全文获取类型
收费全文 | 10070篇 |
免费 | 1853篇 |
国内免费 | 2317篇 |
专业分类
测绘学 | 214篇 |
大气科学 | 533篇 |
地球物理 | 2715篇 |
地质学 | 8466篇 |
海洋学 | 746篇 |
天文学 | 39篇 |
综合类 | 322篇 |
自然地理 | 1205篇 |
出版年
2024年 | 46篇 |
2023年 | 114篇 |
2022年 | 209篇 |
2021年 | 325篇 |
2020年 | 407篇 |
2019年 | 407篇 |
2018年 | 362篇 |
2017年 | 460篇 |
2016年 | 480篇 |
2015年 | 424篇 |
2014年 | 530篇 |
2013年 | 862篇 |
2012年 | 543篇 |
2011年 | 633篇 |
2010年 | 492篇 |
2009年 | 664篇 |
2008年 | 726篇 |
2007年 | 714篇 |
2006年 | 757篇 |
2005年 | 607篇 |
2004年 | 574篇 |
2003年 | 488篇 |
2002年 | 463篇 |
2001年 | 411篇 |
2000年 | 459篇 |
1999年 | 371篇 |
1998年 | 296篇 |
1997年 | 310篇 |
1996年 | 243篇 |
1995年 | 213篇 |
1994年 | 158篇 |
1993年 | 126篇 |
1992年 | 94篇 |
1991年 | 60篇 |
1990年 | 53篇 |
1989年 | 44篇 |
1988年 | 45篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
论中国东部大型盆地区及邻区地质-地球物理复合尺度解析 总被引:7,自引:3,他引:4
作为对中国东部陆缘地带大型盆地区及邻区地质-地球物理综合研究的部分结果,本文的基本认识:(1)穿过松辽盆地的1孙吴-双辽断裂可能是东倾伯低角度壳内断裂;(2)松辽盆地和渤海湾盆地可能属于“混合型裂谷盆地”;(3)东海盆地台北坳陷处在多期次张性应力场环境中,使在其西部附近产生张性正断层系;(4)欧亚大陆东部新生代区域构造运动总体处于右旋走滑拉张环境,其动力因素包括板块运动和地幔物质运动;(5)研究区莫霍面具有较为复杂的变化;(6)复合尺度研究方法是地质-地球物理综合分析的必要手段。 相似文献
992.
Groundwater flow and solute transport at the Mourquong saline-water disposal basin, Murray Basin, southeastern Australia 总被引:5,自引:0,他引:5
Craig T. Simmons Kumar A. Narayan Juliette A. Woods Andrew L. Herczeg 《Hydrogeology Journal》2002,10(2):278-295
Saline groundwater and drainage effluent from irrigation are commonly stored in some 200 natural and artificial saline-water
disposal basins throughout the Murray-Darling Basin of Australia. Their impact on underlying aquifers and the River Murray,
one of Australia's major water supplies, is of serious concern. In one such scheme, saline groundwater is pumped into Lake
Mourquong, a natural groundwater discharge complex. The disposal basin is hydrodynamically restricted by low-permeability
lacustrine clays, but there are vulnerable areas in the southeast where the clay is apparently missing. The extent of vertical
and lateral leakage of basin brines and the processes controlling their migration are examined using (1) analyses of chloride
and stable isotopes of water (2H/1H and 18O/16O) to infer mixing between regional groundwater and lake water, and (2) the variable-density groundwater flow and solute-transport
code SUTRA. Hydrochemical results indicate that evaporated disposal water has moved at least 100 m in an easterly direction
and that there is negligible movement of brines in a southerly direction towards the River Murray. The model is used to consider
various management scenarios. Salt-load movement to the River Murray was highest in a "worst-case" scenario with irrigation
employed between the basin and the River Murray. Present-day operating conditions lead to little, if any, direct movement
of brine from the basin into the river.
Electronic Publication 相似文献
993.
994.
沙区绿洲人地系统演进探讨——以民勤盆地为例 总被引:4,自引:0,他引:4
资源与环境问题已成为当代人类生存与发展的重大问题,它通过人地系统中人与地之间的相互联系,以各种方式和强度作用于人类。人地系统有其运行规律和演进机制,要建立协调的人地关系、促进沙区绿洲的可持续发展,就必须清楚地了解其人的地系统的动态演进机制。通过分析民勤盆地人地系统的演进过程,提出了人地系统演进的机制和驱动力,从而为更好地调控沙区绿洲人地系统的演进提供依据。 相似文献
995.
996.
柴达木盆地东部地区侏罗系烃源岩地球化学特征及生烃潜力评价 总被引:4,自引:2,他引:2
借助于Rock -Eval生油岩评价仪、色谱 -质谱、稳定同位素质谱仪、显微镜等分析测试手段,对柴达木盆地东部地区侏罗系烃源岩进行了地球化学特征分析。从有机碳含量、可溶有机质含量及其转化率、热解参数、饱和烃的生物标志化合物特征、有机岩石学特征和饱和烃单体烃碳同位素分布特征几个方面综合分析了侏罗系烃源岩的有机质丰度、类型和成熟度,并对其生烃潜力进行了评价。结果表明:(1 )侏罗系烃源岩有机碳含量高,多数样品属中等~好的生油岩范畴。 (2 )有机质类型多为Ⅲ型,少数为Ⅰ型和Ⅱ型。 (3)有机质处于低熟 -成熟阶段。 (4)烃源岩多为来源于高等植物的滨浅湖相和沼泽相沉积,具有煤系烃源岩的特点。 (5 )部分地区的生烃潜力较大。 相似文献
997.
塔里木盆地北部隆起牙哈断裂带负反转过程与油气聚集 总被引:19,自引:0,他引:19
采用地层厚度分析、“零点”分析、位移 /距离曲线分析和断层生长指数分析等方法,讨论了牙哈负反转断裂带的几何学和运动学特征、主反转期及控油作用,结果表明牙哈主断裂主反转期为早白垩世,负反转活动结束于中新世康村期-上新世库车期。牙 1号断裂主反转期为中新世苏维依期,牙 2号断裂主反转期为晚白垩世-老第三纪,二者都于中新世康村期结束反转活动。牙哈断裂带油气聚集和分布与断裂的负反转活动有关。 相似文献
998.
Evolution of Ore-Forming Fluids and Ag-Cu Polymetal Mineralization in the Lanping Basin, Yunnan 总被引:1,自引:0,他引:1
EVOLUTION OF ORE-FORMING FLUIDS AND Ag-Cu POLYMETAL MINERALIZATION IN THE LANPING BASIN, YUNNAN“KeyProjectforResourcesandEconomics” (95 0 2 0 0 1 0 1)oftheMinistryofLandResources 相似文献
999.
Solute recycling from irrigation can be described as the process that occurs when the salt load that is extracted from irrigation wells and distributed on the fields is returned to the groundwater below irrigated surfaces by deep percolation. Unless the salt load leaves the system by means of drains or surface runoff, transfer to the groundwater will take place, sooner or later. This can lead to solute accumulation and thus to groundwater degradation, particularly in areas where extraction rates exceed infiltration rates (semi-arid and arid regions). Thus, considerable errors can occur in a predictive solute mass budget if the recycling process is not accounted for in the calculation. A method is proposed which allows direct simulation of solute recycling. The transient solute response at an extraction well is shown to be a superposition of solute mass flux contributions from n recycling cycles and is described as a function of the travel time distribution between a recycling point and a well. This leads to an expression for a transient ‘recycling source’ term in the advection–dispersion equation, which generates the effect of solute recycling. At long times, the ‘recycling source’ is a function of the local capture probability of the irrigation well and the solute mass flux captured by the well from the boundaries. The predicted concentration distribution at steady state reflects the maximum spatial concentration distribution in response to solute recycling and can thus be considered as the solute recycling potential or vulnerability of the entire domain for a given hydraulic setting and exploitation scheme. Simulation of the solute recycling potential is computationally undemanding and can therefore, for instance, be used for optimisation purposes. Also, the proposed method allows transient simulation of solute recycling with any standard flow and transport code. 相似文献
1000.
The SHETRAN physically based, spatially distributed model is used to investigate the scaling relationship linking specific sediment yield to river basin area, for two contrasting topographies of upland and more homogeneous terrain and as a function of sediment source, land use and rainfall distribution. Modelling enables the effects of the controls to be examined on a systematic basis, while avoiding the difficulties associated with the use of field data (which include limited data, lack of measurements for nested basins and inability to isolate the effects of individual controls). Conventionally sediment yield is held to decrease as basin area increases, as the river network becomes more remote from the headwater sediment sources (an inverse relationship). However, recent studies have reported the opposite variation, depending on the river basin characteristics. The simulation results are consistent with these studies. If the sediment is supplied solely from hillslope erosion (no channel bank erosion) then, with uniform land use, sediment yield either decreases or is constant as area increases. The downstream decrease is accentuated if rainfall (and thence erosion) is higher in the headwaters than at lower elevations. Introducing a non‐uniform land use (e.g. forest at higher elevations, wheat at lower elevations) can reverse the trend, so that sediment yield increases downstream. If the sediment is supplied solely from bank erosion (no hillslope erosion), the sediment yield increases downstream for all conditions. The sediment yield/basin area relationship can thus be inverse or direct, depending on basin characteristics. There still remains, therefore, considerable scope for defining a universal scaling law for sediment yield. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献