolomitization) or lower crustal/mantle, source of the ore-forming fluids.According to microprobe U–Pb–Th dating of monazite, the stibnite-bearing veins formed during early Cretaceous thrusting of the Gemeric basement over the adjacent Veporic unit. The 15- to 18-km depth of burial estimated from the fluid inclusion trapping PT parameters indicates a 8- to 11-km-thick Upper Palaeozoic–Jurassic accretionary complex overlying the Gemeric basement and its Permo-Triassic autochthonous cover. 相似文献
93.
N. Takafuji K. Fujino T. Nagai Y. Seto D. Hamane 《Physics and Chemistry of Minerals》2006,33(10):651-654
High-pressure and temperature experiments (28–62 GPa, and 1,490–2,000 K, corresponding to approximately 770–1,500 km depth in the mantle) have been conducted on a MgCO3 + SiO2 mixture using a laser-heated diamond anvil cell combined with analytical transmission electron microscope observation of the product phases to constrain the fate of carbonates carried on the subducting basalt into the lower mantle. At these conditions, the decarbonation reaction MgCO3 (magnesite) + SiO2 (stishovite) → MgSiO3 (perovskite) + CO2 (solid) has been recognized. This indicates that above reaction takes place as a candidate for decarbonation of the carbonated subducting mid ocean ridge basalts in the Earth’s lower mantle. 相似文献
94.
合成并表征了新螯合树脂———邻苯二酚螯合树脂(XAD-2-Catechol),研究了XAD-2-Catechol吸附铝的特性和茜素红-铝的显色反应,在pH4.5的HAc-NaAc缓冲介质中,茜素红和铝(Ⅲ)反应生成红色络合物,λm ax=500 nm,铝的含量在0-50μg/25 mL内符合比耳定律。建立了邻苯二酚螯合树脂分离/富集-茜素红分光光度法测定天然水样中铝的新方法,对水样中铝形态进行测定,结果满意。 相似文献
95.
SUN Xiao-jie LI Chao-lin WANG Li-bin REN Ri-chun LI Hai-yan ZHUANG Yi-ming LIU Ying-xin SUN Ke .Daqing Petroleum Institute Daqing Heilongjiang China .Coalfield Geological Geophysical Exploration Company of Jilin Province Changchun China .Coal Field Geology Bureun of Jilin Province Changchun China 《吉林大学学报(地球科学版)》2006,(Z2)
已知勘查区深度范围前提下,最大炮检X和道间距ΔX,不可以太大也不可以太小,施工前能够计算出它的允许值范围。 相似文献
96.
本文简要地介绍了办公自动化的发展过程,分析了其常用的功能、特点,以及内容分类,论述了目前办公自动化系统的技术支撑和实现,并指出政府办公自动化系统在开发和应用中存在的问题和解决思路。对系统的推广使用具有一定的参考意义。 相似文献
97.
CHENChujiang LIDeren ZHUQing 《地球空间信息科学学报》2005,8(1):33-38
This paper presents the studies of the refining of IKONOS-2 RPC, the transform of the datum, the mode of the control point distribution and the method of IKONOS stereo triangulation, so that IKONOS imagery can be used to collect the precise geospatial data and produce the large scale map. The transform between the IKONOS-2 image space and the national coordinate system based on the RPC have been developed, and the results of block adjustment with various control schemes in a practical project near Himalayas have been examined and analysed. The encouraging results of high positioning accuracy have been obtained. 相似文献
98.
本文提出了基于二维电子地图与三维虚拟场景之间相互响应的思想来克服它们各自的局限性.简要的描述了相互响应的原理、表现形式、实现流程及实现方法.最后提出了一些结论和展望. 相似文献
99.
100.