全文获取类型
收费全文 | 7209篇 |
免费 | 1750篇 |
国内免费 | 1712篇 |
专业分类
测绘学 | 236篇 |
大气科学 | 486篇 |
地球物理 | 2189篇 |
地质学 | 5412篇 |
海洋学 | 958篇 |
天文学 | 18篇 |
综合类 | 508篇 |
自然地理 | 864篇 |
出版年
2024年 | 28篇 |
2023年 | 84篇 |
2022年 | 186篇 |
2021年 | 280篇 |
2020年 | 299篇 |
2019年 | 314篇 |
2018年 | 300篇 |
2017年 | 314篇 |
2016年 | 351篇 |
2015年 | 332篇 |
2014年 | 427篇 |
2013年 | 469篇 |
2012年 | 420篇 |
2011年 | 437篇 |
2010年 | 394篇 |
2009年 | 478篇 |
2008年 | 494篇 |
2007年 | 504篇 |
2006年 | 461篇 |
2005年 | 410篇 |
2004年 | 429篇 |
2003年 | 358篇 |
2002年 | 338篇 |
2001年 | 290篇 |
2000年 | 291篇 |
1999年 | 264篇 |
1998年 | 245篇 |
1997年 | 217篇 |
1996年 | 216篇 |
1995年 | 213篇 |
1994年 | 168篇 |
1993年 | 153篇 |
1992年 | 118篇 |
1991年 | 91篇 |
1990年 | 73篇 |
1989年 | 78篇 |
1988年 | 46篇 |
1987年 | 35篇 |
1986年 | 19篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
31.
Qiang Wang Derek A. Wyman Jifeng Xu Yusheng Wan Chaofeng Li Feng Zi Ziqi Jiang Huaning Qiu Zhuyin Chu Zhenhua Zhao Yanhui Dong 《Contributions to Mineralogy and Petrology》2008,155(4):473-490
New chronological, geochemical, and isotopic data are reported for Triassic (219–236 Ma) adakite-magnesian andesite-Nb-enriched
basaltic rock associations from the Tuotuohe area, central Qiangtang terrane. The adakites and magnesian andesites are characterized
by high Sr/Y (25–45), La/Yb (14–42) and Na2O/K2O (12–49) ratios, high Al2O3 (15.34–18.28 wt%) and moderate to high Sr concentrations (220–498 ppm) and εND (t) (+0.86 to +1.21) values. Low enrichments of Th, Rb relative to Nb, and subequal normalized Nb and La contents, and enrichments
of light rare earth elements combine to distinguish a group of Nb-enriched basaltic rocks (NEBs). They have positive εND (t) (+2.57 to +5.16) values. Positive correlations between Th, La and Nb and an absence of negative Nb anomalies on mantle
normalized plots indicate the NEBs are products of a mantle source metasomatized by a slab melt rather than by hydrous fluids.
A continuous compositional variation between adakites and magnesian andesites confirms slab melt interaction with mantle peridotite.
The spatial association of the NEBs with adakites and magnesian andesites define an “adakitic metasomatic volcanic series”
recognized in many demonstrably subduction-related environments (e.g., Mindanao arc, Philippines; Kamchatka arc, Russia; and
southern Baja California arc, Mexico). The age of the Touhuohe suite, and its correlation with Triassic NEB to the north indicates
that volcanism derived from subduction-modified mantle was abundant prior to 220 Ma in the central Qiangtang terrane. 相似文献
32.
The character of convergence along the Arabian–Iranian plate boundary changes radically eastward from the Zagros ranges to
the Makran region. This appears to be due to collision of continental crust in the west, in contrast to subduction of oceanic
crust in the east. The Makran subduction zone with a length of about 900 km display progressively older and highly deformed
sedimentary units northward from the coast, together with an increase in elevation of the ranges. North of the Makran ranges
are large subsiding basins, flanked to the north by active volcanoes. Based on 2D seismic reflection data obtained in this
study, the main structural provinces and elements in the Gulf of Oman include: (i) the structural elements on the northeastern
part of the Arabian Plate and, (ii) the Offshore Makran Accretionary Complex. Based on detailed analysis of these data on
the northeastern part of the Arabian Plate five structural provinces and elements—the Musendam High, the Musendam Peneplain,
the Musendam Slope, the Dibba Zone, and the Abyssal Plain have been identified. Further, the Offshore Makran Accretionary
Complex shown is to consist Accretionary Prism and the For-Arc Basin, while the Accretionary Prism has been subdivided into
the Accretionary Wedge and the Accreted/Colored Mélange. Lastly, it is important to note that the Makran subduction zone lacks
the trench. The identification of these structural elements should help in better understanding the seismicity of the Makran
region in general and the subduction zone in particular. The 1945 magnitude 8.1 tsunamigenic earthquake of the Makran and
some other historical events are illustrative of the coastal region’s vulnerability to future tsunami in the area, and such
data should be of value to the developing Indian Ocean Tsunami Warning System. 相似文献
33.
34.
作者研究三维变系数抛物方程 Douglas交替方向隐格式的稳定性和收敛性。采用 H1能量估计方法 ,证明格式按离散 H1范数是绝对稳定的 ,并且收敛阶为 O(Δ t2 + h2 ) 相似文献
35.
在分析综合辽宁省海岸带调查和沿海经济贝类污染监测资料基础上,根据辽宁海岸带水质,沉积物和生物污染现状及发展趋势。针对所存在的问题,讨论了辽宁省海洋污染特别是赤潮对海洋资源的破坏,并在组织机构,地方立法,海岸带环境保护规划,污染源控制与整体环境改进,监测方案等方面提出了建设海上辽宁、加强辽宁省海洋环境保护与海岸可持续开发利用的建议。 相似文献
36.
37.
象山港、三门湾软相潮间带底栖动物数量的水平分布与港湾的屏蔽性程度有一定的关系,生物量是三门湾(180.95g/m2)高于象山港(94.47g/m2),生物密度是象山港(816个/m2)高于三门湾(347个/m2)。决定所面生物数量变化的主要底栖动物种类数随着港湾屏蔽性程度的提高而相应地减少。生物数量的垂直分布主要受潮汐作用的影响,以中潮区为最高。生物量以6月份最大,密度是4月份最大。 相似文献
38.
Gu Jialong Shen Xianrong
Professor Hohai University Nanjing
Engineer The Investigation Design Institute Bureau of Communications of Zhejiang Province Hangzhou 《中国海洋工程》1991,(2)
In accordance with the similarity between breaking waves and hydraulic jumps, the expressions for estimating wave decay and wave energy dissipation in the surf zone are derived based on the fundamental equations of fluid mechanics. Using the numerical solution of cnoidal wave theory, the various kinematic properties of waves in the surf zone, including the relative wave crest height, wave energy, and radiation stress are discussed. The values calculated with the method proposed in this paper are in good agreement with the experimental data gained by other researchers. The present expressions can be used in the studies of sediment transport on gently sloping beaches, especially on muddy beaches. 相似文献
39.
In this paper, we analyse the ability of the nonlinear shallow-water (NSW) equations to predict wave distortion and energy dissipation of periodic broken waves in the inner surf zone. This analysis is based on the weak-solution theory for conservative equations. We derive a new one-way model, which applies to the transformation of non-reflective periodic broken waves on gently sloping beaches. This model can be useful to develop breaking-wave parameterizations (in particular broken-wave celerity expression) in both time-averaged wave models and time-dependent Boussinesq-type models. We also derive a new wave set-up equation which provides a simple and explicit relation between wave set-up and energy dissipation. Finally, we compare numerical simulations of both, the NSW model and the simplified one-way model, with spilling wave breaking experiments and we find a good agreement. 相似文献
40.
C. Riedel A. Tryggvason B. Brandsdottír T. Dahm R. Stéfansson M. Hensch R. Böðvarsson K. S. Vogfjord S. Jakobsdottír T. Eken R. Herber J. Holmjarn M. Schnese M. Thölen B. Hofmann B. Sigurdsson S. Winter 《Marine Geophysical Researches》2006,27(4):267-281
Between June 2004 and September 2004 a temporary seismic network was installed on the northern insular shelf of Iceland and onshore in north Iceland. The seismic setup aimed at resolving the subsurface structure and, thus, the geodynamical transition from Icelandic crust to typical oceanic crust along Kolbeinsey Ridge. The experiment recorded about 1,000 earthquakes. The region encloses the Tjörnes Fracture Zone containing the Husavik–Flatey strike-slip fault and the extensional seismic Grimsey Lineament. Most of the seismicity occurs in swarms offshore. Preliminary results reveal typical mid-ocean crust north of Grimsey and a heterogeneous structure with major velocity anomalies along the seismic lineaments and north–south trending subsurface features. Complementary bathymetric mapping highlight numerous extrusion features along the Grimsey Lineament and Kolbeinsey Ridge. The seismic dataset promises to deliver new insights into the tectonic framework for earthquakes in an extensional transform zone along the global mid-ocean ridge system. 相似文献