全文获取类型
收费全文 | 2495篇 |
免费 | 446篇 |
国内免费 | 636篇 |
专业分类
测绘学 | 281篇 |
大气科学 | 336篇 |
地球物理 | 502篇 |
地质学 | 1325篇 |
海洋学 | 387篇 |
天文学 | 19篇 |
综合类 | 255篇 |
自然地理 | 472篇 |
出版年
2024年 | 7篇 |
2023年 | 39篇 |
2022年 | 69篇 |
2021年 | 111篇 |
2020年 | 103篇 |
2019年 | 123篇 |
2018年 | 103篇 |
2017年 | 110篇 |
2016年 | 129篇 |
2015年 | 107篇 |
2014年 | 187篇 |
2013年 | 169篇 |
2012年 | 156篇 |
2011年 | 168篇 |
2010年 | 164篇 |
2009年 | 157篇 |
2008年 | 188篇 |
2007年 | 199篇 |
2006年 | 175篇 |
2005年 | 131篇 |
2004年 | 156篇 |
2003年 | 135篇 |
2002年 | 108篇 |
2001年 | 107篇 |
2000年 | 97篇 |
1999年 | 57篇 |
1998年 | 67篇 |
1997年 | 52篇 |
1996年 | 48篇 |
1995年 | 25篇 |
1994年 | 25篇 |
1993年 | 28篇 |
1992年 | 20篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3577条查询结果,搜索用时 15 毫秒
41.
An algorithm (differential mode) is presented for the improvement of harmonic tidal analysis along T/P tracks, in which the differences between the observed sea surface heights at adjacent points are taken as observations. Also, the observation equations are constrained with the results of the crossover analysis; the parameter estimations are performed at 0.1° latitude intervals by the least squares. Cycle 10 to 330 T/P altimeter data covering the China Sea and the Northwest Pacific Ocean (2°-50° N,105°-150° E) are adopted for a refined along-track harmonic tidal analysis, and harmonic constants of 12 constituents in 8 474 points are obtained, which indicates that the algorithm can efficiently remove non-tidal effects in the altimeter observations, and improve the precision of tide parameters. Moreover, parameters along altimetry tracks represent a smoother distribution than those obtained by traditional algorithms. The root mean squares of the fitting errors between the tidal height model and the observations reduce from 11 cm to 1.3 cm. 相似文献
42.
选择位于长江下游的固城湖流域作为研究区域,基于分布式流域水文模型SWAT,采用数值模拟的手段,反演了1951~2000年流域农业非点源氮、磷的输移规律。模拟结果与实测值的一致性反映了模型的良好模拟能力。比较两个时段的模拟结果发现,1981~2000年,流域农业非点源氮、磷年平均浓度和输移量分别为:总氮0.82mg/L和411.88×103kg/a,总磷0.084mg/L和43.04×103kg/a;远高于1951~1960年的氮、磷年平均浓度和输移量分别为:总氮0.22mg/L和49.55×103kg/a,总磷0.036mg/L和7.67×103kg/a。模拟主要反映了流域下垫面条件和农作物耕作模式对农业非点源氮、磷浓度及输移量的影响。 相似文献
43.
44.
Firstly, the macroscopic chemical equilibrium state of a series of chemical reactions between intercrystal brine and its media salt layer (salt deposit) in Qarhan Salt Lake was studied by using the Pitzer theory. The concept of macroscopic solubility product and its relation with accumulated ore dissolving ratio were presented, which are used in the numerical model of dissolving and driving exploitation of potassium salt in Qarhan Salt Lake. And secondly, with a model forming idea oftransport model for reacting solutes in the multi-component fresh groundwater system in porous media being a reference, a two-dimensional transport model coupled with a series of chemical reactions in a multi-component brine porous system (salt deposits) was developed by using the Pitzer theory.Meanwhile, the model was applied to model potassium/magnesium transport in Qarhan Salt Lake in order to study the transfer law of solid and liquid phases in the dissolving and driving process and to design the optimal injection/abstraction strategy for dissolving and capturing maximum Potassium/Magnesium in the mining of salt deposits in Qarhan Salt Lake. 相似文献
45.
LI Wenpeng 《《地质学报》英文版》2008,(5)
Firstly,the macroscopic chemical equilibrium state of a series of chemical reactions between intercrystal brine and its media salt layer (salt deposit) in Qarhan Salt Lake was studied by using the Pitzer theory.The concept of macroscopic solubility product and its relation with accumulated ore dissolving ratio were presented,which are used in the numerical model of dissolving and driving exploitation of potassium salt in Qarhan Salt Lake.And secondly,with a model forming idea of transport model for reacting solutes in the multi-component fresh groundwater system in porous media being a reference,a two-dimensional transport model coupled with a series of chemical reactions in a multi-component brine porous system (salt deposits) was developed by using the Pitzer theory. Meanwhile,the model was applied to model potassium/magnesium transport in Qarban Salt Lake in order to study the transfer law of solid and liquid phases in the dissolving and driving process and to design the optimal injection/abstraction strategy for dissolving and capturing maximum Potassium/ Magnesium in the mining of salt deposits in Qarban Salt Lake. 相似文献
46.
Xin Li Dongliang Wang Baoquan Liu Chunling Ren Jianying Guo Xuefeng Su Jian Wang 《中国地球化学学报》2008,27(4):412-419
The northern margin of the Qaidam Basin is one of the main oil-gas exploration areas in western China, where source rocks are composed mostly of Middle and Lower Jurassic dark mud shale, carbargillite and coal. A large number of subsurface and outcrop samples differing in lithology with different types of organic matter were selected for resource evaluation, research and calculation. And among them, 13 samples were used for simulation experiment on hydrocarbon generating potential of various source rocks. At first, two kinds of heating modes were compared through simulation experiment, including single temperature-step heating and continual heating. Perhaps, the process of hydrocarbon generation and expulsion occurred naturally between a close system and an open system. In addition, the first heating mode was convenient, and all its reaction products were involved in the whole thermal evolution, and the final simulation experimental results were basically in consistency with the natural evolution trend Therefore, the first heating mode was adopted and the hydrocarbon yield of every sample was worked out. According to the type and lithology of organic matter and the hydrocarbon yield of samples for simulation experiment, hydrocarbon generation and expulsion mode with three kinds of lithology and five types of source rock has been established to provide the basis for hydrocarbon generation evaluation, research and resource calculation. 相似文献
47.
48.
49.
天津市地下水开采对地面沉降影响的多元回归分析 总被引:1,自引:0,他引:1
地下水的过量开采是天津市引起地面沉降的主要原因。因此天津市提出了“压缩地下水开采量”、“地下水人工回灌”、“调整地下水开采层次”等控制地面沉降的3大技术措施。经过多年的努力,控制地面沉降效果明显。如何解决地下水开发与控制地面沉降的关系,更好的贯彻这3大技术措施,是该文编写的初衷。即在开采同样地下水量的情况下,如何使地面沉降量最小;或在地面沉降量容许的情况下,如何开采最大量的地下水。压缩地下水开采量是治理地面沉降的根本措施,亦即如何压缩采水量或调整开采层次会达到最好效果。论文对天津市某区各个地下水开采层的多年累计开采量、累计沉降量进行数据统计分析,建立了该地区累计沉降量及各个地下水开采层的多元相关方程。在此基础上,分析了各个地下水开采层对地面沉降影响的相关程度。以此为该区控制地面沉降的提供依据。 相似文献
50.