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611.
构造煤和高温高压实验变形煤的EPR实验结果,充分显示了变形煤的EPR参数具有随Ro,max的增大而呈现规律性演化的特征,在Ro,max〉4%以后煤结构演化机理向拼叠作用的转化在实验变形煤和构造煤中也有很好的体现。但是,变形煤Ro,max的增大除与温度和围压条件有关外,还深刻地受到定向压力或构造应力的影响,尤其是对镜质组反射率各向异性的增强、煤大分子结构有序畴及定向性的增大更具有极为重要的控制作用。 相似文献
612.
Glass samples from alkali-trachytic pumice of the Lower Member (LM, level LM1) and Upper Member (UM) of the Neapolitan Yellow
Tuff at Campi Flegrei Caldera were studied by nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy.
The EPR data show that the relative occupancy of the different iron sites varies in samples from the Lower Member LM1 and
Upper Member of the eruptive sequence. The LM1 glasses are characterized by a more homogeneous distribution of the cationic
site population of iron compared with UM and by a different Fe3+/Al3+ substitution in the C2v symmetrical sites of the silicate framework. 29Si MAS NMR spectra on glasses indicate that LM1 glasses are more depolymerized than UM glasses, indicating the existence of
structurally distinct magma batches. 27Al MAS NMR spectra indicate the occurrence in UM glasses of aluminum in both tetrahedral and octahedral coordination; the
observed AlVI is believed to be a primary feature of the glass, since 27Al CP-MAS NMR experiments do not reveal detectable esa-hydrated Al. The Al in sixfold coordination could be ascribed either
to the more abundant alkali–OH terminations in UM, in which alkalies would be extracted from their charge-balance role for
Al, thus altering its fourfold structural position, or to permanent compaction during fast cooling and decompression of high-pressure
melts. 23Na CP-MAS NMR experiments indicate the existence of Na–OH groups in both LM1 and UM glasses, relatively more abundant in the
latter. Although preliminary, the results indicate the possible application of atomic-scale studies to variables that determine
the regimes of explosive volcanism.
Received: 1 July 1998 / Accepted: 1 October 1998 相似文献
613.
MR检查65例髓外硬膜下肿瘤。所有病例均经手术和病理证实。40例神经鞘瘤,8例神经纤维瘤,17例脊膜瘤。髓外硬膜下肿瘤具有相同的定位MRI表现:1、推移脊髓向对侧移位;2、肿瘤侧上下蛛网膜下腔扩大。本文讨论了每一种肿瘤的信号特征。MRI在评价椎管肿瘤方面显示出世大的优越性:无电离辐射、无创伤性、无骨伪影、多平面成像、不需椎管内注入造影剂、多发病变一次成像,直接显示肿瘤信号及其与周围结构的关系,定位及定性准确率高。尤其是Gd-DTPA的应用,对微小肿瘤的检出及鉴别肿瘤囊变与实体部分都是十分有用的。目前,MRI在很大程度上已经替代椎管造影或CT检查。 相似文献
614.
核磁共振测量技术已能够快速而无损地获得孔隙介质的物性信息, 但对于颗粒表面润湿性的测量还处于定性到半定量的水平.采用毛细管法和玻璃板法对经不同浓度二甲基二氯硅烷溶液处理的玻璃表面润湿性测量, 然后对核磁共振方法测量的孔隙介质润湿性结果进行标定, 进而得到孔隙介质润湿性系列的刻度特征.实验表明, 对于玻璃颗粒孔隙介质, 核磁共振测量的结果在作为表面处理剂的二甲基二氯硅烷溶液浓度0 %~ 0.7%变化范围内才与孔隙介质润湿性的变化有着明确的对应关系.在此范围之外, 对应的驰豫时间的变化虽然较大, 但其对于润湿性的刻度已没有明确的作用. 相似文献
615.
616.
Modelling of multi-bodies in close proximity under water waves—Fluid forces on floating bodies 总被引:1,自引:0,他引:1
This work presents two-dimensional numerical results of the dependence of wave forces of multiple floating bodies in close proximity on the incident wave frequency, gap width, body draft, body breadth and body number based on both viscous fluid and potential flow models. The numerical models were validated by the available experimental data of fluid oscillation in narrow gaps. Numerical investigations show that the large amplitude responses of horizontal and vertical wave forces appear around the fluid resonant frequencies. The convectional potential flow model is observed to un-physically overestimate the magnitudes of wave forces as the fluid resonance takes place. By introducing artificial damping term with appropriate damping coefficients μ∈[0.4, 0.5], the potential flow model may work as well as the viscous fluid model, which agree with the damping coefficients used in our previous work for the predication of wave height under gap resonance. In addition, the numerical results of viscous fluid model suggest that the horizontal wave force is highly dependent on the water level difference between the opposite sides of an individual body and the overall horizontal wave force on the floating system is generally smaller than the summation of wave force on each body. 相似文献
617.
618.
Alessandro Morbidelli Antonio Giorgilli 《Celestial Mechanics and Dynamical Astronomy》1989,47(2):145-172
The classical problem of the dynamics in the asteroids belt is revisited in the light of recently developed perturbation methods. We consider the spatial problem of three bodies both in the circular and in the elliptic case, looking for families of periodic or quasi periodic orbits. Some criteria for deciding the stability of these families are also indicated. 相似文献
619.
Tadashi Yokoyama 《Celestial Mechanics and Dynamical Astronomy》1996,64(3):243-260
A simple generalization of Wisdom's perturbative method, as originally proposed by Wisdom (1985), is obtained. Any number of resonant cosines can be handled and the method can also accommodate more involved disturbing functions. Averaged trajectories are easily obtained by drawing level curves of the action. Here, the method is first tested for simple models of 3:1 and 2:1 resonant problems. Comparisons with numerical integration and surface-section curves show very good agreements. 相似文献
620.
J. J. Rawal 《Journal of Astrophysics and Astronomy》1989,10(3):257-259
The relation between the planetary distance law and the resonant structures in the solar system and in the satellite systems
is shown, in that, the resonance relation has been expressed in terms of Roche’s (Bode’s) constant defined in the text. This
brings forth a coherent, elegant and unified picture of the formation and structure of the solar system and the satellite
systems. The Roche’s (Bode’s) constant is seen to play a central role in this unified picture, in that, it also appears to
govern the resonance phenomenon in the systems 相似文献