全文获取类型
收费全文 | 47139篇 |
免费 | 8307篇 |
国内免费 | 11314篇 |
专业分类
测绘学 | 3652篇 |
大气科学 | 9746篇 |
地球物理 | 11608篇 |
地质学 | 23282篇 |
海洋学 | 5885篇 |
天文学 | 1951篇 |
综合类 | 5003篇 |
自然地理 | 5633篇 |
出版年
2024年 | 250篇 |
2023年 | 842篇 |
2022年 | 2032篇 |
2021年 | 2463篇 |
2020年 | 1971篇 |
2019年 | 2276篇 |
2018年 | 2516篇 |
2017年 | 2315篇 |
2016年 | 2648篇 |
2015年 | 2276篇 |
2014年 | 2809篇 |
2013年 | 2668篇 |
2012年 | 2570篇 |
2011年 | 2748篇 |
2010年 | 2834篇 |
2009年 | 2685篇 |
2008年 | 2445篇 |
2007年 | 2368篇 |
2006年 | 1973篇 |
2005年 | 1787篇 |
2004年 | 1378篇 |
2003年 | 1372篇 |
2002年 | 1330篇 |
2001年 | 1364篇 |
2000年 | 1522篇 |
1999年 | 2149篇 |
1998年 | 1757篇 |
1997年 | 1685篇 |
1996年 | 1570篇 |
1995年 | 1363篇 |
1994年 | 1218篇 |
1993年 | 1137篇 |
1992年 | 888篇 |
1991年 | 731篇 |
1990年 | 540篇 |
1989年 | 483篇 |
1988年 | 412篇 |
1987年 | 237篇 |
1986年 | 225篇 |
1985年 | 150篇 |
1984年 | 144篇 |
1983年 | 105篇 |
1982年 | 114篇 |
1981年 | 77篇 |
1980年 | 66篇 |
1979年 | 49篇 |
1978年 | 22篇 |
1977年 | 20篇 |
1965年 | 19篇 |
1958年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
L.J. Hou M. Liu J.J. Lu S.Y. Xu D.N. Ou Y. Yang D.G. Zheng 《Environmental Geology》2006,49(7):937-945
The influences of exposure to the atmosphere on ammonium cycle in the intertidal surface sediments were in situ studied with
a geochemical approach at a typical station in the Yangtze Estuary during three tidal cycles in September 2003. During an
about 8-h emersion period of each diurnal tide, six high-resolution vertical profiles of adsorbed and dissolved ammonium were
measured. It was observed that both adsorbed and dissolved ammonium generally had an increasing trend in sediment cores during
the exposure. The rate of ammonium regeneration in sediments was estimated using the accumulation amount of ammonium including
adsorbed and soluble fractions during the daytime emersion. The calculation result showed that there was relatively high ammonification
rate (˜500 nmol N cm−3 day−1), which reflected that organic nitrogen in sediments was quickly decomposed with a residence time of ˜52.7 days. Due to the
dramatic temperature difference observed in sediment profiles, free convection was considered an important mechanism of regulating
the efflux of produced ammonium into overlying waters. The total estimated amount of regenerated ammonium was ˜1.35×105 t N year−1 in the intertidal flat of the Yangtze Estuary, which occupied 7.6% of the total inorganic nitrogen annually transported to
the estuarine ecosystem. 相似文献
42.
淄博市洪山、寨里煤矿区隐伏的奥陶系灰岩裂隙岩溶水污染严重。水质污染突发于矿坑全面闭坑以后,污染范围与矿坑水区一致,地下水污染组份与矿坑水的高含量组份相同。水质恶化主要由矿坑水串层污染所致。在此针对串层污染形成原因及影响因素,提出了防治对策。 相似文献
43.
法国是世界测绘强国之一。法国国家测绘局(IGN)是法国测绘的领导机构。本文介绍了IGN的概况,并对IGN大地测量、地图制图、对外服务、研究机构等情况作了较详细的描述。在此基础上对IGN的未来发展特点提出了几点看法。 相似文献
44.
45.
46.
Origin of a large breccia-vein system in the Sanerlin uranium deposit, southern China: a reinterpretation 总被引:1,自引:0,他引:1
The early Tertiary Sanerlin uranium deposit is located near the southwestern margin of the Chaling-Yongxing pull-apart basin defined by the Chaling-Yongxing and Chenxian-Linwu sinistral strike-slip faults in southern China. The uranium ores are hosted in 15 breccia-vein bodies, which are separately located in the cores of three secondary anticlines of the Upper Permian Dangchong Formation. Individual breccia-vein bodies are composed of fragments of silicified shale and sandstone from the Dangchong Formation, and quartz veinlets as cements. These fragments, together with quartz veins, form a mosaic texture. Hydrothermal pitchblende is the only commercial uranium mineral, mainly occurring as disseminated grains within quartz veins or coating fragments. Other metallic minerals include molybdenite, pyrite, chalcopyrite, galena, sphalerite, and red microcrystalline hematite. Fluid inclusions in quartz veins have homogenization temperatures ranging from 150 to 280 °C, and calculated salinity values between 5.6 and 13.4 wt% NaCl equivalent. Stable isotope analyses show that the mineralizing fluid was characterized by '18O values of -2.2 to +2.6 and 'DH2O values of -134 to -110. These analytical data demonstrate that hydrothermal fluids were mainly derived from formation waters (brines) of the Chaling-Yongxing basin. Fluid overpressuring was caused by an abnormal geothermal gradient and impermeable shales in the deposit area. The geometry, texture, and structure of the breccia-vein system, along with the fluid pressure estimates, suggest that hydraulic fracturing generated the mineralized breccia-vein system. Pitchblende and associated minerals were deposited when gaseous phases were released abruptly from the ore fluids due to the hydraulic fracturing. 相似文献
47.
About 30 samples representing major lithologies of Sulu ultrahigh-pressure (UHP) metamorphic rocks were collected from surface exposures and exploration wells, and compressional (Vp) and shear wave (Vs) velocities and their directional dependence (anisotropy) were determined over a range of constant confining pressures up to 600 MPa and temperatures ranging from 20 to 600 °C. Samples range in composition from acidic to ultramafic. P- and S-wave velocities measured at 600 MPa vary from 5.08 to 8.64 km/s and 2.34 to 4.93 km/s, respectively. Densities are in the range from 2.60 to 3.68 g/cm3. To make a direct tie between seismic measurements (refraction and reflection) and subsurface lithologies, the experimental velocity data (corresponding to shallow depths) were used to calculate velocity profiles for the different lithologies and profiles of reflection coefficients at possible lithologic interfaces across the projected 5000-m Chinese Continental Scientific Drilling Program (CCSD) crustal segment. Comparison of calculated in situ velocities with respective intrinsic velocities suggests that the in situ velocities at shallow depths are lowered by an increased abundance of open microcracks. The strongly reflective zone beneath the Donghai drill site can be explained by the impedance contrasts between the different lithologies. Contacts between eclogite/peridotite and felsic rocks (gt-gneiss, granitic gneiss), in particular, may give rise to strong seismic reflections. In addition, shear-induced (lattice preferred orientation (LPO)-related) seismic anisotropy can increase reflectivity. For the explanation of the high velocity bodies (>6.4 km/s) around 1000 m and below 3200-m depth, large proportions of eclogite/peridotite (about 40 and 30 vol.%, respectively) are needed. 相似文献
48.
49.
采用一致的地震震相和台网布局,应用昆明数字地震台网资料,对2002年月1月4日-1月7日的漾濞地震及序列作进一步核定,得出了更精确的地震震源位置,并作出三维空间图。 相似文献
50.
长江巨洪前期物理因子的配置 总被引:4,自引:4,他引:4
提出了长江巨洪前期物理因子配置的概念,在每一次巨洪发生之前,影响巨洪的主要物理因子之间一般都会表现出相似的特征,即出现一些固有的配置,这些配置正是长江发生巨洪的强信号,对长江巨洪的预测研究具有重要的指示作用。 相似文献