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A novel method has been examined for monitoring tropospheric hydroxyl radicals (OH), the most important oxidant in tropospheric chemistry. Aqueous phase salicylic acid reacts with atmospheric OH to produce 2,5-dihydroxy benzoic acid (2,5-DHBA) and other products. High Performance Liquid Chromatography (HPLC) is used to separate the post-reaction solution and the products are quantified using fluorescence detection. Unlike other methods, it has been reported to be inexpensive, portable and relatively simple. Although the sensitivity was sufficient to measure typical daytime OH concentrations of 0.04–0.4 ppt., the method was hindered by numerous interferences. Successive identification and elimination of these still resulted in a signal that was much larger than expected. Tests showed that this was not likely to be due to ozone, HO2, NOx, H2O2, aerosols, light or bacteria. Experimental and numerical studies suggest that the interference could be due to methyl peroxy radicals. The effect of many other components in the atmosphere, both individual and combined, must also be tested before the method can be used reliably in the field. The validity of previous reports of ambient hydroxyl measurements using this technique is therefore brought into question. 相似文献
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Z. X. Zhang T. Naarttij rvi 《Fragblast: International Journal for Blasting and Fragmentation》2005,9(2):61-78
Due to the large-scale sub-level caving in Malmberget mine and the short distance between the mine and Malmberget town, the ground vibrations in the town have reached a high level since the year 2001 when large scale caving mining started. In order to control and reduce the high vibrations, LKAB launched a research project on active reduction of vibrations in Malmberget by using the wave interference or wave superposition method with electronic detonators. By means of this method, the vertical vibrations were reduced by 10% and the total vibration time for a ring blast was reduced by 80% according to five ring tests in the mine. For a further reduction of the vibrations, a second method, named changing initiation sequence in ring blasts, was developed on the basis of stress wave theory and the geographic conditions of the town and the mine. The second method has so far been applied in all of the drifts near the town, and the vibrations measured at the town show that the vertical vibrations caused by production blasts in the mine have been reduced by more than 31% on average. In addition, a third method, dividing a ring into two parts during blasting, was developed and used to reduce the ground vibrations from a number of very large rings in the mine. The results indicate that the vibrations have been reduced by more than 33%, and a more interesting and surprising result is that ore extraction has been increased by the third method. 相似文献
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Measurements of the response of the ¼‐scale reinforced concrete Hualien (Taiwan) containment model obtained during forced vibration tests are used to identify some of the characteristics of the superstructure and the soil. In particular, attempts are made to determine the fixed‐base modal frequencies, modal damping ratios, modal masses and participation factors associated with translation and rocking of the base. The shell superstructure appears to be softer than could have been predicted on the basis of the given geometry and of test data for the properties of concrete. Estimates of the shear‐wave velocity and damping ratio in the top layer of soil are obtained by matching the observed and theoretical system frequency and peak amplitude of the response at the top of the structure. The resulting models for the superstructure and the soil lead to theoretical results for the displacement and rotations at the base and top of the structure which closely match the observed response. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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体外预应力梁振动特性的分析与研究 总被引:14,自引:0,他引:14
本文分析了体外预应力混凝土梁在动力荷载作用下的振动特性。对Ayaho Miyamoto给出的公式进行了修正和扩充,推导出包括单折线型、双折线型、直线型3种线型布置下的体外预应力混凝土简支梁的自振频率计算公式,针对各种因素对体外预应力混凝土梁振动频率的影响加以探讨,提出一些体外预应力梁体系防振动的有效措施。 相似文献