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941.
The ANELFA scale for hailfall intensity is proposed on the model of the 6-class Fujita scale for tornadoes. It is based on more than three thousand point hailfalls measured by hailpads over a 16-year period in France. The class number of a hailfall is determined by the integer value of the largest measured hailstone diameter in cm, or by equivalence with current objects: A0 to A5 for pea, grape, pigeon's egg, walnut, hen's egg, orange. The class number is followed by a plus or minus sign if the ground is significantly more or less than half-covered by hailstones respectively. When the scale is applied to the ANELFA data, a log-normal distribution is found for the class distribution, allowing the frequency determination of the upper class ever observed until now at the hailpad stations. 相似文献
942.
943.
通常固定增益的放大器在兼顾大的动态范围和较高的小信号精度的情况下很难满足预期的要求。本文针对增益为 2 0~ 2 3倍的可编程阶码放大器 AD5 2 6集成片 ,摆脱传统的设计方法 ,提出一种反馈式程控放大电路。该电路能够在瞬时调整信号的放大增益 ,具有很高的精度和较大的动态范围 ,能够在模数转换前端处理中发挥重要作用。 相似文献
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945.
P. H. S. W. Kulatilake P. Balasingam Jinyong Park R. Morgan 《Geotechnical and Geological Engineering》2006,24(5):1181-1202
Accurate quantification of roughness is important in modeling hydro-mechanical behavior of rock joints. A highly refined variogram
technique was used to investigate possible existence of anisotropy in natural rock joint roughness. Investigated natural rock
joints showed randomly varying roughness anisotropy with the direction. A scale dependant fractal parameter, K
v, seems to play a prominent role than the fractal dimension, D
r1d, with respect to quantification of roughness of natural rock joints. Because the roughness varies randomly, it is impossible
to predict the roughness variation of rock joint surfaces from measurements made in only two perpendicular directions on a
particular sample. The parameter D
r1d × K
v seems to capture the overall roughness characteristics of natural rock joints well. The one-dimensional modified divider
technique was extended to two dimensions to quantify the two-dimensional roughness of rock joints. The developed technique
was validated by applying to a generated fractional Brownian surface with fractal dimension equal to 2.5. It was found that
the calculated fractal parameters quantify the rock joint roughness well. A new technique is introduced to study the effect
of scale on two-dimensional roughness variability and anisotropy. The roughness anisotropy and variability reduced with increasing
scale. 相似文献
946.
The hydraulic conductivity (K) of many low permeability materials is strongly scale‐dependent. In raised mires and other types of peat deposit the effects of features such as abandoned infilled ditches, root holes and localized woody material, cause K to be heterogeneous and scale‐dependent. Despite this, field measurements are routinely made using auger hole (slug) tests at the scale of only a few tens of centimetres. Such measurements are locally valid, but where the regional subsurface movement of water through peat bogs is simulated using groundwater models, typically at the scale of hundreds of metres, they give rise to a systematic underestimate of flows and an overprediction of water table elevations. Until now, techniques to obtain values at a scale sufficiently large to include the effects of localized features of higher permeability have not been applied routinely. Research at Thorne Moor, a large raised mire, demonstrates that the K of peat varies over several orders of magnitude when measured at different scales, using a variety of techniques. Laboratory and auger hole tests cannot be relied upon to provide results that represent the hydraulic conductivity of large expanses of peatland. This has significant implications for the management and long‐term restoration of peatlands where both regional and local control of water levels is crucial. For groundwater models to be used successfully to plan such schemes, it is essential to apply the K values relevant to the scale of the simulation. This paper describes and tests novel techniques, using ditches, for the derivation of K at large scales which overcome many of the problems that have been identified with conventional techniques and are capable of producing estimates that are appropriate to the application of physically based regional flow models. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
947.
A.?PerrinEmail author C.?Puzzarini J.-M.?Colmont C.?Verdes G.?Wlodarczak G.?Cazzoli S.?Buehler J.-M.?Flaud J.?Demaison 《Journal of Atmospheric Chemistry》2005,51(2):161-205
In order to investigate the upper troposphere/lower stratosphere (UTLS) region of the earth's atmosphere, ESA/ESTEC (European
space agency) is considering the opportunity to develop the spaceborne limb sounding millimeter sensor “MASTER” (millimeter
wave acquisitions for stratosphere/troposphere exchange research). This instrument is part of the “atmospheric composition
explorer for chemistry and climate interactions” (ACECHEM) project. In addition, ESA/ESTEC is developing the “MARSCHALS” (millimeter-wave
airborne receiver for spectroscopic characterization of atmospheric limb sounding) airborne instrument which will demonstrate
the feasibility of MASTER. The present paper describes the line-by-line database which was generated in order to meet at best
the needs of the MASTER (or MARSCHALS) instrument. The linelist involves line positions, line intensities, line broadening
and line shift parameters in the 294–305, 316–325, 342–348, 497–506 and 624–626 GHz spectral microwindows. This database was
first generated for the target molecules for MASTER (H2O, O3, N2O, CO, O2, HNO3, HCl, ClO, CH3Cl, BrO). In addition, ten additional molecules (SO2, NO2, OCS, H2CO, HOCl, HCN, H2O2, COF2, HO2 and HOBr) had also to be considered in the database as “possible interfering species” for the retrieval of the target molecules
of MASTER. The line parameters were derived, depending on their estimated accuracy, (i) from a combination of spectral parameters
included in the JPL and HITRAN catalogs (ii) from data taken into the literature or (iii) using data obtained through experimental
measurements (and/or) calculations performed during the present study. 相似文献
948.
轨道调谐法是确定第四纪地层时间标尺的主要手段,但人工进行轨道调谐确定时间标尺具有可操作性差、客观性差、工作量大及很难得到最佳结果等缺陷,本文描述了利用计算机自动进行轨道调谐以厘定古气候记录时间标尺的方法步骤.对于不同的气候替代性指标时间序列之间在主要周期频率上的相位关系,作者提出了利用演化凝聚函数法进行计算的新方法.作为实例,利用上述方法对塔吉克斯坦Chashmanigar黄土记录进行了时间标尺和相位关系演化的计算. 相似文献
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950.