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861.
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The search to improve protective techniques against natural phenomena such as snow avalanches continues to use classic methods to calculate flexible structures. This paper deals with a new method for designing avalanche protection nets; this method is based on a coupled analysis of both the net structure and the snow mantel using a coupled Lagrangian‐discrete approach. This has led to the development of computational software so that avalanche nets can be easily designed. This tool provides for the evolving forces acting on several parts of the net as a function of the snow situation. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
863.
Jun Lin 《中国天文和天体物理学报》2007,7(4):457-476
Large-scale magnetic structures are the main carrier of major eruptions in the solar atmosphere. These structures are rooted in the photosphere and are driven by the unceas-ing motion of the photospheric material through a series of equilibrium configurations. The motion brings energy into the coronal magnetic field until the system ceases to be in equilib-rium. The catastrophe theory for solar eruptions indicates that loss of mechanical equilibrium constitutes the main trigger mechanism of major eruptions, usually shown up as solar flares, eruptive prominences, and coronal mass ejections (CMEs). Magnetic reconnection which takes place at the very beginning of the eruption as a result of plasma instabilities/turbulence inside the current sheet, converts magnetic energy into heating and kinetic energy that are responsible for solar flares, and for accelerating both plasma ejecta (flows and CMEs) and energetic particles. Various manifestations are thus related to one another, and the physics behind these relationships is catastrophe and magnetic reconnection. This work reports on re- cent progress in both theoretical research and observations on eruptive phenomena showing the above manifestations. We start by displaying the properties of large-scale structures in the corona and the related magnetic fields prior to an eruption, and show various morphological features of the disrupting magnetic fields. Then, in the framework of the catastrophe theory, we look into the physics behind those features investigated in a succession of previous works, and discuss the approaches they used. 相似文献
864.
Using data collected at the Spanish low troposphere research centre CIBA (Centro de Investigación de la Baja Atmósfera) and at the Cabauw Experimental Site for Atmospheric Research (CESAR) in the Netherlands, we analyzed the most significant features of different coherent structures occurring in the stable atmospheric boundary layer. In particular, we used both the Reynolds and wavelet methods to analyze a solitary wave, a gravity wave, a density current and a low-level jet. For each of these structures, we found that wavelet analysis had the capacity to distinguish the different scales involved in these events due to the different timing and heights of the thermal instabilities and downdrafts associated with the disturbances. In addition, the wavelet method highlights the different roles of turbulence and coherent structures in the transfer of heat, moisture and CO2 in the nocturnal boundary layer. 相似文献
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Hydrodynamic modeling of perforated structures 总被引:2,自引:0,他引:2
B. Molin 《Applied Ocean Research》2011,33(1):1-11
A hydrodynamic model of perforated or slotted structures is proposed. It is asymptotic in the sense that the openings are supposed to be infinitely small and numerous, and the wall thickness to be nil. At variance with other work, a quadratic, not linear, law, relating the pressure differential to the traversing velocity, is assumed. As a result the hydrodynamic coefficients (added mass and damping) become amplitude dependent. The model is applied to bodies of various shapes including cylinders, plates and disks, in forced motion or submitted to incoming waves. Good agreement with experimental data is generally observed. 相似文献
869.
八家子铅锌矿田位于华北地台之燕山台褶带内之辽西台陷南部边缘,靠近山海关隆起。地层为燕山型中、上元古界、侏罗系,中生代花岗岩为印支—早燕山期碱厂“S”型同运动似斑状花岗岩超单元、燕山中晚期圣宗庙“Ⅰ”型花岗岩两个序列。构造应变图形复杂可分为印支期褶皱推覆构造系统,燕山中期出现的裂谷盆地和正断层系组成的伸展构造系统,燕山晚期形成的逆冲推覆构造系统,燕山末期出现的走滑构造系统。逆冲推覆构造系统沿八家子盆地东缘和北西缘分布,控制铅锌矿床的就位与分布,为成矿期构造。八家子铅辞矿床为矽卡岩型热液矿床,与圣宗庙“Ⅰ”型花岗岩超单元有成因联系,特别是与晚期岩浆热液活动密切相关,受逆冲推覆构造的控制。 相似文献
870.
高频VLBI观测揭示出河外射电源在pc或者亚pc尺度上大都有核-喷流的内部结构。尤其是对平谱致密射电源中毫角秒尺度的子源,能以相当高的概率观测到它的视超光速现象。多频观测可监测到一些新喷流子源的出现,特别在射电激变源中这些新喷流子源的出现与宽带内(从光学到γ射线)的爆发相关。且得到的一些源的核区谱指数分布,为确认源的VLBI核提供了支持。 相似文献