全文获取类型
收费全文 | 27022篇 |
免费 | 390篇 |
国内免费 | 223篇 |
专业分类
测绘学 | 533篇 |
大气科学 | 2043篇 |
地球物理 | 5453篇 |
地质学 | 9406篇 |
海洋学 | 2231篇 |
天文学 | 6146篇 |
综合类 | 51篇 |
自然地理 | 1772篇 |
出版年
2021年 | 169篇 |
2020年 | 205篇 |
2019年 | 219篇 |
2018年 | 517篇 |
2017年 | 482篇 |
2016年 | 585篇 |
2015年 | 452篇 |
2014年 | 638篇 |
2013年 | 1251篇 |
2012年 | 750篇 |
2011年 | 1056篇 |
2010年 | 919篇 |
2009年 | 1264篇 |
2008年 | 1109篇 |
2007年 | 1093篇 |
2006年 | 1028篇 |
2005年 | 857篇 |
2004年 | 866篇 |
2003年 | 832篇 |
2002年 | 771篇 |
2001年 | 705篇 |
2000年 | 663篇 |
1999年 | 587篇 |
1998年 | 596篇 |
1997年 | 599篇 |
1996年 | 455篇 |
1995年 | 436篇 |
1994年 | 401篇 |
1993年 | 347篇 |
1992年 | 325篇 |
1991年 | 289篇 |
1990年 | 313篇 |
1989年 | 292篇 |
1988年 | 243篇 |
1987年 | 326篇 |
1986年 | 268篇 |
1985年 | 363篇 |
1984年 | 409篇 |
1983年 | 392篇 |
1982年 | 358篇 |
1981年 | 330篇 |
1980年 | 327篇 |
1979年 | 291篇 |
1978年 | 322篇 |
1977年 | 274篇 |
1976年 | 276篇 |
1975年 | 286篇 |
1974年 | 244篇 |
1973年 | 247篇 |
1972年 | 163篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
F LanaroP Tolppanen 《Engineering Geology》2002,65(1):17-30
A new and accurate characterization method for dimensions, shape and roughness of aggregate particles has been developed. The method is based on the 3D-laser scanning technique and evaluation of coarse-grain aggregate-particle images. Parameters are obtained with either analytical Fourier analysis or geometrical analysis. The results from the two methods are compared with each other as well as with manual measurements. Although the Fourier-based analysis gives about 10% smaller size values, the comparison of the results shows, in general, a good agreement between the different techniques. This new method for analysis of coarse-grain aggregates gives reliable results for both the shape and topographical parameters of particles. 相似文献
92.
93.
Source scaling of intermediate-depth Vrancea earthquakes 总被引:3,自引:0,他引:3
94.
95.
Habitat, occurrence and conservation of Saharo-Arabian-Turanian element Forsskaolea tenacissima L. in the Iberian Peninsula 总被引:1,自引:0,他引:1
Javier Cabello Domingo Alcaraz Francisco Gmez-Mercado Juan F. Mota Javier Navarro Julio Peas Esther Gimnez 《Journal of Arid Environments》2003,53(4):491-500
The aim of this study is to assess the Iberian populations of Forsskaolea tenacissima L. according to its biogeographical interest, habitat, geographical range and conservation status. Results point out that they are restricted to gravel wadis of Tabernas Desert (SE Spain), are scarcely included in protected areas and represent historically isolated populations with relict behaviour. We also describe a new association, Senecioni-Forsskaoleetum tenacissimae. Conservation status of species is cause for concern and two conservation actions must be carried out. Firstly, protected areas should house Forsskaolea populations and secondly, phytosociological characterization of a community allows inventorying its habitat and directing conservation efforts to community level. 相似文献
96.
97.
98.
N. V. Sobolev F. V. Kaminsky W. L. Griffin E. S. Yefimova T. T. Win C. G. Ryan A. I. Botkunov 《Lithos》1997,39(3-4):135-157
The Sputnik kimberlite pipe is a small “satellite” of the larger Mir pipe in central Yakutia (Sakha), Russia. Study of 38 large diamonds (0.7-4.9 carats) showed that nine contain inclusions of the eclogitic paragenesis, while the remainder contain inclusions of the peridotitic paragenesis, or of uncertain paragenesis. The peridotitic inclusion suite comprises olivine, enstatite, Cr-diopside, chromite, Cr-pyrope garnet (both lherzolitic and harzburgitic), ilmenite, Ni-rich sulfide and a Ti-Cr-Fe-Mg-Sr-K phase of the lindsleyite-mathiasite (LIMA) series. The eclogitic inclusion suite comprises omphacite, garnet, Ni-poor sulfide, phlogopite and rutile. Peridotitic ilmenite inclusions have high Mg, Cr and Ni contents and high Nb/Zr ratios; they may be related to metasomatic ilmenites known from peridotite xenoliths in kimberlite. Eclogitic phlogopite is intergrown with omphacite, coexists with garnet, and has an unusually high TiO2 content. Comparison with inclusions in diamonds from Mir shows general similarities, but differences in details of trace-element patterns. Large compositional variations among inclusions of one phase (olivine, garnet, chromite) within single diamonds indicate that the chemical environment of diamond crystallisation changed rapidly relative to diamond growth rates in many cases. P-T conditions of formation were calculated from multiphase inclusions and from trace element geothermobarometry of single inclusions. The geotherm at the time of diamond formation was near a 35 mW/m2 conductive model; that is indistinguishable from the Paleozoic geotherm derived by studies of xenoliths and concentrate minerals from Mir. A range of Ni temperatures between garnet inclusions in single diamonds from both Mir and Sputnik suggests that many of the diamonds grew during thermal events affecting a relatively narrow depth range of the lithosphere, within the diamond stability field. The minor differences between inclusions in Mir and Sputnik may reflect lateral heterogeneity in the upper mantle. 相似文献
99.
100.