全文获取类型
收费全文 | 3782篇 |
免费 | 465篇 |
国内免费 | 630篇 |
专业分类
测绘学 | 1406篇 |
大气科学 | 663篇 |
地球物理 | 605篇 |
地质学 | 843篇 |
海洋学 | 600篇 |
天文学 | 104篇 |
综合类 | 411篇 |
自然地理 | 245篇 |
出版年
2024年 | 7篇 |
2023年 | 30篇 |
2022年 | 75篇 |
2021年 | 100篇 |
2020年 | 116篇 |
2019年 | 153篇 |
2018年 | 94篇 |
2017年 | 147篇 |
2016年 | 206篇 |
2015年 | 184篇 |
2014年 | 225篇 |
2013年 | 301篇 |
2012年 | 246篇 |
2011年 | 276篇 |
2010年 | 190篇 |
2009年 | 232篇 |
2008年 | 219篇 |
2007年 | 252篇 |
2006年 | 260篇 |
2005年 | 203篇 |
2004年 | 172篇 |
2003年 | 147篇 |
2002年 | 130篇 |
2001年 | 112篇 |
2000年 | 84篇 |
1999年 | 94篇 |
1998年 | 125篇 |
1997年 | 83篇 |
1996年 | 70篇 |
1995年 | 63篇 |
1994年 | 55篇 |
1993年 | 43篇 |
1992年 | 40篇 |
1991年 | 24篇 |
1990年 | 24篇 |
1989年 | 30篇 |
1988年 | 18篇 |
1987年 | 20篇 |
1986年 | 8篇 |
1985年 | 5篇 |
1984年 | 6篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4877条查询结果,搜索用时 515 毫秒
71.
Rigoberto G. Sanabria Castro Sandra M. C. Malta Abimael F. D. Loula Luiz Landau 《Computational Geosciences》2002,5(4):301-330
A finite element formulation is proposed to approximate a nonlinear system of partial differential equations, composed by an elliptic subsystem for the pressure–velocity and a transport equation (convection–diffusion) for the concentration, which models the incompressible miscible displacement of one fluid by another in a rigid porous media. The pressure is approximated by the classical Galerkin method and the velocity is calculated by a post-processing technique. Then, the concentration is obtained by a Galerkin/least-squares space–time (GLS/ST) finite element method. A numerical analysis is developed for the concentration approximation. Then, stability, convergence and numerical results are presented confirming the a priori error estimates. 相似文献
72.
JIANG Guorong ZHANG Ren SHA Wenyu YAN Junyue YAO Huadong 《Acta Meteorologica Sinica》2002,16(1):123-132
In the context of tower measured radiation datasets.following the correction principle meeting a diagnostic equation in data quality control and in terms of a technique for model construction on data and ANN (artificial neural network) retrieval for BP correction of radiation measurements with rough errors available,a BP model is presented.Evidence suggests that the developed model works well and is superior to a convenient multivariate linear regression model,indicating its wide applications. 相似文献
73.
The garnet-muscovite geothermometer was refined through empirical calibration by using natural rocks metamorphosed under the physical conditions of 238—1306 MPa and 490—700℃. Input temperatures and pressures were determined through simultaneously applying the garnet-biotite geothermometer and the garnet-biotite-plagioclase-quartz barometer, assuming that all FeO in muscovite and garnet be ferrous. Garnet was treated as the asymmetric quaternary solid solution, and muscovite as the symmetric binary solid solution. Input muscovite compositions include Fe atoms between 0.03—0.19 and Mg atoms between 0.04—0.16 on the basis of 11 oxygen atoms, and input garnet compositions include spessartine fractions between 0.01—0.289, grossular fractions between 0.028—0.273, and the Fe/Mg ratio between 3.387-18.986. The resulting garnet-muscovite geothermometer reproduces temperatures within (50℃ compared with the garnet-biotite thermometer. Total random error of ±37℃ of the new thermometer may stem from the pressure uncertainty of ±200 MPa, and uncertainties of ±5% of Fe and Mg components in muscovite, and ±5% of Fe, Mg, Mn and Ca components in garnet, altogether. When there exist 10%, 20%, 30%, 40% and 50% Fe3+ in muscovite, respectively, the computed garnet-muscovite temperatures will be 1—6℃, 2—12℃, 3—16℃, 5—24℃ and 7—29℃, respectively, lower than those obtained when assuming that all FeO be ferrous. The new garnet-muscovite geothermometer can efficiently reflect temperature change of typical prograde sequences and contact aureole rocks, and may be applied to low- to high-grade and low- to high-pressure metamorphic rocks. 相似文献
74.
The non-parametric Mann–Whitney (MW) statistic test has been popularly used to assess the significance of a shift in median
or mean of hydro-meteorological time series. It has been considered that the test is more suitable for non-normally distributed
data and it may be not sensitive to the distribution type of sample data. However, no evidence has been provided to demonstrate
these. This study investigates the power of the test in various circumstances by means of Monte Carlo simulation. Simulation
results demonstrate that the power of the test is very sensitive to various properties of sample data. The power depends on
the pre-assigned significance level, magnitude of a shift, sample size, and its occurrence position within a time series;
and it is also strongly affected by the variation, skewness, and distribution type of a time series. The bigger the magnitude
of a shift, the more powerful the test is; the larger the sample size, the more powerful the test is; and the bigger the variation
within a time series, the less power the test has. The test has the highest power if a shift occurs at the midpoint of a time
series. For the samples with different distribution types, the power of the test is dramatically different. The test has the
highest power for time series with the extreme value type III (EV3) distribution while it indicates the lowest power for time
series with the lognormal distribution. 相似文献
75.
改进的灰色模型在中国能源消费及其CO2排放预测中的研究 总被引:5,自引:1,他引:5
中国高速的经济发展导致了快速的能源消费和地球温暖化气体的排放量。本文应用灰色理论建立了中国的终端能源消费量的动态预测模型,同时应用等维递补及带有马尔科夫链符号估计的残差修正,对原始模型进行了改进。后验检验的结果证明了改进的预测模型具有较高的计算精度。预测结果表明,两种经济发展情况(高速及低速)下,从2000年到2030年期间的终端能源消费量的平均增长率将分别达到3.06%和2.18%,2030年CO2 的排放量将分别达到2000年的 2. 15及 1.60倍。其中工业及居民生活的能源消费量的增加速度快于其他部门。这表明了中国将要加快其工业化及都市化的进程.终端消费中,煤炭的消费量所占的比例将要逐年减少,而电力的比例则将逐年增大。 相似文献
76.
Data and model uncertainty estimation for linear inversion 总被引:1,自引:0,他引:1
Kasper van Wijk John A. Scales William Navidi Luis Tenorio 《Geophysical Journal International》2002,149(3):625-632
77.
The Hercynian basement of the Iberian Peninsula was uplifted by the Alpine orogeny during the Tertiary. It gave rise to a set of block mountains and tectonic grabens, one of which is the Ciudad Rodrigo Basin. It is located in Western Spain and forms a westward extension of the great Tertiary Duero Basin. The sediments filling this graben are of continental origin, their ages ranging from Palaeogene to Quaternary. Morphologically, the southern part of this basin forms a set of piedmont surfaces (the “Raña” surfaces) appearing above the terrace system of the present rivers. This paper examines the weathering processes developed over these old piedmont surfaces using micromorphological, XR diffraction, scanning electron microscopy (SEM) and microporosity techniques.The Raña sediments are rich in quartzite pebbles and gravel within a clayey matrix. Once deposited, these materials underwent important in situ weathering processes under somewhat hydromorphic conditions, of which hydrolysis, ferrolysis and xerolysis were the most important. All these processes gave rise to: (1) transformation of most of the clasts of shists and slates into a matrix causing the destruction of the original sedimentary structures and a relative concentration of the resistant lithologies (quartzites and quartz); (2) important changes in the clay fraction, leading to a predominance of kaolinite in the upper levels of the profiles, (3) release of elements from primary minerals, Fe being one of the most important, and (4) redistribution of matter, mainly clay and Fe oxyhydroxides, within the profiles.The coexistence of seasonal periods with pF higher than 4.2 repeated over a long time, together with poor internal and external drainage conditions, are the cause of the special features displayed by Raña deposits. 相似文献
78.
GPS在地面沉降监测中的应用探讨 总被引:5,自引:0,他引:5
利用GPS进行地面沉降监测能够解决传统测量方法工作量大、周期长的问题。该文结合实例,论述了GPS在地面沉降监测中的应用,分析了GPS测量方法的优点和误差,提出了GPS测量地面沉降的适用条件。 相似文献
79.
略论目标规划及交互方法在小康示范村规划中的实践--以西藏贡嘎县沃拉村为例 总被引:1,自引:0,他引:1
建设全面小康社会是我国本世纪头20年的核心内容,目前已经有越来越多的人加入到这一研究领域中,该领域的规划研究工作正在逐渐加强。本文以西藏贡嘎县沃拉村为例,介绍了目标规划及交互方法小康示范村规划中的实践,讨论了规划的过程、建模方法及模型的精度等问题,认为在研究人员的指导下,由村民学习并建模的方法是今后小康村规划的发展方向。 相似文献
80.