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991.
Tao Hu Qiu-He Peng Hong-Shi Zong 《中国天文和天体物理学报》2007,7(4):579-589
We present disk thicknesses, some other parameters and their statistics of 108 non-edge-on spiral galaxies. The method for determining the disk thickness is based on solving Poisson's equation for a disturbance of matter density in three-dimensional spiral galaxies. From the spiral arms found we could obtain the pitch angles, the inclination of the galactic disk, and the position of the innermost point (the forbidden region with radius r 0 to the galactic center) of the spiral arm, and finally the thickness. 相似文献
992.
王浩 《大地测量与地球动力学》2007,27(Z1):140-142
阐述了适合高速无线数据传输的正交频分复用(OFDM)调制方式的基本原理及调制解调的快速傅立叶变换(FFT)实现,并给出OFDM基带处理系统的结构图和硬件模块框图。 相似文献
993.
A complete set of one-month Acoustic Doppler Profiler (ADP) current data at a station in the southern Yellow Sea (SYS) is analyzed using the rotary spectrum method. The results revealed different rotary properties between barotropic and baroclinic tidal currents. The barotropic and baroclinic tidal currents rotate elliptically counter-clockwise and clockwise, respectively. Meanwhile, baroclinic bottom tidal currents are almost along-isobath. The baroclinic cross-isobath velocities attenuate quickly at the bottom, implying important effects of bottom topography on the cross-isobath motions. 相似文献
994.
995.
Baotian Pan Huai Su Zhenbo Hu Xiaofei Hu Hongshan Gao Jijun Li Eric Kirby 《Quaternary Science Reviews》2009,28(27-28):3281-3290
The competing roles of bedrock uplift and climatic change in the formation of fluvial terraces remain uncertain. Most of recent studies have attributed terrace formation to climatic changes and held that, even in tectonically active settings, climate variations control cycles of terrace planation and abandonment. Based on field investigations of loess-paleosol sequences, magnetostratigraphy and optically stimulated luminescence (OSL) dating, we develop a new chronology for a spectacular flight of terraces along the Yellow River near Lanzhou, China over past 1.24 Ma. All the terraces are strikingly similar in that they have several meters of paleosol developed directly above fluvial deposits on the terrace treads, suggesting that the abandonment of each terrace due to river incision occurs during the transition from glacial to interglacial climates. However, the ages of terraces cluster in two relatively short time periods (1.24–0.86 Ma and 0.13 Ma – present). During the intervening time between 0.86 Ma and 0.13 Ma, terraces either did not form or were not preserved. We suggest that this record indicates that rock uplift rates varied through time and influenced terrace formation/preservation. Thus, our results demonstrate the utility of deep chronologic records from fluvial terraces for deconvolving the effects of tectonics and climate on fluvial incision. 相似文献
996.
The vertical bearing capacity of spudcan foundations in strength anisotropic soils is investigated numerically using the MIT-S1 model implemented in the AFENA finite element package. The model in AFENA is validated against existing laboratory test data of normally consolidated soil. The bearing capacities of spudcans in soils with isotropic and anisotropic strengths are compared. Soil with isotropic strength is simulated using an elasto-plastic model. It is found that the bearing capacity of a spudcan in an anisotropic soil is reduced by about 9% for a rough spudcan and 3% for a smooth spudcan on average. There is a combined effect of soil anisotropy and spudcan roughness on the spudcan bearing capacity. Moreover, the effect of the pressuremeter strength of an anisotropic soil on foundation capacity can’t be ignored. 相似文献
997.
A simplified analytical method is presented for the vertical dynamic analysis of a rigid, massive, cylindrical foundation embedded in a poroelastic soil layer. The foundation is subjected to a time‐harmonic vertical loading and is perfectly bonded to the surrounding soil in the vertical direction. The soil underlying the foundation base is represented by a single‐layered poroelastic soil based on rigid bedrock while the soil at the side of the foundation is modeled as an independent poroelastic layer composed of a series of infinitesimally thin layers. The behavior of the soil is governed by Biot's poroelastodynamic theory and its governing equations are solved by the use of Hankel integral transform. The contact surface between the foundation base and the soil is smooth and fully permeable. The dynamic interaction problem is solved following standard numerical procedures. The accuracy of the present solution is verified by comparisons with the well‐known solutions obtained from other approaches for both the elastodynamic interaction problem and poroelastodynamic interaction problem. Numerical results for the vertical dynamic impedance and response factor of the foundation are presented to demonstrate the influence of nondimensional frequency of excitation, soil layer thickness, poroelastic material parameters, depth ratio and mass ratio on the dynamic response of a rigid foundation embedded in a poroelastic soil layer. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
998.
The raindrop impact and overland flow are two major factors causing soil detachment and particle transportation. In this study, the turbulent characteristics of the shallow rain‐impacted water flow were investigated using a 2‐D fibre‐optic laser Doppler velocimetry (FLDV) and an artificial rainfall simulator. The fluctuating turbulent shear stress was computed using digital data processing techniques. The experimental data showed that the Reynolds shear stress follows a probability distribution with heavy tails. The tail probability increases with an increase of rainfall intensity or raindrop diameter, and it decreases with an increase of Reynolds number. A modified empirical equation was derived using both the raindrop diameter and rainfall intensity as independent variables to provide a better prediction of the Darcy‐Weisbach friction coefficient f under rainfall conditions. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
999.
???????????????????????????????????????????????????????????????????????ж?λ?????????????????????????????????Σ??????λ?????????????????????????????????????????????μ???????????????б???????????????????????????????ú???????????????????????????????????????Ч?????б??????????????????ò??ù??????о????λ???λ????? 相似文献
1000.
F. X. Hu G. X. Wu G. X. Song Q. R. Yuan S. Okamura 《Astrophysics and Space Science》2006,302(1-4):43-59
The progress of the studies on the orientation of galaxies in the Local Supercluster (LSC) is reviewed and a summary of recent
results is given. Following a brief introduction of the LSC, we describe the results of early studies based on two-dimensional
analysis, which were mostly not conclusive. We describe next the three-dimensional analysis, which is used widely today. Difficulties
and systematic effects are explained and the importance of selection effects is described. Then, results based on the new
method and modern databases are given, which are summarized as follows. When the LSC is seen as a whole, galaxy planes tend
to align perpendicular to the LSC plane with lenticulars showing the most pronounced tendency. Projections onto the LSC plane
of the spin vectors of Virgo cluster member galaxies, and to some extent, those of the total LSC galaxies, tend to point to
the Virgo cluster center. This tendency is more pronounced for lenticulars than for spirals. It is suggested that ‘field’
galaxies, i.e., those which do not belong to groups with more than three members, may be better objects than other galaxies
to probe the information at the early epoch of the LSC formation through the analysis of galaxy orientations. Field lenticulars
show a pronounced anisotropic distribution of spin vectors in the sense that they lay their spin vectors parallel to the LSC
plane while field spirals show an isotropic spin-vector distribution. 相似文献