全文获取类型
收费全文 | 4296篇 |
免费 | 146篇 |
国内免费 | 92篇 |
专业分类
测绘学 | 157篇 |
大气科学 | 295篇 |
地球物理 | 1115篇 |
地质学 | 1516篇 |
海洋学 | 376篇 |
天文学 | 694篇 |
综合类 | 21篇 |
自然地理 | 360篇 |
出版年
2022年 | 30篇 |
2021年 | 48篇 |
2020年 | 47篇 |
2019年 | 63篇 |
2018年 | 85篇 |
2017年 | 104篇 |
2016年 | 119篇 |
2015年 | 110篇 |
2014年 | 136篇 |
2013年 | 258篇 |
2012年 | 130篇 |
2011年 | 231篇 |
2010年 | 164篇 |
2009年 | 225篇 |
2008年 | 237篇 |
2007年 | 208篇 |
2006年 | 191篇 |
2005年 | 171篇 |
2004年 | 136篇 |
2003年 | 162篇 |
2002年 | 136篇 |
2001年 | 84篇 |
2000年 | 87篇 |
1999年 | 61篇 |
1998年 | 69篇 |
1997年 | 56篇 |
1996年 | 65篇 |
1995年 | 52篇 |
1994年 | 55篇 |
1993年 | 42篇 |
1992年 | 48篇 |
1991年 | 42篇 |
1990年 | 35篇 |
1989年 | 37篇 |
1988年 | 37篇 |
1987年 | 40篇 |
1986年 | 44篇 |
1985年 | 57篇 |
1984年 | 47篇 |
1983年 | 50篇 |
1982年 | 52篇 |
1981年 | 57篇 |
1980年 | 48篇 |
1979年 | 39篇 |
1978年 | 47篇 |
1977年 | 28篇 |
1976年 | 29篇 |
1975年 | 24篇 |
1974年 | 31篇 |
1973年 | 29篇 |
排序方式: 共有4534条查询结果,搜索用时 15 毫秒
21.
22.
23.
Zhengtong Xie Peter R. Voke Paul Hayden Alan G. Robins 《Boundary-Layer Meteorology》2004,111(3):417-440
A family of wall models is proposed that exhibits moresatisfactory performance than previousmodels for the large-eddy simulation (LES) of the turbulentboundary layer over a rough surface.The time and horizontally averaged statistics such asmean vertical profiles of windvelocity, Reynolds stress, turbulent intensities, turbulentkinetic energy and alsospectra are compared with wind-tunnel experimental data.The purpose of the present study is to obtain simulatedturbulent flows that are comparable with wind-tunnelmeasurements for use as the wind environment for thenumerical prediction by LES of source dispersion in theneutral atmospheric boundary layer. 相似文献
24.
25.
26.
27.
28.
KANG Shi chang QIN Da he YAO Tan dong PAUL A. Mayewski SALLIE Whitlow 《中国地理科学(英文版)》2000,10(3):218-225
Investigations of atmospheric composition in the Himalayas has been limited in both temporal and spatial scales, mainly due to difficult logistics. Ideal sites for monitoring atmospheric composition and its evolution should be free from local pollution and representative of the remote troposphere (HUEBERT et al., 1980). As the Himalayas are far removed from highly industrialized regions they provide suitable locations to monitor the chemistry of the remote troposphere and to study the evolu… 相似文献
29.
Improved Platinum-Group Element Extraction by NiS Fire Assay from Chromitite Ore Samples Using a Flux Containing Sodium Metaphosphate 总被引:1,自引:0,他引:1
Many chromite-rich rocks contain relatively high concentrations of the platinum-group elements (PGE). In many cases, the phases carrying PGE occur as either platinum-group minerals (PGM) or as base metal sulfides in solid solution in sulfides. In some cases, such as the UG-2 unit of the Bushveld Complex, the PGM are occluded inside chromite grains. Chromites are notably difficult to dissolve in most fluxes and if the chromite contains some PGM the possibility exists that not all the PGE will be recovered during fusion. In this work, shortcomings in published methods of analysis based on the nickel sulfide fire assay procedure were investigated and a new procedure developed based on the addition of sodium metaphosphate to the fusion mixture. Optimum composition of the fusion mixture was found to be 10 g sodium metaphosphate and 9 g silica to 10 g sample, 15 g sodium carbonate, 30 g lithium tetraborate, 7.5 g nickel and 4.5 g sulfur to achieve complete dissolution of chromite grains. The new flux mixture was evaluated by the analysis of reference material CHR-Pt+ (which is known to contain PGM inside chromite grains) and no undissolved chromite grains were found in the glassy slag. Analysis of the nickel sulfide beads from this fire assay using neutron activation analysis showed similar results for Rh and Ru when compared with published conventional true (or accepted) values, while Au, Ir, Os, Pd and Pt values determined here were 10 to 30% higher than the corresponding published conventional true values. It was concluded that the addition of sodium metaphosphate improved chromite dissolution in the flux and appears to improve PGE recovery. 相似文献
30.
The analysis of rural social change has reached a point of somewhat saturated orthodoxy. Numerous studies over the last 20 years have served to reinforce a standard view that it is the ‘newcomer vs local’ conflict which lies at the heart of social and cultural changes in rural communities. Moreover, these broad categorisations have often been translated into class terms without due regard for the detailed circumstances of locality or intra-class fractions. This paper presents some evidence from an intensive study of 10 parishes in rural Gloucestershire, and seeks to provide a detailed background to the distribution of selected indicators of social change in that area. It focuses on the diversions and needs experienced by different social groups and suggests additional complexities to those recognised in traditional treatments of rural conflict. 相似文献