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991.
本文利用2005年1月—2009年12月DEMETER电磁卫星观测的极低频/甚低频(ELF/VLF)39 Hz~6 kHz频段电场功率谱密度(PSD)观测量, 将研究频段划分为5个子频段对东北亚地区(38°N~58°N; 105°E~145°E)内发生的8个MS≥5.0地震前后空间电场时空演化特征进行研究。 研究发现同一地震不同频段异常扰动区域并不完全在同一位置, 且同一地震的不同频段地震前后扰动形态也并不一致; 8个地震40次统计中有25% 的统计数据虽然基本在地震前后所有时间段都超过阈值2σ, 但未见明显扰动规律, 其余75%的统计数据中发现其扰动特征可以归纳为3类: 52%的统计数据在震前扰动幅度增大, 达到最大时发震, 震后持续降低; 7.5%的统计数据在震前扰动幅度达到高值, 而后下降过程中发震; 15%的统计数据在震前扰动幅度一直在增加且绝大部分时间低于2σ, 直至震后超过2σ, 且出现这种类型的异常均为震例的第五频段演化特征。 异常扰动区域主要集中在震中±4°以外的区域。 相似文献
992.
993.
From the similarity theorem, an expression of bubble population is derived as a function of the air en-trainment rate, the turbulent kinetic energy (TKE) spectrum density and the surface tension. The bubble size spectrum that we obtain has a dependence of a?2.5 nd on the bubble radius, in which nd is positive and dependent on the form of TKE spectrum within the viscous dissipation range. To relate the bubble population with wave parameters, an expression about the air entrainment rate is deduced by intro-ducing two statistical relations to wave breaking. The bubble population vertical distribution is also derived, based on two assumptions from two typical observation results. 相似文献
994.
995.
996.
探测Slichter模态三重分裂可有效约束内核密度、内核半径及内外核边界密度跳跃。虽然Smylie(1992)声称探测到了Slichter模态三重分裂,但至今未被国际学术界公认。本文结合一个实验算例,阐述了Hilbert-Huang变换(HHT)分析方法的核心思想,并将该方法应用于探测Slichter模三重分裂谱线的研究。我们选取了全球分布的8个台站连续记录两年的小时间隔超导重力数据,进行了潮汐和气压改正后,将它们叠加获得重力残差;然后对重力残差作HHT分析,得到能量谱,进而选出了12种可能的谱峰组合,其中两组结果与Smylie的结果很接近,且本文得到的谱峰分裂相比于Smylie的结果具有更好的对称性。 相似文献
997.
在城乡协调发展的背景下,本文以自然属性为基础分析了北京具有不同经济属性的5类耕地的空间结构。波谱分析显示,不同类型耕地的空间分布具有不同的周期,它们共同形成了距天安门约23~44km(近郊平原)、44~66km(远郊平原)、66~126km(山区)的耕地宏观空间结构。通过计算各类耕地的空间维数和Hurst指数,认为景观农田区、美化农田区、近郊山区22~47km圈层的耕地不具备分形特征;规模农田区、景观廊道带、中远郊山区48~126km圈层的耕地由于受城市发展、自然条件、距离等因素的影响具有明显的分形特征。总体上,北京不同类型的耕地处于一种离散、连续和具有共度性、没有公度性的融合状态。 相似文献
998.
M. Viel E. Branchini K. Dolag M. Grossi S. Matarrese L. Moscardini 《Monthly notices of the Royal Astronomical Society》2009,393(3):774-782
We present results from the first high-resolution hydrodynamical simulations of non-Gaussian cosmological models. We focus on the statistical properties of the transmitted Lyman-α flux in the high-redshift intergalactic medium. Imprints of non-Gaussianity are present and are larger at high redshifts. Differences larger than 20 per cent at z > 3 in the flux probability distribution function for high-transmissivity regions (voids) are expected for values of the non-linearity parameter f NL =±100 when compared to a standard Λ cold dark matter cosmology with f NL = 0 . We also investigate the one-dimensional flux bispectrum: at the largest scales (corresponding to tens of Mpc), we expect deviations in the flux bispectrum up to 20 per cent at z ∼ 4 (for f NL =±100 ), significantly larger than deviations of ∼3 per cent in the flux power spectrum. We briefly discuss possible systematic errors that can contaminate the signal. Although challenging, a detection of non-Gaussianities in the interesting regime of scales and redshifts probed by the Lyman-α forest could be possible with future data sets. 相似文献
999.
We develop a diagnostic tool for determination of the electron densities in solar prominences using eclipse data. The method
is based on analysis of the hydrogen Balmer-line intensities (namely Hα and Hβ) and the white-light emission due to Thomson
scattering on the prominence electrons. Our approach represents a generalization of the ratio method already used by Koutchmy,
Lebecq, and Stellmacher (Astron. Astrophys.
119, 261, 1983). In this paper we use an extended grid of non-LTE prominence models of Gouttebroze, Heinzel, and Vial (Astron. Astrophys. Suppl. Ser.
99, 513, 1993) and derive various useful relations between prominence radiation properties and electron densities. Simultaneously, an effective
geometrical thickness of the prominence can also be obtained. As an example we apply our general technique to original eclipse
data of Koutchmy, Lebecq, and Stellmacher (Astron. Astrophys.
119, 261, 1983). Finally, we use our results to determine the color of prominences as it should be seen during total eclipses. 相似文献
1000.
James S. Bolton S. Peng Oh Steven R. Furlanetto 《Monthly notices of the Royal Astronomical Society》2009,396(4):2405-2418
Three independent observational studies have now detected a narrow (Δ z ≃ 0.5) dip centred at z = 3.2 in the otherwise smooth redshift evolution of the Lyα forest effective optical depth. This feature has previously been interpreted as an indirect signature of rapid photoheating in the intergalactic medium (IGM) during the epoch of He ii reionization. We examine this interpretation using a semi-analytic model of inhomogeneous He ii reionization and high-resolution hydrodynamical simulations of the Lyα forest. We instead find that a rapid (Δ z ≃ 0.2) boost to the IGM temperature (Δ T ≃ 104 K) beginning at z = 3.4 produces a well understood and generic evolution in the Lyα effective optical depth, where a sudden reduction in the opacity is followed by a gradual, monotonic recovery driven largely by adiabatic cooling in the low-density IGM. This behaviour is inconsistent with the narrow feature in the observational data. If photoheating during He ii reionization is instead extended over several redshift units, as recent theoretical studies suggest, then the Lyα opacity will evolve smoothly with redshift. We conclude that the sharp dip observed in the Lyα forest effective optical depth is instead most likely due to a narrow peak in the hydrogen photoionization rate around z = 3.2 , and suggest that it may arise from the modulation of either reprocessed radiation during He ii reionization, or the opacity of Lyman limit systems. 相似文献